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February 13

Travelling to the future

I believe that the following is correct:

• If you approach the speed of light, then relative to a slower moving body, time will seem to move more slowly
• Therefore, if you circled the Earth at close to the speed of light, time on Earth would appear to pass more quickly than time on your "spaceship"
• So, if you left now, got up to the speed of light quickly and then can back in five years, far more than five years could have elapsed on Earth (so you are in a sense travelling into the future)

Also:

• With the lack of friction in space, you could potentially use a form of propulsion to gradually accelerate yourself to the speed of light
• It would be within the reach of current technology to create a spaceship that could withstand being accelerated to close to the speed of light (because the accelaration forces would be very low) - although if it hit anything it could be destroyed
• With the like of ion drives and a nuclear power source it is feasible to build a propulsion system that could accelate the spacecraft to close to the speed of light

My questions are:

• Are all of the above assumptions correct?
• Is there anything else that makes this completely unfeasible?
• If it is unfeasible, what kind of technological advances would be needed to make it feasible? (or will it likely always be impossible)?
• Could the spacecraft be accelerated close enough to the speed of light, quickly enough to mean that somebody launching tomorrow, would be able to travel a significant way into the future, and how far could they travel?
  • For example, if a 20 year old man, with a life expectancy of 80, left today, how far could he travel into the future, taking into account that he would have to accelerate and decelerate again, with the 60 years of his remaining lifespan.

Any thoughts on this would be really appreciated. Thanks Blooper Watcher (talk) 01:23, 13 February 2010 (UTC)

I did some quick calculations myself, based upon a thrust figure of 88,000 mN (which seems to be the highest achieved by an ion engine). Assuming a mass of 10,000 kg for the spacecraft, I reckon that over 1,000 years you would accelarate to approximately 283,000 km/s (which is just shy of the speed of light). The calculation being:

(88 N * (1,000 * 365 * 24 * 60 * 60)) / 10,000 = 283,824,000 m/s

Obviously that is too long for a human lifespan (although I am not sure how close you need to get to the speed of light to see significant variations in relative time), and the engine would need to be 100 times more powerful to get to the speed of light in 10 years (and 10 more years to decelerate). But a 100 fold increase in power does not seem beyond the realms of possibility. Blooper Watcher (talk) 01:42, 13 February 2010 (UTC)

There is no doubt that if you could somehow accelerate yourself to somewhere close to the speed of light - then return to Earth again - then you would have "travelled to the future" - the faster you went, and the longer you stayed at that speed, the further into the future you'd go. In as much as you would seem to others to have lived more than your expected lifespan - and you would be "in the future" - complete with flying cars, personal rocket packs and a small fortune sitting in your bank account thanks to the one penny you left in there and the actions of compound interest!

That's a scientific fact that almost all scientists would agree on.

However, we don't have a way to get something as large as a human up to anything remotely close to that speed...just look at the hardware in the Large Hadron Collider, needed just to get some teeny-tiny sub-atomic particle up to close to light speed! But it's been calculated that the Apollo astronauts (who travelled faster than anyone else on earth ever has) did travel a tiny amount into the future. Apollo 8 astronaut Frank Borman is said to have actually demanded 400 microseconds of overtime pay from NASA because of the time dilation incurred in his trip.

So yeah - we have the technology to push someone 400 microsecond into The World Of The Future! SteveBaker (talk) 01:54, 13 February 2010 (UTC)

Thanks Steve. Do my figures for the acceleration using the most powerful current ion drive look correct? It would seem to me that a 100 improvement in the technology would be feasible which, again, if my figures are correct would be acceleration up to the speed of light in 10 years, and then decelarating back down in another 10 years. The thing is, how close do you need to get to the speed of light to get a noticable effect?

Let's say that we used the current drive, and over 10 years got up to 1% of the speed of light, stayed there for 40 years and then decelrated back down to stationary. How far, beyond the 60 year journey, would we have travelled? If we could accelarate up to 99% using a more powerful drive, and did the same 10 year accelarate, 40 years travel, 10 years decelerate, how much time travelling would we have done?

Also, aside from getting up to speed. Is there anything else that would always make this unfeasible? Blooper Watcher (talk) 02:04, 13 February 2010 (UTC)

One more thing, shouldn't NASA have been chasing Borman to pay some money back? Seems to me that he worked 400 microseconds *less* than the guys on the ground. Blooper Watcher (talk) 02:08, 13 February 2010 (UTC)

You should remember that mass is also relative. As you accelerate, the mass increases and you'll need more force to achieve the same acceleration (that's why you cannot reach the speed of light - see Speed of light#Upper limit on speeds about that). Your calculations do not seem to take that into account. Also, about "Therefore, if you circled the Earth at close to the speed of light, time on Earth would appear to pass more quickly than time on your "spaceship"" - it is going to be very hard to circle the Earth at such speed as it is going to be much higher than the escape velocity... --Martynas Patasius (talk) 02:42, 13 February 2010 (UTC)

For sure there is no way you could do this in orbit. The effects of relativity as you approach the speed of light make it increasingly difficult to push your speed that little bit faster. Even ion drives require reaction mass - and if you made them 100 times better, they'd need 100 times the amount of reaction mass - which would drastically increase the mass of your spacecraft and thereby eat most of the benefit you got from better engines. This has been thought about many times before by many smarter people than us - and it's quite utterly impractical. SteveBaker (talk) 05:03, 13 February 2010 (UTC)

As you say, there would be a big problem if the spacecraft hit anything when going at relativistic velocities. Unfortunately, it is guaranteed to hit something - the interstellar medium. In the vicinity of the Sun, the interstellar medium contains about 50,000 atoms (we'll assume they are all atoms of hydrogen, which is close enough to the truth) per metre cubed. If we assume a speed of 0.99c, that's a gamma factor of about 7. That means that, from the perspective of the spacecraft 50,000*7=350,000 atoms per metre cubed (due to length contraction) and each has a mass of 7 times that of hydrogen (due to relativistic mass) and they are all travelling at 0.99c. That means that, in every second, for every metre squared of cross sectional area, the ship will hit 350,000*300,000,000*7 u of gas moving as 0.99c, that applies a force of 0.00037 N. That compares to a car travelling at 30 m/s (70mph) having air resistance of 1080 N. Clearly, that isn't a big problem (although it is still a problem, since ion drives typically produce far far less force than a car's engine), but if we increase the velocity to 0.999999997c, it becomes roughly the same resistance as the car. So, as you can see, the resistance from the interstellar medium does provide a limit to how fast you can travel, although that limit is pretty high. (All of these calculations are assuming perfectly elastic collisions - if the hydrogen doesn't just bounce off the ship then you need to look at the energy of the atoms, which is extremely high since it is proportional to velocity squared, so we would probably find the ship being significantly eroded by the constant collisions.) --Tango (talk) 13:26, 13 February 2010 (UTC)

Tango, all that hydrogen can be seen as an aset instead of a liability. In principle it could be collected and used to power a fusion reactor that suplies energy to the ion drive. Dauto (talk) 15:40, 13 February 2010 (UTC)

Bussard ramjet perhaps? 220.101.28.25 (talk) 16:36, 13 February 2010 (UTC)

That article discusses the feasibility. Most studies seem to show that it wouldn't work (you get greater drag from the collector than you can generate thrust). Our article gives an example where it would work, but assumes an extremely high exhaust velocity with no justification for it being possible. --Tango (talk) 17:09, 13 February 2010 (UTC)

The now-cancelled Project Orion was to get a spacecraft to a theoretical upper limit of 10% of the speed of light. ~AH1^(TCU) 23:25, 13 February 2010 (UTC)

As a torchship scuts through space at near the speed of light, a scoop on the front funnels any molecules encountered into the reaction chamber where they are accelerated to provide additional thrust. The scoop and the channel the molecules pass through are made of Unobtanium, a metal which is not readily available at present (but neither is Plutonium), but which has 157 hits at Google Book Search. Edison (talk) 04:35, 14 February 2010 (UTC)

See Unobtainium. Amazing the things we have articles on! --220.101.28.25 (talk) 06:00, 14 February 2010 (UTC)

isnt this similar to the question I had asked earlier about time travel, when I experienced " time travel" in flying between Dubai and Doha in 55 minutes and coming to a time zone 1 hour behind, thereby experiencing 5 minutes of the evning again... but as one person pointed out, this is not time travel, this is basically readjusting the watch. similarly your question - "if you left now, got up to the speed of light quickly and then can back in five years, far more than five years could have elapsed on Earth (so you are in a sense travelling into the future" is flawed becos while you feel you travelled for 5 years its merely readjusting the cclocks with regard to what the time is on earth. so this actually doesnt qualify as time travel... and all this if someone mages to fly almost the speed of light. —Preceding unsigned comment added by 213.130.123.12 (talk) 11:23, 16 February 2010 (UTC)

but the problem you have to realy consider, is that even with artificial gravity, im space you loose weight. thats why astronauts workout and still come back lighter then they where when they left. the thing just is, ower bodys arnt made to be in space. --Talk Shugoːː 20:51, 16 February 2010 (UTC)

Carbon dioxide and plants at night

A question has come up on a sleep forum, in regard to plants in the bedroom. I've tried to read the photosynthesis articles (difficult here, too simple at simple), and haven't found an answer. Do (some? all?) plants release carbon dioxide in the dark? Thank you. - Hordaland (talk) 10:36, 13 February 2010 (UTC)

Plants release carbon dioxide continuously, since they respire in the same way animals do. However, during the day (when they are in light) they also photosynthesise, and this converts carbon dioxide to oxygen. Therefore, it is generally true that the amount of carbon dioxide they take in during the day exceeds the amount they give out. This is not true at night time. However, the amount of CO2 they release should not be enough to cause any problems to people in the same room. --Phil Holmes (talk) 11:20, 13 February 2010 (UTC)

Yes, all plants do this - but the amount they produce is completely negligable compared to the amount a person sleeping in that room would produce. There are families in poorer countries who sleep 10 people to a room - and they don't suffocate! This is SO far from being a possible problem that might concern a "sleep forum" that it's almost laughable - so tell the people there "Don't worry - it's such a tiny effect that it's completely unimportant." SteveBaker (talk) 15:09, 13 February 2010 (UTC)

Thank you both! The forum (listserve, actually) is for sufferers of severe Delayed sleep phase syndrome, and we take each others' questions seriously. There is no effective treatment, so we question any little thing that might help -- or not. I will politely explain that the questioner needn't consider the CO2 from the "humungus bamboo tree" next to the bed. Thanks again! Hordaland (talk) 16:24, 13 February 2010 (UTC)

Steve, "suffocate" is your word. We haven't contemplated any such thing. Hordaland (talk) 16:31, 13 February 2010 (UTC)

The room would have to be airtight if something like hypercapnia were to occur. ~AH1^(TCU) 23:20, 13 February 2010 (UTC)

That's the point. Virtually no rooms are airtight, also due to building regulations. --Ayacop (talk) 18:15, 14 February 2010 (UTC)

I have seen architectural plans of hospitals from the 1920's which had a "plant room" on each floor. Plants from patient rooms were stored in the plant room at night for fear they might deprive the patient of some oxygen if left in the patient room. I do not know what year this practice arose or when it was phased out. Schaum's Outline of Biology(2009) Q. 20.3 says that plant removal from hospital rooms at night is still done in some locations. Edison (talk) 20:59, 14 February 2010 (UTC)

magnetic vector potential actual meaning?

whats exactly ment by magnetic vector potential?is it only a conceptual idea? what tha physical meaning of magnetic vector potential. —Preceding unsigned comment added by Dakshu (talk • contribs) 10:51, 13 February 2010 (UTC)

The vector potential is definatly real. read for instance Aharonov–Bohm effect. Dauto (talk) 13:54, 13 February 2010 (UTC)

Well... the Aharonov–Bohm effect depends only on the integral of A around a closed loop. E and B tell you the integral of A around all infinitesimal loops. Assuming space is simply connected, you can integrate the infinitesimal loops inside the finite loop to get the integral around the finite loop, unless there's a singularity inside. So the only case in which the Aharonov–Bohm effect depends on something beyond the E and B fields is when there's a singularity in the field. Even then you can get it from the E and B fields alone if you treat them as generalized functions.

On the other hand, to calculate the Aharonov–Bohm effect from the E and B fields you have to integrate them over a region where the electron doesn't go. This isn't even a quantum-mechanical takes-all-paths situation, because this region is excluded from the path integral too—the electron really isn't there. But if you use A, the effect depends only on the region where the electron does go. In that sense, A is closer to the reality. But A has a large gauge freedom, meaning that only part of it is real, while the E and B fields do a perfect job of capturing the part of A that's real. What Aharonov–Bohm shows is that they capture it in a way that's nonlocal with respect to (some of) the physics.

There's a GR counterpart to Aharonov–Bohm in lensing around cosmic strings. The exterior gravitational field of a cosmic string is zero. Spacetime is flat around the string; objects do not fall towards the string. But if two objects moving in parallel pass on opposite sides of a cosmic string, they'll end up heading towards each other on the other side, because the integral of the metric on a loop around the string is less than a full circle. Instead of using the metric, you can get the same result by integrating the scalar curvature over a surface that intersects the cosmic string, as long as you don't mind that you're integrating over a region where the particles don't go. -- BenRG (talk) 23:07, 13 February 2010 (UTC)

Think of it as the magnetic field's version of a voltage (or, electric potential). As the voltage is just a mathematically different way to express an electric field, the vector potential is simply another way to represent the magnetic field, in terms of relative potential energy. Then there are just different mathematical conveniences and uses than the B and H fields. Magnetic potential goes into more detail with math and stuff if you haven't read it yet. —Akrabbim^talk 14:15, 13 February 2010 (UTC)

The reason a magnetic field's energy must be described with a vector potential, as opposed to a scalar potential, is because the force imparted by a magnetic field does not only depend on position (it also depends on relative velocities and orientations). In order to quantify this field in a way that satisfies conservation of energy, the potential field must be described by a vector. This is a direct consequence of the Lorentz force law, which is empircally observed. It helps to thoroughly understand what a potential field means in general before trying to apply that mathematical concept to the somewhat pathological case of magnetism (whose force is defined by a vector cross product and a time derivative - not difficult concepts, but enough to make the math much harder than the electrostatic potential case!) Nimur (talk) 16:44, 13 February 2010 (UTC)

Nimur, does an isolated positive electric charge move if you place it in a scalar electric potential field? Cuddlyable3 (talk) 17:49, 13 February 2010 (UTC)

A meaning of pathological is Relating to or caused by a physical or mental disorder.[1]. Nimur, is there another word you could use to characterise the case of magnetism? Cuddlyable3 (talk) 17:19, 13 February 2010 (UTC)

Sorry. I meant it in the sense that the mathematical convention seriously breaks from the normal form of a scalar potential field. I use "pathological" in the sense of any instance that diverges from the norm in a way that breaks simplifications. I think this usage is very common in math, physics, and computer programming - it has evolved and is distinct from the meaning in the medical field. I don't think I'm coining a neologism - let me find some prior usage. Nimur (talk) 17:27, 13 February 2010 (UTC)

See pathological (mathematics). -- BenRG (talk) 23:07, 13 February 2010 (UTC)

There's nothing wrong with using the word 'pathological' per si. But I don't agree with what Nimur is saying since the electric field expression also depends on the vector potential. Dauto (talk) 17:25, 13 February 2010 (UTC)

Sure - but we can construct a totally scalar electric potential field - that's the simplification I'm referring to above. It is possible (although it limits the situations you can consider) to construct the electric potential in scalar form. No possible simplification exists to represent the magnetic potential in scalar form. Nimur (talk) 17:29, 13 February 2010 (UTC)

$\mathbf {E} =-\nabla \phi -{\frac {\partial \mathbf {A} }{\partial t}}.$

Dauto (talk) 17:29, 13 February 2010 (UTC)

Electrostatics - therefore, there is no time variation. I think I mentioned this before. Nimur (talk) 17:30, 13 February 2010 (UTC)

Read Magnetic potential#Magnetic scalar potential.Dauto (talk) 17:43, 13 February 2010 (UTC)

Nimur, does an isolated positive charge move if you place it in a scalar electric potential field? Cuddlyable3 (talk) 17:49, 13 February 2010 (UTC)

Yes. That does not mean the field is time-varying - that does not mean a full electrodynamics treatment is necessary. See test particle if you don't understand why. This is called electrostatics and it is a well-developed, mathematically rigorous approach. Obviously, it is inapplicable in situations where the time-variance is non-negligible - that is, by definition, electrodynamics - and it is more general, requires harder math, and requires the vector potential Dauto has spelled out above. Nimur (talk) 00:07, 14 February 2010 (UTC)

Nimur, I read Test particle#Test particles in plasma physics or electrodynamics and don't understand how there can be a force to move the positive charge without a vector to define the force direction. Is not every electric potential field a vector field? Cuddlyable3 (talk) 18:42, 14 February 2010 (UTC)

Force is the gradient of the scalar potential. The gradient operator can create a vector field out of a scalar field. This is a very common formulation of energy-force relationships, even outside the realm of electricity and magnetism. The extension of the potential to a full vector field throws some non-trivial kinks into the matter, which is what the OP was asking about in the first place. As I've mentioned above, because magnetic force is defined by the lorentz force (which involves a vector cross product and a time derivative), the corresponding potential field is most succinctly described as a vector potential. Dauto has listed above a magnetic scalar potential - I have never seen this used in practice. But, what do I know, I'm only a professional numerical physicist... Nimur (talk) 18:46, 14 February 2010 (UTC)

Thus an electric potential field (except in the degenerate case of a uniform field where all points have the same or zero potential) is inseparable from a vector field. Yes the vectors are the gradients of the potentials at each point. This is we agree a common formulation. So Nimur I don't know how you claim "we can construct a totally scalar electric potential field". Cuddlyable3 (talk) 23:18, 14 February 2010 (UTC)

I think you should review the gradient article. Nimur (talk) 03:41, 15 February 2010 (UTC)

Yes. And? Cuddlyable3 (talk) 16:08, 15 February 2010 (UTC) who is also familiar with the Jacobian.

The vector potential does have a physical meaning, but it's somewhat difficult to visualize. I'll try to explain it by a toy example. Imagine you have a cylinder of wire mesh, kind of like this. But it's twisted: the circles are still circles, and they're still parallel to each other, but they've been rotated relative to each other so the wires running between them aren't straight any more. No matter how twisted the cylinder is, you can always untwist it if you're strong enough. Now imagine you have a torus of wire mesh, kind of like this. Again, it's twisted. You can always locally untwist any part of it, but in contrast to the cylinder, you can't necessarily untwist the whole thing. If the sum of all the relative rotations of adjacent circles all the way around the torus is zero, then you can untwist the whole thing; otherwise, you can't.

This "freedom to twist" is called "gauge freedom". The only properties of the wire mesh that we care about are those that you can't untwist. This means that in the case of the cylinder, none of the twisting matters; it's all "just gauge". In the case of the torus, the only thing that matters is a single number giving the total amount of twist around the whole torus.

Now (here's where it gets hard) increase the number of dimensions. You can think of it this way: if you take a line and replace each point with a circle, you get a cylinder. If you take a loop and replace each point with a circle, you get a torus. What you want to do now is take space and replace each point with a circle. As you go from point to point in space, there's a corresponding twisting of the circles, and the question is to what extent you can untwist them and to what extent you can't. The answer is that what you can't untwist is completely captured by the total twist around all closed loops in space (the total twist around the loop being defined in the same way as it was for the torus). You can get the twist around large loops by adding the twist around smaller loops inside the large loop, as illustrated at Stokes' theorem#Underlying principle. This means that if you know the twisting around infinitesimal loops then you can find the twisting around all loops, and hence you know everything there is to know about the twisting. This is what the B field tells you. The magnitude of the B field at a point is the maximal amount of twisting of any infinitesimal loop at that point, and the direction of the B field tells you which loop is maximally twisted (namely, the one in the plane perpendicular to the field).

What the A field tells you is the amount of twisting as you move from one point to another. The direction of the A field at a point is the direction in which the twisting is maximal, and the magnitude of the A field is the amount of twisting in that direction. The A field has a gauge freedom corresponding to your freedom to twist. The B field doesn't; it tells you just the part of A that matters.

This analogy is much closer to reality than it might seem. If you imagine there really is a circle at every point in spacetime, twisted in the way I described, and write down the general relativistic equations for 5D gravity in that 5D space, you actually get Maxwell's equations and 4D gravity, the A and B fields literally mean what I just said they mean, and electric charge corresponds to momentum around the extra dimension. This idea dates back to the 1920s and is called Kaluza–Klein theory. -- BenRG (talk) 23:07, 13 February 2010 (UTC)

Paranormal

Did Jung have any faith in supernatural ? As far as I know Freud did not beleive that any entity does survive bodily death. But Jung's collective unconscious is some what near and dear to spooks...no ?

 Jon Ascton  (talk) 11:39, 13 February 2010 (UTC)

Many interpretations of Jung's writing do exist - it wouldn't be too far to consider his archetypal unconscious as a "supernatural" concept - even though he surely considered it "science". Because the collective unconscious was not based on empircal evidence, though, it's not really a scientific conclusion. Later generations of psychologists categorically discredit that line of reasoning in favor of observation-based theories of psychology. Nimur (talk) 16:39, 13 February 2010 (UTC)

See our article on synchronicity -- most people think of that as supernatural. Looie496 (talk) 18:15, 13 February 2010 (UTC)

Also look at collective unconscious. ~AH1^(TCU) 23:17, 13 February 2010 (UTC)

Why did the Challenger shuttle explode in a white cloud?

When watching the explosion again recently, I was struck by the fact that the "smoke" was all white, rather than black/grey that I would expect to see from an explosion. Is this because the white stuff is actually refrigerated fuel that did not combust and instead turned to a ball of vapour that obscured any of the smoke? Blooper Watcher (talk) 14:42, 13 February 2010 (UTC)

The fuel in the external tank is about 800 tons of liquid hydrogen and liquid oxygen. When that exploded, the reaction produced 800 tons of water vapor - which is white. What you're seeing is a small cloud - in the sense of a "rain cloud". (Um - actually, less than 800 tons - it would have used a good chunk of that during the launch sequence - but still a heck of a lot.) SteveBaker (talk) 15:00, 13 February 2010 (UTC)

(ec)Small quibble. The Shuttle itself did not explode, it was the external fuel tank that exploded 'deflagrated'(?). Aerodynamic forces broke up the orbiter. See Shuttle challenger disaster. The long continuous trails are exhaust from the solid rocket boosters. As per SteveBaker & cloud See Shuttle_challenger_disaster#Post-breakup_flight_controller_dialog 220.101.28.25 (talk) 15:09, 13 February 2010 (UTC)

This NASA link can probably answer any questions about the Challenger STS-511 --220.101.28.25 (talk) 15:19, 13 February 2010 (UTC)

As an interesting aside, since it produces so much water, the launches of shuttles like these cause sudden downpours a few hours later. Vimescarrot (talk) 16:27, 13 February 2010 (UTC)

^{(citation needed?)} Eight hundred tons of water spread over a path 100 km long and 100 meters wide (let's say) works out to a lousy 80 grams per square meter -- less than a tenth of a millimeter of liquid water, so I don't imagine it's just the Shuttle exhaust falling out of the sky. What I could believe is that the long trail of water vapour could nucleate cloud formation and trigger rainfall that way.... TenOfAllTrades(talk) 17:02, 13 February 2010 (UTC)

A (probably overly-dramatic) show presented by James May. Probably James May's 20th Century. Vimescarrot (talk) 17:07, 13 February 2010 (UTC)

Even smaller quibble. Water vapor itself is basically colorless in the visible spectrum. The white stuff, like any cloud, is condensed water (i.e. tiny droplets of liquid). Buddy431 (talk) 16:33, 13 February 2010 (UTC)

drag vs Reynolds #

There is a relationship between coefficient of drag and Reynolds number. When the object is sphere, the relationship can be pictured like this. I've seen versions of this figure in a number of chemical engineering textbooks. What I haven't been able to find out is whether this relationship is an empirical correlation, or an analytical solution, i.e. is this a relationship that is just observed to be true in experiments, or is it a relationship that must be just so according to the theory in this area? ike9898 (talk) 19:23, 13 February 2010 (UTC)

The limiting behavior (i.e. the behavior at very high and very low Reynolds number) can be derived analytically. The intermediate regimes can probably be modeled computationally for idealized fluids, but are more likely to be measured empirically for any actual fluid. Dragons flight (talk) 08:11, 14 February 2010 (UTC)

February 14

boiling

when water and milk are boiled, water boils but milk overflows. why?? —Preceding unsigned comment added by 59.96.24.220 (talk) 05:43, 14 February 2010 (UTC)

The milk's cream forms a layer at the top. When the milk boils the steam pushes that layer up making a mess. Dauto (talk) 05:47, 14 February 2010 (UTC)

But is it the increase in the tensile strength of the bubble walls by the protein+fat film on the surface, or the reduction in surface tension? BTW I am not the OP; sorry for hijacking the question this way.--Dr Dima (talk) 05:55, 14 February 2010 (UTC)

It is probably complex. There is probably more than one factor in play. Milk is a complex substance. Probably the bubbles break less easily, thereby they hold their volume, propelling the liquid portion of the substance over the rim of the pot. Bus stop (talk) 06:00, 14 February 2010 (UTC)

... so what is the mechanism for preventing boiling over by placing a ribbed circular metal device at the bottom of the pan? It causes the milk to boil almost like water. How does it work? Dbfirs 07:47, 14 February 2010 (UTC)

All your questions are answered at milk watcher.--Shantavira|^{feed me} 08:17, 14 February 2010 (UTC)

Thanks. I didn't know what they were called. I've never seen the ceramic and glass versions. Dbfirs 08:56, 14 February 2010 (UTC)

As for the "layer" of cream at the top, see scalded milk. ~AH1^(TCU) 03:24, 16 February 2010 (UTC)

Signal White Now - Why?

There is a new product called that makes your teeth instantly white. The manufacturer offer following explanation of its effect: "Signal White Now, our latest innovation, transfers optical-effect technology developed by Unilever’s laundry team to the field of oral care, using a blue pigment to make yellow teeth appear whiter." My question is, why would blue on yellow make your teeth white? (even if it is only for a while). Shouldn't it make the teeth actually green? —Preceding unsigned comment added by Quest09 (talk • contribs) 11:38, 14 February 2010 (UTC)

Yes, it should make them green. Blue+Yellow=White for light, but not for pigments, for pigments it makes green (see additive colour and subtractive colour for details). --Tango (talk) 12:51, 14 February 2010 (UTC)

The OP may be referring to some sort of optical brightener which are commonly used for clothes and do I believe work with the article offering some explaination for how. Or perhaps it is just some simple blue dye as with bluing (fabric) agents such as Mrs. Stewart's Bluing which also work although according to our article have now been largely replaced with optical brighteners. Our article mentions some cosmetic uses for both, particularly for hair. This [2] offers some, not extremely scientific (and obviously not an unbiased source but I don't think there is any real dispute that it works) explaination of why dying white/offwhite blue can make them seem more white. If you overuse the dye, then it's likely to look too blue and if it's something extremely yellow then it's going to look green but this isn't how bluing is done. As an aside bluing agents are also useful for growing rock crystal gardens [3] [4] (also mentioned in the article) although I never found any in Malaysia when I was looking in around 2000 as a suggestion for a friends project. Nil Einne (talk) 14:31, 14 February 2010 (UTC)

Most Americans see something that's truly white as a bit yellowish (I don't have a source, other than my father). My dad helps manufacture plastics, and it's customery to add just a bit of blue coloring to white plastics to make them more attractive. He says that in plastics destined for certain other parts of the world, though, they add different colors. I don't recall what colors get added for what areas, but it's interesting that it appears to be a cultural thing, rather than something hardwired into us. Buddy431 (talk) 17:16, 14 February 2010 (UTC)

This is not exactly how color vision works. The spectrum of light that reaches the eye depends both on the emission properties (such as intensity as a function of wavelength) of the illuminant and the reflection properties (such as reflection coefficient as a function of wavelength) of the surface. The photographic film registers faithfully the light that arrives: use yellow-rich illuminant and the picture will have mostly shades of yellow, use blue-rich illuminant and the picture will have mostly shades of blue. Not so for the human eye. We have a "built-in" color constancy mechanism that allows us to discard (or at least to separate out) the illuminant information and to infer the reflectance of the objects, so that the colors of objects that we see look roughly the same under different illuminants. A gray piece of cloth will look gray both at midday, at sunset, under incandescent lights, and under the fluorescent lights; all the same. The white point therefore is not only subjective, but also depends strongly on the choice of illuminant. Now, yellow and blue are opposite each-other on the color wheel. Thus, adding more blue to the reflection spectrum is indeed making an object look less yellow (more white), as yellowish objects have relatively more yellow and less blue in their reflection spectrum. Oxidation tends to render paper, fabric, and plastics yellow; thus, at least in the past, it was customary to add a small quantity of a blue dye to the laundry rinse water and such. I am not entirely sure, but this is not AFAIK a cultural thing. Color naming is a cultural thing; but color perception is universal among humans with normal trichromatic color vision (which is the vast majority of mankind). And, regarding the question whether you get white or green when you mix blue and yellow, it is explained very well in our Color mixing article. --Dr Dima (talk) 22:42, 14 February 2010 (UTC)

heat loss

a vertical sq. plate 30 cm on a side is maintained at 50 c and exposed to room air at 20 c(temperature) the surface emmisity is 0.8 calculate total heat loss by both sides of plate?

It says at the top of the page, "If your question is homework, show that you have attempted an answer first". This looks like a homework question to me.Heat transfer might help. --ColinFine (talk) 17:22, 14 February 2010 (UTC)

(ec) This looks like a homework question to me, and we don't do people's homework for them. If you have a go at it and get stuck, we'll try and help you out, but you need to show you have tried and tell us precisely where you are getting stuck. --Tango (talk) 17:24, 14 February 2010 (UTC)

Malicious pigeon

The silly title refers to this question: From how high up can one (say: pigeon) drop an object (say: poop) and be certain that it will fall exactly on a given target (say: victim). Let us assume the object is a smooth sphere dropped in still air and we may choose its diameter and weight. Initial velocity is zero. I believe that its trajectory is predictable until either A) due to its increasing velocity the Reynolds number exceeds Re = 0.1 whereupon the path will be deviated unpredictably by turbulence, or B) it reaches terminal velocity while still in laminar flow. I lack an equation for the Reynolds number of a sphere falling in air. I shall assume the pigeon is a perfect marksbird but wonder whether the ultimate bombing accuracy is set by Brownian motion of the surrounding air which would impact accuracy less on a cold day than a hot day. Can anyone help put numbers to these considerations? Cuddlyable3 (talk) 18:26, 14 February 2010 (UTC)

Before you even begin discussing turbulence, brownian motion, and chaos theory, let's start out with an even simpler problem in predicting the actual impact location. Wind can be described (with great simplification) as a vector field for every x,y,z point. At each point <x,y,z>, there is a vector, <wx,wy,wz>(t) - a time-varying windspeed. Assuming you can estimate this 7-degree-of-freedom vector field, you can estimate the force on the falling object at all times. How do you plan to estimate those parameters? Once you have that problem solved, turbulence will be a minor perturbation. The trajectory is predictable only insofar as you know the wind speed at the time that the object passes through all points in its trajectory. I think you will find that people who spend their days laying targets for ballistic objects are satisfied to assume an "exact targeted location, with a point spread". Some will even account for an average wind speed and time-of-flight estimate, to give a first-order correction to impact position. The error caused because you can't estimate wind speed is much larger than any error due to turbulence. If you had, for example, by advanced doppler radar, a reasonably accurate estimate of the wind speed in your volume of interest, you might refine your estimates and need to start worrying about turbulence and nonlaminar flow to increase your accuracy. A better way to phrase your problem would be to ask about the order-of-magnitude error that is due to wind, vs. due to turbulence. On all but the very calmest of days inside the most carefully controlled wind tunnel, I think we could safely say your pigeon would need to worry much more about the former (wind-speed estimation error) than the latter (trajectory estimation error due to non-laminar flow). Nimur (talk) 20:46, 14 February 2010 (UTC)

Nimur your information would have been relevant if I had not said in still air. Cuddlyable3 (talk) 22:58, 14 February 2010 (UTC)

Turbulence happens in still air anytime the object is falling too fast to be in laminar air flow. Turbulence is a chaotic process - hence Nimurs information is highly relevant. SteveBaker (talk) 23:25, 14 February 2010 (UTC)

The Mathematics of Exterior Ballistics, The American Mathematical Monthly (1940), provides an analytic and numerical integral solution based on the Siacci method. The presented model may include any number of parameters, each increasing theoretical accuracy, while practically introducing huge estimation errors. The model includes, in no particular order, gravity, aerodynamic drag that linearly depends on velocity, non-flatness of trajectory, estimation of initial velocity, estimation of air density and air temperature structure, approximation of the projectile as a constant/standard weight, assumption of negligible wind, neglection of the Coriolis force, and finally, error due to numerical integration. Turbulence probably falls into the category of air density and air temperature effects, though it is not mentioned explicitly in this paper. Trajectory Models for Heavy Particles in Atmospheric Turbulence: Comparison with Observations, (2000), Journal of Applied Meteorology, details some more modern methods and mathematics; again, though, "the Langevin model estimated the location and width of the bead deposit swath very well and fixed the peak deposit density to within (at worst) about 100% error" and "uncertainties in the treatment of deposition proved more significant than nuances of the trajectory algorithm." Your insistence on modeling turbulence will categorically put you on a path to a very error-prone subset of all possible models - it would be much more useful to assume turbulence is a statistical perturbation on an otherwise ballistic trajectory, and model the more relevant ballistic effects. In any case, these papers can help "put numbers to these considerations." You might also find the Wikipedia article on external ballistics informative. It presents a large number of common models and some realistic numerical parameters to feed into them. Finally, as you found my earlier comment irrelevant, I'd just follow up and suggest that my response is tailored by experience here - so with all due respect, I may be a better judge of relevance than you're giving me credit for. Your question is asking about a marginal perturbation and neglecting a much more important and realistic effect. It's equivalent to asking the impact of brownian motion on gravity. An effect surely exists - but it's so far below the noise floor, that in anything except a staged, theoretical problem, you would never need to worry about it. Air temperature will have more of an effect on air density and air stratification - which will both affect trajectory - and any effect of brownian motion will be dwarfed by those effects. In any case, today's pigeons are rarely dropping ballistic packages - between precision-guided munition and simple passive aerodynamic munitions, the targeting accuracy is defined by a much more heavily engineered, complicated algorithm than a simple trajectory. Nimur (talk) 03:19, 15 February 2010 (UTC)

Nimur, doubt not that I respect your experience. I reframe my question: a smooth sphere diameter d weight m is dropped from vertical position y=0 with initial velocity u=0 in still air, as would be the case inside a vertical tube (with internal diameter much larger than d). Assume atmospheric pressure, room temperature and Earth gravity. At what (negative) y value is the sphere no longer falling exactly vertically? (Please forget the dynamics of pigeons and munitions and I apologise for introducing the former distraction or implying the latter. This concerns dropping a little ball in laminar flow and not shooting anything.) Cuddlyable3 (talk) 16:58, 15 February 2010 (UTC)

If we assume an ideal sphere with no surface imperfection, and assume an ideal tube with no wall surface imperfections, then the system will be totally symmetric, and any turbulence or nonlaminar flow will be similarly symmetric. The dropped sphere will never deviate from a perfect vertical fall. In reality, the perfect sphere has some nonuniformity - perhaps its mass isn't uniformly distributed, or it has some miniscule scratches or grinding patterns on its surface - and that is what will cause the fluid flow around it to become turbulent asymmetric (which is not the same as turbulent). Your effort to characterize this phenomenon with a Reynolds number can only go so far - remember, that is a quantification of "non-ideal behavior" - but you're trying to set up an ideal problem! So, without some parameterization about the sphere, this is an unsolvable setup. In practice, we would drop the sphere in a test tunnel and measure its properties and construct a table or perform a data fit to some empirical model. In theory, we would apply flow-in-a-pipe equations. But I can't stress enough - when dealing with turbulent flow, your theoretical estimates are going to overwhelmed by estimation-errors that can be orders of magnitude larger than any other parameter you're trying to fit. So, the effort to construct a perfect analytic model of a perfect sphere in perfectly still air is fundamentally flawed. Nimur (talk) 18:01, 15 February 2010 (UTC)

Nimur we need to make more effort to understand one another. I have assumed you understand the empirical significance of Reynolds number. Transition from symmetrical laminar flow to chaotic turbulent flow occurs when inertial forces become too large compared to viscous forces. The onset cannot be prolonged by extreme smoothness of a sphere in fluid which is the simplest case of an object in fluid that has been tested empirically. Equations for fluid Flow-in-Pipe are irrelevant because my setup does not involve movement of air relative to the pipe (which I introduced only to persuade you that the fall is in windstill air). You seem conflicted about turbulence being symmetric; see this. If your response is to be only "Go drop some spheres and do a data fit" then I thank you for that. BTW This question apart from the pigeons relates to a real application and not a geometrical abstraction. Cuddlyable3 (talk) 19:58, 15 February 2010 (UTC)

Are you thinking of reproducing the Book of Tobit? Nyttend (talk) 01:03, 16 February 2010 (UTC)

Tobit 2:10 is about sparrows not pigeons. Cuddlyable3 (talk) 19:48, 16 February 2010 (UTC)

Since Brownian motion etc would be symmetric, Presumably the largest effect causing deviation from a completely straight trajectory would be from the Coriolis effect. Or are we assuming the pigeon takes this into account? 82.132.248.94 (talk) 02:12, 18 February 2010 (UTC)

good alternative to chess?

I love chess, its depth and balance are awesome, but it is very frustrating for me that high-level play implies huge amounts of memorization instead of creativity or mind power, you know what I mean... So does anyone know a comparable game but without that disadvantage? --Belchman (talk) 20:11, 14 February 2010 (UTC)

Go (game)? There have been varients of Go, such as Othello (game), Gomoku, or Pente. Go, and all of the varients, are about as simple to play as Tic-Tac-Toe (or Crosses and Naughts for our Britishy readers) but have very complex and intellectually deep strategies. --Jayron32 20:28, 14 February 2010 (UTC)

[It's "Noughts and Crosses" (or "Naughts..."), for the record, Jayron.] To alter the set-up completely, perhaps Bridge might interest you. Admittedly it's four player, but once you get past a beginner level, it requires the sort of thinking you want (there are several variants which make it almost completely skill and not chance). - Jarry1250 ^{[Humorous? Discuss.]} 20:32, 14 February 2010 (UTC)

Bridge up to the club level, maybe. Beyond that, unfortunately, the contemporary game has become a lot about memorization, as the natural bid has almost disappeared. The first natural bid you make in one of these systems may very well be the contract you intend to play. Defensive signaling is similarly baroque. At an academic level these systems are interesting; in actual play I just find it an annoyance.

I would like to see more Individual events. Without any artificial restrictions on systems. The way I'd run an Individual is, you get to find out who your partner is and talk to him for three minutes. Anything you can agree on in three minutes is kosher, but you have to be able to accurately explain it to the opponents, and if you can't, the risk is on you. --Trovatore (talk) 21:49, 14 February 2010 (UTC)

I agree, the whole "bidding system" stinks of being a way to circumvent the rules - and all manner of meta-rules end up being imposed. I couldn't recommend bridge to someone who wished to avoid memorization. SteveBaker (talk) 23:06, 14 February 2010 (UTC)

The rules do require you to explain your system to your opponents (although usually that's just done by saying "We use the X system with Y variation" or similar). I really don't get the appeal of bridge for the simple reason that I am sure I could write a computer program that would play better than I can, and probably better than most experienced bridge players. Bidding is, as you say, formulaic and the actual play is extremely easy as long as you are capable of memorising the cards that have already been played and all the information you received during the bidding stage. Following algorithms and memorising things are precisely what computers were invented for. --Tango (talk) 23:19, 14 February 2010 (UTC)

Oh no, the play of the hand is not by any means easy. At least finding the best play is not. Granted, on a large percentage of hands, the best play will be found by any player who understands the basic principles and remembers the available information, but that still leaves lots of hands where that isn't true, more than enough to swing a tournament if the bidding is equal.

To me the play of the hand, whether as declarer or as defender, is the soul of the game, and I wish the bidding phase were less important. But it is what it is. The amount of effort put into bidding by the most successful players indicates that that must be where the tournaments are largely to be won or lost. --Trovatore (talk) 00:44, 15 February 2010 (UTC)

I disagree. The first few tricks may have some challenge in them, but after that you have so much information available that it becomes fairly predictable. The problems with the game are evidenced by the prevalence of duplicate bridge in tournaments - there is so little skill in the game (for experienced players) that you can only tell who has the most skill by removing (almost) all the luck. Most games with comparable randomness (eg. poker and Magic: The Gathering, to name two that I have played a significant amount of) you can determine the more skillful players just by playing a reasonable number of games, but that isn't the case for bridge. --Tango (talk) 00:59, 15 February 2010 (UTC)

Well, if you disagree, it means you don't know the game. The play of the has great subtlety and complexity. As I say, it doesn't show up on every hand, but it does on lots of hands.

If you want to find out what I'm talking about, you can't do better than Louis Watson's masterpiece The Play of the Hand at Bridge. You can get it from Amazon UK for about eight pounds. --Trovatore (talk) 01:06, 15 February 2010 (UTC)

I second the vote for "Go". We have computers that can play chess better than the best humans alive - but Go is so difficult that computer Go players are scarcely able to approach the level of professional players. The beauty of it is that there is no memorization of openings - no memorization of end games - and the rules are spectacularly simple. IMHO, it's a much 'purer' game than chess. I think you'll like it. SteveBaker (talk) 23:02, 14 February 2010 (UTC)

Chess computers don't play chess the way people do; the fact that those techniques fail for go doesn't reflect on go's difficulty for human beings. Not that that's an argument against learning go, unless you wanted to learn by playing a computer opponent. -- BenRG (talk) 02:16, 15 February 2010 (UTC)

Or there are variants of chess itself, which are not played at professional level so they don't have that much official and well-researched sequences one has to memorize. Two popular of them in my former high school were:

• White moves once, black moves two times, white moves three times, and so on, always increasing the number by one. Chess is allowed only as the last move in the sequence, and in this case the adversary's first move has to be stopping the chess in one move or being defeated by checkmate. One can win by checkmate or capturing everything except for the enemy king. As the later is much more common, in a tournament the checkmate win can be worth more points than the "simple win". The game is usually over in around 12-13 moves.
• For 4 players, have two chess sets, preferably of similar size. It is played by teams of two, each playing with different colors, side by side. After capturing an enemy piece, you give it to your teammate, who can place it on his/her own board. The rules are:
  • Captured pieces are given to the teammate.
  • When the opponent ended his turn, you can take all the pieces given by your teammate (while your opponent was thinking) in your hand. After this no other captured pieces given by your teammate can be used in this turn, only those already in your hand. (This is to avoid deadlocks which could occur by refusing to make a move until your teammate can capture something you need.)
  • You can choose to place a piece from your hand on the board instead of a normal move. You are not allowed to place something that would put your opponents king instantly in chess, neither can pawns be placed on the last row. Pawns reaching the last row do not promote, they are instantly captured by your opponent. This does not limit the usefulness of the pawns, as a double row of pawns are a very god defense or a good support of an attack, sometimes players ask their teammate to sacrifice a minor piece for a much needed pawn.
  • Achieving checkmate or stalemate on one board instantly ends the game and the situation on the other board becomes irrelevant in scoring.
  • There is a common variant where blocking a chess by placing a captured piece is not allowed.
  • There are other minor variants reducing the chaos in the game, such as only allowing the placement of captured pieces on your own side (first 4 rows) or even more restricting, only on that piece's starting position.

These two game variants are much more chaotic than the original chess, so quick tactical decisions are much more important than lengthy studies and thousands of memorized openings. --131.188.3.21 (talk) 00:39, 15 February 2010 (UTC)

I think you mean "check", not "chess", several times in that post. --Tango (talk) 00:44, 15 February 2010 (UTC)

You are right, I rushed the writing a bit and was not paying enough attention. Not to mention in my native language the two are spelled the same way. I'm sorry, and I hope it's still understandable. I forgot one important rule from the first game variant: "Pawns are only allowed to promote to pieces already captured. In the rare occasion nothing has been captured yet, the pawn is simply lost." And i hope it was clear enough that the second, team based game is completely different, with normal "one move per turn" rules. Enjoy! :) --131.188.3.21 (talk) 00:50, 15 February 2010 (UTC)

There's also Chess960 where the opening positions of the pieces are randomised. This makes it very difficult to memorise openings. - Akamad (talk) 01:49, 15 February 2010 (UTC)

In fact, Chess 960 was developed for that very reason. It's not as fun as ordinary Chess though. There are many other Chess variants to choose from. Zain Ebrahim (talk) 08:10, 15 February 2010 (UTC)

Cribbage and a special favourite of mine, Stratego. --Dweller (talk) 10:46, 15 February 2010 (UTC)

For a break I often play online Reversi, as it is a quick game that only lasts a few minutes. If you have Windows, then you may already have it installed under games, or you may be able to download it from Zone dot com. I wish it was possible to choose different board sizes and shapes to make the game more varied. 89.240.201.172 (talk) 13:59, 15 February 2010 (UTC)

Kasparov advocates Advanced Chess, in which one human/computer team competes with another human/computer team.

Frankly, I'm not convinced. I think Kasparov overstates the role of "Creativity" and the human element in Chess. Especially after his allegations that Deep Blue was playing "creatively". (And therefore cheating.)

But what do I know? I'm certainly not even close to being a Grand Master. APL (talk) 16:11, 15 February 2010 (UTC)

Thanks for your replies. I have been considering Go as a possible alternative for a long time, but the problem is that I prefer the more tactically-oriented or (sometimes) aggressive nature of chess to the strategically and slow-paced nature of Go. This is a serious dilemma that I have. --Belchman (talk) 16:25, 16 February 2010 (UTC)

why is formic acid so much more toxic than acetic acid?

I don't really get it ... does formic acid have a greater affinity for dissolving into biological tissues? John Riemann Soong (talk) 21:23, 14 February 2010 (UTC)

I believe the pH level of formic acid is 2 (more toxic), and acetic acid is 3. -^Avicenna_sis @ 21:38, 14 February 2010 (UTC)

I went to google, typed in "formic acid" toxicity and on the very first page of hits was an except of an article "Formic acid (or formate) is apparently more toxic than other fatty acids, possibly owing to its enzyme-inhibiting activity". The wikipedia article formic acid states that it specifically affects a certain biological structure--that would be another useful search-term to help you find your information. DMacks (talk) 21:44, 14 February 2010 (UTC)

Miller-Urey

Miller-Urey experiments with better predictions of Earth's early atmosphere produce most (not all) amino acids and other organic compounds. However, they also produce toxins like formaldehyde and hydrogen cyanide which would kill any life which did happen to form. How are these experiments considered evidence for abiogenesis/evolution when they fail to produce all of the necessary compounds, and they also produce horrible poisons? --70.129.187.17 (talk) 21:59, 14 February 2010 (UTC)

All "necessary compounds" for what purpose? Remember, life doesn't have to be something we recognize to match our current life-forms in terms of their complete biochemical makeup. Likewise "toxins" is only in your current experience of certain biochemical processes. See for example, Hydrogen cyanide#HCN and the origin of life. DMacks (talk) 22:23, 14 February 2010 (UTC)

What is toxic to you may not be toxic to early life. There are plenty of extremophiles that live in places inhospitable to human yet it is still life. Also something to note is that evolution has nothing to do with abiogenesis. Evolution describes a continuous adaptation of life to its environments; it does not nor does it attempt to explain the origin of life itself (Darwin's book is called "On the Origin of Species" for a reason). --antilived^{T | C | G} 22:30, 14 February 2010 (UTC)

(ec) The primitive life forms which would have hypothetically arrived during Miller-Urey type conditions would be far too basic for HCN and formaldehyde to be "toxic" to them. I'm guessing they would just be a membrane with some nucleotides inside. HCN is toxic to us due to interactions with mitochondrial enzymes, I believe. It also should be noted that there is a hypothesis for the role of polycyclic aromatic hydrocarbons (which are carcinogenic) in the origin of life (see PAH world). This is another example which shows how fallacious it is to assume that "chemicals toxic to current organisms = chemicals toxic to primitive organisms". --Mark PEA (talk) 22:34, 14 February 2010 (UTC)

Firstly, (as our article points out) subsequent recreations of the Miller-Urey experiment produced all 22 standard amino acids. Secondly, the experiment is supposed to prove that it's possible for these compounds to have formed spontaneously from a plausible set of initial conditions. It is emphatically NOT claimed that "this is how it happened". There are a trillion possible variations of temperature, pressure, chemical precursors and energy sources that could have produced the actual abiogenesis event - and it's unlikely that we'll ever know precisely what happened because conditions changed repeatedly and dramatically over the billion years between the formation of the Earth and the first fossilised lifeforms that we have discovered.

This experiment should be viewed as a "proof of plausibility" rather than a "recreation". In dozens of other experiments with wildly different starting conditions, we get very similar results, showing that even if the conditions were quite different from the Miller-Urey experiment, there can be no doubt that these compounds would have been present in early earth history.

As for the poisons - we know that life can survive and evolve in an amazing variety of conditions (see Extremophiles) and it's no stretch at all to imagine that it could have formed despite those seemingly nasty compounds.

• This site suggests that cyanide was actually part of the chemical pathway to make Purine Adenine.
• This PBS documentary described how extremophiles survive in cave with normally lethal doses of formaldehyde.

So it's perfectly plausible that life could have formed even in such a seemingly-toxic environment. Also, we do not know what other reactions or physical separations were going on that could have subsequently eliminated these other compounds. Since we know that life most definitely exists and that it certainly evolves, it's really only necessary to find a plausible path to that initial abiogenesis event to complete the story to an acceptable degree of scientific proof. SteveBaker (talk) 22:56, 14 February 2010 (UTC)

Cyanide would actually have been pretty useful if you were trying to form the first cells. It's a basic building block for organic substances. Do you know why cyanide is poisonous to us? Today we're obligate aerobes and we need aerobic respiration. A long long time ago, oxygen was a poison whereas normally poisonous gases (to us) like methane, phosgene, etc. would have been useful. John Riemann Soong (talk) 21:57, 15 February 2010 (UTC)

February 15

Cooking rice under pressure

Electric rice cooker including scoop, containing uncooked rice

Inexpensive electric rice cooker containing cooked rice

• Rice cooker

The two pictures used by the article rice cooker provide an interesting contrast:

• The more expensive one on the left has a valve in the lid. It is a pressure cooker.
• The cheaper one on the right, as you can see, has a small opening in its thick glass lid. It cooks under normal air pressure and steam is not retained in the cooker.

I think people who eat sticky rice mainly use pressure cookers. Even if you are not using these advanced computerized models, the less expensive cookers use a very heavy lid as a pressure valve. I have seen some traditional wood-burning rice cookers in eastern Asian countries. They use over-sized heavy wooden lids. Some high-end sushi restaurants still use these traditional cookers because they are simply GREAT!

• http://www.quickspice.com/scstore/images/cookware-ricecooker-national-nsr42hn_lg.jpg

I guess the one on the right is generally used to cook non-sticky long grain rice (e.g., Basmati rice). I am not really sure about it. If steam can easily escape the cooker, how do they cook the rice? -- Toytoy (talk) 02:11, 15 February 2010 (UTC)

The difference is rice being cooked at around 100 degrees C and 1 atmospheres pressure; and rice being cooked at say 125 degress C and 1.5-ish atmospheres pressure. In both cases the rice is cooked; in the latter case, more quickly. See Pressure cooking. --Tagishsimon (talk) 02:25, 15 February 2010 (UTC)

How would a heavy lid act as a pressure valve? I have an old Panasonic rice cooker from the 80s, and there's no pressure cooking involved. It just has a small hole in the big plastic hinged lid. The steam escapes, yes, but at a much slower rate than if there were no lid at all. By the time the rice is finished cooking, there's still plenty of steam left in the pot.

AFAIK, it doesn't take any kind of fancy rice-cooker to make sticky rice. You just need some glutinous rice. Indeterminate (talk) 03:38, 15 February 2010 (UTC)

Certainly you can cook using a pot and a light-weight lid. The rice shall be edible but it may not be tasty. I have been told not to open the lid while cooking and "resting" countless times. That's why I thought keeping steam inside the cooker must be a way to make rice taste good. Failure to do so may compromise the taste. The heavy lid does not increase the pressure as much as a pressure cooker. However, the heavy lid without a hole may still retain steam much more than the lid-with-a-hole cookers. -- Toytoy (talk) 04:53, 15 February 2010 (UTC)

Is this girl lying to me?

I have been talking to this girl for quite some time, and she has been telling me she weighs 125-130 lbs. A month and a half ago she went into to hospital for an emergency appendectomy and was released the same day. 3 weeks ago she had to go to the ER twice because of bleeding in her esophagus and had to have stitches put in to stop bleeding. She said she was given some pills to gain weight as well as some other medicine, at this time she tells me she weighed 140 lbs. This weekend I saw her for the first time and she was FAT. She tells me she gained 40 lbs in 3 weeks (to 180 lbs) and that it is a result of her medical treatment and largely "just water" whatever the hell that means...

1) Is this at all plausible--can someone gain 40 lbs in 3 weeks?

2) what is "water weight"

3) Will she revert back to her previous size (if she is being truthful) and if so how long will it take and will her skin be all stretched and stuff?

4) Are there any ways I can tell if she is being truthful or lying?

XM (talk) 02:20, 15 February 2010 (UTC)

• I deleted this as a medical question. The OP disagrees, and has reposted it. Another opinion, please. -- Flyguy649 ^talk 03:56, 15 February 2010 (UTC)

He's not technically asking for medical advice. Well, he technically is asking for medical advice. I don't see the problem with this one though, he isn't seeking treatment or anything like that. Beach drifter (talk) 03:59, 15 February 2010 (UTC)

What I am asking is not medical advice. No medical decisions will be made based on whatever information I get here. I am asking for advice on whether or not a situation is medically possible and if so, how long it will take to resolve back to the previous state. XM (talk) 04:04, 15 February 2010 (UTC)

This girl is not going to become skinny, if that is want you want to hear. Beach drifter (talk) 04:05, 15 February 2010 (UTC)

AFTER EDIT CONFLICT:

Well I was hoping for a bit more depth in an answer. Do you think she actually gained the weight rapidly, or was just fat all along and lying to me? If it is the former, could she lose it once she resumes her normal lifestyle along with some aggressive exersize? XM (talk) 04:11, 15 February 2010 (UTC)

But it seems it would be pretty impossible to squarely address the question without entering the realm of analyzing a medical condition, and the big problem with that is all the missing pieces that we know nothing about. In my opinion it is an unanswerable question, and any attempt to respond to it entails giving out medical opinions in a reckless fashion. Bus stop (talk) 04:08, 15 February 2010 (UTC)

Again, nothing said here is going to effect (or is it affect) any medical decisions at all. I just want to know if something is medically possible. Medical opinions in this situation would not be reckless as they arent going to have any medical affect whatsoever. XM (talk) 04:18, 15 February 2010 (UTC)

1. yes, it's possible, depending on the kind of medication she's been given
2. 'water weight' usually means that the body is retaining excess water rather than excreting it. This can happen because of hormonal imbalances, kidney problems, certain medications, or other causes. 40 lbs of water weight gain strikes me as an awful lot, but I'm not a doctor.
3. She may or may not lose the excess weight - without knowing the cause, the medicines she's on, what her natural weight is, or other information there is no way to tell
4. why is it important? she's probably struggling with her own self image (whether the weight is natural or recently gained makes no difference); you're struggling with your own self image (you're apparently more worried about what she'll look like on your arm than what she's like as a person). If you're going to be a jerk and reject her because she's heavy, then go ahead and be an honest jerk; don't try to put the blame on her by making her into a liar. --Ludwigs2 04:12, 15 February 2010 (UTC)

Ludwigs, which is more likely, that she will lose the weight, or that she wont? And to answer your forth question there are two possible explainations for this situation, in one the girl is honest and her weight is temporary in the other the girl isn't and she is going to be permanently fat. I am okay with one of those explainations, not with the other. But I do need to find out which it is, or at least which is most likely XM (talk) 04:23, 15 February 2010 (UTC)

That question is literally impossible for us to answer. Ludwigs is speaking in purely general terms. It is possible for a person to gain weight due to water retention; it is possible for a person to gain weight due to medical treatments, and it is possible for a person to gain a large amount of weight in a short amount of time. Those are all possibilities based on biology, and without any real comment on the specifics of any one particular case, especially on the one you cite. Wikipedia's reference desk contributors are unable to make specific comments on a specific case as that would constitute a form of medical advice. No one here, or indeed anywhere on the internet, can make any comments as to the specifics of your friends case, as to why she may have gained weight, whether she is telling the truth or not, how she may lose it, etc. etc. All of that is between her and her doctors, we can only answer the general biological questions, not on her case. It will be up to you to decide what it all means in her case. --Jayron32 04:52, 15 February 2010 (UTC)

Jayron, So it is possible to gain that much in such a short time? If what she is telling me is medically possible, then I am inclined to believe her until other evidence presents itself. But 40 lbs in 3 weeks seems like a lot to me. XM (talk) 04:59, 15 February 2010 (UTC)

I have no idea if that specific amount in that specific time is actually possible. What you should do is read the Wikipedia article weight gain and follow any links from that article, including external links, and arrive at your own conclusions. This is not an endorsement of any information contained in either that article or especially in any of those links. I have no idea if the information is valid or reliable, but if you want some information, its a better start than asking for medical advice from random strangers on teh intrewebz. If you want a poorly informed and unverifiable medical opinion, at least make it your own poorly informed and unverifiable opinion, and don't rely on someone elses. --Jayron32 05:14, 15 February 2010 (UTC)

@ jayron: This isn't a medical question, it's an emotional one. XM is trying to find some excuse to be pissed off at this girl because she's violated his heartfelt expectations. He has all the medical information he needs to decide whether he can realistically work himself up to an effective level of self-righteous indignation; I suggest we leave him to explore his inner self on his own. --Ludwigs2 07:22, 15 February 2010 (UTC)

You know, Ludwigs, your condescending comments aren't really appericiated by me or probably anyone else on the Ref desk. I find your comments extremely rude, emotionally charged, and without basis. I asked if the claim of someone was within the realm of possibility, because if they aren't then that means I have been lied to. Additionally, in the event that she is being truthful, I want to know the likelihood that she will revert to an attractive state. Evidently this is what you have a problem with causing you refer to me as self-righteous. I'm sorry if someone decided they didn't want to be with you because of your physical appearance, but comments like yours are simply uncalled for and most unwelcome. XM (talk) 07:51, 15 February 2010 (UTC)

They're appreciated by me, and I suspect by most other people on the desk. If you're going to be a douche, be a douche, but don't try to dress it up as morally righteous. 86.176.48.57 (talk) 13:13, 15 February 2010 (UTC)

XM - If you don't trust the explanation given by the girl, ultimately what difference do the explanations given by complete strangers make? Your statement "I want to know the likelihood that she will revert to an attractive state" says pretty much everything anybody needs to know. The truth makes no difference in either matter - you appear not to trust her, and you appaer not to care for her sufficiently to disregard her current weight. 194.221.133.226 (talk) 12:30, 15 February 2010 (UTC)

Is the girl in question an infallible vector of information on weight gain and weight loss and related questions? Or is she capable of slipping up in some minor detail concerning the dialogue of self analysis concerning the recent body changes? It is possible that the biomass in question is inconsistently distributed and the dialogue being reported is not as accurate as it should be. Therefore the referred to weight gain should perhaps be monitored to allow for the perceptual adjustments that sometimes occur over time. Bus stop (talk) 13:11, 15 February 2010 (UTC)

Presumably the hidden question here is that you'd like to know if you should carry on the friendship/relationship, based on (regardless of whether or not she was/is lying) whether or not she can lose the weight sufficiently to attract you. I think if you have to ask, do her a favour. Even if she does lose the water weight/fat, there is no guarantee that weight gain won't occur in the future, particularly with pregnancy being the way it is, and you're clearly not going to be happy with that. She's better off investing her time and emotions elsewhere, eh? Maedin\^talk 13:29, 15 February 2010 (UTC)

Better make sure she doesn't see your browser history. I'm sure she wouldn't be thrilled that you trust random internet strangers more than her! APL (talk) 16:01, 15 February 2010 (UTC)

However, if someone plans to gain "water weight" by drinking water, this is dangerous due to the likelihood for water intoxication. ~AH1^(TCU) 03:18, 16 February 2010 (UTC)

Fujiwhara effect

The Fujiwhara effect says that "When cyclones approach each other, their centers will begin orbiting cyclonically about a point between the two systems." This is all fine except for one thing: How would it affect two storms in opposite hemispheres, say at 5°0′0″N 170°0′0″W and 5°0′0″S 170°0′0″W? If the two cyclones began to orbit, it would result in them crossing the equator, which I seem to recall tropical cyclones cannot do. Does this mean that the Fujiwhara effect would kill the two storms, or would it just not affect them at all? Ks0stm ^(T•C•G) 04:19, 15 February 2010 (UTC)

I have fixed your coordinate template. Nimur (talk) 04:24, 15 February 2010 (UTC)

Thanks. Ks0stm ^(T•C•G) 04:29, 15 February 2010 (UTC)

There's not a hard rule about a tropical cyclone crossing the equator. The coriolis force tends to push storms away from the equator and towards the poles, but climate and storm dynamics are complicated things - if a local pressure perturbation was strong enough to suck a storm across the equator, it could happen. I suspect that since both the Fujiwhara effect and the internal cyclone spiral are both consequences of the coriolis effect, which is weaker near the equator, the tendency for this spiraling to impact storms that happen to be close the equator (which are rare to begin with) would be low. If two storms were on opposite sides of the equator simultaneously (which would be very rare), then the effect would still be weak-to-non-present - again, with the caveat that local conditions can behave counter to the global-scale trends. Nimur (talk) 04:39, 15 February 2010 (UTC)

In thousands of examples, no cyclone has ever crossed the equator. [5] Dragons flight (talk) 06:39, 15 February 2010 (UTC)

There's also the fact that if cyclones were on opposite sides of the equator they would spin in opposite directions, which would make the whole business break down. Looie496 (talk) 18:43, 15 February 2010 (UTC)

For tornadoes (which are sometimes called cyclones around here) there are some which spin the wrong way around, but they are on the order of about 1:1000. Does the same hold true for hurricanes-typhoons? 65.121.141.34 (talk) 20:46, 15 February 2010 (UTC)

I say that both storms would be pushed east and then away from the equator, due to the circulation on both storms on the side facing the equator. ~AH1^(TCU) 03:16, 16 February 2010 (UTC)

Relative temperature of fabrics

Why do different fabrics feel colder than others? For instance, I have flannel sheets as well as some (probably) nylon/cotton blend sheets. The flannel "feels" warmer when getting into bed than the other sheets yet my room is the same temperature. Or another example would be when you slip on a coat or jacket that has a nylon lining in the sleeves. The nylon feels cooler than if you were to put on a flannel shirt. Why? Dismas|^(talk) 05:03, 15 February 2010 (UTC)

This has nothing to do with temperature, and everything to do with specific heat. The temperatures may be identical, but what is different is the rate at which different materials will conduct heat away from your skin. Your perception of the temperature of the fabiric really isn't a perception of temperature, its a perception of heat flow either into or out of your skin, which is dependent not only on the relative temperature difference between your skin and the fabric, but also on the relative difference in properties between the materials involved with regard to how heat energy affects them, aka specific heat. --Jayron32 05:09, 15 February 2010 (UTC)

Thanks! I knew there was a concept that explained it but couldn't remember what it was. Dismas|^(talk) 14:07, 15 February 2010 (UTC)

about the wounds

why the wounds get,s dark blue coulour after ome time?? —Preceding unsigned comment added by 200.55.135.211 (talk) 05:16, 15 February 2010 (UTC)

Wikipedia contributors cannot provide medical advice. The best we can do is direct you to articles like bruise which may contain information on the topic, but we can only tell you that you should not act on any information you find at Wikipedia, but should instead seek the direct advice of a qualified physician or other medical professional. --Jayron32 05:18, 15 February 2010 (UTC)

Another cause for wound discoloration is gangrene or necrosis. That is a very serious condition and would definitely need medical attention. Nimur (talk) 05:29, 15 February 2010 (UTC)

torro ant poison

i have carpenter ants. i got torro ant poison BAIT TRAPS there not eating it thou why —Preceding unsigned comment added by 67.246.254.35 (talk) 05:59, 15 February 2010 (UTC)

If you are not having success using store-bought pest control products to control the ants, you should call in a professional. Carpenter ants, like termites and some other pests, can cause structural damage and should not be taken lightly. I would recommend that you look up "pest control" in your local phone book, and seek a qualified professional. --Jayron32 06:08, 15 February 2010 (UTC)

Terro is a sweet bait. I suspect that carpenter ants are more interested in wood than fruit or carrion. -Craig Pemberton 06:44, 15 February 2010 (UTC)

do carpenter ants like sweet bait or greasy bait?--Thekiller35789 (talk) 07:10, 15 February 2010 (UTC)

hello?

Doesn't Craig Pemberton's reply give you the answer to that? --TammyMoet (talk) 20:26, 15 February 2010 (UTC)

Not really. I'm not an expert, so it is just an informed guess. -Craig Pemberton

There is another possibility - I know that the ant bait that you buy here in Texas has a relatively short shelf life - if it's more than a few weeks old, it doesn't work. That's not to say that the stuff you are using is like that - I don't know - but it's definitely a possibility. SteveBaker (talk) 23:40, 15 February 2010 (UTC)

Googling "carpenter ant bait" shows that the University of Minnesota disagrees with Craig [6], and says that carpenter ants don't eat wood, but rather like protein and sugar. That page says 1% boric acid in 10% sugar water (probably close to what Terro is) can be effective, but "is very slow acting and must be constantly replenished". It also says that "carpenter ants have complex food preferences, and some of the sugar-based baits will not be attractive to the ants long enough to be successful". It instead recommends (carefully) drilling holes into the nest and applying pesticides directly, or more effectively, calling a professional to do the job. The University of Nebraska-Lincoln also has a few things to say about ant baits [7], but mentions that baits don't work as well for carpenter ants as for other species. I'm sure there is more information in that Google search - those were just the first two pages I visited. -- 174.21.247.23 (talk) 15:46, 16 February 2010 (UTC)

Is clear a color?

??? 69.77.247.18 (talk) 06:03, 15 February 2010 (UTC)

Not really. In computer graphics, opacity is measured on a separate channel from color - see alpha compositing. Whether this meets your definition for "color" is a matter of semantics. Outside of the realm of computers, most people use color to mean that quality which is the perceptual representation of the wavelength of light in the visible spectrum. Again, opacity is a separate quality from color in this context - it has to do with the transmission coefficient or transmittance of a material. Nimur (talk) 06:08, 15 February 2010 (UTC)

It also depends on how you define "color". In some applications, and under some definitions, it may. Color is a nebulous quantity, and without knowing what context we are talking about, it is hard to discuss it in detail. Though Nimur's answer is pretty good. --Jayron32 06:11, 15 February 2010 (UTC)

Can't hardy wait for Steve to weigh in on this one ;) hydnjo (talk) 06:43, 15 February 2010 (UTC)

However, if you were, selling shower curtains, for example, then it would seem quite reasonable to say that colours available were white, black, yellow or clear.--Frumpo (talk) 12:40, 15 February 2010 (UTC)

This is more of a linguistics question than a science question - what does the word "colo(u)r" mean - and, therefore, does "clear" count? Well, let's see how Wiktionary defines "color":

1. The spectral composition of visible light.
2. A particular set of visible spectral compositions, perceived or named as a class; blee.
3. Hue as opposed to achromatic colors (black, white and greys).

...and some others that obviously don't apply here.

Well, there is no "clear" in the spectral composition of light which rules out the first two definitions - and the third just serves to say that sometimes when people ask whether something has a color - they mean to exclude black/grey/white.

So the answer is "No". Clear is not a color. Clear is a property of a material that alters the way we see it - but so is "shiny" and "rough" - but those are not colors.

The tricky part (and we had this the other day) is to ask what color a clear object is. That's like asking what color a mirror is (the answer to which is "black"...IMHO).

SteveBaker (talk) 15:31, 15 February 2010 (UTC)

"Silver" doesn't cut it as a color then? (Or isn't appropriate for mirrors?) -- 174.21.247.23 (talk) 15:35, 16 February 2010 (UTC)

Silver is not a color. We talked about this extensively in the discussion of the color of mirrors last month. I recommend you read that discussion. SteveBaker (talk) 21:10, 16 February 2010 (UTC)

Java loving roaches

Hi

I don't know if it's just me, but has anyone ever noticed (those of you who've had problems with cockroaches in your homes) that they seem to have a love for either coffee or something that's inside the coffee. A lot of times when someone has left half a cup of coffee or less overnight, we'd find the next morning that they're inside the cup floating on the coffee... dead and at times there would be more than one in a cup. Now I don't know if they like the coffee that much, but are unaware of something inside the coffee that can kill them or if they like the coffee so much that they drink themselves to death.

Thanks, NirocFX 41.193.16.234 (talk) 10:34, 15 February 2010 (UTC)

I suspect they drown, rather than drink themselves to death or have adverse reactions. Sounds like you have a solution to your roach problem, too. --Tagishsimon (talk) 10:38, 15 February 2010 (UTC)

No, luckily we sorted them out (for good) in a different manner otherwise they would have probably opened their own Starbucks in our house sooner or later.

Thanks, NirocFX 41.193.16.234 (talk) 11:23, 15 February 2010 (UTC)

You might be interested to take a look at caffeine. It acts as a pretty effective pesticide on insects, and that appears to be its primary role in nature. – ClockworkSoul 17:05, 15 February 2010 (UTC)

Scientific experiments on brainwave activity when chanting nam myoho renge kyo

Have any scientific experiments on changes in brainwave activity been done while chanting nam myoho renge kyo? If so can I see the results please. Please indicate to me by my email <e-mail address removed to protect from spambots> where I can search for and find my question and answer (when it arrives) on wikipedia. Thanks.—Preceding unsigned comment added by 92.12.118.205 (talk) 12:09, 15 February 2010 (UTC)

I can't lay my hands on any studies at the moment, but this organisation would be the one to contact for further research work: [8]--TammyMoet (talk) 12:33, 15 February 2010 (UTC)

The only one I can spot is PMID 7300432. Looie496 (talk) 18:40, 15 February 2010 (UTC)

Snowfall in Hawaii

Has there ever in record history been snow in state of hawaii? (Dr hursday (talk) 12:28, 15 February 2010 (UTC))

Happens regularly at high elevations. Our article on Mauna Kea says "Snowfall often occurs at elevations above 11,000 feet (3,400 m) during the period from November through March". Gandalf61 (talk) 12:35, 15 February 2010 (UTC)

I do not know how to make this question second section in question as have seen here but not want to make new question since subject is related] what is the farthest south snow has ever recorded to have fallen in earth? (Dr hursday (talk) 12:59, 15 February 2010 (UTC))

At the South Pole, obviously! To answer the question I think you are asking, I'm sure it has snowed in the mountains of Ecuador, right on the Equator. anonymous6494 12:59, 15 February 2010 (UTC)

Wouldn't be so sure of that. Extreme points of Antarctica claims "Antarctica has the world's lowest rainfall average (zero at the Geographic South Pole) and thus is the world's driest continent". That said, it's uncited. edit: I'm assuming snowfall and rainfall are treated the same, I don't know.Vimescarrot (talk) 14:56, 15 February 2010 (UTC)

That's too big an assumption. They are not the same.--Shantavira|^{feed me} 15:56, 15 February 2010 (UTC)

The assumption is valid, though. While the article says "rainfall", it actually means "precipitation". See Climate of Antarctica#Precipitation for some details, although it doesn't confirm the zero precipitation at the South Pole, I have heard that before somewhere. --Tango (talk) 20:27, 15 February 2010 (UTC)

There is a good photo in Andes that shows the reason for lack of snow in the Andes of Ecuador is the desert conditions. Being a desert doesn't mean that there is absolutely no precipitation. There is some. Above 10,000 feet, that precipitation will often become snow - snow on the equator. -- kainaw™ 15:05, 15 February 2010 (UTC)

Mount Kilimanjaro is 3 degress from the equator, and is known for its snows. (C.f. The Snows of Kilimanjaro). --Jayron32 16:28, 15 February 2010 (UTC)

Right now it might be - but give it a dozen more years and it won't be known for that anymore. Global warming... SteveBaker (talk) 23:31, 15 February 2010 (UTC)

I thought it was "Climate Change", not "Global Warming" in order to hedge your bets. Googlemeister (talk) 14:43, 16 February 2010 (UTC)

It's not about hedging bets, it's about a (failed) attempt to head off the folks who say "Global warming?!? But it is currently cold outside!! Haha! Stupid scientists!"

"Global Warming" gives the (false) impression that one day the planet will be sweltering hot from pole to pole, when they're really just talking about a few degrees overall worldwide. APL (talk) 22:21, 17 February 2010 (UTC)

Not to belabor the point, but certain scientists have recently found themselves in hot water over specific pseudoscientific claims about particular melt rates for particular mountains... In light of this, one might want to use caution when forecasting a particular glacial melt rate within the next dozen years for Kilimanjaro unless it's attributed to a realistic and scientific model. The last thing we need now is misinformation and reputation-damaging inaccuracy to cloud the very real and important science which does back up actual anthropogenic climate change. Not every glacier is melting, and not every mountain will be barren by 2030! Here is a report - Kilimanjaro Glaciers..., (Geophys. Research Letters, 2006), which discusses the retreat rates and implications therein. The glaciers are retreating, but predicting a rate is, as always, very difficult. "This strong imbalance can only be explained by a sudden shift in climate, which is not observed in the early 20th century. Results suggest glaciers on Kilimanjaro are merely remnants of a past climate rather than sensitive indicators of 20th century climate change." Nimur (talk) 01:23, 16 February 2010 (UTC)

The Andes cross the Equator too, and are snow-capped. BrainyBabe (talk) 17:40, 17 February 2010 (UTC)

Chess

Hello i have always thought game of chess would be such that first player could win by analyzing possible moves and all possible responses to that move and so on is this possible to do if so could not a computer just be programed to analyze the possible paths and pick the move on the path where victory is certain and repeat until victory? also could this not also be true about other much more complex competion games even one like starcraft where evaluation of all possiblities of all avalible actions be allow to pick the path or branch that lead to definate victory? (Dr hursday (talk) 12:49, 15 February 2010 (UTC))

The problem is that "all possible moves" is way too many. I'm pretty sure that if you stored each possible chess game on a single atom, you'd have enough to build several extra universes. Your intuition that chess is theoretically solvable is correct, in game theory, it's known that games like Chess and Go (though not games like Starcraft, because the players don't have complete information (and Starcraft might also have random events)) are solvable, and therefore either white or black can force a win every time. It's just utterly intractable to figure out which one, or how.

One cute example is the game Hex, in which mathematicians were able to prove that the first player can force a win; but the proof was non-constructive, meaning that they don't know how. Paul Stansifer 13:11, 15 February 2010 (UTC)

See computer chess, combinatorial explosion, game complexity and solved game. The most complex game that has been weakly solved (i.e. final result is known from starting position assuming perfect play on both sides) appears to be Nine Men's Morris with a game-tree complexity of 10⁵⁰. Chess has a game-tree complexity of at least 10¹²⁰ (some estimates are higher), so a complete solution is a long way out of reach. However, chess end-game positions with up to five or six pieces can be exhaustively analysed by a computer. Gandalf61 (talk) 13:29, 15 February 2010 (UTC)

Note that Deep Blue worked, in part, by analyzing millions of possible results from its moves, picking the best ones. It was nowhere near the ability to analyze all possible moves, but it is along similar lines of thought. --Mr.98 (talk) 14:29, 15 February 2010 (UTC)

Chess computers work by searching as many moves ahead as they have time for - then using a (typically crude) estimate of the "value" of each of the positions that they end up with. Typically they'll count things like the value of the pieces each side has, the number of pieces that are pinned - enable to move without another piece being vulnerable - and measurements like how much control of the center of the board they have. The best programs then search the most promising moves more deeply still. But they certainly can't search exhaustively more than a few moves ahead. Just think about it - there might be a dozen pieces you could move - and many of those could move in half a dozen ways - so there might easily be 50 possible moves at any given time. Each of those 50 moves might have 50 possible responses - so to search N moves ahead requires you to search 50^N positions! To search just four moves ahead (you play, he plays, you play, he plays) requires you to evaluate 6 million possible outcomes! Even if the final evaluation function is rather simple, that's going to take a typical computer maybe a minute or so. Pushing it just one more move to evaluate 5 pushes the time out to an hour and going to six moves might easily take the computer a couple of days! SteveBaker (talk) 15:18, 15 February 2010 (UTC)

Wikipedia has an article, of course : First-move_advantage_in_chess. It's pretty in depth, but basically, since Chess is not yet a solved game, we don't know for sure if there's an unbeatable solution for the white player. APL (talk) 15:51, 15 February 2010 (UTC)

As far as I'm aware, no one has proved even that chess is not an outright win for Black. Whether we can be said to "know" that chess is not a win for black depends to some extent on what you mean by know. That happens a lot. I'm quite happy, for example, to say we know that Goldbach's conjecture is true, even though no one has a proof from any widely accepted axiom set.

That's a bit of a digression, of course, as it's my understanding that the possibility that chess is a draw with perfect play is one that many experts believe; I have never heard of one who thinks it's a win for Black. --Trovatore (talk) 22:32, 15 February 2010 (UTC)

Playing a complex game at competition level demands exceptional mental resources (video). Cuddlyable3 (talk) 19:00, 15 February 2010 (UTC)

Malt Beverages and brewers yeast

Does Mike's Hard Cider (a malt beverage) contain brewers yeast? Is yeast used in the making of all malt beverages? —Preceding unsigned comment added by 75.38.232.192 (talk) 12:56, 15 February 2010 (UTC)

Malt has the answers to your questions. Malting is about getting the grains to sprout, then drying them. It isn't about using yeast. 86.176.48.57 (talk) 13:05, 15 February 2010 (UTC)

They probably do use brewer's yeast. Pretty much any fermented drink uses brewer's yeast, as bread yeast tends to give the drink a weird (bread-like, not surprisingly) taste. If you make your own hard cider or ginger beer, it is likewise best to use brewer's yeast. That said, I don't have any specific knowledge of Mike's Hard Cider. (For all I know, they could take cider, add a shot of grain alcohol and carbonate with seltzer). — Sam 76.24.222.22 (talk) 14:17, 15 February 2010 (UTC)

Is cider a "malt beverage?" In the UK, cider is purely fermented apple juice - no malted grain involved. Scrumpy ciders tend to only use the natural wild yeasts found on the skins of the fruit for fermentation purposes. --TammyMoet (talk) 14:50, 15 February 2010 (UTC)

I was confused about this too, but apparently Mike's whole line is "malt beverages." I don't really understand why you would have malt in hard cider, though, and even one of the home-brew recipes I saw purporting to be a clone of "Mike's Hard Cider" used just cider. In the US, Woodchuck cider is made with just cider. Anyway, whatever is being fermented (if it's actually being fermented, which I assume it is), they would probably be using brewer's yeast, although I guess naturally-occuring yeasts might be found on some of the more high-end stuff. — Sam 76.24.222.22 (talk) 15:05, 15 February 2010 (UTC)

I can't find anything called "Mike's Hard Cider" online, except home-made recipes. There is a Mike's Hard Spiced Apple, but it isn't part of Mike's Hard malt line. Could you provide details of this drink? --Tango (talk) 15:53, 15 February 2010 (UTC)

An expert on beer brewing told me that Champagne yeast is what I should use to brew hard cider. I have also had hard cider which fermented only from the wild yeast present on the apples before they were chopped and pressed. That was before all cider had to be sterilized. See Allexperts.com. Edison (talk) 19:37, 15 February 2010 (UTC)

INFORMATION ABOUT ENGINEERING VARIOUS EXPERIMENTS

I want know about applications and uses in industies and in day to day life of 1.Double purchase crab,2.Compound pendulum,3.Polygon law of forces,4.Worm of worm wheel —Preceding unsigned comment added by Ashlesh dahiwale (talk • contribs) 13:02, 15 February 2010 (UTC)

Some of your terminology is a little archaic (or maybe it's region-specific). You might find more information if you search for winch instead of crab. We have an article on compound pendulum - the first "application" I think of is a robot manipulator arm like a Canadarm or a backhoe. I don't know what you mean by polygon law of forces. Finally, we have an article on worm drive. If you can ask a more specific question, we can give you more specific answers. Nimur (talk) 14:10, 15 February 2010 (UTC)

1. Do you mean "Grab"? If so, then I think that this is normally called a "Clamshell grab". See Grab (tool)
2. I can't imagine any uses for a free-swinging compound pendulum. (See Double pendulum). As Nimur says though, there are many double-linked mechanical structures that would be considered to be a compound pendulum if left to swing freely.
3. I suspect you mean Parallelogram of forces - a method of adding together forces.
4. Do you mean a Worm drive?

SteveBaker (talk) 15:03, 15 February 2010 (UTC)

1. See [9]

2. See Earthquake_engineering#Tuned_mass_damper

3. See Pantograph

4. See Machine head

Cuddlyable3 (talk) 18:53, 15 February 2010 (UTC)

I think he really did mean double-purchase crab - one of these. It is a "crab" because the drive crank turns a large-diameter axle shaft which is actually doing the winding; and it is "double purchase" apparently because there are at least two gear reductions. This is some really arcane terminology. Nimur (talk) 19:00, 15 February 2010 (UTC)

Can soda cans rust?

Hi all,

I was thinking of using cut-open soda cans as a roof to my chicken coop, after seeing an instructible on it. However, my girlfriend says that it would eventually rust. I say that aluminum doesn't rust, and that soda cans have a plastic lining and then a hard layer of aluminum oxide. She says we've all seen rusted cans.

So... will the soda cans rust? Will they corrode in some other way? Thanks! — Sam 76.24.222.22 (talk) 13:59, 15 February 2010 (UTC)

"Rust" specifically refers to the formation of iron oxide. Used loosely, the terminology can also mean "the equivalent oxidation reaction as it applies to other metals." Aluminum forms aluminum oxide - which is known as a "self-limiting" oxide. In other words, the outermost layer of "rust" (oxidized aluminum) is impermeable and forms a protective coating which slows the rate of oxidation to the rest of the metal to almost negligible rates. (The introduction to our aluminum article discusses this formation of a passivation layer). In addition, any clear-coat or paint on the can will also slow the reaction. So, the simple answer is that the cans will not corrode for a very long time. Nimur (talk) 14:13, 15 February 2010 (UTC)

Three sorts of cans: 1) all ferrous - tend not to be used for "soda"; 2) ferrous ends and aluminum sides - increasingly uncommon - will rust at the ends; 3) all aluminum - what Nimus said - essentially will not rust. Choose your can wisely. --Tagishsimon (talk) 14:18, 15 February 2010 (UTC)

Although aluminum can predominate in the U.S. that is a recent deveolpment and not true worldwide. 75.41.110.200 (talk) 15:43, 15 February 2010 (UTC)

Not sure how it would become an issue for the roof, but the only cases where I've heard of aluminum rusting badly is when it's in contact with saltwater. Falconus^{p t c} 15:58, 15 February 2010 (UTC)

Remind me someone, why can't we have aluminium mufflers (UK: silencers) for cars? Cuddlyable3 (talk) 17:26, 15 February 2010 (UTC)

Because aluminium is only stable in an oxygen environment. In a reducing environment (like car exhaust) the alumina coating gets reduced back to aluminum. And it crumbles. Put some aluminium foil in a flame and you can see it happen. (It also doesn't have a great melting point. Not sure how hot exhaust gets though.) [OK, so I made all that up, rather than learned it. I think I'm right though.] Ariel. (talk) 11:01, 16 February 2010 (UTC)

I'll point out that (for aluminum cans) if a corrosion problem does develop, it will likely only affect one easily replaced can/tile. I'd make sure, however, to seal the cans first - don't want water to get inside the can and create small pockets of stagnant water. --Ludwigs2 17:53, 15 February 2010 (UTC)

Soda cans won't rust. But regular cans will. Your girlfriend probably saw rusty cans. Ariel. (talk) 20:43, 15 February 2010 (UTC)

In the US, at least, "regular" cans are often referred to as "tin cans". They're not actually made of tin, but rather they're tinplate or galvanized steel. The thin tin/zinc coating is a protective layer to prevent rusting. After a while, though, the coating wears through, and the steel underneath rusts. -- 174.21.247.23 (talk) 15:33, 16 February 2010 (UTC)

Cutting open cans for a roof sounds like a lot of work. Such a roof will have aesthetics that are desirable though. But cast-off materials, destined for the dump or recycling might be as good an option. Bus stop (talk) 15:39, 16 February 2010 (UTC)

Radar silence

I heard or read somewhere that battleships sometimes go into "radar silence". If the location of various fixed radio transmitters on land was known, would it be possible to construct (using a lot of computing power I imagine) an image of the surroundings, due to those radio waves being distorted by objects? 89.240.201.172 (talk) 15:10, 15 February 2010 (UTC)

Yes, but from the top of my head, I think you'd only get mountains and such, that you already know is there. The reason is the wavelength of radio transmissions, they'r too long. EverGreg (talk) 15:24, 15 February 2010 (UTC)

Shortwave radio uses comparable wavelengths to radar, so I suppose it is possible. --Tango (talk) 15:44, 15 February 2010 (UTC)

It's not exactly battleships, but aircraft could achieve "radar silence" (I assume you mean not appear on radar) by using the cone of silence. Ks0stm ^(T•C•G) 15:54, 15 February 2010 (UTC)

I think the OP means turning off their active radar to stop the enemy detecting it. --Tango (talk) 16:36, 15 February 2010 (UTC)

Few radars would use as low a frequency as 30 MHz (Wavelength=10 metres). See Radar#Frequency_bands. You would need rather large dishes for it to be practical at such a frequency. If a battleship goes 'quiet' it would be more to stop an enemy picking up their RF transmissions. It sounds a little like passive sonar, which works for submarines as all vessels give off some sound, but not everything gives off RF. Or reflects it in a predictable manner for analysis. Anything is possible, but I don't think it would be practical. —220.101.28.25 (talk) 16:17, 15 February 2010 (UTC)

Indeed, "radar silence" is a matter of EMCON. Mind you, radar silence does not equal radio silence; radio transmissions and communication can be too crucial for the mission, and may continue. It is true that all emissions (both the typical radar and radio) can be picked up, and used by ELINT forces to triangulate and position the source. A notable difference is that radars are easily picked up by modern fighter aircraft. As such, the practise of "radar silence" is popular in scenarios where one does not have air superiority, and the enemy is likely to have control of the airspace. Standard radio transmissions, it should be noted, do not appear on any ordinary fighter jet. 77.18.11.24 (talk) 16:49, 15 February 2010 (UTC)

Some work has been done on obtaining an image of surroundings by analyzing reflection (not distortions) of existing fixed televison transmitters. Commercial television transmitters operate at VHF and UHF frequencies so resolutions of a few meters are expected, enough to distinguish a vehicle. For calculation one needs a database giving transmitter locations and frequencies. It needs information on the timing of the TV modulations. Only the horizontal blanking part of the TV waveform can be used. While the idea is workable it is unlikely to be of military use because of the long integration times needed to get usable signal/noise ratio, impenetrable shadow areas and the dependance on civilian TV. Cuddlyable3 (talk) 17:20, 15 February 2010 (UTC)

Don't forget the utility of bistatic radar. A battleship can be totally passive, while a buoy, ELINT aircraft, ground-based target illuminator, satellite, or indeed any other source somewhere very far away, shines up the sky a little. The observers on the battleship can thus see everything while never broadcasting from their own location. As far as 30 MHz RADARs, they do exist, but they're of limited practical use for most purposes. I believe some civilian aircraft use such HF bands for electronically assisted "docking" (estimating closing-distance) with a jetway. Also worth pointing out the HAARP (a research RADAR), which operates at HF, and uses a variety of tricks to modulate up or down to a desired operating frequency that is usually out of band for most other RADARs. Nimur (talk) 18:15, 15 February 2010 (UTC)

Yes, it's possible. You can use cell phone base towers (with known positions) to do that. They were able to detect airplanes. Here: [10] [11] [12] and of course Passive radar. Ariel. (talk) 20:40, 15 February 2010 (UTC)

Physics for launching rockets.

I am not actually against chemistry but can we use physics to launch the rockets. I mean due to chemical reactions the force is produced which helps the rocket to launch in its orbit but can we create such type of force by physics. I mean we can use a force something like which produces equal(more than equal to launch)(equal for hovering in space) and opposite to the gravitational force which may save the environment being polluted. —Preceding unsigned comment added by Itsrohit (talk • contribs) 17:24, 15 February 2010 (UTC)

There are several ideas like that. The mass driver is a common one. Non-rocket spacelaunch has some others too. Staecker (talk) 17:39, 15 February 2010 (UTC)

Not really, no. If we could launch rockets without burning fuel we'd already be doing it.

Rockets can't be launched into orbit balistically (like, from a giant cannon or slingshot) because the starting speed would have to be so incredibly fast that they would burn up in the air.

You could do other non-chemical rockets, like pressurized water or steam. But none of those options are currently practical. APL (talk) 17:44, 15 February 2010 (UTC)

Personally I would take a little more care to differentiate between that which is practical and that which is possible. You seem to have blurred them together in your response. There are a number of methods that might prove possible, and research is being done into them, especially if nano-materials become more readily available and so forth. Whether they will be practical (or economical) is a different question altogether. Whether we can do them at the moment does not reflect on their possibility. To assume our current way of doing it is the only or best way to do it seems a little short-sighted to me, and puts a little bit too much faith in the giant bureaucracies and historical contingencies that have led us to our current situation. --Mr.98 (talk) 17:58, 15 February 2010 (UTC)

Ultimately, a rocket works by throwing off mass at some velocity (and thus conserving momentum). The idea of using an inert gas blowing out the back of a rocket has been floated around many times. Reaction control systems often use an inert-gas pressure reservoir, or an electric heater to pressurize a tank of otherwise inert gas. When safety is an issue, this is a great way to ensure controlled release of energy. (Toy rockets often use a bicycle-pump to compress air; some even use a CO2 cartridge). But this approach limits the maximum exhaust velocity because the only source of energy is the Pressure-Volume product of your inert gas. A few off-the-wall ideas have suggested carrying an inert gas like nitrogen or argon and pressurizing it (adding energy) by heating it from another source (e.g. a nuclear fission reactor). The goal is of course to reach higher pressures, hence higher exhaust velocities, than you would by simply ejecting the stored gas. Similarly, ion engines use electric- or electromagnetic energy to get a very tiny mass of propellant flowing out at extraordinarily high velocities.

Fundamentally, if you are using an impulse engine (e.g. propelling the rocket by conserving momentum), you want the product of (exhaust mass) x (exhaust velocity) to be very large. Typically, the best way to do this is to impart as much velocity (ergo, as much energy) as possible to the fixed mass of propellant that you're carrying. So far, the safest and most efficient way to energize that exhaust gas is via chemical reaction. This serves a double-whammy - you use the stored chemical energy AND mass stored in your propellant to improve your impulse product. Any other scheme you can think of to get momentum flowing out the back end of a rocket will work, but it might be dangerous, inefficient, or impractical with today's technology. Nimur (talk) 19:12, 15 February 2010 (UTC)

Build a Space elevator. then you can use physics rather than chemistry to get rockets into space.--SPhilbrickT 22:00, 16 February 2010 (UTC)

Iron sulphide

Is iron sulphide a metal or a non-metal? —Preceding unsigned comment added by Tikasara (talk • contribs) 17:52, 15 February 2010 (UTC)

I may not have this right (not a chemist), but I believe iron sulfide would be considered a salt. --Ludwigs2 18:06, 15 February 2010 (UTC)

"metal" vs "non-metal" is usually a description of an element, not a compound. Please read your homework and textbook carefully to figure out what you really are dealing with. DMacks (talk) 18:07, 15 February 2010 (UTC)

According to our metal article, there are metallic compounds as well as metallic elements. However, iron sulphide doesn't seem to be one. It also isn't a salt -- salts break up into their constituent ions when dissolved in water, and iron sulphide doesn't. Looie496 (talk) 18:25, 15 February 2010 (UTC)

Yup, that's some good Nobel work in the metallic-compounds arena. Usually high-school-age science classes (and even into intro college) teach a dichotomy between "metal and nonmetal elements" as a way of categorizing them by certain properties and seeing patterns in the layout of the periodic table. Once they get into more advanced classes, the whole idea becomes fuzzed, as "metal" elements become anionic, compounds of non-metals have metallic properties, etc. I hate questions with no context:( DMacks (talk) 18:43, 15 February 2010 (UTC)

Broken glass

Hello! When someone goes into hospital with pieces of broken glass lodged in them, what methods are used to remove the glass? How do they know that they have got all the glass out of the person? Has it ever occured that someone has been walking around with a piece of broken glass in their foot that was overlooked by the surgeon, for example? What happens in this instance? Ice Pencil Made of Glass (talk) 18:02, 15 February 2010 (UTC)

Tweezers. Cuddlyable3 (talk) 18:16, 15 February 2010 (UTC)

Radiographic evaluation of some sort will usually be made prior to suturing of lacerations. Any glass that has entered a wound (including one it has produced) will be removed with forceps of some sort (unless it has entered and then rotated, in which case additional incision(s) may be necessary to properly remove it). DRosenbach ^{(Talk | Contribs)} 18:51, 15 February 2010 (UTC)

This suggests that glass is reasonably visible in X-rays and this says they're also visible in ultrasound. -- Finlay McWalter • Talk 18:19, 15 February 2010 (UTC)

I suspect that I still have a small piece of glass in my hand from an accident 2000. It's hard to tell because of the scar though. -Craig Pemberton 18:35, 15 February 2010 (UTC)

very small pieces of glass (or any other material) will be enveloped by a cyst that will protect the surrounding tissue. the cyst may eventually work its way out (it it's close to the surface of the skin), or may remain in the body indefinitely. --Ludwigs2 18:49, 15 February 2010 (UTC)

One of the tiny pieces left after surgical removal under x-ray control came out of my thumb several years later, more probably still to come :-) Cacycle (talk) 22:21, 15 February 2010 (UTC)

Note: OP was indef'd for trolling. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:26, 16 February 2010 (UTC)

how?

Do non-spatial countable infinities occur in nature?

I've been trying to think an example of a countable infinity which occurs in nature. The only examples I have been able to find are rational subsets of irrational uncountably infinite sets occuring in space-time. For example, my meter-stick has a countably infinite number of points along its length such that they fall at the 1/n meters mark. The same sort of argument can be applied to time. That is assuming you don't eventually start violating quantum mechanics. I can't find any other examples. Can you? What is the deeper truth here? -Craig Pemberton 18:20, 15 February 2010 (UTC)

Oh yeah, forgot to say this; things like pressure and force are derived from space-time dimensions so they don't really seem instructive. -Craig Pemberton 18:22, 15 February 2010 (UTC)

There is a story about an alien who visited Earth to collect from libraries the total of human knowledge. To save space the alien digitised the data as a single binary number. To carry the number home the alien took a metal bar and scribed a mark at the point on its length where the ratio to the whole length equalled the number. Cuddlyable3 (talk) 18:32, 15 February 2010 (UTC)

In exchange for such a nice story, I'll share one too.-Craig Pemberton 18:47, 15 February 2010 (UTC)

I did some math on your alien story, using quartz as the bar (I think it would have to be a crystal), each molecule of quartz weighs 9.9772x10^-23 g, the linear density is 1.3809 g/cm, so you have 1.384x10^24 atoms in a meter of quartz, the log base 2 is 80.1, so you have about 80 bits of information in your rod. Not much. You would do much better to use the atoms as bits, and notch the rod multiple times. Hope I did the math right. Ariel. (talk) 20:24, 15 February 2010 (UTC)

The linear density is 1.38 g^1/3/cm, not 1.38 g/cm. The answer should be closer to 10⁹ (30 bits). -- BenRG (talk) 00:47, 16 February 2010 (UTC)

How do you work with g^1/3? When I multiply it by mass per molecule the units won't work. Are you sure that's correct? Ariel. (talk) 11:02, 16 February 2010 (UTC)

The deeper truth is that no infinities of any sort occur in nature. Even the meter stick is an abstraction, not a real infinity. Looie496 (talk) 19:38, 15 February 2010 (UTC)

There are some countable infinities in our best current physical theories. For example, there's a countable infinity of galaxies/stars/atoms in ΛCDM, and bound quantum systems have a countable infinity of energy levels. But there's nothing in nature that we know for sure to be infinite, countably or uncountably. Just because we model spacetime as a continuum doesn't mean it is a continuum. Every other physical system that we model with calculus is known to actually be discrete at some level (individual molecules, individual members of a population, thousandths of a dollar). -- BenRG (talk) 19:47, 15 February 2010 (UTC)

The inescapable reciprocal of that statement, though, is that "just because we model quantum mechanics as a discrete system doesn't mean it's actually discrete." It just so happens that our discrete model matches our observations very well. The universe simply is - its reality is independent of our attempt to apply abstract descriptions about continuity or discreteness to it. Nimur (talk) 15:09, 17 February 2010 (UTC)

Is the universe definitely infinite in ΛCDM? I know it is flat, but our article doesn't say anything about whether it is infinite or not. Could you not have, say, a toroidal universe? --Tango (talk) 20:00, 15 February 2010 (UTC)

I'd say that, technically, ΛCDM describes a spatially infinite universe. To describe a toroidal universe you'd need extra parameters governing the size and orientation of the torus, and ΛCDM doesn't have those parameters. But hardly anybody takes this "prediction" of ΛCDM seriously, which was my point. It's not a very good example, but I can't think of any others. -- BenRG (talk) 00:47, 16 February 2010 (UTC)

Antibiotic vs. antimicrobial

What is the source for the distinction given to anti-bacterial products, such that (at least in the US) would be strictly referred to in general as an antibiotic (such as penicillin) while others would be referred to as an antimicrobial (such as chlorhexidine). I've read the linked article (sections) but don't seem to grasp why chlorhexidine is rarely is ever called an antibiotic rinse, even though it is one. DRosenbach ^{(Talk | Contribs)} 18:39, 15 February 2010 (UTC)

Is it, perhaps, that via their respective methods of activity, acquired bacterial immunity to antiseptics is impossible? DRosenbach ^{(Talk | Contribs)} 19:04, 15 February 2010 (UTC)

Our article on antibiotics narrows the definition to include only compounds which have (specifically) antibacterial effect. Antimicrobials would include antibiotics as well as agents which kill other pathogenic organisms (fungi, protozoans) in addition to bacteria. TenOfAllTrades(talk) 19:15, 15 February 2010 (UTC)

Alpha Centauri

I am working on something at the moment and I really want to know a star which is near to the Alpha Centauri star system? Don't answer 'Our sun' or 'Proxima Centauri', I'm looking for something different. Thanks.--Editor510 ^{drop us a line, mate} 19:16, 15 February 2010 (UTC)

So I guess you want a list like this but for alpha centauri rather than us... Maybe some astronomy software can calculate that? TastyCakes (talk) 19:22, 15 February 2010 (UTC)

Centauri A, Centauri B, and Proxima are in the star system. Are you looking for what is the next closest system to this system? Beach drifter (talk) 19:23, 15 February 2010 (UTC)

How about Beta Centauri? Beach drifter (talk) 19:25, 15 February 2010 (UTC)

Beta Centauri is nowhere near Alpha Centauri, it just happens to be in the same general direction from Earth, so appears close to it in the night sky. They are actually hundreds of light years apart. --Tango (talk) 20:11, 15 February 2010 (UTC)

A map of nearby stars

This map may help. It is a little difficult to tell which star is nearest, because it's a 2D map of a 3D space, but Barnard's Star and GJ 628 look fairly close. --Tango (talk) 20:11, 15 February 2010 (UTC)

Alpha Centauri also known as Rigel Kentaurus is a triple system (stars -A, -B and -C) of the closest stars to the Sun, about four light-years distant in the constellation Centaurus. I think Proxima Centauri, the closest star to the sun at 4.26 light-years, is a part of this star system. The visually closest stars marked in Google Earth Sky View are NGC5817, HD127724, HD131342 etc. all of which are closer than Beta Cantauri or Hadar. Cuddlyable3 (talk) 20:26, 15 February 2010 (UTC)

Map of very closest stars. Cuddlyable3 (talk) 20:32, 15 February 2010 (UTC)

If my inexpert mucking around with Celestia is to be believed, the nearest stars to the Rigel Kentaurus system are the Sun (4.4 ly), Barnard's Star (6.5 ly), Ross 154 (8.1 ly), Wolf 359 (8.3 ly), SCR 1845-6357 (binary, 8.9 ly), and Sirius (binary, 9.5 ly) Paul Stansifer 00:24, 16 February 2010 (UTC) P.S. Celestia is free software and relatively easy-to-use, so if you like space, you might like it.

I think the gravitational "spheres of influence" of the Sun and Alpha Cen overlap, so that a small object travelling through interstellar space could be gravitationally affected by both stars at the same time. ~AH1^(TCU) 02:01, 16 February 2010 (UTC)

Well, strictly speaking the gravitational "spheres of influence" of all bodies (within each others light cones, to be pedantic) are overlapping and objects will be influenced by all other objects. What is quite likely true, however, is that the regions of space where the sun's gravity is the dominant force and the region where Alpha Centauri's gravity is are directly adjacent. --Stephan Schulz (talk) 10:04, 16 February 2010 (UTC)

"Sphere of influence" usually means the sphere where the influence is dominant. For a planet, that's the Hill sphere. The same concept applies to stars, but it's more complicated due to there not being a single massive object that the star is orbiting. --Tango (talk) 13:37, 16 February 2010 (UTC)

Your results appear to largely agree with this source of stars within 10 light years except that lacks SCR 1845-6357 I guess because it not yet been fully included in their database [13] and includes Epsilon Indi which is 9.7 and I guess you didn't include because you stopped at Sirius. The database Celestia uses evidentally contains 120k stars, I'm not sure how complete it is for near earth stars particularly non visible ones but it doesn't seem there can be that many missing that we currently know of. For example GJ 1061 is not closer then 10 light years to alpha centauri [14]. Note sure about GJ 628 which Tango mentioned above but I doubt it's within 10 either (while lacking a page, it's not particularly recent so would probably be in the earlier list I guess). In any case anything that isn't with ~14.4 light years of sol, as [15] for example can be presumed to be further then 10 light years I think. Nil Einne (talk) 16:39, 16 February 2010 (UTC)

Humans to become extinct

Is this possible for humans to extinct? Ice Ages usually whites out alot of species, to FIW 5 million years from now we suppose to have another ice age, they will wipe out alot of species, or ultil 100 million years when earth is a hot house, posslbe for humans to extinct before next Pangaea even appears?--69.229.36.56 (talk) 20:55, 15 February 2010 (UTC)

Of course it's possible. Humans themselves would certainly survive another ice age, though our current civilization might be wrecked by a severe one (or severe global warming). In the longer term, Earth itself is doomed; see Sun#Life cycle. If humans accumulate enough technology before our oceans boil away, then we could eventually create generation ships and continue the species. If you believe in the heat death of the universe, then that would be the final endpoint of our species. Comet Tuttle (talk) 21:02, 15 February 2010 (UTC)

In long term fate 5 to 6 billion years from now, humans won't have any place in our solar system to escape fate. Outer planets would only achieve habitable surface temperature but it would not meet the basic enviornments. That is the problem, unless if humans find another solar system and stars that might work. Dinosaurs have been extinct 65 million years ago though.--69.229.36.56 (talk) 21:23, 15 February 2010 (UTC)

Yes, of course it is possible. I'm not sure an ice age would wipe out the entire species - we survived the last one and we were just hunter-gatherers then. With modern technology, it would be easy for at least a few million people to survive near the equator. More likely to wipe us out are things like an asteroid hitting the Earth or nuclear war. I don't think either or those are very likely, but they are both possible. --Tango (talk) 21:06, 15 February 2010 (UTC)

Would you really say that nuclear war would be the most likely of the least likely things that would wipe out humans? I would have guessed a fatal infectious disease. DRosenbach ^{(Talk | Contribs)} 21:13, 15 February 2010 (UTC)

We have a Human extinction article that discusses some possibilities. CS Miller (talk) 21:26, 15 February 2010 (UTC)

I think there are very few examples in nature of a disease alone wiping out an entire species. It is a risk for species like bananas that don't have enough genetic variation to develop immunity. Most every other disease I can think of doesn't kill 100% of a very large population, for humans the worst case on record was probably the black plague, and that was nowhere near 100% lethal (Ebola is apparently 90% fatal in some outbreaks). Rabbits in Australia were given a disease that killed 5/6 of them, but the remaining 1/6 had some degree of immunity and the population didn't die out, and indeed bounced back. So no, I don't think a fatal infection disease is likely to, alone, kill all humans, but one could be devastating for human civilization. TastyCakes (talk) 21:30, 15 February 2010 (UTC)

Of course if an organization were to specifically create a series of diseases (say 10 different, unrelated diseases) with high lethality and virulence and intentionally release them, that would be much more likely to wipe out everyone then a single natural disease. Googlemeister (talk) 21:39, 15 February 2010 (UTC)

That's true, I remember reading somewhere (I can't find it now) about attempts to create a disease for mosquitoes (something like this one) that isn't fatal in the first generation, it requires a certain number of generations to become "active" somehow, and then by the time it becomes fatal the genes have spread to all of the population and they all die. I don't remember the details, I think it may have been that they introduce a vulnerability to another disease that is not present in the wild, somehow release enough mosquitoes with a genetically designed vulnerability to that disease and then when they think that gene is present throughout the population, introduce the second disease. Bioweapons do seem like one of the more likely ways one would go about killing everyone, but like you say, the perpetrator would probably have to intentionally be trying to kill everyone; a case of one bioweapon being used on an enemy and getting out of control would likely not be enough. TastyCakes (talk) 21:57, 15 February 2010 (UTC)

currently, pollution is the biggest threat to the human species. The one thing a species can never adapt to (almost by definition) is the accumulation of its own waste. --Ludwigs2 21:42, 15 February 2010 (UTC)

The solution to pollution is dilution. Googlemeister (talk) 22:24, 15 February 2010 (UTC)

Many species adapt to overpopulation - they do it by reproducing less. --Tango (talk) 23:01, 15 February 2010 (UTC)

I'm personally sceptical of any doomsday scenario to the banana, at least not without other human contributions. There are plenty of wild and different bananas (e.g. [16]) although many of these suffer some risks from human activity [17].

I know there's been a lot of discussion about the risks to banana cultivation [18] [19] [20] [21] [22] and I'm not denying that given the reliance on the Cavendish for export by most banana growers there's a risk of banana cultivation collapsing unless a suitable replacement is found with good yields and which exports well and meets the expectations (taste, texture etc) of consumers and this replacement starts to be used fairly soon; and such a collapse which would have a corresponding catastrophic effect on the economies of countries heavily depend on bananas and may mean the almost disappearance (at least for a time) of the banana from shelves of supermarkets and fruit markets in most non-tropical countries. And panama's disease (and other diseases) is and is likely to continue to spread to other non-resistant varieties (one of the big issues appears to be that it stays in the soil for a long time so cultivating disease free but non resistant bananas in that soil becomes impossible) having a bad effect on both cultivated and probably some wild populations and a corresponding bad effect on people who rely on the banana for reasons other then export (note that according to our article "Almost all export bananas are of the dessert types; however, only about 10–15% of production is for export").

In other words it's of course possible perhaps even likely that the population of banana trees may drop drastically and this will have a terrible effect on those that rely on the banana for a variety of purposes.

However this doesn't mean the banana itself will die out. Worst case scenario, the banana may die out as a food crop but some varieties may still survive (particularly in SEA and South Asia) provided deforestation etc doesn't kill these. More likely some cultivation will continue. Particularly since we already have some semi-resistant or resistant cultivars even if they lack the consumer acceptance of Cavendish in many countries.

IMHO the Cavendish isn't even that good a tasting banana anyway (I like the ms:Pisang Mas). This has some interesting info on Panama's Disease BTW [23]

Nil Einne (talk) 09:46, 16 February 2010 (UTC)

There is no scientific reason to think that humanity has anything but extinction in its long-term future, like all species. There is really no shame in that—such is how the universe works. At some point it will run out of energy. I suspect humans will be extinct long before that—we apparently lack the ability to tackle long-term problems in a truly effective way, which will effectively preclude us getting off this rock, and will doom us when the resources run out, the heat turns up, and we go with our usual tendencies of tearing each other apart. Peaceful civilization is, so far, just a blip in the history of our universe, and even it hasn't really ever been very peaceful. --Mr.98 (talk) 22:50, 15 February 2010 (UTC)

There are plenty of species that have survived for a very long time and show no signs of dying off. You also need to be careful to distinguish species that went extinct due to being wiped out and those than went extinct due to evolving into a new species. --Tango (talk) 23:01, 15 February 2010 (UTC)

I think I've read an estimate that humans will most likely become extinct about 2 to 5 million years from now. See human extinction and exitmundi. Also the recent release of clathrates may help to explain the Fermi paradox as suggested on the RefDesk more than a year ago. ~AH1^(TCU) 01:51, 16 February 2010 (UTC)

I've wondered why I'm here now instead of being whatever humans evolve into in say another 100 million years. The chances just seem against my being alive at the start of it all rather than later. I see no reason that descendants of humans won't be around then and hopefully they'll be a bit more intelligent than the vandals that beset wikipedia. Dmcq (talk) 04:46, 16 February 2010 (UTC)

read "The Time Machine". most of the systems administrators I know are already halfway down the path to Morlock-hood, and I run into people every day who could pass for Eloi. it's just a matter of degree at this point, and a bit of a shift down the Soylent Green path... --Ludwigs2 09:40, 16 February 2010 (UTC)

"extinct due to being wiped out and those than went extinct due to evolving into a new species"—Do I? Why? Extinction is as extinction does, from the point of view of the extinct species. The birds are not the dinosaurs. --Mr.98 (talk) 21:12, 16 February 2010 (UTC)

The problem then becomes how you decide when and whether a species became 'extinct' due to the the complicated issues we've discussed before of what a species is and how you determine when a species has diverged to become a new species. Humans and chimpanzees (of both kinds) may seem to be clearly different species from our last common ancestor but we obviously never co-existed with said ancestor and the question of when humans became humans, the chimps became their individual species and our ancestor went extinct some may consider meaningless.

Even under a Punctuated equilibrium model and regardless of which definition of a species you use, it's probably fairly common you can't give a fixed point in time when one species evolved into another, that's not how evolution works. Species that underwent some polyploidy event may seem one obvious general case but even that's not always clear cut Speciation#Speciation via polyploidization and things like chromosomal fusion such as occured with human chromosome 2 even less so [24] [25] [26]).

In fact the speciation event as it were may simply be some non biological change, such as a seperation of two different populations but it seems rather odd to consider these two different populations different 'species' as soon as they seperate. If some sort of catastrophic event destroys most human populations leaving only a few fragments in different geographically seperated places and no way to regain contact between the two in at least several thousands of years and given the likely major problems each population will have to face in a world which underwent this event, it's easy to imagine speciation could occur. Does this mean you and I are different species now (as I don't believe you live in NZ)? Or the moment after this event if we both survive?

Some taxonomists prefer to avoid giving species names for extinct (particularly ancienct) species (or at least treat them specially) given these reasons and more. It's worth remembering that unlike what some creationists like to believe, evolution doesn't 'stop'. Even living fossils like the tuatara have changed significantly (whether enough to be meaningfully considered a different species I don't know although I would guess yes and as I mentioned some may consider that a meaningless question anyway).

P.S. I came across [27] which I didn't read but may be of some interest to this issue.

Nil Einne (talk) 21:52, 16 February 2010 (UTC)

Actually, cladists do consider birds to be dinosaurs and say "non-avian dinosaur" when they want to refer to what laymen call dinosaurs. I think the distinction is important because I wouldn't consider the human race evolving to a point where they can't reproduce with current humans to be a bad thing, while all humans dying out would be a bad thing. --Tango (talk) 03:19, 17 February 2010 (UTC)

Stupid question about molecular symmetry

Is anthraquinone in the D2h point group? I'm having a real blonde moment and confusing myself with normally comprehensible textbooks......I normally can just work them out fairly quickly in my head, but I've got myself in a tizz. 188.221.55.165 (talk) 21:20, 15 February 2010 (UTC)

I wouldn't call that a stupid question; crystallography is important. 99.22.95.61 (talk) 01:08, 16 February 2010 (UTC)

D2h sounds right (assuming no deviations from idealized atomic geometries heh:). The ext-links at Point_group and Crystallographic point group are pretty good examples of all of the different possibilities. Doi:10.1063/1.1841008 says that D2h is either correct experimentally or at least a useful approximation for analyzing experimental structural parameters. DMacks (talk) 22:57, 15 February 2010 (UTC)

Emergency, normal care, etc

Want to know this because forgot the answer to this and way too lazy to do a search for this. At the same time results for the search are complicated to follow.

Want to know how long does a midwife (all types of midwifes) spend with her patients compared to doctors?

Extended content

Had my yearly GYN exam, today with my OB/GYN. Time spent with her was less then 5 minutes and she hardly looked into my chart. Especially after getting BRAC Test done (8/09) and getting positive result back. That means I have a chance of getting breast cancer because of that positive result. By the way my fraternal twin sister got that test done (around the same time as me) because our mother was diagnosed with stage 4 ovarian cancer (almost 2 yr ago, 6/08). Thats a long story and prefer not to get into on her. My mom gone though several rounds of chemo, surgery to remove it, and maintence rounds of chemo as well. In my opinion she gone though more chemo then she should had to and etc. Then, my sister and my friend's mom was diagnosed with breast cancer (9/09 or 10/09), but forgot what stage it was in. After founding a lump in one of her breasts and she already had the surgery to remove it. Shes also undergoing rounds of chemo and radiation theraphy as well. At the same time left parts of our friends mom story out as well. My OB/GYN a new mother (shes was pregnant with it when I 1st saw her, last yr). She worked though the pregnancy, had the baby, and was back at work after being on maternity leave for the minium amount of time. As know of she didn't didn't or intend bf it because of her work and etc. By the way her father is also is OB/GYN as well, but mainly GYN now. Unsure when he stopped with OB part of the practice.

—Preceding unsigned comment added by Mybodymyself (talk • contribs) 22:05, 15 February 2010 (UTC)

I collapsed your medical details because the Reference Desk doesn't give any medical advice, for ethical reasons — suppose we were wrong and you took our advice anyway? If you are uncomfortable with the medical care that you received from the midwife, one option is to get a second opinion from a physician. If you happen to live in the US, I believe most insurance plans cover a second opinion. If it were me, I'd get a second opinion anyway if I was not comfortable with the care received. Comet Tuttle (talk) 22:37, 15 February 2010 (UTC)

In general midwifes spend longer, but they also deal with less complicated cases than doctors, and their job includes a lot more support, and less "action". In any case, I think you went to the wrong type of doctor for the genetic test. Go to a cancer doctor or a geneticist, not an OB/GYN. Ariel. (talk) 23:14, 15 February 2010 (UTC)

Thank you for your answers and editing the details part of this. Both were interesting. As for where I'm in the US (Metro New York on New Jersey Side of it) its mostly OBs/GYNs, unsure if theres any FP (Family Practioners), some midwifes. Mostly the midwifes are CNMs (certified nurse midwifes) then CPMs (certified proferrisonal midwifes) or CMs (certified midwifes) or other types (which I have no clue what they are).--Jessica A Bruno (talk) 00:17, 16 February 2010 (UTC)

Why does Energy Information Administration predict a fall-off in wind power growth?

Why is there an inflection point on the wind power projections at about year 2013 on page 21 of this presentation? Given some regions' projections that 30% renewable will be possible in 2020 "with or without legislation" is there any reason to suspect that wind, along with pumped storage hydroelectricity (heavily funded in this year's U.S. Army Corps of Engineers budget, where it is also referred to as flood mitigation capability) and thermal storage will not continue to dominate energy growth world wide? 99.22.95.61 (talk) 22:38, 15 February 2010 (UTC)

This point was brought up in a discussion last month. Some suggestions were provided, but ultimately, we don't make speculations on the reference desk. If you really want to know, you might want to contact the author of the presentation, who is listed on every page; or follow up with the various sources that are cited throughout that presentation. Nimur (talk) 14:51, 16 February 2010 (UTC)

After being transferred four times, I spoke with Chris Namovicz in the EIA who said that the National Energy Modeling System, which takes 8-12 hours to run on a fast CPU and produces these projections based on assumptions about the state of the laws in September of each year, always assumes that tax credits for wind will not be renewed (even though they always have been after no more than a year, and when they have expired temporarily, they did not substantially impact the growth rates for new wind) and assumes that fossil fuel subsidies will never be repealed. Chris agreed that there was no effective way to measure the accuracy of the Modeling System's projections, because it doesn't produce projection confidence intervals or expected errors of prediction in its output. Chris referred me to John Conti on that point, who called me back after I emailed, confirming my misgivings about false and unfounded assumptions skewed in the direction of fossil fuel producers on technicality judgements. Conti claimed that discrete economic simulations are incapable of producing projection confidence intervals or expected errors of measurements, and gave no reasons that leaving those out does not destroy the ability to correct the Model in the face of historical outcomes compared against earlier projections. When confronted with my feelings on the matter, Conti asked for the name of my employer. I told him I wanted our future communications to be in writing, and he said he would respond in writing. 99.22.95.61 (talk) 22:09, 16 February 2010 (UTC)

Huh? flood mitigation capability is not the same as pumped storage hydro. 75.41.110.200 (talk) 17:15, 16 February 2010 (UTC)

The capabilities overlap. 99.22.95.61 (talk) 20:25, 16 February 2010 (UTC)

Brain damage and pacing in animals

What is the neuropathology of pacing / walking in circles after some sort of brain injuries in animals (most obviously in dogs and cats)? Is tere a similar phenomenon in humans? What is the clinical term? —Preceding unsigned comment added by 166.137.137.154 (talk) 23:14, 15 February 2010 (UTC)

Causes of a dog walking in circles. Cuddlyable3 (talk) 23:29, 15 February 2010 (UTC)

Thanks. I've seen those kinds of articles as well. I'm specifically interested in the details of what brain structures are involved. Those kinds of pages focus on broad explainations like "brain damage". I would like an idea of the clinical terminology amd context so I can search indepth 166.137.137.154 (talk) 23:51, 15 February 2010 (UTC)

There are a number of interventions that can produce circling when delivered to one side of the brain -- search for "ipsilateral circling" and "contralateral circling" and you'll find quite a number of publications. Structures belonging to the basal ganglia are the best-known, but damage to the vestibular system can also produce circling by altering balance. In humans I believe that circling is rare, but shows up occasionally in cases of hemispatial neglect. Looie496 (talk) 00:02, 16 February 2010 (UTC)

An unrelated illness, scrapie, causes hopping gait syndrome in sheep and other livestock. Scrapie is a type of spongiform encephalopathy, commonly known as "mad cow disease." Nimur (talk) 14:55, 16 February 2010 (UTC)

To be clear, scrapie is used to refer to the PrP-caused transmissible spongiform encephalopathy in sheep and goats. Mad cow disease (properly bovine spongiform encephalopathy or BSE) is only used to describe the disease in cows. TenOfAllTrades(talk) 15:12, 16 February 2010 (UTC)

The term, by the way, for this sort of repetitive behavior is Stereotypy, perusing that article may help the OP and others interested in learning a bit more. --Jayron32 03:13, 17 February 2010 (UTC)

February 16

Very large cube

What is the largest solid steel cube that could, floating in free space, sustain its shape against the force of its own internal gravity (i.e. avoid the tendency to become spherical)? What solid material would allow the largest such cube? 86.133.247.182 (talk) 00:44, 16 February 2010 (UTC)

Any cube would deform to some extent under its own gravity, given that stress produces strain and thus some deformation. So. strictly speaking, no steel cube of any size whatever, even 1 cm, could maintain its form in space, with no deformation whatsoever. How much deformation is tolerable? Likewise, it is unlikely that a humongous cube of steel many lightyears across would become a perfect sphere under the deformation of its own gravity. Edison (talk) 01:17, 16 February 2010 (UTC)

well, I suppose you could reframe this question to read 'how big does a steel cube have to be before its own gravity causes plastic (rather than elastic) deformation, but even given idealized assumptions I wouldn't know where to begin with the calculations. perhaps we should ask the Borg, since they seem to be into the large cube thing.

Are roche limit and hydrostatic equilibrium relavent? ~AH1^(TCU) 01:46, 16 February 2010 (UTC)

I'm pretty sure that a steel cube many lightyears across would become a perfect sphere with radius zero Paul Stansifer 02:13, 16 February 2010 (UTC)

My thought too! 86.133.247.182 (talk) 02:20, 16 February 2010 (UTC)

Why would you think that? A lot of things can be very massive without becoming a black hole. Nimur (talk) 04:29, 16 February 2010 (UTC)

At 7.8 g / cm^3, a steel sphere would exceed the Schwarzschild radius limit at only 2.7 AU (415 million km). Any cubic solid that is light years across is already doomed to be a black hole. Dragons flight (talk) 05:09, 16 February 2010 (UTC)

Oops.My hyperbole collapsed under its own weight. I intended just to make the point that as steel cubes became larger and larger they would deform, but as they approached a sphere some small trace of the corners and edges might be seen. Edison (talk) 16:09, 16 February 2010 (UTC)

@Edison: If you like, turn the question round and ask what would happen to a cube, say, 1,000 miles across, or 10,000 miles across, and so on. I'm only after ball-park ideas. For example, would a cube 1,000 miles across, or 10,000 miles across, or whatever, remain a cube as far as you could visually distinguish from a distance, or would it noticeably sag, or would it be completely mashed? 86.133.247.182 (talk) 02:20, 16 February 2010 (UTC)

When discussing possible definitions of "planet" some 11 years ago, I came across the following passages in the junior-level The Universe and Planet Earth by Josip Kleczek and Petr Jakeš (Artia, Prague 1985; Translated by Stephen Finn, Octopus Books, London 1987) -

Figure 48 on p35 shows a crystal, a rock, a 500 km-diameter irregular asteroid and a larger, rounded, internally molten body, with the caption: "Small bodies are kept together by electromagnetic force, large ones by self-gravitation."

Discussing crystal structure, text on pp58-9 reads: " . . . The energy released by the crystal during its growth is also called binding energy. The greater it is, the more stable the system of molecules - the crystal - is, and the more resistant to external influences. It must be heated to a higher temperature before it melts. Or a greater pressure must be exerted on it to crush the crystal lattice. In the interior of solid bodies consisting of more than 10⁴⁶ elementary particles (Figure 48) self-gravitation is strong enough to achieve this."

Text on p61 discussing solar system bodies reads: "Small solid bodies made of rocks, such as meteoroids, the nuclei of comets, small satellites and the vast majority of minor planets, are held together by electrical force. Their mass is small, so their self gravitation is also low. [Various examples elided] Inside solid bodies more than 500 km (310 miles) in diameter the self-gravitation is so great that it breaks up the crystalline structure of the rocks. The solid rock thus becomes a pliable, dough-like material where the pressures in different directions are evened out. The irregularity of the body thus disappears: tall projections are heavy and sink downwards towards the middle while light, thin parts of the body (depressions) are pushed through the doughy material to the top. This is called isostatic equilibrium. The body tries to assume a round shape through its own gravitation (Figure 48)."

The figures of 10⁴⁶ elementary particles and 500 k (310 miles) diameter (which I've not come across elsewhere) may be of relevance - I suspect the difference between rock and steel at these dimensions may not be very significant. 87.81.230.195 (talk) 03:32, 16 February 2010 (UTC)

I beg to differ, only because my exoplanet geology textbook classifies planetary formation geology into three types of material: "things that are like water," "things that are like silica," (rock), and "things that are like metal." (They use a little more technical terminology, but I left my copy in my office, so I'm glossing over the details). Iron is much denser and has a variety of different parameters than rock (melting point, compressability, bulk modulus, electromagnetic effects...). In other words, there is a major qualitative and quantitative difference between rock and steel at the dimensional scales we're talking about here. But, this is all just hand-wavey science anyway... In any case, one could solve for the hydrostatic equilibrium of a 100% metallic planet, as AH1 has linked above, and calculate the minimum mass needed to form a sphere under self-gravitation. Nimur (talk) 04:35, 16 February 2010 (UTC)

The yield stress for steel ranges from ~250 MPa to ~1650 MPa depending on composition. Steel has a density of order 7.8 g/cm³. Using that and the higher yield stress, a solid steel cube could grow to about 650 km in side length before it deforms plastically. As for the largest cube, I think diamond would be in the running (yield stress 35 GPa) and should get you up to about 7000 km in side length.

Thanks! I'm impressed by the figure for diamond... never thought any solid material could grow that big! 86.134.30.55 (talk) 14:32, 16 February 2010 (UTC).

Don't we already know those heavenly bodies that don't become spheres? And don't we have an idea of the smallest heavenly bodies that are spherical, and that are likely to have become that way under the stresses of their own gravitational forces? Bus stop (talk) 15:25, 16 February 2010 (UTC)

Yes, but the OP asked specifically about a steel cube. We are partly arguing about (and avoiding actually calculating, because that would be too much like hard work) how much a steel cube would differ from comparable lumps of rock about which, as you say, we have observational as well as theoretical evidence. 87.81.230.195 (talk) 17:48, 16 February 2010 (UTC)

Effect of temperature change on skiing?

I'm watching the Olympic men's downhill right now, and the television commentators observed that there was a 5°C temperature difference from the top of the ski hill to the bottom — from 28°F to 36°F. What effect, if any, does this have on the conditions that the skier would notice? Nyttend (talk) 01:08, 16 February 2010 (UTC)

Just for the record, the recent warm weather is caused by an El Nino and PNA pattern, and Canada is at a lack of snow while the US gets most of the snowstorms.[28] As for the ski hill, I'm guessing that there would be a difference in snow conditions in powder vs. packing. ~AH1^(TCU) 01:38, 16 February 2010 (UTC)

The article doesn't help me very much — I understand that powder is better from the skier's point of view, but is it enough that he'd notice it while going down the slope? However, I'm well aware of the weather at large; I'm in western Ohio, and I spent most of last week shovelling :-( Nyttend (talk) 02:50, 16 February 2010 (UTC)

The skier likely wont notice a difference in the type of snow encountered (barring any ice that forms on the surface), as race courses are heavily groomed for a consistent surface. That said, the type of wax applied to the ski depends entirely on the snow temperature, and proper wax application is key to trimming those all important tenths of seconds off of times. Wired did a little write up that introduces the subject fairly well -here IMO, the most interesting thing is getting the layering of waxes just right so that the outer layer for colder snow is worn away by the time the skier gets to the warmer part of the course. 161.222.160.8 (talk) 05:10, 16 February 2010 (UTC)

Powder snow may be great for snowboarding, but for downhill skiers it puts the brakes on damn quick! A downhill ski course must be mainly ice for the skiers to get any sort of speed. Given that, temperatures above freezing would create a film of water above the ice and make things much quicker - and possibly dangerous. For the later skiers, prolonged temperatures above freezing combined with the pressure of the wafer-thin ski blades would mean the piste would rapidly turn to mush, and that's no good for speed skiing at all. --TammyMoet (talk) 12:35, 16 February 2010 (UTC)

Skiing on ice is horrible - you can't dig the edges of your skis in, which makes it hard to maintain control when turning. --Tango (talk) 13:53, 16 February 2010 (UTC)

For optimal traction and glide, Ski_wax is applied to the underside of skis. Which type of ski wax is applied is highly dependent on temperature. A single surprisingly bad performance by an athlete skier is often explained (rightly or not) by him or her having had the wrong type of ski wax. Amateur skiers will also be familiar with this problem, sometimes the snow stick to your skis because of the wrong wax. So yeah, the temperature could have a very big impact. EverGreg (talk) 13:05, 16 February 2010 (UTC)

The Planets

Why are the planets in the solar system so different in composition? Wouldnt the solar dust they were made of have been mixed up, so they should be made of similar material? 78.146.222.3 (talk) 01:44, 16 February 2010 (UTC)

One would hope that Formation_of_the_solar_system#Formation_of_planets would have the answers you need. Vimescarrot (talk) 02:25, 16 February 2010 (UTC)

Actually this is fairly similar to question which I've heard is one of the current difficulties in the theory of planetary formation. This is why the elements in the earth are often found in clumps. Like metal ores are generally found in big lumps of one type. No reason has been found yet why it isn't all arbitrarily mixed together. I wouldn't be at all surprised if there was at least some website out there claiming that just because we don't have a theory, must mean god did it. Vespine (talk) 04:10, 16 February 2010 (UTC)

...that seems incorrect. Ore Genesis —Preceding unsigned comment added by 24.137.114.204 (talk) 04:23, 16 February 2010 (UTC)

That's extremely interesting! I only just heard that recently and I thought it was a fairly reliable source, maybe it's some related problem that I just misunderstood. I'll have to see if I can find where it was. Vespine (talk) 04:41, 16 February 2010 (UTC)

The short answer is that different elements and compounds are retained by planets of different temperatures and masses. The Earth, for example, is to small to hold on to hydrogen, so the only hydrogen we have is locked up in compounds (eg. water). Jupiter is plenty big enough to hold on to hydrogen, so its atmosphere is about 70% free hydrogen. --Tango (talk) 14:05, 16 February 2010 (UTC)

Whereas Uranus is mostly filled with gases of various sorts. —Preceding unsigned comment added by 79.76.229.198 (talk) 00:41, 17 February 2010 (UTC)

LOL 146.74.230.82 (talk) 00:59, 17 February 2010 (UTC)

See Atmosphere of Uranus. At the core, Uranus and Neptune are thought to contain a layer of diamond[29]. ~AH1^(TCU) 03:11, 17 February 2010 (UTC)

So if we could get close enough to Uranus, could we detect ammonia and methane expulsions? What about H2S? Is there any of that gas inside Uranus? —Preceding unsigned comment added by 79.76.229.198 (talk) 13:58, 17 February 2010 (UTC)

If Titan do not heat to earthlike temperatures

If Titan do not heat to earthlike temperatures and stay below 50 C would Titan keep some atmosphere or at least 3/4 of it would be gone. This forum agrees with us and even said if Titan gets to Earthlike atmoshpere it would just be gray like our moon, I wonder if Titan only gets to -60 C, then probably the atmoshpere would be thin like Mars?--69.229.36.56 (talk) 01:47, 16 February 2010 (UTC)

I think the question is, if Titan's atmosphere is heated to Earth-like temperatures (possibly due to the expansion of the sun into a red giant), would its atmosphere evaporate from the heat and get thinner? ~AH1^(TCU) 02:35, 17 February 2010 (UTC)

Hydrogen

I have three questions to ask you:

1. Are there any commercial power stations that produce electricity by burning hydrogen?

2. Are there any motorbikes, buses, trucks, trains, boats, ships, submarines, or airplanes, etc, that use hydrogen as a fuel?

3. Are there any cooking appliances, heaters, or water heaters, etc, that use hydrogen as a fuel?

An Unknown Person (talk) 04:13, 16 February 2010 (UTC)

The article Hydrogen vehicle has a few answers your second question. But mostly experimental stuff. APL (talk) 04:16, 16 February 2010 (UTC)

BMW has sold an extremely limited number of BMW Hydrogen 7 vehicles. It would be a stretch to call them "commercially available." I'm not aware of any (commercial) power plants that use hydrogen combustion for electric production. A few spacecraft do use hydrogen as a fuel. The big orange part of the Space Shuttle (rather, the "STS", to use the terminology correctly), is mostly a large hydrogen tank. Nimur (talk) 04:24, 16 February 2010 (UTC)

List of fuel cell vehicles Hydrogen fuel Hydrogen economy. BP had part of a power plant running on hydrogen but they pulled the plug. Italy has the 1st hydrogen power plant due to come online this year. strips hydrogen from methane. question 3, not sure. There is no readily available source of hydrogen yet, so most of those kind of things run on natural gas or electricity. I can't imagine they contribute enough to the problem to be considered a priority for conversion. Vespine (talk) 04:31, 16 February 2010 (UTC)

(ec)Was the BP plant really burning hydrogen for energy, or was it reprocessing it as part of an enhanced hydrocarbon recovery/refinery project? I see some mention of directly using the hydrogen stream, but given that BP is an oil company, I'd believe it more if they were investing in other uses for hydrogen - both in cracking and desulfuring. Nimur (talk) 04:41, 16 February 2010 (UTC)

(edit conflict)Hydrogen's potential as a fuel is better realized in its use in a device known as a fuel cell rather than in open combustion, such as in a standard internal combustion engine. Hydrogen has a rather low combustion potential; as actually burning it releases much less energy per gram than does burning most hydrocarbons, and the fact that it is a very light weight gas makes its use in open-combustion applications, like a standard car engine, quite impractical.

The hydrogen fuel cell, however, is hardly new technology; the basic design concept had been demonstrated in the 1800's and has been in use commercially since the 1950's; hydrogen fuel cells powered all of the electronics on the Apollo missions, and continue to be used by NASA for all of their electricity generation on all of their Space Shuttle missions. Hydrogen fuel cells are perfectly fine ways to power just about anything, you can run a fully electric car on one, producing only water vapor as a by product, and they don't burn anything, so there is no combustion. They operate like any battery, but with hydrogen rather than a metal as the cathode. Electric cars powered by fuel cells have been made which operate at modern highway speeds, and which can run at distances comperable to the distances a gasoline or diesel powered car can run on a full tank. See this C-net article about a fuel cell vehicle developed by Honda, which has a top speed of 100 mph and can run 270 miles on a tank of hydrogen. Indeed, such technology to do so has been around for years. The biggest issue is not in the way the car runs. A fuel cell car isn't the problem in converting cars to fuel cells, its hydrogen delivery infrastructure. An efficient and safe means of a) producing enough hydrogen to power a national fleet of fuel-cell cars and b) distributing the hydrogen to people so they can run their cars on it are the two main reasons why hydrogen has not taken off.

There are home generators which can make hydrogen for you using residential natural gas or just plain water and solar power; so hypothetically one possible solution is to allow everyone to make their own hydrogen at home rather than get it at fueling stations, see this description of both water and natural gas based systems, availible from Honda. --Jayron32 04:38, 16 February 2010 (UTC)

Regarding commercial power stations, hydrogen gas doesn't occur naturally, so you'd be better off using whatever you where going to use to make the hydrogen. It's useful in cars and such because it can still produce power relatively efficiently at a small scale, and driving with your car plugged in isn't an option. — DanielLC 05:34, 17 February 2010 (UTC)

That's a really key point: hydrogen is useful as an energy storage/transport medium, but not as a primary fuel itself. It's easy to make on large scale using some other energy source and then use to power other things elsewhere that are far from primary sources or somehow else can't use the primary source conveniently. But "generate hydrogen then use it" has an energetic cost, so you're better off not bothering with this intermediate form unless there is a reason. DMacks (talk) 05:43, 17 February 2010 (UTC)

Ground State Energy

What would be the potential real-world application(s) of knowing the ground state energy of one or more molecules? Truthforitsownsake (talk) 05:13, 16 February 2010 (UTC)

Knowing the relationship between ground state energy and exicited energy states has lots of applications. Exciting the nuclei of atoms to an excited state and alowing them to relax to the ground state is a fundemental part of nuclear magnetic resonance and its medical analogue, magnetic resonance imaging. Understanding concepts like Phosphorescence and Fluorescence requires understanding how energy states work. If you don't know what the concept of a ground state is, the entire quantum model of the atom will not be understandable, and not knowing how atoms work means you won't know how to effectively analyze them and use them. The entire field of analytical chemistry basically requires understanding how electrons and other parts of the atom behave as they are excited and allowed to relax to the ground state. Also, you can't pull some fact out of an entire discipline like this and say "how does this have a real world application". Take a holistic view; understanding Chemistry is useful; and this is a core concept to understanding chemistry. --Jayron32 05:29, 16 February 2010 (UTC)

It seems like your answer addressed the issue of knowing what the term "ground state energy" means. The question was in relation to knowing the actual specific energy value for a specific molecule. Truthforitsownsake (talk) 05:49, 16 February 2010 (UTC)

it allows you to predict the energy and therefore the wavelength of a photon emitted by an electron falling from an excited state to the ground state, and thus it allows you to figure out which elements are in certain light-emitting objects (e.g. stars) by observing the emitted light. I'm sre there are hundreds of other applications too. —Preceding unsigned comment added by 83.134.159.68 (talk) 07:25, 16 February 2010 (UTC)

The problem with that is that it would seem to require knowing the energy of one of or more of the excited states as well. Are there any you could think of using only the ground state energy? For example, is it possible to progress from the ground state energy of several molecules to a useful thermodynamic or kinetic property that could be used to predict the outcome of a reaction? I appreciate very much all the help being volunteered. Truthforitsownsake (talk) 16:31, 16 February 2010 (UTC)

KOH + CO2 → KHCO3

How much CO2 (in lbs or cu. ft.) will a gallon of reagent KOH convert to KHCO3 at STP and 100 deg. Celsius at standard pressure? (BTW - this is not a homework question but a question about how much KOH is needed to convert CO2 from IC engine exhaust to KHCO3. Also this is not a trick question since KOH is a solid or liquid and CO2 is a gas.) 71.100.8.16 (talk) 06:36, 16 February 2010 (UTC)

First, take a look at stoichiometry, which explains the mathematics of conserving mass in chemistry reactions. As far as I know, this reaction will not occur at standard temperature and pressure. We have a brief mention at Potassium_carbonate#Production and potassium bicarbonate, which make reference to electrolysis (generating K+ ions) as a necessary precursor step. Maybe an expert chemist can fill in the details. Nimur (talk) 14:11, 16 February 2010 (UTC)

I suppose that in a few hours, days or weeks I could calculate the output from an IC engine according to RPM x number of cylinder x cylinder bore and stroke, etc. and then how many lbs or gallons of KOH I would need to convert each cubic foot of CO2 to KHCO3 and at what temperature and pressure if I just knew how many lbs or grams of KOH I would need to convert just one cubic foot of CO2 to KHCO3. I was hoping this might have already been calculated somewhere and posted on the internet. 71.100.8.16 (talk) 14:37, 16 February 2010 (UTC)

Two points: First, KOH is a solid, so you need to know either the mass of KOH or quantity in solution (e.g. molarity). Second, you probably shouldn't be mixing US standard measures or Imperial with SI (you have gallons and 100 °C in your problem above). -- Flyguy649 ^talk 14:43, 16 February 2010 (UTC)

The issues you mention are also matters of conversion to the correct units, which should likewise be available somewhere on the Internet. So far I have only found this:

  1.  CO2 + H2O --> H2CO3
  2. H2CO3 + 2 NaOH (or KOH) --> Na2CO3 (or K2CO3) + 2 H2O + Energy
  3. Na2CO3 (or K2CO3) + Ca(OH)2 --> CaCO3 + 2 NaOH (or KOH) 

71.100.8.16 (talk) 16:00, 16 February 2010 (UTC)

Good, now you have the balanaced reactions for getting what you want. These reactions are in terms of molecules ("1 CO2 molecule + 1 H2O molecule gives 1 H2CO3 molecule", etc.), so you can use the molecular weight of each compound to convert those molecule ratios to mass ratios. You can check our article about each chemical to find these conversion factors. You could even do that for the theoretical reaction you proposed in the initial question. The only other ingredient in your later equations is water, and you already heard you need a lot of water just to dissolve and mix everything. DMacks (talk) 17:43, 16 February 2010 (UTC)

I'll assume that you want to use a temperature of 100 C, or 373.15 K, even though STP (Standard Temperature and Pressure) usually means 0 C or 273.15 K. First, lets assume we have a 1 molar solution of KOH. With a molar mass of 56.1 g/mol, that works out to be 56.1 g of KOH (1 mole) in 1 L of water. This means that the solution can theoretically absorb 1 mole of CO2, which weighs 44.1 g. Using the gas equation PV = nRT, we can solve for V using P = 0.986 atm (STP), n = 1 mole, T = 373.15 K and R = 0.08205746 atm*L/mol*K we get a volume of 31 L. This is all assuming that CO2 at these conditions can be treated as an ideal gas, but this should be a good estimate.

24.150.18.30 (talk) 02:26, 18 February 2010 (UTC)

sterno in racing

why did they use sterno in racing wouldent it make more sense to just use ethanol rather than hundreds of cans of sterno —Preceding unsigned comment added by 67.246.254.35 (talk) 08:49, 16 February 2010 (UTC)

Are you referring to the allegation the Michael Waltrip used Sterno during 2007 Daytona qualifying, as mentioned at Sterno#Use in racing? Three things come to mind - it's unlikely that the "bluish gel" was Sterno brand canned fuel, since Sterno is dyed pink; "hundreds of cans" would not have been used for that incident, since it was during qualifying, which is only a limited number of laps, and whatever the substance was could conceivably have been purchased in bulk, rather than cans. --LarryMac | Talk 13:50, 16 February 2010 (UTC)

WHY NOT JUST USE ETHANOL THOU? —Preceding unsigned comment added by Thekiller35789 (talk • contribs) 23:55, 16 February 2010 (UTC)

Possibly for timed release, or to avoid detection by inspectors looking for prohibited additives mixed directly into the fuel. --Smack (talk) 19:09, 17 February 2010 (UTC)

Wings and the human anatomy

I know this is impossible, but a human were to be born with feathered wings as pictured in typical angel pics, what kind of anatomy would he/she have to have? Meaning, will there be extra muscles, bones, etc? --Reticuli88 (talk) 13:51, 16 February 2010 (UTC)

Are the wings just ornamental or are they supposed to actually make one fly? The latter would require a massive anatomical overhaul in terms of more muscles, lighter bones, etc., if it were even going to be a little tiny bit possible. If they are just ornamental, then it just depends on the weight of them. --Mr.98 (talk) 14:07, 16 February 2010 (UTC)

Not ornamental. I just want someone to detail to me how it will not look like the typical angel pictures. --Reticuli88 (talk) 14:09, 16 February 2010 (UTC)

Angels are usually shown as having wings and arms. That means they have 6 limbs, which is a very different anatomy. If you replaced their arms with wings, it is much simpler. You can get an idea of how the arms and hands would need to change by looking at bats. The other major change in that the muscles in the chest would need to be much, much larger if you want them to be able to get off the ground. --Tango (talk) 14:12, 16 February 2010 (UTC)

(ec) We can't answer specific details about your hypothetical situation. You've already stepped outside the bounds of reality by suggesting the impossible - so requesting scientific analysis at this point is futile. There is no correct answer to this kind of "what-if" question. However, if you want to consider something scientific, you might notice that the closest winged relatives to humans are bats. Because they are mammals, like humans, they do not have feathers (their skin cells have adapted to form hair, not feathers). The wings are made of a skin membrane stretched across specially-adapted finger bones. Nimur (talk) 14:15, 16 February 2010 (UTC)

In the case of wing muscles they might look more muscular rather than larger since insect wing muscles are the most powerful muscles known... (correct me if I'm wrong.) 71.100.8.16 (talk) 14:16, 16 February 2010 (UTC)

The square-cube law means insects can fly extremely easily because they are so small, so using them as an example isn't useful. "More muscular" and "larger" are the same thing, anyway - muscles get stronger by getting bigger. --Tango (talk) 14:28, 16 February 2010 (UTC)

That is for true flight. Gliding would be much more feasible with only minor changes. In fact, they have clothing that will let you do that. Googlemeister (talk) 14:29, 16 February 2010 (UTC)

Obligatory link to Wingsuit flying. --Mr.98 (talk) 14:40, 16 February 2010 (UTC)

Gliding in a wingsuit is lot like plummeting.APL (talk) 15:35, 16 February 2010 (UTC)

errr... I'll point out that gliding usually preferences a non-feathered wing (feathers give control over lift, but introduce drag), but a human figure with huge bat-like wings starts to look decidedly non-angelic. --Ludwigs2 16:29, 16 February 2010 (UTC)

And that calls for the obligatory link to Childhood's End... alteripse (talk) 21:09, 16 February 2010 (UTC)

Also, angels are usually depicted with wingspans shorter than their armspans! Unless they can beat them faster than a hummingbird, that's not nearly long enough. Hangliders typically have wingspans of 30ft or more, and human-powered aircraft like the Gossamer Condor of nearly 100ft. It's difficult to imagine how that could fold comfortably onto the back of a humanoid when not in flight. APL (talk) 15:35, 16 February 2010 (UTC)

I remember reading that they would requie a huge musculartor to fly - so tthey wouldnt look like they do in paintings. 89.242.101.230 (talk) 20:41, 16 February 2010 (UTC)

Genetically - this is an essentially impossible mutation. It's conceivable that someone could be born with 6 limbs (this has probably happened more than once in human history) - but it's really hard to imagine how feathers could be there. The gene(s) for feathers came about as dinosaurs evolved into birds - but the mammal line had already branched off by then - so there isn't really a way for such a complex set of genes to appear in humans all in one go. Feathers are a modification of scales - and humans aren't scaley. So this would require truly massive amounts of incredibly lucky mutation. It's essentially impossible. SteveBaker (talk) 20:57, 16 February 2010 (UTC)

If we go down the bat-like wings route, rather than the angel-like wings route, then it is a little more feasible (bats are quite closely related to humans). You swap some human genes for bat genes and see what happens. With current knowledge of genetics, I would expect it to require a significant amount of trial and error to get it even close. I expect the most difficult part would be turning human arms/hands into bat's wings while leaving the legs/feet unchanged - as I understand it, the same genes are used, in part, for both. You also need to do something about the muscles, but perhaps that could be done with some well placed hormones during gestation or shortly after birth. --Tango (talk) 03:12, 17 February 2010 (UTC)

There are four levels we need to think about. First, could you make something the size and weight of an adult human fly under his/her own power? Theoretically, the answer is yes - there are birds and pterosaurs larger than humans who have flown under their own power. Second, could you make an animal with three sets of limbs? This is a hand-wavey theoretically "maybe" - I don't think it's completely and utterly impossible for there to be a second shoulder girdle at the bottom of the rib cage, for example. Third, could you make something the size of a human fly with wings as commonly depicted? No, not unless you seriously muck around with the mass involved. Of course, since an infinite number of angels can dance on the head of a pin without crushing it, perhaps this isn't really a problem! Finally, could you have wings in the place commonly depicted? No, there's just no extra space there for anything; your back muscles are a very complicated set of muscles that slide over and under one another; there's no room to just go adding extra bones and stuff there. And then you get into feathers... Matt Deres (talk) 22:05, 16 February 2010 (UTC)

Bear in mind that many people think angels are spiritual beings, and as such are "transcendent and therefore metaphysical" in nature (ie. incorporeal and therefore without mass). In other words, angels don't need large wings with even larger muscles to enable them to fly. Astronaut (talk) 01:08, 17 February 2010 (UTC)

There are flying birds the size of humans, but they are far lighter than humans due to different bone composition, etc. --Tango (talk) 01:12, 17 February 2010 (UTC)

According to the article I linked to, Argentavis has been estimated to weigh between 60-110 kg. Close enough! Either way, it ain't gonna happen. Matt Deres (talk) 01:37, 17 February 2010 (UTC)

According to the Bible, angels have neither wings nor a ring around their head. Maybe they look like humans but only "fly" vertically upward. ~AH1^(TCU) 02:26, 17 February 2010 (UTC)

We aren't being asked about supernatural angels - and we're not being asked whether such a creature could fly - we're being asked whether someone could be born looking that way - and for all practical purposes, the answer is a very clear "No". SteveBaker (talk) 02:57, 17 February 2010 (UTC)

The OP said "not ornamental", which I interpret to mean they are supposed to be able to make the person fly. --Tango (talk) 03:12, 17 February 2010 (UTC)

Thanks everyone for their input. I was trying to imagine if a human being had 6 limbs, two of those being wings (feathered or not) how much would it not look human. I mean, would the back look twice as huge? Or the chest? Will it have to have longer legs or a longer neck? --Reticuli88 (talk) 16:15, 17 February 2010 (UTC)

So I imagine that this human might have to look something like this. --Reticuli88 (talk) 19:28, 17 February 2010 (UTC)

Signal White Now II

This question - [[30]] - let me thinking. If this dye absorbs light in the ultraviolet spectrum and emits light in the blue spectrum, it would yield a better or worse result depending on the amount of UV hitting the teeth. So, in a room with indirect natural light that comes in through a glass, its effect would possibly not be noticeable. However, under a black light in a night club the teeth could look whiter or perhaps simply blue (depending on how yellow they were), right?--ProteanEd (talk) 16:47, 16 February 2010 (UTC)

Right, and under such lights, to my personal observations, teeth often do glow blue-white, just as do white clothes washed in detergents containing similar 'white-enhancing agents.' Note that although this particular product apparently claims to (and doubtless does) contain a newly formulated (or utilised) ingredient, toothpaste manufacturers have been using other such ingredients with similar properties for some time. 87.81.230.195 (talk) 17:29, 16 February 2010 (UTC)

Teeth are made of apatite which fluoresces without any conspiracy involved ;-) Cacycle (talk) 22:56, 17 February 2010 (UTC)

Ferris/Chelsea wheel?

While researching the invention of the Ferris wheel I remebered years ago a story about a dispute over who had the invention first. The story was that a gentleman named Chelsea had first set out to build what is now the modern Ferris wheel. His invention was called "The Chelsea Roundabout" Has anyone heard this story or is it just some folk tale?Nijia2010 (talk) 19:09, 16 February 2010 (UTC)

I couldn't find any reference to this story at all. However, it is known that after Ferris built his wheel for the 1893 World Fair in Chicago, many people copied the idea and he spent most of the rest of his life launching (and defending against) lawsuits. So it's very possible that other people claimed to have beaten him to the idea. It might help if you told us where you heard about this "Chelsea Roundabout". SteveBaker (talk) 02:54, 17 February 2010 (UTC)

Parts of brain responsible for street smartness and academic intelligence

Some indivdiuals, who are quite good academically are easily duped in real life. They lack what is called street smartness or tact . There are others with bad grades but are very clever in real life and go on to become businessman etc. There are a few who are strong in both areas. However, since one sees quite clear division of skills. One may conclude that different parts of brain are responsible for academic / real life intelligence. Could you please throw some light on that? —Preceding unsigned comment added by 131.220.46.25 (talk) 19:19, 16 February 2010 (UTC)

Actually, terms like "street smarts" and "common sense" are probably most often used by the less-educated to claim some mental advantage over the more-educated. Your claims are quite dubious. A tangentially related article is Staircase wit, about people who are witty but slow in coming up with the response. Supposedly this described Rousseau. Comet Tuttle (talk) 19:49, 16 February 2010 (UTC)

I don't think there is any scientific evidence for this phenomenon - and without that, we're not going to have any explanations. I suspect it's not true. SteveBaker (talk) 20:50, 16 February 2010 (UTC)

In any case, I'm not sure how you would try to measure it. Compare someone's SAT scores with the number of times they've been mugged? "Street smarts" and "common sense" are necessarily fuzzy terms.

That being said, I would hazard to guess that in the U.S., anyway, whatever we call "street smarts" (which is not the same thing as "common sense") does probably correlate with the economic conditions of one's upbringing, and so, probably, does advanced academic achievement. In my anecdotal experience, people who are very far along academically (e.g. Ph.D.s) at very prestigious East Coast institutions (e.g. Ivy League) are quite disproportionately from very wealthy personal backgrounds, and as a result have been, again from my experience, quite sheltered compared to the rest of the population (or, indeed, my own upbringing). As a result I have witnessed them be what I considered to be quite naive about the "facts of life" for the rest of the world out there, even if they are quite good in their own academic field of study. Again, totally anecdotal, not data. And I don't even know if my anecdotal examples are very representative. I also know a number of people who have achieved high academic status from remarkably low economic origins, even criminal backgrounds. None of it really tells us whether this is strong correlation, or just a stereotype. --Mr.98 (talk) 21:09, 16 February 2010 (UTC)

In more general terms, there's the question about what you mean by street smarts. Sure these people from wealthy and sheltered backgrounds may not do well in the mean streets of LA (or whatever). How will the average person from the mean streets of LA, even with their 'street smarts' do in a wealthy neighbourhood or when interacting with these wealthy people? For that matter, people from uneducated backgrounds are prone to being ripped off by banks, money lenders, dubious service providers and other such things, while academics are far from immune to this they do tend to less commonly fall for some of the common practices and pitfalls (and not just because they don't have to or they have advisors). Nil Einne (talk) 22:43, 16 February 2010 (UTC)

Additionally, if we fault the clueless academic for getting ripped off by the "I just need $5 to catch a bus" line, do we fault the uneducated for spending thousands of dollars (across their life) on lottery tickets? --Mr.98 (talk) 15:49, 17 February 2010 (UTC)

It's a naive, not an unanswerable or meaningless question. First, read our intelligence article on the different kinds of intelligence. Second, contemplate all the types that can go into "street smarts": usually a combination of being good at reading strangers' behaviors and intentions and familiarity with local customs, resources, and hazards. Third, contemplate the types of intelligence that make for "book smart": good grades usually means school study skills, comfort in a school environment, and being good at giving teachers what they want, perhaps with unusual reading background. These are somewhat overlapping skills: people-reading and knowledgeability about social demands of a specific environment. Obviously there are other dimensions to both types of success: numeracy, risk taking, perseverance, ability to learn from mistakes, use of contacts, luck, charm, attractiveness, etc. I would not be so quick to deprecate the level of intelligence needed for success in the two areas. alteripse (talk) 21:41, 16 February 2010 (UTC)

I think there's a reasonably good case for distinctions between spatial/mathematical intelligence, verbal intelligence, and social intelligence (ability to interact productively with other people), at the least. Street smarts, though, are largely a product of harsh experience rather than intelligence per se, I would guess. Looie496 (talk) 22:03, 16 February 2010 (UTC)

My take on this would be that people who are used to a professional culture are inexperienced when they find themselves in a machismo culture. For example they may expect people to be reasonably honest or altruistic. Vice versa as well, but because professionalim is 'nice' then people from the dark side are not so harmed by it. People from a professional culture are also at a disadvantage by being ethically constrained from using the manipulation or coercion that the machismos use. 89.242.101.230 (talk) 23:51, 16 February 2010 (UTC)

To the original poster: you might find the theory of multiple intelligences introduced by Howard Gardner in the 1980s of interest. It proposes different types of intelligence (usually eight), although none of them can be characterized as "street smarts". However, the "interpersonal" type is perhaps the closest to what you are talking about.--Eriastrum (talk) 00:00, 17 February 2010 (UTC)

False dichotomy. The subprime loan applicants are one example. People can be smart or stupid in academic and non-academic areas. It all depends on what you're talking about. Imagine Reason (talk) 00:03, 17 February 2010 (UTC)

Everybody has to paddle their own canoe. When one door closes another door opens. Bus stop (talk) 01:09, 17 February 2010 (UTC)

The closest article I could find on Wikipedia to "street smarts" was youth subculture. ~AH1^(TCU) 02:18, 17 February 2010 (UTC)

Ganymede

Is the large blue part ocean or is it just iron mantle, since the tan-white part is the icy crust? I don't think Ganymede's surface ocean is as big as Europa's.--209.129.85.4 (talk) 21:43, 16 February 2010 (UTC)

Neither of them have a surface ocean, they are far too cold. Europa is believed to have a liquid ocean underneath the ice and Ganymede might too, but the description of that image (which concurs with Ganymede (moon)#Internal structure) describes the blue layer as "a deep layer of warm soft ice" ("warm" is presumably a relative term). --Tango (talk) 23:15, 16 February 2010 (UTC)

Fuel Consumption Problem - (How Much Extra Fuel Would I Use by Carrying More Fuel to Begin With?)

Let's say I have a car that weighs w kilograms and it is driving in a straight line at a constant speed along a perfectly flat road of zero gradient and zero camber. Let's assume we want to travel a total distance of d kilometres, and we start with s litres of fuel. Now, let's assume that we used u litres of fuel to make that journey. Next time we start with m litres more fuel than last time and make the same journey, in the same conditions, along the same road.

1. How much extra fuel, say e litres, would I have used by starting off carrying more fuel?
2. How far less, say l kilometres will the same u litres of fuel carry me given that I am starting off carrying more fuel?

To make things simple, assume that fuel consumption only depends on the weight of the car. Don't worry about the temperature of the fuel or of the tyres, etc. Add some assumptions if you like, and take some away if you like. I just want to know how much extra fuel I would use by carrying more fuel to begin with. I have a maths degree, and a strong theoretical grasp of differential equations, so don't worry about being too complicated. Thanks is advance. •• Fly by Night (talk) 22:13, 16 February 2010 (UTC)

P.S. I tried the maths reference desk and I got a single, unhelpful, reply. •• Fly by Night (talk) 22:14, 16 February 2010 (UTC)

The real question here is: How much does weight affect fuel efficiency for a typical car? Once you have that, the rest is algebra. This website says: "An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones." I'm not sure how reliable that is, but it will do for now. Petrol#Density says petrol ways about 6 lb per gallon. That means your MPG is going to reduce by about 0.12% per extra gallon of fuel. I suspect that is well within the margin of error of fuel efficiencies anyway, due to different driving styles, journey types, etc. --Tango (talk) 23:07, 16 February 2010 (UTC)

Thank you. I thought that some differential equations might have been needed, but the amount of wasted fuel is so small that I would probably waste more brain power solving the equations than I would on the extra petrol. Thanks again. •• Fly by Night (talk) 23:32, 16 February 2010 (UTC)

That single parameter will vary by type of vehicle. A truck which is already towing 25 tons will be largely unaffected by an extra 250 pounds of fuel. Meanwhile, a Prius (whose fuel efficiency is significantly improved by its extremely light weight may notice as much as a 10% fuel efficiency decrease when you add 250 pounds of fuel. Of course, a truck's fuel efficiency is already low - ~ 6.5 mpg, compared to a 45 mpg Prius. Nimur (talk) 23:12, 16 February 2010 (UTC)

What Prius has a 40 gallon fuel tank??? Googlemeister (talk) 13:53, 17 February 2010 (UTC)

The Prius HM - Hypothetical Model. The entire backseat was converted to a fuel tank. The connector hose goes out the window and connects to the main tank. Unfortunately, we forgot to account for the extra mass and aerodynamic effects of the tank, hose, and secondary fuel pump. Nimur (talk) 15:14, 17 February 2010 (UTC)

I have to wonder: does weight really change the fuel consumption rate in a car going at a constant speed on a flat road? The only forces that need to be overcome by burning fuel are drag and mechanical friction, neither of which are affected by weight. Weight only increases fuel consumption in start-stop traffic where a larger force must be exerted to the larger mass in order achieve the same acceleration. That is irrelevant here as the car is going at a constant speed. Planes, on the other hand, are much more sensitive to weight as additional weight requires a higher angle of attack to generate the required lift, increasing the drag it faces. --antilived^{T | C | G} 02:00, 17 February 2010 (UTC)

Wait... I'm pretty sure weight affects friction via the normal force. Weight is not an issue with a frictionless surface. John Riemann Soong (talk) 03:07, 17 February 2010 (UTC)

For a car it is the rolling resistance that is of interest more than any sliding friction. 58.147.58.28 (talk) 05:53, 17 February 2010 (UTC)

The problem is that it depends on how you drive. At a high constant speed on a level freeway, almost all of the energy goes into overcoming air resistance - the amount of power required to overcome air resistance goes up as the cube of the speed. Hence the weight hardly matters at all at freeway speeds. The amount of energy needed to go uphill or to accelerate depends largely on the weight and relatively little on everything else. At slow, constant speeds, the energy mostly goes into overcoming friction - some fraction of which depends on the weight of the payload and some fraction does not. This factor depends on the design and relative weight of the car itself. Consequently, we're not going to be able to come up with a definite formula. But at constant speed - the general answer is that the amount of weight in the car matters much less at high speed than it does at low speed because at high speed the energy consumption is dominated by drag and at low speed by friction. Because of the "cube of the speed" thing, you can get dramatically different fuel consumption driving into the wind versus with a tail wind because drag is determined largely by the speed relative to the air - not relative to the road. SteveBaker (talk) 02:33, 17 February 2010 (UTC)

Nice answer, thanks. But doesn't momentum need to be taken into account when considering wind resistance? If I throw a table tennis ball into the wind then it won't travel very far. It has very little momentum and the wind overcomes it very quickly. If I fill the same table tennis ball with lead and then throw it with exactly the same initial conditions it will travel much, much further. I will use more energy getting the heavier ball up to speed and so it will travel further. The same is true for a light car and a heavier car. Let's say the two cars are exactly the same but one has a bigger engine (i.e. more weight and more power). We get the cars up to the same speed on the same road in the same conditions and then cut the power and let them glide. The lighter car will use less fuel to get to the starting speed but will also stop sooner. The heavier car will use more fuel to get up to speed but will travel further. Plus, a lot of this momentum is built up at low speeds when friction really does matter. •• Fly by Night (talk) 18:37, 17 February 2010 (UTC)

P.S. The cube of the speed law needs some constants to make sense. A cube will grow faster than a square, that is true. But just because it grows faster it doesn't mean that it is larger. Consider x^3/1000 and x^2. We need x > 1000 for x^3/1000 > x^2. •• Fly by Night (talk) 18:47, 17 February 2010 (UTC)

Even for the specified conditions straight, perfectly level road and constant speed, rarely to be found on this planet, more weight means more friction in bearings and more work done on the tires. Granted, at highway speeds wind resistance is the main factor limiting fuel mileage, and adding more weight of fuel need not increase wind resistance. A higher load should mean more tire heating and less mileage. On practical roads, there generally is some hill climbing, and accelerating and decelerating due to traffic conditions, so the extra weight would decrease mileage (except on a hybrid with ideal regenerative breaking). Real cars must accelerate up to speed, and inability to merge onto an expressway due to undersized engine for the weight is dangerous. A lighter car allows a smaller and more efficient engine and transmission. Some information on weight versus fuel economy in real cars driven on real roads: [31], [32].Edison (talk) 21:35, 17 February 2010 (UTC)

Mars Colony

How much would it cost, in 2010 dollars with 2010 technology, to establish a self-sustainable colony of 50 men and 50 women on Mars? TheFutureAwaits (talk) 22:27, 16 February 2010 (UTC)

Well, it can't be done with 2010 technology. We don't currently have a spacecraft capable of taking people to Mars. Most of the cost is in developing the technology we need. How much that costs depends largely on how quickly you want to do it and what degree of safety you want. --Tango (talk) 22:55, 16 February 2010 (UTC)

Conceivably, you could try to run up a sum of all the necessary costs to build and launch the space mission; estimate going-rates for all the needed technology, etc; and generate a cost-estimate that way. I think that would probably be an alright way to do a cost-estimate, but it's very sensitive to the details of your mission plan. This is the way I would approach the cost-estimation problem - without presupposing any particular mission scheme or technology design. It would be a reasonable, albeit loose, claim, to state that such an endeavor would require the entire force of the current space administration in order to drive the enormous project and sub-projects needed to make that voyage possible. If political bickering was not an issue and you could throw today's entire space program budget at that particular task, it might still take five or ten years to ramp up the technology. So, noting that NASA's annual budget is ~ 17 billion US dollars, and the project may take 5 to 10 years, I would estimate that it might cost on the order of 100 to 200 billion dollars. Since "$100 billion" is a hard-to-conceptualize quantity of money, here's some other ways to think of it. It'd order about 10 billion cheese pizza deliveries, if you could find enough cheese pizza shops to deliver them. Or, it would be about as expensive as 500 deep-water oil rigs, or about as expensive as one year of sustaining a large overseas military campaign, or about as expensive as five to ten years worth of nuclear deterrence. These numbers aren't meant to be particularly accurate - but they highlight another mode of thinking about the budgets for such enormous projects. When NASA embarked on the Apollo Program, it was not like they could hold a bake-sale and raise some money, and then waltz down to the nearest retail store and pick up a Moon Spaceship once they had the right change. These kinds of enormous projects are better viewed in the context of nation-scale economic prioritization - not total dollar cost. Take a look, for example, at the Space Shuttle program budget. You can boil down the price to a succinct number (as NASA has done here) - but that number's pretty meaningless without context. (Phrased differently - could a billionaire with disposable income purchase a Space Shuttle for $1.7 billion dollars? If not, then is that really how much they cost? Nimur (talk) 23:22, 16 February 2010 (UTC)

5-10 years sounds like a big underestimate to me. 10 years might be enough for a small scale manned mission to Mars, but not to establish a large colony. I think 20-30 years is more realistic, even if the whole of NASA is devoted to it. --Tango (talk) 01:28, 17 February 2010 (UTC)

Well, when President Kennedy announced the plan to go to the moon in 1961, we had logged a total of 15 minutes of manned spaceflight - and had never even reached orbit. Yet, by devoting the entire national scientific establishment and a very significant chunk of our industrial base towards this simply-defined goal, we managed to make it happen. Mars missions bring a host of new technical challenges, but we have also advanced the state of the art very significantly since 1961. I think that we could do it in 5 to 10 years if we had the unfaltering, united will of the entire nation. Nimur (talk) 03:19, 17 February 2010 (UTC)

I suppose if we were willing for the first manned mission to Mars to have 100 people on board then it could be done, but I expect people would want to do at least one test flight with a handful of people first. That adds several years. (Remember, just getting to Mars takes nearly a year.) --Tango (talk) 14:09, 17 February 2010 (UTC)

Whatever estimate you come up with, you need to at least double it. It's always the way. 86.138.42.82 (talk) 01:03, 17 February 2010 (UTC)

How about this for a starting point: 100 people and their personal luggage have a mass of around 10 tonnes. All their food for a 4 year trip (18 months journey + something to get them started in their first martian year), all their water, and all their air would come to considerably more. Altogether a total payload of 100 tonnes or more. With launch costs of around $20,000 per kg that makes $2 billion just to get the payload into low earth orbit. You then have to develop the materials and tools to construct a martian habitat; and you have to develop, construct and fuel a spacecraft to get it all to Mars. And you have to get that lot into orbit as well. I wouldn't expect any change from Nimur's 100 - 200 billion dollars budget. Astronaut (talk) 01:50, 17 February 2010 (UTC)

The Constellation Program had a budget of $230B through 2025 and that was supposed to get us to a small manned lunar outpost. I would suspect the Mars mission proposed above would be closer to a trillion dollars. Dragons flight (talk) 02:03, 17 February 2010 (UTC)

Also, "self-sustaining" raises a lot of questions. It would be easier to make a "permanent" colony that requires regular rocket refills (which wouldn't need to be manned) than a truly "self-sustaining" one. --Mr.98 (talk) 02:31, 17 February 2010 (UTC)

Agree with above. People have tried making an isolated self sustaining habitat on earth, Biosphere 2 and it did not work out all that great. It only involved 8 people and a habitat area of 3.2 acres. Googlemeister (talk) 13:52, 17 February 2010 (UTC)

They tried to make an entirely biological system. That is useful for research purposes, but isn't required for an actual colony. For example, they had massive fluctuations in CO2 during each day due to photosynthesis dominating during the day and respiration at night. That is very difficult to solve with biology, but should be pretty easy with chemistry. There are plenty of ways of absorbing CO2 during the night and then releasing it during the day. --Tango (talk) 23:16, 17 February 2010 (UTC)

You could estimate it by guessing how many more times more expensive than landing people on the moon it would be. I'd say ten times more expensive. So the cost would be ten times more expensive than the Apollo cost in real terms. 89.240.100.129 (talk) 15:03, 17 February 2010 (UTC)

What kind of "Self sustaining" are we talking about? Is it acceptable to ship food from Earth? What about shipping supplies from Earth? What about shipping supplies from Earth, but they pay for them somehow by exporting martian goods? Or are you talking about a truly self sustaining colony where they can never get any help from Earth ever again?

That last might be very difficult. To do that, everything the martian colony depends on must be able to be manufactured locally. When a microchip fails, how will they replace it? When they start needing new spacesuits, how will they make them? If Mars had breathable air they could live a simple frontier life, but sadly, it doesn't. APL (talk) 15:57, 17 February 2010 (UTC)

(EC) I have to agree this "self-sustaining" bit is likely to be very difficult to achieve in the near term and probably even in the medium term. Most of the cost and time estimates above appear to be largely ignoring it yet it is surely one of the most difficult and costly things to achieve. Having food for 4 years sounds great, but is it really realistic to become self-sustaining in 4 years? Highly doubtful. We're still not even sure how to get water. Nil Einne (talk) 16:03, 17 February 2010 (UTC)

There's water ice underground in many places on Mars, that isn't a problem. --Tango (talk) 22:45, 17 February 2010 (UTC)

The details are not the same (far fewer than 100 people, not permanent, not self sustaining, and not necessarily relying on only 2010 technology) but estimates have varied widely. The first Bush administration called for a study and they came up with $400-$541 billion in 1989 dollars. Robert Zubrin and his Mars Direct plan say a mission is feasible for $55 billion (I think in 1990 dollars, possibly 1996 dollars when The Case for Mars was published). I think the real cost for a basic mission to mars would likely be somewhere in between - the 1989 estimate was way overboard and not a cost effective or sensible way to do things, Zubrin's estimate is optimistic and involves doing things on a shoe string budget that probably isn't practical (or is unacceptably risky). Based on even Zubrin's optimistic estimate, I don't think $100 to $200 billion is a realistic number for such a large colony (Zubrin's plan was for teams of 4). If I had to guess I'd say a 100 person colony would cost over a trillion dollars, possibly several trillion. TastyCakes (talk) 23:39, 17 February 2010 (UTC)

February 17

Cabbage, salt and water... blue?

Hi all,

I'm making pickled cabbage. I shredded a bunch of red and savoy cabbage, sprinkled a few tablespoons of salt on it, and left it for 24 hours. Then I removed the cabbage. At the bottom of the bowl, there was a puddle of red liquid. I then brought the bowl to the sink and started pouring some water in it. To my surprise, the water turned bright blue!

Can anyone explain the chemical reaction that must have occurred?

Thanks! — Sam 76.24.222.22 (talk) 01:40, 17 February 2010 (UTC)

Red cabbage is a traditional pH indicator. [33] Dragons flight (talk) 01:43, 17 February 2010 (UTC)

The salt might have extracted the acidic component without extracting a basic component, maybe? John Riemann Soong (talk) 01:51, 17 February 2010 (UTC)

Very interesting. Any thoughts as to why it only appeared when I added water? (I was able to replicate this later.) I doubt my water is that basic! — Sam 76.24.222.22 (talk) 03:55, 17 February 2010 (UTC)

According to the "How to Make Red Cabbage pH Indicator" link on the Red Cabbage page, at pH 6 the solution is violet, and is blue at pH 8. I imagine at pH 7 it would be classified as "blue". Most tap water is around pH 7 (indeed, if it falls much outside that range, your water company will adjust the pH to avoid damage to the pipes and to keep the sanitizing power of the added chlorine). Now, why does the water *change* the pH? Most tap water isn't just H₂O, it also contains a number of buffering agents, especially if it comes from something like a limestone aquifer. The buffering capacity of the water probably overwhelmed the small amount of acid in the cabbage drippings, bringing the pH back to ~7 and turning the color blue. It's not that the tap water was very basic, it's just that it was less acidic than the juice. -- 174.21.247.23 (talk) 04:10, 17 February 2010 (UTC)

Orientation of the International Space Station

I've been watching live video of the STS-130 mission to the ISS online on NASA TV. At times (when they are not receiving video from the ISS) they display a graphic showing the ISS, from three views, as it orbits. From the relative motion of the Earth displayed below and what I assume are velocity and acceleration vectors displayed on the side view, it appears as if they are representing ISS orbiting with the Russian section leading and the shuttle, docked to PMA-2 (attached to Note 2, Harmony), trailing. This is the opposite orientation as described at International Space Station#Attitude (orientation) control. Exterior ISS video I saw yesterday of the PMA-3 attachment to Note 3 seemed to agree with the WP description. So, is the NASA graphic backwards, or do they occasionally reverse the orientation of the ISS, perhaps to help protect EVA crew from MMOD? 58.147.58.28 (talk) 01:53, 17 February 2010 (UTC)

It is hit and miss whether the orbital orientation graphic is displayed on NASA TV at any one time. I will try to find it in another source, but I don't know how easy that will be as it is not the sort of thing that typically makes it into the daily highlights videos. 58.147.58.28 (talk) 02:03, 17 February 2010 (UTC)

I haven't found another source for the graphic, but exterior ISS video of the EVA in progress showing Note 3, PMA-3, and cupola with the Earth seen moving below seems match the reversed orientation of the graphic. 58.147.58.28 (talk) 03:41, 17 February 2010 (UTC)

While the Shuttle is docked to ISS, the ISS attitude is yawed 180 degrees from normal such that the Russian Segment is in front and the Shuttle trailing, exactly as you describe. This is done to protect the Shuttle Thermal Protection System from micrometeroids and orbital debris. anonymous6494 08:49, 17 February 2010 (UTC)

Thanks. With the answer in hand I was able to search and find this reference which deals specifically with STS-130. I'd like to find one that mentions the practice in general, but I suppose that this one would be sufficient to expand International Space Station#Attitude (orientation) control. 58.147.58.28 (talk) 01:08, 18 February 2010 (UTC)

Linear density

I computed the linear dord of quartz for a question earlier using wolfram alpha as ${\sqrt[{3}]{density}}$. The units for the result are ${{\sqrt[{3}]{g}} \over cm}$. I understand why it gave that result, but it doesn't make sense. Shouldn't it simply be $g \over cm$? What did I do wrong? Ariel. (talk) 02:45, 17 February 2010 (UTC)

The cube root of density is the cube root of (g/cm) not the (cube root of grams)/cm. Plus "dord" isn't a real word - as you'd know if you'd followed the link you kindly left us! SteveBaker (talk) 03:02, 17 February 2010 (UTC)

I know dord isn't a real word. It was a joke. You and Jayron below you said exactly the opposite things about the units. Ariel. (talk) 03:14, 17 February 2010 (UTC)

(edit conflict)Density is grams per cubic centimeter, or g/cm³. Taking the cube root of that returns g^1/3/cm or as you note above, the cube root of grams over centimeters. --Jayron32 03:05, 17 February 2010 (UTC)

If you take the cube root of g/cm³ you get g^1/3/cm, and yet linear density is g/cm - so what gives? Ariel. (talk) 03:14, 17 February 2010 (UTC)

That's because linear density is defined as mass per length, NOT as the cube root of density. So, you are starting from the wrong premise. Linear density is NOT the cube root of density; its just grams per centimeter. Wouldn't it be nice if there were some sort of free information resource on the web where you could look this stuff up? --Jayron32 03:25, 17 February 2010 (UTC)

OK, so in that case, if I calculate: I have matter with a linear density of 2 g/cm, by 4 g/cm by 1 g/cm the density is then 8 g³/cm³. So then why is density defined as g/cm³? And I did look stuff up, I read Dimensional analysis and Quantity calculus, and density and Linear density, and none of them explained why the units don't work. Ariel. (talk) 03:41, 17 February 2010 (UTC)

Linear density is not defined for material in general, but for a structure in particular. To determine the linear density of your quartz bar you need to know its cross sectional area. The linear density is then the density divided multiplied by the area, not the cube root of the density.58.147.58.28 (talk) 03:48, 17 February 2010 (UTC)

(edit conflict) Linear density is sort of a specialized unit; you can't cube it and get actual density. To get denisty from linear density, you don't multiply the linear density in three dimensions, you divide linear density (g/cm) by the cross-sectional area (cm²) and then you'll get the density. The reason for this is that the linear density of a substance is a measure of all of its mass divided by its length in one dimension. If you want volume density, you need to include the other two dimensions in terms of length, but you don't need to count the mass again, since that number is already included in the linear density. So linear density divided by cross-sectional area will give you volume density (i.e standard density). --Jayron32 03:54, 17 February 2010 (UTC)

If your quartz bar had a cross section of 1 cm x 1 cm, its linear density would be 2.634 g/cm. If it had a cross section of 2 cm x 2 cm, its linear density would be 10.536 g/cm. — Sam 76.24.222.22 (talk) 04:00, 17 February 2010 (UTC)

Thank you all. I understand it now. For some reason I thought linear density is a measure of "number of units of mass" per length, i.e. that it's the same for all shapes of objects, just like density is the same for all shapes. Clearly my math in this question was wrong, and I will redo it. Ariel. (talk) 04:10, 17 February 2010 (UTC)

Yeah. Density is a intensive property because it is a property of the material itself irrespective of the amount of material. Linear density is NOT an intensive property, except in limited applications. Linear density is intensive with respect to length ONLY, and only if cross-sectional area is kept constant. If you alter the crosssectional area, you change the linear density of the material. It generally has to do with the applications of linear density. You only usually use it in situations where you are dealing with a material which you work with in relatively uniform, long amounts of it, like say yarn or railroad rails or 2x4's. You would, for example, be interested in the linear density of a particular type of cotton thread, but two different types of cotton thread would have different linear densities, even if the cotton fiber they were both composed of has the same volume density. --Jayron32 04:31, 17 February 2010 (UTC)

Medical devices, WWII-era occupied Poland

The device in this archival photo was used in the Lodz ghetto, ca. 1940–1944. My questions: what is it, and was it used for diagnosis or for treatment? -- Deborahjay (talk) 09:08, 17 February 2010 (UTC)

And this one as well: same questions as above. -- Deborahjay (talk) 10:24, 17 February 2010 (UTC)

Guesses: First may be a medical diathermy machine. Second may be radiation therapy, or maybe just diagnostic x ray. The second setting is clearly institutional like a hosp x ray dept. The first setting may be a home doctors office. alteripse (talk) 11:12, 17 February 2010 (UTC)

I'm on a barge travelling across Neptune, towed by a cable connected to the moon Psamathe...

... how fast would I be moving, if my moon-towed barge was skimming the uppermost clouds?

Thanks Adambrowne666 (talk) 11:15, 17 February 2010 (UTC)

Since the moon takes 9074.30 days to orbit neptune, your barge circles neptune once every 9074.30 days. Neptune has a circumference of 155600 km. So you are going 155600 km per 9074.30 days = 0.443952 miles per hour. Try this as well (click on the text of the result, then the orange link under it to get it in other units). Ariel. (talk) 11:38, 17 February 2010 (UTC)

wow - so that's what you plugged into wolfram alpha, and it understood what you wanted? Cool. Adambrowne666 (talk) 20:32, 17 February 2010 (UTC)

155600km / 9074.30days = 0.4440 miles per hour. Don't forget your significant digits. Dauto (talk) 14:25, 17 February 2010 (UTC)

As a comparison, a sloth will be cruising by you at 3x your speed. Googlemeister (talk) 17:24, 17 February 2010 (UTC)

Thanks, everyone. Of course, the Neptunian sloth is a little faster, so would be cruising by at almost 4X my speed. Adambrowne666 (talk) 20:32, 17 February 2010 (UTC)

I think it would be more natural to measure speed relative to the clouds, not relative to stationary space. Neptune rotates once every 16 hours. Your boat anchored to the moon is nearly stationary in the external frame, so if you are at the equator the clouds would be whizzing by you at ~9500 km / hr. Not exactly a leisurely pace. Dragons flight (talk) 20:52, 17 February 2010 (UTC)

A extremely good point! Here it is in wolframalpha. Since Psamathe has a retrograde orbit the speeds add. Ariel. (talk) 22:42, 17 February 2010 (UTC)

Yes, of course! thanks both of you, didn't think of that either. Adambrowne666 (talk) 23:08, 17 February 2010 (UTC)

Time Capsule

If I took my iPhone and buried it in a sealed vacuum capsule, how long would it remain useable (assuming the discovers could put in a new battery/power source). Which components would fail first? Would the OS start up? TheFutureAwaits (talk) 11:49, 17 February 2010 (UTC)

Indefinitely, I expect. You need to bury it deep enough that it won't suffer significant temperature changes, and you need to make sure the seal will last, but if you do that I can't think of anything that would damage it. --Tango (talk) 14:19, 17 February 2010 (UTC)

Does an iPhone contain any electrolytic capacitors? They eventually leak. Cuddlyable3 (talk) 14:34, 17 February 2010 (UTC)

Some types of battery can leak after a few years, however. 195.35.160.133 (talk) 14:56, 17 February 2010 (UTC) Martin.

You'd probably want to remove the batteries before you tried this. APL (talk) 15:38, 17 February 2010 (UTC)

How many years before the wireless technology has completely evolved and dropped backward-compatibility? I would estimate at least 25-30 years, but it's hard to say. Some analog mobile telephone technologies from the late 1980s are still supported by the transmitter towers and network providers; stepping even farther back, many land-line phone providers still provide support for rotary telephones or pulse dialing (probably using emulation with a software system). It seems plausible that 802.11 or "3G" GSM / WCDMA telephones might still be supported decades from now, even if they are no longer mainstream. Nimur (talk) 15:03, 17 February 2010 (UTC)

i would agree that any electrolytic capacitors are likely to become more leaky with time. Other components should not show significant ageing effects. However, some semiconductors may be compromised by the effects of nuclear radiation (gamma rays and cosmic rays). —Preceding unsigned comment added by 79.76.229.198 (talk) 15:36, 17 February 2010 (UTC)

After a while, tin whiskers may (or may not) start to form, these could cause shorts. The causes of tTin whiskers are not fully understood, so I'm not sure that a good estimate can be given.

This could theoretically be repaired by the benevolent future-people who also replaced the batteries, but it wouldn't be easy. APL (talk) 15:38, 17 February 2010 (UTC)

Dopants within semiconductors could migrate, rendering the chips nonfunctional, over a very extended time. You specified vacuum, which would prevent the oxidation of copper or brass I have seen in hundred year old telephones and telegraph instruments. But I have heard that vacuum can promote switch contacts welding together (that might apply more to those carrying high current, not so much a problem in a phone). It can also cause evaporation of films of lubricant which help switches and contacts operate. Vacuum would accelerate leakage of electrolytic capacitors. I would not expect typical rechargeable batteries to survive long storage under the conditions specified. Temperature variation could cause by the breaking of conductive paths and connections. Communications protocols will likely move on so that the signals used in the distant future would be incompatible with those used by a wireless phone of today. General Motors sold very expensive OnStar systems for car communication from 1996-2002 model years which became unusable after 2007 (this coming obsolescence was not mentioned at the times the expensive systems were being sold). The 1996-2002 system was analog, and was abandoned in favor of digital, with no retrofit of a new transceiver offered to keep the service going. From that example it is hard to see why operators of wireless systems would go to great lengths to make decades-old communications systems still operable. Planned obsolescence dictates that old software packages or hardware systems be "no longer supported" a few years later so the consumer has to shell out for a new one. Edison (talk) 17:21, 17 February 2010 (UTC)

Even with the cel-phone network gone or incompatible, the iPhone would still be a decent PDA. APL (talk) 18:41, 17 February 2010 (UTC)

One more angle, how long before Itunes is no longer backward compatible with version x (whatever version you bury it with), making it useless unless you posses the proper version of Itunes to perform intermediate updates? It won't be any fun to have to suffer along with the collection of music from right now... --144.191.148.3 (talk) 21:47, 17 February 2010 (UTC)

Average world temperature

What is the average world temperature? I want to compare one country with an average of 21–33 °C with world average, but can’t find any reliable sources of world average. Caspian Rehbinder (talk) 13:59, 17 February 2010 (UTC)

The first picture of the global warming article might have the answer you are looking for. Dauto (talk) 14:33, 17 February 2010 (UTC)

Actually, the article I linked uses temperature anomaly instead of actual temperature. The article Temperature record since 1880 quotes: "1901-2000 global mean of 13.9°C". Dauto (talk) 14:45, 17 February 2010 (UTC)

Ion list

Where can I find a complete list of cations and anions?--Mikespedia (talk) 14:13, 17 February 2010 (UTC)

The short answer is, "You can't". An anion is any moderately stable negatively-charged atom or covalently-linked collection of atoms, and there is an infinite number of such. Among the anions, there are a finite number of monatomic ones (like chloride, Cl^-), but when you start allowing multiple atoms you get things like hypochlorite (ClO^-), acetate (CH₃COO^-), and dodecyl sulfate (C₁₂H₂₅SO₄^-). It gets complicated fast. Our article on ions lists a very few monatomic and small polyatomic ions, but you can't create an exhaustive list. TenOfAllTrades(talk) 14:50, 17 February 2010 (UTC)

In other words, because there are an infinite number of stable ways to combine atoms, there are thus an infinite number of ionized forms. A comprehensive list might contain all the relevant ions for a particular domain, but it will never really be complete. Nimur (talk) 14:58, 17 February 2010 (UTC)

Since this is relatively answered, I'll steer it away with some nit-picking. Is there really an "infinite" number of stable ways to combine atoms? there clearly aren't an infinite amount of different components to molecules (elements and their isotopes), and I'm skeptical that their is an infinite amount of ways you can arrange atoms into molecules to get "stable" arrangements. I will add to this the note that I don't know nearly as much about chemistry as I would like, but the use of the phrase "infinite arrangements" for a concrete thing such as an Ions made question mark appear. Please elaborate if you don't mind, thanks! Chris M. (talk) 17:26, 17 February 2010 (UTC)

Actually, there probably are an infinite number of ways, owing to substances such as polymers and network solids. For example, a diamond is essentially a single giant molecule of carbon atoms, and something like polyethylene contains molecules containing millions of atoms each. With carbon-based molecules alone, there is no finite limit to the size of the molecule, so there is no functional upper bound to the ways they can be combined. --Jayron32 18:38, 17 February 2010 (UTC)

Ah, I had a feeling my lack of knowledge of chemistry would show when asking that question. Thanks! Chris M. (talk) 21:14, 17 February 2010 (UTC)

Eating coffee beans

Say that I have a bag of coffee beans and wish to obtain the effects of caffeination, but I lack the means to grind and brew the beans to produce coffee. How much caffeination will I experience by simply eating the beans versus drinking brewed coffee? Do the digestive fluids "brew" the grounds in the stomach, or will they pass through the digestive system without yielding up their caffeine? 129.174.184.114 (talk) 16:16, 17 February 2010 (UTC)

Are you planning on swolling them whole? Dauto (talk) 16:40, 17 February 2010 (UTC)

Brewing doesn't create caffeine and there are a number of foods that include solid coffee beans (tiramisu, chocolate-covered expresso beans). But the results of civet cat consumption of raw beans is worth a mention: (Kopi Luwak). Rmhermen (talk) 18:34, 17 February 2010 (UTC)

Yes, I am aware that brewing doesn't create caffeine. My question is whether brewing in near-boiling water is necessary to release caffeine from the beans. In other words, if I eat coffee grounds (not intact beans), will the caffeine in the grounds leech out in my stomach or will the caffeine remain "locked" in the grounds? 129.174.184.114 (talk) 23:01, 17 February 2010 (UTC)

You refer, of course, to the Asian Palm Civet and not all the other types of civet cat listed on that disambiguation page. Edison (talk) 21:25, 17 February 2010 (UTC)

Cosmological argument and the fine-tuned Universe

I have browsed some related articles and from what I understand, the biological evolution is inapplicable in explaining the formation of the Universe and its components, as well as the symbiosis of beauty and functionality of some of its components. The expanding Universe should expand in some surrounding space, that is it’s a closed system in terms of the 2nd law of thermodynamics, and yet demonstrates a quite strange decrease in entropy since its formation. So could the intricacy of the Universe, which features numerous self-sustained, sophisticated components in itself, serve as an evidence of initial intelligent design (if there is nothing from nothing)? From what I've read, the murky Planck epoch for example does not explain, how the four fundamental forces have formed. Neither does the science explain, where all micro essentials like elementary particles come from (instead that could be easily explained with FTU concept, assuming that the Big Bang stuff for example was meticulously concocted in a stock cube fashion and then launched off to run). The article on cosmological argument cites Kaku's critical example on gas molecules, but I think the bouncing molecules or any such stuff moving in a Brownian motion pattern will never form something complicated and useful, unless driven externally.

Another issue of the fined-tuned Universe that came to my mind is the Earth atmosphere. It’s one of the Universe components, which features multifunctionality (protection from asteroids and excessive solar radiation, etc.), combined with nearly unquestionable beauty. We admire it since Gagarin and most likely even an ancient or medieval man would notice its beauty on photo without even knowing what it is. That is, neither the Earth atmosphere has evolved to suit us, nor we evolved to, which means that most likely it was made to be such intentionally. Also, are stars the closed systems under thermodynamic principles? If so, the historical decrease of entropy in space would be striking. So how such long-lasting set of nesting dolls could form and evolve randomly, including the Universe itself? Brand[t] 19:20, 17 February 2010 (UTC)

I don't know what you've been reading, but there is no surrounding space around the universe, the universe is, by definition, everything. The universe is expanding, but it isn't expanding into anything. Also, the total entropy of the universe has increased since the big bang, not decreased. Beauty is an entirely human concept that we have evolved. Things aren't inherently beautiful, there has just been a reproductive advantage to us considering them beautiful. I think once you resolve these misconceptions of yours, you'll find your questions are moot. --Tango (talk) 19:42, 17 February 2010 (UTC)

See Metric expansion of space, which has sections called "Understanding the expansion of space" and "What is the universe expanding into?" (Though I don't know why that section says that if space is infinite, this would be "easy to conceptualize".) Comet Tuttle (talk) 20:19, 17 February 2010 (UTC)

I am content to allow our concept of beauty to abide in metaphysics. The OP may find the article Intelligent design helpful. It is not a mainstream view that there is convincing evidence of initial intelligent design. Cuddlyable3 (talk) 20:22, 17 February 2010 (UTC)

Re: "That is, neither the Earth atmosphere has evolved to suit us, nor we evolved to, which means that most likely it was made to be such intentionally." I'd have to say we most certainly evolved to suit the atmosphere, if we had not we would of course not have survived. The atmosphere has changed plenty in the billion+ years life has been around and the life that did not evolve to suit it died off, as you would expect. Chris M. (talk) 21:13, 17 February 2010 (UTC)

The only honest answer is that we don't know why the universe has the properties and physical laws that it has. Our knowledge today is far better than that of our ancestors (to whom nearly anything could seem magical), and presumably our descendants will have a better and more fundamental understanding of the universe than we do today. However, we may never know the answer to "Why are things just so?". It is easy to say that life as we know it could not exist if the universe was much different than we know it to be. Of course, we also can not know whether other forms of sentient life might come to exist had things been otherwise, so it is difficult to know how significant our existence truly is.

Given our current state of ignorance (and the possibility that we will never know), I'd say that it is an entirely valid - as an article of faith - to assume that God or some other intelligent creator set up the laws of physics in just such a way so as to allow life to flourish. Such beliefs are essentially unscientific in the modern era since we have no meaningful way to test them, but if they help people find comfort and meaning in their lives, then I would say that they are nonetheless useful for those people. Dragons flight (talk) 21:20, 17 February 2010 (UTC)

Actually, research by Victor J. Stenger has shown that this whole business of the universe being "fine tuned" doesn't entirely hold water. His work isn't published yet (AFAIK) but from what I gather he's found that provided that you assume only the conservation laws (which seem pretty reasonable 'immutable' properties of all universes), then you can't vary single fundamental properties - you have to move them in groups. When you do THAT, you wind up with a very large percentage of possible universes having the necessary properties to allow life to form. If that work turns out to be true - then rolling the dice and coming up with a universe with different constants which obeys these conservation laws would almost always result in a "reasonable" universe. He has written some details here. SteveBaker (talk) 22:18, 17 February 2010 (UTC)

Selectivity effect. Countless universes with each its set of laws, and us humans happen to be in one of them wondering how come it sound this fine tuned. -RobertMel (talk) 23:40, 17 February 2010 (UTC)

That is one solution that has been proposed. There is not, and probably never will be, any evidence for the existence of other universes, though. --Tango (talk) 00:06, 18 February 2010 (UTC)

The idea of a Fine-tuned Universe is an interesting one to consider, but the degree of "fine tuning" (if any actually exists) is often grossly overstated, or at the very least stated in a way the leads to gross misunderstanding. I've heard some proponents of the fine tuning argument state that if you used a scale that stretched across the entire universe to representing the possible range of values for the strength of the force of gravity, then life would not be possible if the actual value varied by as much as one inch from what it is. People may take from this that the gravitational constant must not vary by one part in more than 10²⁸ (1 inch / 93 billion light-years) when in fact the actual value of G (6.67428(67) x 10^-11 m³kg^-1s^-2) is not even know to a precision greater than one part in 10⁴, and could presumable vary by considerably more than that without life extinguishing consequences. The trick is choosing the "range of possible values" (possible according to who and why?) as mind boggling huge as desired. I do wish that our Fine-tuned Universe article went more deeply into the numbers that are used and the justification offered for their use. 58.147.58.28 (talk) 02:04, 18 February 2010 (UTC)

Capacitor

When a capacitor charges, both the negative and positive plates will always have the same charge (ie current in = current out). Why is that? —Preceding unsigned comment added by 173.179.59.66 (talk) 19:29, 17 February 2010 (UTC)

Current passes through the capacitor which builds up a charge of stored potential energy in the form of a voltage difference between the plates. See the article Capacitor. Cuddlyable3 (talk) 20:13, 17 February 2010 (UTC)

Yeah, I understand that...but why are the two charges equal, and not different? —Preceding unsigned comment added by 173.179.59.66 (talk) 21:13, 17 February 2010 (UTC)

Isn't the charge stored in the dielectric separating the plates? One dielectric, one value for charge. Add or take away electrons from either plate, and the one value of charge in the dielectric changes. In a Leyden Jar, the two conductors (inner and outer can be removed and grounded, then the capacitor reassembled, and found to be charged, because the charge was stored in the dielectric. Edison (talk) 21:22, 17 February 2010 (UTC)

No, the charge is in the plates, the dielectric must be nonconductive. The two sides normally hold equal amounts of charge because they are connected to metallic wires which supply large quantities of movable electrons -- if one side had an excess of charge, it would attract charges from the wire on the other side until the charges were balanced. If you disconnected both sides of the capacitor, it would become possible to have unequal charges on the two sides. Looie496 (talk) 23:10, 17 February 2010 (UTC)

Of course the dielectric is nonconductive. But note that a disassembles capacitor, with the metal plates thoroughly grounded, when reassembled is found to be charged once again, supposedly because of the charge stored in the dielectric. If it were stored only in the plates, then shorting them together and to ground after disassembling a Leyden Jar ( a common lab demo in college physics) would prevent the reassembled capacitor from being charged ( without connecting it again to some source of electricity). Edison (talk) 00:39, 18 February 2010 (UTC)

Thanks for the simple answer! —Preceding unsigned comment added by 76.68.246.12 (talk) 23:42, 17 February 2010 (UTC)

My thoughts are: charge (electrons etc) is moved from one plate to the other when charging. So one plate ends up with a charge +Q that has been supplied by and moved from the other plate that now has acharge of -Q. Charge exists on the plates (or the surface of the dielectric). By contrast, the energy is stored in the dielectric. In the above case, when the plates are removed, (most of) the stored charge will then reside on the surface of the dielectric. This charge will spreed out onto the plates when they are reattached. What happens when one side of the capacitor is connected to the earth (a source of infinite charge)? —Preceding unsigned comment added by 79.76.229.198 (talk) 01:57, 18 February 2010 (UTC)

Geological history of CT or North Eastern US coastline

I don't know where to go to find the geological history of CT, US (or NE US coast). Mostly interested in knowing if and when a huge galacier passed through this area. --Reticuli88 (talk) 19:53, 17 February 2010 (UTC)

• Wisconsin glaciation. Rmhermen (talk) 21:34, 17 February 2010 (UTC)

See also Laurentide ice sheet. Deor (talk) 23:45, 17 February 2010 (UTC)

And here is a brief account that focuses on Connecticut in particular. Deor (talk) 00:28, 18 February 2010 (UTC)

Semen and skin

okay, this question could be slightly improprious, so stop reading if you want.

I heard that human semen is excellent for the compexion of the face; is this true? Would rubbing semen in one's face actually be good for the skin? If so, then why? 82.113.106.198 (talk) 19:53, 17 February 2010 (UTC)

We can refer you to the article Semen. I know of no reliable source for what you have heard. I have changed the question title for easier reference noting that WP:NOTCENSORED. Cuddlyable3 (talk) 20:09, 17 February 2010 (UTC)

It would be a very amusing study to read if a study was carried out to study this hypothesis (or maybe it already has been done?). Acquiring funding and volunteers though might be a challenge. --antilived^{T | C | G} 23:58, 17 February 2010 (UTC)

I find it tends to make my skin rather tight and shiny when dry. —Preceding unsigned comment added by 79.76.229.198 (talk) 01:59, 18 February 2010 (UTC)

There are some data on Facial_(sex_act)#Cosmetic_usage regarding this matter.--121.54.2.188 (talk) 02:00, 18 February 2010 (UTC)

Tangentially related is Semen#Psychological aspects. Which is worse, acne or depression? 58.147.58.28 (talk) 02:16, 18 February 2010 (UTC)

Variables in procession

can anyone explain what the various constants in this article stand for, notably R and q are given without explanation Lense–Thirring precession

Cheers —Preceding unsigned comment added by 129.67.116.172 (talk) 20:47, 17 February 2010 (UTC)

Outgassing on Earth and Mars

Earth is beleive to have runaway greenhouse effect when it is on the way as the sun warms up. Because Earth and Mars is bigger I thought the outgassing would be slower than the outer planet's moons. I still don't what what it means when Earth becomes Venus like planet. Will it's atmopshere become thicker. During this time it is possible that as Mars's surface temperature gradually rises, carbon dioxide and water currently frozen under the surface soil will be liberated into the atmosphere, creating a greenhouse effect which will heat up the planet until it achieves conditions parallel to those on Earth today, providing a potential future abode for life. From Mars citation from Formation and evolution of the solar system said Mars may become like earth again and Mars is only little bigger than Titan when sun just heats up Mars atmosphere can become thicker but I wonder if it can have any oxygen and can have a watery surface. This shows Mars atmosphere won't just leak away. This source is cite from google books and it is not speculation.--209.129.85.4 (talk) 20:50, 17 February 2010 (UTC)

Atmosphere to boil away on Earth

On earth ocean boil at 100 C (212 F) but what temperature will our atmosphere black out into space and become like Moon is it over 600 F?--209.129.85.4 (talk) 20:52, 17 February 2010 (UTC)

I don't know what the actually temperature would have to be, but given that Venus has >90 times as much atmosphere as we do and a surface temperature over 850 F (450 C), I think we can confidentially assume that the temperature to boil away the whole atmosphere is over 600 F. Dragons flight (talk) 20:58, 17 February 2010 (UTC)

The ocean certainly would not boil at 100C. It is salt water which means it has a lower boiling point then regular water, various sources in quick google searches point to a change of around 20 degrees in boiling point, but it various depending on the salinity of the particular part of the ocean. Chris M. (talk) 21:09, 17 February 2010 (UTC)

Salt water boils at a higher temperature than fresh water, not a lower one, per Boiling-point elevation. Having something in solution also lowers the freezing point, per Freezing-point depression. Sea water is said to boil at 103.7 C (compared to 100 C for pure water). Edison (talk) 21:17, 17 February 2010 (UTC)

Not sure how useful a comparison with Venus is since the gas properties of CO2 and the N2 O2 mixture we have are quite different. Googlemeister (talk) 21:10, 17 February 2010 (UTC)

On the other hand, Venus has more N2 than we do, and if you boil the biosphere and the oceans you'd destroy our O2 and get a lot of CO2 on Earth as well (though no where near as much as Venus has accumulated over billions of years). Dragons flight (talk) 21:39, 17 February 2010 (UTC)

Question about male genitalis

Why do male genitalia flop around?

The testes work best at temperatures slightly less than core body temperature. This is presumably why the testes are located outside the body. See the article Testicle. The Penis that forms the other part of the male genitalia must project in order to be able to penetrate the female genitalia. Please sign your posts. Cuddlyable3 (talk) 21:39, 17 February 2010 (UTC)

glacial lake in siberia

File:Last glacial vegetation map.png This map shows an enormous lake covering eastern Siberia during the last ice age. What was its name so i can look it up? —Preceding unsigned comment added by 70.29.47.142 (talk) 21:32, 17 February 2010 (UTC)

It's hard to tell which lake you mean - but if you bring up Google Maps, you should be able to zoom in and find it very quickly - IF it's still there...it probably isn't - in which case it may not have a name. SteveBaker (talk) 21:47, 17 February 2010 (UTC)

It is the blue area covering eastern Sibera and north of the bering land bridge. Blue on the map means a lake. It is not still there, it was there in the ice age. I would like to find out more about it. there are names for the ice age lakes in north america like Lake Ojibway. 70.29.47.142 —Preceding unsigned comment added by 70.29.47.142 (talk) 22:07, 17 February 2010 (UTC)

I don't think that's a lake; it's an area of "polar and alpine desert". The two colors in the legend of File:Last glacial vegetation map.png are virtually indistinguishable, at least on my monitor. Deor (talk) 23:34, 17 February 2010 (UTC)

I checked the colours with Gimp and you're correct. FYI lake colour is 0094c8 and polar-and-alpine is 00a4c0; the two are very close indeed. -- Finlay McWalter • Talk 00:07, 18 February 2010 (UTC)

thank you. Does that mean Tibet was not a lake either? I don't see how it could be if there were still mountains there. Thank you for helpimg. 70.29.47.142 —Preceding unsigned comment added by 70.29.47.142 (talk) 00:47, 18 February 2010 (UTC)

A greenhouse on Mars

If you put a large air-tight greenhouse on Mars and fuilled it with air, how warm would it get? Would earth-plants grow in the Martian "soil"? Maybe with some human 'compost' mixed in? 78.146.206.38 (talk) 00:00, 18 February 2010 (UTC)

To answer the first part, there is no theoretical barrier to designing a solar greenhouse on Mars that operated at comfortable temperatures of plant life. Dragons flight (talk) 00:14, 18 February 2010 (UTC)

The temperature would depend on the latitude. Climate of Mars#Temperature indicates that temperatures do get up to nice warm temperatures (27 °C max), presumably on the equator. With the (literal) greenhouse effect, the temperature inside your greenhouse would be higher than the surroundings, so anywhere reasonably close to the equator should be fine temperature-wise. The Martian soil might be suitable for the growth of Earth-plants - it seems from that article that more research is required. --Tango (talk) 00:18, 18 February 2010 (UTC)

The temperature would drop quite low, especially at night in the winter, unless there was sufficient thermal mass and a high insulation level. Mars gets on average only 43% the solar intensity or "insolation" received on Earth per [34]. The mean surface temperature (outside the greenhouse) is only -63C (per the NASA site, varying with season and latitude). The air pressure is very low, so a greenhouse dome would have to be quite strong to hold in enough airpressure for earth type plants. See also a NASA project looking at a Mars greenhouse. Apparently 1/4 of earth normal pressure would suffice. Actually sounds doable. The Mars Society also has some suggestions how to build the greenhouse. Edison (talk) 00:21, 18 February 2010 (UTC)

As that Mars Society link says, you can keep it warm with what is essentially an enhanced greenhouse effect - they suggest a silver compound in the plastic that will allow visible light and near-IR (ie. sunlight) through but stop far-IR from getting out. --Tango (talk) 00:45, 18 February 2010 (UTC)

a little help with equilibrium constants and partition coefficients as they relate to solubility

Admittedly, the whole "mole product / mole reactant" thing goes over my head when I imagine scenarios like adding more reactant or taking away more product. So ... like take these titration results.

There's approx 0.013 mmol of dissolved iodine (without iodide) in 50 mL solution.

When I add 5 mL cyclohexane, approximately 0.008 mmol of it escapes into the cyclohexane, resulting in a concentration-in-cyclohexane figure of 0.0016 M. From the new concentrations I calculate a partition coefficient of approximately 16.

When I add 8 mL cyclohexane, despite a 60% increase in the amount of lipophilic solvent there's only a 25% increase in extraction ... Indeed, the concentration of iodine in cyclohexane is now 0.00125 M, a concentration fall. This sort of makes sense since as the iodine gets less-concentrated in the water phase, iodine becomes harder and harder to extract from aqueous solution. The concentration in aqueous phase is now 5.6 * 10^-5 M and the new partition coefficient is 22.

This is clearly experimental error right? Shouldn't the partition coefficients remain roughly the same? (We measured concentrations by titration.) Let's take an ideal case with no experimental error and say I'm adding more water or more cyclohexane. How would I use the partition coefficient to predict new concentrations? What does the partition coefficient really mean, as an equilibrium constant? How likely is it that mistitration or something like that is the source of my error? Basically, I don't know how to think of "mol product over mol reactant" when I say add more of one type of solvent to the mixture. Are the concentrations going to rearrange themselves such that the ratios of concentrations in the different solvents will somehow remain constant.

I get even more lost when I deal with saturated solutions and there's apparently an equilibrium constant between the pure solid phase and a dissolved phase as a solute, because if I add more excess solute to a saturated solution, clearly the ratios cannot adjust themselves to the equilibrium constant since the solution is already saturated. John Riemann Soong (talk) 01:34, 18 February 2010 (UTC)