Wikipedia:Reference desk/Archives/Science/2008 June 8

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June 8

Suppose that we discovered a large-ish asteroid on a collision course with the earth...

How close would it have to get to us before we could accurately calculate where the point of impact would be? --Kurt Shaped Box (talk) 01:46, 8 June 2008 (UTC)

Don't shoot until you can see the whites of their eyes. Hmm.. perhaps the point at which any changes in its speed or direction are found to be due mostly to the Earth's gravitational pull. The acceleration would theoretically have to be constant, or at least known at all times.--Russoc4 (talk) 01:53, 8 June 2008 (UTC)

Modelling orbits is mostly about having a large number of observations over a long time. Think of it this way. If an object is moving at a typical orbital speed of ~20 km/s, then a 1 m/s variation in that speed would lead to a change in the expected location of 150,000 km over 5 years, which would be a very noticable range of variation. If you have a long enough period of observations, you can be very precise about future orbital positions. For example 99942 Apophis, which will make a close approach in 2036, has it's predicted distance to Earth at that time nailed down to 3381 +/- 8 km (1-sigma). Dragons flight (talk) 02:44, 8 June 2008 (UTC)

Hi. 1950 DA, for example, has a roughly 1-in-300 chance of colliding with Earth in the 2800's, and we've calculated that the Earth's Atlantic Ocean faces the asteroid on its near pass/possible collision date. We don't know its exact chances yet, but we have observed its rotation enough to know this. Hope this helps. Thanks. ~AH1^(TCU) 16:49, 8 June 2008 (UTC)

Looking into the past

moved from talk page

If when we look towards the center of the Universe, we are looking billions of years into the past how is it, the Earth traveled to the distance it is now from the center of the Universe before the light from billions of years ago?

Did the matter that made up the Earth and the rest of the planets materialize in place?

Or did we actually travel faster than the speed of light?

Please excuse grammar and spelling.—Preceding unsigned comment added by 97.89.59.10 (talk) 01:29, 8 June 2008 (UTC)

Well we're obviously not anymore if we can see it. Not sure how that happened though. Probably we were quite close to those stars a looong time ago and space has been expanding at nearly the speed of light or something, so the light has been sloooowly catching up to us. So by the time it finally finishes its 1-inch trip by overtaking us, it's already billions of years old. I don't know, sounds wrong? --.froth. (talk) 03:32, 8 June 2008 (UTC)

There is no centre of the universe. When we say the universe is expanding, we don't mean it's all moving out from a centre, it's more like blowing up a balloon. The 2D rubber surface (ignore the fact that it's contained in 3D space, just think about the rubber) doesn't have a centre, each bit is stretching as you blow it up. If you draw some dots on it before you start you'll see those dots get further and further apart, but they never actually move, it's just the rubber inbetween them gets bigger. When all the matter was created shortly after the big bang, it filled the whole universe and has been spreading out as the universe expands ever since. This means bits of matter can be very far apart without having to have actually moved at all. --Tango (talk) 10:35, 8 June 2008 (UTC)

<----> Ok, even if there is not a center of the Universe, Which I’m not sure is true.

In order to look back in time and space to the Big Bang,

Would we have had to travel faster than the light in order to arrive here first in order to see it?

Is it possible the matter that makes us up arrived here before the light that was emitted from the Big Bang arrived.

could that be possible unless we actually traveled faster than that light, right?

I mean according to the rules; matter can not travel faster than light, so the light that was emitted then would have been at this point in time/space way before we arrived at this point in time/space right?

Please help me understand the logic.

Again please excuse grammar and spelling

<------>

See inflation (cosmology). Yes, the universe grew faster than the speed of light for a microscopic fraction of a second during the Big Bang. As a result, we are only now seeing light from matter we were next to previously (though at that time, none of the current matter had yet condensed). It is also worth noting that the cosmic microwave background, i.e. the "light of the big bang" actually was created ~3 minutes after the "bang", so that light comes from after we were seperated. Also see: Timeline of the Big Bang. Dragons flight (talk) 21:10, 8 June 2008 (UTC)

It's not true that the universe expanded faster than light during the inflationary epoch. Depending on how you define "expanding faster than light", either the universe never expands faster than light or it always expands faster than light; there's no definition that singles out the inflationary epoch. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

(ec) The ideas of expansion of space, seeing "old photons" that are only now arriving to us, etc. comes up fairly often on the Science Ref-Desk. Here's a recent discussion focussing on how things can be further away than conventional "object at speed-of-light" would suggest: Wikipedia:Reference desk/Archives/Science/2008 March 26#Faster than light/Big Bang question. Not a direct answer to your question (which I don't fully understand), but something that may clarify some general/related ideas. DMacks (talk) 21:18, 8 June 2008 (UTC)

Actually, the CMB was released about 400,000 years after the big bang. You were close. ;) --Tango (talk) 21:33, 8 June 2008 (UTC)

The photon epoch begins at 3 minutes, the last scattering event (and end of equilibrium) came a few hundred thousand years later, but I think arguing that point is splitting hairs about what you mean by light created by the big bang. Dragons flight (talk) 21:49, 8 June 2008 (UTC)

We can see light from the early universe because the universe is homogeneous. The primordial fireball that emitted the light filled the whole universe, and the light that it emitted also filled the universe, and it still does, there being nowhere else for it to go. Cosmic inflation is the currently favored explanation for the homogeneity, but there's too little evidence at this point to say whether it's correct. -- BenRG (talk) 23:27, 8 June 2008 (UTC)

This is weird, and maybe I'm reading things wrong, but I believe you're all answering a question that wasn't asked and possibly even explaining them wrong...the way I'm reading the OP's question is "Why can we see into the past by looking at light from far away objects?" The answer is: Because the speed of light is finite instead of infinite. An easier example to understand is sound and the echo effect. When you shout at a large cliff, there is a delay between when your voice is projected and when it comes back as an echo. That time delay is due to the finite speed of sound. In fact, if you knew the speed of sound and the distance to that cliff you could calculate how long it took for your voice to get there (or knowing time you could calculate distance). In the same way, because we can determine the distance to the star using astronomical observation techniques, and knowing the speed of light and the fact that it is constant in the universe, we can determine how long ago the star emitted that light. EagleFalconn (talk) 14:13, 9 June 2008 (UTC)

Lunar Module Ascent Stage

A rocket launch on Earth is a jarring event even for a spectator. The sound and the fury of getting even a modest payload to Earth orbit is simply awesome. The scales involved seem overwhelming.

Why is it that a Lunar Module's Ascent Stage taking off for lunar orbit ( youtube link[1]) seems like such a walk in the park? It's not hundreds of feet tall, just 12. It only weighs as much as 5-10 cars. No ground crew required, no days sitting on a launch pad prepping. No drama whatsoever. Shouldn't the theatrics be 1/6th as much as they are on Earth? Sappysap (talk) 02:51, 8 June 2008 (UTC)

Well, it was just a vehicle to get the astronauts up into orbit (a few hundred miles?), not all the way to the Moon, so they didn't need much life support equipment. It also didn't have to overcome our stronger gravity, plus there was no air resistance or weather to worry about. For all these reasons, it didn't have to be as humongous as the Saturn V. Besides, who says there wasn't a lot of prep work anyway? Clarityfiend (talk) 03:25, 8 June 2008 (UTC)

It's not strictly proportional because you also need more fuel to lift the additional fuel, and more fuel to lift that extra fuel, ad infinitum. So, the higher the force of gravity, the larger percentage of the rocket that must be fuel. A chemical fuel rocket would hit some limit where it could never even achieve orbit from a planet with gravity above a certain level. (I wonder what that point would be ?). StuRat (talk) 14:16, 8 June 2008 (UTC)

Let's do some math to illustrate my point. If we say some type of fuel has enough energy so 10 lbs of fuel can lift 100 lbs of cargo into lunar orbit from the Moon, we would then need 60 lbs of fuel to lift that cargo into Earth orbit from the Earth, before we take into account the fuel needed to lift the fuel. Now, the 10 lbs of fuel would require 1 lb of fuel to lift, and that 1 lb would require 0.1 lb of fuel, for a total fuel weight of 11.1111... The 60 lbs of fuel would require 36 lbs to lift and that would require 21.6 lbs, etc., for a total fuel weight of 150 lbs. Note that the ratio between 150 lbs of fuel and 11.1111... lbs is 13.5:1, far more than the 6:1 ratio of gravity. This effect gets even worse when using fuels with less energy to mass.

So, we have the following reasons so far:

1) This "compounding effect" of fuel weight.

2) Only going to orbit versus escape velocity.

3) Air resistance.

4) The much lighter payload. StuRat (talk) 14:34, 8 June 2008 (UTC)

Don't forget the other implications of having no air resistance on the Moon. The lander is not required to have an cylindral, aerodynamic shape, so it doesn't need to be supported prior to launch while on the platform. Tail fins and other stablization systems are also not needed. On Earth, a rocket's exterior must be at least strong enough to withstand the air pressing on it. I'm not sure whether the casing adds significant weight to the craft, but no such strong structure is required on the Moon. --Bowlhover (talk) 15:59, 8 June 2008 (UTC)

Energy to orbit (neglecting air resistance) in terms of the central mass, M, radius of the object, R, and altitude to orbit, h, is approximately proportional to $M{R+h \over Rh}$. The mass of the moon is 7×10²² kg, versus 6×10²⁴ kg for the Earth. The radius of the Earth is 6370 km, versus 1740 km for the moon. And lastly you need ~180 km altitude to clear the Earth's atmosphere, versus only 20 km for the moon (to clear the mountains, though Apollo actually used 100 km).

Equating terms, you can see that for a given orbiter mass in order to get to orbit the moon you need only 1% as much energy as you do to orbit the Earth, mostly due to the Moon's greatly reduced mass. Since energy is basically proportional to fuel, you can do with far less fuel on the moon than on the Earth. And that's before considering air resistance, booster weight, and everything else one needs at Earth that you don't need at the moon. Dragons flight (talk) 17:17, 8 June 2008 (UTC)

That doesn't seem right; you should get 0, not infinite, energy as $h\rightarrow 0$. Just comparing the gravitational potential energy at R and $R+h$ gives me ${\frac {Mh}{R(R+h)}}$, giving 1.8% as much for the Moon/20km as for the Earth; is that what you meant? --Tardis (talk) 17:10, 9 June 2008 (UTC)

help-- i need some support in my research

hello great brains!!! i am trying to prove reflection of electromagnetic waves from metallic surfaces using basic principle of physics.does any one knows that is the proof going to be unique or it has been already done.actually i am trying to provide a firm reason for reflection of electromagnetic waves,in opposition to hypothetical proof provided by hugens.kindly help me that to which university would entertain such proofs.such that it gets recognized.

Reveal.mystery (talk) 2nd year Mechancal Engineering student India. —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 03:34, 8 June 2008 (UTC)

I'm sorry but I don't understand the question. What are the "basic principles of physics" you're starting from? Maxwell's equations? Quantum electrodynamics? String theory? In at least the first two cases it's already been done. Why do you want to do this? —Keenan Pepper 04:00, 8 June 2008 (UTC)

I think what Reveal.mystery really asks is, "why does Huygens–Fresnel principle hold for the electromagnetic waves, and what fundamental principles of modern physics does it follow from?". Well, as Keenan said, if Maxwell equations are basic enough then, yes, it follows from them almost trivially. Simply assume the incident perturbation in electromagnetic field to be a harmonic plane wave (see equation in article if unsure what it is), and solve either numerically or analytically, whichever you like best. Play with shapes of obstacles and their dielectric constant to get the feeling for how the waves interact with surfaces and edges; this is not always easy analytically, so I would recommend using MATLAB. Now, on the other hand, if you are asking where Maxwell equations are coming from, then things really become much more complicated. First and foremost, there is a chicken and egg relation between special relativity and classical electromagnetism. And I really suggest you look no further than that at least until you are well familiar with the latter two. Hope this helps. --Dr Dima (talk) 06:09, 8 June 2008 (UTC)

I have moved the following new question here as it appears to be a continuation of this question. SpinningSpark 12:47, 8 June 2008 (UTC)

many many thanks to active wikipedists for their support. let me explain what actually i tried for: considering the wave nature of em waves i considered the interaction of the magnetic component of the wave with the metallic surface.now further on by applying lenzs law i propose the generation of an opposite directioned current in the plate.the interaction of the orginal and the field generated by lenzs law finally proves my point.

please helpme so that i may further more proceed in this area.basically i require it to be recognized by some university professor or any journal.since the subject dosent pertains to my branch ,such recognition would help me in my resume for my gre(M tech) interview.

Reveal.mystery (talk) 2nd year,Mechanical Engineering student (email removed per Ref Desk guidelines) india —Preceding unsigned comment added by Reveal.mystery (talk • contribs) 12:38, 8 June 2008 (UTC)

See Heinrich Hertz. He did the experiment you describe in 1886 and showed that electromagnetic waves can be reflected. You could experiment with it using a small dipole transmitting antenna, receiving antenna, and a transmitter and receiver, with a means of measuring signal strength, perhaps by measuring the AVC voltage in the receiver. I have read of physics demonstrations using the RF output (often US channel 3) from a video cassette recorder, with a small dipole antenna, and the same channel input on a TV receiver connected to a similar antenna. See [2] , [3] , [4]. Edison (talk) 19:28, 9 June 2008 (UTC)

I had to this as homework early last decade. To solve the Maxwell's equation you have to put on a few extra constraints, such as no electric field parallel to the surface of the plate. Electric charge can only travel on the surface of the plate. Lens's Law is already included in the Maxwell's equations. Graeme Bartlett (talk) 21:34, 9 June 2008 (UTC)

IF IT IS ALREADY DONE BY HERTZ .LET US DISCUSS WHETHER I AM CORRECT OR NOT .(sorry for caps). Consider the interaction of an electromagnetic wave with a flat metal surface ABCD.consider the wave to be incident along MN and reflected along NO.point of reflection being N. • According to the figure given above we consider a plane wave front of a electromagnetic wave which could be easily represented by a right handed system of axes. the wave propagates along z axis hence the wave propagation vector points along positive x axis.let us assume when the electromagnetic wave strikes the metalsurface at N with magnetic component along Z axis and the electric component along y axis.the dotted rectangle shows a small part of the metal.which we have used to represent the eddy current generated by em eave and the opposing current due to lenz's law as shown in figure.i had studied about the phase change of an em wave by 90 degrees on reflection from a rigid surface .i suppose phase chancge to be as such represented in figure.any em expert wikipedist pay some attention on my research.

Reveal.mystery mech engg student india

(talk)

Cancer screening

Does cancer screening refer only to the search for extant disease, and not individuals at risk from disease but that don't actually have it or can the term be used to encompass both? From my brief search it seems that the term is used to cover the search for existing disease only (even if in the early stages) so the ability to predict development of disease may not be inferred from the term. ----Seans Potato Business 11:26, 8 June 2008 (UTC)

You screen only for actual conditions, not for predispositions. If, for example, one tests a population for a gene that predisposes to cancer (say BRCA1), you're screening for the gene, not for cancer. - Nunh-huh 11:52, 8 June 2008 (UTC)

I think you're being too strict about the usage of "screening". In the US, pregnant women are routinely given prenatal screening for certain conditions of the fetus (such as Down's syndrome and spina bifidia). The screening detects elevated risks associated with certain conditions but does not give definitive diagnoses. In fact, the article on triple screen says:

The test is for screening, not for diagnosis,[4] and does not have nearly the same predictive power of amniocentesis or chorionic villus sampling.

--71.162.233.218 (talk) 13:46, 8 June 2008 (UTC)

Not too strict at all, they are screening for conditions that actually exist - but with imperfect tests. Nearly all screening tests need followup tests for diagnosis, because by their very nature, screening tests will have false positives. - Nunh-huh 03:01, 9 June 2008 (UTC)

Weather forecast

I'm not happy with current forecasts. I'd also like:

1) The predicted time of the highs and lows, and better yet a graph of predicted temps throughout the day.

2) A humidity forecast in a form similar to that listed above.

3) A wind speed forecast similar to that listed above.

Does anybody know where I can get such data ? StuRat (talk) 12:36, 8 June 2008 (UTC)

It might help if you said where you are (ie which country). And also what you are currently looking at. SpinningSpark 13:28, 8 June 2008 (UTC)

I'm in the US (Detroit) and use an Internet site for ad-free weather: [[5]]. I also can get forecasts for the temps every 3 hours or so from digital TV station 4-2, but only for the current day. StuRat (talk) 13:49, 8 June 2008 (UTC)

Have you looked at the NOAA site for your area[6] ? I didn't check if it meets all your spec but its a lot more than what you have already. Here's the link to their front page in case I got your local area wrong [7]. SpinningSpark 14:34, 8 June 2008 (UTC)

That works. I found their "tabular forecast" is what I want: [8]. Thanks ! StuRat (talk) 14:45, 8 June 2008 (UTC)

Hi. I live in Canada, and I can find a way to get all three. Here, The Weather Network[9] gives us hourly forecasts. As for hourly humidity and wind forecasts, The Weather Network gives us that every quarter part of the day, but I can also get it at Cleardarksky, although the measurements are vague. Hope this helps. Thanks. ~AH1^(TCU) 16:53, 8 June 2008 (UTC)

Thanks for the answers so far. Does anyone know of a weather forecast given as a graph ? StuRat (talk) 12:48, 9 June 2008 (UTC)

You've already tried the hourly weather graph tab[10] on the NOAA site right? What is missing there that you need? SpinningSpark 19:37, 9 June 2008 (UTC)

No, I hadn't found the graphs, only the tables. That looks good, except that it's for Detroit, Illinois instead of Detroit, Michigan, and I'm not sure how to change the city. StuRat (talk) 03:15, 10 June 2008 (UTC)

Ok, I figured out how to change the city, but, geez, that site's a real bi*** to navigate, isn't it ? I expected to be able to just pick on "Detroit IL" and type in "Detroit MI", but it's never that simple, is it ? StuRat (talk) 03:49, 10 June 2008 (UTC)

doh - sorry for the crap geography on my part, not my country. The easiest way I found to navigate that site is to start at the top level of weather chart http://www.weather.gov/ then click on the map on the area you want then repeatedly do that through (I think) three levels till you come down to a city. Then click on the type of data you want, which in your case is hourly weather graph. Hope that helps. SpinningSpark 02:39, 12 June 2008 (UTC)

That seems to work. It sure doesn't seem very intuitive, though. I expected to select the type of forecast (hourly graph), and then type in the city and state. StuRat (talk) 04:46, 13 June 2008 (UTC)

Wing layout

Why do most planes have only two wings?

Why layouts with double or three wings on each aren't more common?

And what about having a set of short wings stapled - not broader as the plane - over each other until the plane gets enough drag to fly? GoingOnTracks (talk) 12:53, 8 June 2008 (UTC)

See Biplane#Advantages and drawbacks to biplane designs. Xn4 13:31, 8 June 2008 (UTC)

We don't seem to have anything explaining the unpopularity of tandem wing designs, though. Algebraist 13:32, 8 June 2008 (UTC)

The unpopularity of tandem wing might be explained by its increased stability, which surprisingly, is not always desirable. Certainly for fighter aircraft, maneuverability is king and stability and maneuverability are mutually exclusive. Also, if sufficient stability can be achieved by other means (high mounted wings, dihedral etc) why go to the expense of additional wings. Also some large commercial aircraft (eg Boeing 747) achieve distributed CL (the reason for tandem wings increased stability) by means of the lifting body effect. SpinningSpark 14:05, 8 June 2008 (UTC)

Just one more point, the designer of the aircraft (Rutan Quickie) in the picture in the tandem wing article says he designed it that way so that it resembled the Stars Wars X wing starfighter. Probably not a lot of call for that outside of the kit plane market. SpinningSpark 14:17, 8 June 2008 (UTC)

One big factor seems to be the speed of aircraft. More wings means more lift but also more drag, both of which also increase with speed. Early planes went quite slowly, so needed all the lift they could get, and drag wasn't much of an issue. Current planes are much faster, so getting sufficient lift is possible from fewer wings, while keeping drag low is also more of an issue. StuRat (talk) 14:09, 8 June 2008 (UTC)

Excessive numbers of wings were included in some very early plane designs like the Phillips Multiplane [11] but triplanes are gone now, biplanes rares. Some canards seem like second sets of wings (Beechcraft Starship). Rmhermen (talk) 18:12, 8 June 2008 (UTC)

StuRat has it right - it's to do with drag (and mass). A single main lifting wing is usually the most efficient design to achieve a given lift with minimal weight and drag. In addition, the calculations required to design a multi-wing plane are much more complex, since there is a lot of interaction going on between the various wings (see the canard article for some of the trade-offs of using canards), so it's easier to optimise a one-wing design. — QuantumEleven 15:29, 10 June 2008 (UTC)

How do astronauts commit suicide?

Do they have some sort of suicide pill? Or are they expected to "sink" with the "ship"? —Preceding unsigned comment added by 88.6.118.85 (talk) 17:30, 8 June 2008 (UTC)

We are not a crystal ball - no astronaut has committed suicide in space yet. In fact, only three people have died while in space, the crew of Soyuz 11 due to a malfunctioning vent. (See also space accidents and incidents) While on Earth they have access to any suicide technique the rest of us do. Rmhermen (talk) 17:57, 8 June 2008 (UTC)

I think the original poster was asking about a situation where astronauts were stranded with no hope of rescue—would they be provided with means to commit suicide in lieu of 'waiting it out'? Obviously it hasn't happened yet, but it doesn't mean that no one has planned for it.

To reply to the question, as far as I can discern there is no record of NASA astronauts carrying suicide pills, nor is it likely that Soviet astronauts carried them. (Links to Q&A with shuttle crew, reference to Jim Lovell's book on the Apollo 13 mission.) Several astronauts and commentators note that there's no need to carry suicide pills on a space mission—venting the air from the capsule will do the job quite nicely, and loss of consciousness will occur in about fifteen seconds. TenOfAllTrades(talk) 18:09, 8 June 2008 (UTC)

The first person to perform a spacewalk, Leonov aboard Voskhod 2, secretly carried a suicide pill in case he had been unable to enter the spacecraft and had to be cut loose. --Bowlhover (talk) 18:50, 8 June 2008 (UTC)

Nonsense! How would he take the pill, considering he had a bloody big helmet on?--ChokinBako (talk) 11:30, 10 June 2008 (UTC)

I'm similarly puzzled, but it seems that Wikipedia is far from being the only source of the information. --Bowlhover (talk) 23:34, 12 June 2008 (UTC)

But is venting the air painless? How quickly can it be done? I doubt there's a "vent the air" button on the control panel. Wouldn't that be equivalent to a self destruct button? What if your buddies don't want to die with you? I think the original poster may have gotten the idea of a suicide pill from the movie Contact based on the novel by Carl Sagan. In it, Jodie Foster's character is given a suicide pill before she goes into the machine to take her to make contact with aliens. She is told that the pill has been given out to astronauts ever since the space program began, but it was never made public. She was told that the pill can be useful if she's stuck somewhere with no way to get back home, or trapped. Faced with the possibility of a slow painful death, the pill would put her out of her misery quickly and painlessly. She was also told that the pill is for all the reasons that they "could not think of". ScienceApe (talk) 18:53, 8 June 2008 (UTC)

That's fiction of course (rather a long drawn out one as I recall). I'd be more interested to know just how Leonov intended to administer his pill during the speacewalk given that's he'd be wearing his spacesuit.--Shantavira|^{feed me} 19:15, 8 June 2008 (UTC)

Nope, not drawn out at all. It was a very good movie. ScienceApe (talk) 02:45, 9 June 2008 (UTC)

Couldn't you just like take off your space helmet outside and suffocate?-- —Preceding unsigned comment added by Crystal eyes17 (talk • contribs) 20:59, 8 June 2008 (UTC)

I don't know about the Russian space program, but NASA spacesuits are designed in a way that the wearer can't possibly reach all the latches necessary to remove the helmet, and the assistance of a second astronaut is simply required to get out of it. Dragons flight (talk) 21:04, 8 June 2008 (UTC)

And even if you could get it off, the pressure would kill you before you suffocate since your blood (and all other fluids) would literally boil in the zero pressure of space.--十八 08:27, 9 June 2008 (UTC)

Well boil yes, but not "completely and instantly boil away" and not "astronaut swells up and explodes like in the cartoons":) Actually, the injury/death mechanisms don't seem related to the fluid-boiling issue at all See Vacuum#Effects on humans and animals for more info. DMacks (talk) 08:39, 9 June 2008 (UTC)

There's zero pressure outside your body, but inside, where the fluids are, there is still pressure supplied by your body. Assuming you don't try and hold your breath, which could result in your lungs exploding, death is usually by suffocation and if very quick (about 15 seconds to lose conciousness) - the vacuum almost "sucks" the oxygen out of your blood. --Tango (talk) 14:54, 9 June 2008 (UTC)

I'm pretty sure I heard of one instance where NASA astronauts were accidently subjected to a vacuum during training. I believe they passed out within 15 seconds before realizing anything was amiss, and without lasting injury. Someone may correct me if I'm wrong. Paul Davidson (talk) 13:50, 10 June 2008 (UTC)

I think they knew something was amiss. If memory serves, they reported their last memory before losing conciousness was of the saliva on their tongue boiling. Otherwise, you're right, they repressurised the room pretty quickly and the subject regained conciousness once the pressure got back up to a reasonable level, with no ill effects. I'm sure the incident is described on Wikipedia somewhere, I'll try and find it. --Tango (talk) 13:58, 10 June 2008 (UTC)

Found it: Human adaptation to space#Unprotected effects. Once again, we find that Wikipedia has an article on everything! --Tango (talk) 14:03, 10 June 2008 (UTC)

Garbage into oil?

Was there an attempt to turn garbage or sewage into oil? ScienceApe (talk) 18:42, 8 June 2008 (UTC)

Discover magazine says yes. The company responsible is Changing World Technologies. Clarityfiend (talk) 19:42, 8 June 2008 (UTC)

Why isn't this done on a much larger scale? We have enormous landfills that can be turned into oil. ScienceApe (talk) 02:47, 9 June 2008 (UTC)

When I expanded the CWT article, I found that their particular method costs $80 to produce a barrel of diesel, so until recently, it wasn't very profitable. Besides, the stuff in landfills would almost certainly have to have metals and other inorganic material removed, further raising costs. Clarityfiend (talk) 02:52, 9 June 2008 (UTC)

I can't provide a reference, but I know that the one large-scale implementation of this process (discussed in our article on CWT) had significant problems, including being shut down temporarily for generating very strong odors. ike9898 (talk) 20:24, 10 June 2008 (UTC)

See List_of_solid_waste_treatment_technologies#Advanced_waste_treatment_technologies methods include pyrolysis Gasification#Waste_disposal Thermal depolymerization amongst others - food waste is popular, as is garbage. Sewage is a possibility but more likely to be treated by Sewage_treatment#Anaerobic_digestion (as it is very wet) making 'biogas' which can be made into oil. If you are still interested try Waste management and follow the links...87.102.86.73 (talk) 17:23, 9 June 2008 (UTC)

The worst case of food allergies and religious food laws

What are the worst known cases of food allergies combined with restrictive religious food laws? E.g., you are not allowed to eat certain foods, but you are allergic to most of the foods that you are allowed to eat. Furthermore, most of the non-allergic and legal foods are not available in the place that you live. -- Toytoy (talk) 19:03, 8 June 2008 (UTC)

Religious food laws rarely limit the diet that much. For example, kosher and halal (which are similar in scope) limit barely a fraction of the pantheon of foods we could eat. I can't imagine a situation where one would need to circumvent these laws in order to avoid eating foods to which we are allergic. Fribbler (talk) 23:00, 8 June 2008 (UTC)

There was a somewhat related case mentioned in the radio recently. Certain christian priests complained that they have to administer masses in towns far away from their home so it would be best if they could drive, but they also have to drink wine for celebratory purposes on the mass, which of course excludes driving. – b_jonas 09:36, 9 June 2008 (UTC)

It's possible to be allergic to alcohol. Both that and gluten intolerance can make Holy Communion difficult. I read (but have lost the link) that members of the congregation may take only one, but Catholic priests must take both the bread and wine. 81.174.226.229 (talk) 11:00, 9 June 2008 (UTC)

http://www.catholicceliacs.org/Bishops.html ? —Keenan Pepper 12:05, 10 June 2008 (UTC)

To be technical, there's no such thing as an alcohol allergy, in large part because the ethanol molecule is way too small to be recognized by the immune system. One can however, have an alcohol sensitivity, which something else entirely. I can't find a specific reference to this on Wikipedia, but Mayo Clinic does a pretty good job. – ClockworkSoul 14:33, 10 June 2008 (UTC)

Let me add on to my statement a bit: there seem be be a number of reliable sources that suggest alcohol allergies do exist but are very uncommon. I'm more than a little skeptical, but I should at least acknowledge them. – ClockworkSoul 14:39, 10 June 2008 (UTC)

If you haven't come across it already, you may be interested in this [12] which mentions several case studies Nil Einne (talk) 18:38, 10 June 2008 (UTC)

Actually wikipedia covers Alcohol flush reaction and Alcohol tolerance resonably okay, which appears to be what the Mayo Clinic link is referring to. I'm not sure about alcohol allergies however. BTW, people with the alcohol flush reaction are unlikely to be trouble by receiving communion since the amount consumed is so low, it's unlikely to cause any problems. Nil Einne (talk) 18:35, 10 June 2008 (UTC)

Actually I was referring to the way my Dad's cousin vomits if a sauce contains alcohol which hasn't been completely evaporated by cooking, which may not be a proper allergy but doesn't sound like a mere tolerance issue. 81.174.226.229 (talk) 09:16, 11 June 2008 (UTC)

Rubber

Does all rubber contain latex? —Preceding unsigned comment added by 76.125.70.46 (talk) 20:01, 8 June 2008 (UTC)

In the area of rubber, latex does not indicate the contents of the rubber. It indicates that the rubber has not been vulcanized. -- kainaw™ 20:38, 8 June 2008 (UTC)

Latex is a pretty slippery term; its meaning depends quite a bit on context. Our article includes a fuller description of the different meanings. People who have a latex allergy are sensitive to natural rubber; they're likely not bothered by latex paint (which contains acrylic polymers). Generally – but not always – so-called 'latex rubber' is not vulcanized.

Synthetic rubber can be manufactured using a variety of compounds, many of which bear little resemblance to the ingredients of natural latex. Finally, the pedants will point out that 'latex' describes an aqueous emulsion; 'rubber' is what you get after the latex dries. Confused yet? TenOfAllTrades(talk) 15:54, 9 June 2008 (UTC)

Strange hypnagogic sensations

Sometimes when I'm just falling asleep, I experience a strange sensation -- it feels like my body is being distorted, changing in size or becoming stretched and compressed. It's not painful, but sort of dizzying and disorienting. This often accompanies the usual sensation of floating or falling, and sometimes sleep paralysis occurs at the same time. Is this a documented phenomenon, and what could its psychological or physiological basis be? 69.111.189.55 (talk) 21:45, 8 June 2008 (UTC)

Well, from your subject heading I guess you know about Hypnagogia... the article doesn't describe your experience exactly, but it seems in keeping with the broad set of weird things that happen in that state. Other than that, I don't know. --Allen (talk) 01:24, 9 June 2008 (UTC)

Wow. I used to feel that way often when I was a child and teen. I had forgotten all about that until I read this. At the time it was a bit disconcerting and I didn't know if it was something physiological or if it was all in my mind. My memories of the experience really don't sound anything like what is described in the hypnagogia article. It was more like my sense of scale was all weird; like my body was flattening, or if I closed my eyes I could see/feel in the blackness a perfect line, and I could let myself fall partly into it in a sense. At others it was like my fingers were huge, and it was a wonder I could move them. It is a very hard thing to describe. I don't think I could have then, and obviously I'm not doing a very good job of it now.

I think such sensations usually did happen when I was going to sleep, but I can't tell you if that was the only time or not (it's possible it also happened at other times when I was at rest and had a chance to calmly observe my sensations--e.g. meditation). Maybe it has something to do with the growing process; I haven't felt that way in my adult years. Then again, my sleeping habits have changed significantly since then too.

Anyway, sorry for the non-answer. It was great to hear someone else express the same kind of sensations that puzzled me, and I hope my rambling might in some way help you too, even if it isn't anything close to an "answer". (Keep in mind I'm not giving advise; if this is something you are at all concerned about, consult a medical professional.) --Prestidigitator (talk) 04:37, 9 June 2008 (UTC)

The "huge fingers" sensation happens to me, too; I also lose track of what position my arms are in. Indeed, it's kind of a relief to know that I'm not the only person who has these weird half-dream experiences. 69.111.189.55 (talk) 02:23, 10 June 2008 (UTC)

I used to get it when I was a teenager too. That is when I started to get sleep paralysis, too. My hands would feel enormous but not heavy in any way, just really big. The sleep paralysis was a seperate thing, though, and I experienced it more and more as I got into and went through my 20s. Take a look at the article Kanashibari. --ChokinBako (talk) 11:26, 10 June 2008 (UTC)