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August 25

What if Earth stopped rotating?

Assume that its rotation is slowed gradually enough that the deceleration doesn't cause any major effects. --168.7.232.12 (talk) 00:35, 25 August 2012 (UTC)[reply]

We get this question a lot. If I may quote myself, from March of this year, when I quoted myself from a similar question in September of last year: (I have taken some liberties to modify the quote to increase relevance to the current question)

“

The answer to this type of physics question always depends: how would [the earth stop spinning]? If you can specify that, we can follow through with the consequences by solving the equations of motion for the Earth-Moon[-Sun] system.

For example, if you hypothesize that a giant comet large and fast enough to change the [Earth's rotation] impacted our planet, .... well, we would need to calculate the effect that such a large comet has on the orbits of Earth and everything else in the solar system, too. We could solve that problem by setting up an n-body problem to model the solar system, including Earth, Moon, Sun, and other planets; and we would use perturbation theory to study how sensitively the system reacts when we add in a new comet on a course to impact the moon. The results are difficult to compute, but this can be done in a reasonable amount of time with a reasonable amount of effort.

...

On the other hand, if you just want to make something up, "just imagine" that the [Earth] magically changes its [rotation], all bets are off. We can't meaningfully speculate what consequences follow when one law of physics breaks "because of magic." Anything could happen. Everything we know about the way the Moon's orbit couples into the Earth's rotation depends on the rules of physics as we currently understand them.

”

— Nimur

So - does that answer your question? Anything. Anything could happen. Nimur (talk) 01:00, 25 August 2012 (UTC)[reply]

So, hold on, how does a comet on a course to impact the moon cause the Earth to stop rotating? 203.27.72.5 (talk) 01:14, 25 August 2012 (UTC)[reply]

In general, it does not. You could conceivably concoct some unusual special circumstance where the angular momentum of the comet and the Earth's rotation were perfectly matched up so that it would cancel to zero after a collision, and then solve for the necessary conditions that would make such an impact possible. Nimur (talk) 04:06, 25 August 2012 (UTC)[reply]

I still don't see why the moon is coming into this... 203.27.72.5 (talk) 04:09, 25 August 2012 (UTC)[reply]

Also, my original comment was addressed to a similar question, linked above, about the moon ceasing to revolve around Earth, ... so that might be the source of the confusion. Nimur (talk) 04:11, 25 August 2012 (UTC)[reply]

The OP specified a gradual slowdown. At the very least, doesn't the rotation help distribute the heat through the atmosphere? If so, wouldn't the same side facing the sun all the time cause big-time trouble? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:59, 25 August 2012 (UTC)[reply]

Well, that raises an interesting problem to figure out, and that is what does "stop rotating" mean. Stop rotating relative to the sun (i.e. the solar day) or stop rotating relative to the background stars (i.e. the sidereal day)? In the former case, the same side faces the sun all the time (this is roughly what Mercury does, IIRC), but from an observer hanging outside the solar system, the earth would turn very slowly in order to maintain that same side facing the sun. In the latter case, the sun will rise and set (from the earth's perspective) over the course of a year, but an outside observer would view the earth as not rotating at all. Yet another complication from the poorly thought out question... --Jayron32 05:10, 25 August 2012 (UTC)[reply]

Mercury rotates at a rate such that the sun (roughly) stops at perihelion when the tide is strongest. —Tamfang (talk) 00:39, 26 August 2012 (UTC)[reply]

Um, Bugs, if the Earth 'stopped rotating', the same side wouldn't face the sun all the time, given that the Earth goes round it once a year... AndyTheGrump (talk) 05:07, 25 August 2012 (UTC)[reply]

OK, "stopped rotating" in relation to what? The Andromeda galaxy, perhaps? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:09, 25 August 2012 (UTC)[reply]

Ooo, can somebody link to that thought-experiment about a bucket of water rotating, and what it is rotating relative to? I can't remember what it was called, but I seem to recall that serious scientists disagreed and it included Einstein's opinion somewhere. 86.169.212.200 (talk) 14:42, 25 August 2012 (UTC)[reply]

I don't know a good link (I read about it in a book) but it is a very interesting thought experiment. The idea is that you can tell if a bucket of water (or just two masses joined by a pieces of string) is rotating just by looking at the shape of the surface of the water (if it is rotating, the surface will be curved), without reference to anything external. The question is then what happens to a bucket in an otherwise empty universe. It is meaningless to ask whether it is rotating or not because there is nothing for it to rotate relative to, so is the surface of the water curved or flat? (Or, is the pieces of string taut or slack.) I'm not aware of there being a generally accepted answer. --Tango (talk) 19:49, 25 August 2012 (UTC)[reply]

Bucket argument is the article. See also Mach's principle. -- BenRG (talk) 22:09, 25 August 2012 (UTC)[reply]

There was some National Geographic mockumentary about this idea, which I assume is where all the questions come from. I might offend the local copyright clergy if I post a link, but let's just say that "Aftermath: When the Earth Stops Spinning" is abundantly known to YouTube. See also [1] Wnt (talk) 12:43, 25 August 2012 (UTC)[reply]

However improbable stopping Earth's rotation is, we can still describe what conditions on Earth would be like. Assuming that the Earth becomes tidally-locked to the Sun, the Sun-facing side would be very hot, the far side very cold. This would induce powerful winds flowing along the surface from the dark side to the Sun-side, with high altitude winds in the opposite direction. It is likely that there will be a zone, with the Sun low on the horizon, where there would be begin conditions for human life. However, it is likely that most life would find it hard to adapt to 24hr sunlight, with no seasonal variation. CS Miller (talk) 14:04, 25 August 2012 (UTC)[reply]

If we're ignoring the physical effects of the transition, we can certainly ignore the biological effects. The idea of life living near the terminator on a tidally-locked planet has been explored in science fiction, but it would probably be difficult for complex life to thrive in such an environment. Simple life (bacteria, etc.) living underground where the extreme climate can't affect them should be fine, though. --Tango (talk) 15:11, 25 August 2012 (UTC)[reply]

But if the Earth became tidally locked to the Sun, then it wouldn't have stopped rotating: its rotation speed would be a year. If the Earth really stopped rotating, then one day would last a whole year, and you'd have six months of daylight and then six months of night (if I'm thinking correctly). Double sharp (talk) 05:39, 26 August 2012 (UTC)[reply]

I was going to say they would need to cancel As the World Turns, but they apparently already did so, preemptively. :-) StuRat (talk) 20:06, 25 August 2012 (UTC) [reply]

The Earth's rotation is already slowing due to tides and the expanding orbit of the moon. μηδείς (talk) 02:12, 26 August 2012 (UTC)[reply]

Take the OP's question as stated, without the carping about how it could be achieved. Assume that God, or Alien Overlords, either "Will" it, or apply "tractor beams" to slow the rotation over a reasonably long time, to avoid the H.G. Wells effect (from a story in which the Earth stopped abruptly, but people and things shot forward at their previous speed). Assume that "stoppage of rotation" means that one meridian has High Noon without change, and another 180 degree opposite meridian has perpetual Midnight. The Earth makes one rotation per year. Assume the Sun always shines over the Prime Meridian in Greenwich, (so the Sun "never sets on the British Empire.") London would get very, very hot, and likely become uninhabitable, as would much of Europe.Places along the International Dateline at the Antimeridian would get very, very cold, likely become uninhabitable, and agriculture there would become very difficult. Lots of ocean creatures would die from it being too hot or cold. The ocean near antimeridian might become permanently frozen. There would be a "Happy Medium," or "Goldilocks Zone," perhaps a bit Sunward from the 90th meridians east and west, only a small fraction of the present zone where people flourish, where the temperature and insolation would be most advantageous. A large portion of the population would likely starve, burn, freeze, or die in conflict as people sought to migrate to the place where it was not too hot and where crops could be grown. Some extreme weather might occur, with massive storms due to the vast temperature differential. Edison (talk) 04:10, 26 August 2012 (UTC) *[reply]

That's another star-deserving answer. One can posit the Earth slowing to no rotation relative to the sun due to long-term tidal slowing due to the moon. Once the Earth became tidally-locked, the effect would be as Edison said. See our article Aurelia and Blue Moon and the full free video, NGC Presents : Extraterrestrial. μηδείς (talk) 06:33, 26 August 2012 (UTC)[reply]

Edison, when you simply violate conservation of angular momentum, have you considered all the consequences? You've jumped straight in to analyzing how life will adjust to temperatures on a non-rotating planet, but you are assuming a lot of non-sequitors! In this hypothetical universe when angular momentum may magically just "disappear," what will happen to, for example, chemical reaction kinetics? Will life-forms still be able to metabolize glucose, now that we've obliterated fundamental rules about the way mass and inertia work? Will atomic or molecular structure still be stable in a universe that may freely "cancel" angular momentum without cause? Carping about how something happens is precisely what a scientific analysis is predicated on. Without an assumption of consistent physical law, validated by consistent observed phenomena, it's absolutely impossible to predict outcomes. Nimur (talk) 15:01, 26 August 2012 (UTC)[reply]

Why didn't the world enter a nuclear winter in the mid-20th Cent.?

Yes, this is two nuke-related questions in less than a week for me. I'm weird like that. Anyway...

These guys estimate that a "nuclear conflict ... with 100 Hiroshima-size weapons ... would significantly disrupt the global climate for at least a decade." By this chart's reckoning, 116 atomic bombs were detonated worldwide in 1958; 71 in 1961; 178 in 1962; and no less than fifty on a yearly basis from '63 through '80. However, according to this, there has been absolutely no measurable decrease in the amount of sunlight that reaches the earth's surface because of any nuclear detonation or series of detonations ever.

Is it just me or does all of this seem somewhat contradictory? Since most nuclear weapons are at least in the Hiroshima range (many of them larger by several orders of magnitude), and since we clearly had periods in the 20th century where well in excess of one hundred nuclear weapons were detonated within several months of each other, shouldn't we have seen some sort of effect on the weather, even a minor one, at some point between 1958 and 1980, given the estimate I initially quoted? Evanh2008 ^{(talk|contribs)} 01:29, 25 August 2012 (UTC)[reply]

The climactic effects of nuclear weapons come from burning lots of stuff (cities, forests, what have you) — it's about releasing carbon dioxide into the atmosphere. Only two of the nuclear weapons in the 20th century were set off over areas with significant stuff to burn. The others were set off on remote atolls or islands, in deserts, in the very high atmosphere, or underground (the majority). A more interesting question to me would be whether there were any measurable effects from the amount of carbon put into the atmosphere during World War II, when there were systematic programs of city burning perpetuated by many of the participants. As for mass burning affecting climate change in general, one of the theorized explanations for the Little Ice Age is a decrease (because of rapid depopulation) of planned burns that had gone on for centuries in the New World. Just an interesting idea. --Mr.98 (talk) 01:37, 25 August 2012 (UTC)[reply]

It's not about carbon dioxide. See Nuclear winter. It's about soot and other particulates that get kicked up into the atmosphere. 203.27.72.5 (talk) 01:51, 25 August 2012 (UTC)[reply]

Well, right, other stuff as well. My point still stands... --Mr.98 (talk) 23:25, 25 August 2012 (UTC)[reply]

Some researchers have speculated that we may have had a "petit nuclear winter" in the second half of last century [2]. 203.27.72.5 (talk) 02:17, 25 August 2012 (UTC)[reply]

Seems unlikely to have anything to do with testing, though. The amount of particulate matter added to the atmosphere by nuclear testing is but a drop in the ocean of human-added effluents in the late 20th century. The logic of that particular paper doesn't strike me as terribly compelling. --Mr.98 (talk) 23:25, 25 August 2012 (UTC)[reply]

I'm inclined to take that first source (claiming no effect) with something of a grain of salt; it was published in June 1957, prior to really large-scale atmospheric testing. (1956 had only 33 atmospheric tests, 1955 just 23; there were fewer than 20 per year between 1951 and 1955, and just 6 in total between the end of World War 2 and 1950.) Further, the publication was prepared by the Armed Forces Special Weapons Project of the Department of Defense—an agency that might have a certain interest in concluding that nuclear weapons use had fewer long-term hazardous effects. Even then, they acknowledge in the fine print that firestorms caused by large-scale conventional bombing had been known to affect weather; it seems to be splitting hairs to absolve the bomb for responsibility for the fires it starts.

When you look at the number of nuclear tests each year, you also need to consider where those tests occurred. (Take note of the terms of the various treaties described under Comprehensive Nuclear-Test-Ban Treaty.) While there were more than fifty tests per year from 1963 through 1980, there were fifty or more aboveground (atmospheric) tests in just '57, '58, '61, and '62. After 1963, there were never more than ten aboveground tests in any one year, and no such tests in most years. Underground tests – while certainly problematic for an assortment of reasons – would not be expected to have any major effect on climate. Tests that were conducted aboveground always took place in remote areas (deserts, oceans) where substantial fires would not be sustained by forests or buildings.

Finally, even if 1950s climate sensing and modelling technology failed to detect the effect of a few dozen explosions, one should not be sanguine about the effect of thousands of warheads (including large numbers of high-yield bombs) that could potentially be fired in a major nuclear exchange. TenOfAllTrades(talk) 04:40, 25 August 2012 (UTC)[reply]

Interestingly, there is a connection between climate change and nuclear weapons — but it's because many of the methods for making sense of climate change today originated in studying the dispersal of nuclear fallout. There was a good article on this recently in the Bulletin of the Atomic Scientists. (Incidentally, Samuel Glasstone was a very well-respected writer on the topic of nuclear weapons effects. Whatever he wrote then would have been accurate knowledge for its time. His Effects books — there are multiple editions — were government-produced works but they pulled no punches.) --Mr.98 (talk) 23:30, 25 August 2012 (UTC)[reply]

For real, measurable, global effects of nuclear testing, you may be interested in how bomb carbon factors in to carbon dating, as well as many other areas of Biogeochemistry. See e.g. [3] SemanticMantis (talk) 06:25, 25 August 2012 (UTC)[reply]

How many calories in a shot of vodka?

How many calories are in one shot (1.5 fl oz) of 80 proof vodka? Googling seems to give a variety of answers, but does about 100 calories per shot seem reasonable? Thank you, 99.92.102.199 (talk) 04:22, 25 August 2012 (UTC)[reply]

This site says there are 97 calories in a shot of Smirnoff 80 proof. Evanh2008 ^{(talk|contribs)} 04:27, 25 August 2012 (UTC)[reply]

This elegant website, http://nutritiondata.self.com gives excellent full nutritional data on all foods and beverages. It indicates 64 calories for one oz 80 proof. μηδείς (talk) 17:44, 25 August 2012 (UTC)[reply]

In Russia, vodka shoots you. Clarityfiend (talk) 21:36, 25 August 2012 (UTC)[reply]

Is that Yaakov Smirnov? μηδείς (talk) 02:10, 26 August 2012 (UTC)[reply]

Unless my subconscious is dredging up somebody's comedy routine, it's me. Or maybe it's the Smirnoff talking. Clarityfiend (talk) 04:48, 26 August 2012 (UTC)[reply]

That is definitely a take-off from a joke I have heard. μηδείς (talk) 05:01, 26 August 2012 (UTC) See http://avalon.power-rpg.com/t320-in-soviet-russia-jokes [reply]

I'm not taking credit for this subgenre of joke, only this particular instantiation (until somebody comes along and proves otherwise). Clarityfiend (talk) 07:15, 26 August 2012 (UTC) [reply]

Bad jokes cluttering the Ref Desk is one thing, must we pick them apart here as well? BigNate37_(T) 07:27, 26 August 2012 (UTC)[reply]

See Russian Reversal. Sorry... :) Wnt (talk) 12:07, 27 August 2012 (UTC)[reply]

Note that one shot in most countries is 1.5 ounces, so your figure of 64 roughly agrees with the 97–100 figures above. See Shot glass#Sizes. BigNate37_(T) 07:27, 26 August 2012 (UTC)[reply]

Wow, this was mentioned in the question itself, my bad. When I start missing things that obvious, it's time for bed. BigNate37_(T) 07:35, 26 August 2012 (UTC)[reply]

Kuiper belt object

Are those objects orbit around the sun or are they just flying around randomly?184.97.233.160 (talk) 05:08, 25 August 2012 (UTC)[reply]

The article indicates they're in orbit, e.g. one of its members, Pluto, is in a significantly elliptical orbit. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:20, 25 August 2012 (UTC)[reply]

Also note that "flying around randomly" isn't possible. Since "an object in motion stays in motion (at the same speed and direction) unless a force acts upon it", they would soon leave the solar system. Therefore, they must be gravitationally bound to some object in the solar system, in this case, the Sun. StuRat (talk) 06:01, 25 August 2012 (UTC)[reply]

Good point. Tell me if I'm wrong about the following: My assumption about the Big Bang is that immediately afterward, things were pretty much "flying around randomly". Over time, they began to coalesce into various objects, like stars and planets and of course galaxies. Given the many billions of years since then, would it not be the case that there are far fewer objects "flying around randomly" than there might have been after the beginning? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:07, 25 August 2012 (UTC)[reply]

Actually, the process is poorly understood, and we don't have a good answer for what happened. We know two things: from the Cosmic microwave background radiation we know that the very young universe was homogeneous: that is, it was evenly distributed and looked uniform in all directions and at all scales. The second thing we know is that it doesn't look like that today. What happened in between, that is what happened to cause the universe to go from a state of homogeneity to one of heterogeneity (from looking like milk to looking like cottage cheese) isn't well understood. This is explained at Structure formation. --Jayron32 06:15, 25 August 2012 (UTC)[reply]

"We know two things: from the Cosmic microwave background radiation we know that the very young universe was homogeneous: that is, it was evenly distributed and looked uniform in all directions and at all scales. The second thing we know is that it doesn't look like that today." actualy your post is partialy rong (at least if I have understood you correctly) because although the universe is not homogeneous at a small scale but it is homogenious at a large scale.

While it is tru that we do not know how the erly universe looked like the big bang article segests that there were far fewer objects "flying around randomly" just after the big bang than there are nau.Aliafroz1901 (talk) 10:32, 25 August 2012 (UTC)[reply]

What the universe looks like on a large scale is dependent on what the shape of the universe is, which is also something we don't know. If the universe is really infinite in extent, then yes, it is perfectly homogeneous on a large enough scale, because trivially any local unevenness "smooths out" when looked at from the perspective of infinity. The problem is a) this isn't exactly the same as what I said above, because in the early universe it was homogeneous at all scales, not just if you back out to (near) infinity. That is, under our current understanding of the early universe, it doesn't matter whether you look at it on the atomic scale, the human scale, the solar system scale, or the entire universe scale, it would all look homogeneous. Today, the only scale that may work on (and again, it depends on what the universe really looks like, which we don't have a firm grasp on at that scale) is the "entire universe scale". Today, the universe is decidedly heterogeneous on all other scales, rather self-evidently: I'm standing here, and I'm not standing over there. There's star material in some places, and not in others. There are atoms and molecules, and then there are places with empty space. In the early universe, this wasn't true. It was all a uniform matter/energy soup. The mystery is how it got from that state to what we have now. --Jayron32 14:20, 25 August 2012 (UTC)[reply]

That's not a mystery. Things gravitated together. The details may be complicated but we do basically know what happened. Biological evolution is very complicated but it would be misleading to say that there were only prokaryotes a few billion years ago and there are humans now and it's a mystery how that change happened. -- BenRG (talk) 21:52, 25 August 2012 (UTC)[reply]

On a very fuzzy level, we know that there were "perturbations" which caused local areas of higher density, which lead to a sort of gravitational positive feedback that led to objects coalessing out of the soup. Cosmological perturbation theory does a nice job of explaining what it would look like (though the current article looks like a technical glossary vomited all over it, and covered up any text which may be useful to the lay reader), but it still isn't well understood what the antecedants for the events that led to structure formation were. There's a lot of handwaving going on that still needs to be resolved by physics. --Jayron32 05:09, 26 August 2012 (UTC)[reply]

Why would there be things that could gravitate together? In a truly homogeneous universe, there is absolutely nothing different between here and there. One of the greatest unanswered questions is where the present inhomogeneity originated from. Was itnhomogeneity always present, but latent, in some kind of hidden-variable of an otherwise homogeneous soup? Or was the early universe always inhomogeneous? Nimur (talk) 15:12, 26 August 2012 (UTC)[reply]

COBE found fluctuations in the temperature of the cosmic microwave background in 1992, shown in this famous image. This was one of the most important experimental results in the history of modern cosmology and a key piece of evidence that big bang cosmology (as opposed to some steady-state cosmology) is actually correct and the CMB is a relic of the early universe. Inflation predicts fluctuations with a spectrum that matches what was seen by COBE (and later refined by WMAP). Both of you sound as though you've never heard of this. -- BenRG (talk) 05:37, 27 August 2012 (UTC)[reply]

A better solution than chastising us then is to fix the relevent Wikipedia articles. I can only report to readers here what I find when reading the relevent articles I link to, and if it says, as it does, at Structure formation, that this is a, and I quote, "largely unsolved" problem. If what that is supposed to say is "well-understood and mostly figured out" than it shouldn't say "largely unsolved" then, n'est ce pas? You could also, you know, take a crack at the 90% of the physics and cosmology articles whose text is entirely unreadable by anyone except a select few people, but that might also be asking too much. --Jayron32 05:44, 27 August 2012 (UTC)[reply]

I'm familiar with the COBE spacecraft and its follow-on missions to map the cosmic background radiation. Of course I've seen the pictures, and it's trivial to recognize the obvious inhomogeneity in the experimental result. But I have no shame in admitting my limitations: as I understand the theory, nothing yet explains this observation - at least, not in a way I understand. This physics is sufficiently complicated that it was worth the 2006 Nobel prize. BenRG stated: "inflation predicts fluctuations"... but this is not an obviously-true statement. If his statement is, in fact, valid, then it's predicated on some very difficult theoretical work about inflation. I'll second Jayron's request: please improve the relevant articles, and help us find the appropriate source material. From what I read, the observations only result in more questions about early universe cosmology. And, as I read efforts to explain initial condition, I see a lot of effort to dodge this question: was the very early universe inhomogeneous? Nimur (talk) 16:47, 27 August 2012 (UTC)[reply]

Correct, and I never said you were fully rong-what I said was that you were partialy rong (which you mite not be of course).Aliafroz1901 (talk) 14:46, 25 August 2012 (UTC)[reply]

What I mean is are "ALL" the Kuiper belt objects are orbiting around the sun? What if some of them are too far away for the sun gravity or anything gravity to act upon them so aren't they just flying around randomly or just stand still? (I know they are, including the Solar system, also spinning around the galaxy too, in the big picture) Anyway they could flying around randomly in a smaller scale compare to galaxy scale. Just like Earth is orbiting the Sun but bigger scale, the Earth is also spinning around the Milky way galaxy.184.97.233.160 (talk) 08:03, 25 August 2012 (UTC)[reply]

Gravitation has an infinite range. Everything in the belt is under the influence of the sun's gravity. If they were standing still relative to the sun for an instant, they would still accelerate towards it and begin to move in it's direction. 203.27.72.5 (talk) 08:20, 25 August 2012 (UTC)[reply]

True, but at some distance objects will never complete an orbit during the life of the universe, so saying it is "in orbit" seems iffy. StuRat (talk) 08:32, 25 August 2012 (UTC)[reply]

The Kuiper Belt, and the Solar System itself, are defined as objects which are gravitational bound to the Sun. So, if some object is just "passing through" the Kuiper belt, fast enough to not fall into orbit, it isn't really a Kuiper Belt object (although it might be mistaken for one until it's motion is charted). StuRat (talk) 08:30, 25 August 2012 (UTC)[reply]

It is certainly possible to have objects passing through the solar system without being gravitationally bound to the sun (that is, without being in a closed orbit). They need to be moving quite fast, though. In fact, we can quite easily work out how fast. I will ignore any complications from interactions with planets or light pressure or any of that stuff, and just treat the situation as a simple 2-body problem. The thing that determines whether an object is in an open or closed orbit (ie. whether it can reach infinite distance or not) is its total energy, it's gravitational potential energy plus its kinetic energy. Note, gravitational potential energy is defined, for convenience, to be zero at infinity and to get more and more negative as you get closer to an object (this seems really weird, but you'll see why it is useful in a second). The total energy of an object will be the same at all points in its orbit (conversation of energy). If that total is positive, then that means the object will still have positive speed at infinite distance, so it is an open orbit. If the total is zero, then it will "come to rest at infinity", so it can reach infinity but only just. If the total is negative, then it would need to have negative kinetic energy at infinity, which can't happen, so the object can't reach infinity - this means it is a closed orbit.

So, to figure out how fast an object needs to be going to avoid being captured by the sun, we just need to calculate the (negative) potential energy at a particular distance and work out what velocity gives an equal (but positive) kinetic energy. Pluto is, on average, about 6 billion km from the sun, so let's use that as our example distance. Using the formula at gravitational potential energy, we get the potential energy (of a 1kg object - mass will cancel out when we calculate the speed, so it doesn't matter) to be 22 megajoules. If we convert that into a speed (using E=1/2 mv²) , we get about 6.6 km/s. Pluto's average orbit speed is 4.7 km/s (average speed isn't quite the same as speed at average distance, but it is close enough) so we can see that it is easily in orbit around the Sun. An object at the same distance travelling about 40% faster would not be in orbit and would eventually escape. --Tango (talk) 13:20, 25 August 2012 (UTC)[reply]

So what happen for the objects that outside the belt or outside of the Solar system? Are they going to fly around randomly?184.97.225.6 (talk) 21:30, 25 August 2012 (UTC)[reply]

Hopefully you'll find the Hill sphere article informative. If a body's orbit falls entirely within the Sun's Hill sphere (take a note of the calculation in that article's talk page, and at Talk:Comet, for some estimates about the diameter of the Sun's Hill sphere; it's bigger than once thought - big enough to encompass the Oort cloud). For some body in the galaxy whose path doesn't fall entirely within the Sun's Hill sphere, you wouldn't say it orbited the Sun. It might be within the Hill sphere of another star (or star group, like Alpha Centauri), so you'd say it orbited that, and its path would follow an elliptical orbit around that system's barycentre. But it might not be, so it would orbit the galaxy's barycentre, as the Sun does. The galaxy is mostly empty, so such an object could go a billion years without its orbit happening to take it close enough to something else - when it did, that could bend that nice mathematical ellipse a bit (but mostly not close enough for it to be captured in that something else's system). Although all the stuff orbiting in the galaxy is chaotic (it's a colossal n-body problem) it's not random or arbitrary; for most such things orbiting the galaxy's barycentre, their orbits are of near-mathematical elliptical perfection, over very lengthy periods of time. -- Finlay McWalterჷTalk 23:43, 25 August 2012 (UTC)[reply]

Estuary

"pollutants including heavy metals, PCBs, radionuclides and hydrocarbons from sewage inputs". What is the PCBs in this context stands for?184.97.233.160 (talk) 08:04, 25 August 2012 (UTC)[reply]

Polychlorinated_biphenyl 109.144.167.204 (talk) 08:09, 25 August 2012 (UTC)[reply]

Vaporizer, cannibis

Is it true that a vaporizer will virtually eliminate any risk of lung cancer or other cancers related to smoking? And is it possible to use a vaporizer with tobacco? ScienceApe (talk) 15:48, 25 August 2012 (UTC)[reply]

Only if you don't inhale. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:04, 25 August 2012 (UTC)[reply]

Wikipedia has an article titled Vaporizer (cannabis) which has some information you may seek. I don't know of the use of tobacco in cannabis vaporizers, but the have recently hit the market Electronic cigarettes which may or may not be similar in construction and use. --Jayron32 16:38, 25 August 2012 (UTC)[reply]

Unlike nicotine, cannabinol is a rather heavy molecule and not water-soluble. Vaporizers won't work at all well. Cleaning marijuana of stems and seeds and steeping it in hot but not boiling melted butter before then cooking the mixture in brownies will totally avoid the lungs, but not fat or cholesterol. μηδείς (talk) 17:39, 25 August 2012 (UTC)[reply]

Assuming inhalers are possible for THC, it might reduce the risk, since presumably there would be less "tar", but inhaling any foreign substance into the lungs carries some risk. Also note that the THC itself may continue to cause other problems, such as memory loss. StuRat (talk) 18:54, 25 August 2012 (UTC)[reply]

Note that the safety of vaporizers is being presumed - given the legal obstacles and recent nature of the advance, I doubt there have been large, careful, long-term studies. Remember that it takes only a small amount of a carcinogen to cause harm, and any new process of heating and other processing potentially could create one. It seems like a good bet that it's a good idea, but in biology only the actual data can give an answer. Wnt (talk) 20:15, 25 August 2012 (UTC)[reply]

Responding to Medeis - cannabis vaporizers do not rely on water solubility. I can't speak to their effect on health, but I do know that they are capable of delivering THC to the lungs. thx1138 (talk) 17:55, 27 August 2012 (UTC)[reply]

Yes, according to the article they heat the oils to near their flash points. μηδείς (talk) 18:18, 27 August 2012 (UTC)[reply]

Why do different air masses equilibriate slowly ?

When I open my refrigerator door to the open air, or an oven door, the air masses inside them equilibriate very quickly, generally within 15-30 minutes. Why does this not scale for large air masses in the atmosphere? 128.143.1.192 (talk) 23:00, 25 August 2012 (UTC)[reply]

Are you sure it doesn't scale ? That is, does 1000 times the volume take 1000 times as long to reach equilibrium ?

That 15-30 minutes is probably only that long because the solid components or contents of the oven or fridge continue to give off or absorb heat over that period. Similarly, heat is being added to the atmosphere from the Sun and ground/water, and removed by radiation into space, at all times, so never really reaches an equilibrium.

There are also differences in scale regarding what type of heat transfer occurs the most (radiation, convection, etc.). StuRat (talk) 23:11, 25 August 2012 (UTC)[reply]

Yes, there's wind and convection and so forth and yet a stationary front can take several days to become a shear line (when the sharp contrast ceases to exist and becomes more of a diffuse gradient). Why is it so slow? 128.143.1.192 (talk) 00:16, 26 August 2012 (UTC)[reply]

I would be quite surprised if such transfers scaled linearly (1000 times the volume takes 1000 times as long) due to the square-cube law (specifically surface-area-to-volume ratio effects). The amount of heat energy an air mass has scales with it's volume. 1000 times the volume of air means 1000 times the amount of heat energy which needs to be transferred to equilibration. However, the transfer itself only occurs on the interface between the two air masses. The interface and interface-related effects don't typically scale as the volume, but as the surface area. An airmass of the same shape but with 1000 times the volume would not have 1000 times the surface area, but only 100 times the surface area. Thus naively you would expect the heat transfer (if it proceeds by exactly the same process in the two cases) to take 1000/100 = 10 times as long for the larger air mass. Of course, the relevant surface area and interface effects aren't going to scale *exactly* 100 fold, and with the larger air mass there may be different effects (wind generation and Coriolis effects may come into play, etc.), but the square-cube law gives a good first-order approximation as to why a small mass cools faster than a large mass. -- 205.175.124.30 (talk) 01:35, 26 August 2012 (UTC)[reply]

Also, how good is the adiabatic approximation in the weather modelling of air mass interactions? 128.143.1.192 (talk) 23:01, 25 August 2012 (UTC)[reply]

Buoyancy driven flow is governed by the Richardson number. Robinh (talk) 01:28, 27 August 2012 (UTC)[reply]

DNA

Whats the significance of knowing that DNA is double helix? 203.112.82.2 (talk) 23:25, 25 August 2012 (UTC)[reply]

1) It's rather critical to knowing how it replicates (it unzips and both halves then form a new complete strand).

2) It's also critical to knowing how the genes are stored. StuRat (talk) 23:32, 25 August 2012 (UTC)[reply]

Actrually, neither of those necessitates the "double helix". If it just looked like a long ladder, it would still need to unzip to decode, and it would still replicate the same way. The deal with the double helix is is that it is a very efficient means of storing the information. If you think about how a telephone cord used to look (back when people had corded phones in their house), it's coiled up. The fact that DNA is coiled (rather than straight) allows it to fit a longer chain into a tighter space, and that improves the amount of information you can fit onto it. There's limited space inside a nucleus of a cell, and the way that DNA is coiled greatly effects how much information you can cram into it. The tertiary structure of DNA (how the double helix itself is packed) is also very important in this regard. --Jayron32 00:50, 26 August 2012 (UTC)[reply]

There's a nice diagram of that here. Coils upon coils upon coils. --Mr.98 (talk) 01:29, 26 August 2012 (UTC)[reply]

(ec) There is a famous line at the end of the original Watson and Crick paper: "It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.". That was all they said about it at the time, but it was enough. Looie496 (talk) 00:51, 26 August 2012 (UTC)[reply]

Yes, but the base-pair organization doesn't have much to do with the double-helix structure. ~~RNA, for example, doesn't form double helixes.~~ It forms Stem-loop structures. The base-pair organization explains how DNA codes for gentic information, the double helix helps explain how DNA codes for so much information because it allows the DNA to fit more information bits into a much tighter space than a straight chain would. --Jayron32 01:11, 26 August 2012 (UTC)[reply]

RNA doesn't form double helices? Hmm... that'll be a big disappointment to the double-stranded RNA viruses and other organisms and cellular functions that depend on dsRNA (which include stem-loop structures, which are - double helical!). dsRNA tends to take on A-form double helical conformation. -- Scray (talk) 02:30, 26 August 2012 (UTC)[reply]

Yeah, you're right. I'm an idiot. Carry on. --Jayron32 05:01, 26 August 2012 (UTC)[reply]

To be clear, every nucleic acid, DNA and RNA alike, replicates based on a double-helix structure. In the case of RNA transcription, the DNA strands are parted and one is replicated by forming a temporary DNA-RNA double helix structure. In a sense, even the translation of proteins from RNA is based on the double helix, in the sense that tRNA base-pairs with the RNA on the ribosome. The double helix is important for lining up the right nucleotides for replication, for checking for errors afterward, but also for maintaining relative inactivity of the sequence afterward - a simple double-stranded RNA won't act as a ribozyme because it's just a straight rod, at least at the small scale relevant to forming catalytic sites. There are, of course, a great many little oddities that you could mention in regard to it - artificial nanoscale engineering of complex structures, sequence-specific reception of radio-frequency or terahertz signals, the ability of supercoiling to convert overall torsion of the structure into a separation of strands, or vice versa, the ability to nick the structure so that topoisomerase I can release said supercoiling, under control, the ability of PCNA and other proteins to clamp onto the strand and run it like a more or less smooth "string" through holes in a protein complex ... there must be thousands of specific relevant significances. Wnt (talk) 03:40, 26 August 2012 (UTC)[reply]

Now, that is a great answer... Well explained, Wnt. --Jayron32 05:01, 26 August 2012 (UTC)[reply]

August 26

landers and boulders

Neil Armstrong steered the Eagle to avoid a boulder field at the last minute. What can unmanned landers do about boulders? In this movie of Curiosity's descent someone says "We've found a nice flat place"; does that mean the lander had a way to look for one, or merely that "we" got lucky? —Tamfang (talk) 00:47, 26 August 2012 (UTC)[reply]

Mars today is much better mapped than the moon was during the 1960s. I wouldn't doubt that we have high resolution maps of the surface of Mars to a similar level that we have on earth; that was part of the idea of previous Mars missions like the Mars Reconnaissance Orbiter, which among its multifaceted mission is to scout and plan for landing sites for landers. --Jayron32 00:53, 26 August 2012 (UTC)[reply]

(ec)Recent landers on Mars and the Moon have benefited from surveys from long-term orbiting spacecraft like Mars Global Surveyor. That gives the mission planners a map from which they can select especially boulder-free areas. They pick an area quite a bit bigger than the error-bars for their lander's anticipated landing. -- Finlay McWalterჷTalk 00:58, 26 August 2012 (UTC)[reply]

It's worth mentioning the Lunar Orbiter program, the satellites which scouted the moon for Apollo landing sites. These remarkable gadgets exposed film, developed it themselves when orbiting the moon, and then tv-scanned the results back to Earth. They got a 2m resolution of the selected sites. The current Lunar Reconnaissance Orbiter gets about 0.5m resolution (so 16 times more data). Because its digital cameras aren't going to run out of film it can re-survey the same location over and over, when the Sun is at a different angle: comparing the shadows on different pictures gives further clues as to the terrain. -- Finlay McWalterჷTalk 01:44, 26 August 2012 (UTC)[reply]

This NASA blog entry implies that mission planners relied on whatever surveys were available (for the Curiosity mission, those would be 0.3 meter resolution surveys from the Mars Reconnaissance Orbiter) to select a region that was as boulder-free as possible, and then prayed like crazy that they didn't make an unlucky landing. TenOfAllTrades(talk) 03:59, 26 August 2012 (UTC)[reply]

In 2006 we had better images from Mars (Mars Reconnaissance Orbiter) than we were allowed to get from earth (military satellites made better immages but they were not available to everybody). Viking did a landing with very little knowledge on the places they landed. It seems that Nasa was lucky many times not to hit a rock or fall into a gully. --Stone (talk) 08:40, 27 August 2012 (UTC)[reply]

The only instrument Curiosity had for measuring the surface was an altimeter that returned a single value. The altimeter couldn't even be pointed, and measured the distance to wherever it happened to be pointed due to the spacecraft's oscillations. The descent imager, MARDI, imaged the surface during descent, but its images were not used to guide the descent in any way.

I think when mission control said "we've found a nice flat place", what they mean is that Curiosity avoided the black line and impact craters inside the landing ellipse: http://www.redorbit.com/media/gallery/mars-science-laboratory/573690main_pia14295-anno-full_full.jpg. The black material is sand dunes, the same ones in Curiosity's images from the surface, which aren't as flat as the rest of the landing area and are composed of soft sand that the rover easily sinks into. I don't know how mission control knew the rover had avoided those areas--presumably the tracking was accurate enough to determine that. --99.227.95.108 (talk) 05:26, 26 August 2012 (UTC)[reply]

The Opportunity rover famously landed by chance in 2004 in the middle of a crater (later named Eagle crater) in the generally flat and featureless Meridiani Plain. I assume the plain was chosen because it didn't have rock fields that might bog down or damage the rover, so the crater was a surprise. The scientists were not aiming for it nor did they even know it existed. The landing site itself was 25 km off-target.-- OBSIDIAN†SOUL 05:35, 26 August 2012 (UTC)[reply]

The landing site selection is done from two sides. The scientists choose places which are interesting and the engineers choose flat low areas. The landing ellipse has to be very save. When you built a rover with 5km drive distance and a landing ellipse of 100km you end up in the not that interesting area chosen by the engineers. With a rover with 50km drive distance and a landing ellipse of 20kmyou might be lucky. For a fixed lander like phoenix you have to take more risk.--Stone (talk) 08:40, 27 August 2012 (UTC)[reply]

re: "...and are composed of soft sand that the rover easily sinks into". They may be indurated, but I'm really looking forward to Curiosity having a look at them. Quite a lot of work has been done on dunefields in Gale crater and Curiosity has to get through that one. It certainly looks like it's active, or at least the ripples on the dunes are, according to a COSI-Corr analysis using HiRISE imagery. Sean.hoyland - talk 10:07, 27 August 2012 (UTC)[reply]

Is It Possible to Change One's "Handedness"?

Is it possible in certain cases to become able to write well with one's right hand when one was born left-handed (not ambidextrous), or vice versa? The reason I'm asking is that my dad was born left-handed but was forced to learn to write with his right hand in school, and is now able to write well with both hands (despite not being able to do this before). In contrast, I've heard and read that most left-handed people are unable to become able to write will with their right hand. My question is how frequent are cases like my dad's and why was my dad much more capable in this than most other people? Futurist110 (talk) 06:00, 26 August 2012 (UTC)[reply]

It simply takes practice. What do you think happens when people lose a limb? My father was beaten out of using his left hand, my sister wrote backwards for years with her left hand, and her son writes with both hands now, boustrophedonically. μηδείς (talk) 06:49, 26 August 2012 (UTC)[reply]

I assume King George VI wrote legibly. Clarityfiend (talk) 07:11, 26 August 2012 (UTC)[reply]

It was common in Australia up until the 1950's for primary school teachers, particularly with older teachers, to enforce writing with the right hand. However, it was later considered undesirable to force handedness. Theres was, supposedly, evidence that that if you were born left-handed, and if you were forced to be right-handed, then you would stutter or have some other speech impediment. I myself was born left handed, and made to write right-handed by a particularly nasty Grade 1 thru Grade 3 teacher. It happens that I did stutter for a while, but I managed to cure that in my 20's. Coincidence? A matter of how the brain is wired up, and some part forced to do what it was not intended to do? Could be. Incidentally, for years I could use tools equally well in either hand. Looking back, I reckon that schoolteacher did me a favour. Some things, such as guns & chainsaws, are dangerous for a left-hander to use, and being able to swap hands to do things is a great party trick. Wickwack124.182.52.89 (talk) 08:26, 26 August 2012 (UTC)[reply]

That attitude lingered for some time. My younger son is now 27 and has always been left-handed. When he first started exhibiting this, my mother was most concerned, and suggested we do something to nip what she saw as a negative trait in the bud. We respectfully declined to follow her advice. -- ♬ Jack of Oz ♬ ^{[your turn]} 09:14, 26 August 2012 (UTC)[reply]

My husband also was forced to use his right hand at school but is now totally ambidextrous. I can't tell which hand he's used to write something with. As has been said, it's practice. --TammyMoet (talk) 08:45, 26 August 2012 (UTC)[reply]

I'm right-handed, but when a colleague invited me to go trap shooting I decided to try it left-handed, because my left eye is the one that's better for distance. I hit two targets out of 25. But who knows — maybe I wouldn't have hit any, right-handed. Never did try it again to find out. --Trovatore (talk) 09:21, 26 August 2012 (UTC)[reply]

My right eye is the best, for both distance and close up. But my left ear is the clearest hearing. I think all these things are unrelated. Wickwack124.182.52.89 (talk) 10:40, 26 August 2012 (UTC)[reply]

Unrelated? Have you never heard of "The Fundamental Interconnectedness of All Things"? -- ♬ Jack of Oz ♬ ^{[your turn]} 12:59, 26 August 2012 (UTC)[reply]

In target shooting and archery, eye dominance is more important than handedness in determining whether you should shoot left or right handed. For about 30% of people, eye dominance and handedness are different, which is known as being "cross dominant". Alansplodge (talk) 02:12, 27 August 2012 (UTC)[reply]

I've done the little tests for eye dominance but I've never been quite sure what the results mean. My eyes have different focal lengths and I think that swamps any neurological difference. --Trovatore (talk) 03:06, 27 August 2012 (UTC)[reply]

A few people have "central vision" (ie neither eye is dominant) - this article tells all. Alansplodge (talk) 10:58, 27 August 2012 (UTC)[reply]

The U.S. president James A. Garfield could write equally well with both hands. As a parlor trick, he trained himself to write simultaneously, but different passages, with each hand. It isn't mentioned in his main article, but List of multilingual Presidents of the United States notes that he would write in Latin with one hand and Greek with the other. --Jayron32 02:16, 27 August 2012 (UTC)[reply]

See http://www.jneurosci.org/content/27/29/7847.full.

—Wavelength (talk) 02:37, 27 August 2012 (UTC)[reply]

Naked images from interstices in fabric?

This one literally came to me in a dream. :) With the ever-increasing resolution of gigapixel images and increasing camera speed and precision of digital photos to make it meaningful, is it possible to look at a seemingly routine photo of someone wearing a light fabric which is commonly regarded as opaque, and have software pick out specifically the holes in the fabric and interpolate them into a naked image? Or for fabric without any holes, however small, with some further processing, to automatically infer effective hole values by comparing the values from the spots where the fabric is thickest and thinnest? Wnt (talk) 10:40, 26 August 2012 (UTC)[reply]

The ultimate resolution of a camera is set by fundamental principles of optics. Diffraction sets a limit on the detail that can be resolved, so utilising the holes to look through a fabric would not be possible unless the fabric is so open you can do it with your own eyes (assuming your eyes are good). Some facility is possible by using an extended color response and filtering. Some fabrics have partial infrared transparency. I remember some early (1950's) colour transparency films had an extended infrared response and, depending on the dress material, would sometimes reveal a lady's underclothing and legs outline that was not visible to the naked eye, generally blury because of lens chromatic aberation. See http://en.wikipedia.org/wiki/Diffraction-limited Wickwack124.182.52.89 (talk) 11:23, 26 August 2012 (UTC)[reply]

I don't think the size of the gaps between individual threads in a piece of clothing is anywhere near the diffraction limit. :) While it is possible that the eye comes near this limit in observing detail, a camera with a larger CCD chip or a higher zoom level should not, I think. The point of the idea was that in a high-resolution image the individual swatches of non-fabric color can be joined together in an image, removing the distracting impression of the fabric. Wnt (talk) 12:01, 27 August 2012 (UTC)~[reply]

If the eye can't do the job, and is operating near the diffraction limit, then obviously a camera can't do it either. Wickwack60.228.241.5 (talk) 15:14, 27 August 2012 (UTC)[reply]

Optics, image size, and other possible things apart… I think you can have any given image with some area you want to leave (in your case, the skin, ->‘As’) and other area that you want to replace (the cloth, ->‘Ac’) and all depends of the relationship of this two areas, ‘As/Ac’ if there is too much ‘Ac’ or not enough ‘As’ is very probable that the interpolation algorithm will not work properly.

Some fabrics are a little bit trasnparent to the eye. That's because the eys is doing the interpolation between the threads and the gaps, as the thread pitch is too fine for the eye to behold. Its the same thing as you not seeing the dots in your computer monitor image unless you peer very closely. Do you realy think an camera is going to be different, unless it senses wavelengths the eye cannot. Sheesh. Wickwack60.228.241.5 (talk) 15:14, 27 August 2012 (UTC)[reply]

But even in the case you have enough ‘As’ there is not 100% certainty that you will have an accurate result, this will depends on the interpolation algorithm

Perhaps you will end faster by telling the lady: honey… clothes off!! And then taking the picture!

Iskánder Vigoa Pérez 14:34, 27 August 2012 (UTC)

If by "end" you mean "be mocked mercilessly". -- NellieBlyMobile (talk) 16:47, 29 August 2012 (UTC)[reply]

Does Unriped fruits contain less sugars?

Or, in other words, does they potentially makes u less fat?, thanks from all heart !!! 109.64.151.131 (talk) 13:21, 26 August 2012 (UTC)[reply]

Yes, unripe fruit contains less sugar. But since it also contains less flavor, I don't think that's a reasonable way to avoid gaining weight. You might as well eat paper, which contains no sugar at all. Looie496 (talk) 17:31, 26 August 2012 (UTC)[reply]

Just because the starches have yet to be broken down into simpler sugars via enzymes does not mean there will be less carbohydrate-based calories, though. As an amateur brewer I say this because of my understanding of malting, not from scientific background per se, so take it with a grain of salt. I recommend reading Starch#Starch sugars and Fruit ripening#Ripening indicators for a start, since those bits of reading are less technical in nature. This LiveStrong.com article seems to be implying that starches and sugars in bananas both have the same calorie/gram concentration. Diastase is a particular type of enzyme, and that article may shed more light into exactly what goes on, should you be interested in technical reading to determine the caloric difference in these processes. BigNate37_(T) 17:48, 26 August 2012 (UTC)[reply]

With a grain of salt? Would this equate to homoeopathic Burtonising? {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 14:34, 28 August 2012 (UTC)[reply]

It isn't just calories/gram however that effects how carbohydrates affect things like weight gain, however. The glycemic index also is relevent: foods with a high glycemic index cause rapid spikes in blood sugar, and lower GI foods cause a more steady, slower increase in blood sugar. Higher GI foods have an association with greater weight gain and also with things like type-II diabetes, so it isn't just how many calories you are getting, the source of the calories has an effect on how your body processes the food and the effect it has on weight gain. --Jayron32 02:09, 27 August 2012 (UTC)[reply]

Rather than eat unripe fruit, I suggest you mix ripe fruit with something that needs sweetening to be palatable, like shredded wheat cereal and milk. This is a better approach than either adding table sugar or buying sweetened cereal (fructose may be healthier than sucrose, and especially sweeteners like corn syrup) . StuRat (talk) 10:02, 27 August 2012 (UTC)[reply]

No medical advice, StuRat ... after all, he could have gluten intolerance or something. ;) Besides, in terms of calories, there's little difference between sugar and starch - only the fiber portion of the wheat would be advantageous. Wnt (talk) 12:03, 27 August 2012 (UTC)[reply]

As previously mentioned, there's the glycemic index. Also, unsweetened wheat cereals have other nutrients besides fiber (some of which are due to fortifying the cereals): [4]. Another good option is adding ripe fruit to unsweetened oatmeal (the real stuff in the cylinders, not the crap in the packets). StuRat (talk) 12:15, 27 August 2012 (UTC)[reply]

-- Good point! I was reading the headline, missed the question. The calories in sugar are the same, but the effect on weight can be different because it triggers insulin production (thus fat accumulation) rather than slowly sustaining metabolism. Wnt (talk) 03:11, 29 August 2012 (UTC)[reply]

Men always taller than their mothers?

An acquaintance recently told me that except for congenital disorders and diseases mature male humans are always taller than their mothers. Is it true? Roger (talk) 14:05, 26 August 2012 (UTC)[reply]

Factors affecting height are discussed in Human height#Determinants of growth and height. A number of factors make the probability that a son will not be taller than his mother quite low. However, if a tall woman has a son by a short father, the probaility is increased - congenital disorders and diseases are not required. A mother who was quite young at the time of birth, perhaps food shortages during the early life of the son, and moving to a cold climate may increase the probability. In western countries, there was an improvement in food quality in the years 1850 to 1950. This has apparently resulted in a gradual increase in height. Since then, food quality has not usefully improved, so the probality of a son not taller than his mother has increased slightly. Wickwack124.182.52.89 (talk) 14:58, 26 August 2012 (UTC)[reply]

(ec) The short answer is 'no', but men are often taller than their mothers, for a number of reasons.

Men are, on average, taller than women, so if you were to randomly select one man and one completely unrelated woman from the population there's still a better-than-even chance he'll be taller than her.
The average adult height has been increasing for decades. The typical individual born twenty years ago is taller than one born forty years ago, who is in turn taller than one born sixty years ago. (This can be attributed to a range of lifestyle and medical changes.) [5]
Even on an otherwise identical genetic background, a male will tend to reach a taller adult height than a female. (This follows plausibly from the first point.) In other words, your mother would likely have been taller if she had swapped an X for a Y chromosome at conception, and her (his?) body had been exposed to the usual male complement and doses of hormones. This assumption may break down if she had a 'tall' variant of one of the genes affecting human height on the chromosome you swapped out.
Most women, for cultural reasons (and/or evolutionarily-driven cues), procreate with men who are taller than they are.

Put all of those together, and you get the observed result—most male children are taller than their mothers. That said, neither congenital disorders nor disease would be required to explain a short son. The easiest case is where Mom is tall and Dad is rather short; you'd expect their offspring's height to – on average – fall somewhere in the middle, and if their height disparity is sufficiently large then even the top-ups Son gets from being male, born in a later decade, and with access to better health care and food won't make him taller than Mom.

That said, you can certainly get ahealthy Son shorter than both Mom and Dad. So far there are something like two hundred genes that have been associated with human adult height. Aside from the ones on Dad's X and Y chromosomes, both parents carry two copies (sometimes the same, often different) of each of those genes. In the random lottery of conception, Son gets one copy from each parent; if he's particularly (un)lucky, he gets the 'short' copy of most of those, and ends up shorter than Mom. TenOfAllTrades(talk) 15:05, 26 August 2012 (UTC)[reply]

The paper [6] cited by TenOfAllTrades may be skewed - it focused on European countries. I think that if it included data from North America and British Commonwealth contries, it would be shown that in recent decades height has not increased. In Australia, there was a drop in height after each World War - it is thought that taller men are more likely to be killed in trench and jungle warfare - a sor of evolutionary selection for low height. Wickwack124.182.52.89 (talk) 15:16, 26 August 2012 (UTC)[reply]

[7] suggests average height has been increasing in Australia, but not by much. Similarly [8] for the US. Both sources concur the increase in recent times hasn't been as much as in many European countries. Nil Einne (talk) 17:01, 26 August 2012 (UTC)[reply]

I found Nil Einne's first reference interesting until I got to the part where it says human evolutionary change is speeding up - that's a startling claim. Then when I got to the part where it implies this is happened within the last 80 years - that destroyed the article's credibility for me. Evolution can only happen if the evolutionary presure affects the death rate of folk before they have children, or affects the birth rate, or affects the survivability of children, either directly, or in some cases, affecting survivability thru the availability of older parents and grandparents. In Western countries in the last 80 years, improved medical care & cultural change has removed all these factors. We have just about stopped human evolution.

The second reference only talks about height increase in children, which has increased due to high calory diets causing earlier growth spurts. Its a different thingsto what the OP was asking. Wickwack22:59, 26 August 2012 (UTC) — Preceding unsigned comment added by 124.178.50.4 (talk)

Careful, selective pressure can also be based on sexual selection, as well as group selection, kin selection, cultural selection, and so on. Biocultural evolution contains a few more links. In short, I believe your criteria for selection are a bit too strict. All these factors can potentially influence the "speed of evolution", independent of generation time. SemanticMantis (talk) 23:17, 26 August 2012 (UTC)[reply]

Good point. However, in western countries at any rate, virtually all men find a partner, and virtually all women find a partner, and they have their statistical 2.1 children or whatever, and modern medicine ensures that nearly all children get old enough to reproduce. An example: I have a friend who is parallyzed from the waist down due to childhood disease. He never the less is employed (in IT) on a good salary, found a wife who has her own challenges due to a severe road accident, and they have had 2 children. Not so many decades ago that could not have happened. Both of them would have been institutionalised at best. The road accident rate, higher for teenagers and young adults who have not yet married, drug addiction, and military service seem to be the only reproduction rate interferences and thus evolutionary drivers left. Of these, only military service can affect height, negatively. Wickwack60.228.241.5 (talk) 01:55, 27 August 2012 (UTC)[reply]

I read several years ago that among Americans the increasing height trend suddenly stopped with those born about 1960 – my cohort – and no one knew why. (I'm distinctively tall myself.) In the last couple of years I've noticed a lot of startlingly tall young people, so maybe the trend started up again. —Tamfang (talk) 07:12, 27 August 2012 (UTC)[reply]

Maybe it was all the dope their parents smoked/snorted/swallowed/shot up. Seriously, I've seen indications that the "hippie generation" was generally less healthy than the previous and subsequent cohorts. Roger (talk) 07:48, 27 August 2012 (UTC)[reply]

Or maybe hippie women had more appreciation for short men with a great personality? Who knows - you can't re-run the experiment with a control group - but I've never heard of dope affecting the growth of successive generations, even if it is nominally conceivable as one of any number of potential epigenetics related phenomena. Wnt (talk) 12:13, 27 August 2012 (UTC)[reply]

My "dope" comment was a joke - the serious part is the generally worse health of that cohort of parents. Roger (talk) 16:53, 28 August 2012 (UTC)[reply]

Worse health? I'm not aware of life expectancy going down. And there was a lot of wising up about toxic chemicals and pollution in that general era - no more scrubbing the floors with carbon tetrachloride! I'd think the general increase in middle class income during the 1950s would have improved health, though I didn't look it up so take that with a grain of salt. Wnt (talk) 03:07, 29 August 2012 (UTC)[reply]

Every recent study I have read indicates that evolution in humans is running quite fast now. Historically, groups like the Ashkenazim have expanded quite quickly. Nowadays sexual selection is the thing, with women with fathers with average-sized penes choosing men with large endowments to father their offspring. See baby mamas. μηδείς (talk) 04:23, 28 August 2012 (UTC)[reply]

Huh!!?? How does an article on an American slang arising from Creole prove that??? Wickwack124.178.52.176 (talk) 14:56, 28 August 2012 (UTC)[reply]

When women don't marry the father of their child for his brains or money, on what criteria do you suspect they choose him? μηδείς (talk) 16:43, 28 August 2012 (UTC)[reply]

Love. --NellieBlyMobile (talk) 16:52, 29 August 2012 (UTC)[reply]

They can't explain, it's surely not his brain. Fish gotta swim, birds gotta fly. Kern explains it all for you. --Trovatore (talk) 05:44, 30 August 2012 (UTC)[reply]

August 27

This Last Mars rover

It’s just me, or someone else thinks the Curiosity rover’s cameras are a bit low in resolution terms??
I mean, you can sum all the megapixels of all the onboard cameras and don’t even match the Mpix count of a Nikon d800 and this is just a consumer level camera
All the specs in this page are really “true”? and in this case… Why!? Iskánder Vigoa Pérez 13:45, 27 August 2012 (UTC) — Preceding unsigned comment added by Iskander HFC (talk • contribs)

One reason may be that the rover's instruments were selected and tested back in 2004: Curiosity_rover#Timeline. - Lindert (talk) 13:56, 27 August 2012 (UTC)[reply]

See: Mars rover camera project manager explains 2MP camera choice.--Aspro (talk) 14:00, 27 August 2012 (UTC)[reply]

(ec)Curiosity was designed in 2004 Mars Science Laboratory#History and build by 2008. Aerospace equipment, and particularly equipment that once deployed cannot be replaced, is very conservatively designed. The low-weight, low-power, vibration-tolerant, radiation-resistant, high-thermal-range requirements mean they always lag consumer technology by a long way, in terms of raw numbers. Check Comparison of embedded computer systems on board the Mars rovers and see how much better your phone is than what they run. -- Finlay McWalterჷTalk 14:02, 27 August 2012 (UTC)[reply]

There's also apparently a bandwidth issue - often we only get to see thumbnails until the next day, and some of the images from the first panorama were backlogged for quite a while before finally being transmitted. I guess they have lousy cell phone coverage on Mars. :) Wnt (talk) 14:08, 27 August 2012 (UTC)[reply]

Bandwidth is only a problem if you want the full resolution all the time which you never dare to ask.--Stone (talk) 14:10, 27 August 2012 (UTC)[reply]

The cameras are better than those in the MER rovers. The problem is and always will be that you need flight qualified parts to be allowed to get into a NASA mission. Qualification takes years and adds 3 to 5 zeros to the price and if NASA has to do it on their own it will be a million or several. To get a microchip for space is hard work. A FPGA cost you 50000 $ and than you have a chip capable to do not more than a newest calculator of your kids. Military quality is easy to get, but space qualified makes your life complicated. NASA would simply never consider to fly parts which might harm the success of the mission, even if the cameras are not the most important science tool they are the most important PR tool. --Stone (talk) 14:10, 27 August 2012 (UTC)[reply]

This article [9] discusses the issue. Acroterion (talk) 14:39, 27 August 2012 (UTC)[reply]

The CCD KAI-2020CM for MER and the Mitel (DALSA) doi:10.1029/2003JE002070 for MSL are not 2012 style, but still they were the best choice.--Stone (talk) 14:57, 27 August 2012 (UTC)[reply]

Stopping neutrinos

Since neutrinos have mass, does that mean they could, in theory, be slowed or even stopped relative to some stationery observer? Likewise, our article on photons mentions that they could as well have a very small amount of mass. If that turned out to be the case, would that mean that even light could be stopped? Goodbye Galaxy (talk) 15:26, 27 August 2012 (UTC)[reply]

Light is slowed, by literally every material it passes through. See Refractive index. Individual photons always travel at the speed of light, but this is not the same thing as the speed of the light (as a bulk phenomenon) itself. It sounds like you understand this, but I just wanted to clarify incase you, or others reading, don't. The speed at which light (as a phenomenon) travels depends greatly on exactly what is meant by the words "speed", "light" and "travels". --Jayron32 15:32, 27 August 2012 (UTC)[reply]

Yes, slow neutrinos are a possibility, but you can't really keep them in one place because of the uncertainty principle and the lack of any way to confine them (since they interact so weakly with everything else).

The standard model predicts that the photon is exactly massless, but experimentally you can never prove the mass is exactly zero; you can only establish better and better upper bounds. -- BenRG (talk) 15:56, 27 August 2012 (UTC)[reply]

And what if we presuppose that the photon has a slight mass? Goodbye Galaxy (talk) 16:55, 27 August 2012 (UTC)[reply]

In that case, you could create a Bose-Einstein condenstate of consisting of photons. The macroscopic description would be given in terms of a "classical" Proca action. Count Iblis (talk) 17:06, 27 August 2012 (UTC)[reply]

Would that be any different from an ordinary standing electromagnetic wave? Naively looking at the B-E transition temperature, it goes to infinity as the mass goes to zero, implying that this is the normal state for photons anyway. -- BenRG (talk) 17:53, 27 August 2012 (UTC)[reply]

Like the neutrino it would be hard to keep it in one place. You could confine it in a mirrored box, but you can confine a massless photon in a mirrored box too. Having a very tiny mass is not much different from having no mass at all. -- BenRG (talk) 17:53, 27 August 2012 (UTC)[reply]

Does the quantum foam (or Higgs field) slow observed photon velocities in vacuum to slightly less than the true speed of light? Hcobb (talk) 00:24, 28 August 2012 (UTC)[reply]

No, not in the standard model and not as far as experiments can tell. The vacuum is Lorentz invariant and the only Lorentz invariant thing it could do to the photon is give it a Lorentz invariant mass, so your question is equivalent to asking whether the photon has mass. In the standard model the photon is massless by construction: not all of the electroweak symmetry is broken, and the particle associated with the unbroken part is called the photon. I don't know what the story is in beyond-standard-model theories. -- BenRG (talk) 03:09, 28 August 2012 (UTC)[reply]

Finding Electric Field Magnitude and Direction at a Point Charge

Given three point charges positioned in a plane at the vertices of an equilateral triangle, is it possible to find the electric field magnitude and direction at the position of one of the point charges as a function of the charges of the three points and the length of the sides of the triangle? For example, given point charges with specified electric charges at points ABC located at the vertices of equilateral triangle ABC with side length l, could I determine the electric field magnitude and direction at point A?

—Dromioofephesus (talk) 17:02, 27 August 2012 (UTC)[reply]

No. The electric field direction is discontinuous at A, and the magnitude is singular at A. Red Act (talk) 20:01, 27 August 2012 (UTC)[reply]

Classical electromagnetism does not really admit of point-charges, as these would have infinite energy and therefore infinite mass (see classical electron radius). At any of the vertices, you can however calculate the contribution to the E-field from the point-charges at the other two vertices - and this immediately gives you the force on each of the three point-charges (under the assumption that a point-charge does not exert a force on itself). --catslash (talk) 00:16, 28 August 2012 (UTC)[reply]

How come my Prickly Pears won't bloom?

A few years ago I transplanted some Opuntia humifusa (Eastern Prickly Pear) from one property to another. They bloomed yearly at the old location. The six or so lobes I moved to the new location are doing spectacularly, and there are about 30 lobes now. They are in a well drained partially sandy area with strong direct sunlight all day until June, when they would normally bloom, and about 6 hours of direct sunlight once the oaks leaf out and partially shade them in the late afternoon. (They usually bloom around June 1, so I don't think the leaf cover is at all significant.) I have only had one single flower in all that time, and it was while the plant was still in the pot I used to move it in, before it was put back in the ground. The same with one I keep indoors. I planted it as a cutting and it bloomed once in the pot, and never since. Any suggestions as to why this may be and what to do about it? Google searches have been of no use at all. Thanks. μηδείς (talk) 18:12, 27 August 2012 (UTC)[reply]

FWIW (and I have flowered quite a few Opuntiae) I think the most likely problem is the roots are unconstrained and the soil is too rich, a bit like with (completely unrelated) figs. They tended to flower for me when they had no option to grow instead. I suggest stress them a bit; limit the roots and ensure the soil is a bit barren. Or even just cover the soil so they get less water. --BozMo talk 18:21, 27 August 2012 (UTC)[reply]

It did occur to me that they might need stress. The interesting thing is that the potted one indoors is very constrained and gets water only when it starts wilting, but still hasn't bloomed in three years. The ones outdoors may be a bit hard to stress, since they are going to receive a lot of water unless there is an east coast drought. Are you suggesting they will perhaps bloom once they get crowded? μηδείς (talk) 18:40, 27 August 2012 (UTC)[reply]

I would also suggest that they are more likely to bloom when crowded. Think of it in terms of investment in sexual reproduction vs. clonal growth. If it is easy to spread vegetatively, why invest precious resources in low-odds sexual reproduction? You could install a bed-guard around the perimeter like those used in landscaping, or even just increase competition by planting a different plant all around the perimeter. Lastly, the easiest thing might be to sever the below-ground connections, so that all the individuals in the middle are competing against their neighbors (if they are connected, competition between ramets is much much less). SemanticMantis (talk) 19:17, 27 August 2012 (UTC)[reply]

Chilling requirement? Count Iblis (talk) 19:20, 27 August 2012 (UTC)[reply]

One of my undergrad majors was in Biology with a focus on plant ecology, so I grok the above comments. I have also found a suggestion that 0/10/10 fertilizer helps with flowering, which is the only solution that seems doable without digging up the bed. The chilling requirement might be relevant for the indoor plant. It doesn't freeze, but it is in an unheated and unlit (except for sunlight) room that I use to force my Poinsettias to bloom. There would be no trouble putting the potted plant outside. Unfortunately we can't expect results till next June, long after the Mayan apocalypse. μηδείς (talk) 19:31, 27 August 2012 (UTC)[reply]

PS, this is obviously a clone of a plant that did bloom well before, and which was not really crowded, even by itself. The prior soil was a bit more sandy, and it was never watered. (These plants are wattered occasionally and indirectly, but not a lot.) The old soil probably had a much higher salt content (it was occasionally flooded by the ocean during storms). Perhaps covering the plants in a few inches of beach sand will help? μηδείς (talk) 19:37, 27 August 2012 (UTC)[reply]

Maybe beach sand will help. Another thing to keep in mind is the age of the genet. Some plants, especially succulents, will only bloom once they've reached some ratio of above ground/below ground mass, or even a critical threshold of total biomass. So, assuming you didn't also start the last colony from a few cuttings, I suspect doing nothing will generate plenty of blooms within a few years. SemanticMantis (talk) 14:40, 28 August 2012 (UTC)[reply]

Light source measurement in CRI/Ra

What does the "Ra" part of CRI/Ra stand for? Electron9 (talk) 22:29, 27 August 2012 (UTC)[reply]

The R seems to stand for "rendering", but the "a" I'm unsure of. According to [10] "General Color Rendering Index R_a" contrasts with "Special Color Rendering Indices R_i" (apparently the "i" is for index). Perhaps "a" was just chosen as the first variable in the alphabet (were there R_b and R_c values initially, too ?). StuRat (talk) 23:00, 27 August 2012 (UTC)[reply]

Ra = the general color rendering index. It's an average value, hence the "a." Zoonoses (talk) 03:45, 29 August 2012 (UTC)[reply]

August 28

Symmetries of the Universe

The book, Concepts of modern mathematics by Ian Stewart in its chapter on symmetry, states that:

In mathematical physics, laws like the conservation of energy follow from certain (postulated) symmetries of the universe.

My questions are,

1)What are those postulated symmetries?

2)How does the law of conservation of energy follow from them intutively speaking?

Thanks--Shahab (talk) 05:34, 28 August 2012 (UTC)[reply]

See Noether's theorem, which should explain all about the relationship between conservation laws and symmetry. --Jayron32 05:40, 28 August 2012 (UTC)[reply]

Was the flies in Autstalia tamed so that they mainly feed on plants but not trash?

I have heard in a Chinese article that the Australians put a fly on the $50 bank note, and the reason is that they tamed by cleaning every dirty place and forced the flies to change their diets into plant nectars and no longer becoming a health hazard. Is that ever possible? There can be animal feces everywhere in the wild and I think just cleaning trashes in cities will not affect the flies’ diet much.--211.162.75.202 (talk) 06:05, 28 August 2012 (UTC)[reply]

I am looking at an Australian fifty-dollar note. Wikipedia's article about it says nothing about flies. I can't see a fly anywhere on it, so it sounds like the Chinese article has got it wrong. I have never heard anything about every dirty place in Australia being cleaned to the extent that flies changed their dietary habits. Dolphin (t) 06:34, 28 August 2012 (UTC)[reply]

I suspected that this weird post was from a troll, but as he gelocates to Guandong China, and the linked articles is a Chinese site, here is a definitive answer:-

1. I am an Australian, located in Australia;

2. I have an Australian $50 note in front of me right now;

3. There are no flies on this note. It only has pictures of famous Australians, a Goverment building, and drawings of what appear to be sheep shearing equipment.

4. Flies were once quite a problem in the Australian city in which I live, but the authorities about 18 or 20 years ago changed everybody over from using galvanised iron rubbish bins to specially designed rigid plastic rubbish bins (known as "wheelie bins"), as well as using better landfill practices. These plastic bins have lids that make a good seal on the bin, so the flies can't get at the rubbish. This produced a marked drop in the fly population, making it possible to eat outside for the first time. Since then, the flies have evolved into a more resourcefull and hardy sort, and numbers have increased a little, but they remain not a problem. It is also normal practice to seal food rubbish in palstic bags before placing in the bin, making it very difficult for flies, and eliminating any smell.

Incidentally, most local goverments have passed ordinances making it an offence to leave faeces (e.g., from pet dogs) in place on the ground, but this is to make footpaths and parks pleasant for walkers and joggers, not to control the fly population. Wickwack124.178.52.176 (talk) 06:43, 28 August 2012 (UTC)[reply]

I guess the 2 dollar coin has the Southern Cross which could look like flies to the easily confused. Sean.hoyland - talk 06:52, 28 August 2012 (UTC)[reply]

The fifty-dollar note also has the Southern Cross - in the transparent window. These five stars might look like splattered flies, but they don't look much like live ones. Dolphin (t) 07:10, 28 August 2012 (UTC)[reply]

They don't look anything like splatted ones either - they are way too precisely drawn uniform and delimitted 7-pointed stars, with one 5-pointed one. Wickwack124.178.52.176 (talk) 10:15, 28 August 2012 (UTC)[reply]

There's been a reduction in the fly population in Australia over the past 30 years or so due to the introduction of carefully chosen dung beetles. HiLo48 (talk) 07:21, 28 August 2012 (UTC)[reply]

But I should also assure the OP that we haven't eliminated the fly problem. In parts of the country, at certain times of the year, little bush flies can still be very common, and March flies, which seem to have trouble reading the calendar and appear in far more months than March, can still be bloody pests! HiLo48 (talk) 09:13, 28 August 2012 (UTC)[reply]

Dung beetles are only relavent in farming areas. Most Australians live in cities - where cattle dung is not available. Wickwack124.178.52.176 (talk) 10:12, 28 August 2012 (UTC)[reply]

As I understand it (and I don't claim to be an expert) the reduction of flies on country areas is reflected in city areas too. Flies travel on the wind. We couldn't have had all our modern outdoor eating areas 40 years ago. HiLo48 (talk) 10:23, 28 August 2012 (UTC)[reply]

We couldn't have them 20 years ago. It was the wheelie bins that fixed it, and was the justification for the cost. Flies might travel on the winds, but in Perth, we are right in the trade wind zone, and on the coast. Those poor flies 20 years ago must have come from Africa 6000 km away then. Wickwack124.178.52.176 (talk) 14:52, 28 August 2012 (UTC)[reply]

Fair comment. I'm in Melbourne where the hot summer winds come from the north, and that's where all the flies are. HiLo48 (talk) 20:40, 28 August 2012 (UTC)[reply]

Thanks for the information above. Is it true that fly never ever appeared on any Australian notes--the ones being used now and the previous ones?--211.162.75.202 (talk) 07:28, 29 August 2012 (UTC)[reply]

Yes, it is true. Dolphin (t) 07:36, 29 August 2012 (UTC)[reply]

The resolution of reality

Hi a number of thoughts have just swept through me and I have to ask this multi-pronged question. Assuming what we see is made up of zillions of pixels, what is the resolution of reality (let's say per cubic metre)? When do you think audiovisual equipment will be able to catch up with the processing power and resolution needed to create an (holographic?) image identical to our eye's optical mechanism? Then, finally, do we dream in the same resolution as what we see? If so, does this imply that our brain has enough computing power to interpret stored images in the same way it interprets reality passed on from the retina? Sandman30s (talk) 15:06, 28 August 2012 (UTC)[reply]

Some basic starting comments; you only see very good resolution on a small area of focus at any moment. Your brain interprets a whole load of things in different places (so you are much more sensitive to movement and change than to other details); "processing" is therefore highly selective. Also dreams are mainly symbolic, rather than pixelated. --BozMo talk 15:11, 28 August 2012 (UTC)[reply]

The basic reception equipment in each eye is about 120 million rods (brightness and darkness) and 7 million cones (color). These don't really map onto "pixels" — the eye doesn't work the way you are describing it, it's not a simple photoreceptor circuit — but it gives you some idea about the richness of human visual perception. Fooling eyes is in some ways a lot easier than that — distance matters a lot, as does lighting. We can already do plenty of things that would fool the human eye at a distance. What is trickier is when someone is looking at something very close up. --Mr.98 (talk) 17:07, 28 August 2012 (UTC)[reply]

It isn't the eye you have to fool, it's the brain. The visual system also doesn't work like a camera, not so much because there aren't pixels, but because there's nothing at all like film. The modern digital camera is a better analogy for the human visual system because, just like you need a computer program to translate the data file that contains the image before it looks like an image, you need the brain to interpret the data from the eyes in order to understand what the eyes are seeing. Just as playing around with the code on said computer file will drastically change the picture captured by the camera, the visual perception system is easily fooled. See Visual perception. It is quite easy to devise optical illusions which don't fool the eye at all. The eye records the same visual data, but the data is carefully constructed as to fool the brain. The brain does all sorts of processing to make sense of our three-dimensional world, and not all of it is so straight forward. Gestalt psychology is one perspective that deals some with how the brain visually processes incoming data. It isn't a universally accepted explanation, but it is insightful in places. --Jayron32 17:41, 28 August 2012 (UTC)[reply]

What our brains perceive through our senses is a very tiny part of what information is actually out there in the electromagnetic spectrum. And that's not including dark matter and energy. So the "resolution of reality" concept is flawed: if we answered that question according to the capacity of the human brain, it wouldn't be a representation of reality itself, merely a representation of the human perception of reality - and there's a vast difference. --TammyMoet (talk) 18:08, 28 August 2012 (UTC)[reply]

Would entities exist without minds to distinguish them?

The free will discussion above is about to be archived, but there is still a pending question, so I have continued it here.

prior free will discussion for context

The following discussion has been closed. Please do not modify it.

A machine with free will (arbitrary break 1)

We are all mathematical algorithms, there is no such thing as a physical universe, all that exists is math. Qualia are computational states of algorithms. Count Iblis (talk) 22:38, 24 August 2012 (UTC)[reply]

We are not mathematical algorithms at all, there is no such thing as math: all that exists is the physical universe.... AndyTheGrump (talk) 22:44, 24 August 2012 (UTC)[reply]

The truth, as usual, lies somewhere between those 2 extreme positions. -- ♬ Jack of Oz ♬ ^{[your turn]} 22:49, 24 August 2012 (UTC)[reply]

No. The truth is that all that exists is the physical universe by definition. To say otherwise is farcical. 203.27.72.5 (talk) 23:21, 24 August 2012 (UTC)[reply]

Not to spoil the fun by throwing in a reference (which suggests this should really be running on the humanities desk, or maybe misc, since we're well into philosophy and logic), but try some Wittgenstein:

1 The world is all that is the case.

1.1 The world is the totality of facts, not of things.

1.11 The world is determined by the facts, and by their being all the facts.

1.12 For the totality of facts determines what is the case, and also whatever is not the case.

1.13 The facts in logical space are the world.

1.2 The world divides into facts.

1.21 Each item can be the case or not the case while everything else remains the same.

Tractatus Logico-Philosophicus. 86.169.212.200 (talk) 21:05, 25 August 2012 (UTC)[reply]

Correct me if I'm wrong, but haven't later philosophers rejected this position - including Wittgenstein himself? AndyTheGrump (talk) 04:15, 26 August 2012 (UTC)[reply]

It is still true that math exists. To say otherwise would cause great distress to the workers at the Mathematics Reference Desk. And it is still true that not everything is math. And it is true that not everything is encapsulated in "the physical universe". For example: ideas, thoughts, feelings, mathematical concepts ... -- ♬ Jack of Oz ♬ ^{[your turn]} 05:09, 25 August 2012 (UTC)[reply]

What is an thought besides a collection of electrical signals firing along synapses in your brain? Is that not physical? --Jayron32 05:15, 25 August 2012 (UTC)[reply]

Let me just point out that 203.27's supposed "definition" of the universe pre-supposes that everything in the universe is physical. That is just about the most unscientific and prejudiced and close-minded position one could possibly take. It's also not a universe that I have any knowledge or experience or understanding of. -- ♬ Jack of Oz ♬ ^{[your turn]} 10:11, 25 August 2012 (UTC)[reply]

I'll note by my personal crazy model above, everything actually isn't math - math is deterministic, and the point of the causality violation is to create an opening for something outside the known universe, beyond our ability to examine and perhaps to comprehend, to potentially affect it. The free-willed decisions actually all become boundary conditions of the universe. Wnt (talk) 12:50, 25 August 2012 (UTC)[reply]

It is a World 2 object in Popper's three worlds ... besides being a collection of electrical signals firing along synapses in your brain. To put it that way is true, but reductionist - other collections of electrical signals firing in your brain might not be thoughts, but smells, or migraines, or fits, so a higher-level description is commonly more meaningful. (Wait, all those things are probably world 2 objects as well. Damn. Still, a thought is a thing in its own right, an emergent thing.) Card Zero (talk) 15:40, 25 August 2012 (UTC)[reply]

You are correct- things like mathematical and sciontific concepts are not part of the physical universe by any menes.Aliafroz1901 (talk) 10:45, 25 August 2012 (UTC)[reply]

Or maybe they are, the jury is still out, but the effort put into discussions like this are probably better put into articles like physicalism. Sean.hoyland - talk 11:20, 25 August 2012 (UTC)[reply]

Yeah, but then we'd need sources. Philosophy is like feces or potential employees - everyone has excess to give away, but who wants to consume it? Wnt (talk) 12:46, 25 August 2012 (UTC)[reply]

Like I said above, everything is math. When we assume that what we experience is a physical world that is somehow more than a purely mathematical entity, we actually don't know what that fundamentally is. So, assuming that a physical world that is different from pure math exists is religion, it isn't science. Most scientist do believe in a physical world, but then more than a century ago, most scientists were deeply religious people.

If you feel pain, then this is not fundamentally caused by electrical signals, it is caused by the computation your brain performs. A huge analogue computer that would run the same algorithm as your brain is running and processing the same data would experience the same pain, even though it consists of gears. Count Iblis (talk) 19:10, 25 August 2012 (UTC)[reply]

So, if nothing physical exists then what's running the algorithms? 203.27.72.5 (talk) 20:20, 25 August 2012 (UTC)[reply]

The algorithms are not really run, they only exist in a mathematical sense. All possible algorithms thus exist. One of these algorithms is the formal description of your brain at this moment when you read this part of the sentence, one slightly different algorithm is the formal description of your brain at this slightly later moment when you read this. Count Iblis (talk) 04:07, 26 August 2012 (UTC)[reply]

To answer the original question, it is easy to create a machine with free will as it is conventionally defined. The creation process is called Procreation. --BozMo talk 21:34, 25 August 2012 (UTC)[reply]

Our brains can take in information and we can use that information — plus our existing world views, emotional states, and what have you — to make deliberative decisions about our actions. We can weigh possible outcomes, things we desire or desire to avoid, and come to conclusions. We can even come to very unintuitive or unexpected conclusions. We can use information, values, and empathy to decide what sorts of activities we agree we feel comfortable undertaking, and those which we would desire to never undertake. To me, this is as much as anyone seems to ever really mean by "free will" — I don't actually see debates about causality and materialism to be germane to the topic. Even setting aside the question of what consciousness really is — we have no clue, and it is a mighty significant thing to know nothing about when talking about such things — to me all anyone really wants to know is, "Are we responsible for our actions? Do we actually make decisions?" We feel that we are. We act like we are. Very few people who are not looking to excuse their prior actions ever seem to really ascribe to the philosophy that they are completely out of control of their own actions. That strikes me as pretty "good enough." I am not quite willing to say that my consciousness is totally illusory — it feels pretty "real" to me, and though that is just one datapoint, over time I've come to believe (when I ignore all of the postmodernism and language-games talk that was drilled into me by professors and try to evaluate it in a completely honest, personal way) that it's actually a pretty significant datapoint.

But moving to the meat of the original question: I see no a priori reason to think that we could not imbue a machine with the same faculties as a human brain. This would include whatever appears to be a component of "free will", as defined above. How to do this, I have no idea, and I doubt anyone else alive does either. The human brain is still virtually terra incognita when it comes to understanding the physical basis of consciousness. I suspect we're still a long way off from making sense of it. We probably need to make sense of what makes us us before we can make other things us. --Mr.98 (talk) 01:54, 26 August 2012 (UTC)[reply]

Bodies (hylomorphic substances) and those things that exist in relation to bodies (aristotelian categories) exist. Mathematics doesn't exist by itself. If it did, would it be in base two? Or base ten? Or base e? The assertion is absurd. Mathematics is a perspective on reality that observes quantity but ignores quality. Consciousness is not a thing, or a body. Consciousness is a relationship, a sort of harmony that exists between certain types of bodies, in respect to their forms, and mathematics is a complex sort of such relationship. To insist that mathematics as such existed back when there were only fish or only molten planetoids or dense clouds of plasma makes as much sense as insisting that documentary films did. μηδείς (talk) 02:18, 26 August 2012 (UTC)[reply]

Medeis - I am not sure I completely follow what you mean by "mathematics doesn't exist by itself". Your analogy with documentary films (which I think we can agree have a form of existence) seems to imply that mathematics exists in some sense of "exists", just not "by itself". Is that correct ? If so, can you clarify what "by itself" means by giving an example of something that does "exist by itself" ? Gandalf61 (talk) 09:00, 26 August 2012 (UTC)[reply]

Fundamentally, existence just is what it is. We use various concepts to manipulate it mentally, allowing us to act effectively in it. We view reality fundamentally as consisting of entities, "things", which exist in themselves. We can say, there is a tree, there is a person, there is a rock. Entities have attributes (qualities) and exist in certain relationships. A ball can be red, can be round, can have all sorts of attributes. But we don't talk of there being a red, or there being a round, walking down the street, apart from a red or round thing. Attributes exist, but they don't exist in themselves, but rather of entities.

Likewise relationships. To be aware of, to be as big as, to be the father of, these relationships exist between entities (and in more complex ways, like analogies, which are relationships between relationships, and so on.) Again, we do not (unless we lose focus) talk about an "aware of" (i.e., a consciousness) or an "as big as" walking down the street independent of any entity. Don't get me wrong, redness doesn't exist any less than ballness or nearness. They all exist. An entity is the sum of its attributes and its relationships through time. It is also the sum of its substance (or "parts") and of its form (or "shape").

All of these things are real. Sweetness is real--it just doesn't exist on its own, or separate from a sweet thing and a creature capable of tasting it. Sweetness is a relational attribute, not a thing, not a part of a thing, not an atom. See Aristotelian category for some of the various ways in which we say things exist.

Mathematics is a complex set of ideas (which are relations, not entities) about quantitative relationships. Mathematics is quite real, but it is an abstraction that exists as a relation between conscious entities and their environments. And the form in which we express those relations is to some extent arbitrary. We can cut an apple in two equal pieces (the same as 10 equal pieces in base two) and talk about 1/2 of it or 50% of it. The thing itself is what it is, the mathematical description of it is just as real, but real as a relation between us as conscious measurers and the entities in question.

Humans are quite adept at abstraction. We can ignore our senses for the moment and picture everything in terms of its mathematical description (pythagorean idealism) or in terms of atoms and void (naive/reductive materialism) or in terms of minds and Ideas (Platonism). And we might in flights of fancy even be tempted to say that only numbers or particles are real. But without our direct awareness of entities and attributes (the ability to read the red hand on the meter of the geiger counter) we would have no contact with them. Numbers and particles and the like cannot claim to be real if the perceptions they are abstracted from are not. μηδείς (talk) 19:20, 26 August 2012 (UTC)[reply]

Suggested reading in order of difficulty: Ten Philosophical Mistakes by Mortimer Adler, Introduction to Objectivist Epistemology, 2nd Ed. by Ayn Rand, An Introduction to Logic by H. W. B. Joseph μηδείς (talk) 19:46, 26 August 2012 (UTC)[reply]

Okay, so when you say "We view reality fundamentally as consisting of entities ...", does this mean that the distinction you are making between entities, attributes and relationships is a function of how we (i.e. human beings) perceive reality, not something that is inherent in reality itself ? So categorising a tree as an entity is a subjective judgement, not an objective fact ? That makes sense to me because singling out the tree rather than its branches, leaves or cells, or the forest of which it is a part, or the acorn from which it grew, or the planks which it will become is clearly a somewhat arbitrary slicing of reality. Gandalf61 (talk) 11:57, 27 August 2012 (UTC)[reply]

Very pertinent question. Remember that consciousness is a relationship between a certain type of being and its environment. If we were beings of a vastly different scale, galactic or atomic in size, we would obviously have different ways of perceiving reality. If one takes the consensus view of quantum mechanics, it is unlikely we would perceive atoms the way we as humans perceive billiard balls. (I don't want to endorse any theory a priori here, philosophy doesn't entitle us to speculate on facts that only science can discover.) If we were "atomies" we would not perceive trees directly, or likely even color, given the scale difference. But our scientists might discover these things in the way that ours have discovered radio waves and that the Milky Way is a spiral galaxy. Whether or not "atomies" would apprehend things in terms of entities and events is a matter of speculation.

But the fact that we perceive things that way is not subjective, so much as relative, and relative in an objective way. Humans have an objective nature--their brains and sense organs have a definite nature; they work in a definite way. Reality has a definite nature--it is what it is. Our consciousness of reality is veridical if it conforms to the nature of our sense organs and of reality. We can open our eyes and carefully observe things, or stick our fingers in our ears and hum, or have our tea-leaves read instead of our MRI. The fingers-in-the-ears or the tea-leaves strategies are the subjective ones. They are the ones where the subject creates the contents of its consciousness without relation to the facts of reality. The people who open their eyes and see reality are the ones getting objective knowledge--even if one man is colorblind, and the other not, the statement "this is the way these things look to me in these circumstances" is objectively true for both.

The mistake would be to insist that the concepts of entity and attribute and relation are intrinsic to reality. It would be just as presumptuous to say those concepts exist in reality as its ultimate fundamental makeup without relation to our consciousness of reality as it would be mistaken to say those concepts exist only in our minds without relationship to reality. For most of the history of philosophy people have insisted on an a priori metaphysics. "Ultimate" reality is: earth, air, water and fire; atoms and void; number and harmony; spirit and clay. That is substituting metaphysics for science. And it means every scientific discovery threatens to overthrow your philosophy. Things are what they are. Our concepts are useful if they conform to our means of comprehending reality. Concepts like substance and form; entity, attribute relation (and event, and so forth) are invaluable. Most philosophical mistakes result from their misapplication. Consciousness is not an entity. Evil is not a substance: "It contains pure evil!") Ideas are not things. But neither are these things unreal.

On the nature of concepts and objectivity as relational, read Introduction to Objectivist Epistemology. On the ubiquity and danger of category mistakes read Ten Philosophical Mistakes]. μηδείς (talk) 16:52, 27 August 2012 (UTC)[reply]

Okay, so without the relationship that we call conciousness (and, specifically, human conciousness or something very similar to it) there can be no entities that we call trees or rocks, in the same way as there can be no mathematics without conciousness. Gandalf61 (talk) 09:13, 28 August 2012 (UTC)[reply]

The notion that the reality of the universe could exist purely as mathematics is, well, disturbing for a number of reasons, not the least of which is, that for every irrational number A.BCDEFGHI..., there are truncated versions A.0, A.B, A.BC, A.BCD, etc. So for every instant in the cosmos when you're sitting there reading this message the way you think you should be, there are an infinite number of instants where you're sitting there missing your feet, legs, waist ... and an even "larger" infinite number where they're replaced with some other thing, cat bodies, refrigerators, Cthulhean monsters. But I think that because the existence of a single perfect, "properly formed" moment in space and time is so infinitely unlikely amid the mass of numbers, and we perceive (I hope) such an instant presently, it is therefore equally improbable that this model of the formation of reality is truth. Wnt (talk) 10:28, 26 August 2012 (UTC)[reply]

That's (sort of) an analogue if the Boltzmann brain problem for the mathematical universe. But then all known physical theories of the universe suffer from the same disease. However, I have found a solution to this problem for the case of the mathematical multiverse, which is natural, not some ad hoc fix, which doesn't have an analogue for "physical theories". Count Iblis (talk) 15:20, 26 August 2012 (UTC)[reply]

I'm not familiar with Boltzmann brain, but the "paradox" they describe in that article is easily solved; I've ranted on about it here half a dozen times before. We are always in a state of relatively low entropy because we always keep moving the goalposts. The universe apparently gets larger and cooler in very rough proportion to its age, and the time its residents are willing to wait for "interesting events" expands in like proportion. From the subjective point of view, the most important laws of physics are always changing. Someday protons will be exotic particles found only in cutting edge laboratories, but the people studying them will be made out of "neutrino nuggets" or something, tiny insubstantial particles that take billions of years for one tick of the clock to pass. But I digress, and admittedly, on a favorite crank idea. Wnt (talk) 03:50, 27 August 2012 (UTC)[reply]

http://arxiv.org/abs/1202.4545

"The Relativity of Existence Stuart Heinrich (Submitted on 21 Feb 2012 (v1), last revised 23 Aug 2012 (this version, v2)) Despite the success of modern physics in formulating mathematical theories that can predict the outcome of experiments, we have made remarkably little progress towards answering the most fundamental question of: why is there a universe at all, as opposed to nothingness? In this paper, it is shown that this seemingly mind-boggling question has a simple logical answer if we accept that existence in the universe is nothing more than mathematical existence relative to the axioms of our universe. This premise is not baseless; it is shown here that there are indeed several independent strong logical arguments for why we should believe that mathematical existence is the only kind of existence. Moreover, it is shown that, under this premise, the answers to many other puzzling questions about our universe come almost immediately. Among these questions are: why is the universe apparently fine-tuned to be able to support life? Why are the laws of physics so elegant? Why do we have three dimensions of space and one of time, with approximate locality and causality at macroscopic scales? How can the universe be non-local and non-causal at the quantum scale? How can the laws of quantum mechanics rely on true randomness?"

Count Iblis (talk) 23:33, 26 August 2012 (UTC)[reply]

You don't need to write a paper to explain why existence exists. It takes just six words: There was nothing to prevent it. μηδείς (talk) 02:23, 27 August 2012 (UTC)[reply]

Wow, all this, and nobody's yet pointed out that we do have a very thorough article called Free will. Red Act (talk) 03:39, 27 August 2012 (UTC)[reply]

LOL, we can put this discussion into BJAODN. ibicdlcod (talk) 15:03, 27 August 2012 (UTC)[reply]

Okay, so without the relationship that we call conciousness (and, specifically, human conciousness or something very similar to it) there can be no entities that we call trees or rocks, in the same way as there can be no mathematics without conciousness. Gandalf61 (talk) 09:13, 28 August 2012 (UTC)[reply]

Briefly, things are what they are. So before minds existed, there were still what we call things. We can see that this must be the case because the universe evolved from the big bang and life evolved to produce animals and minds and mankind. What couldn't exist before minds existed was the mental categories of things, such as entities versus attributes, in abstraction. Mathematics is abstraction. All of the mathematical relations that held between things before there were minds to identify them still held. But they held in reality itself, not as numbers, which are concepts--symbols, in effect--that we use to grasp those proportions. Consider the problem of finding the longest piece of dry spaghetti. You can get a ruler and measure each one according to some unit and identify the largest number corresponding to the length of one of the pieces of spaghetti. Or you can stand them in a glass with a flat bottom, and the one that stands tallest is the longest. The first means requires a mind that does math. The second doesn't. (Although obviously glasses and spaghetti are products of beings with minds--but this is just an example.) The result is the same in each case, because the underlying reality is the same. But the math requires a mind. To say that the math itself is the underlying reality is at best a mind game. μηδείς (talk) 17:13, 28 August 2012 (UTC)[reply]

A vital read in this discussion (which is much more about philosophy than science, but whatever) would be Existence precedes essence, which discusses the philosophical conundrum of which comes first: whether something exists first and aquires meaning after it existance, or whether something needs to be defined before it says it exists. There are differing schools of thought as to which makes sense. --Jayron32 17:34, 28 August 2012 (UTC)[reply]

Thanks, Jayron. I have been wondering if there was an article like that. μηδείς (talk) 19:12, 28 August 2012 (UTC)[reply]

μηδείς, how do you know that there was a time when consciousness did not exist? if it does not fit in the physical universe now, then I would assume that it never did.165.212.189.187 (talk) 19:31, 28 August 2012 (UTC)[reply]

So far as we understand scientifically (and not imagine), minds and consciousness are faculties and properties of a certain type of living being. Based on quite a bit of evidence, I am willing to attribute consciousness to animals as simple as all birds and mammals and even octopuses, if not fish. But I have no evidence that there was consciousness when there were only single-celled organisms, and absolutely not before life existed. One has to provide prima facie evidence for something, else it is just an arbitrary assertion. As Hitchens asserts, "What can be asserted without proof, can be dismissed without proof." μηδείς (talk) 20:26, 28 August 2012 (UTC)[reply]

Absence of evidence is not evidence of absence... --TammyMoet (talk) 08:14, 29 August 2012 (UTC)[reply]

If a body reverses direction, does it momentarily stop?

If I throw a ball up into the air, at the apex of its flight before beginning its descent, is the ball motionless or is it constantly either moving up or down? Ankh.Morpork 18:38, 28 August 2012 (UTC)[reply]

If a ball is thrown straight up and follows the same path down as it does up, its instantaneous velocity will be zero at the apex. If the ball has any kind of arc, the horizontal component of the velocity will remain constant (subject to slight slowing due to air resistance, usually ignored for spherical cows) while the verical component of the velocity will be zero for an instant. Note that this is a literal instant, there is no measurement of time small enough over which the ball is not in some sort of absolute motion. However, when you reduce the time scale between measurements to zero, there will be a time, right at the apex, where the instantaneous velocity is actually zero. This takes some calculus to understand better, but if you know calculus, what that means mathematically is that the first derivative of the vertical position function of the balls path will be zero at the point in the path where the ball starts its decent. --Jayron32 18:44, 28 August 2012 (UTC)[reply]

Can you help me understand why when a fly flies horizontally into an oncoming car and then travels in the opposite direction squashed on the windscreen, there can be a period while the fly is motionless, since as soon as it makes contact, it would begin to move in the opposite direction ? Ankh.Morpork 19:09, 28 August 2012 (UTC)[reply]

Certainly. If you picture the fly's velocity towards the windshield and express it as simple scalar quantity, say we define the motion of the fly as positive numbers, therefore any motion in the opposite direction could be expressed as negative numbers. So, lets say the fly is going at +1 meter/second and a car is coming along at a speed (defined by our convention) at -10 meters/second. The fly would then have to change its velocity from +1 meters/second to -10 meters/second. You can't travel between the number +1 to -10 without passing through the number 0, so at some point the fly's velocity will be actually zero. This, remember, is a measure of instantaneous velocity and not average velocity. There is no period of time when the fly is not moving (that is, if we actually watch the fly, there is no two times, t₁ and t₂ between which the fly is not in motion. However, there will be a specific instant of time, in the limit where t₂-t₁ = 0 (that is, where no time passes) that the fly will have an instantaneous velocity of zero. This is a lot easier to understand with some rudimentary calculus under your belt, but even without it, I think my example above of the fly needing to get from a speed of +1 meters/second to -10 meters/second should work. Does it? --Jayron32 19:32, 28 August 2012 (UTC)[reply]

Thank you for your explanation. Can you reconcile "at some point the fly's velocity will be actually zero." with "there is no period of time when the fly is not moving" as not being mathematically adept, I don't quite understand this important distinction. The cross-over from a positive to a negative velocity must surely occur at a specific point in time, and if the fly is in constant motion, how do these two facts correlate? Ankh.Morpork 19:55, 28 August 2012 (UTC)[reply]

Sure. Picture a movie about the fly's motion which is say, one second long. At no point in that film will the fly not be moving. Now, picture a movie that is 0.1 seconds long. At no point in that movie will the fly not be moving. Now, picture a movie that is 0.000001 seconds long. At no point will the fly not be moving. Do you see what I am doing? I'm making the time span when I start and stop the movie recorder smaller and smaller. As long as there is an actual movie, there will be actual motion. Now, what calculus allows us to do is to consider the situation of the 0 second movie. Not 0.1. Not 0.0000001. Not even 0.0000000000000000001 second movie, but an actual 0 time movie. See, even in a 0 time movie, the fly is still in motion, we've just stopped the film at an instant. It is a bit like pausing the film and asking "At what speed is the fly moving in this still frame" For nearly all points in time, the fly will have a non-zero velocity. However, in the transition when he changes direction from forwards to backwards, on a single frame of that film, his velocity will actually be zero. This is an idealized film, however, where each frame is an infinitely small moment of time after the next (not a real film, where each frame has a gap when it isn't recording anything). In calculus, we call this the instantaneous rate of change and it is the rate of change of a function where the domain over which you are measuring the function is reduced to a single point. Does that work? If not, I have more analogies and examples. --Jayron32 20:06, 28 August 2012 (UTC)[reply]

OK I understand (I think) that for any period of time there will be motion, but yet for a specific time frame - the O time, the frozen film - the fly is capable of having a velocity of zero. I confess I still can't wrap my head around this concept so will bother you with some inane questions.

Doesn't this this 0 time occur within a period of constant motion? On a velocity-time graph, doesn't the line intersect the time axis at a specific point while the fly is in motion?
Why doesn't the fly have zero velocity in the transition of forwards to more forwards because so too, at every specific time frame, the fly is motionless. You can pause a movie whenever you want to and when you do all the frames are still - sorry if I'm taking the analogy to literally. Ankh.Morpork 20:33, 28 August 2012 (UTC)[reply]
- Think of plotting a fly's velocity on a number line and watching a video of the dot travel along the number line as the fly's velocity changes. When the fly changes from moving forward to moving backwards (or the opposite), and only at that time will the dot cross the "zero" point on its trips up and down the number line. If the fly were traveling forward at 5 m/s and then was slowed constantly to 3 m/s or sped up to 8 m/s, it never actually crosses the zero velocity point. It is only when the sign of the velocity changes that you cross zero, so it is only in events that cause the sign to change (i.e. from forward to backward) that make the instantaneous velocity of the fly zero at any one point. Also, you misread the explanation a bit. In any specific "frame" of the film, the fly does have a velocity. It is only in the one singlular frame that captures the exact instant when he's transitioning from forwards to backwards when his instantaneous velocity is actually zero. --Jayron32 21:59, 28 August 2012 (UTC)[reply]

Maybe if its an incompressible spherical fly. lol. Isn't there a time when the front half of the fly is going backward while the back half is still going forward?165.212.189.187 (talk) 19:46, 28 August 2012 (UTC)[reply]

bsolutely. That's why they say that the last thing to go through a fly's mind when it hits a windshield is its ass.--Shantavira|^{feed me} 20:17, 28 August 2012 (UTC)[reply]

Historical alternatives to Darwinism (AKA Darwinian evolution)?

This question lies between history and science.

So far, I can only think of Larmarckism and Saltationism. How do they become unsupportable? What information supports Darwinism and fails to support the other two theories of evolution? What is the difference between acclimitization of an individual to the environment and Larmarckism? Do people fail to support Saltationism because changes in populations can only occur one step at a time and not all together (i.e. organ systems can not just pop out of nowhere but must build on something as a template)? Any other alternatives or is that all? Does Biblical creation suggest that all living creatures on earth just pop out of nowhere? Wouldn't the central idea of Biblical creation be closer to the meat experiment in which bugs would grow in the open jar but not the closed jar because creatures would only reproduce after their own kind and not just pop out of nowhere? If that is the case, then didn't that scientist failed to support Biblical creation (sorry, I can't say "reject"; I say "support" or "fail to support"; I could have also used "fail to reject" and "reject"; I do not say "accept" or "reject" because those terms are not equal), which suggested that creatures would just pop out of nowhere under given nutritious conditions instead reproducing after their own kind? 21:05, 28 August 2012 (UTC) — Preceding unsigned comment added by 140.254.226.201 (talk)

I count seven questions there. If you ask seven questions at once on a Ref desk, all you get is disorganized chaos. Could you try to distill this down to one or two questions that matter most, and then ask the others later? Looie496 (talk) 21:36, 28 August 2012 (UTC)[reply]

Some historical alternatives to Darwinian evolution in roughly chronological order:

Creationism
Lamarckism
(Darwin qua Darwin goes here)
Theistic evolution
Saltationism
Mutationism
Biometric evolutionism (Karl Pearson, Walter Frank Raphael Weldon, to some degree Sir Francis Galton)
Modern evolutionary synthesis (not strictly identical with Darwin qua Darwin)
Punctuated equilibrium (which is not strictly Darwinian)
Intelligent Design

As for what leads to one or another, there are the short (somewhat wrong) answers (e.g. "Lamarckism was disproved by August Weissman when he observed that cutting off the tails of mice did not produce mice with shorter tails" — even Weissman knew that under orthodox Lamarckism this would not produce a result) and longer (somewhat dull) answers (like Peter J. Bowler's long but somewhat dry book, Evolution: The History of an Idea). The short version is, when you correlate all of the different types of data — observational, fossilized, genetic — the modern evolutionary synthesis (neo-Darwinism, or Darwinian evolution plus modern population genetics) still comes out on top.

There are many forms of Creationism; some are quite magical ("God woke up one day and said, let's have some giraffes"), some are more naturalistic (e.g. theistic evolution or intelligent design, in which God is either driving evolution or just occasionally intervening when things get hard). In the case of things popping out of nowhere, the actual popping in and out of existence is assumed to be miraculous and not subject to experimentation. --Mr.98 (talk) 22:14, 28 August 2012 (UTC)[reply]

Lamarckism fails for two reasons. There is no experimental confirmation. (I don't remember what experiments were actually tried, but, for example, cutting the tails of mice would not, after any long number of generations, result in a trend toward shortening tails.) Second, there is no mechanism to encode a physical change back into the genome. Causality goes in one direction only, genes > proteins > development > form and not the other way around. This question does seem like a homework question. μηδείς (talk) 01:20, 29 August 2012 (UTC)[reply]

Classical Lamarckism required a "vital force" within the animal — it doesn't happen from just external forces, but was the result of "striving" by the animal itself. So the cutting off of the tail experiment was something of a canard. That doesn't make it correct, of course. Similarly, there are some cases that the central dogma doesn't cover, e.g. epigenetics. --Mr.98 (talk) 02:25, 29 August 2012 (UTC)[reply]

But was the mouse experiment itself ever done? I know that experiments were done. As for striving, I never heard that dark or light skin was caused by striving, just due to tanning or the lack of. μηδείς (talk) 02:55, 29 August 2012 (UTC)[reply]

Actually there is a physical mechanism: proteins -> gene activation/repression -> histone methylation/acetylation/etc. -> DNA methylation -> CpG transition mutations. But you'd still need some circulating hormone to transfer a specific signal to the gonads. A higher level of growth hormone, triggered by environmental circumstances favoring larger animals in one generation, leading to mutations in genes affecting physical size - maybe. I don't know of any proof of such things, but I'm suspicious (for example, successful species tend to get larger, and humans have inexplicably gotten taller lately -though that could more likely be epigenetic based on the two preceding steps) But a signal to say "OMG my tail's been chopped off"? Probably not. Though you never really know until you try... Wnt (talk) 03:02, 29 August 2012 (UTC)[reply]

That's extremely technical, of doubtful use to a layman, and still doesn't amount to actual change in gene sequence caused by reverse design--just a rather random from the viewpoint of the phenotype environmentally induced change in gene expression.

Here's a paper on cutting off Daphnia antennae from 1931: A LAMARCKIAN EXPERIMENT INVOLVING A HUNDRED GENERATIONS WITH NEGATIVE RESULTS μηδείς (talk) 03:11, 29 August 2012 (UTC)[reply]

In case anyone isn't aware, I'll mention that Lamarckianism, in the form of "inheritance of acquired characteristics", has indeed been verified in some lineages. Though not available to charismatic macrofauna, Horizontal_gene_transfer_in_evolution is an important non-Darwinian feature of evolution that is broadly accepted in modern science. SemanticMantis (talk) 04:16, 29 August 2012 (UTC)[reply]

August 29

Kepler-47

The caption on image 6 of this image gallery about Kepler-47 reads: "This screenshot from a NASA animation shows the orbital paths taken by the two known planets in the Kepler-47 system, which both orbit the same two stars." That last part seems intriguing to me. Do we know of an example where two planets in the same system orbit different stars? Dismas|^(talk) 00:26, 29 August 2012 (UTC)[reply]

My understanding was that the separate orbiting of one star in a binary system was the norm, and this "tatooine" situation was notable because it was the first confirmed where a planet orbited both binaries. μηδείς (talk) 02:59, 29 August 2012 (UTC)[reply]

The binary stars HD 20781 and HD 20782 have 2 and 1 confirmed exoplanets respectively. The binary stars HD 11964 and HD 11977 have 2 and 1 confirmed exoplanets respectively. Since these are wide-binaries, astronomers classified them as separate systems, so technically the answer to your question would be no.

In case a similar question comes up again in the reference desk, I found the answer by going to List_of_exoplanetary_host_stars, sort the table by the number of confirmed planets, and then shift-cliking every yellow row. Then I just do a ctrl-f for "binary" in each new tab.A8875 (talk) 03:54, 29 August 2012 (UTC)[reply]

Superheating and nucleation

From the superheating article: "Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites, while taking care not to disturb the liquid. ... Water is said to "boil" when bubbles of water vapor grow without bound, bursting at the surface. For a vapor bubble to expand, the temperature must be high enough that the vapor pressure exceeds the ambient pressure – the atmospheric pressure, primarily. Below that temperature, a water vapor bubble will shrink and vanish. Superheating is an exception to this simple rule: a liquid is sometimes observed not to boil even though its vapor pressure does exceed the ambient pressure. The cause is an additional force, the surface tension, which suppresses the growth of bubbles."

I have three questions: 1) what are the usual nucleation sites in a "regular" pot of water that cause it to boil at 100C? Irregularities in the surface of the pot which trap pockets of air are one. Are there any others? 2) how do these nucleation sites actually promote bubble-making. (I don't see how trapping air will make it easier to form bubbles). 3) why do these bubbles only need to overcome the ambient pressure, and not the ambient pressure + pressure due to surface tension?

Thanks. 65.92.7.148 (talk) 00:57, 29 August 2012 (UTC)[reply]

Also, in bubble chambers, why doesn't the sudden formation of bubbles cause the whole thing to boil? 65.92.7.148 (talk) 01:01, 29 August 2012 (UTC)[reply]

Metal pots likely have LOTS of good nucleation sites, metals have a crystal structure and at the microscopic level are rarely very smooth, regardless of how they feel. It is almost impossible to superheat a liquid in a metal container for this reason. Amorphous solids like glass, that lack a crystal structure, make better containers to superheat a liquid in because they are truly smooth, and so lack nucleation sites. How nucleation sites work is explained in some detail at Nucleation, but the (over)simplified version is that nucleation sites provide a place for bubbles to collect roughly the same way that surface catalysts do: they provide a mechanism which lowers the activation energy necessary to make the transition from the liquid to the gas phase. In super simple terms: they give bubbles something to cling to while they form. Once a tiny bubble forms, it creates a surface; smaller bubbles have a greater surface tension per unit volume than larger ones do (that's because surface area grows as a square function but volume as a cubic function, so as the volume goes up by a factor of 1000, the surface area only goes up by a factor of 100, and the gap between the two gets bigger as the size continues to increase). That means the greatest surface tension exists for the smallest possible bubbles, and their just isn't enough gas inside these bubbles to exert enough pressure against the surrounding liquid to overcome their own surface tension, so they collapse on themselves and never grow. Nucleation sites basically break up the surface tension of these nacent bubbles, giving them the opportunity to form a stable bubble and float to the surface. --Jayron32 03:02, 29 August 2012 (UTC)[reply]

Mars Science Laboratory Flight Path

Hi, I'm looking for the Curiosity Rover's flight path, something similar to this:.

I checked the Mars Science Laboratory article and some of the related articles (like the timeline), but I can't seem to find it. Basically, I want to see the placement of the Earth & Mars during the takeoff & landing, and view the orbit of the planets while also keeping track of Curiosity's position, all of this relative to the Sun.

A snapshot of the celestial bodies' positions at takeoff, and a separate snapshot of the celestial bodies' at landing, would be helpful, but what I'm looking for is either an animation, or month by month snapshots at least.

Any help is appreciated, thanks!--99.179.20.157 (talk) 03:48, 29 August 2012 (UTC)[reply]

You can quickly estimate this via any Hohmann transfer orbit image, such as the one here. Most of them (like this one) are going to show you Earth position at launch and Mars position at landing, but it's pretty easy to extrapolate the rest. A ~230 day flight means that Earth has moved approx 2/3rds around its orbit by the point of landing, and that Mars needs to be backed up approx 1/3rd around its orbit to show the correct position at launch time. The speeds of both planets and the spacecraft can be reasonably approximated as constant. — Lomn 04:26, 29 August 2012 (UTC)[reply]

One way to watch the flight is JPL's Eyes on the Solar System (Java in browser required). Enter the launch date in Date+Time and use Speed+Rate to fly forward and backward in time. Click the spacecraft's name to center on it, and use the mouse to rotate the view, and just play with the controls. You can also see a quick demo at TED.

There are other planet position simulators, search the web, e.g. [11] - won't show the spacecraft but you can move in time from launch date to landing to see how the planets moved. 88.112.47.131 (talk) 11:46, 29 August 2012 (UTC)[reply]

professions

I've been reading these helpdesk answers for years and there are such brilliant replies. Which of the 'regulars' here actually work as scientists or as teachers/professors? I'm not looking for stats but just some short replies from the regulars. Thanks. Sandman30s (talk) 06:57, 29 August 2012 (UTC)[reply]

I used to be a freelance lecturer in colleges and universities in the UK. Now retired through ill health. --TammyMoet (talk) 08:11, 29 August 2012 (UTC)[reply]

Rocket scientist. --Stone (talk) 08:18, 29 August 2012 (UTC)[reply]

You left out an important class of knowledgeable people - Engineers. I started my career in Electronic Engineering, then when Govt policy killed off the Electronics industry in Australia, I worked in IT as a software Engineer & project manager, then became a diesel power generation Engineer. I have multiple diploma and degree level qualifications. Now semi-retired as in Australia if you are over 65 you can't be covered by accident insurance at work. I still do some consulting, and I'm also doing research. Ratbone121.215.24.39 (talk) 10:12, 29 August 2012 (UTC)[reply]

It wasn't intentional... also if you throw in engineers then there are many other classes who would regard themselves just as knowledgeable :) I was more interested in the academic/educational professions. Engineers are more than just academic... Sandman30s (talk) 11:31, 29 August 2012 (UTC)[reply]

General anaesthesia

Normally when general anaesthesia is administered to a patient, there is a lot of preparation before hand such as assessments, emptying bowels, ensurin the patient doesn't eat or drink before hand etc but how is all this done in emergency surgery in life threatening cases where patients are taken straight to surgery from emergency. Also are relaxants etc used before general anaesthesia to relax patients? Clover345 (talk) 10:56, 29 August 2012 (UTC)[reply]

@@ Line 325: / Line 325: @@
 :You can quickly estimate this via any [[Hohmann transfer orbit]] image, such as the one [http://www.alicesastroinfo.com/2010/02/which-way-to-mars/ here].  Most of them (like this one) are going to show you Earth position at launch and Mars position at landing, but it's pretty easy to extrapolate the rest.  A ~230 day flight means that Earth has moved approx 2/3rds around its orbit by the point of landing, and that Mars needs to be backed up approx 1/3rd around its orbit to show the correct position at launch time.  The speeds of both planets and the spacecraft can be reasonably approximated as constant. &mdash; [[User talk:Lomn|Lomn]] 04:26, 29 August 2012 (UTC)
+:One way to watch the flight is [http://eyes.nasa.gov/ JPL's Eyes on the Solar System] (Java in browser required). Enter the launch date in Date+Time and use Speed+Rate to fly forward and backward in time. Click the spacecraft's name to center on it, and use the mouse to rotate the view, and just play with the controls. You can also see [http://www.ted.com/talks/jon_nguyen_tour_the_solar_system_from_home.html a quick demo] at [[TED (conference)|TED]].
+:There are other planet position simulators, search the web, e.g. [http://www.theplanetstoday.com/] - won't show the spacecraft but you can move in time from launch date to landing to see how the planets moved. [[Special:Contributions/88.112.47.131|88.112.47.131]] ([[User talk:88.112.47.131|talk]]) 11:46, 29 August 2012 (UTC)
 == professions ==