Wikipedia:Reference desk/Archives/Science/2008 August 24

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August 24

Earth's Magnetic Poles

Will Earth's magnetic poles reverse in the near future, causing chaos? 66.53.220.56 (talk) 01:42, 24 August 2008 (UTC)

Geomagnetic reversal#Future of the present field suggests that it's not likely to happen soon, but the whole thing's too poorly understood to predict with any certainty. Algebraist 01:47, 24 August 2008 (UTC)

I suppose it depends on what you mean by "near" future. The poles do reverse at intervals - but the intervals aren't very regular or predictable - so it could happen any moment now or not for hundreds of thousands of years. A reversed field would certainly cause some confusion and difficulties - but the real worry is that WHILE it's flipping, there might be no magnetic field at all for a period of years to decades. That's very bad indeed because the magnetic field is implicated in the processes for deflecting radiation from the sun harmlessly around the planet. When the magnetic field simply disappears prior to the flip - we're going to be irradiated. That's going to play hell with human health and do bad things to electronics and such. Life has survived these flips before - but there is a big difference between the species surviving and the horrors for the individuals of the species. SteveBaker (talk) 04:14, 24 August 2008 (UTC)

The dangers are far from certain - there are theories that the ionosphere may protect us sufficiently, even without a magnetic field. --Tango (talk) 04:31, 24 August 2008 (UTC)

Spontaneous human combustion

Is this real?? —Preceding unsigned comment added by Moonspeaker (talk • contribs) 02:20, 24 August 2008 (UTC)

Try Spontaneous human combustion. --Tango (talk) 02:47, 24 August 2008 (UTC)

Experiments with body gases and blow back

I herd some chemistry students say they could set fire to their own rectal gases like methane, but if the velocity of combustion is greater than the velocity of expelled gas, would that cause a blow back and severe injury? —Preceding unsigned comment added by Moonspeaker (talk • contribs) 02:23, 24 August 2008 (UTC)

While it doesn't mention it that I can find, there is an article on fart lighting (really??). There may be a problem with a lack of oxygen inside, but could certainly burn some sensitive areas. --Bennybp (talk) 02:38, 24 August 2008 (UTC)

According to Flatulence#Composition_of_flatus_gases, the oxygen content of a fart (I presume whilst still inside the body) is much less than the 21% you'd find in the air. So, I guess it would be substantially more difficult to ignite the internal gases - unless you were using something like a blowtorch. --Kurt Shaped Box (talk) 02:52, 24 August 2008 (UTC)

thanks for the link Kurt BennyP. I just edited that page to correct some inaccuracies! —Preceding unsigned comment added by Moonspeaker (talk • contribs) 03:16, 24 August 2008 (UTC)

I know a woman who claims such 'blow back' resulted in a trip to the emergency room for her. ike9898 (talk) 17:39, 25 August 2008 (UTC)

Earths core

What is the elemental composition of the earths molten core? —Preceding unsigned comment added by Moonspeaker (talk • contribs) 03:25, 24 August 2008 (UTC)

The earth's core isn't molten, it's solid, and it's mostly iron. The outer core is molten though, and I believe it's mostly iron too. ScienceApe (talk) 03:34, 24 August 2008 (UTC)

See Structure of the Earth. The core is mostly iron and nickel. --Tango (talk) 04:28, 24 August 2008 (UTC)

I think there is lots of gold at the center of the earth, at least considering the amounts in human terms and mining experience. Gravitation would have made it accumulate there when the entire earth was gaseous, and later molten. The only gold at the surface today would be a small amount taken there by turbulence in earlier times. Platinum and other heavy metals are probably in the center of the earth in copious amounts too, at least in human terms. What does the average density of the earth tell us about that possibility? If I remember right, the average density of the earth is 4-1/2 to 5 times the density of water. It follows that material (including iron) other than heavy metal is present in much greater volume and mass than heavy metal. But the amount of heavy metal near the center may be stupendous in every-day human terms and mining experience. Spectroscopic analysis of stars does not show an abundance of heavy metals in the universe. Quite the opposite - lots and lots of hydrogen everywhere. But the stars are still in gaseous form, and furthermore we can only do spectroscopic analysis of light that comes from the surface of stars. Who knows what goes on deep within stars, with the enormous pressure and heat. There could be lots of heavy metal there, retained below the surface by gravity. However, spectroscopic analysis of self-luminous (non-dust) nebulae, I think, shows mostly hydrogen. But is the pressure within nebulae relatively small? Andme2 (talk) 21:28, 24 August 2008 (UTC)

You're talking about this as if it's some undiscovered mystery - when in truth we know fairly well what's going on there.

The mean density of the earth is around 5.5 - iron is around 7 and nickel nearer to 8. This suggests that the nickel-iron core is NOT likely to contain massive quantities of heavier elements. However, by observing how seismic waves from earthquakes are reflected and refracted through the core, we can deduce a lot about the composition and density - so this isn't just a guess.

As for stars - sure, the majority of stars are busily converting hydrogen and helium into higher atomic number elements - but old stars (the vast majority of them that aren't so heavy that they collapse into neutron stars or black holes) will eventually run out of those lightweight fuels. They start to convert progressively heavier elements in to yet heavier elements. When eventually the star can't gain enough energy to do that anymore - it may go nova and explode. That causes it to send out massive quantities of heavy elements - carbon, oxygen, silicon, iron, nickel...you name it. That's the origin of all of the heavier elements in the universe and appears to adequately explain the prevelance of those materials in rocky planets such as the Earth.

SteveBaker (talk) 14:38, 25 August 2008 (UTC)

Pure fusion bomb

Over at pure fusion weapon the article states that the hypothetical weapon offers the possibility of generating very small nuclear yields. I'm assuming this is done simply by limiting the amount of fusionable materials in the bomb to a minimum. So it begs the question, what is preventing fission bombs from also being very small in explosive yield? I'm aware of the Davy Crockett (nuclear device) but it says that "The Mk-54 weighed about 51 lb (23 kg), with a selectable yield of 10 or 20 tons (very close to the minimum practical size and yield for a fission warhead)". What is stopping a fission warhead from being smaller in yield? Can't you just limit the amount of fissionable material in the bomb? ScienceApe (talk) 03:33, 24 August 2008 (UTC)

My guess is that the chain reaction in a fission bomb requires that there are enough neutrons to initiate it. There is a 'critical mass' of radioactive material - beneath which fission won't occur. That puts a limit on the minimum size of the resulting explosion. A fusion reaction relies on an external source of energy (which is currently going to be a small fission bomb) to sustain the reaction - but it's not chain reaction - so you can have much smaller amounts of material. As you point out though - pure fusion bombs don't exist - and that's probably because of the difficulty of packing a suitable energy source into the weapon. SteveBaker (talk) 04:08, 24 August 2008 (UTC)

That was a very inexact answer for you, Steve: the critical mass is not the lower limit below which fission won't occur, as fission occurs naturally all the time in radioactive material, but you don't even need those natural neutrons to initiate fission, as you can get a cheap and powerful neutron generator to get it going. The critical mass is the limit below which a self-sustaining (or runaway, in the case of a bomb) series of non-spontaneous fissions occur (i.e., fissions caused by a heavy nucleus being pinged by a flying neutron, which itself came from a just-fizzed nucleus, and whose own neutrons then go on to ping someone else). The reason there's a lower limit is that the smaller the lump of material, the greater the chance that a neutron will fly uselessly away before it happens to hit one of those wobbly nuclei (which of course make up only the tiny center of an atom, which is mostly empty space).

Think of your question this way, ScienceApe: imagine the smallest possible fission bomb: two plutonium atoms and one free neutron. You shoot one of the Pu atoms with the neutron, it splits, and its own free neutron(s) go flying off in a random direction. What are the chances that they happen to hit the other Pu atom? Pretty low. But if instead the target atom was surrounded by other atoms ... --Sean 15:27, 25 August 2008 (UTC)

See critical mass. --Tango (talk) 04:29, 24 August 2008 (UTC)

I think to go much below the critical mass is not possible. You can add additional neutron source and compress the material with explosives, both done in warheads to make it smaller. But with the method to tickling the dragon's tail I think you get the minimum explosion possible, just enough to seperate the two halfs of critical mass bay a short bounce. There is a filme where one guy smashes two halfs of a bomb together by hand in a ballroom. Only a small blue light and nothing eles.--Stone (talk) 08:06, 24 August 2008 (UTC)

Note to anyone with hemispheres of plutonium lying around: read criticality accident before trying what Stone suggested. --Sean 15:27, 25 August 2008 (UTC)

You can have sub-critical fission devices but they're not worth the expense (they've happened accidentally a few times—see fizzle—and are sometimes made as a way to skirt nuclear test ban treaties but still get hydrodynamic information about plutonium, etc.). You don't get much more bang out of them than the explosives necessary to set them off, and while you do end up with a little radioactive contamination, its not nearly as much as would be the case with a concerted "dirty bomb", and at maybe a million times the cost. (Note also that the Davy Crockett bomb, and other such small weapons, are actually extremely inefficient when you look at their yield to weight ratio—less efficient than Fat Man and Little Boy.) --98.217.8.46 (talk) 14:11, 26 August 2008 (UTC)

Heliocentrism

In light of Galilean relativity, which seems to say that "the question of who is at the center is meaningless" [1], in what sense were Copernicus and Galileo right about heliocentrism? I've heard that heliocentric models have more predictive power, but according to [[2]], "The ideas presented by Copernicus were not markedly easier to use than the geocentric theory and did not produce more accurate predictions of planetary positions." Is it right in the sense that in terms of classical physics, a point inside the sun is the center of mass of the Earth/Sun system? Or is heliocentrism right in the sense that an inertial reference frame can be constructed where the Earth revolves around the Sun but not vice versa? --Histirisis (talk) 03:43, 24 August 2008 (UTC)

Well, the Copernican view was getting very complicated - from the perspective of an observer looking at a two-dimensional sky, the idea of the planets being attached to spheres, attached to spheres...possibly attached to spheres - essentially boils down to the sum of a set of sine-waves. But Fourier analysis says that we know that any function can be represented by the sum of a set of sine waves. Hence, the Copernican model could have explained literally any planetary motion given enough spheres. If the orbit of Mars spelled out COPERNICUS in an elegant script font - with enough spheres, you could describe it.

So while it's possible to describe orbits that way, the resulting math tells you nothing about why the planets move like that. It has predictive value - but no descriptive power.

The modern view of planetary motion is a much simpler equation - the very form of the math predicts the gravitational forces that cause the motion.

It's also not true that there is no difference between the heliocentric view and the geocentric. The redshift of a distant star is different in summer and in winter due to the motion of the earth around the sun. If the earth was stationary and the sun were moving, there would be no such redshift.

SteveBaker (talk) 04:02, 24 August 2008 (UTC)

Your explanation regarding simplicity makes sense to me, but your last point about redshift seems to beg the question of whether the Earth-Sun system is heliocentric. If redshift is caused by relative motion between the stars and the Earth, we could just as well (though not as easily) construct a geocentric model where the earth is stationary and the stars move in epicycles and so on. --Histirisis (talk) 04:58, 24 August 2008 (UTC)

There is no such thing as absolute rest, so you could consider either the Earth or the Sun to be stationary, however if you consider the Earth as stationary then the motion of the other planets becomes extremely complicated. If you consider the Sun as stationary, then the other planets just move in ellipses. --Tango (talk) 04:24, 24 August 2008 (UTC)

Correct me if I'm wrong, but the question of whether the Sun or the Earth is at the centre is definitely not meaningless. The Sun is in an inertial frame of reference while Earth, because it is accelerating due to the Sun's gravity, is not. Physical laws do not apply in non-intertial frames unless they are specifically modified; thus, whichever object is not accelerating can be said to have the correct perspective. Saying the planets orbit the Sun makes perfect sense, but a geocentric model requires a model of gravitation because the question of why Earth's gravity should dominate or why celestial bodies follow their observed paths have to be explained.

Note that the Sun is not in a strictly inertial reference frame since the same gravitational force applied to Earth is exerted on it; however, because of the Sun's high mass, the force's effect is negligible. The Earth-Sun system's barycenter is well below the Sun's surface.

"The ideas presented by Copernicus were not markedly easier to use than the geocentric theory and did not produce more accurate predictions of planetary positions" Copernicus still assumed the planets follow perfectly circular orbits rather than the elliptical Kepler orbits.

"Is it right in the sense that in terms of classical physics, a point inside the sun is the center of mass of the Earth/Sun system?'

Yes, and this point is the barycenter I mentioned earlier. --Bowlhover (talk) 07:11, 24 August 2008 (UTC)

(e/c - indenting) Huh? I thought that Einstein said that anything could be defined as the reference frame? And Mach said that the reference frame was the distant stars. Franamax (talk) 20:46, 24 August 2008 (UTC)

The idea that only inertial frames of reference are equally valid is only part of special relativity. To introduce gravity, you need to work in general relativity and there all reference frames are equally valid (gravity is just curvature of space, so acceleration due to gravity doesn't really count as acceleration, you're still on a geodesic). --Tango (talk) 20:41, 24 August 2008 (UTC)

Is there any possible explanation of Foucault pendulum in geocentric theory? - 203.129.237.147 (talk) 05:41, 25 August 2008 (UTC)

Yes and no. The Foucault pendulum demonstrates the effects of Earth's rotation - so to that extent it is geocentric. However, the only way we know the pendulum is precessing is because we are able to measure by reference to the distant stars. If there were no stars in the sky, we would have know way of knowing whether the Earth was turning the pendulum, or the pendulum was turning the Earth (and the Sun). Without external reference points, it's a pendulo-centric theory. Franamax (talk) 07:25, 25 August 2008 (UTC)

Hygiene

When human beings defecate, they will clean/wipe the area afterwards ... not only for cosmetic reasons, but also for hygienic ones. I assume that cleaning the area afterwards reduces germs, bacteria, infection, disease, etc., ... ultimately promoting better health. Do animals engage in any similar conduct of cleaning/wiping ... or do they simply defecate and move on? Thanks. (Joseph A. Spadaro (talk) 03:46, 24 August 2008 (UTC))

Dogs and cats scooch sometimes. I assume it is to relieve an irritation.--80.176.225.249 (talk) 12:43, 24 August 2008 (UTC)

As far as I know, animals which can be seen in cities and villages like cats, dogs, cows etc. defecate and move on. I do not know the individual behavior of animals in wild. Otolemur crassicaudatus (talk) 13:09, 24 August 2008 (UTC)

Domestic cats clean themselves meticulously, which is partly why they make such good pets. As far as I know, no other animal is as fussy, although some animals, such as rabbits and rodents, produce quite solid pellets so there is really no mess to clean up. Birds eject a thick liquid so again no cleaning is necessary. Aquatic animals don't need to bother of course. Some tails help to keep flies away.--Shantavira|^{feed me} 15:25, 24 August 2008 (UTC)

Budgerigars will clean their vent area meticulously with both beak and claws if any poop happens to stick to the surrounding feathers on the way out. They don't like matted plumage. --Kurt Shaped Box (talk) 16:55, 24 August 2008 (UTC)

We're also the only animals that wear clothes. Animals don't have to worry about dirty underwear like us. I think that when dogs and cats "scooch" (as 80.176 pointed out) it's because they itch. --Shaggorama (talk) 19:09, 24 August 2008 (UTC)

NADO - but don't dogs sometimes 'scooch' when their anal glands are overfull? --Kurt Shaped Box (talk) 00:57, 25 August 2008 (UTC)

I've noticed that when my dog shits, her anus is totally clean afterward, with no wiping or anything, and that she performs this magic trick by extending her anus/rectum out a little ways (like turning a sock inside out) so that it's like she's pooping from a tube. When the poop has plopped, she pulls the tube back in with the outer anus never having touched anything unpleasant. It probably helps that she doesn't have buttocks. Humans do that same tube thing a little, but not enough to avoid needing "bathroom tissue", I guess. You can see what I mean in this picture (graphic image warning): tubgirl. --Sean 15:37, 25 August 2008 (UTC)

What is the nature of consciousness?

What is the bridge between thoughts appearing in the brain and becoming conscious property? By "property" I mean your identity "claims" it and says "yes, I thought this" when, in reality, your brain thought of it. As one often perplexed by the inner light, I must ask what this energy is. The energy we're clearly borrowing that we then claim as our own that....controls us? It seems we exist as an odd mix of mental slavery and postthought free will. How do I know? It's what my brain just told me. Or did it? Perhaps I'm just at one with it and I didnt "think" anything at all. Of course my brain just "told" me that also. I'm so confused.--Hey, I'm Just Curious (talk) 04:14, 24 August 2008 (UTC)

Exhaust Consciousness and the related links near the bottom. You may also find Dendrite of interest. As for the fundamental nature - I must defer to Diogenes of Sinope - "When asked how he wished to be buried, he left instructions to be thrown outside the city wall so wild animals could feast on his body. When asked if he minded this, he said, "Not at all, as long as you provide me with a stick to chase the creatures away!" When asked how he could use the stick since he would lack awareness, he replied "If I lack awareness, then why should I care what happens to me when I am dead?" 98.169.163.20 (talk) 04:55, 24 August 2008 (UTC)

See also Epiphenomenon. Some have argued that what seems like thinking, reasoning, and decision making, or intentional movements are mere associative byplay, like a television viewer imagining he affects what happens on the screen by wishing or by yelling orders. Edison2 (talk) 05:36, 24 August 2008 (UTC)

This is a very vigorous field of research right now - new findings are popping up from brain scanners and subtle experiments on an almost weekly basis. From the way things are going, I'd say that we've learned these things:

• Our consciousness is a relatively recent evolutionary development - which seems reasonable given that so few animals seem to exhibit it. That means that we had to be fully functional working beings before we had consciousness. At least one researcher believes that we only developed it maybe 10,000 years ago! But either way, that in turn means that we don't need it in order to perform most mundane tasks. Evolution works by small incremental change - and switching over the entire way the brain works from "automatic" to "conscious" processing just doesn't seem like the kind of thing that could have happened.

• The amount of data that can flow into and out of our conscious mind is between 11 and 40 bits per second. That's an actual measured flow rate. Anyone who does anything with computers knows that is an AMAZINGLY low data rate. It's not enough (for example) to allow us to read at normal reading speeds. It's certainly not enough to allow us to see everything we think we can see. With so few bits, it's clear that (for example) the conscious mind can't drive a car.

• Many brain-scan experiments have found that we make decisions many seconds before we are conscious of doing so.

• Other studies suggest that our consciousness operates several seconds behind "real time" and that the subconscious contains mechanisms to "edit" the timeline that the conscious mind perceives so that it merely seems like we're operating in realtime. If that's true then the conscious mind doesn't make any decisions whatever...it functions merely as a monitoring mechanism that operates long after the 'animal mind' has done everything that needed to be done.

So I guess the answer to your question is "many seconds".

SteveBaker (talk) 16:17, 24 August 2008 (UTC)

See Daniel Dennett's multiple drafts theory of conciousness, a response to the problems created by the Cartesian theater view. Gandalf61 (talk) 16:59, 24 August 2008 (UTC)

Very interesting what SteveBaker says. In fact, if you remember the sources where you came upon this information, we should add it to our article on consciousness.--El aprendelenguas (talk) 20:36, 24 August 2008 (UTC)

Keep in mind when reading SteveBaker's response that he's probably speaking about access consciousness, as opposed to phenomenal consciousness (which is probably appropriate since this is the science reference desk, and phenomenal consciousness, assuming it exists, cannot be measured independently). Steve, correct me if I'm wrong. --Allen (talk) 23:26, 24 August 2008 (UTC)

The book I've been reading is "The User Illusion" by Tor Norretranders ISBN 0-670-87579-1. I don't recommend it though - it was an exceedingly annoying read - it drifts FAR off-topic into areas the author clearly doesn't understand well. However, it covers a good number of the weird experiments that are popping up in reasonable detail. A fairly entertaining take on it is from Radio Lab on NPR - all of their shows are podcasted - I forget the exact titles. My wife had some journals I was reading also - sadly they are 180 miles away from my present location so I can't quote exact refs. Sorry I can't be more exact - it's not exactly my field. SteveBaker (talk) 00:25, 25 August 2008 (UTC)

Then there is instinct. Sometimes the conscious human mind can overcome it and not act in an instinctive manner. With animals, if you have seen how a domestic house cat acts when it spots a bird on the ground, it is amazing how it switches from being a sweet, friendly animal to being a hunting animal guided solely by instinct - it is a binary switch. The cat will even instinctively crouch behind a rock or other obstruction to hide its body as much as possible from the bird. Even kittens with no previous hunting experience will conceal themselves like that. Humans, also, can switch suddenly from civilized to violent behavior - from being consciously guided to being guided by instinct. As for learned (non-instinctive) behavior in humans, it may start by being consciously accepted and enacted, and in some cases may then become mainly involuntary and unconscious - that can be seen in soldiers as a result of their training. The military endeavors to make them automatons - to obey orders instantly without even thinking about it. Andme2 (talk) 06:08, 25 August 2008 (UTC)

Every one of Steve's claims is pretty significant, it seems, but I too would like to see sourcing and just how such experiments were performed. Certainly our "blink" response could not occur with an 11bit/s data processing rate. Also, 11 bit/s in what? Input, mid-level processing, or conscious processing? Because certainly we see and hear much more than 11 bit/s. SamuelRiv (talk) 06:38, 25 August 2008 (UTC)

The screen of a computer monitor displays hundreds of thousands of pixels of data. Each pixel is a dot of light, and it requires several bits of data to indicate its color, brightess, and screen position. Similarly, when we move our eyes to change the field of vision, a great many pixels of data (detected by rods and cones) are almost instantaneously changed and perceived by the conscious mind. Some of it will be in peripheral vision, but the central part would still be many pixels, with the mind fully aware of the change of these many pixels of visual data. My monitor screen displays 480,000 pixels; other monitors display even more. Andme2 (talk) 07:33, 25 August 2008 (UTC)

Both SamuelRiv and Andme2 are not understanding what I'm saying. I'm not saying that the entire brain can only process 11 bits per second - that's OBVIOUSLY not true. I'm saying that the very small portion of the brain that is the presumed seat of "consciousness" can only process between 11 and 40 bits per second. So we can blink (that's an autonomic system thing - we CAN do it consciously - but generally it happens automatically). When we move our eyes, the claim is that our SUB-conscious mind processes the multi-megabytes of data involved - takes any necessary actions and then (possibly some seconds later) tells the conscious mind what was there - at a level of broad concepts, not details. The claim is that the conscious mind may subsequently (and S-L-O-W-L-Y) interrogate the subconscious about details within the scene - but we only hear about things we want to hear.

I'm sure you're going to complain about that. But before you do, try this for me. Go to this page [3] - look where it says "View the "basketball" video" - read the instructions very carefully (that's important) - then click on the link and view the video. Then come back here and post your answer - then I'll tell you something amazing. SteveBaker (talk) 14:19, 25 August 2008 (UTC)

I actually had alot of problems with that one too. Although it is a huge simplification, the mind is sort of like software operating on the hardware of the brain. It doesn't make sense to talk about the speed at which a program handles data, since that speed is dependent on the hardware it runs on. I'd like to know what is considered a "bit" of information with respect to the conscious mind, because I think the numbers you give are pretty silly and quite frankly meaningless. Mreover, there is no identified seat of consciousness in the brain; there is no homonculus in there either. That basketball video is about attention and doesn't make any claims about bits of processed information. If you really wnat to be wowed by the conscious experience of vision, read about blindsight. I'd still like to see the study you mentioned.

I also had problems with Steve's first point about the evolution of mind. Our ancestors were using tools millions of years ago, and Homo sapiens evolved over 200,000 years ago, so the timeline you give makes no sense. Also 10,000 years precludes the possibility of animal consciousness being similar to ours (without convergent evolution on a massive scale).

The fourth point, about experience of time, is extremely exagerated. It's impossible for us to experience the world in "real time" because we only have access to sense data, but we receive it sufficiently fast for our experience to match up enough to respond to the world very quickly, otherwise we'd notice the time lapse. Parallel processing is amazing stuff.

The mind and brain don't exist in the kind of dualistic dichotomy Steve seems to suggest. Although I earlier threw out the functionalist computer analogy, the fact is your mind IS your brain. The are some facets of your cognition that you have conscious access too, and some you don't. More than investigating epiphenomenalism, I'd suggest you read into the unity of mind (much scarier and more compelling stuff, IMHO). To Steve's credit though, I can at least vouch for his third point: the research he's talking about is into something called the Readiness potential and the interpretation of the results he mentions is one first advocated by Benjamin Libet. The results of the experiment have since been interpreted differently and are still contentious, but it's an interesting read. If you get back to me later, I'll dig around my notes and find some fun UOM stuff for ya. --Shaggorama (talk) 14:34, 25 August 2008 (UTC)

"The User Illusion" by Tor Norretranders ISBN 0-670-87579-1 - chapter 6 "The bandwidth of consciousness" pp 124 to 156 in my hardcover copy. It cites half a dozen references and experiments starting in 1952 and ranging all the way up to the present - these appear to all have been printed in peer-reviewed journals or books that are considered standard texts - so they aren't whacko-theories, they reach at least Wikipedia's standards for mainstream science. What more can I say? Find a copy in a bookstore or library and check it out. SteveBaker (talk) 03:39, 26 August 2008 (UTC)

Thanks, I'll try to. If I don't get around to it before this thread gets archived, I'll try to get a response to your talk page. --Shaggorama (talk) 06:27, 26 August 2008 (UTC)

Oxycodone and Morphine: Detection periods?

I was wondering how long these two opioids are detectable in the urine and if quantity use can be measured. Have attempted to find a definitive answer, such as a medical journal, but have only found sites recommending one detox product or another with no definitive scientific data.

Ruairí Óg the Rogue (talk) 05:37, 24 August 2008 (UTC)

If you Google Scholar and search for: "Morphine detection urine" you will find lots of scholarly articles that address your question. A definitive answer is difficult to give because it depends "mainly on the dose and sensitivity of the method used and also on the preparation and route of administration, the duration of use (acute or chronic), the molecule or metabolite that is looked for, the pH and concentration of the urine, and the inter-individual variation in metabolic and renal clearance." [4] Some of the methods available include Latex agglutination inhibition (LAI), Thin layer chromatography (TLC), Radioimmunoassay (RIA), High Performance Liquid Chromatography (HPLC) and Gas chromatography and mass spectrometry (GC/MS). But, as an example, in addicts that used on average 0.635 grams of heroin per day, using a RIA method, morphine could be detected in the urine every day for seven days after last use. [5] Dostioffski (talk) 19:34, 24 August 2008 (UTC)

Inhalent detection (inspired by question above)

Why is it that inhalants are difficult/impossible to detect in drug tests? I would like to add this to our article but couldn't find anything through a cursory search. --mboverload@ 06:06, 24 August 2008 (UTC)

Just a guess but I would think that inhalants can range from gasoline to paper cement to Clorox Bleach, etc. So it offers a huge variety of chemicals that wouldn't be practical to test for all of them. ScienceApe (talk) 06:42, 24 August 2008 (UTC)

I presume some inhalents can't be detected since they are absorbed straight into the blood rather than going through the usual digestion process (which ususally leaves behind a remnant of some sort). Presumably, some inhalents can be completely broken down by the liver into compounds which are indistinguishable from other non-drug compounds. This is complete speculation, I'm just guessing. —Cyclonenim (talk · contribs) 18:08, 24 August 2008 (UTC)

Actually, I think it's the reverse - digested compounds are processed by the liver to yield the active compound, and a secondary metabolite is left over which can be detected? Whereas an inhalant is the active compound itself, broken down completely within the cell whose receptor it docks with during normal cell-receptor recycling. I too am guessing! Franamax (talk) 20:35, 24 August 2008 (UTC)

Well the liver breaks down what is in the blood stream, not just digested. Digested stuff gets absorbed into the blood stream and is then processed by the liver. My point is, say, caffeine is processed by the liver to form paraxanthine, theobromine and theophylline, each of which are then metabolised a bit more then excreted. Often this metabolism process doesn't completely break things down into simple compounds or elements and they leave remnants. Perhaps some inhalents are made of substances which, when metabolised, are broken down into very simple substances in which is becomes impossible to tell what substance they originally were part of. But yeah, your explanation makes sense too, I guess we should wait for someone who knows what they're on about! —Cyclonenim (talk · contribs) 22:40, 24 August 2008 (UTC)

Hairspray vs. Houseflies

I'm wondering what happens to a housefly when I spray it with hairspray. I've been doing this for years as a cheap alternative to insect sprays, which smell bad and can't be sprayed near food because of their toxic nature. It works like a dream, and the fly will generally get up and fly around for a minute or so before settling down and not doing anything ever again (because you can pick them up with tissue and throw them in the toilet). My theory was that the hairspray was sticking the wings together, but now I doubt this is the case, because while they are flying the wings are permanently moving. Now I think it may be the eyes. Anyone with any ideas? --ChokinBako (talk) 10:23, 24 August 2008 (UTC)

I doubt that even if the hairspray blinded the fly that it would stop it from flying. I think, probably, it is more likely that the hairspray has blocked the insect's spiracles and it is having difficulty breathing.

Your economics are a bit dubious by the way. A branded hairspray costs 70-100p per 100ml according to the ASDA website. A branded flyspray costs 33p/100ml. The supermarket's own brand of hairspray is 19p/100ml however. SpinningSpark 11:07, 24 August 2008 (UTC)

Thanks. That makes a lot of sense. My economics is perfect, considering I already use hairspray anyway so I don't have to go out and buy anything. :) --ChokinBako (talk) 11:12, 24 August 2008 (UTC)

Insects don't have lungs - the get their oxygen by absorbing it through spiracles - which are little holes down the sides of their bodies. I kinda suspect that you are clogging those up - so the animal suffocates. It could still be the wings though. Remember, insects don't have soft, flexible skin - they have chitinous plates that fit together like a suit of armor. If you are gumming up the joints, that could stop them from flying or walking. The effect might be a little delayed because the stuff has to dry out and gradually get stickier and stickier. Hair spray is basically a polymer glue dissolved in alcohol to keep it liquid. As the alcohol evaporates, the hairspray turns into a gummy glue. Hairspray is not exactly nice stuff - I wouldn't be spraying it near food!

(True story of husband and wife who find a very large spider: Wife screams - husband rushes off to find some kind of spray to deal the spider. He comes back with the only thing he can find...Windex...she says "You can't kill a spider with Windex!"..."Just watch me"...at which point he whacks the spider with the windex bottle and squishes it. QED)

SteveBaker (talk) 15:41, 24 August 2008 (UTC)

It does take a while, around a minute, for the creature to stop flying and to sit down for a bit. If I leave it alone, it eventually gets up again and will start flying around, but I've found that another quick spray permanently disables it after that. Oh, and when I say 'near food', I didn't really mean directly at it, I just meant in the same room. It may not be the toxicity of the fly-spray that makes me sick, but the thought of eating with that sickly sweet smell wafting round me certainly does! Hairspray, however, though not my favourite choice of condiment, certainly is preferred over fly-spray!--ChokinBako (talk) 16:05, 24 August 2008 (UTC)

Interesting! But I don't think that changes my theory - it maybe just takes a couple of layers of goo to finally gum up the mechanism. SteveBaker (talk) 00:14, 25 August 2008 (UTC)

neo cortical physiology and art/drama/music therapy

On a neo cortical level what effect does art/music/drama therapy have upon the brains functionality? Could art therapy be used for the development of weaker hemisphere functionality, for example in the case of single hemisphere brain damage. What research is there available in this vein? —Preceding unsigned comment added by 193.36.79.207 (talk) 10:42, 24 August 2008 (UTC)

The Size Of The Universe

I was watching a Carl Sagan tribute a few nights ago, and it said that the universe is 78 billion light years across. How is this possible? The universe is only approx. 14 billion years old. Since nothing can travel faster than the speed of light, how can it have grown to this size, considering everything would have had to travel at least 39 billion light years (the radius of the universe) in only 14 billion years? Can someone explain what I am missing?--ChokinBako (talk) 15:54, 24 August 2008 (UTC)

Hmm, this seems to have answered my question, but says that the universe is actually 156 billion light years across......--ChokinBako (talk) 16:38, 24 August 2008 (UTC)

I believe the furthest that we can see is light from 14 billion years ago. --Russoc4 (talk) 16:42, 24 August 2008 (UTC)

Good question. Read our article on the observable universe, especially the sections on Size and Misconceptions. Simplified explanation is that light from (soon after) the Big Bang has been travelling for 14 billion years but space has been expanding during that time so the point from where the photon that reaches us was emitted (or rather the matter than was in that vicinity) is now much more than 14 billion light years distant in each direction. Gandalf61 (talk) 16:47, 24 August 2008 (UTC)

(ec) Both numbers are wrong, as mentioned in Observable universe#Misconceptions. But the correct figure is larger than c times the age of the universe. The picture in Metric expansion of space#Understanding the expansion of space might be helpful in understanding what's going on. (edit: Incidentally, where did you see the Carl Sagan tribute? Was it on real-world commercial TV? I'm curious how far that humble space.com article has spread.) -- BenRG (talk) 16:48, 24 August 2008 (UTC)

(ec) See also cosmic inflation. TenOfAllTrades(talk) 16:55, 24 August 2008 (UTC)

It has nothing to do with inflation, actually. Big bang cosmology without inflation still says that the observable universe is larger than c times the age of the universe. -- BenRG (talk) 17:18, 24 August 2008 (UTC)

So, basically, what we're saying is, because the furthest we can see is 14 billion light years away, that means that the universe must be 14 billion years old, because these are the first photons hitting us? But, the objects that emitted those photons are further away than that because the universe is expanding, right? As much as 5 times further away? Shouldn't it take them 5 times the present age of the universe to get that far, IF they were travelling at the speed of light? (The Carl Sagan tribute I saw on a website I stumbled upon. I just tried looking for it again but couldn't find it). --ChokinBako (talk) 19:18, 24 August 2008 (UTC)

BenRG will have to comment whether this is appropriate to this question, but I bookmarked their previous response to a similar question here - I was quite impressed at the time, since I'd never seen "loxodrome" used in a sentence before. :) Franamax (talk) 20:28, 24 August 2008 (UTC)

Yes, thanks for linking that because it's what I would have said here anyway. Basically you should abandon the idea that light travels a distance ct in a time t. The universe is about 14 billion years old, but light doesn't travel 14 billion light years in that time. Talking about "the distance something travels" is always a bit iffy because measuring along the worldline doesn't get you a distance (it gets you the elapsed proper time, which for light is always zero). To get a distance you have to measure along some other line, and there's no one correct choice. In that diagram, the path of the light is the red line, whose length is zero. The distances quoted in Wikipedia articles (the ones I've gotten my hands on, anyway) are measured along the orange line, which is not the path taken by the light. The reason to use that particular distance measure is that it's the only one with respect to which Hubble's law holds and with respect to which the universe is homogeneous. Other distance measures make the Earth's location look special. Ned Wright has a page about this (and read his excellent cosmology tutorial if you haven't). -- BenRG (talk) 01:09, 25 August 2008 (UTC)

The way I think of it (which I think is accurate) is that after the photon was emitted, the space between where it was emitted and where it is now expanded, so after the photon has travelled for one year and has gone one light year, it's source is more than one light year away because that light year of space has expanded. --Tango (talk) 21:00, 24 August 2008 (UTC)

This makes me think ... . If a photon was emitted with frequency, say, 46THz at what now is the edge of the universe, at what frequency dose it arrive at a detector on earth now? 93.132.191.111 (talk) 19:57, 24 August 2008 (UTC)

We can't see the edge of the universe (if it even has one). If you mean the most distant object we can see, which is a part of the primordial fireball that produced the CMBR, then the photon would be redshifted by the same factor as the CMBR, which is about 1100. So, about 40 GHz. That's assuming it wasn't absorbed along the way. -- BenRG (talk) 01:09, 25 August 2008 (UTC)

Also note the age of the universe is often approximated by putting Hubble's constant in reverse, assuming the rate of expansion of the universe has remained constant (which it has not). This also gives an approximation of size vs. age of the universe. SamuelRiv (talk) 05:52, 25 August 2008 (UTC)

I just heard a (popular science) talk by Brian Greene in which he claimed that the size and shape of the universe was unknown and that the size may be infinite. ike9898 (talk) 17:02, 25 August 2008 (UTC)

Yes. We've been discussing the size of the observable universe. Algebraist 17:12, 25 August 2008 (UTC)

It seems to me like the OP referred to the actual size of the universe. If I had intend my post to be part of the main thread above, I would have indented accordingly. ike9898 (talk) 20:04, 25 August 2008 (UTC)

I thought I had said this above, but I now recall it got lost in an edit conflict: We have no knowledge of the size of the full, not necessarily observable, universe. Algebraist 23:10, 25 August 2008 (UTC)

Terminology re: motion created by amniotic fluid

Pkdisme (talk) 17:09, 24 August 2008 (UTC) Please help!

I know that there is a specific term/phrase for "the motion in the womb simulated after birth by rocking" and I cannot find it.

I have checked for 2 days now and would very greatly appreciate your help.

Thank you.

After birth, the amniotic fluid is already released. Did you mean pelvic rocking to help detatch the placenta ? SpinningSpark 18:19, 24 August 2008 (UTC)

Perhaps "prenatal vestibular stimulation" ? You may find something more specific in the pre- and perinatal psychology literature. See also [6] Dostioffski (talk) 19:16, 24 August 2008 (UTC)

You're talking about how rocking a newborn baby is comforting to it because it simulates the motion of the amniotic fluid? SteveBaker (talk) 00:10, 25 August 2008 (UTC)

Future studies in areospace

hi, I am rigth now a undergraduate pursuing my mechanical degree. I wish to join the best university for my post graduation in aerospace. So what are the feilds I should research in as a mechanical engineer. —Preceding unsigned comment added by 125.16.89.84 (talk) 17:43, 24 August 2008 (UTC)

find definitions

the following words is what i need definitons for and i cant seem to find them. 1. advanced treatment options 2.level one trauma center 3.reactionary 4. proactive 5. not-for-profit, 501(c)(3) corporation 6. procuring 7. interns&internships 8. public service announcement 9. data support topic —Preceding unsigned comment added by 74.46.245.252 (talk) 21:31, 24 August 2008 (UTC)

1. No idea without context
2. See Trauma center
3. See wikt:reactionary
4. See wikt:proactive
5. See 501(c)(3)
6. See wikt:procure
7. See intern
8. See public service announcement
9. No idea without context

Hope that helps. --Tango (talk) 21:39, 24 August 2008 (UTC)

"Advanced treatment options" is a common medical phrase for "forms of treatment that are not considered until normal forms of treatment are exhausted." It mainly has to do with insurance. You can bill more for advanced treatment than you can for normal treatment, but you must meet eligibility restrictions mandated by the insurance company. -- kainaw™ 22:10, 24 August 2008 (UTC)

Ah, that would explain why I hadn't heard of it - I'm British, so don't have medical insurance (see NHS!). --Tango (talk) 23:47, 24 August 2008 (UTC)

It is also used under national health care systems. While healthcare is free, doctors are not free to perform any healthcare they like. They must justify use of "advanced treatment options" if the options are allowed at all. -- kainaw™ 02:06, 25 August 2008 (UTC)

(One should also explain that the NHS is free in the UK - but just like the USA, you can purchase health insurance if you want to. When I last worked in the UK, I got company-provided private health insurance just as I do here in the USA. However, our family doctor did a pretty good job and the only time I actually used the private insurance was for major surgery where it was possible to get treatment sooner and get perks like a private room and restaurant quality food while recovering. People complain a lot about the NHS but that's because they haven't experienced the alternative!) SteveBaker (talk) 04:49, 25 August 2008 (UTC)

What is this bird?

2 birds.

Per instructions on the WP:PPR page, I'm supposed to ask you guys if I need to identify a bird. The birds I need IDing are the 2 birds to the right. Any other info like what gender they are, what they're doing would be appreciated. Pie is good ^{(Apple is the best)} 22:30, 24 August 2008 (UTC)

They're young gulls. At that age, they'll either be looking for food or looking for their mother. It's impossible to determine sex visually when young (it's *virtually* impossible when they're adults!). As for species, I don't really know for sure. I like interacting with gulls but I've never been a 'gull spotter', if you know what I mean. Young gulls can be tricky to identify but they're definitely 'large white-headed gulls', as described at Gull#Taxonomy. Only way I could tell you for sure is if I saw them with their mother. --Kurt Shaped Box (talk) 23:06, 24 August 2008 (UTC)

Concur, compare Image:Herring Gull Fledgling.jpg. Nanonic (talk) 23:12, 24 August 2008 (UTC)

Concur with everyone so far, and add that the folks at Wikipedia talk:WikiProject Birds are usually helpful with bird ID requests. -- Coneslayer (talk) 15:07, 25 August 2008 (UTC)

advantage of youth in gymnastics

The article Age falsification in gymnastics says younger (female) gymnasts have an advantage because "Smaller, lighter girls generally excelled in the more challenging acrobatic elements required by the redesigned Code of Points". But if this is correct, wouldn't the sport set minimum heights and weight requirements rather than age limits? So... is it really correct or is there some other advantage? —Preceding unsigned comment added by 64.228.91.86 (talk) 23:18, 24 August 2008 (UTC)

I don't know if it's true, but what they've been saying on the teevee is that the younger gymnasts are more fearless... that they have less visceral appreciation for how badly one can get hurt doing these gymnastics, and can therefore do more dangerous, impressive moves with confidence and steadiness. So that would be an advantage directly related to age. If sourced, maybe this would be good for the article. --Allen (talk) 00:06, 25 August 2008 (UTC)

I saw a news special (CNN?) at the airport on this and the gymnastic expert they had (some former gold medalist—maybe Mary Lou Retton? I was only paying half attention) said that younger girls are much more flexible and pliable and that this helps a lot in certain events. They said the downside though is that lack of experience can really hinder you, so it's not a surefire tradeoff at all. --98.217.8.46 (talk) 02:04, 25 August 2008 (UTC)

Another advantage to using underage gymnasts is that because there is more of the population to choose from, finding extremely competent athletes is easier. If younger gymnasts also have a physical advantage, the two factors combine to give a very significant advantage to the team with underage athletes. --Bowlhover (talk) 09:05, 25 August 2008 (UTC)

What would be the point of banning short people? I'm guessing here, but I suspect that they ban children to try to prevent the sport from being an exercise in child exploitation like Camel racing. APL (talk) 03:06, 25 August 2008 (UTC)

One expert on child development was quoted as saying that the if he had to design an activity that would be most likely to harm young children, the Olympic gymastic exercises would be a pretty close match. He went on to explain how the stresses imposed on only partly developed muscular/skeletal system by gymnastics are almost certain to cause damage that would persist into adulthood. It's certainly not just height and weight - and it's not even a matter of fairness for the older athletes - it's about not harming children. SteveBaker (talk) 04:44, 25 August 2008 (UTC)

FYI - I have amended the article mentioned by 64.228.91.86 (Age falsification in gymnastics) with this info provided by y'all and added fact tags where I got stuck for sources – so if anyone does remember your sources, please drop by and add them! The two new sections are called Reasons for age falsification and Reasons for age restrictions. Best, WikiJedits (talk) 17:19, 26 August 2008 (UTC)

One of the advantages kids have in gymnastics is that they have less momentum than older and heavier people. This can easily be visualized by thinking of an ice skater doing a sharp curve on ice. Compared with a heavier skater, a light-weight skater can skate a sharper curve. Also, a light-weight skater can more easily control the body in a gradual curve, thereby avoiding over-control or under-control and can concentrate on grace rather than mere mechanics and maintaining balance. Momentum also is an important factor in certain other sports. How about having weight classes in gymnastics and other sports in which the body is thrown about or must suddenly move in another direction?Andme2 (talk) 07:03, 28 August 2008 (UTC)

Space Questions

Why do all the planets orbit in pretty much the same plane, and not spherical? The best reason I can come up with is that because of the suns rotation, it isn't a perfect sphere, even though at distance I don't think that would matter.

Why is it so hard to get out of Earth's (or any objects) gravity? Why can't say a specially fitted F-22 just keep applying thrust and getting higher and higher?59.100.251.111 (talk) 23:45, 24 August 2008 (UTC)

The solar system formed out of a big cloud of dust and gas that collapsed. Due to conservation of angular momentum, as it collapsed, it rotated faster and faster (spin round and round on the spot with your arms out, bring your arms in and you suddenly speed up - it's the same principle). When something rotates, in naturally spreads out into a disc (ever seen someone making pizza bases by spinning them around rather than using a rolling pin?), the planets them formed out of that disc, which is why they are all in the same plane. The reason an aeroplane can't keep thrusting and go higher and higher is because the atmosphere gets thinner and thinner and aeroplane engines need air to work (there are specially designed engines for flying at really high altitude which require less air, but there is still a limit to how high they can go). To get into space you need rockets, which don't need air to work (actually, they are more efficient in a vacuum, I think). --Tango (talk) 23:53, 24 August 2008 (UTC)

That's all correct, but there are two additional reasons why you can't "get out of Earth's gravity" using an airplane. First, not only do the engines need air, so do the wings. In the thin atmosphere at high altitude, they won't provide any lift and the plane can't keep rising unless it uses engine power alone to overcome its weight, i.e. climbing more or less straight up. Fighter airplanes do have engines powerful enough to do that, or some of them do, but they don't carry nearly enough fuel to do it for very long.

And second, in order to get free of the Earth's gravity, you need to reach escape velocity. If you're anywhere within a few hundred miles of the Earth's surface, this is about 25,000 mph (40,000 km/h). Airplanes don't carry nearly enough fuel to accelerate to such speeds, even if the atmosphere was not an issue. At a higher altitude the escape velocity is lower, but to first lift to a high altitude and then reach escape velocity would require even more fuel, so this isn't impossible either. If you look at a space shuttle or any sort of rocket intended to launch things into orbit or deeper into space, when it's sitting on the launch pad, most of its volume is fuel (and oxidizer). That's not true of airplanes.

So escaping Earth's gravity with an airplane is impossible for three different reasons. --Anonymous, 03:57 UTC, August 25, 2008.

No - you don't need to reach escape velocity. If you have a rocket engine and enough fuel you can power your way out of earth orbit at (say) ten miles per hour. Escape velocity refers to ballistic objects. If you can reach escape velocity then you can turn your engine off and still escape from the earth's gravity before falling back to earth. But if you have engines - then that's irrelevent. Think about it this way. Suppose you launch at half of escape velocity. You'd shoot up into the air - then gradually slow down more and more until your upward speed was zero. But if you fired your engine again at that exact moment, then instead of falling back down, you'd go up a little bit more. If you have enough fuel, you can keep doing that until you reach any desired altitude without ever reaching escape velocity. The only real problem is that jet engines need oxygen which they get from the air. There have been attempts to design engines that could switch modes as they change altitude. One that I happen to recall was the (unfunded) British HOTOL craft with it's RB545 engines. It would have been able to take off from an ordinary airfield just like any other plane - flown up until it's engines were gasping for oxygen - then started using liquid oxygen to supply them - effectively converting them from jets into rockets to provide the last boost into orbit. No escape velocity - no dramatic vertical launch - a true space plane. Sadly, it was never built. SteveBaker (talk) 04:39, 25 August 2008 (UTC)

You don't need to reach escape velocity if your desire is to reach orbit (you need to reach orbital speed, though), but if you want to escape Earth's gravity then you'll need to reach escape velocity at some point - you can't continue thrusting forever unless you are able to collect reaction mass from the space you travel through, which isn't a feasible way to do it. If you can thrust long enough to get a significant distance from Earth, then escape velocity is less, but you still have to reach it or you'll fall back to Earth once you run out of fuel. --Tango (talk) 17:26, 25 August 2008 (UTC)

So, essentially, you're saying that as you leave earth's gravity under power the escape velocity will go down until it reaches the speed you're already going? That makes sense. But if you were in such a space ship you wouldn't say that you were "trying to reach escape velocity" You'd just say "I'm trying to reach Mars (or wherever) under full thrust.". If you never intended to shut down your engines then escape velocity wouldn't have much practical meaning. APL (talk) 18:14, 25 August 2008 (UTC)

Yeah, that's about it. I was kind of assuming you were heading off to infinity, since that's how escape velocity is defined. If you're talking about the real world, then things are slightly different. A journey to Mars requires you to account for the Sun's gravity and Mars' gravity in addition to the Earth's. --Tango (talk) 19:01, 25 August 2008 (UTC)

I'd just like to point out that I mentioned this method in my previous item, and also pointed out that it consumes more fuel than rapidly reaching the higher escape velocity near ground level -- which is why real-life space launches always accelerate rapidly. The reason is that the engines must produce an amount of energy equal in magnitude to the spacecraft's gravitational potential energy not matter whether they do it rapidly or slowly, but if doing it slowly, they also need to use additional energy to keep the craft from falling to Earth in the meantime. Incidentally, in contrast to the physics goofs common to many movies, this bit of orbital mechanics was correctly depicted in the 1963 comedy The Mouse on the Moon. --Anonymous, 21:59 UTC, August 25, 2008.

Not - so - you don't need to expend energy to "keep the craft from falling to Earth in the meantime" - you can increase your distance from the earth by flying in a gradual spiral path - you don't need to expend energy to avoid falling. Theoretically, the energy you need to expend to thrust out of orbit gradually is exactly the same as blowing it all up in a couple of minutes to get escape velocity. It's slow, boring - but possible - although if you do that, you'll still have to reach escape velocity - but you could do it gradually. Remember: The ISS has been maintaining its distance from earth without falling back OR expending energy for years. SteveBaker (talk) 02:59, 26 August 2008 (UTC)

You do need to thrust to maintain position, see gravity drag. A gradual spiral path only works once you're outside the atmosphere, inside it atmospheric drag would make it extremely inefficient. Also, at the risk of being pedantic, the ISS has required frequent boosts from other craft over the years to compensate for drag caused by the very thin, but still present, atmosphere at it's altitude. --Tango (talk) 20:23, 26 August 2008 (UTC)

Okay, I concede that once you reach orbital speed you don't need to expend energy to maintain altitude. But until then you do. --Anon, 05:21 UTC, August 27.

Woah there. In THEORY to "escape the earth's gravity" you need that much speed - but to escape earth's gravity you have to travel an infinite distance away - which is fine if this is a thought experiment that requires me to travel an infinite distance but doesn't let me have infinite fuel. But otherwise - for any practical purpise - it's bogus - you'll enter the gravity well of some other object sooner or later so you DON'T need escape velocity to get wherever you want to go...and even with escape velocity, the friction due to teeny-tiny amounts of gas and dust will eventually slow you down below escape velocity and you'll fall back down again.

For any practical mission - those infinities are irrelevent. If I only have to get a hell of a way from earth (to the nearest star - or to the next galaxy over to the left) - then with enough fuel we can do it all at 10mph. Sure, it's a lot of energy - but it's not forbidden by the laws of physics. I can get anyplace in the actual universe without needing to attain escape velocity - and having escape velocity is not guaranteed to be enough to reach some places in the universe because of friction.

Sure, it's currently more efficient to set off a gigantic rocket more or less all at once - hit escape velocity and then coast - but that's because of the nature of the technology we're currently using. With energy extracted from sunlight and relativistic rocket exhaust velocities (think Ion drive) - or solar sails powered from gigantic lasers - or magnetic ram-scoops it's OK to thrust continually and never come close to escape velocity - and you'll still get where you're going.

So the correct answer to the OP's question is "Sure you could thrust your way out there" - not "No, you can't". SteveBaker (talk) 02:54, 26 August 2008 (UTC)

The OP's question regarded doing it with an aeroplane, not some hypothetical future technology. --Tango (talk) 20:23, 26 August 2008 (UTC)

We're allowed a "specially fitted F-22" - I decided to fit an ion drive and some solar sails. :-P SteveBaker (talk) 21:42, 26 August 2008 (UTC)

Regrettably, neither of which are likely to do the job, since they don't work all that well inside the atmosphere! ;) --Tango (talk) 22:08, 26 August 2008 (UTC)

Would I be correct to say that you need a sufficient amount of energy to escape the dominance of Earth's gravity? So starting from ground level, a rocket acquires a large amount of kinetic energy (it accelerates to escape velocity) and this kinetic energy gets traded for gravitational potential energy (the rocket flies higher) - and at a certain point Earth's gravity becomes just a small factor considered along with all the other small gravity factors (Jupiter, Alpha Centauri, etc.)?

The "do it at 10 mph" thing seems somewhat of a canard, moving through the atmosphere at 10 mph requires a definite amount of energy expended as friction (drag), whereas moving through space at 10 mph requires almost no energy expenditure if you're moving in an orbit - but moving upwards at 10 mph needs a whole bunch of energy.

I struggle with these concepts, so please fill me in. Let's assume that the F-22 has a constant succession of refueling tankers showing up just in time, and there's another F-22 flying beside it with a big oxygen tank so the engines can maintain thrust. Franamax (talk) 07:04, 27 August 2008 (UTC)

Yes, the minimum possible amount of energy required to reach a certain altitude is given by the gravitational potential energy at that altitude. But because the earth's gravitational field gets weaker the higher you go, the energy required to get to INFINITE altitude can be imparted on the object as kinetic energy on launch - hence, you can get an object moving at escape velocity - and it's kinetic energy will exceed the amount of gravitational energy it'll have - even at infinite altitude. But (and this has been my point to the nay-sayers) there is no reason why you have to expend all of that energy at the get-go. You can also get to an arbitary height by expending the energy more gradually.

Certainly, doing it slowly will require a lot more energy in practice than in theory - and that's why we don't usually do that. But certainly, your thought experiment with the F22, oxygen tanks, etc, etc would work. And (as I said WAY up the top of this discussion) spacecraft like the (failed) British HOTOL would have done exactly that. The HOTOL was intended to use engines that would use atmospheric oxygen - like an F22 - up to whatever altitude that works at - then start using on-board oxygen tanks to turn the engines into rockets in order to fly up to orbit. The HOTOL failed for reasons relating to funding - it's clear that it's possible technologically. So it's more than just a thought experiment - you really could build a practical space-plane that would fly conventionally up to enough height and then keep on going. SteveBaker (talk) 13:59, 27 August 2008 (UTC)