Wikipedia:Reference desk/Archives/Science/2011 July 9

= July 9 =

Solid Oxygen Combustion
Hi, I resintly han a discussion with my mom about the dangers of consentrated oxygen, specificly using solid oxygen to disperse smoke in a controlled amount while it dissolves.

I have witnessed alen nursall freely handling solid oxygen with no apperent ill affects. Dose this mean that it's safe to handle?

More basiclly, is oxygen combustable or dose it require a fuel to oxidize with? — Preceding unsigned comment added by 174.2.44.103 (talk) 04:56, 9 July 2011 (UTC)


 * Ordinary combustion is basically a fuel reacting with oxygen (or something that supplies oxygen). Some substances will spontaneously react with oxygen at room temperature, others not. Combustion can be very rapid (explosion!) or not, so there's definitely a safety question depending on the reactivity of the fuel, the temperature, and the concentration. Twang (talk) 05:13, 9 July 2011 (UTC)


 * Solid oxygen ? You have to seriously lower the temperature and/or raise the pressure just to get oxygen to liquify.  To get it to freeze at normal pressure you need to lower the temp to -361.82 °F.  That seems rather dangerous to handle because of the low temp. StuRat (talk) 05:17, 9 July 2011 (UTC)


 * Oh yes, oxygen will definitely freeze if you get it cold enough. The only thing that won't freeze at 1 atmosphere pressure, at any temperature no matter how cold, is helium (that's for some rather strange quantum reasons).
 * However I do seriously doubt that the OP saw someone "handling" solid oxygen. More likely it was something like sodium oxide, which is a solid that can be used to generate oxygen. --Trovatore (talk) 05:21, 9 July 2011 (UTC)
 * Hmm, don't know what I was thinking there. You can get oxygen from sodium oxide, but it's not easy.  Maybe I was thinking of sodium peroxide.  Our oxygen generator article has more possibilities. --Trovatore (talk) 07:28, 9 July 2011 (UTC)
 * I don't know - the OP mentions Alan Nursall, who I gather is a television personality with his own popular science television show: the Alan Nursall Experience on the Discovery Channel. It's quite possible that he did get to play with some frozen oxygen as part of a demo.  That said, except under carefully controlled conditions any condensed-phase (solid or liquid) oxygen is potentially very dangerous, as it will sustain vigorous combustion.  (The last half of this video shows a test tube containing a small volume of liquid oxygen 'eating' several lit wooden splints: .) TenOfAllTrades(talk) 13:15, 9 July 2011 (UTC)
 * We have an article on solid oxygen, with some interesting forms, such as red oxygen and metallic oxygen. StuRat (talk) 05:25, 9 July 2011 (UTC)
 * I think that "solid oxygen" is being used colloquially here, to mean e.g. lithium perchlorate, potassium perchlorate, sodium or potassium chlorate, iodine pentoxide etc. I don't think there's any fixed definition for this usage, so we can't make any statement about the safety of doing something with "solid oxygen" in general.  We'd need to know the specifics.  Note however that all strong oxidizers have certain basic hazards.  I'm not quite sure what "disperse smoke" means - is it to clear a room, or to make a firework?  Obviously the only general statement we can make about pyrotechnics and bomb-making is you'd better know what you're doing, and knowing the name of the chemical is only the first baby step in that direction.  (Al Qaida is free to ignore that last, since they have Allah on their side they shouldn't have to worry about safety!) Wnt (talk) 15:36, 9 July 2011 (UTC)

Well, of course the thing that is commonly used to generate fake smoke is dry ice, i.e., solid CO2, not solid oxygen. Looie496 (talk) 17:02, 9 July 2011 (UTC)

Hi, It's me again. I just want to clarify that I am NOT making a bomb, and for my (hypothetical, just speculation) porposes, I think that dry ice wont last long enough, as I wold only have maybe 1 liter of space to make steam-locomotive smoke for 2-3 hours. On the "frozen" note, I think it was compressed and it may have been regular air (it was white), but he Definitly handled it, and it did dissolve back into the atmosphere. And what about Sublimination and Deposition (solid directly to gas and vice-versa)? 174.2.44.103 (talk) 06:14, 10 July 2011 (UTC)


 * Sounds like it was dry ice to me, since it could be easily handled (but you'd probably want to wear gloves). A liter might be enough to last 2-3 hours, depending on the flow rate you need.  And yes, it sublimes directly into the air.  The next step would be liquid nitrogen, but now you're getting into the danger category, so have to buy it at a chemical supply company and keep it in an approved thermos, versus dry ice which you can buy at many grocery stores. StuRat (talk) 08:27, 10 July 2011 (UTC)

Jehovah's Witnesses and oxygen
The Jehovah's Witnesses doctrine expounded to me by a national overseer is that oxygen is pneu the breath of God which was imparted to living things at their creation. He insisted than man can never duplicate pneu. I countered by telling that one can demonstrate keeping a mouse alive breathing oxygen generated by a chemical reaction, and that I therefore could also breathe synthetic oxygen, He became angry and stalked away. Will a Witness or someone who understands their teaching comment about any misunderstanding here? Cuddlyable3 (talk) 08:01, 9 July 2011 (UTC)
 * What you generate in your chemical reaction is not a "duplicate" of oxygen, nor synthetic oxygen. It is simply oxygen. It's really no different from noting that the oxygen we normally breathe is generated chemically too, by photosynthesis. While seeming to be an odd thing for a religion to be concerned about, on this one the perspective seems realistic, whether God made it or not. (Hope you don't mind me having a crack at this, even though I'm not a Witness, nor do I claim to understand their teachings) HiLo48 (talk) 08:09, 9 July 2011 (UTC)
 * Humans can make oxygen through Nuclear transmutation which seems to counter what the Witness was claiming, but HiLo is right that chemical reactions don't create oxygen molecules, they just release them from other bonded elements. -- Daniel 08:16, 9 July 2011 (UTC)

From a JW publication: The account of the creation of man states that God formed man from the dust of the ground and proceeded to "blow (na-phahh') into his nostrils the breath (nesha-mah') of life, and the man came to be a lving soul (ne-phesh)." (Gen. 2:7) I think the overseer referred to the ancient greek word πνεῦμα (pneuma, "wind, air, breath, spirit") today a root of the word pneumatic. I don't see any understanding of elemental oxygen here which in pure form is toxic. Cuddlyable3 (talk) 10:52, 9 July 2011 (UTC)


 * Jehovah's Witnesses are not known for their scientific knowledge, and don't tend to hang out at the science desk.--Shantavira|feed me 11:59, 9 July 2011 (UTC)
 * It would appear that that particular JW didn't even understand what the Bible was saying, never mind how it works scientifically. The "breath of life" is not "oxygen", but rather it's a metaphor for the spirit, the spark of life, whatever you want to call it. No amount of oxygen will revive a dead person, i.e. one whose spark of life has been fully extinguished. Realizing that he must have had it wrong might be what impelled him to leave in a huff (or if that's too soon, a minute 'n a huff). Ironically, though, he was almost right; unless humans have figured out a way to resurrect the dead (in real life, not in Plan 9 from OUter Space) and I didn't hear about it, only God (or Mother Nature, or whatever metaphor) can provide the spark of life. ←Baseball Bugs What's up, Doc? carrots→ 12:23, 9 July 2011 (UTC)
 * Maybe he did understand and thought the OP was making fun of it by taking a different meaning. Grandiose (me, talk, contribs) 14:14, 9 July 2011 (UTC)
 * Maybe just a failure to communicate? ←Baseball Bugs What's up, Doc? carrots→ 14:25, 9 July 2011 (UTC)
 * I don't think there's any reason to call "the breath of life" in Gen. 2:7 a metaphor, it's just an honest attempt by the author to describe something that he was not in a position to understand due to the insufficient development of biology and physics at the time. The sentence is very down-to-earth and materialistic, with quite specific natural substances and organs being mentioned by name. "Gen. 2:7: Then the LORD God formed a man from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being." If it were about "the spark of life", abstractly, there would have been no reason to specify the organ through which the breath was introduced into the body - namely, the nostrils. It's just that the author and his culture knew from experience that what distinguishes living bodies from dead ones is that the former breathe, while the latter don't. Furthermore, this seemed to imply that the soul and the breath, whose presence apparently made a body living, were somehow connected or indeed identical. Thus, in a dying person, the life=soul=breath was thought to exit the body through one last exhalation (this is still visible in various expressions, now really as a mere metaphor). This notion is even expressed in word derivations: in Hebrew, from the verb nāšam "to breathe", one has derived nəšāmā and nešem, both of which can mean "spirit", "soul" (and "breath", although the former may have retained only the abstract meaning in modern Hebrew, I'm not sure about that). Similar connections are found in Latin and Slavic (spiro - spiritus, duh - duša). So it seemed logical that, conversely, in order to make the body living at the final stage of creation, the Creator had to transfer the breath=soul=life into the body.
 * We have turned these notions into mere metaphors, because we now know how these things really work, but the authors and audience of the Bible back then had no reason to see them as metaphors, because they really didn't have anything better than them in terms of a factual description. So the poor fundamentalists' hopeless attempts to tease out from the Bible a precise scientific description of how things work are, in fact, more adequate and faithful to the original purpose of the text than the attempts to avoid the embarrassment by retroactive "metaphoric" readings. --91.148.159.4 (talk) 20:38, 9 July 2011 (UTC)


 * Let me see if I got that right. A Jehovah's Witnesses said some strange thing, You countered with science, They got upset and left. - Sounds about right to me. Dauto (talk) 13:52, 9 July 2011 (UTC)

This sounds like some variation on Gnostic theology, which defines soul as the combination of soma (body) and pneuma (spirit). It's the job of the Holy Spirit to breathe pneuma into the lifeless clay which is soma. Pneuma literally means "air" in Greek, which is what makes me think this is the origin of the confusion regarding oxygen. (For those who may not be aware, much of the original Bible was written in Koine Greek.) -- SmashTheState (talk) 13:54, 9 July 2011 (UTC)
 * The Old Testament was Hebrew and the New Testament largely Greek, right? ←Baseball Bugs What's up, Doc? carrots→ 14:24, 9 July 2011 (UTC)
 * The OT is mostly classical Hebrew and Biblical Aramaic. The NT is probably all Koine Greek, although some claim that Matthew may have had a Hebrew precursor. Jesus probably spoke Armaic (or Texan English, according to some sources ;-). --Stephan Schulz (talk) 14:43, 9 July 2011 (UTC)
 * Do the Jehovah's Witnesses really believe, as a group, that pneu = oxygen? And is that atomic oxygen or molecular oxygen?  Since oxygen was created in the supernova of some star preceding formation of the Earth, the equation with atomic oxygen implies a peculiar but interesting doctrine, which I've never heard before, that the initial "let there be light" was the explosion of this ancient ancestor, to which Earth and moon and sun owe so much of their creation. Wnt (talk) 15:22, 9 July 2011 (UTC)
 * Jehovah's Witnesses are taught to welcome changes to their religion's doctrine, regarding such "adjustments" as "new light" or "new understanding" from God and proving that they are on the "path of the righteous", see Development of Jehovah's Witnesses doctrine. All hail Wnt the bearer of New light! Cuddlyable3 (talk) 15:56, 9 July 2011 (UTC)
 * Unfortunately, they have yet to see the light regarding the word "Jehovah" being a mis-translation. ←Baseball Bugs What's up, Doc? carrots→ 19:09, 9 July 2011 (UTC)

Theory of mind article
The first section begins with, "Theory of mind is a theory insofar as the mind is not directly observable." This seems to me rather odd of a definition of the term theory. I guess it's not a scientific theory then? 66.108.223.179 (talk) 12:39, 9 July 2011 (UTC)
 * The article gives a source for the statement and goes on to explain "The presumption that others have a mind is termed a theory of mind because each human can only intuit the existence of his or her own mind through introspection, and no one has direct access to the mind of another." This is not to define "theory". Instead it uses the dictionary definition of theory n. A coherent statement or set of statements that attempts to explain observed phenomena, A logical structure that enables one to deduce the possible results of every experiment that falls within its purview. Cuddlyable3 (talk) 13:23, 9 July 2011 (UTC)


 * I agree, as I have said on the talk page of the article, that the term "theory" is poorly chosen here: "theory of mind", as used in the literature, is really more of a behavior than a theory -- the behavior of attributing mental states to other individuals.  The simple fact is that many scientific concepts are poorly named -- once a name becomes established it is very difficult to change, even if it was not well chosen in the first place.  The history here is that Premack and Woodruff originated the term in 1978 in an article called "Does the chimpanzee have a theory of mind?", and the literature that followed has simply adopted their term.  By now it has been used so widely that it would be virtually impossible to change.  I prefer Daniel Dennett's term intentional stance, although that too is less than perfect. Looie496 (talk) 16:48, 9 July 2011 (UTC)


 * The use of theory here (which is still not the common use as one would find when people really mean to say "hypothesis") is the same theory one finds when using the word in concepts like color theory and music theory, which is to say it is a collection of ideas and concepts which make up a cohesive whole. This is actually almost exactly what a scientific theory means as well (excepting that the ideas and concepts are those which have undergone rigorous testing using scientific methods).  But basically, "a group of related ideas and concepts" is what a theory is.  -- Jayron  32  18:30, 10 July 2011 (UTC)


 * Okay -- but to me, saying that monkeys have a "theory of mind" because they do things to deceive other monkeys (this is generally considered evidence for ToM in the literature) is equivalent to saying that animals have a "theory of food" because they eat some things but not others. It might possibly be valid in some technical philosophical sense, but I don't think it is a useful way to describe the data. Looie496 (talk) 19:57, 10 July 2011 (UTC)


 * Theory of mind is a clunky phrase for what is probably better described as metacognition. The "theory" in "theory of mind" is there more because of the idea of organization than anything.  Just as a theory is an organized set of ideas, the "theory of mind" requires an inherent level of organization in the mind of the subject itself.  Look at it this way: Atoms existed before Dalton described the Atomic theory.  Evolution existed even before Darwin (and others) organized the Theory of evolution.  An organism can have a mind, but that does not mean it has a "theory of mind".  My sense is that the concept of "theory of mind", which sounds starkly like metacognition, excepting that metacognition is applied to the self (the ability to think about one's own thinking) while theory of mind is applied to those outside of the self (the ability to think about other people's thinking).  But the two concepts seem very intertwined, and the fact that we have two articles, and two terms, probably is more to do with the fact that different people have arrived at roughly the same concept through different means.  -- Jayron  32  22:18, 10 July 2011 (UTC)

Tsunamis on Atolls and Small Islands?
There are over 25,000 islands in the Pacific, and Tsunamis are very common there. What happens when a tsunami hits these small islands, even coming from far away with a very much diminished wavelength? They don't have anywhere near the defense that a larger and developed island would have, but all the stacking up problems that seems like they'd just be washed over and turned to mud. Yet there are endemic ground nesting flightless birds and plants on many of the islands, so obviously this doesn't happen; or doesn't happen very often. Why not? Are the vast distances involved the only thing that saves them? --96.40.227.54 (talk) 16:09, 9 July 2011 (UTC)


 * The devastating effects of tsunamis are largely a product of gradually shallowing water depths, which cause water to pile up as the wave moves toward shore. That doesn't usually happen to small islands if they are surrounded by deep water.  For example, the Indian Ocean tsunami, which had devastating effects on Sri Lanka, went past the island of Diego Garcia (not too much farther from the epicenter) with hardly a ripple -- it had larger effects on the coast of Africa, thousands of miles farther away.  This is not to say that tsunamis cannot have devastating effects on small islands:  they certainly can in some cases. Looie496 (talk) 16:56, 9 July 2011 (UTC)


 * Also, try a Google Scholar search like tsunami seamount atoll. Seamounts and mid-ocean ridges tend to focus tsunamis, so that their heights may be higher near atolls over those bathymetric structures. ~ AH1 (discuss!) 20:03, 9 July 2011 (UTC)

As life expectancy increases, do other events in our life happen proportionally later?
A hundred years ago the life expectancy was 59 years. It's now around 80, depending ont he country you come from. So is puberty and menopause correspondingly later, or do we have the same length of youth as they did before, with more old age? If they are later, are they proportionally later or just a bit later? Or perhaps they're earlier?--92.251.212.78 (talk) 16:33, 9 July 2011 (UTC)
 * Puberty has, I believe, actually become earlier by a fair amount. I think it's down to diet. Grandiose (me, talk, contribs) 16:58, 9 July 2011 (UTC)
 * The strongest association with puberty onset time is childhood obesity, which makes puberty earlier in girls and later in boys. As for the original question, most of the extension of lifespans in humans over the past few centuries can be thought of as simply removing early causes of death, whether through improved nutrition, improved hygiene, vaccines, better treatments for disease, accident prevention, etc. 99.24.223.58 (talk) 18:14, 9 July 2011 (UTC)
 * Also see Infant mortality, a prime factor - even today - in average life expectancy. --Cookatoo.ergo.ZooM (talk) 18:53, 9 July 2011 (UTC)
 * Yes, by implication, we're talking average life expectancy, which does not necessarily have anything to do with individuals. I've got a distant relative who live to be 101 - from the early 18th century to the early 19th century! Another life expectancy factor was the number of women who died in their 20s or 30s in the old days, due to childbirth complications. In the old days, if something serious happened to you, you typically died. If not, then you might live to 80s, 90s, or over 100. Lots of luck factors there. ←Baseball Bugs What's up, Doc? carrots→ 19:07, 9 July 2011 (UTC)
 * Indeed. Take a look at Life expectancy. Even in medieval Britain, if you reached adulthood, you could expect to live what we would expect to be a decent lifespan. That page says an aristocrat 800 years ago aged 21 could expect to live to 64 and by 500 years ago, it was 71. It wouldn't have been unusual to live into your 70's or 80's. It doesn't mention peasants, but it's not obvious to me that they would have had a significantly shorter lifespan. They probably had more accidents, but disease was probably about the same. Peasants probably had better diets (less luxurious, but that's usually a good thing - there's a lot to be said for vegetarianism). I expect the article discusses aristocrats simply because they kept better records, so we know how long they lived.
 * Fast-forward to 1911, and life expectancy once you reached adulthood was very similar to what it is now. Improvements since then have been largely due to fewer people smoking and improved treatments for a few specific diseases (well, that's a best guess - there is still some dispute among actuaries about the exact causes of recent improvements).
 * --Tango (talk) 18:12, 10 July 2011 (UTC)
 * Regarding a business career, if people hang on to their assets or positions because they are living longer, then the advancement of younger people is going to be slower. People living longer gives them more time to accumulate wealth, so inequality may increase. However that does not matter if people innovate and therefore bypass the career ladder. 2.101.12.198 (talk) 10:47, 10 July 2011 (UTC)

Are you only interested in biological events? I think it has been a trend that achievement of financial independence from the parents has been occurring later and later in life. ike9898 (talk) 16:11, 11 July 2011 (UTC)
 * True, and directly proportional to income inequality. 99.24.223.58 (talk) 20:06, 11 July 2011 (UTC)

Bond film realism
License to Kill Is the explosive decompression scene scientifically accurate? In particular; increased pressure followed by severe, but not seemingly "instant", pressure release * , and; the effect on the human head. * As opposed to negative pressure followed by a release. -- Rixxin  ( talk ) 17:58, 9 July 2011 (UTC)
 * Yes I think so. I read on this desk (a while ago, I'm a bit of a lurker) about someone who was caught in an explosive decompression and their head was found metres away up some vent, with nothing left of the body. I believe baseball bugs provided the link.--92.251.212.78 (talk) 19:14, 9 July 2011 (UTC)
 * In the article you linked "explosive decompression" is listed as a fallacy. They do, however, compare it merely to being in a low-pressure situation rather than a rapdily changing pressure system. Grandiose (me, talk, contribs) 19:16, 9 July 2011 (UTC)


 * Whenever this topic comes up on the RDs, it is obligatory to mention the Byford Dolphin incident. Gandalf61 (talk) 19:31, 9 July 2011 (UTC)

Evolutionary pressure for theropod arms
Having recently seen an exhibit about the T.rex at the Boston Museum of Science, I was wondering (as my title implies) what the pressure towards having such little arms would be, why would the more short fore-limbed individuals be more successful in reproduction than a more long-limbed individual?199.94.68.201 (talk) 19:30, 9 July 2011 (UTC)


 * Any body part composed of living cells consumes resources, both to grow and to continue existing -- so if a body part serves no function, its size should be reduced in order to minimize food requirements. Our article on vestigiality gives more information. Looie496 (talk) 19:41, 9 July 2011 (UTC)


 * Maybe the females didn't mate with as many guys whose bigger arms pushed down on their backs. 76.27.175.80 (talk) 19:56, 9 July 2011 (UTC)


 * The males with shorter arms couldn't play with themselves, so had no choice but to chase females. :-) StuRat (talk) 06:18, 10 July 2011 (UTC)


 * Did dinosaurs have penes? I'd have thought, being the ancestors of modern birds, that they'd have had cloaca. -- SmashTheState (talk) 15:10, 10 July 2011 (UTC)


 * Couldn't they play with their cloaca? -- Jayron  32  18:26, 10 July 2011 (UTC)


 * I suspect that longer arms interfered with their ability to balance. That is, since they balanced their tail in back against their head and torso in front, having heavy arms in front too would require either a bigger tail or smaller head and torso.  All of these have associated costs.  Also, big arms would mean more air drag and potential to get snagged on trees, while chasing prey. StuRat (talk) 06:18, 10 July 2011 (UTC)
 * Following on from that view, would the kangaroo be a modern animal with similar characteristics? Although their arms are short, a flexible body allows them to reach most extremities when they feel like a good old scratch. Maybe T-rex was a lot more flexible than the bony skeleton we usually see would suggest. Oh, and a Google search for "kangaroo mating" images should relieve all concerns on that front. HiLo48 (talk) 06:34, 10 July 2011 (UTC)

Just pointing out that any theory seeking to explain the short arms of most giant theropods (such as T-rex) should also explain the relatively long arms of most small-to-medium theropods (such as velociraptor) - why it doesn't apply to them, that is.--91.148.159.4 (talk) 12:59, 10 July 2011 (UTC)

Anti-adhesive material
Is there a material so smooth (non-adhesive) that any insect wouldn't be able to attach to or walk on it?--46.204.57.249 (talk) 22:14, 9 July 2011 (UTC)


 * Maybe only if it also could not retain moisture. ←Baseball Bugs What's up, Doc? carrots→ 23:30, 9 July 2011 (UTC)
 * No, depending on the insect. Smoothness is conducive to housefly foot adhesion. 216.239.45.98 (talk) 23:44, 9 July 2011 (UTC)


 * A lab at the University of Cambridge has invented and patented a material called Insectislide that apparently insects cannot stick to, although smoothness is not the cause. This article gives a bit more information. Looie496 (talk) 00:57, 10 July 2011 (UTC)


 * Pure sodium ? It should hopefully react with the moisture on their feet and blow them off. StuRat (talk) 06:02, 10 July 2011 (UTC)


 * I've heard and read that fluon (teflon in an aqueous adhesive) or teflon tape can be used for this. Apparently most insects cant stick to it.Staticd (talk) 09:24, 10 July 2011 (UTC)


 * Any good against slugs and snails? Itsmejudith (talk) 09:51, 10 July 2011 (UTC)
 * Doubt it. for snails you will need some repellantStaticd (talk) 11:44, 10 July 2011 (UTC)
 * Or diatomaceous earth. -- SmashTheState (talk) 14:41, 10 July 2011 (UTC)


 * I watched a caterpiller try to walk across a Teflon skillet. Every time he tried to rear up, he fell over. His feet could not gain traction of the nonstick surface.He had no problem walking vertically up a painted surface Edison (talk) 17:47, 10 July 2011 (UTC)