Wikipedia:Reference desk/Archives/Science/2013 February 3

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February 3

Gravity in a bounded universe

The divergence of the gravitational field is equal to the mass density, which is non-negative everywhere and positive in some places. The net divergence in a bounded system must be zero. Doesn't this mean that the universe is unbounded, and thus the curvature must be non-positive? For that matter, even if it is, wouldn't an approximately even mass distribution result in an unbounded gravitational field?

My best guess is that the mass density of a vacuum is negative. Is this correct? — DanielLC 05:44, 3 February 2013 (UTC)

Your first statement is only correct within Newtonian gravity which is not applicable to the universe as a whole. Dauto (talk) 15:37, 3 February 2013 (UTC)

You are right that the mass density of vacuum is negative (in sense that it produces repulsion instead of attraction), while the energy density is positive. Ruslik_Zero 19:06, 3 February 2013 (UTC)

What does it mean for energy density to be positive? If you change the potential energy of every state under quantum physics, this does absolutely nothing. I've been told you need general relativity to find any sort of energy density of the vacuum. — DanielLC 23:21, 4 February 2013 (UTC)

while we're on the subject of turtle evolution

We've all seen the videos of the little turtle hatchlings crawling toward the sea as fast as they can while sea birds etc feast on them (also noted in our turtle article); why wouldn't evolution push them all to the point where they lay their eggs like 2 feet above high tide line? Particularly when I notice the aforesaid turtle article notes that turtle eggs kept moist do better than those kept drier? Gzuckier (talk) 06:49, 3 February 2013 (UTC)

Unless I'm missing something here, you have pretty much answered your own question. Above high tide line - less moist. At high tide line just moist enough. Richard Avery (talk) 08:00, 3 February 2013 (UTC)

This article suggests that predation is a likely controlling factor with the optimum nest position being close but not too close to the water's edge, I presume that by widening the strip within which nests may be located, the predator's job is made more difficult. Mikenorton (talk) 08:10, 3 February 2013 (UTC)

Also, predation can help eliminate defective genes, by removing the least fit individuals. StuRat (talk) 08:16, 3 February 2013 (UTC)

Another factor to consider is that nests which are placed too close to the high tide line run the risk of being drowned, and as noted in the "cape" episode of David Attenborough's Africa series, should the nest be flooded before the eggs hatch, they won't survive. douts (talk) 14:15, 3 February 2013 (UTC)

Light bulbs. halogen --> LED

I have 81 50-watt halogen downlighters GU10 ES50 which link to 240v - 12v transformers. Can I get something which will provide the same amount of light in one LED bulb? Kittybrewster ☎ 10:45, 3 February 2013 (UTC)

Assuming you mean to replace EACH 50 W halogen light with one LED fitting, the answer is yes. Have a look at this: http://www.siliconchip.com.au/Issue/2013/February/Replace+Your+Halogen+Down-lights+With+LEDs. Ratbone 124.182.26.251 (talk) 10:59, 3 February 2013 (UTC)

Yes. Good. Warm white, daylight or pure white? 2w 3w 4w or 5w? Is there a reference for these lights at a UK supplier?Do they need a 12w LED Driver Transformer for MR16-MR11-G4 LED Light Bulb by Long Life Lamp Company? Kittybrewster ☎ 15:19, 3 February 2013 (UTC)

I've replaced some GU10 12V halogens with LEDs. They run on 12V AC (IIRC, they have a built-in rectifier). For some reason they don't have the halogen-equivalent wattage marked. However, LEDs about about 3 times as efficient as halogens, so I'd go for about 15W. The lamps are marked as non-dimmable; if you want to dim them you might need to buy a ballast. CS Miller (talk) 20:02, 3 February 2013 (UTC)

The best answer is 'may be'. Presuming you don't mean to replace anything in the fitting, replacing 12V halogens with LED equivalents can be problematic. You can find many complaints from a simple search, some people recommend just replacing them with main voltage ones. The problem is in the transformer, the electronic transformers (switched mode power supply) commonly used may be designed for 50W bulbs and may not like the far lower voltage, some may not work at all. Even if they do work, you sometimes get flickering due to an interaction between the switch mode power supply on the bulb and the switch mode power supply in the fitting. The output from the SMPS is most likely not a simple 50 or 60 hz AC since it doesn't matter to the halogens. More reliable manufacturers often have long lists of transformer compatibility charts for their lights. In the unlikely event your bulb uses a simple transformer, I would guess you shouldn't have problems.

However although not commonly discussed, there is an advantage to the 12V namely safety. In fact I read about [1] [2] which shows even someone like Philips can screw up their design. I personally chose GX5.3 12V as opposed to GU10 240V despite the issues because I prefer cool white bulbs (at least 5000K and preferably higher) and it's not that easy to find high CCT bulbs from reliable manufacturer with a high CRI (even when it comes to the raw LEDs they're far rarer then low CCT high CRI). However I did encounter flickering from some of the bulbs I purchased from AliExpress using Sharp COBs. I believe the ones that flicker for me use a boost drive as the LED forward voltage is above 12V (some of the LED dies are series) which highlights I guess another unfortunate fact, a number of COBs and LED arrays do have a forward voltage above 12V because they're targeted at the line voltage market where it's an advantage since the buck driver doesn't have to reduce the supply so much. One intermediate option between going main voltage is to keep the fitting but replacing the transformer with one designed for LEDs (or better both LEDs and halogens) source from a reliable manufacturer. Of course you could replace the whole fitting with an LED one, I didn't do that here because what's available seems rather poor and limited, even before taking in to account my preferences but things may be better in the UK.

The other consideration is the design of your fitting. If the bulbs are enclosed or recessed in the wall, you're far more likely to have a problem since LEDs really don't like to get hot. For the same reason, 50W halogen equivalent is difficult for a bulb that sized. Some of the Philips GX5.3s (and I think GU10) even have a fan. (In my case I purposely overlighted the area so it doesn't matter if they aren't so bright.) This also depends on your requirements. If you want a high CRI low CCT light you'll need a more powerful bulb since both high CRI and low CCT generally means a lower luminous efficacy. Even when it comes to similar CRI and CCT, LEDs are still rapidly evolving so it depends significantly on the LED used. (As well of course on the efficiency of the driver.)

Nil Einne (talk) 05:31, 4 February 2013 (UTC)

P.S. From a quick search, one more problem you may have is I don't think GU10 12Vs are particularly common. AFAIK, GU10s are usually main voltage and GX5.3 are used for 12V in the MR16 world. Given the similarity, for Chinese manufacturers from AliEpxress you may be able to get them to make some GU10 12Vs easily if you're buying a decent quantity perhaps 10-20. For well known brands, you'll just have to use what's available. Nil Einne (talk) 05:51, 4 February 2013 (UTC)

Male vs female pain

I heard that females are more tolerant to pain than men, because men have more pain receptors. It's linked to the Y chromosome. Is this true?Dbjorck (talk) 08:30, 3 February 2013 (UTC) Copied from Talk:Nociception#Male vs female pain 10:54, 3 February 2013 (UTC)

In Sexual dimorphism it says generally females feel pain more than males. I believe I read somewhere this applies even to babies so it is not something that is just learnt. This makes sense really, males fight more and pain that distracted would be a disadvantage. Dmcq (talk) 14:07, 3 February 2013 (UTC)

This is like asking "is the sky brown?" Common sense should be more than enough to tell you it's blatantly false, and that women are far more sensitive to pain. In case you don't believe common sense, here is an article that quotes a scientific paper. Here is an article from Scientific American. "The reason for this is not known, Fillingim said. Past research suggests a number of factors contribute to perceptions of pain level, including hormones, genetics and psychological factors, which may vary between men and women, Fillingim said. It's also possible the pain systems work differently in men and women, or women experience more severe forms of disease than men, he said." --140.180.247.198 (talk) 17:56, 3 February 2013 (UTC)

Googling "number of pain receptors" returns some pages, amongst a lot of junk, that indicate both sexes have about the same number of pain receptors per unit area of skin. Since men are bigger and have more skin area than women, they have more pain receptors. However, this does not mean more sensitivity, nor less.

The study reported in Scientific American is deeply flawed, as reading the attached reader comments shows. To measure something, whether it is magnitude of pain, volts in an electric circuit, or the weight of a parcel, you need a measurement system that has appropiate resolution, and calibration. They measured by asking patients to rate their pain on a numerical scale, 0 = no pain, to 10 = worst pain imaginable. That's plenty of resolution, probably too much, but there is no calibration. Who is to say whether I can imagine a pain more severe than you? Perhaps I fell off a ladder, breaking my hip. Perhaps you were very sick with an intestinal blockage. Perhaps we both never before had any pain worst than childhood accidents. Perhaps I have a more vivid imagination. Perhaps I only think I do. A better question might be "What is the severity of your pain, 0 = no pain, 1 = I have pain, but I am happy to ignore it, 2 = the pain constantly intrudes on my consciousness, 3 = I cannot think or function at all with this level of pain 4 = I want to die" Since the brain has evolved over a very long period of time to prioritize what gets presented to consciousness with a well defined structure, this would give at least some calibration.

It should also be noted that we have more than one system for sensing pain. There is a specific nerve network ending in pain receptors in the skin. There is a quite separate system of nerves ending in pressure sensors in the digestive system. The brain interprets excess pressure as pain. It may well be that men are more sensitive than women for skin pain, and women more sensitive to gut pain. Or vice versa. Or some other combination. By not recording and accounting for this, the study repoted in Scientific American is futher flawed.

Not only is the preception of pain severity, and the degree which an individual reports it (two different issues confounded in the SA study) culturally influenced ("real men don't cry"), it depends on state of mind. It is well known that humans will put up with almost anything if they have the right state of mind, and/or they can see a light at the end of the tunnel. In World War 1, for example, General Monash was able to inspire troops to put up with hardships unimaginable to folk that have not served in a battle. After my wife had an operation, the nurse came around and asked her to rate her pain. On being told it was as bad as anything, the nurse gave her a narcotic and valium. A little later, my wife asked for more. But the nurse sized her up and said she could have a half dose of narcotic and no valium. My wife protested, saying the pain was again bad. The nurse replied, "You should expect some pain, you are obviously well aware of your surroundings now. If I keep giving you valium, you will become addicted." Whereupon my wife decided the pain was not so bad after all, and talked to me brightly about all the flowers and phone calls she had received from her work mates. — Preceding unsigned comment added by 124.178.53.46 (talk) 01:36, 4 February 2013 (UTC)

Wickwack 121.215.57.3 (talk) 01:03, 4 February 2013 (UTC)

Re calibration: Remembering my psych grad school daze, if people are provided with defined end points to a scale, they can be relied upon to scale stimuli very nicely (usually on a log scale) and repeatably, whereas in the absence of such defined end points the reported intensity wanders all over the scale between different subjects, or the same subject various times. Of course, we weren't paining people (that would be a creepy experiment; "Now, call this pain 10 out of 10" and then do ???), but the finding was so universal that I'd be really surprised if pain receptors were any different. As for the other factor, yeah, everybody who is familiar with dogs or kids has probably seen them smack into a wall full tilt or something when playing and laugh it off, while when they're looking for pity the teeniest scratch or bruise will cause copious agony. Gzuckier (talk) 02:49, 4 February 2013 (UTC)

True. I probably should have said the SA study had poor calibration at the top end, rather than saying there was no calibration. The top end calibration was poor because it requires imagining the most severe pain, and that depends on experience. Wickwack 60.228.245.239 (talk) 03:08, 4 February 2013 (UTC)

I admit the Scientific American article was not the greatest example. Nevertheless, there is abundant evidence that men have a greater pain tolerance than women, and none at all for the opposite viewpoint. This literature review, for example, describes studies that use brain imaging to measure human pain response. Differences in pain tolerance have been unambiguously found in both humans and animals. In humans, these differences appear in subjective questionnaires like the SA study, behavioral tests such as Lowery et al, and PET brain scans such as Paulson et al. In animals, the differences appear in behavioral observations and brain measurements, like measurements of stress-induced analgesia. By "differences", I mean that males have unambiguously higher pain tolerance than females, and not the other way round. This other review article claims that the results of brain imaging studies are mixed, but is nevertheless unambiguous in its conclusion: "Consistent with our previous reviews, current human findings regarding sex differences in experimental pain indicate greater pain sensitivity among females compared with males for most pain modalities, including more recently implemented clinically relevant pain models such as temporal summation of pain and intramuscular injection of algesic substances." Of course all of these studies, just like all of science, are limited or flawed in some way. Even so, they're much more trustworthy than WP:OR based on one anecdote about WWI and another anecdote about somebody's wife. --140.180.247.198 (talk) 02:58, 4 February 2013 (UTC)

The study quoted in our Pain threshold article is Sex Differences and Incentive Effects on Perceptual and Cardiovascular Responses to Cold Pressor Pain by Daniel Lowery, MA, Roger B. Fillingim, PhD and Rex A. Wright, PhD. Alansplodge (talk) 19:23, 4 February 2013 (UTC)

D'oh! Already linked above - sorry 140.180! Alansplodge (talk) 19:25, 4 February 2013 (UTC)

Wasn't there also some surprising finding, in the last few years, that certain painkillers were ineffective for women while being very effective for men? I recall it being taken as further evidence that the pain pathways and natural painkilling mechanisms were different in men and women. It also was taken as a cautionary tale of the dangers of narrow samples being used in drug trials and taken as representative of the wider population. Ring any bells for anyone? 86.163.209.18 (talk) 22:06, 4 February 2013 (UTC)

Black holes: Why the most complex objects in the universe?

Andrew Strominger (and others) state that event horizons are governed by a strikingly simple set of quantum laws which implythat black holes are at once the simplest and most complex objects in the physical universe. I understand the first part, as they are defined by three parameters only - mass, electrical charge and angular momentum (however, this is derived from general relativity, not from quantum laws, isn't it?) But why are they the most complex objects? I understand it has to do with Black hole thermodynamics and the Black hole information paradox, but still fail to explain, not the least in confusion how the concepts entropy, information and complexity interact in this case. --KnightMove (talk) 13:09, 3 February 2013 (UTC)

Utter speculation on my part, but I'm guessing that if you tried to map the event horizon, you might end up with some ridiculously, fractally wiggly line, just like the Mandelbrot set, another surprisingly-complicated system with a surprisingly simple definition. —Steve Summit (talk) 13:41, 3 February 2013 (UTC)

It's probably because black holes have the largest physically possible entropy for an object their size (Bekenstein bound). -- BenRG (talk) 06:15, 4 February 2013 (UTC)

This article exactly demonstrates my confusion: This article uses the terms entropy and information as straight proportional almost-synonyms, while they are generally regarded as almost-opposites and an increase in entropy means a decrease in information. This leads to the next ??? when entropy is supposed to increase in the universe, while information supposedly cannot decrease... --KnightMove (talk) 10:53, 4 February 2013 (UTC)

Yes, the word information is used inconsistently. It means "the logarithm of the number of equiprobable states", but they may be talking about different states in different circumstances. If they're counting indistinguishable microstates, it's the same as entropy. If they're counting phase space volume, it's conserved. If they're counting distinguishable macrostates weighted by the number of indistinguishable microstates in each one, it's the sort of information you're thinking of. -- BenRG (talk) 17:16, 4 February 2013 (UTC)

antimatter

Is there any likelihood that there is a way to change matter to antimatter using a relatively small amount of energy so that you can use matter-antimatter interaction to gain energy? Bubba73 ^{You talkin' to me?} 14:17, 3 February 2013 (UTC)

What do you think, Bubba? Such a thing would make possible a perpertual motion machine, as no doubt you have realised. Floda 120.145.46.100 (talk) 14:46, 3 February 2013 (UTC)

How would you make a perpetual motion machine with this? What Bubba suggested converts matter into energy, so you would need to continually supply matter (fuel) to keep the machine running. - Lindert (talk) 14:54, 3 February 2013 (UTC)

(ec) No, it would not make a perpetual motion machine possible. What you gain in energy, you lose in annihilated matter and antimatter, via E=mc². There may be other reasons why this is impossible, but neither the first nor the second law of thermodynamics stands in the way. --Stephan Schulz (talk) 14:59, 3 February 2013 (UTC)

Erk! You are right. Floda 121.215.4.176 (talk) 16:13, 3 February 2013 (UTC)

My impression is that a very small black hole is just such a catalyst, but I don't know if that is actually true. Wnt (talk) 15:11, 3 February 2013 (UTC)

A very small black hole might conceptually be able to convert matter to energy efficiently - you feed the matter into the black hole at the same rate that it is dissipated in the form or Hawking radiation. However, this is highly unstable. The smaller the black hole becomes, the faster its rate of evaporation. So you need to feed it more matter to make it cool down. If the math at Hawking radiation holds up, a 200 ton black hole will produce 7 billion gigawatts. You need to feed the mass equivalent of that into the black hole to keep it stable, against that radiation pressure. And the major snag here is that we would need a good theory of quantum gravity - I doubt that general relativity scales down to quantum sizes. --Stephan Schulz (talk) 16:24, 3 February 2013 (UTC)

Well, the problem isn't really so much keeping it stable as getting over that hump to create a synthetic black hole in the first place; after that you can bulk it up until it converts energy at a sedate rate and is less likely to explode suddenly if the computer crashes. And yes, the question of what the smallest possible black hole looks like is of the greatest interest, since it is at once the greatest obstacle and, if it can actually be created, perhaps the greatest opportunity, to do the conversion at that step of creation only, never having a black hole that has any possibility of slipping away and eating the Earth. Wnt (talk) 17:07, 3 February 2013 (UTC)

If one had access to a smallish black hole (I'm not talking a furiously-Hawking-radiating size, necessarily, either, just conveniently smaller than a solar or planetary mass) it would be a dandy source of energy. Throw any old matter that you like into it, and you'll get a significant fraction – typically at least 10%, and possibly upwards of 40% depending on the circumstances – of the mass-equivalent energy radiated back out. (Frictional heating makes infalling matter hot. Like, really hot.) This isn't Hawking radiation, this is just plain old blackbody emission from still-outside-the-event-horizon matter making up the accretion disc. Black hole#Accretion of matter touches on this point. (Science fiction buffs may recognize this concept from Imperial Earth, in which Arthur C. Clarke used small black holes in this way to power interplanetary ships.) TenOfAllTrades(talk) 19:33, 3 February 2013 (UTC)

Guys, you seem to be missing the big picture here: the question is one step away from saying "Can we convert matter into energy according to e=mc^2, using a relatively small amount of energy"? If we do take the "logical" next step in the question (use the antimatter to gain energy), that's all this is equivalent to. In other words, using up matter directly, for its high theoretical energy yield, using relatively little energy. Is such a thing theoretically possible? Is it possible by the means suggested, of turning the matter into antimatter first, using relatively little enrgy? 178.48.114.143 (talk) 15:32, 3 February 2013 (UTC)

Well, that's what I described with the small black hole, but I suppose I should have clarified. If you make a very small black hole, smaller than a primordial black hole, then it will evaporate in a very short time by Hawking radiation. So in theory, if a black hole has only mass, charge, and spin that is, you can cram matter down its gullet (emphasis on the cram, as we're speaking of something the size of a subatomic particle, perhaps) and what comes out may be particle pairs, matter + antimatter, that can annihilate and produce light. But ... I don't know for sure myself, what with all the talk of some kind of conservation? of physical information in the Hawking radiation, whether there could be some sort of 'matter-ness' in the black hole you feed this way after all that would somehow foul the scheme. Wnt (talk) 16:16, 3 February 2013 (UTC)

I was talking to a friend who was wondering about getting energy from matter-antimatter interaction. I asked "where do you get the antimatter?". I said that it takes more energy to make antimatter than you would get out. He wondered if it was possible to convert regular matter to antimatter and use it, with a net gain in energy. I doubt it, but I don't know. Bubba73 ^{You talkin' to me?} 16:39, 3 February 2013 (UTC)

I don't think the question is one step away from saying "Can we convert matter into energy according to e=mc^2, using a relatively small amount of energy" ? The question is much more fundamental. Can you change the sign of the charge of a particle. Sean.hoyland - talk 16:48, 3 February 2013 (UTC)

Nay, it's not changing the charge. For example, if you dump only protons into a mini black hole, it will quickly take on a positive charge (one of the three properties they do have by all accounts) and repel taking up more; when a virtual pair becomes Hawking radiation it will be the negative one that drops in the event horizon and the positive one that goes away, most likely, until the balance of charge is restored. Wnt (talk) 17:03, 3 February 2013 (UTC)

The OP's question is "Is there any likelihood that there is a way to change matter to antimatter" Sean.hoyland - talk 17:08, 3 February 2013 (UTC)

Or "Is there any likelihood that there is a way to change matter to antimatter with using a minimal amount of energy", where minimal amount is << 2mc². ---- CS Miller (talk) 17:24, 3 February 2013 (UTC)

Right. And have it so that we can use it, e.g. not inside a black hole. Bubba73 ^{You talkin' to me?} 17:50, 3 February 2013 (UTC)

Wouldn't rotating matter in the fourth dimension make it into antimatter? μηδείς (talk) 21:24, 3 February 2013 (UTC)

Unless there's some exchange between different elemental particles, that would seem to violate Charge conservation, i.e. if an electron can be 'turned' into a positron through the fourth dimension without involving any positively charged matter, the net electric charge of the universe changes, which shouldn't happen. - Lindert (talk) 23:10, 3 February 2013 (UTC)

But charge alone isn't conserved, isn't it something like charge x mass x velocity that is conserved? You will have to forgive me, as I am totally ignorant here, but I seem to remember something like this. μηδείς (talk) 01:28, 4 February 2013 (UTC)

Charge is conserved, energy is conserved. Neither of these is necessarily violated by changing matter to antimatter, but doing that will violate conservation of baryon number. It's not clear whether conservation of baryon number is a fundamental law or just a general observation. Baryon asymmetry would suggest the latter. Someguy1221 (talk) 01:37, 4 February 2013 (UTC)

In the sense of "a black box that you push matter into, and antimatter (and some waste matter & energy) comes out" - yes, of course we can do that. Inside we'd have a fusion reactor which is converting matter into energy (and a lot of waste product) and something as described in Antimatter#Artificial_production using that energy to create antimatter. If you don't look inside the black box, it does what the OP wants - but the relatively small yield of the process means that you'd be better off just using the fusion reactor to do the work.

More directly, Antimatter#Positrons says that you can fire electrons at a small diameter gold target using a laser and get positrons out the other side - which is doing that conversion - but the amount of energy needed in the laser presumably exceeds the amount of energy you'd get by recombining positrons and electrons - or else I'd have something like that inside my electric car! So no free energy device here!

If there is a way to do this conversion cheaply, we don't know what it is because according to Antimatter#Cost, the current price to create antimatter is between $25 billion per gram (positrons) and $62.5 trillion per gram (antihydrogen). The cost of storing the stuff in any quantity would likely be off the charts!

However, the lower of those two numbers looks promising! One gram of antimatter can produce 2mc² = 18,000,000,000,000,000 Joules of energy. A KWh is 3.6MJ - so our gram of positrons makes 50,000,000,000 KWh. A KWh costs about $0.1 in the USA right now...so that's $5bn worth of electricity for a $25bn outlay...well, OK, nobody's getting rich on this anytime soon - but it's not that inefficient. A 20% efficiency would be economical for (for example) powering a car or an airplane. If you could find a way to reliably contain the stuff (and that's a huge "IF"!), you could easily store all of the energy your car would ever use in a box that might fit conveniently into the glove box and which could be installed into the car when it's manufactured! That kind of energy density would certainly be worth having.

SteveBaker (talk) 13:48, 4 February 2013 (UTC)

Assuming that such antimatter powered cars would have about the same efficiency as today's electric cars, and doing a quick back-of-an-envelope calculation (0.1-0.23 kW.h/km accroding to our article, and assuming a design life of 300,000 km), you would need about 100-200 GJ of energy, which is 25-50 tonnes of TNT. I'm not sure I want to be driving round with the equivalent of a small tactical nuclear weapon in the glove box, so the containment question is, as you say, a huge "IF". Apologies if I have made an order of magnitude error somewhere, I did the calculation rather quickly!

Equisetum (talk | contributions) 17:54, 4 February 2013 (UTC)

Yall might find Neutral particle oscillation interesting - a process by which neutral mesons do indeed (Spontaneously !) convert into their antimatter selves. Dauto (talk) 16:19, 4 February 2013 (UTC)

Basically, if there were any way of converting ordinary matter particles (protons, neutrons and electrons) into their antiparticles with a relatively small amount of energy input, it would happen spontaneously by quantum tunneling, and ordinary matter would decay into photons and neutrinos, and there would be no us. So no. -- BenRG (talk) 17:25, 4 February 2013 (UTC)

Chemistry after nuclear decay/transmutation

In most studies of nuclear decay, the atom's electron shell and what it is bound to is not considered. However, this is what I am interested in.

Consider a molecule of dimethylpropane (neopentane), that has been carefully crafted so that the central carbon is ¹⁴C, and then others are ¹²C, i.e. ¹⁴C(¹²CH₃)₄. It is observed until the central atom decays to ¹⁴N⁺, (assuming the electron ejected from the nucleus isn't captured by the shell). Thus we now have ¹⁴N⁺(¹²CH₃)₄.

My question is, is one of the methyl groups ejected by the nitrogen, to form N(CH₃)₃, (assuming that this molecule is stable)? CS Miller (talk) 16:40, 3 February 2013 (UTC)

Trimethylamine is a real and stable – though rather stinky – chemical compound. My first thought was that such a compound arising would be unlikely simply because radioactive decay is a relatively energetic process; one might expect the recoil of the newly-formed nitrogen-14 nucleus to rip it loose from any chemical compound to which it was attached. (For reference, the decay energy for carbon-14 is about 156 keV (156,000 eV), whereas typical covalent C-C and C-H bond-dissociation energies are on the order of 4 or 5 eV. While most of the beta decay energy gets carried off with the emitted beta particle and neutrino, some small fraction of it ends up with the N-14 nucleus.)

It turns out, though, that that isn't necessarily the case. Remarkably, carbon-14 decay is gentle enough (barely) that at least some of the expected derived N-14 compound may survive, under at least some circumstances. Way back in 1956, Wolfgang et al. actually did a similar experiment using C-14 labelled ethane (H₃C-CH₃), and found that 47% of the ethane molecules survived 'intact' post-decay to form the anticipated compound, methylamine: H₃C-NH₂. Whether or not this result generalizes well to the decay of neopentane, I wouldn't hazard a guess. TenOfAllTrades(talk) 17:55, 3 February 2013 (UTC)

Thank your for your speedy reply ToaT, unfortunately I don't have access to that paper. I didn't know that some of the decay energy ends up in the atom, rather than the ejected subatomic particles. Neopentane was just used as an example; I could have chosen any organic molecule. Assuming that the recoil doesn't rip the nuclide out of the molecule, am I correct to think, after the decay, the product nuclide will eject an attached group to retain a stable 8 octet?

A follow up question. If the the groups are different (say the 3rd carbon in 3-methylhexane decays), is it possible to predict what will be ejected? CS Miller (talk) 19:28, 3 February 2013 (UTC)

Tetramethylammonium, or even more complex Quaternary ammonium cations, isn't so unstable that it would be likely to fall apart (you probably have bottles of them in your shower and laundry!). It still does have a stable octet, it just also (now) has a charge. DMacks (talk) 21:32, 3 February 2013 (UTC)

Uh, tetramethylammonium is toxic and is not normally used in household detergents. Most household detergents use alkyl sulfonates, which are more effective in this application in any case. 24.23.196.85 (talk) 04:54, 4 February 2013 (UTC)

Quat-ammonium compounds are commonly found in many products for many reasons (obviously less-toxic ones often suffice). I encourage you to read our article about them to see many applications (including subarticles such as shampoo the common polyquaternium class of ingredients among others). The question was about stability vs flying apart: even the tetramethyl article's studies on toxicity are predicated on it being stable enough to study. DMacks (talk) 12:33, 4 February 2013 (UTC)

What is this crinkly wood - and why is it so?

Split wood showing crinkly grain (approximately circumferential split face uppermost, radial split face on right)

The pictured wood is from the UK, is lightweight and easily split in either plane. It is mainly pale yellow with some red streaks and is very crinkly throughout available samples. The wavelength of the crinkles is 6-7mm and their polarization is circumferential to the tree, so that the surface of radial splits is highly corrugated. No bark remains on the sample.

What is it? and why is it so?

Thanks --catslash (talk) 23:24, 3 February 2013 (UTC)

It's hard to say with certainty without knowing more about its source, but it seems to be a form of burlwood. E.g.:[3], from:[4] ~:74.60.29.141 (talk) 00:41, 4 February 2013 (UTC)

Is it perhaps from a Dutch elm diseased tree? Is Crinkley Wood near Crinkley Bottom? See also Noel's House Party --Senra (talk) 04:19, 4 February 2013 (UTC)

No, Dutch Elm disease affects the bark and the structures immediately below, the woody trunk is unaffected, apart from the fact that it becomes part of a dead tree. Elm is notoriously slow to rot, Old London Bridge sat on elm piles for 650 years. I'm old enough to remember trying to burn the damned stuff; "Elmwood burns with a churchyard mould, E’en the very flames are cold..."[5]. Alansplodge (talk) 13:12, 4 February 2013 (UTC)

'Walter' here has a theory about it. I have seen it in mature oak and olive wood. A real nuisance when you're splitting logs. Richard Avery (talk) 08:20, 4 February 2013 (UTC)

I like the "reaction wood" explanation - and (of course) we have an article about that: Reaction wood. SteveBaker (talk) 13:11, 4 February 2013 (UTC)

Perhaps that photo→   would make a good addition to the article (which could also use a citation to the certified arborist @Wavy Wood - Explained) - However, would this be WP:OR or perhaps wp:synthesis?   ~:74.60.29.141 (talk) 17:56, 4 February 2013 (UTC)

Eventually found it on the web. It would have been easy to find if only I had known that it was called a curly figure. This looks very similar to mine in every particular. Apparently the cause is not known, or at least not agreed. Thanks for the suggestions though. --catslash (talk) 01:10, 7 February 2013 (UTC)