Wikipedia:Reference desk/Archives/Science/2014 April 17

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April 17

How cold would a room temperature superconductor feel?

The more conductive something is the colder it feels right? So would a room temperature superconductor (assuming the room is colder than you are) feel super cold or is there some lower boundary to this? On a sort of related thought, if you were in a very cold room, say -50° F and you touched a superconductor, would it draw the heat out of you so fast it would look ghoulishly cartoonish how fast you turned to ice?--108.46.109.33 (talk) 00:26, 17 April 2014 (UTC)

No matter how fast the object conducts heat internally, you still can't lose it any faster than it can flow out of whatever part of your body is touching the object. --Trovatore (talk) 00:32, 17 April 2014 (UTC)

...in other words, even if you had an infinitely thermally-conductive heat sink chilled to within a whisper of absolute zero, and you decided to be a dumbass and poke it with your finger, your hand (and body) wouldn't instantly freeze solid. The first small fractions of an inch of your finger would freeze quite quickly, but the freezing rate would fall off (rapidly!) as the freezing progressed up your finger. Heat from your hand would have to be slowly conducted down the entire length of your frozen finger, in a process that would probably take hours just to get to your wrist.

That said, it is worth bearing in mind that all known superconductors, while having no apparent resistance to the flow of electrical current, still possess a finite thermal conductivity. Moreover, their thermal conductivities typically aren't much different from what they are in their slightly-warmer non-superconducting states. Infinitely thermally conductive materials remain, sadly, in the realm of science fiction. TenOfAllTrades(talk) 02:49, 17 April 2014 (UTC)

Superconductivity only applies to electrical conductivity. Thermal conductivity does not necessarily increase below the critical temperature. [1] discusses the thermal conductivity in magnesium diboride. Around the critical temperature, the thermal conductivity drops from ~250 mW/cm-K to nearly 0. In YBCO [2], the thermal conductivity does increase, but only by about a factor of 2. At its highest point, it's still only comparable to bronze or stainless steel. [3], [4], [5] are the best explanations I can find that don't require a PhD in solid-state physics to understand.

Liquid helium below the lambda point acts similar to a super thermal conductor (the value is still finite, but is a couple orders of magnitude higher than just about every other known material). But any thermal conductor is still going to tend toward equilibrium with its surroundings. It won't conduct heat in from a hot object faster than it can conduct it out into a cold object. And it will be limited by the thermal conductivity or heat transfer coefficient of the substances in contact with it. So, basically, it's going to feel like whatever it's in contact with, though it would probably be dependent on the size of the piece. A large piece with a large surface area will be able to conduct into more of the contacting material than a small piece, so it will conduct faster. If it's in a room chilled to -50, it will take heat out of your finger and transport it into whatever it's sitting on, warming that up. But it won't chill itself to below -50. Mr.Z-man 03:38, 17 April 2014 (UTC)

• This is an interesting topic that gets far too little attention. First, the association with thermal conductivity in metals is apparently the Wiedemann–Franz law, based on the idea that electrons mediate both in that environment. It would obviously be extremely useful to invent better thermal conductors, for basic purposes like building antennas to radiate waste heat from power plants without heating rivers, cooling computers without fans, etc. But does any genuine zero-resistance thermal conductor exist? Do we know if one even could exist? Is there a theory that would say it should have a critical temperature? Is there something Cooper pairs could do to facilitate it? I should admit, I have no idea about it. Our article gives the impression that there isn't much theory about the whole field of thermal conductivity, and that seems like a really expensive deficit to have. Wnt (talk) 21:37, 18 April 2014 (UTC)

Severe colorblindness

How do normal people understand what monochromats can see, and/or how do monochromats communicate their vision in an manner understandable to normal people? I'm somewhat colorblind, but I can understand my condition because other colors come through fine: I can easily produce correct color descriptions for anything that doesn't involve red or green somehow. However, if you're stuck with just one color, how can you understand your situation in normal people's terms? If I had no color vision, I wouldn't be able to grasp the concept of color, so I wouldn't know what I was missing or how to explain that I was missing it. Alternatively, imagine that all you've ever seen was a single-color computer monitor, such as File:IBM PC 5150.jpg. Since your eyes have never seen anything except "black" and "green", how are you supposed to form a concept of "white" or "blue", or indeed how can you conceive of anything that's not black or green? Surely this has an answer that's not too hard, but I can't imagine what it is. Nyttend (talk) 00:59, 17 April 2014 (UTC)

At a fundamental level you are asking a very deep philosophical question, for which there is no easy answer. Similar to what does a blind person dream? I think qualia is the most relevant article. In the end, your perception is your perception and there is no way to be 100% certain what other people perceive. Lots of more or less colorblind people don't find out that they are colorblind because unless it makes an impact to how you perceive traffic lights, which is quite rare, everyone thinks the situation is normal. Vespine (talk) 07:00, 17 April 2014 (UTC)

As for your first question, we polychromats (is that a word?) have experience with night vision (no color) not to mention BW photography. — At one point in Ed Wood, an actress asks a cameraman, "Which dress do you like better, the red one or the green one?" "Which is which? I'm colorblind." We the audience are colorblind too, because the movie was shot in BW, but suspend our awareness of that fact until this bit of dialogue brings it up! —Tamfang (talk) 08:49, 17 April 2014 (UTC)

Within a particular environment, it's usually possible to associate a particular shade of grey with a colour, but this doesn't transfer reliably between environments. Measurements have shown that individuals "see" colours very differently, but we have been socialised very early in life to interpret the differing signals in a way that fits in with the colour names that others use. In your example of a green monitor, an individual would soon learn that very bright green was called "white" by others, but the concept of "blue" would be tricky or impossible to explain. Even people with "normal" colour vision often can't agree on the blue/green borderline, and an individual interpretation often depends on the background, and on what the eye has previously been looking at. Colour perception has a large element of social learning which overlays the nerve signals transmitted to the brain from individual cones. I assume that you've read the article on Colour vision. Dbfirs 09:02, 17 April 2014 (UTC)

It's worth considering that there are people who are tetrachromats. The woman known as "subject cDa29" is currently the only 'verified' human tetrochromat - but it's certain that there are many more. These people see more colors than we mere trichromats with "normal" vision. Then there are many species of freshwater shrimp who see things in as many as 12 different colors. So we should not kid ourselves that our vision is "full color" - that's very far from the truth. It's true to say that all humans are "color blind" to some degree.

A monochromat can get some appreciation for color by viewing the world through color filters. So, for example, if you cannot normally distinguish red and green - then you can view the world through a red or a green filter and note which objects get dimmer in the red filter and which get dimmer in the green filter. This would allow you to determine whether something is red or green - but (of course) you can no more understand what people with normal human vision are seeing than normal people can grasp what a tetrachromat or a freshwater shrimp can see. I have used infra-red vision devices that let me see hot things as bright and cold things as dark. This lets me distinguish infra-red light - but my perception of it is just the shades of grey that the device's display produced for me.

But how do we know that our own personal feeling of what "blue" is matches what someone else's feeling of "blue" is? We can't share that experience directly - so we can only guess that other people's brains are interpreting the color in the same way that we are. In that sense, it may not even be a meaningful question to ask how people with normal human vision see color. SteveBaker (talk) 18:50, 17 April 2014 (UTC)

I actually wasn't asking about personal feeling: I've wondered about that for a long time, but I've long assumed that it was unknowable. For that reason, Steve, I was only interested in how ophthalmologists could study the presence and absence of color-related sensations, and thus I really appreciate the point about the color filters: I've never before imagined anything that would convey any color-related information whatsoever to a person who couldn't see that color. Of course I understand that the monochromat can't experience the color itself, just as I can't really experience the difference between big increases and big decreases in File:GDP Real Growth.svg (8-10% decrease is identical to >10% increase, as I see it), but I was interested in finding any way in which a monochromat could experience any effect of color whatsoever. As noted above, it's somewhat related to blindness, but very different in that most of us got our colorblindness from Mom and Grandpa (it was congenital), but many blind people lost their sight in adulthood, so they can remember times when they could see; vaguely comparable to the biblical account of the blind man of Bethsaida (he could say that the people looked like trees because he'd seen trees), while we congenital types are like the congenitally blind man who obviously wouldn't have known what a tree or a person looked like. Nyttend (talk) 01:16, 18 April 2014 (UTC)

See:Neil Harbisson - he is a monochromat who has had a device implanted in his skull called an eyeborg that allows him to '"hear'" colour. As for the reply that says "Lots of more or less colorblind people don't find out that they are colorblind because unless it makes an impact to how you perceive traffic lights, which is quite rare" - what a load of nonsense! I have a red green colour deficiency - which occurs in about 8% of the male population - and I found out, like most people, when I took the ishihara test as a child. The only difference it makes to my perception of traffic lights is that the red light looks a little dimmer that the green and amber lights - something I would probably never have noticed if I wasn't looking for it. Mostly I have problems with distinguishing red hues mixed in with other colours when the overall lighting is not very bright. Ophthalmologists use a number of tests to study colour vision such as the Farnsworth-Munsell 100 hue test. Also, colorblindness can be inherited or acquired. Richerman (talk) 10:04, 18 April 2014 (UTC)

Thanks for the Farnsworth test, but again, it measures someone's reaction (if I understand rightly; the article is not well written), just like the Ishihara test: if you're monochromatic, all you get from it is a lack of sensation. Harbisson's interesting, but he obviously had a sense of what color was, even though he couldn't experience it; I was imagining someone who had no real idea of color in the first place. Nyttend (talk) 12:13, 18 April 2014 (UTC)

Decomposition of Urea

I've heard that the odor of urine is a result of urea decomposing back into ammonia. Does this mean that after shedding one of its nitrogen atoms, the molecule is methanolamine? What does the methanolamine (or whatever the correct decomposition product is) decompose into? — Preceding unsigned comment added by 70.171.10.159 (talk) 04:06, 17 April 2014 (UTC)

Actually, I believe the initial decomposition product is carbamic acid, which also smells bad and decomposes into ammonia and carbon dioxide. Methanolamine is a different molecule which would require some serious rearrangement to be produced from decomposition of urea! 24.5.122.13 (talk) 04:23, 17 April 2014 (UTC)

WP:WHAAOE wins again. Ammonia volatilization from urea. And it has diagrams and chemical equations and everything. --Jayron32 13:05, 17 April 2014 (UTC)

Degraded DNA – But is there hope for recreating the genome?

I often hear that strands of ancient DNA found in some fossil or frozen carcass is split and degraded, but I then wonder about how difficult it would be to put together a copy of the original code of the whole genome in question. So yes, what we recover from an ancient carcass may be badly degraded, but then, there would have been millions of copies of it, one genome per cell. So surely, if we can get millions of those cells together, extract their DNA and put them in a bath, then we can watch as they join together. And that’s just the cells from one carcass. We should be able to extract the DNA from every such carcass of a particular extinct organism that we can find, and then put them all together. Ideally, if there is a complete set of the genes out there, spread out or buried in different places, in one body or in many, then we should be able to reconstruct it, just as we can reconstruct a book that has had millions of copies originally, but now only postage size scraps exist.

And on top of that, we can deduce much about what missing genetic material might be by comparing the organism’s genome with the genetic material we can gather from organisms that flank it in evolutionary terms. Perhaps soon we might be able to make deductions from the phenome (bone structure and so on) to the genome, and write the code in reverse! Am I being a pessimist here in supposing that many extinct species will be resurrected when our facility for DNA manipulation gets a little stronger? Maybe the Dinosaurs are too far gone, but many extinct species have only been gone for a few hundred years, some only decades. Many mega fauna extinctions are associated with the spread of hunter-gatherers, and since Homo Sapiens has only been spreading thus from 20 to 40 thousand years, we should come across many well-preserved fossils which have DNA which is only thousands of years old, not millions.

Certainly, I would love to live to see the Tasmanian Tiger, The Elephant Bird and the Moa, and the Woolly Mammoths once again striding the plains. Myles325a (talk) 09:51, 17 April 2014 (UTC)

Much of what you say is correct. In fact, current methods of DNA sequencing actually work by splitting the DNA up into relatively short fragments, sequencing those fragments, and then using overlap data to join the partial sequences together. However, the phrase "watch as they join together" indicates a serious misunderstanding. DNA fragments do not join together of their own accord. It is possible to synthesize long strands of DNA, and as a matter of fact there was very recently a report of artificially synthesizing an entire functional chromosome (for yeast), but it's a very laborious process. In short, what you are proposing is beyond the current state of the art -- but not all that far beyond it. Looie496 (talk) 11:40, 17 April 2014 (UTC)

OP Myles325a back live. Thanks Looie, I was being whimsical when I described the scenario of dumping a lot of DNA into a tub and "watching it all put itself together". This was shorthand for whatever painstaking processes are actually used. But I WAS aware of the "shotgun" method of putting a lot of DNA fragments together and getting them to link up. I still am a optimist about what we can do with DNA restructuring, especially as we become more and more proficient with manipulating its structure. But I AM an amateur, and may be disenchanted by more sober minds with more expertise than I have. Myles325a (talk) 11:54, 17 April 2014 (UTC)

I think you meant to ask if we are being too optimistic, not pessimistic, in your original post. And no, you aren't, it all seems possible to me, with the note above that instead of literally joining all the different pieces of DNA together, you'd determine the genome on computer, then use that to synthesize a full DNA strand. Distinguishing the animal DNA fragments from bacteria DNA might also be a challenge.

There's also the Jurassic Park scenario that we might be able to patch missing DNA with that from current species, although we would want to use similar DNA, not frog DNA, as they used there. Probably more than 99% of mammoth DNA is in common with elephant DNA, for example, so a small missing fragment could likely be patched in with only a tiny chance it would differ from the mammoth's own DNA. But if you did end up with different DNA, then hopefully it would still be compatible, and you'd end up with a hybrid, like a liger.

However, there's still one other thing we need to do, as having an animal's DNA alone doesn't allow you to clone it. You also need a similar female animal into whose ovum you can insert the DNA. That ovum is then implanted back into that female (or another) to grow until birth. If the current species is smaller than the extinct one, such as an elephant being smaller than a mammoth, then natural birth might not work, and you might need to do a C-section instead. The surrogate mother also might not be able to carry it full-term (and note that the length of pregnancy might vary by species).

Now, as for letting an extinct species loose to survive in nature, that doesn't seem wise to me, as we don't quite know how they would fit into our current ecosystem. Would mammoths knock down trees and attack people, for example ? It's probably a better plan to restrict them to nature preserves.

Also note that creating a single breeding pair by reconstructing male and female genomes and individuals alone won't itself recreate the entire species. There's the lack of genetic diversity to consider, and also they may not choose to breed. So, we might have to keep the species going by cloning, and prevent inbreeding, until we can recreate enough individuals to have a viable breeding population.

There also might be lost info on how to behave, as they may have been taught that by their parents in nature. Thus, your baby mammoths may end up behaving like elephants, if raised by elephants. (Of course, some behavior is genetic, not learned, and thus wolves raised as dogs still retain wolf behaviors.)

The extinct species' lack of immunity to current diseases could be a problem, too. The baby mammoth, for example, might not be immune to common elephant diseases. If this turns out to be an issue, we might need to do a bubble boy scenario, where the mammoth is kept in total isolation.

Extinct large predators might pose an additional problem. Current large predators seem to be genetically programmed to avoid hunting humans (with a few exceptions), since, if their ancestors had done so, they would have been wiped out by humans. However, a species that went extinct may have lacked such an instinct, either because they died out before they came in contact with humans, or perhaps they did come in contact with humans but failed to evolve the "stay away from humans" instinct quickly enough to survive. So, such large predators could pose more of a risk if they escape. StuRat (talk) 12:13, 17 April 2014 (UTC)

• FYI cloning/recreating Mammoths may be imminent. Here's some news blurbs, you can google around for more info [6], [7]. The mammoth genome project has been "completed", more info straight from the source here [8]. SemanticMantis (talk) 14:35, 17 April 2014 (UTC)

Ah, "imminent" is a bit of a stretch. You cannot currently create a genome of that size, whether by modifying an existing genome inside a cell, or by synthesizing one de novo. Craig Venter's genome replacement method is probably the best hope, but it is currently operating on genomes a few orders of magnitude too small to recreate a mammoth cell. Someguy1221 (talk) 08:19, 18 April 2014 (UTC)

As another answer to the original question, the problem with sequencing fragmented genomes is not just that some sections are not represented in available collections, but also that some sections are so full of repetitive DNA that we could not tell what goes where even if the entire genome was represented. The solution to this problem in the sequencing of extant organisms has been to use various methods for making full or partial sequences of long fragments. Imagine you are trying to piece together a painting from cut up scraps, but the painting was mostly just the same image repeated many times. You could accurately reconstruct some small chunks, but on the whole, you'd have no idea which scraps went where, even if you had all of them at your disposal. If you had a scrap that was longer than the others, and in fact spanned the entire length of the painting, that could help serve as a guide to put your partially reconstructed chunks together into a complete painting. If an ancient DNA source has decayed to the point that no fragments over a few hundred bases long survive, you're just shit out of luck. Someguy1221 (talk) 08:31, 18 April 2014 (UTC)

Perhaps you can use a similar existing animal, like an elephant, when cloning a mammoth, to get the outline for where everything generally goes. And if you end up with a few mistakes, it may not matter, especially if the mistakes are in the junk DNA. Even in functional DNA segments, while a single error could be fatal, it isn't likely to be. Maybe that section controls something like eye color, for example, that doesn't much matter. StuRat (talk) 18:39, 18 April 2014 (UTC)

Repopulating the planet with more than biblical accuracy

If we suddenly found out that there was going to be a terrible catastrophe and the earth was going to be destroyed very soon, and by a surprising coincidence we also found a planet that was identical to earth in every way except there was no animal life on it, and we had some means of transporting animals and humans to the new planet, but couldn't take everything, what is the minimum amount of each species we'd have to take in order to have a good chance at survival? Like, if we just took 2 of everything like in Noha's ark then some of them would get eaten straight away and the others would starve or have incest offspring which would be genetically bad. Horatio Snickers (talk) 19:06, 17 April 2014 (UTC)

Minimum viable population gives some ideas. 75.41.109.190 (talk) 19:14, 17 April 2014 (UTC)

Also, Population bottleneck. The article mentions that all European bison are descended from 12 individuals. Apparently there are now almost 5000 of them and the population is increasing. By the way, Noah's ark contained 7 animals of some kinds, and 2 of others (in addition to 8 humans). - Lindert (talk) 20:38, 17 April 2014 (UTC)

To be fair, that depends on which source you're reading. Evan ^{(talk|contribs)} 02:29, 18 April 2014 (UTC)

Founder effect also has some food for thought.OttawaAC (talk) 05:23, 18 April 2014 (UTC)

• Very interesting question, and good links above!

I respect the value of counterfactual conditions, and you're touching on many important issues in population biology. But, if taken literally, something that is "identical to earth in every way except there was no animal life on it" -- is basically logically impossible, based on our current understanding of evolution and ecology. For example, the adaptive radiation of flowering plants on Earth was tightly coupled to the mutualisms between plants and insect pollination syndromes. Simply put, without animals, a similar planet would not have anywhere near the diversity of plant life that we see on Earth, because our flora is intimately linked to our fauna. All the plants we know with animal-specific defenses would have no reason to exist O.o SemanticMantis (talk) 02:34, 18 April 2014 (UTC)

And thus there would be no point in taking animals that are strongly specialized in their diet. How many animals that leaves is another interesting question. —Tamfang (talk) 06:16, 18 April 2014 (UTC)

In fiction perhaps it might be explained away with another catastrophic event that happened on planet Earth II very shortly (days?) before it was discovered. Something that wiped out the entire animal population without affecting any of the other kingdoms. Erm .. perhaps. ---Sluzzelin talk 06:26, 18 April 2014 (UTC)

If we keep God in the picture, then whatever He said we needed is correct. As mentioned above, there is a bit of Deus ex Machina to have flora without fauna. If God overcame that problem, genetic diversity and population is a cakewalk. --DHeyward (talk) 09:15, 19 April 2014 (UTC)

Ok, I see the problem. I did wonder about plants at first, but the practicality of transporting a load of seeds and then waiting for them to grow would have made the question even more absurd. And thank you for all the interesting answers! Horatio Snickers (talk) 18:07, 21 April 2014 (UTC)

Sulpher content in foods

Why is the sulfer content not listed when i search the nutrtional value of foods? I have also been searching for a comprehensive chart with thie sulfer content in particular and can not find it. So i thought to search each individual food and its not listed ther either. I would love to find it or to see it added! Thank you 96.50.231.89 (talk) 19:39, 17 April 2014 (UTC)

Well, I'm not aware that sulfur, per se, is thought of as a discrete "nutrient". There are single elements that are thought of like that, but they tend to be metals or near-metals (calcium, magnesium, then trace nutrients like copper and selenium). Are you concerned that you might be getting too little (or too much) sulfur in general? I have never actually heard of that.

Now, sulfur-containing amino acids, like say methionine or taurine, that's another story. I wouldn't expect those to be on the actual nutritional label as that's a little too detailed, but you can probably find their incidence in foods if you search. --Trovatore (talk) 20:24, 17 April 2014 (UTC)

The vast majority of sulfur (sulphur) in one's diet is consumed in the form of sulfur-containing amino acids (principally methionine and cysteine) which are part of all dietary proteins. Specific recommendations for dietary sulfur are not generally provided, as sulfur needs – in a form that the body can use – are almost always readily met by consuming the recommended amounts of total dietary protein.

Note that methionine is one of the essential amino acids, and that individuals on vegetarian/vegan diets do need to pay attention to their protein mix. Elemental sulfur in the diet (as the pure material or as part of most other compounds) cannot substitute for the required essential amino acids, as the human body is unable to synthesize methionine from scratch. TenOfAllTrades(talk) 13:51, 18 April 2014 (UTC)

"Vast majority" is an overstatement -- we also consume substantial amounts of sulfur in other forms. This chart gives a table of sulfur content for many foods. We also have an article about low-sulfur diets that contains some relevant information. Looie496 (talk) 14:32, 18 April 2014 (UTC)