Wikipedia:Reference desk/Archives/Science/2009 October 20

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October 20

Vacuum Ablation

I've heard of a concept called Vacuum Ablation in which given enough time the atoms in a substance boil away into space. Is there such a thing? Josh Parris 02:54, 20 October 2009 (UTC)

Googling "vacuum ablation", it looks like the term refers to a situation where there is a substance in a vacuum, and the substance is ablated by pulsing a laser on it. It's not a matter of just waiting for the ablation to occur, without supplying any source of energy. However, see also Outgassing#Outgassing in a vacuum, which is closer to the situation you're thinking of. Red Act (talk) 03:17, 20 October 2009 (UTC)

You might also want to read Pulsed laser deposition, which is what vacuum ablation is used in. Red Act (talk) 03:21, 20 October 2009 (UTC)

So, in summary: No, Vacuum Ablation is not something extremely long-lived space structures need to worry about due to the high energies required to cause it. Josh Parris 03:34, 20 October 2009 (UTC)

Resolved

largest possible Black Hole

What is the largest possible Black Hole and how long would it take to form? 71.100.9.185 (talk) 03:23, 20 October 2009 (UTC)

I don't think there's any theoretical limit on the upper size of a black hole. Josh Parris 03:34, 20 October 2009 (UTC)

Black holes have a minimum size, in that if they're too small, Hawking radiation will make them evaporate. But the only limit on maximum size is how much matter in the universe gets close enough to get sucked in. The supermassive black hole in OJ 287 is currently the largest black hole known, with a mass of about 18 billion times the mass of the sun. But AFAIK there's no theoretical reason why a black hole couldn't be much larger than even that. Red Act (talk) 04:35, 20 October 2009 (UTC)

Size in terms of mass is one thing. Another is size in terms of diameter. But given the nature of black holes, is "diameter" a meaningful term? If so, do scientists have any clue about the "widest" black hole? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:42, 20 October 2009 (UTC)

For a black hole (or more pedantically precisely, a nonrotating, uncharged black hole), the mass and "diameter" are equivalent. The Schwarzschild radius of a black hole, which is the radius in Schwarzschild coordinates of the black hole's event horizon, is directly proportional to the black hole's mass: r=2Gm/c². So the aforementioned black hole in OJ 287 has a Schwarzschild radius of about 5x10¹³ m. There is no more a theoretical maximum on the Schwarzschild radius of a black hole than there is a theoretical maximum on a black hole's mass. Red Act (talk) 05:09, 20 October 2009 (UTC)

I don't follow how they're "equivalent", but "proportional" makes sense. 5 times 10 to the 13th meters is apparently on the order of an Astronomical Unit, yes? (Distance from sun to earth) That would be sufficiently large. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:15, 20 October 2009 (UTC)

They are equivalent because they are essentially the same thing just measured in different units. --Tango (talk) 10:39, 20 October 2009 (UTC)

What about the amount of time it would take to form the largest possible Black Hole and how long did it take to form the supermassive black hole? Also after the largest possible Black Hole sucks up all the matter in the Universe could it then suck up all of the empty space? 71.100.9.185 (talk) 04:51, 20 October 2009 (UTC)

That's kind-of one hypothesis about the end of the universe, but there's a lot of distance between black holes. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:15, 20 October 2009 (UTC)

That is one theory. However the currently accepted theory is that the expansion of the universe is accelerating, despite gravity pulling everything together. Under that theory a black hole could conceivably suck up all the matter nearby given enough time, which could be quite a lot of stuff, like a galaxy cluster, but not everything in the universe. Rckrone (talk) 05:30, 20 October 2009 (UTC)

Not a single black hole, maybe, but all of them together could theoretically eventually consume everything that wasn't a black hole, just through random drifting? Or most of it. Then all you would have is drifting black holes, which might eventually drift into each other - or might not. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:35, 20 October 2009 (UTC)

"Or not" is more likely, due to the expansion of the universe. And all the black holes will eventually evaporate due to Hawking radiation, starting as soon as the background temperature of the universe drops below their blackbody temperature. Just imagine - a vast, dark, empty, universe, but occasionally some points light up, first very slowly in the long radio frequencies, but culminating in an incredible flash. Possibly the last survivors travel in search of these explosions to harvest the entropy - there should be a (somewhat depressing) SF story in there... --Stephan Schulz (talk) 10:56, 20 October 2009 (UTC)

"An incredible flash..." the next Big Bang? I thought one theory was that space doesn't exactly exist by itself, that it's somehow connected with the objects in it. If there are no objects in it, maybe there's no space either? Not a vast nothingness - but a singularity - and the possibility for the cycle to start over? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:59, 20 October 2009 (UTC)

Well, intriguing as it is, Hawking radiation will only release the energy equivalent of the matter that formed the hole in the first place. In the last second, it will release the energy of about 1 million Hydrogen bombs. Impressive, yes, but not Big Bang stuff. Moreover, this will be a conventional explosion into space, not a metric explosion of space. --Stephan Schulz (talk) 14:53, 21 October 2009 (UTC)

Also, the Hawking radiation would have fairly high entropy, the big bang had very low entropy. (You mentioned harvesting entropy above - I think you were a little confused, you want to harvest the absence of entropy.) --Tango (talk) 15:09, 21 October 2009 (UTC)

Yes, point taken about the entropy. But my way sounds better. ;-). --Stephan Schulz (talk) 17:49, 21 October 2009 (UTC)

There isn't a supermassive black hole; there are a bunch of them. It's believed that most galaxies have a supermassive black hole at the center of them.

Black holes have existed and have been growing since shortly (in cosmological terms) after the big bang. So they've been around, and growing, and occasionally merging, for about 13 billion years now.

A big crunch, in which the universe recollapses down into one black hole singularity, is one possible ultimate fate of the universe. But it's not really known whether that will ever happen. If that does happen, it will be billions of years from now. Red Act (talk) 05:29, 20 October 2009 (UTC)

And, possibly, create another big bang, yes? With a new universe and possibly new laws of physics? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:36, 20 October 2009 (UTC)

Well, there is the Big Bounce possibility. It's highly speculative, as would be any theory that extrapolates past singularities in both directions. And thinking that there might be different laws of physics in each bounce is even much more wildly speculative.

Again, heat death is the currently preferred theory, although I wouldn't take heat death as being engraved in stone, since predictions of the fate of the universe depend heavily on the nature of dark energy, about which we know next to nothing. The field of physical cosmology has changed drastically in the last few decades, and I don't think there's any good reason to expect that it won't continue to change drastically in the next few decades. We just don't have all the answers yet, which makes it an exciting time to be watching the progress as it's being made. Red Act (talk) 06:31, 20 October 2009 (UTC)

P.S.: Although collapsing into one big black hole hasn't been completely ruled out, the preponderance of the evidence at this point is that that probably isn't what will happen. Instead, the ultimate fate of the universe appears more likely to be heat death. Red Act (talk) 05:37, 20 October 2009 (UTC)

Meaning essentially a vast nothingness? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:43, 20 October 2009 (UTC)

an inherently flawed workup to a Grignard synthesis?

So ... my lab synthesis prescribed to me worked like this. First we form phenylmagnesium bromide in ether in situ, then react it with methyl benzoate (in more ether). We hydrolyse the alkoxide salt with dilute sulfuric acid, discard the aqueous layer then dry the organic layer with brine and magnesium sulfate, then evaporate, then recrystallise the crude product with hexanes.

How likely is it that an explanation for a yield of say, 34%, comes from the fact that the magnesium (soft) alkoxide salt ends up forming a carbocation that is then even more soluble in water? The carbocation escapes into another phase, driving carbocation formation to the right ...

Secondly, I notice there isn't a lot in this workup that separates methyl benzoate and bromobenzene from the product ... is it reasonable that they all get consumed to near completion (I had an MP depression of about 5 C); their BPs are really high but the product is a solid; maybe bromobenzene and methyl benzoate form an azeotrope that can be evaporated easily...? (But on a totally different scale than evaporating ether.) Would acid-catalysed hydrolysis of the starting reagent into methanol and benzoic acid help significantly? John Riemann Soong (talk) 04:22, 20 October 2009 (UTC)

Does elevated oxygen allow adjusted respiratory rates?

People who are suddenly at unusually high altitudes tend to feel short of breath. Is the opposite true if we hyper-oxygenate a room?

Let's say respiratory rate is R, and respiration volume is V. Is it as simple as saying that in a room with an oxygen level X times normal at sea level a human will be able to breath at a rate of R/X? Or would the blood oxygen levels fall too low between breaths? Assuming constant respiratory rate, could we instead inhale V/X - taking shorter breaths to satisfy the body's need?

I'm envisioning a dude sitting in a room with 3X average oxygen and breathing *really* infrequently!218.25.32.210 (talk) 05:00, 20 October 2009 (UTC)

Breathing serves two purposes; the intake of oxygen, and actually more importantly, the exhaling of CO2. The body produces CO2 at roughly the same rate, regardless of how much oxygen you are taking in, so there is a minimum required breathing rate necessary to expel CO2 from your system before it builds up to toxic levels. Even in a pure-oxygen atmosphere, you'd still need to breath at roughly the same rate you do in standard 20% oxygen atmosphere, in order to get the CO2 out of your body. --Jayron32 05:16, 20 October 2009 (UTC)

Interesting! In such a situation would you be introducing potentially harmful levels of oxygen into your bloodstream, or can the lungs autocompensate by reducing uptake per inhalation?218.25.32.210 (talk) 06:54, 20 October 2009 (UTC)

It's a bit more subtle than stated above. If you are untrained, your reflex to exhale will kick in long before CO2 becomes critical, and your breathing rate is unaffected by elevated oxygen levels. If you go SCUBA diving, you are breathing an atmosphere that contains increased levels of oxygen in absolute terms - every 10m under the surface doubles increases the atmospheric pressure by one atm and leads to a corresponding increase in oxygen content. Untrained divers will use up their air supply at correspondingly increased rate, but trained divers can slow down their breathing somewhat and hence stay underwater much longer. And indeed, if the oxygen partial pressure exceeds certain values, it does become toxic. IIRC, the upper limit for recreational diving is 1.4 atm. You cannot reach this with plain air under normal depth restrictions, but you can with Nitrox, easily - with Nitrox 36, you can only go 29m down. Military divers seem to dive reasonably safely with up to 2 atm of oxygen partial pressure, but that leaves little room for errors. --Stephan Schulz (talk) 07:41, 20 October 2009 (UTC)

While SCUBA diving, you are supposed to keep your breathing regular, because holding your breath can allow pressure-differences to build up in the lungs if you change depth. However, I have noticed that at depths of ~ 50 or 80 feet, I can easily go a full minute or two minutes on Nitrox without feeling the need for breathing. It's a very unusual feeling - there is no shortness of breath at all, just a feeling of not needing any more air. As Stephan Schulz pointed out, this can help preserve the air supply - using it up slower. Divers at deeper depths need to really be cognizant of these effects to make sure that they are actually getting a safe level of oxygen. To help mitigate this, at great depth, Nitrox is usually supplanted with Trimix (breathing gas) (usually helium, nitrogen, and oxygen). Attempting to breath trimix at atmospheric pressure can be dangerous - there isn't enough oxygen partial pressure - so technical divers usually take the tank down to depth with them and switch out at the bottom. Nimur (talk) 14:14, 20 October 2009 (UTC)

IFT TRANSFORMER

WHY IF=455 INTERNAL CIRCUIT DIAGRAM & WORKING..........???????????

First, it's considered rude to type in all caps becuase it seems to be shouting.

Second, I understand if you haven't mastered the English language. But, even presuming (and since I don't know the technical terms I will guess and give you the benefit of the doubt) that an "IF=455 internal circuit diagram" is your subject, you have not provided us with even a verb to go with it, let alone a question. Yes, "work" can be a verb (action word), but to be understood, you must use the form "work," and ask "why does this circut diagram work in this way?" Then, you need to give some context to your question - what about the way it works confuses you?

If it's another question that you have, you will need to phrase it the same way - with a subject (what you're asking about) and a verb or verb phrase (what it does/doesn't do that you're unsure about.)

So, phrase it that way, so we can understand and help you. Oh, and below "save page" you'll see a list of things you can insert - at the right are the tildes you should sign your question with. Thank you.209.244.187.155 (talk) 12:32, 20 October 2009 (UTC)

The questioner likely wants to know why 455 kHz is used for the intermediate frequency in superheteropdyne AM radio circuits, the most common type of Amplitude modulation radio since the late 1920's. The use of an intermediate frequency allows improved frequency selectivityThe radio frequency signal, which can vary over a wide range, is converted to one constant intermediate frequency (typically 455 khz). It is easier to amplify the constant IF frequency and to detect the signal than is several stages of amplification must function at the original radio frequency. Does the questioner want a simplified verbal explanation or a technical mathematical explanation? Read the articles linked above, and come back with any additional questions. Another explanation is found at "Consumer electronics for engineers pages 12-13. Edison (talk) 15:04, 20 October 2009 (UTC)

IF=455 is someone's shorthand for "Intermediate Frequency = 455 kHz". That frequency is usually chosen in small AM radios because it is a fair compromise between 1) ease of constructing high-Q resonant transformers in the radio IF amplifier; 2) high enough for acceptable image frequency rejection by the radio front-end tuned amplifier; 3) by being a de-facto standard there should be no strong transmissions at 455 kHz and components are standardised e.g. fixed-frequency ceramic filters are now often used instead of wound coils. In my experience 455 kHz is the commonest IF in Japan and US while in UK (when they made radios) it was 465 kHz. Cuddlyable3 (talk) 16:16, 20 October 2009 (UTC)

Neutronium

Science fiction has loved to use neutronium for all sorts of purposes, plating on shields for instance. Is it possible, even in principle, to use neutronium as an engineering material in small components? Or will it immediately return to "normal" matter in a spectacular reaction if by some magical means it is suddenly removed from a neutron star? SpinningSpark 07:01, 20 October 2009 (UTC)

I don't think this is a scientifically meaningful question. Neutronium is almost exclusively a science fiction concept, so answering questions about it would basically be a science fiction answer. As the neutronium article states, the term "neutronium" is rarely if ever used in the scientific literature, and there is no agreed-upon definition for the term. Science fiction uses the term to mean the material present in the cores of neutron stars, but the composition of the material in the cores of neutron stars is uncertain. Supposed bound clusters of neutrons like tetraneutron are not supported by current models of nuclear forces, and the one experiment that supposedly suggested its existance can't be replicated. So trying to answer questions about neutronium's nature scientifically is almost as hard as trying to come up with scientific answers about kryptonite. Red Act (talk) 07:39, 20 October 2009 (UTC)

Sorry, but I think that's evading the question (but I'm happy if the answer is simply we don't know). There is no known source of kryptonite, or, as you say, any meaningful definition of what it is. However there is such a thing as a neutron star and it must be made of some material, and there are at least theories as to what that is. If it makes you happier let's not call this material neutronium. If by some magical (ie unspecified) means I place 1 kilogram of neutron star material on my desk, what will happen? My guess would be a rather nasty explosion since the material is no longer under the pressure required to maintain that density, but I would rather like a scientific answer. SpinningSpark 14:09, 20 October 2009 (UTC)

You might want to read about Neutron temperature to bring yourself up to speed on what is scientifically known about neutrons. The rule of thumb I got from a physics professor (which is very approximate), is that "thermal (slow) neutrons are nearly impossible to detect", and "fast neutrons are for bombs." (...because of the role they play in the chain reaction of nuclear fission). The key point to remember is that a very large chunk of our sensory perception of materials comes from electrostatic and electromagnetic interaction - color, volume, texture - these sensory properties are the result of macroscopic averages of microscopic interactions with the electromagnetic force. Neutrons, categorically, are uncharged - so it will be hard to define their volume; they probably will not have a well-defined color; (though they have a magnetic moment, and certainly can interact with electromagnetic waves, there probably will not be spectral lines like those that yield color in other materials). They'll probably be more like an invisible noble gas (but not quite). If you could imagine pulling a 1 kg lump of neutrons out of a giant source of neutrons, you'd need to know their temperature to estimate their thermal diffusion rate - eventually, they would dissipate. Keep in mind that neutrons can pass right through most matter, excepting the statistically small fraction that collide with a nucleus. If the neutrons have low energy, they will just bump their way through all the atoms they encounter and "fall" through your container (if you tried to store them in a box). If they have high energy, they can really muck up the atomic nuclei of the container (fissioning them, for example, but probably not yielding a chain reaction unless the material is conducive to that). You'd have to be pretty creative to confine the neutrons - they're fairly elusive particles. Nimur (talk) 14:29, 20 October 2009 (UTC)

That's all very interesting Nimur, but it's not an answer to the question asked. So let me address that. Neutronium matter wouldn't be stable without the assistance of the gravitational atraction and your kilogram of neutronium would likely explode. Dauto (talk) 16:04, 20 October 2009 (UTC)

Thermal neutrons do not explode. They drift. The qualitative behavior will depend entirely on the neutron temperature. That is why I suggested that the starting place might be the neutron temperature article. Nimur (talk) 17:01, 20 October 2009 (UTC)

I think that thermal neutrons at high density (which is basically what the OP is implying by "neutronium") drifting apart would constitute an explosion. Think of what happens when a tank of compressed gas gets broken open. Rckrone (talk) 17:51, 20 October 2009 (UTC)

All those decaying neutrons would be producing fast moving protons and electrons, a hydrogen plasma at an extreme temperature, it could be like trying to contain a piece of the sun, just for the decay products. Graeme Bartlett (talk) 20:43, 20 October 2009 (UTC)

According to this version of the Neutron star article:

• "Neutron stars are very hot and are supported against further collapse because of the Pauli exclusion principle."

And this version of the Degenerate matter article has:

• "Neutron degeneracy is analogous to electron degeneracy and is demonstrated in neutron stars, which are supported by the pressure from a degenerate neutron gas."

Which is interesting because it describes "the Pauli exclusion principle" (and, more specifically, "neutron degeneracy") as if it constitutes a "Force." The question I have, then, is: how does this "force" then relate to the "four fundamental forces"...?

But, to restate the original question above, I think: would this "force" cause the neutrons to accelerate away from each other if a small amount of the matter at the core of a neutron star were somehow liberated from it and removed to some region of less gravitational intensity? Wouldn't that then, in a simplified sense, be just a matter of the "potential (gravitational) energy" of the neutrons in our sample being suddenly converted to kinetic energy? Or just like a hot molecular gas being released suddenly from containment to expand into a larger volume, I suppose, as I far as what I understand Graeme Bartlett to be saying in the remark above. But I'm not sure the analogy really holds here; for example, given the "quantum degeneracy" of the material, isn't it possible for that kinetic energy to perhaps be expressed in the same direction for all the neutrons?! (LOL!;)

I guess it doesn't really make much sense to try to imagine what would happen in a case like this in the absence of any plausible way for it to happen -- but, then again, that didn't stop Einstein, right?! Wikiscient 00:31, 21 October 2009 (UTC)

Featured Article - Diamond

In todays featured article it explains that synthetic diamond is used in heat sinks. But in the heat sink article, under 'construction and materials' there is no mention of diamond. When would synthetic diamond be used for a heat sink?91.109.234.25 (talk) 08:20, 20 October 2009 (UTC)

Diamond makes a good heatsink since it has good thermal conductivity and poor electrical conductivity. However, it has the disadvantage that it's rather more expensive than copper plus a thin insulator. So it is used as a heat sink where the components themselves are expensive - we used it in the 1970s to heat sink semiconductor lasers, which themselves cost around £1,000 even then. --Phil Holmes (talk) 09:18, 20 October 2009 (UTC)

There is currently a lot of work being done on ways to manufacture diamonds in a (relatively) cheap and predictable manner for purposes such as that. It's hard figuring out the best shapes, but they're beginning to make progress. ~ Amory (u • t • c) 17:53, 20 October 2009 (UTC)

Artificial "gills" - getting oxygen from water on the fly...

Reading the helpful links about SCUBA and various gas mixes up above led me to wonder about the current hurdles yet to be cleared in creating what would essentially be artificial gills - a device that pulled oxygen straight from the surrounding water allowing a human to breathe submerged for extraordinarily long periods of time. Surely there is tremendous financial potential for such an invention. Does this fall into the category of "as yet impossible, but not theoretically so" or is it lumped in with time travel as "theoretically impossible" ? 218.25.32.210 (talk) 08:50, 20 October 2009 (UTC)

See Artificial gills (human). Red Act (talk) 09:07, 20 October 2009 (UTC)

It's probably a matter of economics. There usually isn't a need to put a human underwater for such a period of time. Compressed gas is well-known, easy to use, and economical. You might want to note that nuclear submarines (which can stay submerged for a long time) are limited by their foodstocks, not their air supplies. Nimur (talk) 14:34, 20 October 2009 (UTC)

Also note that, as mentioned in the item above, pure oxygen is not what you really want to be breathing. Just extracting and breathing oxygen might be safe very near the surface where you aren't under significant pressure, but maybe not for long periods, and certainly not at any depth. I presume the water also contrains large amounts of nitrogen in solution, but you'd need a device that extracted nitrogen and oxygen and produced the correct mixture. And below a certain depth nitrogen isn't safe either, and then you need to bring rare gases like helium to mix with our breathing air, because you'd never find enough of those in the water. --Anonymous, 02:50 UTC, October 21, 2009.

The problem, far as I recall, is that there's less oxygen per volume in water than air. This is why air-breathing whales have been able to grow larger than any fish ever did. So an artificial gill wouldn't just have to be efficient at extracting water, it would have to circulate a lot of water to keep a warm-blooded mammal like our selves happy. That takes power. What we're offering the scuba diver is then a contraption with heavy batteries that run out of power, instead of a tank of air that runs empty. Not an attractive proposal. Nuclear submarines as far as I know, do not extract dissolved oxygen from the water, but splits the water into oxygen and hydrogen by electrolysis. This is also currently the case onboard the international space station. The needed oxygen can be recycled as humans do not consume atmospheric nitrogen. EverGreg (talk) 08:41, 21 October 2009 (UTC)

It's surprising that a fish can grow as large as the whale shark or the basking shark. But if cold-blooded creatures require less oxygen, the question is how much less? Or maybe the answer is obvious - is the need in the same ratio as the amount? That is, is there an upper bound on how large a fish could get before it would suffocate due to being unable to get enough oxygen from the water? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:26, 21 October 2009 (UTC)

yeah the thing is that gills have a surface and bodies have a volume. The gill surface tells you how much oxygen you get in, the body volume how much you need. The trouble is that when you increase the size of something, the volume rises more sharply than the surface area. (try out the math with a cube or a sphere if you like) Insects also depend on their surface to get oxygen. So the reason we don't have bluewhale-sized fish is actually the same as why we don't have dog-sized insects: geometry. EverGreg (talk) 14:11, 21 October 2009 (UTC)

Mere speculation. I think the basking shark example cited is blue-whale-like enough. And dog-sized insects would likely be a greater issue of lack of sufficient support from an exoskeleton rather than an issue of respiration -- more spiracles could provide an adequate tracheal system. DRosenbach ^{(Talk | Contribs)} 03:40, 22 October 2009 (UTC)

Michelson-Morley Experiment Simulation

Can you please check this Flash Animation carefully? Does it simulate the light propagation response with respect to the assumed aether movement precisely?--Email4mobile (talk) 10:48, 20 October 2009 (UTC)

Only in regards to the somewhat arbitrary units they are using (pixels per second, "frames", etc.). The concept is correct (although regarding light as "particulate" to such a degree is not historically valid for the actually M-M experiment, but it doesn't matter much), and it's only meant to illustrate the concept. --Mr.98 (talk) 12:23, 20 October 2009 (UTC)

I had some difficulty rotating the table because its angle jumped unexpectedly. At one point when I wanted 45 it was changing 44.5, 45.5 degrees etc. It seems the "aether evidence" one needs to see is the staggered emergences of the red and blue arrows. In the real experiment one would see an interference pattern of rings at the target and be looking for any drift in the rings as one rotates the table. I suggest that it would be more instructive to have the table rotate when one clicks on Play. Cuddlyable3 (talk) 15:57, 20 October 2009 (UTC)

It looks wrong to me. In the default orientation the horizontal speed of the light should be ${\sqrt {c^{2}-v^{2}}}$ (where v is the wind speed), but it looks like it's just c. In fact, when v is set higher than c the light shouldn't be able to move horizontally at any speed, but the applet still shows it going at c. -- BenRG (talk) 23:06, 20 October 2009 (UTC)

Gargling salt water to prevent swine flu

I got a forward that says gargling warm salt water twice a day will help prevent swine flu because the virus takes 2-3 days in the throat to proliferate. Is this true? It also says drinking warm liquids has the same affect except it takes the virus to your stomach where it can not survive. Thanks. StatisticsMan (talk) 12:35, 20 October 2009 (UTC)

The answer is the same as with any fact given in a chain email - no. I have yet to see a single true statement in a chain email, it just doesn't happen. --Tango (talk) 12:57, 20 October 2009 (UTC)

::If you inhaled the salt water and died it might reduce the chances of you passing the swine flu onto someone else? --BozMo talk 13:00, 20 October 2009 (UTC)

While you should not take information from a chain email at face value, they are also telling us this over the radio. Lovely media, passing on unverified information as truth. The CDC does not have this listed under their suggestions to prevent H1N1 spread, so I would take that information with a grain of salt. Actually, if I can find an audio of them saying it, we can include it in our article as it would be a reliable source! Googlemeister (talk) 13:03, 20 October 2009 (UTC)

Must... avoid... grain of salt... salt water gargling... pun... --Mr.98 (talk) 23:56, 20 October 2009 (UTC)

I feel confident in saying that method should work - provided you've also had your H1N1 flu shot. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:08, 20 October 2009 (UTC)

I would say that there is probably a grain of truth in the salt, but I wouldn't like to rely on the method. Dbfirs 13:23, 20 October 2009 (UTC)

Gargling salt water can theoretically kill bacteria, but it's only really effective for cleaning pus off of the back of your throat and for making a sore throat feel better. Warm liquids will help you, but not for the reason given - it helps because drinking liquids is always good, and most people are usually slightly dehydrated anyway. Drinking water is essentially the first step in the cure for nearly everything that can happen to you. ~ Amory (u • t • c) 13:36, 20 October 2009 (UTC)

Also, different influenza stains bind at different parts of your respiratory tract. Avian flu is so deadly (partially anyway) because it essentially binds in the lungs, and causes pneumonia. Your average flu usually binds to the throat, so since salt water won't cure the flu this remedy therefore can't be true. ~ Amory (u • t • c) 13:39, 20 October 2009 (UTC)

Minimum population to restart the human race?

Assuming we want to minimise inbreeding what's the minimum amount of people you'd have to have to restart the human race, after say... a nuclear war or something? A source or computer model study or something would be useful. I've read wikipedias article on Minimum viable population but didn't really understand it, and couldn't find a solid year 0 number. Gunrun (talk) 13:10, 20 October 2009 (UTC)

The solidity of a "year 0 number" will depend entirely on the solidity of your definition of inbreeding. Go ahead :-)

DVdm (talk) 13:17, 20 October 2009 (UTC)

(edit conflict) The absolute minimum is 2 (or even 1 with modern technology), but, to minimise inbreeding, I would guess at about 100 because I know of populations around a hundred that have mainly inbred without significant consequences. You will get different answers depending on the amount of inbreeding you are prepared to tolerate. Dbfirs 13:21, 20 October 2009 (UTC)

(edit conflict) Well, obviously 2 wouldn't do, because that would require mating of siblings (and/or mating between parent and offspring), which would probably constitute inbreeding. Bus stop (talk) 13:23, 20 October 2009 (UTC)

Generation ship#Biology and society discusses this issue, although in a different context. It has references too. --Tango (talk) 13:33, 20 October 2009 (UTC)

This is horribly useless information, but a friend of mine spent a number of months performing research in Australia and in her spare time would explore the Outback. Long story made short, whether by meeting them or otherwise, she learned that the natives have, over the years, developed a system of reproduction that allows for safe breeding. Moreover, it is supposedly the/an efficient way to sustain a viable population given the absolute minimum of human inhabitants. I have never found any proof outside of her, so you may have to travel around Australia to prove this. ~ Amory (u • t • c) 13:58, 20 October 2009 (UTC)

But Amory, you didn't tell us what the system actually consists of. SpinningSpark 14:29, 20 October 2009 (UTC)

Jah, I don't know. The there's some plan for what kind of cousins can marry, etc. It sounds fascinating and I'd love to know, but "a friend heard from an aboriginal" isn't exactly a good source. ~ Amory (u • t • c) 15:44, 20 October 2009 (UTC)

Unless you can tell use something about how the system works or what evidence there is that it does work, it is entirely useless and I don't know why you mentioned it... --Tango (talk) 17:16, 20 October 2009 (UTC)

Perhaps they mentioned it in the hope of inspiring some else to think "aha" and find a source they already know exists? Franamax (talk) 18:42, 20 October 2009 (UTC)

According to Engels, among hunter-gatherer societies, the gens system was used and I assumed the Australian system referred to by Amory was some variant of this. In its purest form, women stayed within the gens, whilst men were obliged to marry outside the gens and moved into their wife's gens. This system results in some strange rules on incest to modern eyes. Intercourse with any woman within ones own gens is incestuous, cousins no matter how many times removed are forbidden if they are in the same gens. On the other hand a cousin in another gens is perfectly legal, as would be ones paternal grandmother (although probably not first choice in most cases). SpinningSpark 20:18, 20 October 2009 (UTC)

I would take anthropological information from 19thC armchair researchers like that with a huge heap of salt. Did he ever go to Australia? See an Aborigine? 19th century stuff of that type was almost completely hypothetical; they were working within the conceit of people existing in the so-called state of nature (i.e. wandering around after leaving the garden of Eden). I don't know if the information is correct or incorrect, but would bet the house that it was baseless. Matt Deres (talk) 22:25, 20 October 2009 (UTC)

475 according to this book, although what the odd one is supposed to do after all the other 474 have paired off I'm not at all sure. SpinningSpark 14:55, 20 October 2009 (UTC)

That is because you are assuming an even M/F ratio. If it was 1M/4F, things would be even. And work out very nicely for the males by the way. Googlemeister (talk) 15:02, 20 October 2009 (UTC)

Gosh, that did not even occur to me! I believe the original paper the book is referring to is this and there is also this by the same author SpinningSpark 15:05, 20 October 2009 (UTC)

Pitcairn Island is a good case in point - their population is essentially composed of descendents of some female islanders from Tahiti and a few men who survived the Mutiny on the Bounty. They coped for many generations before outsiders joined the community - and even now, it's likely that few if any outsiders have added to their gene pool. So the answer is considerably less than 100 individuals. As others have pointed out, modern technology could solve a lot of potential problems if the people involved were prepared to produce children to a prescribed plan to ensure that the gene pool were used to it's utmost. SteveBaker (talk) 14:56, 20 October 2009 (UTC)

Maybe population bottleneck and Small population size might be useful articles on the subject? Also, they say the 120,000 moose in Newfoundland are descended from 4 brought over in 1904. TastyCakes (talk) 15:30, 20 October 2009 (UTC)

I find the question what is the minimum number of people needed to sustain a modern technological society, I would assume that there is a a bifurcation point (catastrophical collapse) when nobody can make anything due to the lack of someone else's expertise (wikipedia hates how-tos so we can't help!) --Squidonius (talk) 17:35, 20 October 2009 (UTC)

Mice are very different when it comes to breeding than humans. You can breed siblings with each for generations without worrying to much about all the deleterious effects humans see after even just one generation. In fact, modern biological research largely depends on that fact. ~ Amory (u • t • c) 17:56, 20 October 2009 (UTC)

Is that because mice are genetically simpler (or have fewer recessive gene problems) or because we are much more sensitive to "problems" in inbred humans than mice? TastyCakes (talk) 18:11, 20 October 2009 (UTC)

Both, definitely, although much more of the former. The human genome is full of recessive alleles that would all but kill us after a generation or three of pure inbreeding. In all honesty, we probably know much more about murine genetics than human, so we can probably spot a problem with them faster. However, as you say, it's a lot easier to visually identify an abnormal human than a mouse, although we are pretty good at it; besides, the different speed of aging makes it easier. ~ Amory (u • t • c) 18:34, 20 October 2009 (UTC)

That is only true of laboratory mouse strains (which are essentially clones of each other). Wild mice (and most other non inbred animals) are just as likely to suffer from inbreeding as humans are. Rockpocket 01:24, 21 October 2009 (UTC)

Wouldn't it just be the descendants with two recessive alleles that died? Franamax (talk) 18:55, 20 October 2009 (UTC)

I would suggest that a) labmice have been pretty well culled of individual with recessive genetic defects by many generations of inbreeding and b) that we possibly tolerate 5% of mice with heavy genetic illnesses, but we do not find that acceptable in humans. --Stephan Schulz (talk) 19:08, 20 October 2009 (UTC)

My understanding is that inbred mouse lines are maintained precisely for the purpose of maintaining specific recessive defects. They are outcrossed to preserve the recessive allele, then incrossed to produce the syndrome of interest. Am I wrong there? Franamax (talk) 20:11, 20 October 2009 (UTC)

Properly inbred mice strains (such as BALB/c) are homozygous at all loci, therefore they have no recessive alleles (since there are no other alleles for them to be recessive to!) But it is true that some of the recessive alleles that were originally in the founding population are now fixed in the strain. During the inbreeding process, the mice with two copies of the harmful recessive alleles would have died. It was the ones that survived that were bred on. Therefore, by a type of natural selection (in the hands of the breeding scientists), the nasty lethal alleles would be weeded out and the non-lethal ones remained. The same thing would likely happen with a human bottleneck. The issue is whether there are either enough people, or few enough lethal recessives in the founding population, that the right assortments occurred to ensure there were individuals that dodged that bullet. A healthy dose of luck would help too since we probably wouldn't know if the right mating choices were made until it was too late to do anything about it. Rockpocket 01:19, 21 October 2009 (UTC)

Assuming a simple case, yeah, but you've got the right idea. That's why it's so deadly - once something negative gets expressed there's no chance for new genes to come in. Looking at a really simple case of an autosomal recessive deleterious gene, if only one parent carries the gene then the chance of a child getting a copy is 50%. That means there's a 25% that both siblings have the gene after only one generation. ~ Amory (u • t • c) 19:27, 20 October 2009 (UTC)

Side note: I'm still trying to figure out how this sub-thread went from moose to mice. Shouldn't we be talking about "meese", the plural of moose? :) Franamax (talk) 20:19, 20 October 2009 (UTC)

I'm pretty sure it's mooses. Or possibly Moosae. TastyCakes (talk) 20:50, 20 October 2009 (UTC)

It's about to change again. All the billions of Rabbits in Australia, a major national pest, are descended from 24 rabbits released by a well-meaning Englishman, Thomas Austin, in 1859. -- JackofOz (talk) 20:30, 20 October 2009 (UTC)

If you buy the Toba catastrophe theory, then the human population recovered from a bottleneck of somewhere between 2,000 and 20,000. Rockpocket 01:42, 21 October 2009 (UTC)

Searching for minimum human population finds an assortment of material. Including, in the case of a project to populate a planet, the minimum is two females if they have sufficient quantities of stored fetuses, eggs, and sperm. -- SEWilco (talk) 16:19, 26 October 2009 (UTC)

Inbreeding

In a case like described above, would it really be a problem for siblings or offspring or whatever? I'm talking strictly biological/genetic problems. I know that long-term inbreeding can cause problems like Charles II, but with a continually expanding population, the severe inbreeding wouldn't occur after a few generations. So with an initial population of 2, would it be nearly as bad as the Habsburgs? —Akrabbim^talk 18:45, 20 October 2009 (UTC)

If you are starting with only 2 genomes, you are by definition inbreeding, no matter what the eventual population size. The only "new" genetic material would be novel single-nucleotide polymorphisms and syntenic reshuffling / gene duplications introduced by retrotransposons. These processes introduce genetic diversity but act slowly over many generations. Franamax (talk) 19:01, 20 October 2009 (UTC)

A population with so little genetic diversity has difficulty adapting to changes in environment. For example, if a new disease pops up, chances are good that nobody in the population will have any natural immunity and the whole population will be wiped out. Usually you get a few people with immunity that can repopulate, thus avoiding extinction. Alternatively, if everyone is the same height and suddenly the short trees all die and you need to pick your fruit from taller trees there won't be any tall people to pick them and the species will die out, usually it would just evolve to be taller. (Obviously, both those issues can be overcome with technology, which is why people above are mainly talking about recessive congenital problems, which are harder to deal with technologically. For non-technological species, it is a bigger problem.) --Tango (talk) 20:25, 20 October 2009 (UTC)

Adam and Eve? ;) Rockpocket 01:04, 21 October 2009 (UTC)

What Franamax and Tango have said is valid, but that's not what "causes" problems like that of Charles II (or the well-known hemophilia suffered by many other inbred royals).

The real problem there is (very poorly) discussed in Inbreeding#Allele exposure. Basically, in inbred populations individuals are more likely to inherit a maladaptive "recessive" allele from both their parents -- and so, consequently, those individuals are more likely to suffer from the maladaptive traits encoded by those alleles and "more likely" (of course) to pass on those same recessive alleles to any offspring they produce (if any...). Note that in the larger population from which that inbred group came, individuals are much more likely to inherit at least one "dominant" allele (and will in turn pass that on to at least about half their offspring on average) and therefore will not suffer (as much) from such maladaptive traits (even if they inherited the maladaptive "recessive" allele from the other parent).Wikiscient 01:49, 21 October 2009 (UTC)

Indeed, as I said the problem of bad recessive alleles is more significant for a technological society (or when we are only considering a small subset of the population, as we are with royal families). For other species, lack of genetic diversity can be much more of a problem since it can cause complete extinction rather than just a quarter (if the good and bad alleles are equally prevalent, which is unlikely to be true, but nevermind) of the population having a congenital defect. --Tango (talk) 10:31, 21 October 2009 (UTC)

storing freshly charged batteries

What is the best way of storing ( safely and ready for use) all those charged AA, AAA cells freshly out of the recharger?--79.67.32.188 (talk) 17:18, 20 October 2009 (UTC)

(Question restored, because without it the rest of the thread is incomprehensible. Please NEVER delete a very sensible and reasonable question while leaving the responses. Per WP:IAR) Edison (talk) 04:49, 21 October 2009 (UTC)

I use these cases. Keep in mind that NiMH rechargeable batteries will self-discharge in storage. Some (typically the highest capacity versions) will discharge significantly within days. Others are designed to discharge more slowly, and may be usable for months. So keep this in mind when storing them. -- Coneslayer (talk) 17:26, 20 October 2009 (UTC)

It depends what you mean by 'ready for use'. Keeping rechargeable batteries in the freezer drastically lowers the self discharge rate but you should not use them until allowing them to warm up to about room temperature. [1] [2]. Also you need some way to store them avoiding short circuits, for example the containers Coneslayer showed. Also as Coneslayer mentioned, many NiMH have a high self discharge but while it's currently true low self discharge batteries are lower capacity then the highest capacity versions, the best way to tell if they are low self discharge is if they are sold as such. It's likely any battery not sold as a low self discharge battery will not be a low self discharge. As low self discharge batteries were only commercialised about 4 years ago, it's save to assume any battery older then that is not one no matter the capacity. Also because fakes are not uncommon, look out for known reliable brands and from decent retailers. Nil Einne (talk) 18:04, 20 October 2009 (UTC)

Re: "It's likely any battery not sold as a low self discharge battery will not be a low self discharge.": Actually, "pre-charged" batteries are marketed under a variety of names; see Nickel-metal hydride battery#Low self-discharge cells. — Sebastian 19:17, 20 October 2009 (UTC)

I think we need to distinguish between marketing terms and useful information. There's little point IMHO giving a list of low self discharge battery brands names since it's likely to be incomplete. But any low self discharge battery will mention or imply its low self discharge characteristic even if it doesn't call it self a low self discharge battery or use the specific terms. E.g. Sanyo Eneloop "Once charged, eneloop retains its charged capacity even after 6 or 12 months of storage" Maha Imedion "IMEDION can be stored for an extended period of time without substantial loss of power and are ready to use out-of-package" Panasonic Infinium "365 days Standby Power: “Use them, Charge them, Store them, Use them”". I admit, I should have been clearer and in particular said that they would likely either describe a low discharge or mentioned them retaining charge for a long period of time (I considered it but have a tendency to write long and confusing answers so decided to avoid it) and apologise for any confusion but I would also hope anyone reading the article and using the RDS understands that if a battery mentions that it has a low discharge, keeps a high charge over 1 year or whatever is a low self discharge battery even if it doesn't specifically call itself a low self discharge battery. Understanding and cutting through the bullshit of marketting hype is IMHO an important life skill. Incidentally precharged is an exceptional poor name. You don't need to have a low self discharge to be sold precharged and I'm pretty sure if you went back to before low self discharge batteries you will find batteries that mention how they are precharged. The charge may not last long so even if they are precharged it may not be of much use. (In any case I'm not convinced many people even care if they are pre-charged, the only case would be if someone finds they urgently needs batteries and decides they could do with some new rechargables.) Some companies may use the term to mean they remain charged when you want them (if you charged them before hand) however it's still a rather confusing terminology which is IMHO best avoided particularly on the RDS. In any case I stick with my main point. Any battery which does not mentionr imply it has a low self discharge characteristic, whatever way it may market the feature is unlikely to be low self discharge. If you come across some random low capacity battery, don't expect it to be a low self discharge just because it has a low capacity. Nil Einne (talk) 20:36, 20 October 2009 (UTC)

Um, we seem to have had the question deleted but at least some of the answers are still here. Under what circumstances could that be correct? (Maybe this belongs on the talk page, but I'll ask it here.) --Anonymous, 02:56 UTC, October 21, 2009.

The question was asked by a banned user, but didn't get deleted before several well-intentioned editors had provided detailed answers, and, bleeding heart that I am, I couldn't bear to delete their work along with the question. (And, yes, any further discussion should probably be on the talk page.) —Steve Summit (talk) 03:55, 21 October 2009 (UTC)

Human's scent

I am looking for general information about human's personal scents...of the type a dog or cat would recognize one by or like you might smell on someone's clothes. I looked in my psychology book and found a whopping one line on the subject: "As any dog or cat with a good nose could tell us, we each have our own identifiable chemical signature." Our Wikipedia article has even less information (unless I'm missing something?). What exactly is this chemical signature? Why is it not possible to smell your own scent? Has any psychological/biological research been done on human scent? Finally, in theory, would it be possible to take a shirt that's never been worn, have someone sleep in it, run a piece of the shirt through some chemical analysis process (perhaps Mass spectrometry?), discover the composition of the chemical signature/scent, and (this is probably stretching it) perhaps synthesize it? Ks0stm ^(T•C•G) 18:57, 20 October 2009 (UTC)

Well, you can run the t-shirt past a woman's nose. Scents apparently reveal details of the human immune system. Google "mhc scent human compatibility" and you will see lots of results. Franamax (talk) 19:21, 20 October 2009 (UTC)

Its easy to smell your own scent. Rub your finger on the scent glands behind/above your ear (for example). Smell your finger. As a student I seem to remember you could easily tell the gender of the person from the scent rubbed on a cotton bud that way and quite a lot else besides (often you can identify the person) --BozMo talk 20:53, 20 October 2009 (UTC)

Ahh, so that's why they tell us to wash behind our ears? They're teaching us to erase the signs of our own unique existence? Franamax (talk) 22:41, 20 October 2009 (UTC)

My mum teaches 4 year olds and apparently she often has someone in the class with really sensitive smell who can smell a jumper found in the classroom, say, and immediately say whose it is. --Tango (talk) 21:35, 20 October 2009 (UTC)

Richard Feynman describes his skill at this particular art in Surely You're Joking, Mr Feynman!. Our noses are actually fairly good, we just rely on our eyes for practically everything, so we're not usually aware of scents unless they're extremely strong. Tevildo (talk) 22:32, 20 October 2009 (UTC)

Individuals do have their own gestalt of odors that are the combined product of exocrine secretions. Once could ask someone to wear a t-shirt then do mass spec in the manner you suggest and get a spectrometric read out. However, the chances are if you did the same experiment the following day with the same person, you would get a different molecular profile. Why? because the content of out odor secretions will vary with diet, time, health, body flora, temperature, stress etc. So we do not each have a unique, permanent odor signature. That said, it is likely that different individuals would have greater variation than the variation within an individual. So there is some element of individuality.

There is quite a lot of information out there on molecules hypothesized to be involved in human odor identity. The major histocompatibility complex (MHC) has long been suggested to be involved, though a direct link has yet to be shown in humans (see Claus Wedekind, for some indirect evidence). Other molecules have been claimed to be human pheromones, such as estratetraenol and androstadienone, though again, direct evidence is lacking. In reality, the biggest factor in human odor variation is likely to be diet; to put it crudely - what comes in largely comes out, you change what you put in, you change what you get out.

In contrast, genetically encoded olfactory signatures are much better defined in animals, and we know of numerous chemicals that transmit specific olfactory information about others (I'm actually writing an article on some of these at the moment, its incomplete, but you there are plenty of sources you could read ). If you want to learn more, there are interesting chapters in Olfaction, Taste and Cognition by Catherine Rouby et al [3] and Pheromones and Animal Behaviour by Tristram Wyatt [4] Rockpocket 00:55, 21 October 2009 (UTC)

Incidentally, there has been a lot of research on the best ways to store human scent. In the pre-DNA days, it was used by police forces to put individuals at crime scenes, as specialized dogs could determine whether a given scent at a crime scene matched up with a given scent sample (sometimes taken surreptitiously with specialized chairs). The Stasi had a large scent archive for this reason. Apparently the dogs were quite good at it, and could track people based on very old scents that had been stored (on specialized cloth, in mason jars). --Mr.98 (talk) 15:52, 21 October 2009 (UTC)

The last of its kind...

Is there a specific term used to describe species which, whilst not technically extinct at present, are only comprised of a single individual and thus inevitably will be (barring cloning or that hypothetical genetic manipulation of a closely related species)? Something more specific than functional extinction? --Kurt Shaped Box (talk) 21:49, 20 October 2009 (UTC)

I have heard read the term "non-viable population" for a scenario where an extinction pro futuro is but a matter of time. --Cookatoo.ergo.ZooM (talk) 22:08, 20 October 2009 (UTC)

I've heard the term "genetically dead" being used about an animal that will not be able to reproduce. That would usually be the case for the last member of a species. EverGreg (talk) 08:26, 21 October 2009 (UTC)

A similar situation occurs in a very different field: that of disappearing languages. This [site] states that

"According to Unesco's Atlas of the World's Languages in Danger of Disappearing, a language is considered endangered when it is no longer spoken by children, moribund when only a handful of elderly speakers are left, and extinct when it is no longer spoken. The numbers vary by source, but even the most optimistic estimates are alarming, with half of the world's languages struggling to survive. Some sources declare 5,000 of the 6,000 total in some state of endangerment."

Michel M Verstraete (talk) 19:22, 21 October 2009 (UTC).

The word you need is relict. HTH, Robinh (talk) 21:37, 21 October 2009 (UTC)

You nailed it! :-D EverGreg (talk) 09:06, 22 October 2009 (UTC)

Dishwashers

Y'ever had a question you wanted to ask, but you knew that doing so would make you sound like an insane person? This is where I am now. Please bear with me a minute. We have a GE dishwasher that came with the house, we have hard water, but use a water softener. Both items seem to work just fine. We use the regular ol' Cascade dishwasher powder. Here's the thing: when we wash something in the dishwasher it takes much, much longer for it to dry than if we washed it by hand. Like, days versus hours longer; I've literally picked up tupperware bits with water still in them after 36+ hours have elapsed. On the other hand, items washed by hand tend to air dry in a couple of hours; we can put them away the same day we wash them. Now to top it off, here's the twist: if we take the items just washed by the dishwasher and give them a quick rinse, they dry more quickly than if we don't rinse them. If we open the door at noon and rinse a few of the items out at 6pm, those rinsed items will be dry by morning (say) while the other items will not be despite having six extra hours to dry.
I thought my wife was crazy when she said this was going on, but I've seen it time and time again. And yes, I've read the article on confirmation bias. If anything, I wanted to prove her wrong and had to eat my words! So after all that, my question is this: what on earth could case this set of observations? Could something in the detergent be preventing evaporation? That stuff should all get rinsed off anyway; a quick spritz of tap water shouldn't make a difference, right? Matt Deres (talk) 22:15, 20 October 2009 (UTC)

Are you putting the rinsed items back in the dishwasher to dry or on a draining board? Evaporation rates depend heavily on humidity and it will be more humid in your dishwasher than in the rest of the kitchen, even with the dishwasher door open (although with the door open the difference should be fairly small, so I'm not sure if that can completely explain it). --Tango (talk) 22:22, 20 October 2009 (UTC)

Water can "pool" in low spots in Tupperware, etc., and that could take awhile to evaporate. That stuff I take out, shake off the excess, and let it dry in the sink rack. Otherwise, the stuff in my dishwasher is pretty much dry after the drying cycle, so perhaps there's a problem with your machine. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:09, 21 October 2009 (UTC)

That is a good point - most dishwashers I've used blast hot air at everything to dry it before the cycle finishes. There shouldn't be any need to wait for things to dry at all. --Tango (talk) 00:11, 21 October 2009 (UTC)

I don't usually take the dishes out right away except if I suspect there could be overturned (i.e. right-side-up) Tupperware and such to be extracted and air-dryed. Otherwise I leave it alone, except to let things cool off. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:15, 21 October 2009 (UTC)

I'm answering a few things at once, so outdenting. We put the stuff back into the dishwasher, essentially back where it was originally. We don't use any kind of drying cycle on the machine and leave the door open (and trays out) when we're waiting for things to dry. The crevasses in the tupperware are unwaveringly the last things to dry regardless of which method we use, but I believe they exhibit the same behaviour (not sure about that one; will have to pay attention). I haven't tried pinning down which items are worst for drying, but plastic tumblers and ceramic mugs seem repeat offenders (ignoring the tupperware). I know it sounds barmy; I wouldn't didn't believe it either except that, as the guy who normally unloads the washer, it kept on getting hammered home. Imagine opening your dishwasher first thing in the morning (say, 7 am) and finding stuff still too wet to put away 12 hours later - and some stuff still too wet 24 hours later. That's not the case when I do dishes by hand - even, and I know this sounds even less believable, even if I use the dishwasher racks as drying racks for what I've hand washed. Matt Deres (talk) 00:37, 21 October 2009 (UTC)

Are you sure that both the water from the kitchen-sink-tap and the water-supply for the dishwasher are equally "water softened" by whatever system you use for that?

My experience has been that adding a product called "jet dry" to the dishwasher along with the detergent drastically decreases drying-time (whether with or without also using a "dry cycle" (ie., applying someheat after the final rinse)...). Not sure how it does that (and I don't have any on-hand at the moment to see what's in it) but I suspect that the presence or absence of "water softening" might have a similar (ie., chemical) impact on drying-times...Wikiscient 01:13, 21 October 2009 (UTC)

I'm not sure I 100% understand your question and subsequent clarification. To be absolutely clear, EITHER:

1. The stuff washed in the dishwasher stays inside the dishwasher to dry - but the stuff that's hand-washed sits out on the draining board or counter-top or something. If that's what you're saying then the answer is easy - it's a lot more humid inside the dishwasher than outside - and that strongly inhibits drying.
2. Dishes from within the washer are brought outside and still dry slower than hand-washed dishes. If that's what's happening then we have to look at what chemical goop is still dissolved in the water - that's a tougher answer. Detergents and dishwasher goop may be designed to either cause a reduction in surface tension (like hand-washing liquid detergents) - or to increase surface tension to cause 'beading' (like wax on your car) to allow the water to run off or be blasted off with air jets inside the dish-washer. With lower surface tension, the water spreads out over the surface of the dish - you get a larger surface area - so you get faster drying. With higher surface tension, you get spherical droplets - minimal surface area - slower drying.

A proper controlled experiment requires that you wash two identical dishes by hand and two more by machine. Take one of the machine-washed dishes and place it on the countertop where you normally dry hand-washed items - and take one of the hand-washed dishes and place it inside the dishwasher as if it had been machine-washed. Now - observe which ones dry first - let us know what happens!

SteveBaker (talk) 04:26, 21 October 2009 (UTC)

I got the impression from the OP that they use the racks of the dishwasher as the usual place to let dishes dry, whether hand- or machine-washed (I know I do).

Either way, another important control to run would be to hand-wash a set of dishes using machine detergent (and ideally vice versa though N.B. I do not think it advisable to put regular dish-washing soap in a dishwashing-machine -- it might make a mess or even damage your machine if you do!). I'm pretty sure it's got to be either the difference in the detergents used for hand- and machine-washing, respectively, or (less likely) a difference between sink and machine in the "softness" of the water supply for each.

Still curious to know what you find out! Wikiscient 17:37, 26 October 2009 (UTC)