Wikipedia:Reference desk/Archives/Science/2016 October 1

= October 1 =

Possible reasons for gray hair in beard
Tevildo (talk) 13:35, 1 October 2016 (UTC)

Asepsis on Mars, Moon and elsewhere
Is it true that due to total absence of bacteria and other microorganisms on Mars, Moon and other "landable" celestial bodies food like meat or milk will not spoil, wounds will not be infected and corpses will not decompose, so food could be stored without fridge and antiseptics in the first aid kit will be generally redundant? Thanks.--93.174.25.12 (talk) 16:42, 1 October 2016 (UTC)
 * Are the astronauts planning to live on the lifeless surface of the Moon or the thought-to-be-lifeless surface of Mars, or in an air-containing enclosure? On the surface, meat, including corpses, will not decompose in an aerobic fashion, and will only undergo anerobic decomposition if they carry Earth-based anerobic bacteria.  However, humans and other vertebrates, and other aerobic metazoa, cannot live on the airless or nearly airless surface.  If you live in an environment containing oxygen, the only obvious difference between that and Earth will be the lower gravity, and a first aid kit will be a good idea, and refrigeration will be a good idea.  It might be an interesting experiment to put meat into the airless exterior and see if it survives, but that can be done on Earth in an ordinary laboratory vacuum.  My guess, having not researched it, is that outgassing will cause mass to be lost and that complex organic molecules will decompose through loss of water.  Robert McClenon (talk) 17:12, 1 October 2016 (UTC)
 * I recall some commonly sold food being vacuum-packaged, so presumably it would be safe to store food outdoors on Mars or Moon. In that sense I suppose you can live there without refrigerator, unless you want cold beverages. 93.174.25.12 (talk) 18:04, 1 October 2016 (UTC)
 * Not necessarily. See Vacuum packing.  Some kinds of food, such as beans, nuts, cereal, and dried or cured meats or fish, can be vacuum packed.  Fresh meat and fish will dry out.  Since milk is mentioned above, liquids definitely cannot be kept under anerobic conditions, because water will evaporate.  See vapor pressure and boiling point with regard to the difficulty of keeping liquid water at pressure close to zero.  As to a corpse, although there will be no aerobic decomposition, I would expect that it would decompose differently due to the presence of anerobic bacteria.  What was the original reason for the question, anyway?  Maintenance of metazoan life will require oxygen, as it does on Earth.  Robert McClenon (talk) 20:28, 1 October 2016 (UTC)


 * Food, even if vacuum packed, if simply left out in the open on Mars, and especially the Mooon, is going to be subject to intense IV and cosmic radiation, which our atmosphere blocks. After two weeks of direct sunlight on the Moon, you'll have thoroughly roasted whatever, if it's been sitting in the sun.  The temperature of the atmosphere or interstellar space is actually a rather minor factor regarding long-term surface storage. μηδείς (talk) 23:42, 1 October 2016 (UTC)

I think the only important answer is: It's impossible to keep a human living environment sterile. The astronauts will bring with them all the bacteria you'd need to spoil any kind of food that can be spoiled. Regardless, it's already been figured out how to make food that lasts functionally forever: sterilize it, then package it under sterile conditions, and completely seal it from the outside. Some c-rations are still edible 70 years later. Someguy1221 (talk) 23:47, 1 October 2016 (UTC)


 * Impossible? I'm not so sure.  Difficult certainly, but we've created axenic and gnotobiotic plants and animals.  If we can create mice lines with no discernible bacteria, then it is probably possible - in principle - to create a human colony with no bacteria or only specifically chosen bacteria.  Of course, you'd probably have to raise multiple generations of humans in a sterilized environment, which seems both impractical and unethical.  Dragons flight (talk) 08:26, 2 October 2016 (UTC)

Magnet therapy history
Can anyone find me some good resources regarding the history of magnet therapy? Our article doesn't say a thing about the history of the discipline; the earliest event mentioned is the publication of a 1991 study. It sounds like the kind of thing that would have been developed quite recently, but apparently it's at least as old as the eighteenth century, since it appears in Così fan tutte. I've found a lot of unreliable sources, split between advocates of magnet therapy and sites that are dedicated to debunking it; aside from this thing from a philosophy website (hardly reliable for a history of science topic), I'm not even finding anything that merely discusses the concept without engaging in advocacy one way or the other. Presumably anything in this category would be useful if it covers the subject, but I've been stuck using Google because I no longer have access (print or digital) to the history and philosophy of science journals that I had in graduate school. Nyttend (talk) 18:30, 1 October 2016 (UTC)
 * There's simply too much of such a subject to list quickly. One of my favourite books in this genre of mad woo-woo science is my copy of - just for its beautifully designed binding. It's an intermediate-stage hybrid of Mesmer's magnetism as a real physical force, with a claimed influence over animals, and the pop-psychology of the near-contemporary How to Win Friends and Influence People with "magnetism" as an analogy for charisma. Andy Dingley (talk) 21:55, 1 October 2016 (UTC)
 * But if I understand rightly, that's talking about magnet therapy from the biological perspective, not from the historical perspective; the only subject for its WorldCat entry is "Animal magnetism", q.v., with nothing about the history of science or about anything else. Nyttend (talk) 23:37, 1 October 2016 (UTC)
 * It's definitely a primary source and part of the belief, not secondary commentary on it. I like it for its graphic design (I wish I'd bought the set), but the content is bizarre: halfway between Mesmer, treating "magnetism" as magnetism, and a modern self-help book.
 * In surveying such a field I also wouldn't limit it to magnetism, but would include the electrostatic theories too. Andy Dingley (talk) 12:04, 2 October 2016 (UTC)


 * Since magnets were known from antiquity (meaning pre-history), in the form of lodestones, presumably something that seemed as magical as that would have been claimed to have medicinal value by someone. StuRat (talk) 15:29, 2 October 2016 (UTC)

What are the advantages of sexual dimorphism over simultaneous hermaphrodism?
For a species that is sexually dimorphic, what are its advantages over a species whose members are  simultaneous hermaphrodites? Note: This isn't a question about why sexual reproduction is more advantageous than asexual reproduction. Thanks. 118.101.157.175 (talk) 19:34, 1 October 2016 (UTC)


 * It's been proposed that sexual dimorphism may be simpler than simultaneous hermaphrodism, and thus allow for more efficient reproduction . It's also conceivable that true males could arise in a species without sexual dimorphism as a result of selfish genetic elements - a true male could potentially sire far more offspring in the same timeframe/energy-expenditure than a simultaneous hermaphrodite that has to bear offspring, and damn the consequences to the overall fitness of the species. Someguy1221 (talk) 21:27, 1 October 2016 (UTC)


 * You also have to consider morphology and genetic canalization. Humans without specific conditions have either a functioning penis and testicles or a functioning vagina and ovaries.  Since, for the most part, humans can't regenerate tissues, how are they going to shed the penis and grow ovaries and a vagina, or the opposite?  With certain fish which simply have cloacae, all they need to do is produce male versus female gametes, which is a much easier transition. μηδείς (talk) 23:37, 1 October 2016 (UTC)


 * It's a very good, complex question. There are advantages and disadvantages to all forms of sexual reproduction: simultaneous hermaphroditism, each of 3 types of sequential hermaphroditism, gonochorism, etc.. In plants, a variety of strategies can be found, see Plant_reproductive_morphology, some of them solving the self-fertilization problem of simultaneous hermaphroditism mentioned in the paper Someguy1221 cited. In animals, too, simultaneous hermaphroditism is found e.g. in a number of mollusc and annelid species, while sequential hermaphroditism is found in a number of fish species. A clear advantage of gonochorism is that it allows both for sexual dimorphism (please note the correct terminology) and for a far from 1:1 ratio of reproducing males to reproducing females. In many mammals the dominant male mates with most or all the females in his territory or herd. This allows to stringently select the most fit males without reducing the reproduction rate. This also allows for different roles of males and females (or dominant males, non-dominant males, and females). In social insects again a different strategy is seen, where a single female is reproducing. Finally, I frankly don't think that the choice of Sex-determination_system and of gonochorism vs hermaphroditism is always strictly "optimal" for a species. All extant non-monotreme mammals (therians) share XY sex determination system simply because their last common ancestor had it, and it is a moot question now whether it is strictly optimal or not. If it becomes highly deleterious, however, then the organism in question will either die out or evolve a more suitable sex determination system. Monotremes, by the way, have a sex determination system akin to those of birds . Here is another example: most birds have tetrachromatic vision, while most placental mammals are dichromats and minority are trichromats. Why are placental mammals "non-optimal" this way? Either because the last common ancestor of Placentalia was nocturnal and had no use for good color vision, or simply because it just so happened. One needs to be very careful in distinguishing genuine causation from the "just-so stories" in biology. --Dr Dima (talk) 05:20, 2 October 2016 (UTC)

How exactly was the Standard Atmosphere determined ?
How exactly was the standard atmospheric pressure of 101,325 Pa determined ? Local measures in France, possibly readjusted to fit the 45°N parallel rather than the 48.5°N one which passes through Paris ? Primitive theoretical atmospheric models ? A simple conversion of 760 mmHg to some nice round number of dynes ? A combination of the above ? Or something else entirely ? — 79.118.182.183 (talk) 23:29, 1 October 2016 (UTC)


 * According to Atmosphere (unit), This value was intended to represent the mean atmospheric pressure at mean sea level at the latitude of Paris, France, but no citation is provided. Someguy1221 (talk) 23:34, 1 October 2016 (UTC)
 * Perhaps there is something enlightening in the official statement:, but I can't read French. Someguy1221 (talk) 23:36, 1 October 2016 (UTC)
 * Nope. Not in that one. In the previous one, at the bottom of page 93, paragraph 3. Apparently, they took 760 mmHg at a density of 13,5951 g/cm3 with g = 9.80665 kg m/s2 and t = 0°C. I believe this completely answers my question. Thank you ! :-) — 79.118.182.183 (talk) 03:45, 2 October 2016 (UTC)
 * That link is the Proceedings of the 10th Conference of the BIPM, 1954. The BIPM is the international organization that standardizes most units of measure; the NIST is the official representative for the United States to the BIPM.  Its conference-proceedings are an authoritative resource.
 * The document linked by Someguy1221 says something to the effect that the terminology "standard atmosphere" used during the 9th conference left some physicists to think about the validity of the definition, which was limited only to applications in precision thermometry. (The 9th Conference used the standard atmosphere to report the melting points of many common metals, and similar thermometric data; but did not specify what pressure value corresponded to the standard atmosphere).  The astute observer might facetiously note that the "standard atmosphere" would be "whatever pressure" yields the reported melting-points; this is a reasonable, but clumsy, definition.
 * To broaden the applications "for all uses," the 101.325 kPa value was adopted during the 10th conference. It seems that the definition is consistent with the pressure-value which would correspond to the precise temperature-values reported in the previous proceedings.
 * Nimur (talk) 03:29, 2 October 2016 (UTC)