Wikipedia:Reference desk/Archives/Science/2019 May 19

= May 19 =

Locality
For the sake of argument let's say you are observing Location A, but cannot observe Location B unless you are inside Location A, even if B is directly next to A or surrounding it on all sides. Unless you're inside A, you can't see B. Does this violate any laws of physics? déhanchements (talk) 00:39, 19 May 2019 (UTC)
 * So, I am observing a small hut A which is built over a shallow well whose bottom is B. I cannot observe B when outside A, only from within A.
 * Or, I am in a windowless attic looking down through a small hole in the floor into a windowed room A, but I cannot see out of the windows to observe the surrounding landscape B unless I am in A.
 * Are these examples of what you mean?
 * If you have something more abstract and general in mind, you might be thinking of problems in Topology, and might get a better response on the Mathematics desk. Alternatively, if you're thinking of questions pertaining to the Principle of locality, you're in the right place. {The poster formerly known as 87.81.230.195} 2.122.2.132 (talk) 02:08, 19 May 2019 (UTC)
 * Those are great examples, but what about this: You are observing a small hut A surrounded by a barren plain. But only by entering this hut can you now look out of the window and see, not a barren plain, but a meadow B, which surrounds the hut. The meadow and the barren field spontaneously exist. déhanchements (talk) 02:54, 19 May 2019 (UTC)
 * If the meadow surrounds the hut, how did you not see it on the way in? ←Baseball Bugs What's up, Doc? carrots→ 03:55, 19 May 2019 (UTC)
 * And that's exactly what I'm getting at. This is a counter intuitive phenomenon. You can only observe it from a certain reference point, otherwise you might say it doesn't exist at all. déhanchements (talk) 04:00, 19 May 2019 (UTC)
 * It's not counter-intuitive that a view of something is blocked unless one is looking from a specific vantage-point. That's the nature of nature: things look different from different perspectives. And it's beyond even a strong definition of empiricism to claim that "I can't see it myself, so it may as well not even exist at all in fact". I've heard the term "privileged perspective" used to refer to this sort of situation, though I can't find a ref for it now due to this phrase now referring specifically to societal privelege, where something looks unique (or a certain detail is only visible at all) when viewed one particular way. I was at a museum that used an actual physical model that happened to look like Penrose stairs from one specific perspective. We're getting pretty far off "science" here, no? DMacks (talk) 04:40, 19 May 2019 (UTC)
 * It seems like you want to ask a more specific question. For example, a mountaintop might be surrounded by cloudbanks that are only visible from the mountaintop (your "meadow") though it is entered via a "barren plain" (the steep ascent).  I think you're trying to ask if the meadow and the barren plain can be in the same exact physical space in some sense, but different things are seen from different perspectives.  Even there, there is all sorts of philosophical wiggle room.  I mean, a hologram looks different from different perspectives... but it is the same object in the same space.  Does that count?  If it does, well, anything looks different from different perspectives.  But if it doesn't count, then you want to define a space as "really" containing different things depending on how it's looked at, rather than (maybe) saying that the different perspectives look on different spaces ... it's hard to see where to go with this.  The philosophical issue needs to be narrowed. Wnt (talk) 14:19, 19 May 2019 (UTC)
 * I see your point, I guess the only way this phenomenon could be completely separated from more normal variations of it, is if one not only saw a meadow, but could interact with it, as if the barren field was gone somehow. But that would be like walking into a ten foot house and finding out it extends outwards indefinitely inside. Needless to say there's some law that prevents that. déhanchements (talk) 17:45, 20 May 2019 (UTC)
 * You could do something somewhat similar with a Tipler cylinder, which would (if possible) be thought to permit travel through time. There are probably a variety of wormhole type effects somewhat related.  Most involve inconceivably vast amounts of energy and types of matter that can't exist, but I feel like there are new exceptions proposed all the time. Wnt (talk) 01:05, 21 May 2019 (UTC)
 * Your question is not clear to me, but when a mirage makes you see things that are elsewhere, it also prevents you to see things you would see otherwise (ie, for instance, instead of seeing sand, you see a "lake"). You'll need to move (up) to see the sand again.
 * Gem fr (talk) 18:31, 20 May 2019 (UTC)

Dermatoglyphics
I have this article on my watchlist. A user recently added some material - it's referenced, but to a foreign language article. All fine so far, but the use of the word "modalities" is a trigger for me as it often gets thrown around in pseudoscience jargon to obscure the fanciful claims. (In fact, I'm not sure exactly what the inserted line is even claiming, but that's only a side issue for now). Is the journal cited ("Coleção Pesquisa em Educação Física") reputable? reliable? Matt Deres (talk) 12:33, 19 May 2019 (UTC)
 * I agree that the meaning of the insertion is unclear, and I suspect from the English-language abstract of the paper that it may not be using the word 'Dermatoglyphics' in the same sense as our article. I'm afraid I can't comment on the Journal's reliability – you might enquire on the Reliable sources Noticeboard. {The poster formerly known as 87.81.230.195} 2.122.2.132 (talk) 00:44, 21 May 2019 (UTC)
 * Good idea - thanks! Matt Deres (talk) 02:09, 22 May 2019 (UTC)

Stiffest material known ever
Wich material is the stiffest material knwon? might it be carbyne or is there something even stiffer?Saludacymbals (talk) 21:01, 19 May 2019 (UTC)
 * For a real tangible material try diamond. It would be even stiffer under pressure. Graeme Bartlett (talk) 22:34, 19 May 2019 (UTC)


 * Just to get us started, I'll point out that stiffness depends on the actual physical structure constructed out of the material, whereas elastic modulus is the real nature of the material itself (analogy: you seem to be asking about the nature of wood or steel, not a certain truss design built from it). And there are several different types of elastic modulus, depending on the direction(s) of the applied force and the motion resulting from it. Shear modulus might be the closest to the idea of "material stiffness" meaning resistance to bending: diamond, at 476.1 gigapascal, is the largest I can find among standard materials under normal conditions (compare other entries at that ref and also and Elastic properties of the elements (data page)). DMacks (talk) 03:22, 20 May 2019 (UTC)

For how long can "Sarcoptes scabiei" live without having blood?
According to what I read Sarcoptes scabiei is parasitic which is nourished from blood. Then my question what happens if one lived in a apartment and he was infected with scabies, and he'll leaved his apartment for a year. Can these parasite survive there? If so, for how long? (I know that in a real case everything should be clean and washed with hot water, but this questions is more for knowledge.) 93.126.116.89 (talk) 22:28, 19 May 2019 (UTC)
 * I copy-pasted your question into Google. The first hit was this, which states: "Scabies mites can only live about 72 hours without human contact, but once on a person, the mites can live up to two months. Mites survive longer in colder conditions with higher humidity." According to this, their entire life span is not that long (reported estimates vary, but they're a couple of months at most). That second ref also mentions that "A study by Arlian et al. [20] found that S. scabiei var. canis females survived for a week or more when held at 15 °C (59 °F) and relative humidity (RH) above 75% (Fig. ​(Fig.4).4). At a warmer temperature of 25 °C (77 °F), females survived 1–2 days at all of the RHs tested (Fig. ​(Fig.4).4). Male survival time off the host was much shorter compared to females. These studies showed that generally, warmer temperatures drastically reduced survival time at each humidity." Matt Deres (talk) 01:08, 20 May 2019 (UTC)