Wikipedia:Reference desk/Archives/Science/2014 January 14

= January 14 =

Spacetime or Timespace?
Is it at all reasonable to say that each instant in time exhibits no change at all until the collapse of some Coloumb barrier which-instantaneously-puts us into the next time instant? Is this a reasonable consideration? — Preceding unsigned comment added by 99.182.38.146 (talk) 01:04, 14 January 2014 (UTC)


 * I humbly suggest you think carefully about your question, and how to better communicate it to a group of diverse volunteers. You seem to be leaping across several different topics in math/physics, without ever really explaining what you mean. Additionally, your terms are unclear. I am familiar with reaction diffusion systems and advection-diffusion equations (and even Reaction–diffusion–advection_equations), but I have no idea what you mean by "adjunct-diffusion equation." A quick google search indicates that that is not standard nomenclature. Also, please consider asking a single question, instead of several at once. SemanticMantis (talk) 01:26, 14 January 2014 (UTC)
 * NB: the OP has apparently cut out large portions of the question in response to my comment. See history/diffs if you are curious. I only note so that I don't look crazy :) SemanticMantis (talk) 01:42, 14 January 2014 (UTC)


 * What is the resolution of such reaction-diffusion-advection equations? considered infinitesimal? but how exactly?


 * Ignoring the stuff about Coulomb barriers, the question seems to be asking whether it is possible that time is discrete. The answer is yes, it is possible.  But if it is, the quantum of time is likely to be extremely small, as the presumed quantum of space is thought to be (the Planck scale). Looie496 (talk) 03:11, 14 January 2014 (UTC)

This is the proposed quantum of time: http://en.wikipedia.org/wiki/Chronon 217.158.236.14 (talk) 14:21, 14 January 2014 (UTC)

Postulation of Even F-number
There exists one even fibonacci pseudoprime. Can we 'calculate' this number? — Preceding unsigned comment added by 99.182.38.146 (talk) 01:21, 14 January 2014 (UTC)
 * 8539786 is an even Fibonacci pseudoprime. Red Act (talk) 02:39, 14 January 2014 (UTC)


 * It looks like the answer to this question depends on what you mean by "Fibonacci pseudoprime". Lucas pseudoprime lists three references of authors who define a Fibonacci pseudoprime as being a Lucas pseudoprime with parameters P=1 and Q=-1, and Di Portio proved in 1993 that no even Fibonacci pseudoprimes exist using that definition.  However, from that link it looks like some authors consider "Fibonacci pseudoprime" to be synonymous with "Lucas Pseudoprime", and with that alternative definition André-Jeannin proved in 1996 that even Fibonacci pseudoprimes exist for all P>0 and Q=±1 except if P=1.  As far as whether an even Fibonacci pseudoprime using that definition can be "calculated", it seem like the answer would have to be "yes", because even though André-Jeannin's proof isn't a constructive proof, even a brute-force search for an even Fibonacci pseudoprime for given P and Q would count as a "calculation".  Red Act (talk) 06:04, 14 January 2014 (UTC)


 * Shouldn't this be on the math desk? SteveBaker (talk) 13:07, 14 January 2014 (UTC)
 * Yes. Red Act (talk) 17:12, 14 January 2014 (UTC)

Pulse vs heart rate
Why do people measure their pulse at the wrist or neck rather than just measure the heart rate and pattern at the chest, wouldn't this be more accurate? Is it because it can be harder to feel the heart rate for some people? Clover345 (talk) 12:50, 14 January 2014 (UTC)
 * I think there's a number of things at play. For one, it can be difficult to pick up the heart pattern at the chest. Clothing, muscles, breasts, fat deposits, etc. all get in the way of getting a clear reading. On top of that, you have the lungs working, meaning you're trying to take a reading on a moving medium. Further, the chest is definitely within most people's personal space and they may find it a bit upsetting to have someone grope them in that way (even leaving aside the issue of a man taking a woman's pulse). If you take a first aid course, they'll tell you not to take the pulse at the carotid for exactly the same reason - it unnerves people and may freak them out if they're already hurt / in distress. Wrists are not ideal (the pulse is often weak there), but at least there's usually not much tissue or clothing in the way and "holding hands" is much more publicly acceptable. Matt Deres (talk) 14:28, 14 January 2014 (UTC)
 * This source also mentions convience as a reason for the radial pulse (which effectively covers a bit of what you've mentioned and more) [//books.google.co.nz/books?id=odY9mXicPlYC&lpg=PA520&ots=z06Hh-V3qX&dq=radial%20pulse%20apical%20pulse&pg=PA519#v=onepage&q=radial%20pulse%20apical%20pulse]. As I understand it, per that source and others like auscultation, the apical pulse is generally determined by auscultation i.e. listening rather than by tactile feedback or palpation although I'm not totally sure if this applies if no stethoscope is available i.e. you'd need to do immediate auscultation. That source does mention the apical pulse can be palpated in about 50% of adults which suggests it's not a particularly reliable method. And, while not a RS, also mentions problems attempting to palpate, and not surprisingly given the reasons outlined by Matt Deres, that it's easier in children and smaller adults. As the first source also mentions, the apical pulse is preferred in a few cases like in infants or where the radial pulse appears weak or non existent. It's also needed to determine if there is a pulse deficit. Nil Einne (talk) 16:33, 14 January 2014 (UTC)
 * Don't doctors also get a clue on some circulatory issues from the wrist pulse, or am I imagining that? μηδείς (talk) 19:45, 14 January 2014 (UTC)
 * As for accuracy, if you are only interested in the heart rate the wrist or the carotid is just as good as the chest, as long as you can feel the pulse there. What you feel is the increase in pressure from the heart beats, so the heart rate is the same wherever you measure. Sjö (talk) 20:45, 14 January 2014 (UTC)
 * Note that per the sources I mentioned earlier, technically this isn't totally correct since a pulse deficit can exist. See for more (which despite the blog nature and poor formating seems and okay source and I don't think is a copyvio). Of course being aware it exists is generally important so if you suspect it may be the case, I suspect you should take both the apical and radial (or similar?) simultaenously to test for it as per the sources. In other words, you're somewhat correct in that you can generally assume they are the same, because when they aren't you have more serious concerns than simply having the a lower pulse than the heart rate. (This is all presuming you take the pulse correctly.) As a minor aside, I was reminded by Talk:Pulse of something I may or may not have heard before. For 15 months Dick Cheney had no pulse. Although to ward of jokers, this only happened after he left the Vice Presidency  (and our article). Nil Einne (talk) 23:34, 14 January 2014 (UTC)

i have a few questions but ifirst need someone to talk to me about dreams or dreaming
wel first of all i think that the time it takes to fall as sleep thats the same thing about dreaming but like i said i need someone talk to first — Preceding unsigned comment added by 67.225.110.19 (talk) 23:15, 14 January 2014 (UTC)
 * I don't understand what you are saying, but I can't see any way to interpret it that would make it true. Dreams usually don't come until after several hours of sleep.  The transition from waking to sleep is known as hypnagogia -- it is not the same thing as a dream. Looie496 (talk) 23:26, 14 January 2014 (UTC)
 * Hypnopompic being the opposite situation, i.e. the transition from sleeping to waking. These are times when hallucinations can happen, i.e. the feeling that one is being attacked by a ghost or some such. ←Baseball Bugs What's up, Doc? carrots→ 00:32, 15 January 2014 (UTC)

College student behaviour.
Is there a scientific reason so many college students only seem to be able to do things in extreme and not in moderation? For example many drink extreme amounts of alcohol, study fr extreme hours in the library, eat extreme amounts of unhealthy foods. If all of this is done in moderation, surely they can understand it would be healthier and may even help reduce stress levels. Clover345 (talk) 23:44, 14 January 2014 (UTC)


 * There are reasons however those reasons are not scientific. 202.177.218.59 (talk) 23:56, 14 January 2014 (UTC)


 * The term "reckless youth" comes to mind, and has to do with a truism I've often heard, that the young think they are immortal. Hence the typical young person might not worry about the issues that the OP is talking about. ←Baseball Bugs What's up, Doc? carrots→ 00:27, 15 January 2014 (UTC)


 * One related idea on the matter is the Cultural Theory of risk which asserts that one's perception of risk is primarily influenced by one's culture. The culture of college campuses enforces a certain perception of risk (that is, what behaviors are considered "risky" and what behaviors are considered "normal" or "safe") is influenced by the environment, which feeds a "status quo" of risk behaviors that would seem reckless in other contexts.  -- Jayron  32  01:50, 15 January 2014 (UTC)


 * One scientific reason is that college students are in the prime of their life, and can tolerate drinking extreme amounts of alcohol, studying for an extreme number of hours (presumably because they didn't begin studying earlier), etc. A 70-year-old doesn't engage in such behaviors because his body can't handle it, not necessarily because he doesn't want to.  --Bowlhover (talk) 03:43, 15 January 2014 (UTC)

Is this true or just a stereotype? To which country is the question referring? Also, should the question be more about the stereotype that all young people exhibit these types of behaviours and not just students. CambridgeBayWeather (talk) 04:26, 15 January 2014 (UTC)

People between the ages of 12 and 25 behave differently to fully matured adults because their brains are in the process of being rewired. For instance, it says at THE ADOLESCENT BRAIN -- WHY TEENAGERS THINK AND ACT DIFFERENTLY "The frontal lobes help put the brakes on a desire for thrills and taking risk -- a building block of adolescence; but, they're also one of the last areas of the brain to develop fully". So they do things to excess because the part of the brain that should tell them when to stop is not fully developed. Googling "the teenage brain" will reveal a lot more on this subject. Of course, this is also a very creative period and people of this age have had a great influence on the development of human society. As it says here "Teenagers can be a pain in the ass. But they are quite possibly the most fully, crucially adaptive human beings around. Without them, humanity might not have so readily spread across the globe.”  Richerman    (talk) 17:42, 15 January 2014 (UTC)