Wikipedia:Reference desk/Archives/Science/2018 June 28

= June 28 =

Reporter gene affecting expression of other genes?
Are there any cases where a reporter gene in an experiment has affected the expression of other genes which were being studied? --129.215.47.59 (talk) 13:21, 28 June 2018 (UTC)
 * It says right in the article that you have to be careful with your placement lest the reporter affect the expression of the target too much. So in all experiments the reporter gene has affected the expression of other genes which were being studied. Abductive  (reasoning) 05:55, 3 July 2018 (UTC)

Wristwatch + thermometer = useless?
Are thermometers useless in wristwatches? Wouldn't our temperature contribute significantly to any temperature it shows? Specially if you are wearing it under a sleeve, I don't see how it can avoid this effect.Doroletho (talk) 17:40, 28 June 2018 (UTC)


 * Say someone wakes up one day. Wow this is a cold June, I shouldn't have left the window open. I want to know how cold it is. I don't own any other thermometers. So he looks at the wristwatch. Sagittarian Milky Way (talk) 18:05, 28 June 2018 (UTC)


 * The solution, of course, is not to rely on the thermometer while it is in contact with your wrist. Attach it to a backpack, wrap it around outside your coat sleeve, or otherwise insulate it from your body. TenOfAllTrades(talk) 18:52, 28 June 2018 (UTC)


 * So, kind of a useless feature, in a device designed to be in contact with the wrist. --Doroletho (talk) 19:20, 28 June 2018 (UTC)


 * (e/c) It probably has an error correction algorithm to compensate (but I wouldn't expect much accuracy). It is possible (in theory, at least) that if it is a smart-watch that it gets temperature based on geolocation -- I have a "smart" thermometer that gets indoor temp & humidity from sensors, and outdoor readings as if by magic (presumably via geolocation). —107.15.157.44 (talk) 19:24, 28 June 2018 (UTC)


 * I've had a watch with such a feature, and yes, it's entirely useless while worn. According to the manufacturer "If you are wearing your Suunto Core on your wrist, you will need to take it off in order to get an accurate temperature reading because your body temperature will affect the initial reading." Most sensors and many microprocessors have a temperature sensor built-in, so typically manufacturers can display this information for "free", albeit highly inaccurate in this context. Cars try mitigating this by placing the sensor on the bottom of the front grill, although this picks up heat from the road, so it's also not entirely accurate. A watch is too small a device to realistically  decouple it thermally from the body, but yes, quite handy if you looking for your skin temp. Drewmutt ( ^ᴥ^ )  talk  19:46, 28 June 2018 (UTC)


 * Is this watch waterproof? If it is, then, maybe it can be accurate when swimming. In this context, I'd say that it might be a useful feature for those who spend long time in the water like scuba divers, open water swimmers, long-distance swimmers and so on.Hofhof (talk) 23:32, 28 June 2018 (UTC)


 * Casio says essentially the same thing: "Temperature measurements are affected by your body temperature (while you are wearing the watch), direct sunlight, and moisture. To achieve a more accurate temperature measurement, remove the watch from your wrist, place it in a well ventilated location of of direct sunlight, and wipe all moisture from the case."|Thermometer The moisture, of course, can cause evaporate cooling. --Guy Macon (talk) 21:38, 29 June 2018 (UTC)


 * I suppose one could always carry a Stevenson screen around with one, and put the watch in it whenever one wanted to know the temperature. DuncanHill (talk) 21:45, 29 June 2018 (UTC)

Big Bang question
Reading the Wikipedia article on Big Bang I ran into this quote at "Inflation and Baryogenesus" section:

"After inflation stopped, reheating occurred until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles."

Reheating must have required tremendous energy. Where did this energy come from?

Thanks. AboutFace 22 (talk) 22:46, 28 June 2018 (UTC)
 * It comes from the energy stored in the inflaton field see here for details. Count Iblis (talk) 22:56, 28 June 2018 (UTC)
 * A little more detail: Inflation (cosmology). --47.146.63.87 (talk) 06:35, 30 June 2018 (UTC)

Big Bang question II
How can we know that all matter was indeed compressed in an area the size of an apple? Couldn't it be that all matter just sneaked into our universe from a parallel universe thru a tiny hole. --Hofhof (talk) 23:37, 28 June 2018 (UTC)
 * Has a parallel universe ever been observed? ←Baseball Bugs What's up, Doc? carrots→ 01:16, 29 June 2018 (UTC)
 * Has our universe ever been observed being compressed to the size of an apple? Honestly, if a mathematical model can discard this possibility, it could also open the door to the possibility of parallel universes. --Hofhof (talk) 02:24, 29 June 2018 (UTC)
 * Obviously not. But the Big Bang is a scientific theory which does what scientific theories do: explain past observations, and predict future observations. Have there been any observations that suggest there could be a parallel universe? And there's the obvious dilemma: Where did that universe come from? ←Baseball Bugs What's up, Doc? carrots→ 09:54, 29 June 2018 (UTC)
 * They could have been necessary (parallel or sequencial) for a universe to have the necessary elements and proportions to make life possible, but have never been observed, of course. I unfortunately don't have the formulas to evaluate the size of the universe at that point without doing more research myself, but I doubt that it was invented arbitrarily...  Also, it was likely that size only at a precise moment in time (and a very short moment).  — Paleo  Neonate  – 03:51, 29 June 2018 (UTC)
 * There's no evidence the universe was not infinite in size. It is the space in the universe that expands. Dmcq (talk) 13:36, 29 June 2018 (UTC)


 * One puzzlement: If you could magically transport back to the beginning of the universe, by what mechanism would you determine if it was the size of an apple or any other specific object? ←Baseball Bugs What's up, Doc? carrots→ 13:56, 29 June 2018 (UTC)
 * I am not sure if the OP is facetious or not. Anyway we are currently observing that the universe is expanding. We infer that it was smaller in the past. We also have observed singularities, so we know they are definitely possible. Modelling this easily leads us back to a very small universe. That does not explain absolutely everything, but it is more reasonable than magical invisible pink unicorns just wishing the universe to exist, or parallel universes with holes between them, transferring matter and energy that has the mass of an other universe, since we have no observation of that phenomenon, nor any model that leads to that. --Lgriot (talk) 14:49, 29 June 2018 (UTC)
 * Have we observed singularities?? Bubba73 You talkin' to me? 02:00, 1 July 2018 (UTC)
 * Yep, we have observed the gravitational effects of many black holes on other objects like stars, and their gravitational effects on light (lensing), and the energetic emissions of the matter that is falling into them. We have also observed the rippling of space-time of merging black holes. That is enough observations as far as I am concerned. --Lgriot (talk) 14:32, 2 July 2018 (UTC)
 * Small gripe: we have observed the effects of objects consistent with GR black holes, but we most definitely have not observed gravitational singularities. Even in standard GR the singularity is usually hidden behind an event horizon. There have been computations that predict the emergence of naked singularities, but those have not been observed experimentally. The consensus is that GR breaks down before physical singularities form, and AFAIK the jury's out on whether a proper theory of quantum gravity has true singularities. -- Link (t&bull;c&bull;m) 17:46, 2 July 2018 (UTC)
 * By that logic I claim that you have never "observed" your left hand. All you have done is capture some photon using your retina, some of which might have bounced off your hand, but you have never actually seen your hand, just some photons, so maybe you don't have a hand and the photons were emited by some clever device which made their pattern consistent with having a hand. --Lgriot (talk) 12:24, 5 July 2018 (UTC)


 * I may be wrong, but as I understand it, at least some current models of the big bang do not require a small universe, just a dense universe. In other words, the universe might have been infinite at the time of the big bang - it just suddenly expanded a lot. --Stephan Schulz (talk) 21:13, 29 June 2018 (UTC)


 * How can something that's already "infinite" expand? ←Baseball Bugs What's up, Doc? carrots→ 21:53, 29 June 2018 (UTC)
 * Yeah, How can something that's already infinite expand? Limited Brain Cells (talk) 22:20, 29 June 2018 (UTC)
 * See Hilbert's paradox of the Grand Hotel. HiLo48 (talk) 23:05, 29 June 2018 (UTC)
 * The flaw is the tendency to think of infinity as a number. It isn't. ←Baseball Bugs What's up, Doc? carrots→ 23:47, 29 June 2018 (UTC)
 * I'm not sure if that is an enlightenment moment or a criticism of Hilbert ;-). To answer your original question: Just think of the real number line and expand each segment by 10 (.e. by mapping it through the function defined by f(X)=10X). The result will have "the same size", indeed, in this case it will actually be the same, and yet the distance between any two original points now is 10 times larger. --Stephan Schulz (talk) 05:04, 30 June 2018 (UTC)
 * See also cardinality. Not all infinite sets are the same size. A simple way of visualizing this is Cantor's diagonal argument (here's a YouTube video walking you through it). --47.146.63.87 (talk) 06:33, 30 June 2018 (UTC)
 * To answer BB's question directly, in the context of the Big Bang, something that's already infinite can "expand" if the objects in it move farther apart.
 * In the case of an infinite universe, universal expansion doesn't mean that the universe actually gets larger. It just means that galaxies (or in general, objects that are not gravitationally bound to one another) move farther away from one another.
 * On a separate note, yes, there are infinite quantities that can be thought of as "numbers", and they are not all the same size. But that is pretty much unrelated to the Big Bang. --Trovatore (talk) 08:13, 30 June 2018 (UTC)
 * Infinity is not a number. ←Baseball Bugs What's up, Doc? carrots→ 16:39, 30 June 2018 (UTC)
 * That's a common platitude. It's even true, for certain values of "infinity" and "number".  But by itself it's not well enough specified to really mean anything.
 * There are definitely infinite quantities that are useful to consider "numbers" in some contexts. Whether any of these should be called "infinity" full stop, and whether it or those should be called "numbers", is more an argument about terminology than about anything substantive, as far as I can tell. --Trovatore (talk) 17:10, 30 June 2018 (UTC)
 * My math teachers always said "Infinity is not a number; it is a concept of expansion without bounds." ←Baseball Bugs What's up, Doc? carrots→ 18:14, 30 June 2018 (UTC)
 * Bugs, first of all, you have to remember that math teachers have objectives to meet other than mathematical precision. They have a certain amount of material to get through.  They don't want to spend time an awful lot of time answering the question "but Mr Josephson, what happens if you set x=&infin;?".  Especially when they may not understand the concepts related to the mathematical infinite all that deeply themselves.
 * That said, there is a longstanding philosophical debate about potential infinity versus actual infinity. Prior to the work of Georg Cantor, it was probably the default position among mathematicians that only potential infinity was worth taking into account.  That is no longer so, has not been so for more than a century, but it takes a while for math education to catch up, especially when there is no particularly strong incentive for it to catch up. --Trovatore (talk) 03:59, 1 July 2018 (UTC)
 * Bugs, it depends on what you decide to call a number. You could start with the idea of natural numbers (1, 2, 3), but then add the concept of negative numbers, then fractional numbers, irrational numbers, imaginary numbers, infinitesimals, etc.  Infinite numbers are just another extension of the number concept that you can throw into the soup.  Trovatore might have been referring to cardinal numbers from set theory, but infinite values occur in other places too.  The extended real line is the real numbers from calculus, with +&infin; and -&infin; added on.  Or in complex analysis, the point at infinity corresponds to the north pole of the Riemann sphere.  The cool thing about math is you can make up stuff as you go along, and as long as you're consistent about it and interesting stuff comes out, it's "right". 173.228.123.166 (talk) 00:35, 1 July 2018 (UTC)
 * Carl Sagan put it this way: "Think of the largest number you can. That number is no closer to 'infinity' than is the number 1." ←Baseball Bugs What's up, Doc? carrots→ 00:48, 1 July 2018 (UTC)
 * Billions and billions, pah ;-) The largest number I can think of is a large cardinal, which is very very infinite.  It's just a matter of what you decide is a "number", which is a human-language term that's mathematically somewhat flexible, so Carl Sagan and your math teachers simply took a narrow view.  Transfinite number is an article after all.  Philosophers used to lose sleep over completed infinity and maybe still do, but I think in math this is no longer a source of worry (Trovatore would know better than me).  Regarding infinity in math, you might like this site: http://cantorsattic.info 173.228.123.166 (talk) 04:16, 1 July 2018 (UTC)


 * On 'If you could magically transport back to the beginning of the universe, by what mechanism would you determine if it was the size of an apple' I would think one could then also magically transport an apple back and compare the two ;-) Even if the magical transport existed how one would actually fit in the space if it was finite is problematic, if it was like the surface of a balloon in 4D then you simply wouldn't fit even though there would be no boundary. Dmcq (talk) 08:39, 30 June 2018 (UTC)
 * If infinity is not a number, then how can the infinite universe expand? Limited Brain Cells (talk) 22:26, 30 June 2018 (UTC)
 * The number line is infinite. Think of moving each number to double its value.  You end up with a number line that has expanded, but is still the infinite number line.  ( As described by Stephan Schulz above. )   Dbfirs  00:09, 1 July 2018 (UTC)
 * The number line has a scale? ←Baseball Bugs What's up, Doc? carrots→ 00:27, 1 July 2018 (UTC)
 * Yeah, it does; if we're using the number-line as an analogy for the expanding universe then we might say that its scale is the value of the cosmological constant; or we can rearrange the math and distill it into the cosmological scale factor; or we could use an unusual representation of the Hubble constant; or it might be expressed in some other values in the various equations that physicists write to express fundamental interactions. These important equations, like the Einstein equations of general relativity, are very dense: the positioning and value of each squiggly Greek symbol has a profound meaning that requires intensive study to understand, because each symbol in theae advanced equations of physics is a compact abbreviated representation of a lot of very well-developed earlier work.
 * Perhaps most importantly: unlike pseudoscience, cosmology makes quantitative experimentally-verifiable claims - so when we talk about the changing scale/size of the universe, we can draw back to an experimental observation, like measurements of the statistics of observed redshifts in distant astronomical objects. In other words, when we say that the "size" of the universe has changes, this isn't just technobabble: it means something specific that we have measured.
 * Nimur (talk) 12:21, 2 July 2018 (UTC)
 * No matter the "scale", and no matter where you are on the number line, you're still just as far away from infinity. ←Baseball Bugs What's up, Doc? carrots→ 14:07, 2 July 2018 (UTC)
 * Yes, that's true. What's your point? --Trovatore (talk) 20:18, 2 July 2018 (UTC)
 * That infinity is not a number. ←Baseball Bugs What's up, Doc? carrots→ 22:22, 2 July 2018 (UTC)
 * That's a meaningless statement. Well, it doesn't have to be meaningless; if you specify what you mean by "infinity" and "number", then it can be meaningful and true.  But you haven't specified what you mean by it, or explained what that has to do with the Big Bang in an infinite universe. --Trovatore (talk) 22:24, 2 July 2018 (UTC)
 * If you don't understand what "number" and "infinity" mean, you should file a complaint against your high school math teachers. ←Baseball Bugs What's up, Doc? carrots→ 23:43, 2 July 2018 (UTC)
 * Well, the problem is not that I don't have meanings to assign to the words "number" and "infinity". The problem is that there are too many meanings, and for some of them your statement is true, and for some of them it isn't.
 * For example is aleph-naught "infinity", and if so is it a "number"? It's definitely infinite, but that's not necessarily the same as being "infinity".  It's not a natural number or a real number or a complex number.  But it is a (transfinite) cardinal number, and can be identified with a transfinite ordinal number.
 * But more to the point, I don't see how any of this relates to the question of universal expansion in an infinite universe. Can you make your point more explicitly, with attention to that issue? --Trovatore (talk) 23:59, 2 July 2018 (UTC)
 * This is what happens when BB endlessly makes dubious assertions without citations. See 128.229.4.2 (talk) 18:06, 3 July 2018 (UTC)


 * Why should I believe you over my math teachers? Or EO, which says a number is a quantity, while infinity is not a quantity. ←Baseball Bugs What's up, Doc? carrots→ 19:15, 3 July 2018 (UTC)
 * So first of all, 128, no need to bring up old stuff. I'm less interested in chiding Bugs for past behavior than in getting him to specify what he sees the putative non-numberhood of infinity as having to do with universal expansion in an infinite universe.
 * Bugs, if you're going to get into "argument from authority" using your math teachers, then you might ask yourself whether my PhD in pretty much this exact subject counts for anything. It doesn't, of course, not really &mdash; but then neither do your teachers' opinions. As for etymonline, it is not a reliable source as regards mathematics. --Trovatore (talk) 19:22, 3 July 2018 (UTC)
 * Well, you're the one that doesn't seem to understand the terminology. ←Baseball Bugs What's up, Doc? carrots→ 19:31, 3 July 2018 (UTC)
 * Asked and answered, Bugs. There are lots of meanings of both words, "number" and "infinity".  Which do you mean, specifically? --Trovatore (talk) 19:34, 3 July 2018 (UTC)
 * The Wikipedia article Infinity defines it as "a concept describing something without any bound or larger than any natural number." Oddly enough, that's exactly what our math teachers told us. And that was long before there was such a thing as Wikipedia. ←Baseball Bugs What's up, Doc? carrots→ 19:36, 3 July 2018 (UTC)
 * Right. So aleph-naught, for example, is larger than any natural number. Do you count it as "infinity"? If not, why not? Do you count it as a "number"? If not, do you consider its classification as a cardinal number to be a misnomer? --Trovatore (talk) 19:38, 3 July 2018 (UTC)
 * Each of those items are referred to as "countably infinite", which means you can make a list of them... or more accurately, you can start to make a list. You can't ever finish the list because... get ready... it's infinite. ←Baseball Bugs What's up, Doc? carrots→ 19:47, 3 July 2018 (UTC)
 * Well, you can't physically make a list, no. But that doesn't distinguish this case from the finite case.  You can't physically make a list of, say, a vigintillion items, either.
 * From the mathematical realist perspective, such a list exists as a Platonic abstraction, even though you can't physically write it down. Not all mathematicians are realists, but even the formalists still usually find it convenient to talk as though the completed list existed.
 * In any case, you still haven't told us what you think all this has to do with universal expansion in an infinite universe. --Trovatore (talk) 19:52, 3 July 2018 (UTC)

To give a very short answer to a very short question, regardless of the tangents everyone went off on, the expansion of the universe, and the rate at which it is expanding can be expressed mathematically. If you run those numbers in reverse, you arrive at a point when it was all condensed into a single spot. Of course that's a very simplified answer, but I think it's what you were asking.