Wikipedia:Reference desk/Archives/Science/2017 April 2

= April 2 =

questions about asteroids and dwarf planets
Is there a website that has questions that have been asked before about asteroids and dwarf planets? Donmust90 (talk) 15:00, 2 April 2017 (UTC)Donmust90Donmust90 (talk) 15:00, 2 April 2017 (UTC)


 * You can start here --AboutFace 22 (talk) 16:04, 2 April 2017 (UTC)

Is there any organ in the body that's normally not grow after the birth?
Is there any organ in the body that's normally not grow after the birth? When I think about the brain, skull, and the rest of the organs as well I find that they get growing with the age after the birth. then my question is if there's any organ in the body that's normally not grow after the birth? (For now if I'm not mistaken I know about thymus gland for example that with the age it is going and reduced) 93.126.88.30 (talk) 16:53, 2 April 2017 (UTC)
 * You'll have to define what you mean with grow. Get bigger of form new cells? For instance, it was long thought that the brain was born with all cells in place, and growth was due individual cells forming more connections. We now know that's not true (adult neurogenesis). The only thing I can think of right now that might be an answer to your question is the human oocyte population, it's normally assumed that women are born with all their eggs, and no are formed in the adult. However, as out article (oogenesis) suggests, this might not be true either. Fgf10 (talk) 17:42, 2 April 2017 (UTC)
 * Googling human body part does not grow suggests the ossicles, with corneas being a "maybe". 91.155.195.247 (talk) 17:47, 2 April 2017 (UTC)
 * Eyeballs stop growing rather early. It's not birth though. Sagittarian Milky Way (talk) 20:12, 2 April 2017 (UTC)
 * Some organs shrink and become residual, and some others disappear. Eg placenta, yolk sac, Pharyngeal arches, Buccopharyngeal membrane, Chorion, Vitelline duct, umbilical cord, Ductus arteriosus, Foramen ovale (heart), Ductus venosus. Graeme Bartlett (talk) 15:17, 3 April 2017 (UTC)


 * How about the thymus --AboutFace 22 (talk) 20:42, 3 April 2017 (UTC)

Is it better / worse to transplant seed without its coat?
If I want to transplant mango by putting its seed in the ground, then does it matter weather I'll put it together with its coat or not? will it grow faster if I'll take out the coat of the seed or maybe it will interrupt it to grow or it doesn't matter? 93.126.88.30 (talk) 17:00, 2 April 2017 (UTC)
 * See http://www.wikihow.com/Plant-a-Mango-Seed Richerman    (talk) 18:58, 2 April 2017 (UTC)

The "good pain"
What is the physiological or neurological basis for the qualitatively different sensation of pain that feels "good" during a massage, as opposed to the kind of pain that is unpleasant? 66.66.228.95 (talk) 20:46, 2 April 2017 (UTC)
 * Massage releases endorphins that change the perception of pain and give a sense of euphoria   Richerman    (talk) 23:05, 2 April 2017 (UTC)
 * It may help to read Gate control theory. DrChrissy (talk) 23:29, 2 April 2017 (UTC)
 * Massages don't seem to work for me. They hurt! I hate it when I'm offered a massage! 50.4.236.254 (talk) 23:40, 2 April 2017 (UTC)
 * You can always say "no, thank you." There is a whole range of massage, from gentle relaxing rubdowns to intense deep tissue work that's guaranteed to hurt like hell at times. --jpgordon&#x1d122;&#x1d106; &#x1D110;&#x1d107; 04:05, 3 April 2017 (UTC)


 * This is a question that directly exposes the lack of understanding we have with regard to this fascinating variety of qualia. We can, to some extent, isolate the neurophysiological correlates that associate with "good" or "bad" pain (as self-defined by someone experiencing it while taking part in a brain imaging study or other experiment, for example).  Richerman correctly identifies endorphins as a big player in this distinction, but they collectively represent just one factor in an indescribably complex set of mechanisms which are recruited for this kind of perception/sensation.  But its even more complicated than that, because this question touches upon the hard problem of consciousness and of subjective experience.


 * Further, we have a lot of evidence that psychological state can have a profound impact on how a person perceives the exact same stimuli, further reinforcing that how a particular percept is processed within the flow of conscious experience is not strictly defined by the stimuli itself, nor solely by the more "external" components of the physiological processes which give rise to the raw sensory data. It varies greatly by individual per context and, as we all know, significantly between individuals.  And the difficulty in parsing the borders between co-occuring sensations is profound; one person who gets a deep tissue massage may describe it as pain followed by pleasure, where another may just regard it as thoroughly pleasant experience and a third as horrifically painful, through and through.  Who is correctly reporting the sensation, even when they overlap in rating the experience as generally pleasurable (or painful)?  Does the question even make sense in evaluating subjective conscious sensory experience?  How much is the difference due to our lack of an inter-common and accurate empirical metric by which to express the sensation via natural language, and how much is it due to a genuinely different sensation? We have no such thing as first principles when it comes to the understanding of perception at this level.


 * I gather you were probably looking for more of a straightforward biopsychological explanation rather than a dip into metaphysics and ontology. And indeed, there are neurological correlates; if you studied the brain of a person reporting "good" and "bad" pain, you'd not only see different activity in terms of transmitters released, but different levels of heightened activity in different brain regions associated with nociception, the somatic senses generally, alertness regulation, and so forth. But that really is just the start of the inquiry.  S n o w  let's rap 21:05, 3 April 2017 (UTC)


 * This also reminds me of the instinctive need to chew as growing teeth emerge. It is slightly painful but addictive.  Which is not so different than the urge to scratch when intense itching is felt, which can cause injury in some cases.  Another interesting factor is the threshold of pain which varies with individual, age and circumstances.  Some tests have also shown that the density of sensitive nerves varies, i.e. using needles and measuring the distance between points (I forgot the name of this test).  Of course, some also like to experience certain levels of pain, and the previously mentioned endorphins also play a role.  Hot spices, and for some, BDSM activities...  —╰] PaleoNeonate █ ⏎ ? ERROR ╮ 02:23, 6 April 2017 (UTC)

How are other galaxies receding from us
Are other galaxies themselves receding from us,or is space moving them away from us?Uncle dan is home (talk) 23:19, 2 April 2017 (UTC)


 * Yes. 50.4.236.254 (talk) 23:57, 2 April 2017 (UTC)


 * I agree with 254. On average, other galaxies are moving away from us, and the farther away the galaxies are, the faster they are moving away.  See Hubble's law and Hubble flow.  There is a degree of variation, so not every galaxy at the same distance moves at the exact same speed.  (The differences are referred to as peculiar motions.)  For galaxies that are very close to us, some of the peculiar motions will actually mean that a few are getting closer to us rather than farther apart.  But returning to the crux of the question is A) the space between galaxies expanding, or B) the galaxies receding simply because their current velocities carry them away from us?  For distances up to a substantial fraction of the size of the visible universe, the answer is "yes".  Either description A) or B) gives you the same dynamics and describes the universe we observe equally well.  One can either postulate that the space between galaxies is expanding, or one can postulate the galaxies are moving away because their initial velocities are such that they must move away.  The apparent "metric expansion of space" is equivalent to the simple inertial motion of galaxies that were at some point in the past (i.e. the Big Bang) imparted with a initial velocity distribution that causes them to fly apart.  Until one gets to very large scales or early times (i.e. requiring general relativity and/or dark energy), the past and future of the Hubble flow can be accurately modeled using simple Newtonian mechanics, assuming only Newtonian gravity and a rather peculiar distribution of current velocities that increases with current distance.  Of course, general relativity is a better understanding of gravity and the universe than Newton had, and in the relativistic point of view we can form a more complete picture of the evolution (i.e. including large distance and early times).  People who emphasize the understanding of general relativity tend to describe space as expanding.  That is also a reasonable way to look at things, though for my money it is equally fair to say that the galaxies are receding because they have a distribution of velocities that causes them to recede.  Dragons flight (talk) 16:34, 3 April 2017 (UTC)


 * See Expansion of the universe. Loraof (talk) 00:04, 3 April 2017 (UTC)


 * In the manner of dots on a balloon being inflated. Sagittarian Milky Way (talk) 00:09, 3 April 2017 (UTC)


 * Or it could be us that's receding from them. ←Baseball Bugs What's up, Doc? carrots→ 00:14, 3 April 2017 (UTC)


 * Depending on the galaxies, there are several possibilities:


 * 1) There is no relative "regular" motion of the galaxies themselves, so their increasing distance is solely due to the metric expansion of space.


 * 2) Their regular motion is moving away from each other, so that adds to the expansion of space movement.


 * 3) Their regular motion is towards each other, which may slow or even reverse their movement away from each other due to expansion. Thus, they may collide. StuRat (talk) 05:33, 3 April 2017 (UTC)

How? Apparently faster and faster. Edwin Hubble 1889 - 1953 was the first to establish that the universe is expanding. His measured observation does not prove but is consistent with cosmological theories of a bang and/or a bubble. Blooteuth (talk) 16:14, 3 April 2017 (UTC)

So, we are the center of the universe after all?Hofhof (talk) 17:36, 3 April 2017 (UTC)
 * Yes, but so is every other galaxy. At the 'Big Bang', all space was concentrated in one tiny point, which then expanded into (eventually) the whole of the Universe as it is now, so everywhere in the Universe is still at this 'expanded centre', and the 'place' the Big Bang happened was 'everywhere'. This may seem nonsensical, but it's demonstrated by the nature of the Cosmic background radiation.
 * One way to think of it is that we are only aware of 3 dimensions of space (plus the one of time) while the expansion is taking place in a 4th spacial dimension. Sagittarian Milky Way's mention of dots on an expanding balloon is a way of grasping this concept: when the balloon expands, all the dots (equivalent to galaxies containing intelligent life) move away from each other, and at each dot all the others seem to be receding from it, but there is no one centre of expansion on the (nearly) 2-D surface of the balloon – they are actually all receding from the centre of the balloon, but because the dots' inhabitents can only "perceive" the balloon's surface and not its interior they cannot "see" this centre. The actual universe is the same but with 3 dimensions; we cannot perceive the notional 4th spacial dimension in which the expansion is taking place. {The poster formerly known as 87.81.230.195} 2.122.3.250 (talk) 18:24, 3 April 2017 (UTC)
 * Does the extra dimension exist; is it time, or is it just a convenient analogy; or is that a meaningless question?   D b f i r s   19:42, 3 April 2017 (UTC)
 * Though I by no means wish to preempt responses from others here, several of whom have already very skillfully summarized the core cosmological principles involved, I nevertheless, considering your inquiry, present the single best possible person to explain such a concept: .  S n o w  let's rap 05:05, 4 April 2017 (UTC)
 * A fourth large-scale spacial dimension is not part of any theory of cosmology that I've read. Have I not read widely enough?    D b f i r s   08:55, 4 April 2017 (UTC)
 * Mathematically, any curved n-dimensional object can be described as embedded in some flat m-dimensional space which m > n. Such embedding may or may not be useful for doing calculations and understanding the geometry.  In the context of our universe, this is sometimes done at a conceptual / mathematical level (e.g. the balloon analogy).  At present, we have no evidence that the extra dimensions are "real" in the sense of being physically accessible.  It may simply be a mathematical convenience with nothing from our universe able to traverse that outside space.  It is worth noting however that there are some theories that posit gravitons or other hypothetical processes can move through the outside space, but right now those theories lack observational support.  Dragons flight (talk) 12:29, 4 April 2017 (UTC)


 * So the "balloon" metaphor has some definite explanatory nicenesses, but unfortunately it presupposes a "closed" universe (one that has finite volume at any given comoving time). A "closed" universe is analogous to the surface of a balloon, one dimension up.
 * The general relativity equations can equally well describe an "open" universe, one that has infinite volume at any positive time after the Big Bang. This is harder to visualize, but also allows for expansion in which every point is equally the "center".
 * As far as I'm aware, all observations so far known are consistent with both an "open" and a "closed" universe, so the question is still, well, open. See shape of the universe. --Trovatore (talk) 07:25, 4 April 2017 (UTC)
 * The "open" universe can be nicely visualized by drawing a grid of dots on paper, and then a second, slightly more widely spaced grid of dots on a transparent overlay. Mark one dot to distinguish it on each grid.  Mark a second dot on each grid, with the number of dots between the first and second dot being the same on both grids (e.g. 2 up, 3 across).  When you arrange the transparencies so that the first dots overlap, you can clearly see that the grid is expanding from the first dot.  When you arrange them so the second dots overlap, you can clearly see that the grid is expanding from the second dot - and so on for any corresponding pair of dots.  Extending this to an infinite sheet is easier to visualize than considering an infinite sheet as a sphere of infinite radius. MChesterMC (talk) 08:25, 4 April 2017 (UTC)