Wikipedia:Reference desk/Archives/Science/2012 November 16

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 16

Graviton

At the beginning of the article, it says: "the gravitational force appears to have unlimited range"? What is that mean? Let say the Sun's gravitational force and if I'm like a million or a billion light years ago from the Sun, can the Sun's gravitational force affect me? If not then the statement in the article is a false statement.174.20.41.202 (talk) 03:30, 16 November 2012 (UTC)

Yes, gravitation has infinite range, as far as anyone can tell. The laws of gravitation, either using Newton's law of gravitation or the models of general relativity predict that there is no limit to how far away two objects can be while still influencing one another. It is always the case, however, that beyond a certain distance you will no longer be able to detect the influence of some given object, as the attraction gets weaker and weaker. Someguy1221 (talk) 03:35, 16 November 2012 (UTC)

Newton's law of universal gravitation tells us the gravitational force between 2 objects is inversely proportional, not to the distance between them, but the square of the distance between them. That is, double the distance and the force diminishes by a factor of 4. Triple the distance, and the force is now only one-ninth what it was, and so on. So, if 2 objects are a billion light years apart, there's still a gravitational force between them, but it's infinitesimally small. Way too small to be measurable. But not technically non-existent. -- Jack of Oz ^[Talk] 06:22, 16 November 2012 (UTC)

LOL at some distance, it is pretty much like nothing... The concept in unlimited range is pretty mind blowing. 174.20.41.202 (talk) 07:09, 16 November 2012 (UTC)

That's what I meant by "way too small to be measurable". The difference is that, while we could not measure it empirically at all, we could still work out on paper what the infinitesimally small force would be if we could measure it, assuming the paper was large enough to hold all the zeros in the calculation. -- Jack of Oz ^[Talk] 20:57, 17 November 2012 (UTC)

You might be a little careful, given that you don't know whom exactly you're talking to, with the word infinitesimal. I take it that you're using it in the informal sense of "very very small indeed", and not in the precise sense of "smaller than any positive real number". --Trovatore (talk) 21:01, 17 November 2012 (UTC)

There is a limit ultimately, because according to general relativity, fluctuations in gravity actually travel at the speed of light, instead of infinitely fast as Newtonian gravity incorrectly assumes. So gravitating bodies outside of the observable universe have precisely zero effect on us, because the metric expansion of space keeps the gravitational effects of those bodies from ever reaching us. But the distance scales under consideration implicitly in the graviton article when it uses the word "unlimited" are vastly smaller than the diameter of the observable universe. Red Act (talk) 07:29, 16 November 2012 (UTC)

You are applying gravitational force on a number of sun(s) in other galaxies as well as on these galaxies, but they are not being affected by your gravitational force. It doesn't matter whether they are being attracted or not, but you are attracting them. Sunny Singh (DAV) (talk) 11:26, 16 November 2012 (UTC)

lepton

There are 6 kinds of lepton, one of them is electron. I know electron flying around the nucleus, which made up of neutron and proton or more precisely quark, in an atom. So where can you find the other 5 kinds of leptons?174.20.41.202 (talk) 07:09, 16 November 2012 (UTC)

The charged leptons in the second and third generations, i.e. the muon and tauon, decay rapidly, so they don't occur in normal matter, and are only seen in extremely high-energy environments such as cosmic rays or particle accelerators. The electron neutrino would be found in the highest concentration around radioactive matter undergoing beta decay. Neutrinos of all three generations stream throughout the universe, but rarely interact with normal matter. Red Act (talk) 07:47, 16 November 2012 (UTC)

If you could go with a neutrino, you could travel the universe, too, once you lepton, of course. StuRat (talk) 18:21, 16 November 2012 (UTC)

W and Z bosons

W and Z bosons are part of the gauge boson. While gluon and photon are massless then how can W and Z bosons have mass? Where are the W and Z boson come from? What emit and absorb them? 174.20.41.202 (talk) 07:23, 16 November 2012 (UTC)

Read W_boson#Weak_nuclear_force for your second question. Sunny Singh (DAV) (talk) 10:50, 16 November 2012 (UTC)

The W and Z gain mass from the electroweak symmetry breaking. The W⁺ and W^- are the boson that is involved in beta decay. But all fermions interact with it. A Z⁰ can be produced in any interection that can produce a photon (as long as there is enough energy to form it's mass). Also just to clarify the W and Z are gauge bosons as are photons and gluons. Dja1979 (talk) 17:42, 16 November 2012 (UTC)

How's this bird called?

What's this bird? Picture: http://i.imgur.com/sDG5w.jpg 109.173.37.164 (talk) 07:31, 16 November 2012 (UTC)

European Robin (Erathacus rubecula) Richard Avery (talk) 07:58, 16 November 2012 (UTC)

Thanks. 109.173.37.164 (talk) 12:33, 16 November 2012 (UTC)

In the UK, it's a symbol of Christmas [1]. Alansplodge (talk) 10:56, 17 November 2012 (UTC)

Interesting. The Northern Cardinal is the Christmas Bird here in the US. We could export you some to go with the grey squirrels. μηδείς (talk) 19:59, 17 November 2012 (UTC)

Only if they're the St. Louis variety. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:10, 19 November 2012 (UTC)

You may have trouble finding breeding pairs. μηδείς (talk) 17:36, 20 November 2012 (UTC)

Curiosity image

I think this image of Curiosity (found on found on this BBC page) seems to be a pretty sophisticated simulation - because I can't see anything like a boom extending from the rover out of the image that could be holding a camera.

Right? Your Username 08:35, 16 November 2012 (UTC) — Preceding unsigned comment added by Hayttom (talk • contribs)

It is a montage of pictures, see [2]], got from [3] Dmcq (talk) 10:05, 16 November 2012 (UTC)

Thanks very much. (There's a really interesting debate there.)

Resolved

Your Username 09:02, 17 November 2012 (UTC)

Is natural folate metabolized to 5-MeTHF?

"Folic acid" and "folate" are used interchangeably but are not exactly the same chemical compound and have some different properties.

Folic acid is metabolized to 5-MeTHF (aka 5-MTHF, 5-methyltetrahydrofolate, Levomefolic acid) by the human body.

Is natural folate also metabolized to 5-MeTHF?

Thanks. — Preceding unsigned comment added by 134.153.91.186 (talk) 15:31, 16 November 2012 (UTC)

The distinction between the two is only in dry form or on paper or in solutions when you can set the pH to what you want. Let folic acid, or folate, loose in an aqueous solution, and it can freely exchange away a proton (H+) to any passing water molecule, and pick one back up later on, at a very fast time scale. The counterion determines which form you see on the shelf in a lab, but as an ionic compound the folate and counterion are free to wander in aqueous solution, and in a biological solution there are so many other ions floating around for each to hang out with that they will act independently, never reuniting. Wnt (talk) 17:22, 16 November 2012 (UTC)

Thanks, Wnt, but I may have given the impression that I know more chemistry / biochemistry than I actually do. Does your answer mean, "yes, natural folate is metabolized to 5-MeTHF"? If I eat broccoli and bread in the same meal, will the folate from the broccoli and folic acid from the (fortified) bread undergo the same processes in my gut and/or elsewhere? — Preceding unsigned comment added by 134.153.91.186 (talk) 22:00, 16 November 2012 (UTC)

Yes. Wnt (talk) 02:53, 17 November 2012 (UTC)

What happens to the brains of the enlightened?

Is there some serious study about the effect on the brains of the enlightened (in a spiritual way)? If they feel different something must be different somewhere, I suppose. OsmanRF34 (talk) 17:02, 16 November 2012 (UTC)

[4][5][6] ... (the secret to getting these results is only to know the keywords "religiosity" and "fMRI" for a Google search, which spit them out as the first three of a long list of similarly relevant results!) Wnt (talk) 17:25, 16 November 2012 (UTC)

I wanted something more specific. Instead of 'religious' something that's the product of meditation. And instead of anatomy of the brain, something at the level of neurotransmitters and hormones, which is what makes us feel. Unhappily, a simple search for 'neurotransmitter' and 'meditation' pours out a wealth of dubious pages with dubious claims. OsmanRF34 (talk) 18:10, 16 November 2012 (UTC)

Oh Lord, first you're going to have to define enlightenment. I mean, you have to know who to put in your fMRI machine before you can look for differences in the pattern. Trying "Monk" and "fMRI" I get [7] which talks about soon to be published research by an adjunct professor ... surprisingly, here it is. I'm going to leave it at that for now - my wheels are spinning freely when I try to skim through this one. Wnt (talk) 19:25, 16 November 2012 (UTC)

Wnt: your "wheels are spinning freely" because you lost track in this and the question below. I never said religious, and I clearly say neurotransmitters and hormones. OsmanRF34 (talk) 21:23, 16 November 2012 (UTC)

• Temporal lobe epilepsy is interesting. μηδείς (talk) 22:57, 16 November 2012 (UTC)

• One of the most active scientists in this area has been Richard Davidson. Our article about him lists a number of his more important publications. Looie496 (talk) 00:08, 18 November 2012 (UTC)

I don't know if you're interested in this report, as it's on brain scans in psychographers (automatic writing). But it may give you a place to do further research. --TammyMoet (talk) 19:34, 19 November 2012 (UTC)

Sleep more to grow more

I have read somewhere that our height increase only when we sleep. What do you think about this ? Is it true ? Sunny Singh (DAV) (talk) 17:10, 16 November 2012 (UTC)

Sitting, standing, etc. compresses the spine and reduces height. [8] So normally for most people height will decrease during the day and increase at night. This change in height will be much more than the change due to growth. What I don't know is whether more time in a prone position increases the rate of long-term growth - I can't think of a reliable way to do the experiment to look it up. Also I should add that the suggestion the paper I cited seems to be making about hyperextension as some sort of prophylaxis for occupational stress sounds nuts to me, and from a quick glance I don't think they prove it in any way; I suspect it should have some harmful effect on the discs if any at all. Wnt (talk) 17:34, 16 November 2012 (UTC)

I think the OP is asking about development from birth to adulthood, not decompression of the spine. The consensus is that sleep is when most growth occurs, and that disturbed sleep can cause stunting. Since sleep is a necessary but not causative factor getting enough sleep in for the days growth is important, but extra sleep won't lead to extra growth. See this article for sleep and puberty, and these for growth during sleep. If your own or a specific person's height concerns you, see a doctor. There are various causes and treatments for abnormal shortness, and abnormal tallness can be a sign of dangerous but treatable conditions. μηδείς (talk) 18:09, 16 November 2012 (UTC)

I think Wnt was saying it's difficult to study when growth occurs, since it's so overwhelmed by spinal compression. Also, even if you could establish that people who don't get much sleep are shorter, that doesn't necessarily mean the sleep is the causative factor. It might be that whatever stresses keep them from sleeping also stunt growth. StuRat (talk) 18:15, 16 November 2012 (UTC)

Actually, our article on sleep mentions a study of children finding no correlation between growth rate and the amount they slept. But as StuRat says, there are so many complicating factors... besides, just because the amount of sleep doesn't affect the amount of growth still doesn't prove the growth can't occur mostly when one is asleep. Wnt (talk) 19:13, 16 November 2012 (UTC)

Reference 10 of Wikipedia article Growth hormone says growth hormone is secreted during sleep. 'Biological regulation' section of the article growth hormone mentions deep sleep as stimulator of growth hormone. I think there is correlation between growth rate and sleep, but I am sure, so I have asked it here to get the correct answer. Thank you. Sunny Singh (DAV) (talk) 00:29, 18 November 2012 (UTC)

The question is not: if we sleep more, do we grow more. It's only whether we grow while we sleep, which seems to be answered by Medeis above. OsmanRF34 (talk) 21:27, 16 November 2012 (UTC)

Actually I don't think the question really is answered; it's complicated. Apparently in culture bone formation is enhanced by intermittent and even to some degree constant compressive force (such as one would expect while awake) - see PMID 3505768, PMID 22559784 - yet it also increases apoptosis (PMID 16368547). But the actual process of sleep, rather than inactivity, is a more complex phenomenon that can't be replicated in a dish, and I didn't find anything on the effect of it on extracellular matrix deposition or other effects in cartilage in a quick NCBI search. Wnt (talk) 18:04, 17 November 2012 (UTC)

I always see people on reference desk using OP while they answer, but I don't understand its meaning. Please, tell me its full form. Sunny Singh (DAV) (talk) 04:36, 17 November 2012 (UTC)

It is the Original Poster, the Other Person. It comes from internet talk, amounts to a polite genderless way to refer to someone already mentioned. If you see the IP it means the person editing with an IP adress as a user name. In the case above, since you and I haven't really interacted, and since Wnt should realize I was addressing him/her, and talking about you, using OP was not unusual. Had I said "I think Sunny..." it would have implied more certainty on my part in this case. But Sunny would have been fine. I like having more pronouns to use to avoid ambiguity and to make subtler distinctions. Our lack of a formal tu-vos distintion is annoying, but one can say yourself/yourselves and you all. Excluding you request for clarification and my answer, the term is shown used five times on the board as of this edit. In the future, google OP urbandictionary to find out the meaning of any new usage, cutural, internet, adult themed--it's all there. μηδείς (talk) 05:23, 17 November 2012 (UTC)

Acceleration and time dilation

Okay, about a week or two ago I asked about the maximum G-force a person could withstand and a very helpful user told me we can withstand an acceleration of 1g for months on end and could even theoretically speed up to the speed of light in this manor (neglecting the problems surrounding mass and energy obviously).

Now, my question is this. As you speed up, due to time dilation, time for you, relative to an observer travelling at a constant velocity lower than yours, slows down. Acceleration is a vector quantity and is calculated using time.

If you were in a space ship accelerating they could calculate your acceleration using basic suvat equations. But would they have to take time as the time they experience pass or the time you experience pass. And if it is based on their time can you withstand 1g acceleration by their time or is this measurement based on their time? — Preceding unsigned comment added by 109.153.175.182 (talk) 19:13, 16 November 2012 (UTC)

1 g refers to the acceleration in the spaceship's frame of reference. Ruslik_Zero 19:37, 16 November 2012 (UTC)

(EC) Humans are comfortable with a 1g acceleration in their own frame of reference, i.e. a 1g proper acceleration, which is observed as being an acceleration of less than 1g in any inertial frame of reference in which your direction of acceleration is in the same direction as your velocity. You don't use the SUVAT equations, because those are Newtonian. Instead, the relativistic equation of motion for an object with constant proper acceleration is $x^{2}-c^{2}t^{2}=c^{4}/\alpha ^{2}$, as per the article Hyperbolic motion (relativity). Red Act (talk) 19:41, 16 November 2012 (UTC)

Thank you! This is extremely useful, however I am unfamiliar with this equation. What does the alpha and the x represent?

α is the acceleration, x is the position of the rocket (measured in some inertial frame), and t is the coordinate time measured in the same frame. The elapsed time for the person on board the rocket (proper time) is $\tau =(c/\alpha )\sinh ^{-1}(\alpha t/c)$, where sinh is the hyperbolic sine.

Whoever said that people can withstand 1g for "months on end" was presumably joking. Anyone who lives at sea level withstands 1g acceleration for their whole life. But if, hypothetically, a person could only stand a particular acceleration for a few months, that would be a few months of proper time (tau). You could plug that value of tau into the reverse equation $t=(c/\alpha )\sinh(\alpha \tau /c)$ to get t, then plug that into Red Act's equation to get x (which is the distance traveled, more or less—actually, it's the distance traveled plus c²/α). -- BenRG (talk) 01:20, 17 November 2012 (UTC)

Okay, so what is the absolute limit of acceleration a person could withstand? Also by x being the position of the rocket measured in an inertial frame, do you mean some measurement of distance? — Preceding unsigned comment added by 31.54.166.31 (talk) 23:34, 17 November 2012 (UTC)

Also which time is T and which is t? — Preceding unsigned comment added by 31.54.166.31 (talk) 23:38, 17 November 2012 (UTC)

I think you mean tau (τ), not T. Tau is the proper time and t is the coordinate time. -- BenRG (talk) 03:08, 19 November 2012 (UTC)

Unfortunately the body's tolerance for acceleration does not seem to be the limiting factor. At 1g, we could get to foreign star systems in quite reasonable (ship's) times, assuming you're willing to spend years in a tin can. But first, no one knows how to achieve sustained acceleration of 1g. And if we did know a way, we still don't know any way to shield the occupants from the interstellar medium, which at relativistic speeds appears to you as hard radiation.

Larry Niven addressed these problems in some of his works (both in Known Space and otherwise) by some fairly optimistic hypotheses about the workability of the Bussard ramjet). Unfortunately, according to our current state of knowledge, those do not appear to be true. --Trovatore (talk) 02:22, 18 November 2012 (UTC)

This is extremely useful information. When you say "no one knows how to achieve sustained acceleration of 1g", is this because it would require unfeasible amounts of power or are there other reasons? Also are there any references for this interstellar medium appearing as hard radiation? These Larry Niven links are extremely interesting by the way, thank you for the reference/ — Preceding unsigned comment added by 31.54.166.31 (talk) 17:46, 18 November 2012 (UTC)

Because of conservation of momentum you have to push something backwards to accelerate forwards. Your choices are fuel you bring along (a rocket engine), the interstellar medium (a jet engine), or some large astronomical body. This page explains the problem with the rocket, which is that it needs a ludicrous amount of fuel. The problems with a jet engine (Bussard ramjet) seem obvious, but I don't know the details. In the third category there's laser propulsion, which would only be feasible at the beginning of the trip and probably not even then, and gravitational slingshotting, which probably isn't relevant to this thread.

The article I linked explains the radiation problem also, at the very end. -- BenRG (talk) 03:08, 19 November 2012 (UTC)

Neurons in the cochlear nuclei

How many neurons are there in the cochlear nuclei? — Preceding unsigned comment added by 144.96.215.130 (talk) 21:52, 16 November 2012 (UTC)

The book Hearing in Children, by J. L. Northern and M. P. Down, gives a total number of 8800, but doesn't make it clear how that number was obtained. Looie496 (talk) 00:04, 18 November 2012 (UTC)