Talk:Olbers' paradox
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Changed name to "Olbers's Paradox" (from "Olbers'"): Technically that's the grammatically correct spelling of a singular posessive noun :) - qartis
- Google gives 542 votes for "Olbers's Paradox" and 6,128 votes for "Olbers' Paradox". It should be changed back, IMO. Kaldari 06:17, 11 Jan 2005 (UTC)
Is this a paradox ? - anon
I know nothing about this, but might not another explanation be that there is so much dust and gas in the universe that light from very different stars is so dim as to be imperceptible, because it is absorbed along the way? Even in a non-expanding universe, you wouldn't expect very very distant stars to be visible anyway... -- Simon J Kissane
- That was Olbers' original explanation. It doesn't work because of thermodynamics. Energy isn't destroyed: if light isn't getting to us because it got absorbed by dust or gas, then that dust and gas will warm up, eventually becoming incandescent and glowing as brightly as the stars whose light it is blocking. Shimmin 11:45, Feb 7, 2005 (UTC)
I'm not quite clear about the meaning and correctness of the article's last paragraph. Wouldn't thermodynamics forbid us to recycle radiation into matter? --AxelBoldt
Also, I take it that electromagnetic radiation is converted to kinetic energy (heat) all the time. Why should we postulate a hypothetical method for transferring electromagnetic radiation into matter, when there's another observable explanation for how electromagnetic radiation can be converted into another kind of energy? Beyond that if the universe is not bounded, or if it is expanding there's no reason to believe that anything has to happen to the light -- it can just continue to disperse. (But I am certianly no expert in this field...) MRC
With regard to Axel's question: radiation is routinely converted into matter in particle accelerators: most commonly into electron/positron pairs. This is called pair production. The only problem with such recycling is that known methods of matter production result in equal quantities of matter and antimatter, which is not what is observed in nature. Thermodynamics does not forbid recycling. However, it does suggest that a state of equilibrium will eventually be reached, and maintained thereafter. If there is no conversion of energy into matter then the equilibrium state will probably be one in which all except a small remnant of matter has been converted into energy in the form of radiation.
With regard to MRC's points: Yes, EM radiation is converted into kinetic energy. If this were to take place e.g. in a hydrogen gas cloud, some of the kinetic energy would be converted back into low temperature radiation (radio waves). Somebody has already added a paragraph to the main article regarding this possibility, saying that "it would result in strong radiation which is not observed". This also seems to address Simon Kissane's point. However, *some* radiation from gas clouds most certainly is observed.
With regard to light becoming increasingly dispersed in an expanding universe - this is partly covered by the statement about light becoming increasingly redshifted and diminished in brightness in such a universe. However, increasing separation between photons as a possible cause of diminished brightness should perhaps have an explicit mention.
I'll refrain from modifying the main article any further, because I personally favour the idea that energy is recycled into matter, and I find it difficult to evaluate other possibilities objectively.
--Martin Gradwell.
The universe might be infinite, but that doesn't mean the amount of matter/energy in it needs to be infinite. This would easily resolve the paradox.
- True, but then some region of the universe would have more matter/energy than another; the universe would have a "center", which people typically don't like ("why is the center here and not over there?") 207.171.93.45
- Are you sure that's right? How would we define the "extent" (not the right term I'm sure) of the universe except in terms of where there is matter/energy? That is, can there actually be parts of the universe that have no matter and no energy? Mswake 04:36 Jul 24, 2002 (PDT)
Actually, Olbers did not propose the paradox to show that the universe is finite, but that the universe is not transparent, being filled with dust that blocks the light of distant stars. Since the time of Newton, it had been appreciated that if the universe was static (not expanding) as was widely assumed, then it must be infinite, or else the combined gravity of all the objects in the universe would cause it to collapse toward its center of mass.
Olbers (believing the universe to be static and infinite) proposed that the darkness of the night sky showed that the universe was not transparent. However, he did not appreciate the consequences of the first law of thermodynamics (which can be forgiven at his time in history), that if interstellar dust blocked the light of stars, then it would heat up until it shone as brightly as the stars.
I am about to change the main page to reflect this.
- According to Encyclopedia Britannica, Kepler saw it as an argument against an infinitude of stars. Also, the dust wouldn't necessarily shine "as brightly as the stars": it would be invisible microwave radiation, not visible light. AxelBoldt 01:29 Jan 25, 2003 (UTC)
I stand by "as brightly as the stars." It's actually a bit of an understatement. Let me give you a back-of-the-envelope justification.
Consider an infitnite, static universe filled with a uniform scattering of stars. If the distance to any given star is R, then the light recieved from it falls off as 1/R^2. However, if the universe is filled with a uniform scattering of stars, then the number of stars at distance R increases as R^2 (for the same reasons that the surface area of a sphere is 4*pi R^2). So, the light received from stars at distance R is (R^2)*(1/R^2) = a constant, independent of R. This implies that if light from infinitely far away could reach the observer, then all points in this universe would be bathed in infinite luminosity. To radiate this away, they would have to acheive infinite temperature and shine with infinite intensity at all wavelengths.
Or put another way, if a nonexpanding universe is infinitely old, and has contained an infinite number of luminous objects throughout that time, then at the present it must be infinitely luminous at all points.
Or put another way, suppose a dust grain in an infinitely old universe was at one time cold. It absorbed a visible photon, heated up a bit, and radiated away the energy as several microwave photons. However, neighboring dust grains did the same, and in the meantime, it has absorbed several of these microwave photons, in addition to another visible photon, and is a bit hotter. It will radiate this energy away in the infrared, but in the meantime, its neighbors are doing the same... The problem is energy can't be destroyed, and if an infinitely old universe has contained luminous objects during its entire lifetime, then an infinite amount of energy has been released into it, and that energy has to be somewhere.
It should be noted that the calculations given above assume transparent stars. The absorption of stars has never been directly measured because they tend to be brighter than anything behind them, but they display dark line spectra and other signs of internal absorption, so it seems likely they are opaque. In this case, we must add a factor of (1-f)^R where f is the frequency of stars. Since this is exponential, it dominates all existing terms in the limit, and gives us finite luminosity for the sky.
What about the effect on the stars of absorbing all this starlight? Well, they shine a little brighter than they would otherwise, but by a finite amount. Therefore the energy output of a given star is the energy production plus the input, which is a fraction of the output of an average star. So long as the fraction is less than one, this is stable. Calculating the fraction requires arithmatic, but observation shows it to be very small.
Incidentally, none of this changes the fact that the universe must be of finite age or something similar. If every large but finite region of space had been engaging in non-zero amounts of fusion for infinite time, it would contain infinite non-hydrogen. It doesn't, so it hasn't.
I think the title of this article is incorrect. His name was "Olbers" so the title should either be "Olbers' paradox" or "Olbers's paradox". A quick consult to my astronomy textbook published in 2001 prefers the latter and notes that the former is acceptable as well. - 66.81.223.216
- Hang on, why has the article been moved to "Olbers' paradox"? Doesn't the above note recommend "Olbers's paradox"? I would certainly prefer it to be there. The omission of the final "s" in the possessive form of a singular noun or proper noun is a rather idiosyncratic rule that a minority of English-speakers follow, and which rather grates on the ears of most of us. -- Oliver P. 14:01 Jan 31, 2003 (UTC)
- A quick Googling found 142 instances of Olbers's paradox, while Olbers' paradox rang up more than 2200 (although these may include some results from the former search). Whatever the author of that particular astronomy book's preferences may have been, Olbers' is certainly the form that appears more in print. -- User:Shimmin
- Penguin Dictionary of Science has "Olbers' paradox" -- Tarquin 14:07 Feb 5, 2003 (UTC)
- The Encyclopaedia Britannica seems to have it your way, as well. I suppose I lose, then. I still don't like it, though... *grumble, grumble* -- Oliver P. 18:53 Feb 5, 2003 (UTC)
I reverted to Pakaran's changes, sorry. (MJA, I would notify you on your talk page if you had a talk page.) A paragraph was added which I believe is simply incorrect. In part:
- [...] For example, if we were to send a radio signal to the most distantly observed galaxies, the signal would never arrive there, because the rate at which the distant galaxy and ours are receding from each other excedes the rate at which the radio waves travel through space.
This paragraph claims that the two galaxies are receding from each other at faster than c, which is not possible, to my understanding. I saw no support for this concept in any of the external links. I'm far from an expert in the field so feel free to reintroduce the concept if it's true. Tempshill 21:49, 20 Jan 2004 (UTC)
- The expansion is faster than light because the space itself is expanding (check out the Universe article, for example). So I guess this text should be put back (it's not immediately apparent where it was, so I can't do it myself and I don't have time at this very moment to sift through the history). Paranoid 16:10, 4 Jun 2004 (UTC)
On an unrelated note, I just estimated how bright should the sky be, knowing that the Universe it's 13-15 billion l.y. big and there are ~10^22 stars. The answer is it should be about ten times less bright as the full moon, give or take a few orders of magnitude. In order for the whole sky to be as bright as the surface of a star the Universe obviously needs to be a million times larger.
I think that we need to add some calculations like this (more rigorous) to give the article reader a sense of what levels of brightness are we talking about. As it is, only about 1 millionth of the sky is the surface of a star (excluding the Sun and our Galaxy, of course, which are anomalously close, by Universal standards).
I hate to be a spoilsport, but is the blurb at the end about the band suitable? Perhaps it could use some NPOV, but then again, I kind of like it. :) --Golbez 02:58, 17 Jun 2004 (UTC)
Maybe I'm wrong, but shouldn't
"There is no known process that can return heavier elements to Helium in the necessary quantities"
be
"There is no known process that can return heavier elements to Hydrogen in the necessary quantities".
Right now it makes no sense
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Surely the skies would be dark not light?
My grasp of physics is fairly elementary, but surely the wave nature of light means that this paradox should state that the sky should be dark? Light behaves as a wave. For the uniitiated, Putting a source of light through two slits in a card shows this effect with bands of darkness "rippling" outward. This occurs with any waveform when two waves beocme perfectly inversely corrleated with each other (that is to say the pattern of peaks and troughs of one respectively match the torughs and peaks of the other) and they cancel each other out. If there were an inifinite number of light sources, there would be an infinite area of peaks and troughs in every direction resulting there being no visible light. Would a nice science person be kind enough to comment? Dainamo 12:02, 16 Oct 2004 (UTC)
At any point, the total peaks and troughs would both be infinite; the problem is that you're assuming "infinity minus infinity equals zero", which it doesn't.
It might help to think about tossing coins (heads = 'peak', tails = 'trough') and looking at what's left after you cancel out heads with tails - this is effectively the 'amplitude'. If you toss two coins, you'll average one head & one tail, but the average *difference* will be 1/2. If you toss a hundred, you'll average 50 heads & 50 tails... but on any one toss you probably won't get the same number of each. The average difference between heads & tails will be around 10-20. If you toss ten thousand, you'll average 5000 of each, but the average difference will be ~100-200, and so on.
So, as the number of coins rises to infinity, even though the *average* number of heads still matches the average for tails, the average difference between them doesn't tend to zero. Instead, it also rises to infinity, though rather more slowly (roughly proportional to the square root of the number of coins). It works the same way with light: while much of it cancels out, not all of it does, and the amount of uncancelled light rises as the number of sources rise. --Calair 00:44, 18 Oct 2004 (UTC)
Thank you Calair for a fascinating and enlightening answer. Dainamo 20 Oct 2004 (UTC)
Why lower-case?
I moved this to Olbers's paradox with a lower-case p because that is the usage followed in the many hundreds, maybe thousands, of pages titled "Smith's theorem", "Smith's law", "Smith's principle", "Smith's hypothesis", etc., etc. See list of eponymous laws (or list of mathematical topics, for that matter). Michael Hardy 02:22, 28 Oct 2004 (UTC)
PS: I've fixed the double redirects. It will take longer to fix all redirects; could others help? Thanks. Michael Hardy 02:23, 28 Oct 2004 (UTC)
apostrophe
Currently the page is called Olbers's paradox, and the first line begins Olbers' paradox. Both are in some sense okay ways to spell, but we should be consistent. Fowler's Modern English Usage (a standard for British English) favours the latter if the post-apostrphal 's' is unvoiced. I like this way of doing it, too, but don't want to cause a nasty grammar spat by just changing it without discussion. What do you think?
Olbers's paradox → Olbers' paradox
Google gives 542 votes for "Olbers's Paradox" and 6,128 votes for "Olbers' Paradox". Kaldari 06:25, 11 Jan 2005 (UTC)
- Olbers' Paradox doesn't exist, so it doesn't belong here. See top of the page: Sometimes you want to move a page, but cannot do so because a page of that name already exists. This page allows you to request action by a admin to perform such moves. Correct? Cburnett 06:49, 11 Jan 2005 (UTC)
- Sorry I meant to put Olbers's paradox → Olbers' paradox (second word in lowercase). I've changed the listing above to reflect this. The lowercase version already exists as a redirect page. Kaldari 07:06, 11 Jan 2005 (UTC)
- Penguin Dictionary of Science and Britannica both list it as "Olbers' paradox" and this is how it is spelled throughout the article and related articles on Wikipedia. Fowler's Modern English Usage favors the later spelling as well. Kaldari 18:25, 11 Jan 2005 (UTC)
- Support: This is primarily an issue of style (possessive proper name ending in 's') and personal preference. "Olbers' paradox" seems to be the more accepted one (8160 vs. 640 google hits and 2700 vs. 560 teoma hits). Looking at the history shows Qartis moved "Olbers' paradox" to "Olbers's Paradox" in Sep 2004 and Michael Hardy moved "Olbers's Paradox" to "Olbers's paradox". Going farther back, the article was originally at "Olbers's paradox" (see Talk:Olbers's paradox just over half-way down). According to Oliver P., the Encyclopaedia Britannica has "Olbers' paradox". This page has a long history of being moved and shuffled around. Google had more hits for "Olbers' paradox" 2 years ago and still does. It stands to be the accepted style is "Olbers' paradox" and not "Olbers's paradox". Cburnett 21:02, 11 Jan 2005 (UTC)
- Oppose. Proper grammar. Neutralitytalk 21:15, Jan 12, 2005 (UTC)
- Most grammar sources I have looked at say that it is acceptable to use only an apostrophe at the end if the word already ends in an 's' that is pronounced as /z/. Kaldari 22:27, 12 Jan 2005 (UTC)
- Comment. It looks like this is primarily a question of style and grammar. Personally I would have gone with Olbers' paradox, but it looks like the 's on possessive proper nouns ending in s, is an area of grammar which is currently changing. There is a lot of contradictory advice around. I found quite a good summary of current usage with references at google answers (http://answers.google.com/answers/threadview?id=449307). This suggests that although both options are correct, modern usage is moving towards Olbers's paradox. -- Solipsist 10:50, 13 Jan 2005 (UTC)
- Support for reasons given by Cburnett and Kaldari. older≠wiser 14:09, Jan 13, 2005 (UTC)
- Support I'm too used to "Olbers' Paradox". — RJH 20:40, 14 Jan 2005 (UTC)
- Oppose, but suggest that any resolution of this particular question be put on hold, pending the outcome of the general discussion of the apostrophe-s issue at Wikipedia talk:Manual of Style#Possessives of words ending in 's'. JamesMLane 22:03, 15 Jan 2005 (UTC)
- Support - primarily for reasons of usage. Also, my education and the style guides I've read suggest no extra s is required, a perhaps rare case in which grammar and pronunciation agree. :) -- Guybrush 09:46, 18 Jan 2005 (UTC)