Talk:Olbers' paradox

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[edit] Myths and alternative explanations

I've added a line about the Charlier Cosmology. Does anyone have a reference to Mandelbrot's paper? Jonathan Silverlight 21:50, 19 October 2006 (UTC)

[edit] Wave Structure of Matter

The Wave Structure of Matter theory (see: [Wave Structure of Matter]) proclaims a different solution to this paradox. The distancescale of interaction between distantiated material objects is finite, the size of the Hubble distance. Forces drop down (i.e. drop down faster then expected from 1/R^2) for objects in space which are very far distantiated, because they have less common universe (the Hubble sphere). This also explains that far distantiated star light is red-shifted! (WSM theory sees all matter as caused by standing waves in space). Wouldn't that viewpoint need to be mentioned as a solution? Heusdens 23:16, 22 November 2005 (UTC)

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)
A note on English grammar: which one is correct depends more on morphological processes than syntax. If Olbers is a singular noun possessive noun, its structure is: ROOT(Olbers) + POSS('s). If it was plural of Olber, it would be: ROOT(Olber) + PLURAL(s) + POSS('s). Now some people (the Olbers' people) are following this morphological rule: *[ending in s] + POSS('s) => *', thus ROOT(Olbers) + POSS('s) => ROOT(Olbers)+' => Olbers'. The Olbers's people are following this rule: ROOT[singular] + POSS('s) => ROOT's, ROOT[singular] + PLURAL(s) + POSS('s) => ROOT+PLURAL(s)+POSS('). Whose is right? The Olbers' people consider that +'s v. +' is based on morphological considerations, whereas the Olbers's people base it on more grammatical rules.

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

[edit] 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)

[edit] 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)

[edit] 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?

[edit] 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. 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)

[edit] Brightness, distance

I'm pretty sure I don't understand this sentence:

"The brightness of a surface is independent of its distance, so every point in the sky should be as bright as the surface of a star."

What does it mean for brightness to be independent of distance? A distant light source certainly *seems* less bright than a near one--perhaps there's a technical meaning of "brightness" that is different from the commonplace meaning? But if the technical definition of brightness has nothing to do with how the object is perceived, then what's the point of the paradox? If the sky can be "bright" without looking bright, I mean. Nareek 22:45, 3 March 2006 (UTC)

[edit] Isotropic microwave background radiation in Olbers' context

The main article on Olbers' paradox says:

"One explanation attempt is that the universe is not transparent, and the light from distant stars is blocked by intermediate dark stars or absorbed by dust or gas, so that there is a bound on the distance from which light can reach the observer. However, this reasoning does not resolve the paradox. According to the first law of thermodynamics, energy must be conserved, so the intermediate matter would heat up and soon reradiate the energy (possibly at different wavelengths). This would again result in uniform radiation from all directions, which is not observed."

What do you mean, not observed? How about that uniform radiation from all directions that we do observe, the ubiquitous background microwave radiation (which is exactly in the range of interstellar gas secondary emission)? 66.82.53.56 18:41, 22 March 2006 (UTC) Alex Feht

[edit] Accepted explanation false

The darkness of the night sky is not due to the universe's finite size; it is due to it's expansion. The night sky in steady state models (which are spatially unbounded) is also dark. --Michael C. Price talk 04:44, 10 January 2007 (UTC)

I've added the correct explanation. --Michael C. Price talk 17:11, 26 January 2007 (UTC)
But if the universe were infinite in duration, then Olber's Paradox would still hold. The universe could expand all it wanted. Jhobson1 00:42, 17 August 2007 (UTC)
Says who? --Michael C. Price talk 02:46, 17 August 2007 (UTC)

[edit] Deleted section

==Obsolete argument: what paradox?==
The above discussion[clarify] was correct in Olber's time, when the only radiating objects known were stars, or shone by reflected starlight. After blackbody radiation was discovered, one then has to replace the term "star" with the more general term "N degree Kelvin blackbody radiator". The paradox then disappears (N=3).

I've deleted the above text because I think it's not correct. It was also unsourced and rather lacking in explaining why/how the cosmic microwave background resolves the paradox (which it probably doesn't). You might argue that the expansion of the universe implies a CMB (sort of half true) and that the expansion resolves the paradox, but that is a different argument and has already been presented. --Michael C. Price talk 17:11, 26 January 2007 (UTC)

[edit] Finite age is the dominant effect

In the "Accepted Explanations" section it was stated:

"Two effects contribute to the resolution of Olbers' paradox: the finite age of the universe and the redshift. The latter effect is the dominant effect."

In fact, it should be "... the former effect is the dominant effect." I've made the necessary edit. Redshift only contributes a few factors of dimming. The finite age of the universe (actually, the finite lifetimes of stars, but I won't quibble further) is responsible for the orders of magnitude difference between a "bright" night sky and what we observe (i.e. a "dark" night sky). To find out why, see the papers and books that are referenced in this very entry, especially Wesson's paper and Harrison's book (also the latter's "Cosmology: The Science of the Universe", another fine book). Cragwolf 05:00, 19 February 2007 (UTC)


Finite energy density of the universe please

Can someone explain to me how the finite age of stars in wouldn't explain the paradox? Since the amount of energy contained in a star is limited, the energy density of the universe has a similar upper limit. Realizing that is trivial.

The problem with Olbers' paradox is that it assumes an infinite supply of fuel for the stars, i.e. an infinite energy density of the universe. Of course this yields a result with infinite flux (for point-like stars), one would have to be stupid to suggest anything else.

Dispensing with this fake paradox takes us instead to the question on steady-state/infinite vs finite universe, where the former needs to have a way to prevent heat-death after infinite time.

That, however, is another matter altogether. Let's not try to mix this false paradox into the discussion and pretend it has any merit as an argument for a finite universe.

--ChristofferL 19:04, 23 October 2007 (UTC)

The finite age of stars does not necessarily explain the paradox, because if you had a large enough number of stars per unit volume then that might be enough to still make the night sky bright. Harrison (an author referenced in this article), in his cosmology textbook, talks about a "lookback limit" (*), with an associated lookback time, T, and compares the latter to the lifetime of a typical star, t. If t << T then the night sky is dark; if t ≥ T then it's as bright as the surface of a star. T is determined by the number density of stars: high number density, small T; low number density, large T. So it's not really a finite energy density, but an insufficient energy density that explains why the night sky is not bright. In other words, two factors are fighting each other — number density of stars vs lifetime of typical star — and the winner determines whether or not the night sky is as bright as the surface of a star.
(*) What is the lookback limit? It can be thought of as the average distance of a line of sight from observer's eye to the surface of a star. Cragwolf 12:24, 10 November 2007 (UTC)


I don't agree here. A finite energy density is all that matters. Even if all of the energy of the stars are released at once, and distributed evenly across space, the average energy density would not change. You *could* create a situation where if all the energy is immediately distributed (taking away all the stars), when looking up you'd get a glaring hot sky.. Of course, you *could* also create a situation where you get a far dimmer sky. It would depend on the actual energy density and distribution distances (a high density would create a bright sky, low density would create a dark sky).
Still, the fact is, the energy is not released all at once. In fact, you'd could make the case for an equilibrium condition. The energy density would have to remain uniform in any infinite & static universe. This means you could effectively shuffle the energy around any way you like, you are still going to get the exact same amount of energy wherever you look. The only thing that would vary is the timing and location. This could very well create a situation where, no matter how much time passes, the universe would constantly look the same (within a variance of course). It would be a fact that we would EVENTUALLY return to our current view, no matter how big the variances were.
Think about it. Picture a slice of our infinite universe (that looks just like ours), with a finite energy density. What can you do to that slice that would really achieve the end solution of Olber's paradox? You'd have to release massive amount of energy from the stars in a way that reaches our planet, and doesn't get absorbed by something else. Eventually it WILL get abosrbed by something else (whether its us or not). The energy will just be shifted, and the average energy density will be maintained throughout the rest of the universe. The laws of thermodynamics would dictate that even if our planet did heat up, this would only mean another part of the universe would be cooled by the same amount. In other words, if this super heating in Olber's paradox occurs somewhere, a super cooling would have to occur somewhere else. It would all even out. If you still disagree, try to think what you'd need to do to the universe as a whole to change this.
The way I see it, Olber's paradox is immediately invalidated if you assume Stars do not last forever and do not violate the laws of thermodynamics. Whether or not our universe is static & infinite cannot be proven/disproven by Olber's paradox. Nicknomo (talk) 14:45, 28 February 2008 (UTC)

[edit] Contradiction

From the article:

The current scientific consensus is that effects of general relativity relating to the Big Bang and the finite age of the Universe do indeed give a finite size for the observable universe, but that it is the astronomical redshift relationship which really explains the dark sky at night.

From elsewhere in the article:

Three effects contribute to the resolution of Olbers' paradox: the finite age of the universe, the redshift, and the finite radiation life of stars. The first and third effects combined dominate. (Even in steady state theory models, which supposes the universe is infinitely old and spatially unbounded, the night sky would still be dark.)

The second snippet contains a contradiction, and contradicts the first snippet. Please fix it. Shinobu 19:01, 20 April 2007 (UTC)

[edit] Splendid new simulation from kmarina86

Why the sky is not bright in night? Why can this old theorem not critic big bang? Redshift cannot compensate it because there should always be enough for us visible stars! Or not? 84.158.86.156 08:08, 17 May 2007 (UTC)

One must consider that the density of the distrubtion of stars is not the same anywhere. The stars within our galaxy alone are certainly not homogenously distributed. Howver Olber's Paradox was formed during a time when Galaxies were unknown. If every star were 4 light years from each other, 10^22 stars (= 100 billion * 100 billion) could fit within a cube 86 million light years on each side (over 300 times smaller). If we were in the center of such a field, the sky would certainly brighter, about 90,000 times brighter (12 magnitudes brighter). But if our horizon was at the edge of the cube, then certainly the sky would not be infinitely bright, but very, very bright indeed.

http://www.stjarnhimlen.se/comp/radfaq.html#10

                                     Luminance       Magnitudes per square
                                     Nit = cd/m2       arcsec   arcmin
 
 Sun                                   3E+9            -10.7    -19.6
 Venus (max elong)                     15000            +1.9    -7
 Clear daytime sky (at horizon)        10000            +3      -6
 Full Moon                              6000            +3.6    -5.3
 Mars at perihelion                     4000            +3.9    -5.0
 Overcast daytime sky (at horizon)      1000            +5      -4
 Jupiter                                 800            +5.7    -3.2
 Saturn                                  700            +5.9    -3.0
 Heavy daytime overcast (at horiz)       100            +8      -1
 Uranus                                   60            +8.6    -0.3
 Neptune                                  30            +9.3    +0.4
 Sunset at horizon, overcast              10           +10      +1
 Clear sky 15 min after sunset (horiz)     1           +13      +4
 Clear sky 30 min after sunset (horiz)     0.1         +15      +6
 Fairly bright moonlight (at horizon)      0.01        +18      +9
 Moonless, clear night sky (at horiz)      1E-3        +20     +11
 Moonless, overcast night sky (at horiz)   1E-4        +23     +14
 Dark country sky between stars (zenith)   3E-5        +24     +15

20 → -10.7

Even making all stars in the observable universe a distance 4 light years from each other is not enough to counter Olber's Paradox....!

However, the Big Bang theory assumes a homegenous universe just at the at the largest scales that expands with time, with decreasing density. During this process, light from a star weakens with the fourth power of the scale factor (http://www.google.com/search?q=%22fourth+power+of+the+scale+factor%22+big+bang) [note: not distance]. With this, the radiation density drops. But what is significant is not the absence of percievable light, but rather the relative brightness it has with respect to the sun. The brightness is cut off due to expansion from a opaque singularity, so it does not have the chance to sum to what would be the brightness of our sun at all points in the sky. More importantly, the magnitude of stars (in relation to the luminosity distance) in the Big Bang theory drops faster in relation to the angular diameter distance. So a star of similar properties in a galaxy 10 times further away in terms of angular diameter distance would be more than 100 times dimmer. In this way, the Big Bang theory solves Olber's Paradox.Kmarinas86 20:17, 17 May 2007 (UTC)

Except it doesn't. Preliminary work by Harrison and later work by Wesson (see references to this article) have shown that "Big Bang theory", i.e. cosmological expansion, darkens the night sky by a few times (compared to the static case, all other variables equal) — which is nowhere near enough to turn a bright night sky into what we currently see. Cragwolf 13:58, 10 November 2007 (UTC)

[edit] Debunk paradox people forget the size of the universe...

People how made up this paradox forgot the size of the universe. And the amount of stars (and the distribution of them). Let's do some mind experiment.


Imagine your on a football field, in the darknes, and someone at a random place holds a burning cigaret. Now close to your football field connect hundred other football fields (thats a square about 1KM2) in size. Ofcourse you will be able to see the most nearest cigarets, as you have hawks eyes.


Now just imagine that in a random direction somewhere between 50km and 100km away another cluster of footbal fields exist. This is another starsystem (another milkyway). Also overthere there are some people holding cigarets which you might be able to see using optical lenses.


But then the next footbalfield will be away well lets say 50.000km you will not be able to see them. You can keep on repeating this.


But hey let's imagine you've created the ultimate lens a science breaktrough in optic dynamics. Then when looking to your horizon you see on a horizontal line some orange dots of cigaretes. But between the lightdots there will always be a distance. Yes you can zoom into a region but you will only find again (extreme tiny) dots and (and a bit bigger )distances (compared to the new dots size). It is much like a fractal you can never fill the horizon this way


So filling in a horizon this way with cigarete lights will never end up in an orange horizone line.


This is no paradox

Take a look at the photographs by Hubble STS and other distant galaxy images and you see the sky is not just filled with stars but it is filled with galaxies! http://hubblesite.org/newscenter/archive/releases/galaxy/2004/08/ This is only one of many images of numerous galaxies to be found in good viewing. There is no paradox.BillWilliam

If you had any understanding of Physics or indeed cosmology you find that what you are suggesting is not the case. A distant light source only seems dimmed as the photons are scattered by intervening matter. It is true that teh further away a light source is (on Earth) the dimmer it becomes however there is a general lack of matter in space meaning that your interpretation would only hold true if the entirity of space be completly populated by matter in which case distance would affect luminousity. We are not dealing with cigarettes and footballfields with countless moles of gas inbetween but instead unimportant distances. I would check facts further before trying to disbunk a paradox that is likely to be more than twice your age. Your argument about the size of teh light sources is also flawed. The paradox was created during a time of transistion between accepted thinkings, from that of infinite time and space to finite space-time. The paradox only exists when we deal with infinite numbers. No matter how small the points of light are, in an infinite universe there would be infinite numbers of them still creating a solid balnket of light. Olbers' Paradox (I believe should be capitalised) leads us to the finite universe. —Preceding unsigned comment added by Sedecrem (talk • contribs) 08:43, August 27, 2007 (UTC)

I don't think you should've insulted this poster's understanding of physics. Luminosity of the emitted light weakens as you get further away from a bright object due to the fact that there will be the same amount of light in less volume. To have it any other way would induce a violation of thermodynamics. As you put the same amount of energy in a greater amount of space, energy density drops. I think the problem with Olber's paradox is that it makes an error of infinity. Sure there is infinite energy coming at you from all directions, but this does not necessarily mean that you will be receiving infinite energy. If you go to the discussion above, all that really matters is the average energy density (energy per cubic meter). At that point, it just becomes a shuffling match - energy may move around a lot, but it would be counterintuitive to say everywhere starts receiving massive amounts of light. Nicknomo (talk) 14:45, 28 February 2008 (UTC)


Well, I thought I read that the universe doesn't have edges (what would be on the outside, after all?), so, if it's finite, it must curve around to meet itself. But if we live in such a curved universe, then wouldn't the starlight that doesn't directly make it to our eyes be wrapping around the universe and hitting us from another direction? The only thing I can think of is black holes absorbing light. It could be that there's a perfectly good explanation for why black holes wouldn't resolved the paradox, but I am surprised the term 'black hole' is never mentioned even once in the article, even if only to debunk that idea in the next sentence. --Iritscen 15:46, 24 September 2007 (UTC)

[edit] Absorption section needs work

The section on why absorption cannot be an explanation needs work. It completely ignores ways for photons to be absorbed in a manner that precludes re-radiation of another photon (black holes come to mind). Kurt 01:51, 4 July 2007 (UTC)

Even black holes radiate - but the section does need to cover the case explicitly. I guess the "black holes as absorbers" solution wouldn't be be stable in the sense that they would either explode (if hotter than the stellar environment) or grow without limit (if cooler than the stellar environment) and hence be "seen". --Michael C. Price talk 16:49, 24 September 2007 (UTC)
I just noticed Kurt's above post, which is similar in thought to my own post above of a few days ago. I will just second the notion (or third it) that it would be good for someone knowledgeable about black holes to explain why they could not be absorbing light. Perhaps MichaelCPrince is up to the task; he certainly knows more than I do on the subject. But of course there's the very theoretical idea that black holes might have "exits" elsewhere in the universe, which, if true, would certainly explain why black holes are not the answer to Olbers' paradox, if for no other reason. --Iritscen 18:37, 27 September 2007 (UTC)


Vincent - Maybe Im not quite grasping something here but as I understand it- the proposal that the universe might be infinite and static but the infinite radiation is absorbed by some kind of "dust" is rather well debunked by the thermodynamics argument, but how about if this "dust" was dark matter? The topic of dark matter seems to be shrouded in mystery at present. But dark matter itself must have no (or very very little) interaction with electromagnetic radiation whatsoever - this is why it's invisible to us and not directly detectable... Could it be that the "dust" idea is not as weak as the article would have us believe?? 15:26 9th October 2007 —Preceding unsigned comment added by 137.205.8.2 (talk) 14:26, 9 October 2007 (UTC)

[edit] Fractal explaination

I was just curious as to the last part of this description, "Mainstream cosmologists reject this fractal cosmology, on the grounds that studies of large-scale structure in combination with the timeline of the universe have not produced any evidence for it." Is there any refrence avaliable as to its rejection? I find an analogy to a cantor set more than sufficient to explain the paradox, fitting infinite points into a finite space. I would like to know the evidence against it, not simply the lack of corroborating evidence. I would think the fractal nature of the sky is self-evident, if it weren't so the paradox would be unresolved. Nazlfrag (talk) 22:52, 29 December 2007 (UTC)

Re Olbers paradox.

The solution to this puzzle is in basic physics, rather than in the circumstancial nature of the universe. According to the old line of reasoning, if the greater universe were infinitely old and spacious and (thus) contained infinite sources of light/radiation then we should see radiation as bright as the sun or even infinitely bright in every direction. As that is not the case it is deduced that the universe must be finite in space and/or time. But this line of reasoning overlooks the fact that whatever the size or age of the universe (i.e even if it were infinite), we would not be allowed to see very bright or infinite radiation because of the conservation of energy principle. That principle rules that there must be a balance between the radiation received by the 'average position' in the universe and the radiation emitted by same. The radiation emitted by the average position is low because, well most of space is empty of sources of radiation. You cannot therefore have a possibility of every position seeing/receiving infinite radiation. The conservation of energy principle is useful in showing up the fault in the old line of reasoning but it does complete the answer. The answer is provided by Einstein's gravitational shift of light. Apply that equation (that led to the idea of a black hole) to an infinite universe and it should be clear; the infinite collective mass of the surrounding infinite universe should erase Olbers theoretical infinite light. That does not mean that all evidence of an infinite surrounding universe would be erased. I theorized, in 1994, that if the universe were infinite then our cosmos/the visible universe should, due to gravity, be accelerating apart, as has been subsequently observed. No need for 'dark energy'.

Mark Bridger 16 May 2008 —Preceding unsigned comment added by 86.144.170.236 (talk) 11:00, 16 May 2008 (UTC)

[edit] Original research

The initial paragraph of section 2 looks very much like original speculation to me (and also does not look like very encyclopedic). I added a WP:NOR tag. --Cyclopia (talk) 16:47, 18 May 2008 (UTC)