Olbers' Paradox
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Olbers' Paradox
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Re: Olbers' Paradox
#2Cool concept, but doesn't consider planets, or nebulae, or other space objects that can block light. I have no expertise to speak with authority on this, so please, weigh in on this consideration. But wouldn't this break the "homogeneity" assumption?
EDIT: Thinking about this further, could you make approximation rules about the things that block light, too? e.g. By the nature of a star's mass, you can assume that some opaque object is likely between Earth and any given star with some likelihood?
EDIT2: Thanks to everybody for the replies - this really helps clarify! Cheers!
Re: Olbers' Paradox
#3Cool concept, but doesn't consider planets, or nebulae, or other space objects that can block light. I have no expertise to speak with authority on this, so please, weigh in on this consideration. But wouldn't this break the "homogeneity" assumption? EDIT: Thinking about this further, could you make approximation rules about the things that block light, too? e.g. By the nature of a star's mass, you can assume that so…
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Re: Olbers' Paradox
#4Cool concept, but doesn't consider planets, or nebulae, or other space objects that can block light. I have no expertise to speak with authority on this, so please, weigh in on this consideration. But wouldn't this break the "homogeneity" assumption? EDIT: Thinking about this further, could you make approximation rules about the things that block light, too? e.g. By the nature of a star's mass, you can assume that so…
There's no "blocking light": anything that "blocks light" would get hot from absorbing that light and, then, reradiate. By this time (some point along the curve of "infinitely old universe") everything should be radiating a lot.
Re: Olbers' Paradox
#5When I first encountered this idea it quickly jumped to me that the universe does not appear to be "static", or at least our observation of it is constantly changing. This also plays into homogeneity, and the last assumption of being "infinite" is somewhat irrelevant, because if the first 2 aspects don't hold, being infinite still won't make the sky appear 'filled', at least past the point of our observation.
Of course there's still the theory of an imploding universe which could shrink back together all matter and thus maybe achieve this effect, but even then we still don't have a static characteristic, it only makes an argument for an 'infinitely occurring universe', maybe something akin of the theory proposed by Penrose.(which however still has a lot of unanswered questions, imo)
Re: Olbers' Paradox
#6Cool concept, but doesn't consider planets, or nebulae, or other space objects that can block light. I have no expertise to speak with authority on this, so please, weigh in on this consideration. But wouldn't this break the "homogeneity" assumption? EDIT: Thinking about this further, could you make approximation rules about the things that block light, too? e.g. By the nature of a star's mass, you can assume that so…
Blocking light means absorbing energy. In an eternal universe, you have to reach thermal equilibrium eventually, so you have to shed that energy somehow, and for a constant amount of matter just hanging around in empty space radiation is the only logical possibility. At the end of the day, your absorber will reach the same temperature as the emitter and emit the same amounts of light that it absorbs on frequencies where it does absorb, though perhaps in different directions. This is the insight behind Kirchhoff’s law and blackbody radiation.
Re: Olbers' Paradox
#7A more concise explanation can be found in the Usenet Physics FAQ:
https://math.ucr.edu/home/baez/physics/Relativity/GR/olbers....
Re: Olbers' Paradox
#8Cool concept, but doesn't consider planets, or nebulae, or other space objects that can block light. I have no expertise to speak with authority on this, so please, weigh in on this consideration. But wouldn't this break the "homogeneity" assumption? EDIT: Thinking about this further, could you make approximation rules about the things that block light, too? e.g. By the nature of a star's mass, you can assume that so…
If you read the section on "The Paradox" in the article, it's basically using a simplifying geometric assumption to divide the universe into concentric shells, each of which contributes the same intensity of light to the observer. If space is sparse enough that any light reaches us from shell N+1, then you'll get the same amount of light from every shell, and so you'd have a fully-saturated bright sky.
So there are possible infinite/steady-state universes universes (very dense, lots of dust) where you don't see shell N+1. But since we can see stars from shell N+1 and other shells, we know that we don't live in that universe. Therefore our universe isn't a steady-state / infinite time one.
Re: Olbers' Paradox
#9A more concise explanation can be found in the Usenet Physics FAQ: https://math.ucr.edu/home/baez/physics/Relativity/GR/olbers....
> too. It does act like a radiation shield, exponentially damping the distant starlight.
This is wrong, damping is not exponential but to the fourth root.
Re: Olbers' Paradox
#10Assuming an infinite amount of anything seems to be a good way to end up with a paradox.