

Olbers' paradox - anacleto
https://en.wikipedia.org/wiki/Olbers%27_paradox

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bunkydoo
It might seem like a paradox from our perspective, but there is good
possibility that like fish in water - our senses & instruments just haven't
evolved to perceive and function out of water (off earth) A good possible
explanation would be that the seemingly empty void of space is chalk full of
dark matter scientists assume makes up 95% of the universe and our eyes can't
see it like a dog can't see color, and this invisible matter might someday end
up being a biological commodity to future beings that evolve from us just like
fresh air is to our lungs.

The universe might look like a cerulean sky, we just haven't evolved to see it
that way yet.

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cLeEOGPw
No need for dark matter. As it states in explanation paragraph, according to
big bang theory, in the beginning stages there were light everywhere and the
universe was not even transparent. So according to this, when we look at the
sky now we should see that light if we look far enough. But we don't. Reason
for that is that as universe expanded, that light emitted from the early
stages got "stretched out" and shifted from visible light to microwave length.
That's what we call cosmic microwave background. So it's not a possibility -
it's fact.

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baghira
I'm really not convinced by the passages, both in Wikipedia and in the
referenced book, concerning the role of the finite age of stars.

From what I remember from Coles-Lucchin, the finite age of stars does furnish
a partial explanation: keeping the average density of lit stars the universe
constant, does not solve the problem, since in general, when I look in a
particular direction, any star in that direction will either be dead or lit,
but still too far away for its light to have reached me.

Indeed the opposite would require fine-tuning the stars ignition time so that
there is sphere of burning stars at the right distance.

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mangeletti
What about the fact that we can barely see the light from some of the stars
that we know are there (because of space dust, etc.)? How did somebody come to
this conclusion just 150 years ago...

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Sharlin
The energy absorbed by interstellar gas and dust doesn't just disappear, it's
re-emitted at (mostly) infrared wavelengths. If there really were infinite
stars in an eternal universe, everything would be heated to the same white-hot
temperature, including the interstellar medium.

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mangeletti
Think about what you're saying. In our current system, if you do not except
infinity, then you are accepting that there is finite space for energy to
escape to, which means that the lack of much visible light and infrared from
distant stars available to Earthbound viewers implies that any distribution
homogenous and similar to ours currently observable would result in similarly
dark views from any vantage point.

This is a logical truth.

~~~
wsxcde
You should try rephrasing that because the point you're making is not at all
clear.

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mgalka
Isn't this one explained by the speed of light?

Only a finite number of stars have had enough time to reach the earth. So
there can only be a finite number of concentric shells.

~~~
wsxcde
The paradox assumes there are infinite stars that have existed for infinite
time:

> If the universe is static, homogeneous at a large scale, and populated by an
> infinite number of stars

You're assuming an infinite number of stars sprang into existence a finite
amount of time ago.

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MaysonL
Of course, given the quantum nature of light, this breaks down: at some
(admittedly very large) distance, a star will be emitting so few photons in a
given direction that it will be effectively black.

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empiricus
If the universe is infinite, for each particular direction there are an
infinite number of stars. So even if the probability of a photon coming from a
distant star is very low, there are infinitely many stars in that direction,
so that direction will still be very bright. So the quantum nature of light
does not change the paradox.

~~~
empiricus
The wikipedia article surprises me though.. The actual brightness can be
calculated as an infinite sum of start brightnesses getting weaker with the
distance. The result of an infinite sum can be finite or infinite. I would
have though apriori that the sum is finite because the star density is so low.
But at the end of the article they seem to suggest that the universe is dense
enough for the sum to be infinite...

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delecti
I think one resolution is the finite speed of light. Even if there are
infinite stars in any given direction, they haven't been around long enough
for the brightness to be infinite.

This "paradox" is basically just theorizing an aspect of the heat death of the
universe.

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uts
The paradox says that an universe infinite in space and time would have to be
bright in all directions. By infinite in time, I mean that the universe has
been around infinitely long, i.e. it has no beginning. The finite speed of
light wouldn't matter here since the light would have had an infinite amount
of time to reach you.

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thaumasiotes
Huh? We definitely know that that doesn't describe the universe. If two points
are so far apart that the expansion of space inflates the distance between
them faster than light can cross it, then no light can ever reach from one to
the other, even if it travels for an infinitely long time.

~~~
uts
The Olbers' paradox is from the 1800s, before we knew about the expansion of
space. It's arguing against a static, infinitely old universe. As you point
out, we now know that this isn't the case.

