Olbers' paradox
en.wikipedia.org
Olbers' paradox
1–10 of 22 posts
Re: Olbers' paradox
#2Of 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.
Re: Olbers' paradox
#3Breaking news... this just in from the 18th century.
Re: Olbers' paradox
#4Of 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.
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.
Re: Olbers' paradox
#5Of 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.
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.
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...
Re: Olbers' paradox
#6Earlier quoted context omitted.
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.
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...
From a simple standpoint of energy conservation, it's obvious the observed brightness cannot be infinite; the article questions the brightness value of the sky, not whether it is finite. From conservation of energy, for a homogeneous universe, a region around a star must receive as much energy as it gives out. So the total observed brightness of the sky would sum to the brightness of your own star, approximately (but distributed over a solid angle 4pi).
Re: Olbers' paradox
#7Earlier quoted context omitted.
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.
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...
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.
Re: Olbers' paradox
#8Earlier quoted context omitted.
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...
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.
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.
Re: Olbers' paradox
#9What 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...
Re: Olbers' paradox
#10What 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...
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.