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Comment by nusaru | Hacker News Reader

> The redshift hypothesised in the Big Bang model [...]

Doesn't sound to me like it's more than a hypothesis, but I could be wrong.

Well redshift alone explains the paradox. You don't even need to accept the big bang theory. You can just say "stars that are further away are more redshifted" and that alone explains this. Which we know is true. That's not a hypothesis, redshift can be observed directly. And that fact alone explains the apparent paradox. The most distant stars are redshifted away.

To quote the above article

>The redshift hypothesised in the Big Bang model would by itself explain the darkness of the night sky even if the universe were infinitely old.

Redshift is what explains this. There could be different explanations for the redshift but redshift is 100% an observed phenomena.

Saying "stars that are further away are more redshifted" is Hubble's law and leads almost directly to the big bang. It alone, however, does not explain the paradox. For example even with red shifting, you could have a bright night sky if there are infinitely many stars and the speed of light is instantaneous.

It doesn't really, no? Physicists were well convinced of the big bang for ages before it popped out that the expansion was speeding up, not slowing down. Also, it's pretty hard to imagine a universe where light travels infinitely fast, but also redshifting still exists.

Both the big bang and the observation that galaxies are moving away from the Earth at speeds proportional to their distance originated from the same physicist, George Lemaitre in 1927. The observation came first and then subsequently Hubble formalized it further into Hubble's law and Hubble's constant in 1929.

It's hard to imagine a lot of things, including that the speed of light is the same for all observers, but that's not particularly relevant. Any discussion of the nature of the universe including the big bang itself is going to involve things that are hard to imagine.

> Both the big bang and the observation that galaxies are moving away from the Earth at speeds proportional to their distance originated from the same physicist, George Lemaitre in 1927. The observation came first and then subsequently Hubble formalized it further into Hubble's law and Hubble's constant in 1929.

Ope, right you are. Got my history a little mixed up there.

> It's hard to imagine a lot of things, including that the speed of light is the same for all observers, but that's not particularly relevant.

I mean, sure, but if light was infinitely fast it would lack every single quality that might make it redshift. Is it possible? Sure, anything is possible, but you'd need something that isn't a wave and doesn't act like a wave to independently behave exactly like a wave in a single specific circumstance. I'm sure someone could try and construct such a theory, but it would need a lot of epicycles to make it work. If light was infinitely fast, it really wouldn't be light anymore, at least not as we understand it.

ed: I guess relativity does kind of account for redshift in a way that looks the largely the same as it would with the standard Doppler effect combined with a classical electromagnetic wave, but for different reasons. Still, infinite speed is a bigger leap

That being said, rereading the original comment I see that yeah, even if redshifting wasn't tied to relative velocity the fact that distant galaxies are more redshifted absolutely solves Olber's paradox. I short circuited from "observe redshift" to "universe is expanding" due to velocities, but as long as the energy of distant light fades out fast enough obviously it doesn't matter why.

Something being a wave does not require a finite velocity and in fact there is nothing in physics inconsistent with an instantaneous velocity of light. We know that the two-way speed of light is finite, but all currently known laws of physics are consistent with an instantaneous one-way speed of light [1]:

https://en.wikipedia.org/wiki/One-way_speed_of_light

I am not suggesting that light is instantaneous, only that there is nothing inconsistent with it being so, and that consequently trying to reason about these matters on the basis of what appeals to our intuitions is not sufficient to come to any solid understanding of this phenomenon.

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