[hexatin]

The strength of light over a distance obeys an inverse square law[1], causing it to effectively lose power over long distances, since the same amount of energy is being spread over larger and larger spheres as it radiates out. For photons, I think this manifests as there being a lower rate of photons occurring in each section of the sphere since they’re “spread out”.

[1] https://en.wikipedia.org/wiki/Inverse-square_law

[site-packages1]

Doesn't this fail because we're looking at lots of stars spread out evenly, and so the farther you get away, the more stars fill the space?

[jmopp]

This is Olbers' Paradox[1] and is one piece of evidence that the universe isn't static.

1 https://en.wikipedia.org/wiki/Olbers%27_paradox

[setr]

It still depends on their contribution right? If you said all lights are equal in strength, then being on top of one gives a strength of 1. Being x units away from it gives a some value less than 1, based on the sqrt of distance

Being close & between two lights would take the sum of their strengths, say .75 each so 1.5, giving a value greater than 1 (more light than either individually produces)

Being far from the two lights, each contributes .25 strength, so .5 total — half the light of standing on top of one

And of course if you get really far, a ridiculously large number of light sources are contributing a ridiculously small amount of light, which may still sum to something fairly small

I’m imagining it works like an influence map: https://www.gamedev.net/tutorials/programming/artificial-int...

[hypertele-Xii]

Space is mostly empty.

[mananaysiempre]

As a sibling comment to yours says, Olbers’ paradox is that it doesn’t matter.

If we assume that the universe is homogeneous, infinite, and eternal and the density of stars (possibly averaged over a large but constant scale) is constant, then in any direction on the sky there is some (possibly very faraway) star, occupying a finite (possibly minuscule) solid angle in our field of view. The 1/r² falloff (aka conservation of energy) means that the energy received per unit of solid angle is independent of distance from the emitter, equal for example to that on its surface, so every piece of the sky containing a star means we should see stellar-surface amounts of energy shining upon us from every direction.

Assuming some sort of absorbing dust would obscure the stars doesn’t help: if the universe truly is eternal, every dust cloud, being unable to store arbitrarily large amounts of energy, will eventually heat up to the point that it radiates as much as it absorbs and so is as hot as the stars which it obscures (this is the insight behind Kirchhoff’s law and the existence of blackbody radiation).

What does help is either implementing “no point in space is special” through a device other than simply a constant stellar density (e.g. having stars distributed on a self-similar fractal of Hausdorff dimension < 3, our falloff argument having included what amounts to a definition of Hausdorff dimension) or abandoning “no point in time is special” (giving the universe a finite age or at least having no stars in the far past). Observations show the second possibility (named the “Big Bang” by its critics in what was meant to show its ridiculousness) to be true.

(Modern cosmology has much more direct arguments for a finite age of the universe, but they also require more advanced physics and/or observational technology, so the directness is in the eye of the beholder.)

[hypertele-Xii]

But isn't space expanding? And the expansion is accelerating?