I heard an argument that the night sky should be filled with starlight, but since it is not, we know the universe is continuing to expand. More than that, we can measure the movement of stars year over year to deduce speeds and distances to confirm an expanding universe, and we think it is at an accelerating rate, BUT: wouldn’t the sky still be dark even if the universe was static or even contracting?

I mean, I go into the basement with a flashlight and it doesn’t matter how long I have the flashlight on, the room never gets brighter. Yes, it might seem brighter if I shrunk the size of the room, but that has more to do with refraction than intensity. Do we suppose that when starlight hits the edge of the universe it bounces back rather than, say, continuing on or getting absorbed or some such? I suppose we know something about redshift of stars, and I imagine that if space itself was contracting, the existing light be compressed into itself, becoming brighter, but I don’t know enough of the field to work it out. Given how much empty space there is compared to a relatively sparse smattering of stars, would nights really be brighter, would it be noticeable, and how would we know that it wasn’t exactly like what we see?

    • Pons_Aelius@kbin.social
      4·
      11 months ago

      There’s no edge of the universe.

      The universe can be finite and still be unbounded (have no edge). There is no edge to the 3d surface of a 4d hyper-sphere. (eg: you can travel in any direction on the 2d surface of a sphere and never find an edge but the surface is finite)

      Dust gets in the way of starlight.

      If that was the case, which I think the op was implying, the dust would keep heating up to the point to would emit radiation at higher and higher energies and may have gotten to the point where it is doing so in the visible spectrum.