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Is there a good explanation as to why this paradox isn't explained by universal expansion? From wikipedia: "To any observer in the universe, it appears that all
by 015a 5y ago
Is there a good explanation as to why this paradox isn't explained by universal expansion? From wikipedia: "To any observer in the universe, it appears that all of space is expanding, and that all but the nearest galaxies (which are bound by gravity) recede at speeds that are proportional to their distance from the observer.";
Wouldn't this imply that, there was probably a time in the distant past when the night sky was saturated brilliantly with light, but as things expand apart, we simply see less-and-less because those infinitely distant galaxies are so far away that their light cannot ever reach us?
Additionally, and maybe related; we can only see 13 odd billion or so lightyears away. The universe could be infinite; there could be a point of light at every "pixel" of the night sky, twenty billion light years away; we simply cannot see that far, as their light cannot travel faster than the rate they're expanding away from us. Is that accurate?
Additionally; space is pretty empty, but not empty. Even ignoring all this, its not unreasonable to think that, over truly universal distances, this matters. We look at the night sky and see nothing; we point a powerful telescope at that same place and see millions of objects, but still darkness between them. Is there an argument against the notion that, maybe, the light from objects even further away was just absorbed naturally before it could get here? Or maybe our telescopes are not sensitive enough?
Additionally; the paradox makes an assumption that space is uniform, but even our naïve observations of the universe prove this to be inaccurate. Its tremendously non uniform; mostly thanks to gravity. Stellar matter is not distributed uniformly; it coalesces into galaxies. Galaxies are not distributed uniformly; they coalesce into galactic neighborhoods, fibers which stretch across the cosmos. There are many regions like the Bootes Void, which contain magnitudes fewer galaxies as we'd expect. There's the Great Attractor, an abnormally massive area which affects the placement of galaxies around it. Maybe on an absolutely, truly, insanely large scale, trillions of lightyears, infinite lightyears, that non-uniformity averages out, but again it comes down to; the universe may be infinitely large, but it doesn't seem to be infinitely old.
- ravi-delia 5y agoExpansion does fix this problem, as does a "young" universe. We actually have both, which would be nice if it wasn't terrible. There was a time that the universe was saturated with light, which we now see as the cosmic background radiation, but it wasn't from stars. The universe was basically very hot, and thus glowed brightly (it's more complicated than that, physics was weird before things cooled down, but still).
- fknorangesite 5y ago> Is there a good explanation as to why this paradox isn't explained by universal expansion? It is - as described in the second paragraph of the linked article. > we can only see 13 odd billion or so lightyears away The radius of the observable universe is ~45 billion light years, not 13. > but even our naïve observations of the universe prove this to be inaccurate. On the contrary; at a cosmic scale it is very uniform. Galaxies are just blips: https://en.wikipedia.org/wiki/Cosmological_principle https://en.wikipedia.org/wiki/Cosmological_principle
- nathanmcrae 5y agoI don't know how all of the factors you bring up interact, but as far as the last point: the universe is indeed uniform and isotropic at a large enough scale (~300 million ly), called, nicely enough, the End of Greatness ( https://en.wikipedia.org/wiki/Observable_universe#End_of_Greatness https://en.wikipedia.org/wiki/Observable_universe#End_of_Gre... ).
- 015a 5y agoIts confusing to me that this would be the case, when the Bootes Void alone is ~330M ly in diameter; and that's small. The Canes Venatici Supervoid is upward of 1300M ly in diameter; the LOWZ North 13788 void is potentially as large as 3000M ly; the list goes on. We've detected over 100 of these supervoids larger than the "End of Greatness"; and that's just what we've seen so far. Obviously, supervoids are a part of universal uniformity, at a large enough scale, but I'm having a hard time rectifying that the scale we're talking about is ~300M ly, and not significantly larger, with the fact that there are, trivially, a large number of "300M ly windows" one could pick, anywhere in the universe, and see extremely different things. In some cases, an extreme density of billions of galaxies, and in others a number that is dwarfed by even the number of large bodies in our own solar system. Is this a situation where we just didn't know about these 300M+ ly superstructures when that scale was calculated, and it needs to be revised? Or we knew about them, the math would naturally allow for a level of deviation, and to this day they're still rare and small enough that the deviation is low? Or is there something about the math I'm missing whereby discovering any number of these, into the future, still allows that ~300Mly number to work? More to read, I do believe.
- fknorangesite 5y ago> In some cases, an extreme density of billions of galaxies I think you might be overestimating how dense a galaxy is, in the grand scheme of things. You may think it's a long way down the road to the chemist's, but it's still almost entirely empty space.
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