My favorite theory is that the universe is finite, some sort of (hyper)sphere or -torus. If we could just look far enough out there we would see our own galaxy
What would be even cooler is if it was warped like a moebius strip in a higher dimension, so that when we look out there, everything is mirrored from "our" reality :-D
That first theory would be interesting, but wouldn't it be basically impossible to prove unless the finite repeating universe were also pretty small? We see distant objects as they were in the past, and I'm not sure we'd recognize our own galaxy a billion years ago and a billion light years away.
It's actually an interesting thought experiment. If that theory were true, and assuming we could see ourselves face-on (rather than edge-on), then I wonder how far away and far back could we recognize ourselves.
Yeah, I realize we're looking in the past and can't "see" ourselves (probably not even our own galaxy, depending how far out we have to look). But I guess the theory in itself is not any more "weird" or "outlandish" as the idea of an infinite universe.
And maybe if we actually look both ways, we could find another galaxy that could be proven to be the same (because of some particularly remarkable stars/quasars/supernovae etc. in them). Who knows, maybe the universe is smaller than we think and we just don't recognize the "same" galaxies on different images because they are billions of years apart?
For all we know it might be - or it might actually be infinite - but the trouble is that we're limited by what we can see / detect, which is in turn limited by the speed of light.
Another commenter asked something like, what if the universe is much bigger than the observable universe, because everything beyond that 'border' has redshifted out of reach - or hasn't reached us yet / never will, because it's moving away faster than the speed of light.
That assumes that we can somehow see through time, which leads to a whole bunch of inconsistencies (aka time travel paradoxes). There's no way to look through large distances without looking back in time, unfortunately.
I don't see how seeing one's past may lead to paradoxes. Meddling withthe past would still be impossible, due to the,distance and the speed of light limit.
What am I missing?
The funny thing is that since we've been observing the universe for so little time, and we're so small, most of the evidence for the big bang and expansion is not direct, but a chain of deductions.
I mean that we can't observe the expansion because we can't really triangulate at galactic scale. If there is another reason the light from distant galaxies turn to red, kind of a long-distance light fatigue, we couldn't really know.
The reason I always heard that would be a confirmation, because it comes from a different causal path, was precisely the different composition of old galaxies. And now it seems they're not so sure.
> If there is another reason the light from distant galaxies turn to red, kind of a long-distance light fatigue, we couldn't really know.
It's not just red shift that demands an explanation, but also that the sky (space) is dark. If space wasn't expanding then the skies would be bright white.
Another thing is the second law of thermodynamics, which very strongly implies a lot of standard cosmology.
Of course, standard cosmology could be all wrong, but these deductions are quite solid as far as the physics that we know today.
It's not just red shift that demands an explanation, but also that the sky (space) is dark. If space wasn't expanding then the skies would be bright white.
Another thing is the second law of thermodynamics, which very strongly implies a lot of standard cosmology.
Don't you feel that these evidences just make a case from models checked in small scales and tell the whole universe what it should do?
I don't mean the reasoning is incorrect or unwarranted, just that there could be alternative explanations that involve unknowns.
Of course, standard cosmology could be all wrong, but these deductions are quite solid as far as the physics that we know today.
When applying Occam's razor, you try to minimize entities and simplify. But what appears simpler for a physicist is sometimes surprising for the rest of us. The equations don't work as expected? No problem, let's say that the entire universe is expanding or, even better, that space is expanding. Or that all the universe was at some moment in the space of a tennis ball. Or that big bang happened everywhere at the same time...
While some explanation fits the maths, it doesn't matter if it's totally alien to common sense. Actually I find all those weird explanations strangely appealing, they give me a sense of wonder and empowerment. Cosmology feels like a superpower :)
> Don't you feel that these evidences just make a case from models checked in small scales and tell the whole universe what it should do?
Yes, we like to think that the laws of physics we can deduce locally are global. That could be wrong, for sure. But consider that we understand the physics of our solar system (which has a star), and we see other stars in the skies which... implies that at least as much of our local physics that makes stars possible also applies where we see those stars.
Which is insanely far away and all light coming from there will have diminished in energy enough to be barely visible?
Inadequate explanation. Even if the universe was a closed box with perfectly reflecting borders, what you would actually see in the sky is something like an average brightness of the entire universe with some fluctuations.
It's not inadequate. Brightness diminishes for two reasons. One is absorption from cosmic dust (not that big of a factor), the other is that the object appears smaller, but the brightness per unit solid angle from the object does not diminish. If there were just more stars behind that you could see, the sky would have to be much brighter.
Photons do not "diminish" in energy except via red shifting (where does the energy go? into the expansion of the universe!).
Light scatters, gets absorbed and re-emitted, it's true, but if distances don't change then the universe would still be much brighter than it is today.
Any straight line you draw from earth to any direction in the sky will then reach a star.
Only if you think that there is infinite matter, all of it forming the same kind of stars, uniformly spread over the infinite space and there is no unknown form of atenuation for waves traveling millions or billions of years light.
> The reason I always heard that would be a confirmation, because it comes from a different causal path, was precisely the different composition of old galaxies
And you never heard of the CMB? That's generally considered the "smoking gun" evidence for the big bang.
Since everyone is mentioning their favorite whacky theories, mine is the one that says within every particle is a whole universe, made up of particles with their own universes and so on, and what we call our universe is really just a particle in an even bigger universe. And what if all of those universes were actually the same universe, like some infinite recursion?
[…] But to show him another prodigy equally astonishing, let him examine the most delicate things he knows. Let a mite be given him, with its minute body and parts incomparably more minute, limbs with their joints, veins in the limbs, blood in the veins, humours in the blood, drops in the humours, vapours in the drops. Dividing these last things again, let him exhaust his powers of conception, and let the last object at which he can arrive be now that of our discourse. Perhaps he will think that here is the smallest point in nature. I will let him see therein a new abyss. I will paint for him not only the visible universe, but all that he can conceive of nature's immensity in the womb of this abridged atom. Let him see therein an infinity of universes, each of which has its firmament, its planets, its earth, in the same proportion as in the visible world; in each earth animals, and in the last mites, in which he will find again all that the first had, finding still in these others the same thing without end and without cessation. Let him lose himself in wonders as amazing in their littleness as the others in their vastness. For who will not be astounded at the fact that our body, which a little while ago was imperceptible in the universe, itself imperceptible in the bosom of the whole, is now a colossus, a world, or rather a whole, in respect of the nothingness which we cannot reach? He who regards himself in this light will be afraid of himself, and observing himself sustained in the body given him by nature between those two abysses of the Infinite and Nothing, will tremble at the sight of these marvels; and I think that, as his curiosity changes into admiration, he will be more disposed to contemplate them in silence than to examine them with presumption.
For in fact what is man in nature? A Nothing in comparison with the Infinite, an All in comparison with the Nothing, a mean between nothing and everything. Since he is infinitely removed from comprehending the extremes, the end of things and their beginning are hopelessly hidden from him in an impenetrable secret, he is equally incapable of seeing the Nothing from which he was made, and the Infinite in which he is swallowed up.
If steady state gained favor that would be super fun, but this quote from the article seems to throw a little cold water on that.
> At the same time, she notes that yesterday’s disks are different than modern ones. “They’re not today's Milky Way,” she notes. “They're turbulent, they're messy, and we need to study them more.”
https://en.wikipedia.org/wiki/Steady-state_model