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The Return of a Small Universe?
- zoklet-enjoyer 3y agoJust thinking about this gets me on the verge of a panic attack.
- eru 3y agoDon't dwell on the heat death of the universe for too long, either, then.
- A_D_E_P_T 3y agoI wouldn't worry about it. The heat death of the universe isn't the end. The Second Law is a statistical, not an absolute, law. So, even after heat death, structures of all sizes will randomly emerge on large enough timescales. (Read: effectively infinite timescales -- timescales large enough to make Graham's Number look like a small number.) Wait long enough, and you'll get Boltzmann Brains, Boltzmann planets, and even Boltzmann galaxies. All sorts of things. In many respects, the universe after heat death is more interesting than the universe before heat death --- it's an unbound infinite probability space.
- im3w1l 3y agoI agree about the second law, but aren't there also other reasons to expect gloom and doom? Like an ever decreasing energy/mass density as everything drifts away into infinity? I dont think thats a question of probabilities but rather something that must happen based on the equations of motion?
- A_D_E_P_T 3y agoEntropy is a measure of the number of possible states. In unbounded/infinite time, all states will be cycled through. However diffuse, all particles in space will be akin to H2O molecules in an ocean of water: they will move freely, interacting with each other, each assuming any number of positions. In an idealized ocean in boundless time, every H2O molecule will occupy every possible position, and then every possible configuration will repeat. Post heat-death, the number of possible states that describe maximally (or near-maximally) disordered and diffuse systems is almost -- but not quite -- infinitely larger than the number of possible states which describe structures of some sort, indeed of any possible sort, emerging. That "not quite" does a lot of work, in view of unending time. So, in boundless space, in boundless time, should protons and other elementary particles not decay, very interesting things will still come into existence with some degree of statistical regularity.
- im3w1l 3y ago> all states will be cycled through That's only true if there are finitely many states.
- eru 3y agoNot sure. You can cycle through all integers an infinite number of times each, if you have infinite amount of time. An example in Python: import itertools for limit in itertools.count(): for i in range(limit): print(i)
- 1970-01-01 3y agoIt's simply not possible to prove the universe is infinite, unless of course you have infinite time on your schedule.
- postalrat 3y agoWhat can you prove is infinite without defining it as infinite?
- AnimalMuppet 3y agoThe rational numbers.
- tshaddox 3y agoI was gonna say prime numbers.
- quickthrower2 3y agoGood one. You could argue they are defined as infinite though because the proof that there are infinitely many is not hard. If there are finite, multiply them all and add one. This number is prime. QED
- lovecg 3y agoOn that topic, this is a very common misconception about how that proof works. Multiplying all the primes and adding one does not have to be a prime (just try 2 x 3 x … x 13 + 1) - the point is it’s not divisible by any of the supposedly finite number of primes, so it must have some other prime divisor.
- quickthrower2 3y agoThanks I worded it wrong! You are correct.
- nathan_compton 3y agoI'm suspicious of any physics result which places the observable consequences _just_ outside of what we can actually observe.
- nine_k 3y agoI'd say that the Universe is effectively unbounded if it's flat for, say, 1 GLY around us. We will not observe any difference for a billion years, and that's enough time for us to improve our science and technology and find a way to "look" further.
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- MarkusQ 3y agoThat blog feels like it's from a small universe -- a narrow ribbon of text, surrounded by great voids. It would be fine, I suppose, even praiseworthy, if we were still reading on paper, as it would provide ample space for any marvelous proofs we might contrive. But on a blog page? Why?!
- Georgelemental 3y agoI like it—my eyes don't need to move as much to jump to the next line.
- SoftTalker 3y agoYeah I hit reader mode pretty quickly on this one.
- datameta 3y agoSurely we could have selected a better adjective than "small" to describe something that is 93 billion light years across at the lower bound?
- awb 3y agoRelatively to infinity, it’s small.
- datameta 3y agoAh, alright, from this point of view it makes sense.
- BurningFrog 3y ago"Finite" would be a better word for that.
- cwsx 3y agoRelative to infinity, anything finite is small. I agree with OP, if anything it should be "finite universe".
- Tao3300 3y agosmol
- fnordpiglet 3y agoI felt like the blog post got cut off. It felt like it was leading up to some statement, as they outlined how a small curved universe would be identified through patterns etc etc, even link a paper they wrote on it…… then…… nothing. Did I miss something crucial in the reading? Edit: Reading the paper they found correlations indicative of a non flat space but could be explained by other factors and noise. So it wasn’t conclusive but left open the door for curved space and a small universe.
- sigmoid10 3y ago>Reading the paper they found correlations indicative of a non flat space but could be explained by other factors and noise. The paper doesn't question the flatness of space. In fact it uses it as a constraint for its models, because there is extremely strong observational evidence that our universe is globally flat (which is actually its own mystery, since the universe contains energy and energy curves space). What the paper suggests is that if inflation (i.e. the first moments after the big bang) happened in a specific way that is consistent with current experimental data, the universe might be much smaller than previously thought. If it actually is finite and below a certain size, we could even detect it using upcoming observations from large scale structure surveys.
- _hypx_ 3y agoInflation "smooths out" the curves in space-time by stretching space out in an exponential manner. So any curves get flattened until the universe is effectively flat. An inflation-like theory that doesn't stretch space out that much leads to its own mysteries.
- fnordpiglet 3y agoThanks both - IANAP so I appreciate the guide. However, if as he asserts this can be studied and verified, have we really not done that?
- sigmoid10 3y ago
- transfire 3y agoBut it would be the back for your head approximately 13 billion years ago. That’s a rather old head.
- zyang 3y agoFrom a layman that enjoys scifi, I always thought universe appears to be infinite because we are in a lower dimension. Gravity is a product of interaction between parallel 3D universes. And dark matter is just matter from other universes. Is there any basis to this theory or am I over simplifying it.
- fallingfrog 3y agoThat’s a bit too vague to really say whether there’s anything to it. I think you would want to study physics and try to make your ideas more precise.
- ulizzle 3y agoThe universe is expanding not infinite. The weird part is the question is expanding into what or where. There’s not actually any proof for multiverses, that’s a hypothetical, related to the whole sims theory. Not saying that could not be true but there’s more proof that this isn’t the first or the last universe than there are other universes.
- atq2119 3y ago> The weird part is the question is expanding into what or where. Why would there have to be an "into"? It seems like the most parsimonious expansion is that there isn't one. My limited understanding of the math is also that that's what the math says.
- ulizzle 3y agoThat’s the whole controversy of the cosmological constant that this paper brings up. The math squares up in theory but observational data is way off. The universe being small and it’s expansion just a mirage is one attempt to square the data and theory. I’m not an expert so I don’t have any answers or anything. I just went into this rabbit hole recently when I got sick recently.
- akomtu 3y ago"lower dimension" in what sense?
- ezconnect 3y agoWhat I still can't understand is what is our universe sitting on.
- Tao3300 3y agoIt's turtles all the way down.
- ulizzle 3y agoWe don’t assume it’s infinite, we assume it’s expanding. That’s the reason why there is supposed to be an end to the universe, I.e: the Big Bang and the Big Crunch As for physical distance, that’s very large. Relativity is about time not space.
- eru 3y agoIt's not actually clear that the Big Bang was the absolute beginning. There could have been things before. These days, I hear much more talk about 'inflation' than about the big bang. The Big Crunch is currently seen as unlikely: the (observable) universe doesn't have enough matter to slow expansion and pull back together, expansion even seems to be accelerating. > Relativity is about time not space. Isn't it about both?
- gpderetta 3y agoThe current consensus is that the universe is indeed infinite. The fact that it is also expanding is not a contradiction .
- mr_mitm 3y agoWe don't assume either. We assume the universe is homogeneous and isotropic and that GR describes the world. Expansion follows from that and some observations. Finiteness is currently undetermined. It could be infinite, but it could also just be finite and really really big.
- cat_plus_plus 3y agoMy money is on living in a simulation with lazy evaluation and constraints like maximum speed to prevent us from consuming too many resources. Intelligent species seem to love making simulations, so what are the chances we happen to be the first one outside of any?
- rvba 3y agoThe question is: can we escape the simulation? Like some programs escape a virtual machine by escalating priviledges.
- danbruc 3y agoYou can not even determine that you are in a simulation if the simulator does not want you to know.
- rvba 3y agoUnless there are bugs? I read that the computer game Eve online (never played it) slows down when there are big battles with many players. Sounds a lot like black holes. Time slows there down too - too many calculations? Planck time is the tick rate of the universe? Can pauses happen?
- danbruc 3y agoNo. Because you have never seen a universe of which you are sure that it was a real universe, so you do not know how a real universe behaves, so you can not determine whether our universe behaves differently than a real universe. You are just postulating without justification that in a real universe time progresses uniformly and then conclude that our universe is not real because time does not progress uniformly. As I said in a different comment, even if the stars in the Milky Way suddenly rearranged themselves to spell out »You are in a simulation.« on the night sky, you could not tell for sure whether this is a message from the simulators in the outer universe or whether this is just some weird behavior arising from the laws of physics in a real universe.
- eru 3y agoThe blog post is actually a lot more interesting than much of the discussion here. The author knows perfectly well that the observable universe is finite. So the question is about sensible models for what happens beyond.
- optimalsolver 3y agoIf it's unobservable in principle, then it's beyond the realm of science. Any such "models" would be philosophy.
- aydyn 3y agoUnobservable is not the same as unknowable. For example, the form of the universe beyond what can be observed could correlate with a testable hypothesis in the observed universe.
- wholinator2 3y agoI think the idea is that it could but it would be impossible to know that. It can be fun to speculate but by definition it is impossible to know. It's not just that light can't get in at us, it's that literally the idea of causality cannot travel fast enoigh to reach us. I believe our light cone will keep expanding slightly before accelerated expansion takes over and starts reducing it but that timescale will far far outlive us humans. As it stands right now there is an impenetrable barrier. All of our modern theories and technology for astrophysics and cosmology emerged recently. We haven't know about the big bang for 100 years even. I think it's highly likely that our views on these things will change. For all we know we could be inside a hyperbig black hole inside some much larger universe. We can make models that fit what we're able to see and then use those to extrapolate the things we cannot. But we cannot see what we cannot see. By the way, to me, "unobservable is not unknowable", sounds pretty philosophy to me. All of the physics we cannot observe, we currently cannot explain. Maybe some day with some great minds leap nobody saw coming, maybe hundreds of those, but everything i not of that cannot be observed cannot be known certainly. There must be some interaction, whether we're seeing gravitational waves, light, high energy particles doesn't matter, they still all travel at the speed of light and will be outpaced by expansion at some point.