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Why the Universe Didn't Become a Black Hole
StartsWithABang writes: With some 10^90 particles in the observable Universe, even stretched across 92 billion light-years today, the Universe is precariously close to recollapsing. How, then, is it possible that back in the early stages after the Big Bang, when all this matter-and-energy was concentrated within a region of space no bigger than our current Solar System, the Universe didn't collapse down to a black hole? Not only do we have the explanation, but we learn that even if the Universe did recollapse, we wouldn't get a black hole at all!
You can't use the Schwarzschild radius calculation for expanding space. The only kind of new part was the bit about not becoming a black hole if it should re-collapse.
Don't waste your vote! Vote for whoever you want, unless you live in a swing state it won't matter anyways
So does ./ have some kind of promotional relationship with startswithabang? If so you should disclose it.
The blog does have interesting material, and its appropriate for /., so its not like its bad that every article on there is making the /. front page. But its kind of odd that every article on there is making the ./ front page.
@de_machina
In related news, ants develop a religion around the question of why they have not been stepped on by an elephant.
Have gnu, will travel.
If at some point in the past the mass of the universe was in a volume wholly contained within its own Schwarzschild radius, why did the universe not become (or, more accurately, remain) a black hole?
"...Schwarzschild’s solution is a static one, meaning that the metric of space does not evolve as time progresses. But there are plenty of other solutions—de Sitter space, for one, and the Friedmann-Lemaître-Robertson-Walker metric, for another—that describe spacetimes that either expand or contract."
Literally everything else in the article was off-topic, and I can't help but feel this highly evasive 'answer' might have been "Ask Ethan" admitting he just didn't know.
Which is a pity because it is a fascinating question.
If you are going faster than light then you can escape from a black hole.
There is no part of physics that says speed has anything to do with escaping a black hole. If you could produce enough thrust to travel at just one meter per billion years, you could escape a black hole ... assuming you could keep that speed while inside the event horizon of the black hole. Unfortunately, from a mathematical perspective this appears to be impossible.
After a certain point (the event horizon) light simply bends two quickly back on itself to escape a black hole and stays inside the radius of the event horizon. It doesn't slow down, it changes directions, because space is all sorts of fubar inside the event horizon of a black hole.
What they've proved mathematically as that at the event horizon of a black hole the math fails. It falls apart and no longer makes any sense because the numbers get too large on one side of the equation.
In reality, this doesn't mean 'nothing can escape a black hole'. It means 'nothing we've observed can escape a black hole'. Well, except it can. Hawking radiation escapes a black hole as it evaporates, but all the explanations for why are just silly as they are pretty arbitrary compared to 'light' not escaping.
Another obvious but often overlooked theory is that our universe IS a black hole inside a larger universe. It explains a great many aspects that don't make sense ... but then it also introduces a whole bunch of aspects that don't make sense without making a bunch of assumptions about what is outside our universe, and these assumptions are so absurd from our view point that we just assume they are false.
The truth of the matter is ... science knows a lot less than they claim to about black holes, the big bang, and the nature of the universe. Many scientist treat theories with holes the size of the planet in them as obvious fact when they are no such thing. They have no fucking clue why the universe exists in the state it exists today, but many of them refuse to acknowledge that FACT to anyone. The good ones do. Einstein as an example, had no problem admitting his theories were nothing more than theories and that they were often wrong because they were simply based on the little bits of the universe we can observe.
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Wasn't there some conjecture some time ago that entropy decreased inside a black hole, and that our universe corresponded to a time-reversed version of a star collapsing into a black hole? Which of course would be interesting because the "arrow of time" would point two opposite ways in the "meta-universe".
If Pandora's box is destined to be opened, *I* want to be the one to open it.
Stop posting links to medium.com... the worst Science site I've ever seen short of timecube... wait, actually timecubes at least entertaining.
All of their articles boil down to:
Subject "Could *insert some inane scifi topic* really be??"
10 pages of images scraped from geocities homepages, font type and spacing worthy of a freshman English paper and then...
No, not really, but thanks for reading!
You want real science news? Here you go: http://phys.org/physics-news/
Can't you folks see it is just religion disguised as science, how it implies a divine hand?
No, you're thinking about the Divine Monkeyspank hypothesis, which is indeed religion, but not disguised as science.
p.s. - Your troll score is: 0
Sheesh, evil *and* a jerk. -- Jade
God is the fundamental reason for why the universe didn't became a black hole in the early stages after the Big Bang
I can stated with equal evidence and authority that the stray cat I almost ran over yesterday is the fundamental reason for why the universe didn't become a black hole in the early stages after the Big Bang.
Be glad I missed him.
Sheesh, evil *and* a jerk. -- Jade
"What they've proved mathematically as that at the event horizon of a black hole the math fails. It falls apart and no longer makes any sense because the numbers get too large on one side of the equation."
Not so. The maths dies at the singularity at the centre of the hole, but it doesn't at the event horizon except in a badly-chosen coordinate system. Alas, the usual coordinate system we'd present the Schwarzschild solution in is indeed badly-chosen and has an apparent singularity at the horizon, but this is not an actual singularity, as can be seen quickly by calculating a scalar curvature invariant - the Ricci scalar is the immediate choice, it's basically a 4d generalisation of the more-familiar Gaussian curvature - and seeing that it's entirely well-behaved except at the centre of the hole. So we look for a coordinate system well-behaved at the horizon and quickly come across Painleve-Gullstrand coordinates, in which spacetime is locally flat and perfectly behaved at the horizon. The implication is the poor sod wouldn't be able to tell that he'd got to the horizon, except through tidal forces (which depend on the size of the hole), and then he'd struggle to navigate before slamming into a singularity.
Even more confusingly, for a *realistic* hole, the insides are rather different. A Schwarzschild hole has a singularity inevitably in the future - all future-directed paths one can travel on, or light can travel on, end at the singularity. That's a bit of a bummer if you happen to be in a Schwarzschild hole. But a Schwarzschild hole is not physical; it is a non-rotating, uncharged hole, and that's not a realistic setup. In a charged (Reisser-Noerdstrom) or a rotating (Kerr) or, come to that, a charged rotating (Kerr-Newman) hole the singularity is "spacelike" -- there exist paths on which we could, in principle, travel, that avoid the singularity. In the case of a Kerr(-Newman) hole it's even smeared out into the edge of a disc. In reality, good luck navigating in there, but the singularity is not inevitably in the future in there.
A bit closer to the point, you're right that speed doesn't really have anything to do with it. Instead it's the type of path you can travel on, and where *they* go. An event horizon can be defined as the surface on which "null" geodesics, on which light travels, remain equidistant from the hole. If you travel, as massive particles do, on a "timelike" geodesic then you're fucked; you're never going to be able to accelerate enough that you even travel on a null geodesic, let alone a "spacelike" geodesic along which you can basically access anywhere. On a spacelike geodesic you could get out of a hole no problem. You could also travel in time, and you could break causality fifteen times before breakfast. I'd like to travel on a spacelike geodesic - it would be fun. Though managing to get back to a timelike geodesic might be significantly less so.
"Another obvious but often overlooked theory is that our universe IS a black hole inside a larger universe."
That's an extraordinarily strong statement. Our universe might be indistinguishable from a black hole from the outside, yes, but there's a big "might" in there, and an "outside" that doesn't necessarily make much sense either. It all depends on the setup you're assuming. Sure, we could end up finding that the universe is "inside" a black hole for a given definition of "universe", "inside" and "black hole", or we might find that that statement does not make any extent. I wouldn't want to say anything stronger than that, frankly, not least as I'm aware of models of cosmology that are observationally indistinguishable from a standard, infinitely-extended, flat universe, which are also flat, but which have finite extent. One way to do so is to simply put the universe into a toroidal topology. Since GR is a local theory it says nothing about topology, and it would be hard to argue that a universe extended on a torus would look like a black hole from the "outside", since that would be the entire extent of spacetime.
So to extrapolate from the TFA: The laws of physics do not exist in a vacuum...
There's a difference between 'a vacuum' and 'nothing'.
Sheesh, evil *and* a jerk. -- Jade
The speed of light is a limit on how fast you can accelerate something *in* space, but it's not a limit on how fast space can expand.
In fact you can't even state the rate of expansion of space as a velocity, because the velocity apparent as the speed of recession depends on how far away you're looking.
Sheesh, evil *and* a jerk. -- Jade
No point splitting hairs over what qualifies as "religion," but if this is the case, then there's more evidence for the Big Bang than for any other religion ever devised in the history of humanity, and that's saying something.
The evidence (which is nothing new, BTW) is amazing though. If the density of the universe were too low, or too high, we wouldn't have a universe to live in today. OK, that's not too odd - big crunch one way, big rip the other. What's astonishing is that the required density in the 1 ns universe to allow our universe to reach its current age must be correct to 24 significant digits.
Talk about fine tuning! One part in 10^24 higher or lower, and no universe today. That's about as anti-Copernican as you can get. Either we accept the "hand of god" in tuning the universe so precisely, or (far stupider IMO), we believe some silly anthropomorphic principle, or we simply accept that the physics is incomplete.
The last choice is of course where most working cosmologists are. There must be something we don't understand that explains why the early universe was necessarily so fine tuned - that it wasn't a happy accident, but could only be that way, or was very likely to be that way. Work on "inflationary" theories is a big part of the field these days, and this question is central to them.
There are a bunch of hypotheses that say, effectively, "the effect driving the early, very rapid inflation of the universe stopped, by it's very nature, at the point where the universe was exactly 'flat'". The dark energy seen driving expansion today is then explained as a different effect, incredibly weak by comparison.
Socialism: a lie told by totalitarians and believed by fools.
Either we accept the "hand of god" in tuning the universe so precisely, or (far stupider IMO), we believe some silly anthropomorphic principle, or we simply accept that the physics is incomplete.
While I agree the last explanation is probably the most likely one (a dampening effect that occurs at a certain point could be a plausible explanation), don't discount nr. 2: we just don't know (and we cannot know) how many universes are generated at any given point in time. Perhaps quantum fluctuations generate 1 billion "universe seeds" per cubic centimeter at any given second, and since they are random, most don't lead to another universe. Some do, and the ones that are "exactly right" give rise to universes like ours. Should we ever find a way to measure these things (not in the next decades, I think), we might find that option 2 is actually the real one. But I agree that option 3 is the most likely one.
Therefore, by the (faulty) logic you're using, you're just a cow with a keyboard - osu-neko (2604)
There's nothing wrong with the anthropic principle, it just can't be used as the explanation of what is happening. It is not a physical theory.
It simply states that, "the existence of the human inhabitable universe proves only that the existence of such a universe must be possible, because we are here to observe it." It's almost tautological.
It doesn't prove nor disprove deities, or the scientific method, or any theories derived therein. It is only useful for logically refuting the unproven assumption that our existence ipso facto assumes that the universe was designed specifically for us.
That said, it does not disprove the intelligent design theory either, it just points out that there do exist other explanations for the facts. So yeah, it's a valid point to make, but we still might be living in a big terrarium.