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from the did-it-never-happen,-or-was-it-unhappened? dept.
In the real world, your past uniquely determines your future. If a physicist knows how the universe starts out, she can calculate its future for all time and all space.
But a UC Berkeley mathematician has found some types of black holes in which this law breaks down. If someone were to venture into one of these relatively benign black holes, they could survive, but their past would be obliterated and they could have an infinite number of possible futures.
Such claims have been made in the past, and physicists have invoked "strong cosmic censorship" to explain it away. That is, something catastrophic -- typically a horrible death -- would prevent observers from actually entering a region of spacetime where their future was not uniquely determined. This principle, first proposed 40 years ago by physicist Roger Penrose, keeps sacrosanct an idea -- determinism -- key to any physical theory. That is, given the past and present, the physical laws of the universe do not allow more than one possible future.
But, says UC Berkeley postdoctoral fellow Peter Hintz, mathematical calculations show that for some specific types of black holes in a universe like ours, which is expanding at an accelerating rate, it is possible to survive the passage from a deterministic world into a non-deterministic black hole.
What life would be like in a space where the future was unpredictable is unclear. But the finding does not mean that Einstein's equations of general relativity, which so far perfectly describe the evolution of the cosmos, are wrong, said Hintz, a Clay Research Fellow.
Vitor Cardoso, João L. Costa, Kyriakos Destounis, Peter Hintz, Aron Jansen. Quasinormal Modes and Strong Cosmic Censorship. Physical Review Letters, 2018; 120 (3) DOI: 10.1103/PhysRevLett.120.031103
Source: http://news.berkeley.edu/2018/02/20/some-black-holes-erase-your-past/
(Score: 2) by FakeBeldin on Wednesday February 28 2018, @10:56AM (1 child)
Alexander Friedmann asked that question too! He even set about calculating possible answers using general relativity.
He found 3 models:
- One with a big crunch, where the universe first expands but then recollapses
- One with the expansion ever ongoing
- One with the expansion ever slowing down, but never stopping.
(Note that if the expansion ever stopped, gravity would ensure that things would contract, leading to the first model).
The difference between these being the amount of matter in the universe (which encompasses its average density).
Physicists have been on the hunt to find which of these models best describes the universe. Turns out the amount of visible matter is *very* low. it's a few percent of what would be needed. Actually, it turned out to be so low it couldn't even account for the observed structure of the universe. We saw that that the universe contained gravitational structures (stellar systems, galaxies, clusters, super clusters, mega-super-duper clusters and more), but the amount of observable matter in these structures was not sufficient to explain the gravitational bindings.
Hence physicists proposed "dark matter" - there has to be something causing a gravitational effect, but we're not seeing it.
Skipping over other inconsistencies in observations (leading to "dark energy"), we get a very interesting observation:
It seems that the universe is actually expanding faster and faster [wikipedia.org]. (Seriously, wrap your head around that one!)
At any rate, that acceleration has to be caused by something. So what we right now know, is that the average density of the universe is not the only factor involved.
(Score: 2) by HiThere on Wednesday February 28 2018, @06:59PM
Well, if it were rotating quickly enough, then gravity wouldn't necessarily make it collapse. But the question of "rotating with respect to *what*" sort of boggles the mind. And *if* it were the inside of a black hole, the answer would be "rotating with respect to the outside stuff", but does that even make any sense when there's no possibility of communication?
Still, presuming it's a black hole, formed through and accretion disk, then it *must* be rotating, or a conservation law is broken. So it *could* be rotating fast enough to expand, since stuff enters the universe at about light speed WRT the external universe. And I guess it could be pumped up by increasing matter falling in (at about light speed). Now clearly this would imply that the spacial dimensions of the inside of the black hole were decoupled from those of the outside, and the relative speeds might imply that matter transformed into energy during the in-fall and made virtual particles become real within the interior. I can't really wrap my head around the way space twists at the edge of a black hole, but it might mean that the entire interior of the black hole was equally in contact with the exterior. Otherwise the infalling matter would necessarily happen at the edges, i.e. outside our light cone, where it could neither be observer, nor presumably affect us (though perhaps it could affect space strains which we could perceive as either dark mass or dark energy).
This is all playing around with words, because the math is totally beyond me, but the words seem to sort of make sense. So dark energy would be infalling matter converting into energy as it fell in, and dark mass would be some of that energy causing virtual particles to become real. I've no idea whether this is reasonable or not, of course. But none of the other explanations seem to make sense either. It does seem to require either increasingly smaller universes, or that particle size be defined only within the universe within which they exist. If this scenario is correct, then black holes actually do lead to another universe, but there's no apparent method to either survive the transition or to communicate back if you do. (it seems to require being converted into energy, possibly space strains, during the entry process.)
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