Black holes might end their lives by transforming into their exact opposite
nature.com
nature.com
As @jerf points out here as well, LCG has as much experimental support as any of the other competing GUT hypotheses... which is to say, none. This whole "thing" about the lack of experimental support and lack of testable / falsifiable assertions in physics (especially String Theory) is explored at length in two pretty interesting books: Not Even Wrong[1] by Peter Woit and The Trouble With Physics[2] by Lee Smolin.
[1]: http://www.amazon.com/Not-Even-Wrong-Failure-Physical/dp/046...
[2]: http://www.amazon.com/The-Trouble-With-Physics-Science/dp/06...
In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong. And yet neither one has ever made a prediction that has ever been falsified by experiment, so we have no guidance from nature regarding which theory is wrong or how. That's the reason that the theoretical physicists seem to be grasping at straws, and everyone is a little disappointed that the LHC hasn't done anything surprising.
The Higgs mechanism was one possible model which the standard model required, the others have now obviously been disproven thanks to the LHC. If no one had proposed this particular model, we'd still be wondering how fundamental particles gained mass and have another unexplained experimental result with the peak at 125 GeV from the data at the LHC.
Similarly, GR and QM are both extremely well tested, however GR has dark matter and energy to deal with, and we still have no real idea what that is. This could potentially point to GR being wrong, however none of us are able to come up with another theory of gravity that could incorporate this and be better than GR at this stage. If a theory of quantum gravity (or just gravity) came along that could explain dark matter quite effectively then it would be hailed as a better theory than GR.
The reason string theory and loop quantum gravity are considered completely speculative is because their predictions are so far beyond our grasp that even in the relatively far future we still have no way of confirming or denying either of them. Had they predicted things that could've been confirmed within the next century or so, I'm sure we'd all be rallying to try and confirm them. They aren't speculative so much so because we don't know which of GR or QM is wrong, but because their testability is quite precarious at this point.
nope. Incompatible are only stretches of the theories into the areas where conditions contradict basic assumptions of the theories.
QM assumes fixed space-time which we know isn't true, so the QM can be true only where the difference between fixed space-time and real one is negligeable, ie. small scale/local effects. (And even at the small scale, assumption of the fixed space-time may be very limiting - who knows, may be powerful forces at local level do "bad" things to space-time too and this would be an explanation for the things like non-separability of quarks or a for a lot of others "strange" effects observed at quantum level).
GR is about real, non-fixed space-time and disregards any forces/interactions other than gravitation. Thus it is not correct when applied at local scales where other interactions overpower gravitation.
Thus stretching GR into small scale just makes a wrong physical theory the same way as stretching QM into GR space makes for a wrong theory too.
They tend to be less glamorous than string theory or loop quantum gravity, though, and so they don't get as much attention.
I understand that the shrinking of the black hole will cease, if underlying space/time is discrete. And I understand that that will happen quickly from POV inside the black hole, and slowly outside.
What I don't get is why once the newly formed white hole begins to spit out stuff, it will continue to do so. Why won't gravity pull it together agian?
It will, but not fast enough. Basically, the theory (at least as I understand it) says that the "quantum bounce" reverses the collapse process, so a massive object collapsing very fast turns into a massive object expanding very fast. The expansion decelerates because of the gravity of the hole, but the deceleration is not enough to stop it from exploding outward and redistributing all the matter that collapsed back out into the universe.
In general, yes, the escape velocity would need to be overcome. But because it would need to be a quantum and general relativistic phenomenon, there are quantum and curved spacetime effects which make framing the problem as simply "escape velocity", a potentially problematic approach.
I glanced over the paper and I don't see anything that specifically addresses this, but I might be missing it, because I only skimmed, and I'm not particularly knowledgeable about physics.
If so, then maybe many other universes. Very weird to ponder.
the other "universes" are in a kind of different dimension, where each one has different laws of physics.
This theory is basically the end-all of just how insignificant we are, starting from the theory that earth was the center of the universe. Not only are we not the center of the universe, but our universe itself is an insignificant part of the whole.
However, I do seem to recall (some) black holes shoot a stream of particles from either pole (eg. an Astrophysical Jet (http://en.wikipedia.org/wiki/Astrophysical_jet). In that case, it's plausible that it doesn't take on additional mass and thus never reaches a maximum stress point, thus doesn't explode.
Of course there's another theory that they're dumping that matter elsewhere.. but who knows. I imagine much of what we currently believe will be disproved in the decades and centuries to come.
There is no compelling reason, neither theoretical nor observational, that black holes should have a maximum mass. In fact, we've observed some extraordinarily heavy black holes and so far no upper bound has become visible other than factors stemming from the amount of time active and the environment in their vicinity that allowed those holes to grow.
> However, I do seem to recall (some) black holes shoot a stream of particles from either pole
That happens whenever a lot of matter accretes around a source of gravity - a hot disk is formed and matter is accelerated out of the poles. It happens with heavy objects other than black holes as well. The ejected matter comes from the accreted stuff, not from the black hole itself.
> In that case, it's plausible that it doesn't take on additional mass and thus never reaches a maximum stress point, thus doesn't explode
No, only a small part of the accreted matter is ejected.
> Of course there's another theory that they're dumping that matter elsewhere..
There is no plausible theory at this point that suggests anything of that nature. Matter as we know it ceases to exist in a black hole, it becomes compressed in a way that its usual properties are lost - so much so that in fact, how and if information loss happens in a black hole is still a matter of debate and has led to some credible theories on how information and entropy might be preserved at the border to ordinary space.
There is also nothing to suggest that black holes are losing mass at any appreciable rate, other than possibly through Hawking radiation. Combined with the fact that the known cosmos does not exhibit any regions where measurable amounts of matter simply come into existence, the idea that opposite of every black hole is a white hole spewing out the stuff both ignores the fact that black holes get bigger by ingestion and the lack of any evidence for matter spewers.
Of course that does not prove it's not happening, but there is zero reason at the moment to believe this is going on. And that pertains to this article as well, the content being presented here is not supported by any evidence or current theoretical modeling.
Not that it matters from a practical perspective. Once the last stars have gone cold, that's pretty much as good a definition of "the end" as any other, and that will happen long before maximum entropy is reached.
There might not be a definite end state to the universe itself, but there are certainly some thresholds past which everything will become so boring that we may just as well consider them to be final.
[0]: http://en.wikipedia.org/wiki/Timeline_of_the_far_future
With expansion, and the fact that there are objects in space without a practical gravitational bounds, does that imply a form of finality which may inhibit the QM interactions that took place during the initial 'Big Bang'? I've been of the understanding for some time now that the 'Big Bang' could not have happened without the vacuous void which was to exist preceding it, is my understanding incorrect?
Yes, cosmology is hard.
Still, I find it interesting. Recently a hypothesis was floating around that after the universe reaches maximum entropy this would somehow reproduce the conditions where a quantum fluctuation could produce another universe. It's irrational on several levels to just postulate that without any concrete reason, and all the more astonishing since even if it were plausible, no living thing would be in existence at that point, and not even the building blocks of matter would "survive" such an event.
Even if the universe worked that way, there would be absolutely no reason to feel comforted by it.
I get that people are looking for cosmic harmony or maybe a sense of meaning when they postulate these cyclicalities, but in fact over superhuman time spans almost nothing in the universe is actually recurring. We're all just ephemeral patterns helplessly sliding down the big hill of entropy. Our universe is incompatible with the notion of permanence, even if it's introduced through the back door in the form of eternal cycles.
In the current understanding of jets from black holes, the jets originate from outside the black hole. So the jets are not reducing the mass of the black hole. The amount of material launched in a jet is smaller than the amount of material which falls into the black hole. So black holes with jets would gain mass, rather than losing mass or staying the same mass.
For the dumping matter part, they talk in the article of the hawking radiation, I think the astrophysical jet wouldn't reduce the mass of a black hole but only slow its rotation, as the matter haven't reached the event horizon it would not be considered part of it. Again, I'm no expert, so you shouldn't trust me.
Natural question: was the big bang a white hole?
The big bang theory describes the early moments in the Universe's expansion of space, not the projection of matter from a single point in space.