
Black holes might end their lives by transforming into their exact opposite - pps
http://www.nature.com/news/quantum-bounce-could-make-black-holes-explode-1.15573
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Oculus
The feeling I get from reading the article is the theory is highly
speculative. Could be just this line: " _‘loop quantum gravity’ — a
theoretical attempt that has yet to find experimental support_ "

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Argorak
Considering that the Higgs Boson was theorized about in 1964 and finally
proven in an experiment in 2012: this seems to be the way of theoretical
physics. ;)

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lisper
The difference is that the Higgs was a necessary logical consequence of the
Standard Model. Quantum loop gravity is purely speculative, much like string
theory.

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.

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trhway
>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

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.

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lisper
What you say is true, but it is also true that they are logically
incompatible. GR assumes that matter is precisely localized and QM assumes
that it is not. They can't both be right (and in fact we know that GR is wrong
about this). So, for example, GR predicts that the interior of a black hole
contains a singularity at a precise location, while QM (via the Heisenberg
uncertainty principle) says that this is impossible.

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frabcus
I don't quite get the article...

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?

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pdonis
_> 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.

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TheEzEzz
If the "bounce" is perfectly "elastic" then the explosion should not eject
matter fast enough to reach escape velocity from the local system. The
explosion would then collapses back onto itself into a black hole, and the
whole thing would repeat over and over. Kind of like the old theories of the
eternally recurring Big Crunch --> Big Bang.

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privong
The "bounce" is not a classical one, so the conceptual idea of a ball bouncing
or similar intuition could be very misleading.

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dpark
I'm can buy that the bounce it's not a classic bounce, but that doesn't answer
the parent comment. If the ejected matter has sufficient energy to reach
escape velocity, where does the additional energy come from? Does the theory
hypothesize that some of the matter is converted to energy?

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privong
I cannot speak to the theory. But, if one starts out with the classical
"bounce" intution, one then arrives at the escape velocity issue you and the
OP are noting. I was trying to point out that the escape velocity argument may
not be relevant, because of the assumption/intuition which went into framing
the problem, as stated by the OP.

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.

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dpark
I don't think QM or GR really change anything here. Matter and energy in must
equal matter and energy out. So if the "bounce" produces the same amount of
matter that went in, then it seems in general to lack the energy to reach
escape velocity. If some (significant?) amount of matter is converted to
energy, then maybe it works.

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.

~~~
privong
I think we are mostly agreeing with each other. I was not saying energy and
momentum conservation are no longer important. Rather, I was merely noting one
should use caution when trying to intuit how energy and momentum conservation
manifest themselves in non-classical systems such as was proposed in the
Nature article.

~~~
dpark
Agreed. :)

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ck2
I've heard the theory for years that the "big bang" was this event.

If so, then maybe many other universes. Very weird to ponder.

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beaner
Or maybe it's all one universe and the big bang was just a localized event
within it, but since we can't see that far away it seems like everything. (Not
a physicist, this idea may seem silly to the more well-versed in this topic.)

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sixQuarks
The book "The Mathematical Universe" is an interesting read. The author
theorizes that there are 4 types of infinite universes. The one we're in
contains an infinite number of "universes" that are so far away from each
other, that light hasn't had the chance to reach others. These universes all
abide by the same physics.

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.

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Tyrant505
Is this a new thought? Seems like natural thinking to me... Not an expert so
would love someone more knowledgeable to chime in.

~~~
walru
It does seem like natural thought - that at some point even a black hole
reaches it's maximum density.

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](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.

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Udo
_> It does seem like natural thought - that at some point even a black hole
reaches it's maximum density._

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.

~~~
Tyrant505
So will the universe eventually just have black holes?

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Udo
Not strictly speaking. Black holes are just ordinary gravity wells. They're
strong, and stuff falls into them, but they don't actively suck stuff in
anymore than planets or stars do. However, over very long time spans, orbiting
systems should lose energy by radiating gravitational waves. That means after
an inordinately long period of time, and after ejecting a lot of its mass,
each galaxy will likely end up just one big black hole. But there is always
stuff traveling through the universe that is not gravitationally bound to
anything, and since space itself is expanding, a lot of the matter in the
universe will just keep on drifting without ever colliding with anything ever
again.

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.

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serf
Is it no longer a valid concept that 'cold' universes are just another part of
a cyclical 'era' in our universe, awaiting the quantum interactions to start
the 'Big Bang' anew?

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?

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swombat
Your understanding is indeed incorrect. According to the big bang theory,
there is no vacuous void preceding the big bang. I know that it's hard to wrap
your head around that, but there is nothing before the big bang. Not even
time. Time itself begins with the big bang. The idea of "before the big bang"
has no meaning in the big bang theory as we understand it.

Yes, cosmology is hard.

~~~
Udo
I've been thinking about why this idea of cyclicality is so powerful and
persistent in the absence of any evidence, and it's probably not only inspired
by notions of "spirituality" but also because everything on Earth seems to be
cyclical during the normal course of human experience. Maybe we're tuned to
expect things to always work that way, even though not even the conditions on
our home planet are really cyclical when you look at longer time spans.

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.

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acd
Personally I believe black holes are our "real gods", they created us through
the opposite of sucking us in.

