
Black Hole Evolution Traced Out with Loop Quantum Gravity - TsukiZombina
https://physics.aps.org/articles/v11/127
======
nabla9
If I understood the article correctly:

1\. Black hole gradually evaporates (Hawking radiation) until it's Plank size.

2\. Quantum transition and Plank star.

3\. White hole is formed and "the collapsed star is bouncing back".

I Always thought that black hole evaporating energy as Hawking radiation
contains all the energy that went into the black hole when the evaporation is
complete. This theory assumes that there is energy left.

How is the total energy that went in is distributed between the Hawking
radiation and the white hole that follows the evaporation?

Are all white holes equal in size and does Hawking radiation account for the
black hole size difference?

~~~
enkid
My understanding is the transition to a white hole exists instead of a
singularity at the interior of the black hole, and is therefore hidden by the
event horizon. When the event horizon shrinks to the Planck length, the white
hole is exposed.

~~~
nabla9
Yes, but the event horizon shrinks by emitting Hawking radiation, right?

When the white hole is exposed, what it looks like? Is it just hole in the
space that does not emit anything? Nothing exits (because Hawking radiation
already emitted all of the energy) and nothing can enter.

What is the radius of the white hole?

~~~
ianai
I think Roger Penrose’s explanation here is appropriate, but I don’t know if
the similarity between a black holes evaporation and the eventual entropy
death of the universe are similar enough:
[https://youtube.com/watch?v=z2_6h15UCMg](https://youtube.com/watch?v=z2_6h15UCMg).

If so, I think it would mean a Plankt scale black hole would have a
significant probability of spontaneously evolving a white hole?

~~~
nabla9
I just listened Sean Carrol's podcast interview wit Penrose and I think they
are different.
[https://www.preposterousuniverse.com/podcast/2019/01/07/epis...](https://www.preposterousuniverse.com/podcast/2019/01/07/episode-28-roger-
penrose-on-spacetime-consciousness-and-the-universe/)

In the loop quantum gravity there is a bounce because at the lowest level
spacetime is discrete and can't be compressed. The big bounce theory of
relating to big bang in the loop quantum theory might be similar to the black
hole/white hole theory.

In Penrose's theory it's the gravity/mass that is creating time and clumping
things together between the big bang and the heat death of the universe (you
need mass to create clock and time).

At the beginning of the universe temperature was so high that masses did not
matter, at the end of the universe there is no mass, just massless particles
(after googol or so when the biggest black holes have evaporated). Massless
particles (photon, gluon, graviton) don't experience time so they in a sense
fly into the the end of the eternity instantly.

Then there is something geometrical I don't understand and the ends meet and
the new universe matches the end of the previous across timeless eon.

Penrose thinks you could perceive the ripples caused by the massive black
holes from the last universe in the background radiation of our universe.

~~~
ianai
I think it’s like a duality or equivalence through asymptotic states. Ie old
universe becomes timeless energy and new univese.

~~~
nabla9
LQG and big bounce requires big bang and expansion being followed with
contraction of the universe ending with big crunch at the end.

Pernroses CCC (conformal cyclic cosmology) is a big bang followed by an
infinite future expansion and timelike infinity.

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SiempreViernes
Rovelli himself wrote this more popular account and didn't manage to state a
clear physical reason for the bounce, so the title is overstating the result.

I take this to be an interesting technical advance for a theory whose
relevance in general is still an open question.

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featherrust
Is there evidence for or against the interior of black holes being similar to
distinct separate universes? Is that a popular idea at all, in physicists'
circles?

How much (and _what_) would I need to read and understand to get a feeling of
the nature of black holes?

I'm a total layman when it comes to physics and it would put some distant
worries of me to rest.

I'd rather measure a lot of Hawking radiation while throwing bottles in flasks
into a black hole. However, I'm currently preoccupied with figuring out why my
mouth keeps talking when I'm not thinking of anything.

~~~
czbond
PBS Spacetime is a great series, and delves deep enough for interested layman
as well as practitioners to be interested. I find the videos really good. Here
is a link to one of many on black holes.
[https://www.youtube.com/watch?v=vNaEBbFbvcY](https://www.youtube.com/watch?v=vNaEBbFbvcY)

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foobar1962
My quick summary of white holes, which I thought were a product of science
fiction:

Predicted by some solutions to relativity.

They have not been observed yet but recent theories suggest that some burst of
gamma rays may be markers.

Other theories suggest that the expulsion of matter from a white hole may
occur very quickly, almost instantaneously, so unlike say a supernova you’d
need to be looking at the right place and the right time to see it happen.

White hole mass may be behind a horizion that makes them dark = dark matter.

Our Big Bang may have been a super-massive white hole event, so we are a
universe-within a universe.

~~~
featherrust
Has anyone tried sending information into black holes using lasers yet?

It'd be convenient if ET's only lived in black holes, although perhaps a
little lonely, too.

~~~
CGamesPlay
> The closest black hole we know of is V616 Monocerotis, also known as V616
> Mon. It's located about 3,000 light years away. [1]

So no, because we haven’t had lasers for 3000 years yet, and the black holes
we can create here on earth last for microseconds.

[1] [https://phys.org/news/2016-03-closest-black-
hole.html](https://phys.org/news/2016-03-closest-black-hole.html)

~~~
mokus
We can create black holes here in earth? I’d love to read more about that if
you have any starting points

~~~
CGamesPlay
Looks like it is only a theoretical possibility and only if we have more than
4 dimensions.

[https://en.m.wikipedia.org/wiki/Micro_black_hole](https://en.m.wikipedia.org/wiki/Micro_black_hole)

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melling
If you’re interested in black holes, Shep Doeleman’s efforts might be of
interest.

Taking a Photograph of a Black Hole

[https://youtu.be/RTKIZvDQ6Jk](https://youtu.be/RTKIZvDQ6Jk)

Einstein’s Shadow:

[https://www.amazon.com/Einsteins-Shadow-Black-Astronomers-
Un...](https://www.amazon.com/Einsteins-Shadow-Black-Astronomers-
Unseeable/dp/0062312022)

~~~
branislav
I also highly recommend this [1] episode of the Omega Tau podcast which
touches on black holes, holography and quantum gravity.

[1] [http://omegataupodcast.net/191-string-
theory/](http://omegataupodcast.net/191-string-theory/)

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beaner
One thing I never understood is, how does a black hole evaporate, even via
hawking radiation? Doesn't the matter it ejects just fall back in?

~~~
JabavuAdams
My limited understanding is that the Hawking radiation is caused by virtual
particle-antiparticle pairs spawning just outside the event horizon. The event
horizon is by definition the surface on or inside of which not even light can
escape. This seems to imply that outside the event horizon some non-zero mass
objects can still escape, if they're on a favourable trajectory. E.g. aimed
directly away from the event-horizon isosurface.

~~~
SomeHacker44
My layman's understanding mirrors this.

Because one part of a pair of virtual particles crosses the horizon, and the
other one does not, they become separated by said horizon and cannot recombine
and disappear. The particles become actual and not virtual, but one is lost to
the hole. Hence, it looks to the external world as if a particle was emitted
by the hole.

Note that to my (layman's) knowledge, this has not been actually observed, but
does seem to be a modern consensus and involved a paid bet.

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nyc111
Are Gray Holes next? When a White Hole and a Black Hole merge a Gray Hole will
emerge as predicted by the Chromatic Theory of General Relativity.

~~~
nyc111
I was wrong! Grey Holes have been invented already!
[http://adsabs.harvard.edu/full/1993AAS...182.5507B](http://adsabs.harvard.edu/full/1993AAS...182.5507B)

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acd
If white holes exist that are the inverse of black holes. The universe could
exist forever. Black holes would suck matter in and white wholes on the other
side would create new matter on the other side.

Black wholes and white holes would then be gateways to other universes.

Multi verse
[https://en.wikipedia.org/wiki/Multiverse](https://en.wikipedia.org/wiki/Multiverse)

[https://news.nationalgeographic.com/news/2010/04/100409-blac...](https://news.nationalgeographic.com/news/2010/04/100409-black-
holes-alternate-universe-multiverse-einstein-wormholes/)

[https://en.wikipedia.org/wiki/Wormhole](https://en.wikipedia.org/wiki/Wormhole)

