
Why Black Hole Interiors Grow Almost Forever - pavel_lishin
https://www.quantamagazine.org/why-black-hole-interiors-grow-forever-20181206/
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rabito
I wonder if the space region in the interior of a black hole expands the same
way as regular space around it.

If so, it would seem to be possible for a super massive black hole to be so
big that it would be impossible to actually reach the singularity. If there is
enough space the singularity would "move" faster than light. Essentially
another event horizon within the black hole protecting travelers from the
singularity.

This would lead to a stable universe like ours. Though about this a few days
ago and it seemed like an interesting idea.

~~~
comepradz
I remember from a youtube video that the spacetime inside the black hole
flipped around, where space becomes temporal dimension and time becomes
spatial dimension (i.e. time is traversable in either direction while the
singularity becomes an inevitable place in the "future").

~~~
rabito
That is true, the time and space axis gets flipped at the event horizon. This
also happens to a fast moving objects due to relativistic effects, although
the roatation is usually not very high unless you go really fast.
See[https://en.m.wikipedia.org/wiki/Minkowski_diagram](https://en.m.wikipedia.org/wiki/Minkowski_diagram)

However that doesn't mean you can't move when you cross the event horizon. You
can do that like usual (except for gravity pulling you inside. You can. It
only means outside observer won't be able to see what you're doing, because of
the time dilation (and the event horizon of course).

This kinda implies time and space are the same thing, it just depends on your
point of view. Still have to see about that :D

~~~
pdonis
_> the time and space axis gets flipped at the event horizon. This also
happens to a fast moving objects due to relativistic effects_

Neither of these things are true, and I have no idea how you are getting
either of them from the Wikipedia article you linked to. Penrose-Terrell
rotation, which affects how objects appear to observers when they are moving
at relativistic speeds relative to those observers, does not "flip" the time
or space axes; it's an optical effect due to the finite speed of light.

As I noted in another post upthread, the "flip" of time and space axes inside
a black hole's horizon is a property of a particular choice of coordinates,
not of spacetime itself.

 _> This kinda implies time and space are the same thing_

No, they aren't, because there is still a fundamental difference between
timelike and spacelike directions in spacetime. That is true regardless of how
you choose coordinate axes.

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grigjd3
People often mistakenly try to map space time onto an ether-like flat
background, treating spacetime like a drawing where the paper is the
background. It's not an uncommon kind of fumbling as someone tries to grasp
these things.

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mirimir
OK, so what experimental evidence supports the idea that the interior volume
of a black hole is growing? That is, what do we observe about black holes
that'd be different if interior volume _wasn 't_ growing? Or is this just a
consequence of current black hole theory, with no explicit experimental
support?

~~~
qubex
Nothing. The event horizon is an absolute limit on observability and literally
means “the threshold beyond which nothing ever happens”.

~~~
mirimir
Yes. But TFA is all about what's happening there. So (and I apologize, if this
seems rude) how is this different from talk about angels dancing on pins? Is
it just that, somehow, this became a discussion of mathematics?

I am, obviously, a hard-core experimentalist ;)

~~~
mannykannot
I don't know if this is what is going on here, but I get the impression that
these sort of discussions are ways to probe theories for inconsistencies. That
seemed more clearly the case in this recent commentary by Sabine Hossenfelder
on a paper invoking negative mass[1].

You don't have to experimentally observe a posited contradiction before
thinking about whether it really is one, and if so, how it might be resolved.
For one thing, you might find a way to investigate the issue experimentally.

[1] [http://backreaction.blogspot.com/2018/12/no-negative-
masses-...](http://backreaction.blogspot.com/2018/12/no-negative-masses-have-
not.html)

~~~
solotronics
Observing/measuring a quantum state affects it, I always wondered if thinking
about possibilities similarly could affect quantum mechanics.

~~~
mirimir
So what? Observing a black hole could affect it? But because of the event
horizon, we couldn't observe any such effect, right? I suppose that someone
could drop in to check. And maybe then _they 'd_ know.

But what about the rest of us? I gather that Hawking eventually agreed that
black holes preserve information, and could leak it (somehow, eventually).
Rajaniemi exploited the idea that information could be encoded in Hawking
radiation. But that's just SF, I think.

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m_mueller
Could this be the source of dark energy and lead to the realization that the
universe is a black hole interior?

~~~
2bitencryption
that would seem to explain the "big bang" :) an explosion from an infinitely
dense point that is ever-growing, which began in a higher-order universe as a
black hole that we now inhabit.

(of course I know nothing of science, this is all just pop-sci in my head, but
boy is it fun to think about)

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yaks_hairbrush
One very important difference between the big bang and the interior of the
black hole: Within the event horizon of a black hole, there is always a
singularity in your future. In our universe, that singularity is in our past.

One interpretation: the big bang theory describes a white hole -- the time-
reversed version of a black hole.

~~~
IggleSniggle
Imagine our universe is contained within a blackhole.

If time and space invert at the event horizon, could it be that the Big Bang
was the event horizon of our black hole, that we are forced forward through
time by the pull of our black hole interior, and that the expansion of the
universe is actually just metatime passing, and as we move through space we
are actually moving forward and back in metatime, with the expansion of our
universe being an expression of increasing constraints due to metatime’s
metaspace as we get closer to the center of our blackhole?

~~~
m_mueller
I could imagine that the “Big Rip” is what we experience when we
asymptotically approach the singularity. The strangeness of black holes could
mean that falling into a single point is actually experienced as space flying
apart faster than light.

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hn_throwaway_99
Can anyone perhaps explain a little better what is meant by the interior
volume of a black hole grows forever (while the surface area of the event
horizon stays relatively constant)? Felt like the article tried to touch on
that but I certainly didn't understand it.

~~~
stmfreak
Imagine a cone with a fixed diameter for the base. That represents the black
hole’s external event horizon. Now stretch the point of the cone away from the
base... forever, as the singularity warps space time more and more. The volume
of the cone (inside the event horizon) will grow as the point moves further
away from the base.

~~~
pdonis
Can you give a reference to a paper that describes the math behind this?

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raattgift
Neglecting evaporation, it's a lot closer to Yen Chin Ong's results (and those
he cites, especially Christodoulou and Rovelli [2]) than most of the comments
throughout this discussion, in that with a careful choice of time coordinate a
spacelike spherical sector of a Schwarzschild black hole could evolve roughly
similarly.

Of course, one has enormous freedom to choose spacelike hypersurfaces through
a Schwarzschild black hole, so such a result is not especially interesting
without some sort of uniqueness proof for the idea, and I don't think that's
achievable. (cf [2]).

I'm also not sure this is what GP has in mind.

\- --

[1] [https://arxiv.org/abs/1503.08245](https://arxiv.org/abs/1503.08245) (§ 2)
(simpler overview: [https://www.kth.se/profile/ycong/page/the-interior-
volumes-o...](https://www.kth.se/profile/ycong/page/the-interior-volumes-of-
black-holes) )

[2] [https://arxiv.org/abs/1411.2854](https://arxiv.org/abs/1411.2854) (§ IV)

~~~
pdonis
Thanks for the references. The Rovelli paper seems to be the key one deriving
the claimed result. I have to say the result looks contrived to me: they are
constructing spacelike surfaces with increasing volume only by what I would
call severe gerrymandering. But that's probably off topic for this discussion.

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richardw
I've wondered if the increasing acceleration towards the center slows time
down for a particle. As speed tends towards that of light, time slows down and
space expands.

Is that vaguely in alignment with the actual models?

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cobbzilla
Armchair theoretical physics philosophizing— if complexity (~spacetime) inside
the black hole is growing at the fastest rate possible, where does all this
stuff _go_? It doesn’t stay within the black hole, instead it fuels dark
energy expansion throughout the universe, through some unknown process akin to
how oceanic subduction of tectonic plates recycles continental land through
mountain-building and volcanism. There is some mysterious “mantle” of the
universe where all this space gets tumbled and transformed into dark energy
expansion.

Possible? Or crackpot theory?

~~~
darckPlanck
More likely that there’s just _A LOT_ of room at Planck scales, once you
override the strong and weak nuclear forces, and the classic understanding of
subatomic equilibrium that permits electrons to grant atomic nuclei their
usual elbow room.

Consider our traditional model for the atom, according to quantum
electro/chromo-dynamics.

Now take all that extra space provided, and fill it to the brim with squished,
crushed star detritus.

It’s on the order of pinheads to football stadiums. What if you filled up a
cubic football field with pinheads snipped off the top of a pin?

Now, not just the field, but the whole stadium, including the cheap seats.
Fill all the seats with pure atomic nuclei the size of a head of a pin, and
nothing else.

Take a single helium atom, and use that normal volume as a pre-defined
knapsack to stuff more matter into.

Now take the mass of as many helium atoms as you can get your hands on, and
fill up the volume of that first helium atom with the mass of its peers, until
every last planck length is retaining its full quantity of potential mass.

Furthermore, I’m thinking it’s likely that black holes are so extreme that you
get a runaway crush that overrides the normal volume of all the usual protons,
electrons and neutrons, to get degenerate quark soup.

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

~~~
cobbzilla
I’m not talking about the matter within the black hole, but the spacetime
itself that is constantly “flowing” into the hole and getting stretched
infinitely towards the singularity.

What if, before reaching the singularity, which is perhaps not possible, the
spacetime is “shredded” into Planck-scale entities, which populate an
invisible “backplane” that coexists with the visible universe (outside of
black holes). the energy of this backplane somehow “pushes” dark energy to
expand space everywhere in the universe.

~~~
darckPlanck

      invisible backplane
    

Sounds like romanticized wish fulfillment. You want it to be true, so maybe it
is?

On the one hand, we know there’s lots of spare empty space within an ordinary
atom. We can take a known fact and build on that fact, to inform ourselves of
possible details for observed phenomenon. The volume and behavior of
degenerate matter represents hypothetical concepts that could be tested.

On the other hand, we have unknown unknowns and maybe we can hijack these
blindspots and stuff ideas we like inside these cubby holes, even though
there’s no way to test for such possibilities, but let’s formulate an
untestable hypothesis because we think multiverses and wormholes and reality
simulations are cool?

~~~
cobbzilla
i said i was speculating for fun. if you don’t want to play, that’s fine.

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goombastic
Are we inside one of these things as well?

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quickthrower2
Yep, but the outer thing is a simulation running in a kubernetes cluster

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thefounder
Let's find a bug and get out this thing!

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sriku
We must be living inside a black hole.

~~~
quickthrower2
Help I'm trapped inside a universe factory!

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ineedasername
I wonder if the authors here are just making an obscure Dr. Who "bigger on the
inside" reference. Did they claim the exterior of the black hole, were it
visible, would resembles a blue box?

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sroussey
That’s pretty funny!

I think black holes convert matter to dark matter that leaks across the
universe in a different dimension. But my proof was a dream...

