Register to reply

If no singularity, what’s inside a big black hole?

by jimgraber
Tags: black, hole, inside, singularity, what’s
Share this thread:
Bernie G
#73
Sep13-11, 01:01 PM
P: 136
The above post should have read: "Not necessarily that hard to observe."
suprised
#74
Sep13-11, 01:29 PM
P: 407
Quote Quote by Bernie G View Post
The above post should have read: "Not necessarily that hard to observe."
Well you talked about _inside_ the event horizon... that's per def unobservable!
Bernie G
#75
Sep13-11, 01:42 PM
P: 136
"Well you talked about _inside_ the event horizon... that's per def unobservable!"

Not when 2 small black holes merge. At the merger location the effect of gravity is cancelled out.
Constantin
#76
Sep13-11, 01:42 PM
P: 95
What cannot be observed does not exist.
For any observer outside the event horizon, there's nothing inside a black hole. The infalling matter remains frozen near the event horizon.

Discussions about the interior of black holes, observers inside a black hole, or observers falling into a black hole and passing through the event horizon, are just pleasant mind games.
Bernie G
#77
Sep13-11, 01:54 PM
P: 136
"For any observer outside the event horizon, there's nothing inside a black hole. Discussions about the interior of black holes ...... are just pleasant mind games."

Not so. If black holes merge, the gravity situation at the merger location changes dramatically. Are you saying small black holes don't merge?
suprised
#78
Sep13-11, 02:22 PM
P: 407
I don't think that anything concrete is known about what happens quantum mechanically if 2 holes merge. It is not even known what precisely happens if two particles collide with sufficient energy as to form a black hole. As said, non-perturbative quantum gravity is relevant there, and AFIAK so far no existing formalis is able to capture that and eg compute the S-matrix.

And computing such an S-Matrix (say of formation and subsequent evaporation of a bh) is certainly not a mind game but of highest conceptional importance. Because eg violation of unitarity would, by virtual black hole loops, trickle down to low energies.
Constantin
#79
Sep13-11, 02:26 PM
P: 95
I'm sure black holes do merge, but I don't think any information from inside the event horizon can escape during the merger, nor during any other event.

The explanations given by PAllen in his posts in this thread are quite interesting:
http://www.physicsforums.com/showthread.php?t=526367

They shed light on the behavior of the event horizon during a merger.
Bernie G
#80
Sep13-11, 03:19 PM
P: 136
Yes. About BH mergers that thread says: "Thus whatever the details are at the point of collision are, they will quickly be shrouded behind the horizon." Yes. But if something exists inside a BH with 75% of the Schwarzchild radius, there will be a lot of stuff escaping during "quickly", perhaps roughly one solar mass of ejected radiation (for 2 merging 8 solar mass black holes). Thats quite an ejection.
atyy
#81
Sep13-11, 06:00 PM
Sci Advisor
P: 8,802
Quote Quote by suprised View Post
I guess, though this seems controversial, that the infalling observer experiences a coherent superposition of fuzzball states to the effect that he notices nothing particular at the horizon. I understand, though, that he infalling observer problem seems to be the weakest point in this proposal.
I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?

And the event horizon somehow appears by coarse graining to a macroscopic outside observer?

I'd also be interested in knowing whether Takayanagi and Ugajin's ideas are consistent with fuzzball ideas.
tom.stoer
#82
Sep14-11, 12:02 AM
Sci Advisor
P: 5,464
Quote Quote by atyy View Post
I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?
What do you mean by that?

What is so special about event horizons? Classically black hole event horizons are nothing else but lightlike, closed, non-expanding 2-surfaces. The reason why a classical observer feels nothing special when crossing the horizon is simply due to the fact that the difference between an arbitrary lightlike surface and an event horizon cannot be defined locally. There are infinitly many lightlike surfaces the observer can cross. What's special about the horizon is that its closed and non-expanding. But the infalling observer can't detect that b/c it's a global property.

Does such a classical geometry emerge from fuzzballs?
suprised
#83
Sep14-11, 02:05 AM
P: 407
Quote Quote by atyy View Post
I guess in the fuzzball proposal, the microscopic state is that there is actually no event horizon?
Right - the fuzzball microstates do not have horizons.

Incidentally, the fuzzball states really "require" the full compactified 10-dim (or corresponding non-geometric notion) string degrees of freedom. We knew that from state counting before, what is new here is the actual explicit construction of those microstates. And one really needs precisely all of those in order for this mechanism to work. This is a remark to those who believe that this problem can be solved from within pure gravity....

Quote Quote by atyy View Post
And the event horizon somehow appears by coarse graining to a macroscopic outside observer?
This is what is claimed.

Quote Quote by atyy View Post
I'd also be interested in knowing whether Takayanagi and Ugajin's ideas are consistent with fuzzball ideas.
No idea...
Physics Monkey
#84
Sep14-11, 06:31 AM
Sci Advisor
HW Helper
Physics Monkey's Avatar
P: 1,334
I'm curious about the relationship, if there is one, between fuzzballs and black hole complementarity. I have favored the idea of complementarity for some time, but was never able to understand very completely how it relates to fuzzballs.

On a related note and in the spirit of complementarity, I have always found the nice slices used e.g. in Mathur's discussion to be rather disturbing since they include regions behind the horizon. This seems manifestly wrong to me.
Bernie G
#85
Sep16-11, 08:27 PM
P: 136
Correction: Previously I said there may be some BHs with 10^12 solar masses. This is roughly 10X the mass of the Milky Way, not 1000X.
tom.stoer
#86
Sep17-11, 01:30 AM
Sci Advisor
P: 5,464
Quote Quote by suprised View Post
This is a remark to those who believe that this problem can be solved from within pure gravity....
There is a proposal for black holes in LQG which defines horizons in terms of spin networks, i.e. with pure gravity ...
suprised
#87
Sep17-11, 02:53 AM
P: 407
Quote Quote by tom.stoer View Post
There is a proposal for black holes in LQG which defines horizons in terms of spin networks, i.e. with pure gravity ...
And how do they get the necessary states? Quite a few people doubt that it could ever work.
tom.stoer
#88
Sep18-11, 02:26 AM
Sci Advisor
P: 5,464
They count spin network states forming the classical horizon area. The result reprocudes the Bekenstein-Hawking-entropy plus corrections. I bet marcus has a list of publications.
suprised
#89
Sep18-11, 02:53 AM
P: 407
Quote Quote by tom.stoer View Post
They count spin network states forming the classical horizon area. The result reprocudes the Bekenstein-Hawking-entropy plus corrections. I bet marcus has a list of publications.
AFAIK up to an arbitrary factor, which means that the result is meaningless?
tom.stoer
#90
Sep18-11, 05:42 AM
Sci Advisor
P: 5,464
Quote Quote by suprised View Post
AFAIK up to an arbitrary factor, which means that the result is meaningless?
What is the proton mass according to string theory? Up to how many arbitrary factors?

So let's continue seriously? or polemically?


Register to reply

Related Discussions
What's inside a black hole? Special & General Relativity 26
Black hole inside a larger black hole. Cosmology 33
Singularity of a black hole Special & General Relativity 0
Singularity of a black hole Astronomy & Astrophysics 1
Discernment , duality and perception ,singularity (not black hole) General Discussion 4