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

tom.stoer

marcus, there's a big difference, even fapp!

The singularity is at the center whereas the geometry extends to infinity; this geometry is identical (!!!) for all objects of the same mass M, angular momentum J and charge Q, regardless if they are black holes, stars or planets.

marcus

That is what I believe, and that is what I understood Jim to be saying, the whatever-it-is at the center (that takes the place of the classical singularity) has the same mass and the same effect on the geometry, which of course extends from center out to infinity. Perhaps I misunderstood Jim's casual remark? AFAICS you and he are saying the same (obvious) thing. But this seems like a big fuss over nothing, let's move on.

marcus

BTW some nice news related to BHs! In a couple of hours Eugenio Bianchi will be giving a LQG talk over at the Physics building here at UC Berkeley!

The title is Black Hole Entropy and the Shape of the Horizon.

It's an hour talk preceded by tea, should be fun, and a chance to talk with other Berkeley people interested in quantum gravity.

Bianchi was formerly at Marseille in Rovelli's group, and is now at Perimeter Institute in Canada. He's just visiting here for a few days.

jimgraber

Sorry to be such a late slow poster, but it has been a busy week at home and work.

Also, I do not claim to be any kind of expert on either ST or LQG.

The LQG part, in particular, is based on a very preliminary scan of the Modesto et al recent work, which Marcus just pointed out. (I am sorry I missed this the first time around.)

Yes, one thing I meant was that any large (even stellar mass) black hole in the new theory looks almost exactly the same (both inside and outside the event horizon) as the classical Schwarzschild black hole. Or also a ST black hole for that matter. At any scale above a few tens of Planck lengths, space looks classical despite being actually composed of strings or loops.
This is different from the fuzzball model of Mathur where things get all fuzzy right inside the event horizon, or the much older model of Yilmaz which was respected and professional studied when it was first proposed, but is now both mostly forgotten and not much appreciated. The Yilmaz model predicts a 20 to 30 % variation from Schwarzschild at the event horizon for black holes of all sizes. (A variation this big would probably be detected by LISA, but probably not LIGO.)

The second thing I meant is that from a distance (macro scale) the geometrical part of the Modesto type LQG self dual black hole, a Planck scale wormhole with a twist, the geometrical view of the ST black hole consisting of many overlapping strings (or high winding number) and the geometrical view of the classical singularity or infinitely dense mass point, all look pretty much the same. (In particular, they all trap mass in a very small space, if you ignore the other side of the wormhole, and outside this nearly pointlike region, space(time) remains smooth and empty and very well approximated by Schwarzschild.) From a micro scale structure viewpoint these three quasi-singularities are very different and the Hawking-like radiation predictions are different as are the associated lifetimes and temperatures. I think that the ST predictions and the Hawking semi-quantum or semi-classical predictions agree, which is regarded as a good thing by the ST people. But I think I have seen several different nonthermal discrete spectrum predictions associated at least loosely with LQG. I will try to look these up when I have time.

In addition Modesto et al make the very interesting prediction of black holes with masses much smaller than the Planck mass. My first reaction is skepticism, but it seems to be a very direct consequence of their r goes to (1/r) duality. (I am skeptical not about the math, but about the existence of these objects.)

However, my main point is that all these fine points are hidden or unimportant at the macro level, and so the new BIG black holes look very much like the old BIG black holes, unlike the really small ones (Planck scale) which are very different. I am at least a little bit disappointed by this.

Thanks for the comments and further information.

John232

I don't think anything has been accepted among the scientific community of what really exist inside of a black hole. I have read pure energy a few times, in explanations of what happens when a black hole create a white hole (in old books), but white holes have not been found. I don't think they could be made of matter since the density of suppermassive black holes can be really low (close to 1). My hypothesis is that matter would have to be broken down into energy in order to maintain these low densities, and the concentrated energy itself would need to bend spacetime. I don't think it is too far fetched since energy itself is affected by spacetime curvature and has zero rest mass but it would be moveing, it is just that the amount is too small to be detected. That could be why we don't see white holes, the curvature created by energy itself wouldn't be enough to peirce through space to another location.

John232

The amount of matter to energy conversion could be dependant on the size of the black hole. A smaller black hole could have more matter and a black hole with a large radius could have more energy. But with the lack of a definitive quantum gravity there would be no way to know for sure on how much matter or energy a black hole would contain.

John232

Then again, if time stops at the event horizon when would an object find itself at the center of a black hole?

Bernie G

If a quark/radiation star existed in a black hole, and was supported by radiation pressure, would gravity in the star be newtonian or relativistic? (Gravity outside the star would be obviously relativistic.)

John232

I don't get what you mean by the gravity being newtonian. I would hope not since relativity is supposed to describe gravity more accurately than newtonian physics.

John232

I think that, as the exit velocity became greater than the speed of light, it may become farther from being general relativity, than general relativity is from newtoinion physics outside of the black hole, IIF the exit velocity being greater than the speed of light allowed objects in the black hole to travel FTL. Tachyon's have not really been proven to not exist, so then it would look more like tachyon particle physics.

Bernie G

Relativistic gravity is where space or the path of light is significantly curved. If you had a situation where radiation pressure was strong enough to counteract gravity, wouldn’t the path of light be random 3-axis thermal motion instead of a curved line?