# Holey War's far from over

1. Aug 1, 2008

### marcus

http://www.nature.com/nature/journal/v454/n7204/full/454579a.html

4. Aug 1, 2008

### marcus

Excellent! So this time the teaser actually includes the whole article! And yet they still invite us to pay #32 to get the whole article. It doesn't make sense but it's how it is.
Thanks for letting us know.

5. Aug 1, 2008

### yuiop

You do not need to pay the $32. The Preskill-Hawking bet is well documented on the internet (See http://www.google.co.uk/search?hl=en&safe=active&q=Preskill+hawking+bet&btnG=Search&meta= ) and hawking concedes he lost his bet that "Information can be lost forever in black holes" (possibly into other universes). In this article http://news.bbc.co.uk/1/hi/sci/tech/3913145.stm Hawking is quoted as saying "The black hole only appears to form but later opens up and releases information about what fell in, so we can be sure of the past and we can predict the future." (My emphasis) I wonder what hawking really meant by that last statement? It seams to agree with my personal (non conventional) view that blackholes of the type that have a singularity of infinite density never actually form in a finite time scale and that black holes are actually a hollow shell of matter asymptotically aproaching the event horizon. However the statement is somewhat anbiguous and can be interpreted a number of ways. Hawking outlined his new idea on blackhole's but Preskill's responce was "I'll be honest, I didn't understand the talk." A BBC program on the subject suggest Hawking had not really finalised his new concept of black holes so paying$32 will probably leave you none the wiser. "Deciding the matter is a task for a future generation of theoretical physicists." seems to confirm that.

6. Aug 27, 2008

### marcus

kev, you are referring to stuff I and others reported and discussed here at PF back in July 2004. The Dublin GR17 conference. Hawking conceding his bet to Preskill etc etc.

that is not what I meant to focus on in this thread, it is old news.

what I think has happened in the intervening 4 years is that the "baby universe" alternative has gotten a great deal clearer.

More people have been writing about it. There are more definite results. If you want you can search by author with names like Pullin, Vandersloot, Steve Hsu... I can't list them all.

The FQXi just gave a large 2-year grant to a trio of people aiming to look into this alternative (Alexander, Ashtekar, Bojowald). Two of those are big names in quantum gravity and the project description says they plan to involve other people as well.

So what we are seeing is some research momentum building up, aimed at overturning Hawking's conclusion. It is not that, like Preskill, people just don't understand Hawking's would-be "proof". People attending GR17 in 2004 expressed doubts about it at the time and no one has saluted since then as far as I know (unless you count Lenny Susskind claiming victory ) I don't just mean skepticism about what Hawking presented (and the later paper). what I mean is progress towards an actual solution that goes the other way---information actually going out of our section of the universe into another section.

This final paragraph of the review by Davies is just a straw in the wind, in effect recognizing what other researchers are doing.
http://www.nature.com/nature/journal/v454/n7204/full/454579a.html
Here is the key sentence in the review. I will highlight it:
allowing information to shift from one region of space-time into another disconnected one, perhaps from our Universe to a newly born 'baby universe'. Susskind dismisses this possibility, but the matter is far from resolved.

Last edited: Aug 27, 2008
7. Aug 27, 2008

### wolram

Last edited: Aug 27, 2008
8. Aug 27, 2008

### marcus

Wolram, I don't know any expert who thinks that BHs have singularities. I mean the BHs that actually exist in nature. Nobody I know of says they have singularities. Maybe one of our PF posters can correct me.

There is a separate question about General Relativity, the theory (not about Nature). Does GR have singularities? I think most people would agree that it does. But one can challenge this in some specific theoretical case. Say in the case of GR theoretical BHs. The thread you cited is George Jones' thread---you would best ask him what the consensus is about that recent challenge. Someone has claimed that with BHs in GR you don't get theory breakdown. Other people think you do get a BH singularity in GR. It's kind of academic.

In any case I assume that in nature, with a real black hole, you wouldn't get a singularity.

9. Aug 27, 2008

### wolram

I think the singularity is a boil on the bum for GR, the most tested theory, and a major hurdle for QG, if you can get rid of the big one why not the (smaller) ones.

10. Aug 27, 2008

### marcus

:rofl:

well put.

Indeed QG cosmology models do get rid of the big singularity. That still leaves the problem of finding observations that can test them, but I expect that to come in time.

So since the big (bang) one is taken care of, one would think that the little (hole) ones would be amenable as well.

11. Aug 30, 2008

### Haelfix

The standard problem for the information loss is not the singularity but rather the horizon. The singularity is a point or at least a small epsilon area. The problem is the information density in the rest of the blackhole.

There is simply too much information spread around the bh and resolving the singularity (into say a remnant) won't suffice to ensure unitarity. It also violates a number of astrophysics bounds b/c an arbitrary number of very massive particles would exist and come into being after a blackhole dies. We'd see a massive amount of decays all over the place, and that is simply not observed. Also the problem itself is defined by avoiding the singularity by looking at slices before the blackhole is formed, and after it has evaporated.

So the solution, whatever it is, must at the very least resolve both the problem of the horizon (giving it hair) as well as a smoothing of the singularity.

12. Aug 30, 2008

### marcus

Hmmm, sounds like you would disagree with Paul Davies, Haelfix.

Also your viewpoint would seemingly disagree with Steve Hsu, a particle theorist who often co-authors with Tony Zee. He has also proposed this way of resolving the puzzle. Information leaks out into a large expanding universe. Actually number of people have considered this possibility, Steve Hsu and Paul Davies are just a couple who may be familiar to you. If you would like, I can find you the link to Hsu's paper.

Last edited: Aug 30, 2008
13. Aug 31, 2008

### Haelfix

They know the objection(s) of course, by now the arguments are well documented and have been subject of back and forths for over a decade. But simply removing the spatial singularity doesn't solve the unitarity problem, which is already present long before the singularity occurs. Something really drastic has to occur, and has to occur over a large area such that causality is at least locally ensured.

So for instance Davies is in the baby universe camp, which is a possible way of bypassing the issue, but most physicists are very skeptical of that sort of line of reasoning and there is no concrete mechanism in place for that to occur, nor is it clear if it even solves the problem (again the dynamics would have to extend much further than the singularity) in generality. You can imagine a very large blackhole where antipodal regions have large crossing times but that have an overdense central region near the singularity. So by hypothesis a baby universe could form somewhere from complicated QG interactions somewhere in that bulk, but its not clear why it would last long enough for it to accurately gauge all the entropy content of whatever mixed states are left over before the hole evaporates such that it keeps unitarity intact on the opposite end. You can actually move the energy scales around a lot in these sorts of exercises, which further makes things tough on them.
Invariably many of those types of proposals have to wave their hands and posit some complicated global topology changing mechanism.