From: gerry@bindweed.com   
      
   In article ,   
   helbig@asclothestro.multivax.de says...   
   >   
   > In article ,   
   > Gerry Quinn  writes:   
   >   
   > > In extreme cases it does get a bit problematic, i.e. where general   
   > > relativity predicts a non-simple topology, at and inside the   
   > > Schwarzschild radius of a black hole.  (That's why I've always been   
   > > certain that general relativity breaks down at the Schwarzschild radius;   
   > > a belief that is no longer considered particularly eccentric these days   
   > > I think.)   
   >   
   > The general view is that nothing strange happens at the Schwarzschild   
   > radius.  It is, after all, only a coordinate singularity, not a physical   
   > one.  In that respect, it is like a pole of the Earth: the distance   
   > between meridians of longitude is zero, but it doesn't matter.  It's   
   > just that in some circumstances some coordinates might be better than   
   > others.   
   >   
   > This has changed somewhat within the "firewall" controversy, where   
   > indeed some people have claimed that very strange things happen at the   
   > Schwarzschild radius.  I think it's fair to say that the jury is still   
   > out, though my impression is that most who have investigated this don't   
   > think that something strange happens there.  I doubt that that is the   
   > reason why Gerry claims that GR breaks down here, though; I think he was   
   > claiming that before firewalls were a hot topic (pun intended).   
      
   You say that like it's a bad thing!  But you are quite right in that the   
   recent 'firewall' analyses have nothing in particular to do with my   
   rationale.   
      
   The simplest rationale for me has always been that there is no reason   
   why some forces should be best described as fields, and others as   
   geometry.   
      
   And if we can indeed describe gravity as an effective field, what on   
   earth is the logic in continuing to insist on a geometric   
   interpretation?  There are problems enough with simple thermodynamics,   
   and also with the fact that if we avoid confronting the issue of a   
   singularity at the Schwarzschild radius (which at least can be   
   interpreted in a straighforward fashion as a breakdown of general   
   relativity), we are left with a totally intractable central singularity   
   that is not really comprehensible at all.   
      
   The idea that nothing special happens at the Schwarzschild radius   
   depends on taking general relativity on its own terms, even in   
   conditions that by all other descriptions are extreme.   
      
   By contrast, if we assume that gravity is an effective spin-2 field, we   
   expect it to break down at some point.  The Schwarzschild radius is the   
   obvious point, and a firewall is exactly what we should expect (in my   
   opinion), because there's nowhere for things to continue except baryon   
   decay, initally from 'non-frozen interactions' (by which I mean residual   
   effects of slight differences between GR and the exact theory, which   
   will be the only events happening in what under this scenario really   
   does in some ways resemble the old 'frozen star' concept) and eventually   
   catalysed by the firewall itself once the fire gets going.   
      
   (That says nothing about whether we should consider the black hole   
   interior as a 'ball of strings' or whatever - just that it will be in a   
   very hot state such that whatever is going on inside it will not be   
   describable in terms of interactions at energies with which we are   
   familiar.)   
      
   - Gerry Quinn   
      
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