Today Stephen Hawking dropped by the Seventeenth International Conference on Relativity and Gravitation in Dublin, and had this to say:
The Euclidean path integral over all topologically trivial metrics can be done by time slicing, and so is unitary when analytically continued to the Lorentzian. On the other hand, the path integral over all topologically non-trivial metrics isasymptotically independent of the initial state. Thus the total path integral is unitary, and information is not lost in the formation and evaporation of black holes. The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon.
And here’s an easy version of that to hold the rest of us until his whole paper’s published somewhere.
…Here was one other moment that made me laugh, from the page showing abstracts for talks during the plenary session:
The last few years have seen the techniques of loop quantum gravity applied to a growing number of problems. They have been used to compute the entropy of various sorts of black holes, including those with non-minimally coupled matter, for which the entropy is not proportional to the area. Perhaps more importantly, loop quantum gravity has given us a clear {it picture} of the quantum geometry of the horizon, which accounts for the microscopic degrees of freedom responsible for black hole entropy. There are tantalizing connections to Hod’s work on quasinormal modes, but these remain mysterious. Combined with traditional ideas on quantum cosmology, loop quantum gravity has led to newinsights on how quantization can eliminate the singular behavior of geometry at the big bang – perhaps with testable consequences. Predictions of Lorentz symmetry violation may also be experimentally testable, but these remain controversial. Finally, the dynamics of the theory is being studied with the help of spin foam models. My talk will survey all this work with a bare minimum of technical details.
Yes, please, keep those to a minimum! (clutches head)
And further down the abstracts page — “cosmic censorship”?? What the heck is that? (sigh) One more thing to research…
