Comments on: Hawking Buzz

By: Alejandro Rivero

Alejandro Rivero — Wed, 31 Dec 1969 19:00:00 +0000

Another subtlety about Minkowskian signatures is the embedding theorem. Not usually mentioned, but worth to have it at the back of some neuron.

By: Urs Schreiber

Urs Schreiber — Wed, 31 Dec 1969 19:00:00 +0000

Wick rotation in QFT on a fixed background is certainly deep. But for quantum gravity it is for the obvious reason very problematic, as has been discussed at great length on s.p.r. for instance.

Hawking has worked a lot on Euclidean path integrals for cosmology in the past, and he even goes as far as introducing his ‘Universe in a nutshell’ book with saying that our universe is essentially a Euclidean 4-sphere in a sense. (I think he should have mentioned that this is more of a personal view, a hunch, which is not necessarily shared by the community or even demonstrated by results, I’d think.) Maybe it is just due to my ignorance of the literature, but I am having trouble coming up with past results or even hints that the Euclidean path integral for gravity is the thing to look at. Now, maybe Hawking’s new idea about black hole information is just that hint which I am looking for, I don’t know. But currently I am a little sceptical.

By: Godfrey Miller

Godfrey Miller — Wed, 31 Dec 1969 19:00:00 +0000

I saw Sir Roger when he gave the same talk(s) at Princeton on Oct. 17, 20, and 22. On that occasion, Fashion, Faith, and Fantasy were each the subject of one night’s talk.

I thoroughly enjoyed what he had to say, but Princeton is a hub for string theory, and I got the distinct feeling that my position was in the minority.

You can watch them at the following address:
http://www.princeton.edu/WebMedia/lectures/

By: D R Lunsford

D R Lunsford — Wed, 31 Dec 1969 19:00:00 +0000

Peter,

Could you give some information about it?

To me the signature seems physical, and I don’t see how it is possible to alter it.

Complex structures that arise naturally out of geometry are another matter. (Think for example of the circular points at infinity in plane projective geometry.)

By: Alejandro Rivero

Alejandro Rivero — Wed, 31 Dec 1969 19:00:00 +0000

The french girls did a good work to introduce the subtleties of path measuring, at the end of their geometry manual.

By: Bogdanoff

Bogdanoff — Wed, 31 Dec 1969 19:00:00 +0000

Quote : “My own prejudice about quantum field theory is that the relation between the Euclidean and Minkowski space formulations of quantum field theory is actually much more interesting and subtle than people think.”

Well, it is exactly what we think. And by the way, certain questions raised by S.H. are developed in our “Topological field Theory of the Initial Singulariry of Space time” paper (CQG) that was extensively discussed but not really understood as a new formulation regarding the transition between lorentzian metric (real time, still valid et Planck scale) to euclidean metric imaginary time, only valid at 0 scale). In our model, this transition becomes effective between Planck scale and 0 scale and is characterized by quantum fluctuations of lorentzian and euclidean metrics (superposition (KMS) state of metrics). In this model, the “apparent horizon” evoked by Hawking could be the result of an “euclidean evolution” of events in the black hole whose final singularity does not exist in real (lorentzian time) but in imaginary (euclidean) time.

By: Preposterous Universe

Preposterous Universe — Wed, 31 Dec 1969 19:00:00 +0000

Hawking on black holes

The cat is out of the bag about Stephen Hawking’s new ideas about black holes.