The Trouble with The Trouble with deSitter Space

[marcus]

The Trouble with "The Trouble with deSitter Space"

http://arxiv.org/abs/0705.1178
A global picture of quantum de Sitter space
Steven B. Giddings, Donald Marolf
17 pages, 1 figure

"Perturbative gravity about a de Sitter background motivates a global picture of quantum dynamics in `eternal de Sitter space,' the theory of states which are asymptotically de Sitter to both future and past. Eternal de Sitter physics is described by a finite dimensional Hilbert space in which each state is precisely invariant under the full de Sitter group. This resolves a previously-noted tension between de Sitter symmetry and finite entropy. Observables, implications for Boltzmann brains, and Poincare recurrences are briefly discussed."

Giddings is known as a string theorist but this is not a string paper. It finds a mistake in a 2002 paper by Leonard Susskind and others called "The Trouble with deSitter Space" http://arxiv.org/hep-th/0212209
Incidentally, many papers by people in the LQG community are cited---four by Rovelli, several by Ambjorn, others by Thiemann, Ashtekar, Gambini and Pullin. Doubtless still more but I didnt make a careful count. Since Giddings and Marolf are well-known people at KITP Santa Barbara it suggests a significant broadening of horizons.
As we have discussed here, with John Baez help, a substantial amount of nonstring QG research is currently heading in the deSitter direction---Baez was discussion Cartan geometry using the deSitter group instead of Poincaré---DSR (deformed special relativity) deals a lot with deSitter group. This paper may possibly be of interest and have usefulness in broader QG research outside of string.

 

[Haelfix]

Interesting paper. I am still horribly confused about how one expects a finite dimensional hilbert space to have some correspondance when we take the minkowski limit (sending the CC --> 0).

Arkani Hamed's paper regulates this with some inflationary scenario where the degrees of freedom from super horizon modes remains innaccessible to even late time observers (recall that in DeSitter space the diffeomorphisms that go to the identity at infinity that one wants to mod out points into the timelike horizons) so the Hilbert space of states apparently becomes finite dimensional, and this author goes with that philosophy more or less.

Anyway, the semi classical picture of this seems to be coming around nicely but the full quantum treatment seems to remain a mystery, and a vital one at that.

 

[marcus]

New paper by Giddings
this one is also a bridge-builder to the LQG community with some 20 or so citations to LQG research papers.http://arxiv.org/abs/0705.2197
Black holes, information, and locality
Steven B. Giddings
Essay submitted to the Gravity Research Foundation essay contest; with minor updates

"Thirty years of a deepening information paradox suggest the need to revise our basic physical framework. Multiple indicators point toward reassessment of the principle of locality: lack of a precise definition in quantum gravity, behavior of high-energy scattering, hints from strings and AdS/CFT, conundrums of quantum cosmology, and finally lack of good alternative resolutions of the paradox. A plausible conjecture states that the non-perturbative dynamics of gravity is unitary but nonlocal. String theory may directly address these issues but so far important aspects remain elusive. If this viewpoint is correct, critical questions are to understand the 'correspondence' limit where nonlocal physics reduces to local quantum field theory, and beyond, to unveil principles of an underlying nonlocal theory."

I discussed the string-loop bridge-builder aspect of the earlier Giddings Marolf paper in another post. Here is the relevant part of that post

http://arxiv.org/abs/0705.1178
A global picture of quantum de Sitter space
Steven B. Giddings, Donald Marolf
17 pages, 1 figure

"Perturbative gravity about a de Sitter background motivates a global picture of quantum dynamics in 'eternal de Sitter space,' the theory of states which are asymptotically de Sitter to both future and past. Eternal de Sitter physics is described by a finite dimensional Hilbert space in which each state is precisely invariant under the full de Sitter group. This resolves a previously-noted tension between de Sitter symmetry and finite entropy..."

Giddings is known as a string theorist but this is not a string paper. This paper helps to build a conceptual bridge in the direction of the non-string QG community.
Relational observables[/color] developed largely by Rovelli, play a central role here---as they do in recent work of Thiemann, Dittrich, Gambini and Pullin.

De Sitter space is of special interest to researchers in non-string QG. You may remember that when Smolin gave an introductory course in LQG in 20-some video lectures the TEXT he used was his 2002 paper "Quantum Gravity with a Positive Cosmological Constant". The active development in DSR ("deformed special relativity) is related to the de Sitter group. (See for example the papers of Kowalski-Glikman, but almost any recent DSR paper might do.)

So Giddings Marolf paper is right down LQG alley.

Giddings Marolf cite many papers by people in the LQG community---four by Rovelli, several by Ashtekar, several by Ambjorn, by Thiemann, by Gambini and Pullin. Also one by Dittrich. Doubtless others, I didnt make a careful count. This paper will be of interest and will have usefulness outside of string research.

BTW everybody knows the cliché "String War" (which seems largely to have been angry reaction to Lee Smolin's book, often without reading it, and continued loud denial of the interest and progress occurring in nonstring research). My reaction to the socalled String War has been boredom---following it would be a waste of my time. Maybe it has subsided by now.

This paper of Gidding Marolf is what I think STRING PEACE should look like. It is written so as to not only be fundamental valuable research but also so as to build a bridge of mutal recognition between prominent people at KITP (a string research center) on the one hand and non-string QG researchers on the other.