Quantum Spacetime in Bad Honnef

Right now, I’m staying in this mansion:


This is the Physikzentrum in Bad Honnef, Germany. It’s a great place to spend time talking about physics, with an atmosphere that tastefully blends old and new. Inside, there’s a nice modern lecture hall:

but also—and probably even more important—comfortable spaces to talk … or to sit and write after most everyone else has gone to bed, like the room I’m in now:

Anyway, the reason I’m here is a workshop called

Exploring Quantum Spacetime.

This is the kind of quantum gravity conference I like best—one that brings people together who have different viewpoints, and different approaches to the same questions.

Today we heard talks by Jan Ambjørn, Daniel Litim, Petr Hořava, Dario Benedetti, and Gianluca Calcagni. There were some common themes running through several of these talks, especially concerning renormalization group flow and asymptotic safety, and it was nice to see different perspectives. But for me, one the most interesting things was hearing a bit about the relationship between causal dynamical triangulations (which was the subject of Ambjorn’s talk) and Hořava-Lifshitz gravity (the subject of Hořava’s talk, though he modestly didn’t call it that himself).

Both causal dynamical triangulations and Hořava-Lifshitz gravity make a sharper distinction between space and time than general relativity does. The first introduces a fixed slicing of spacetime into discrete time-steps, while the second discards Lorentz symmetry at short distance scales. Since such theories that treat space and time anisotropically seem to be popping in from various starting points (another is “shape dynamics,” which I’ve mentioned here before) it is natural to wonder about relationships between them.

And, it’s good to see that some people are doing more than just wondering:

C. Anderson, S. Carlip, J. H. Cooperman, P. Horava, R. Kommu, P. R. Zulkowski, Quantizing Horava-Lifshitz Gravity via Causal Dynamical Triangulations.

Some of these folks are friends of mine from when I was at UC Davis.

Anyway, today was just the first day of talks, and I’m looking forward to the rest of the conference. Right now, I should probably get some sleep so I don’t doze off during Stefano Liberati’s talk in the morning!


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