Analog Models of General Relativity

Matt Visser, Washington University St. Louis
visser@kiwi.wustl.edu

The workshop ``Analog Models of General Relativity'' was held in Rio de Janeiro from 16 October to 20 October 2000. The organizing committee consisted of Mario Novello, Grigori Volovik, and myself. Invited speakers talked about a wide range of issues concerning the use of condensed matter systems as analogues of (and analogs for) general relativity. Condensed matter analogs can be used to help us understand GR, or GR can be used to help us understand condensed matter physics. More boldly, you can use condensed matter analogs to suggest possible replacements for GR, physical systems that approximate ordinary GR in the appropriate limit. Among the invited presentations:

(1) The workshop started with an introductory survey, presented by myself, that set the basic parameters for the week.

(2) Bill Unruh talked about his acoustic black holes (``dumb holes''), illustrating the way that acoustics in a moving fluid leads to the notion of an ``effective acoustic metric''.

(3) Grigori Volovik discussed the use of as a model of, and indeed for, GR. (Low-energy quasiparticles near the Fermi surface can in certain circumstances generically exhibit a relativistic spectrum, and induced gravity a la Sakharov can then be argued to lead to an effective dynamics similar to Einstein gravity.)

(4) Brandon Carter carefully distinguished the notions of quasi-gravity from pseudo-gravity. (q-gravity: systems that mathematically simulate GR but are qualitatively different, e.g. acoustic geometries; p-gravity: systems that physically mimic gravitational fields, e.g. centrifugal force). He also discussed a model of how to use braneworld cosmologies to mimic gravity in a non-standard way.

(5) Ulf Leonhardt described his proposal for an ``optical horizon'' using ``slow light'' (resonance induced transparency in a Bose-Einstein condensate; a BEC).

(6) Renaud Parentani talked about quantum metric fluctuations and Hawking radiation. He argued that the near horizon propagation of outgoing quanta resembles that of photons in a moving random medium.

(7) Haret Rosu discussed a number of topics concerning exotic effects in the GR quantum interface.

(8) Mario Novello described nonlinear electrodynamics (for example, Born-Infeld, Schwinger, or Euler-Heisenberg electrodynamics) and the way it leads to the notion of an effective metric governing photon propagation.

(9) Ted Jacobson talked about a particular implementation of the notion of ``analog horizon'' in a superfluid system.

(10) Mike Stone presented a careful discussion of how notions of effective metric and the machinery of general relativity can help understand the concepts of pseudo-momentum and physical momentum in condensed matter systems.

In addition there were a number of contributed talks (Santiago Bergliaffa presented examples of gravity-like systems in non-linear electrodynamics, Jose Salim discussed closed spacelike photon paths in nonlinear electrodynamics, Nami Fux Svaiter discussed the rotating vacuum and the quantum Mach principle, and Carlos Barcelo presented a discussion of analog gravity based on Bose-Einstein condensates; BECs).

Additionally, approximately 50 graduate students and postdocs attended the workshop.

There was considerable animated discussion, aided by an open workshop format that left plenty of time for give-and-take. The most promising systems for experimentally mimicking ``event horizons'' seem to be based on (a) ``slow light'' in BEC systems with resonance induced transparency, (b) quasiparticles in superfluids, and (c) acoustic oscillations of the phase of the condensate field in BECs. Considerable enthusiasm and hope was expressed that one or more of these ``analog systems'' might be brought to laboratory fruition in the near (5 to 10 year) future.

Many of the transparencies from the presentations (plus some
write-ups, web-links, and other technical information) is now
available from the post-conference website:
`
http://www.lafex.cbpf.br/~bscg/analog/`

A mirror of this website is maintained in the USA at:
`
http://www.physics.wustl.edu/~visser/Analog/`