Submitted on 9 Aug 2004 (v1), last revised 1 Sep 2004 (this version, v2).-- Contains 51 pages, 39 figures (23 colour figures, colour used to convey physics information). V2: Two references added, some additional discussion of maximal analytic extension, plus minor cosmetic changes.
The so-called "analogue models of general relativity" provide a number of specific physical systems, well outside the traditional realm of general relativity, that nevertheless are well-described by the differential geometry of curved spacetime. Specifically, the propagation of acoustic disturbances in moving fluids are described by "effective metrics" that carry with them notions of "causal structure" as determined by an exchange of sound signals. These acoustic causal structures serve as specific examples of what can be done in the presence of a Lorentzian metric without having recourse to the Einstein equations of general relativity. (After all, the underlying fluid mechanics is governed by the equations of traditional hydrodynamics, not by the Einstein equations). In this article we take a careful look at what can be said about the causal structure of acoustic spacetimes, focusing on those containing sonic points or horizons, both with a view to seeing what is different from standard general relativity, and to seeing what the similarities might be.
The research of Carlos Barceló is supported by the Education Council of the Junta de
Andalucía (Spain). Matt Visser is supported by a Marsden grant administered by the
Royal Society of New Zealand.
Peer reviewed