Abstract
Analogue models of (and for) gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing) and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity).
Highlights
The basic physics is this: A moving fluid will drag sound waves along with it, and if the speed of the fluid ever becomes supersonic, in the supersonic sound waves will never be able to fight their way back upstream [376, 387, 391, 389]
The features of general relativity that one typically captures in an “analogue model” are the kinematic features that have to do with how fields are defined on curved spacetime, and the sine qua non of any analogue model is the existence of some “effective metric” that captures the notion of the curved spacetimes that arise in general relativity. (At the very least, one might wish to capture the notion of the Minkowski geometry of special relativity.) the verbal description above can be converted into a precise mathematical and physical statement, which is the reason that analogue models are of physical interest
There were several papers in the 1980’s using an acoustic analogy to investigate the propagation of shockwaves in astrophysical situations, most notably those of Moncrief [268] and Matarrese [259, 17Indeed historically, though not of direct relevance to general relativity, analogue models played a key role in the development of electromagnetism – Maxwell’s derivation of his equations for the electromagnetic field was guided by a rather complicated analogue model in terms of spinning vortices of aether
Summary
I cherish more than anything else the Analogies, my most trustworthy masters. They know all the secrets of Nature, and they ought least to be neglected in Geometry. Supersonic fluid flow can generate a “dumb hole”, the acoustic analogue of a “black hole”, and the analogy can be extended all the way to mathematically demonstrating the presence of phononic Hawking radiation from the acoustic horizon. This particular provides (at least in principle) a concrete laboratory model for curvedspace quantum field theory in a realm that is technologically accessible to experiment. There are many other “analogue models” that may be useful for this or other reasons – some of the analogue models are interesting for experimental reasons, others are useful for the way they provide new light on perplexing theoretical questions. By that stage the interested reader will have had a quite thorough introduction to the ideas, techniques, and hopes of the analogue gravity programme
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