Causality and the speed of sound
George Ellis, Roy Maartens, Malcolm MacCallum
TL;DR
This paper revisits the causal constraint that the speed of sound in matter must not exceed the speed of light, addressing recent debates and examining issues faced by theories violating this limit.
Contribution
It critically analyzes the implications and challenges of theories proposing superluminal sound speeds, reaffirming the traditional causality constraint.
Findings
Identifies issues with superluminal sound theories
Reinforces the causal speed limit in matter
Addresses recent debates questioning the limit
Abstract
A usual causal requirement on a viable theory of matter is that the speed of sound be at most the speed of light. In view of various recent papers querying this limit, the question is revisited here. We point to various issues confronting theories that violate the usual constraint.
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