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Particle detectors, geodesic motion and the equivalence principle

Sebastiano Sonego1 and Hans Westman2

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It is shown that quantum particle detectors are not reliable probes of spacetime structure. In particular, they fail to distinguish between inertial and non-inertial motion in a general spacetime. To prove this, we consider detectors undergoing circular motion in an arbitrary static spherically symmetric spacetime, and give a necessary and sufficient condition for the response function to vanish when the field is in the static vacuum state. By examining two particular cases, we show that there is no relation, in general, between the vanishing of the response function and the fact that the detector motion is, or is not, geodesic. In static asymptotically flat spacetimes, however, all rotating detectors are excited in the static vacuum. Thus, in this particular case the static vacuum appears to be associated with a non-rotating frame. The implications of these results for the equivalence principle are considered. In particular, we discuss how to properly formulate the principle for particle detectors, and show that it is satisfied.


PACS

04.20.Gz Spacetime topology, causal structure, spinor structure

02.40.-k Geometry, differential geometry, and topology

04.62.+v Quantum fields in curved spacetime

MSC

83C75 Space-time singularities, cosmic censorship, etc.

83C47 Methods of quantum field theory (See also 81T20)

53Bxx Local differential geometry

81T20 Quantum field theory on curved space backgrounds

Subjects

Mathematical physics

Gravitation and cosmology

Dates

Issue 2 (21 January 2004)

Received 9 July 2003

Published 5 December 2003



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