1,379 research outputs found
The End of Time?
I discuss J. Barbour's Machian theories of dynamics, and his proposal that a
Machian perspective enables one to solve the problem of time in quantum
geometrodynamics (by saying that there is no time). I concentrate on his recent
book 'The End of Time' (1999).Comment: 48 pages Latex. A shortened version will appear in 'The British
Journal for Philosophy of Science
Quantum Gravity signatures in the Unruh effect
We study quantum gravity signatures emerging from phenomenologically
motivated multiscale models, spectral actions, and Causal Set Theory within the
detector approach to the Unruh effect. We show that while the Unruh temperature
is unaffected, Lorentz-invariant corrections to the two-point function leave a
characteristic fingerprint in the induced emission rate of the accelerated
detector. Generically, quantum gravity models exhibiting dynamical dimensional
reduction exhibit a suppression of the Unruh rate at high energy while the rate
is enhanced in Kaluza-Klein theories with compact extra dimensions. We quantify
this behavior by introducing the "Unruh dimension" as the effective spacetime
dimension seen by the Unruh effect and show that it is related, though not
identical, to the spectral dimension used to characterize spacetime in quantum
gravity. We comment on the physical origins of these effects and their
relevance for black hole evaporation.Comment: 38 pages, 7 figures; v3: section 2 rewritten, references adde
Gravitational Decoherence
We discuss effects of loss of coherence in low energy quantum systems caused
by or related to gravitation, referred to as gravitational decoherence. These
effects, resulting from random metric fluctuations, for instance, promise to be
accessible by relatively inexpensive table-top experiments, way before the
scales where true quantum gravity effects become important. Therefore, they can
provide a first experimental view on gravity in the quantum regime. We will
survey models of decoherence induced both by classical and quantum
gravitational fluctuations; it will be manifest that a clear understanding of
gravitational decoherence is still lacking. Next we will review models where
quantum theory is modified, under the assumption that gravity causes the
collapse of the wave functions, when systems are large enough. These models
challenge the quantum-gravity interplay, and can be tested experimentally. In
the last part we have a look at the state of the art of experimental research.
We will review efforts aiming at more and more accurate measurements of gravity
(G and g) and ideas for measuring conventional and unconventional gravity
effects on nonrelativistic quantum systems.Comment: Invited topical review article for Classical and Quantum Gravity, 78
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