Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Varying Constants, Black Holes, and Quantum Gravity   Tentative observations and theoretical considerations have recently led to
renewed interest in models of fundamental physics in which certain
``constants'' vary in time. Assuming fixed black hole mass and the standard
form of the Bekenstein-Hawking entropy, Davies, Davis and Lineweaver have
argued that the laws of black hole thermodynamics disfavor models in which the
fundamental electric charge $e$ changes. I show that with these assumptions,
similar considerations severely constrain ``varying speed of light'' models,
unless we are prepared to abandon cherished assumptions about quantum gravity.
Relaxation of these assumptions permits sensible theories of quantum gravity
with ``varying constants,'' but also eliminates the thermodynamic constraints,
though the black hole mass spectrum may still provide some restrictions on the
range of allowable models.

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The categories of this paper are: comp-gas
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
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The categories of this paper are: adap-org
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The categories of this paper are: chao-dyn
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The categories of this paper are: solv-int
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The categories of this paper are: econ