10,805 research outputs found
Lattice Black Holes
We study the Hawking process on lattices falling into static black holes. The
motivation is to understand how the outgoing modes and Hawking radiation can
arise in a setting with a strict short distance cutoff in the free-fall frame.
We employ two-dimensional free scalar field theory. For a falling lattice with
a discrete time-translation symmetry we use analytical methods to establish
that, for Killing frequency and surface gravity satisfying
in lattice units, the continuum Hawking spectrum
is recovered. The low frequency outgoing modes arise from exotic ingoing modes
with large proper wavevectors that "refract" off the horizon. In this model
with time translation symmetry the proper lattice spacing goes to zero at
spatial infinity. We also consider instead falling lattices whose proper
lattice spacing is constant at infinity and therefore grows with time at any
finite radius. This violation of time translation symmetry is visible only at
wavelengths comparable to the lattice spacing, and it is responsible for
transmuting ingoing high Killing frequency modes into low frequency outgoing
modes.Comment: 26 pages, LaTeX, 2 figures included with psfig. Several improvements
in the presentation. One figure added. Final version to appear in Phys.Rev.
General relativity and cosmology derived from principle of maximum power or force
The field equations of general relativity are shown to derive from the
existence of a limit force or of a limit power in nature. The limits have the
value of c^4/4G and c^5/4G. The proof makes use of a result by Jacobson. All
known experimental data is consistent with the limits. Applied to the universe,
the limits predict its darkness at night and the observed scale factor. Some
experimental tests of the limits are proposed. The main counter-arguments and
paradoxes are discussed, such as the transformation under boosts, the force
felt at a black hole horizon, the mountain problem, and the contrast to
scalar--tensor theories of gravitation. The resolution of the paradoxes also
clarifies why the maximum force and the maximum power have remained hidden for
so long. The derivation of the field equations shows that the maximum force or
power plays the same role for general relativity as the maximum speed plays for
special relativity.Comment: 24 pages, 1 figure, LaTeX, published versio
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