278 research outputs found
The (Elusive) Theory of Everything
Stephen Hawking's work on black holes and the origin of the universe is arguably the most concrete progress theoretical physicists have made toward reconciling Einstein's gravitation and quantum physics into one final theory of everything.
Physicists have a favorite candidate for such a theory, string theory, but it comes in five different formulations, each covering a restricted range of situations.
A network of mathematical connections, however, links the different string theories into one overarching system, enigmatically called M-theory: perhaps the network is itself the final theory.
In a new book, The Grand Design, Hawking and Caltech physicist Leonard Mlodinow argue that the quest to discover a final theory may in fact never lead to a unique set of equations. Every scientific theory, they write, comes with its own model of reality, and it may not make sense to talk of what reality actually is. This essay is based on that book
The first law for slowly evolving horizons
We study the mechanics of Hayward's trapping horizons, taking isolated
horizons as equilibrium states. Zeroth and second laws of dynamic horizon
mechanics come from the isolated and trapping horizon formalisms respectively.
We derive a dynamical first law by introducing a new perturbative formulation
for dynamic horizons in which "slowly evolving" trapping horizons may be viewed
as perturbatively non-isolated.Comment: 4 pages, typos fixed, minor changes in wording for clarity, to appear
in PR
DeSitter entropy, quantum entanglement and ADS/CFT
A deSitter brane-world bounding regions of anti-deSitter space has a
macroscopic entropy given by one-quarter the area of the observer horizon. A
proposed variant of the AdS/CFT correspondence gives a dual description of this
cosmology as conformal field theory coupled to gravity in deSitter space. In
the case of two-dimensional deSitter space this provides a microscopic
derivation of the entropy, including the one-quarter, as quantum entanglement
of the conformal field theory across the horizon.Comment: harvmac, 2 figure
The probability for primordial black holes
We consider two quantum cosmological models with a massive scalar field: an ordinary Friedmann universe and a universe containing primordial black holes. For both models we discuss the complex solutions to the Euclidean Einstein equations. Using the probability measure obtained from the Hartle-Hawking no-boundary proposal, we find that the only unsuppressed black holes start at the Planck size but can grow with the horizon scale during the roll down of the scalar field to the minimum
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