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Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers
Spacetime foam, also known as quantum foam, has its origin in quantum
fluctuations of spacetime. Arguably it is the source of the holographic
principle, which severely limits how densely information can be packed in
space. Its physics is also intimately linked to that of black holes and
computation. In particular, the same underlying physics is shown to govern the
computational power of black hole quantum computers.Comment: 8 pages, LaTeX; Talk given by Jack Ng, in celebration of Paul
Frampton's 60th birthday, at the Coral Gables Conference (in Fort Lauderdale,
Florida on December 17, 2003). To appear in the Proceedings of the 2003 Coral
Gables Conferenc
Dimensionful deformations of Poincare' symmetries for a Quantum Gravity without ideal observers
Quantum Mechanics is revisited as the appropriate theoretical framework for
the description of the outcome of experiments that rely on the use of classical
devices. In particular, it is emphasized that the limitations on the
measurability of (pairs of conjugate) observables encoded in the formalism of
Quantum Mechanics reproduce faithfully the ``classical-device limit'' of the
corresponding limitations encountered in (real or gedanken) experimental
setups. It is then argued that devices cannot behave classically in Quantum
Gravity, and that this might raise serious problems for the search of a class
of experiments described by theories obtained by ``applying Quantum Mechanics
to Gravity.'' It is also observed that using heuristic/intuitive arguments
based on the absence of classical devices one is led to consider some candidate
Quantum-Gravity phenomena involving dimensionful deformations of the Poincare'
symmetries.Comment: 7 pages, Latex. (This essay received an ``honorable mention'' from
the Gravity Research Foundation, 1998-Ed.
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