59 research outputs found
Context, spacetime loops, and the interpretation of quantum mechanics
Three postulates are discussed: first that well-defined properties cannot be
assigned to an isolated system, secondly that quantum unitary evolution is
atemporal, and thirdly that some physical processes are never reversed. It is
argued that these give useful insight into quantum behaviour. The first
postulate emphasizes the fundamental role in physics of interactions and
correlations, as opposed to internal properties of systems. Statements about
physical interactions can only be framed in a context of further interactions.
This undermines the possibility of objectivity in physics. However, quantum
mechanics retains objectivity through the combination of the second and third
postulates. A rule is given for determining the circumstances in which physical
evolution is non-unitary. This rule appeals to the absence of spacetime loops
in the future evolution of a set of interacting systems. A single universe
undergoing non-unitary evolution is a viable interpretation.Comment: 19 pages. For special issue of J.Phys.A, "The Quantum Universe", on
the occasion of 70th birthday of Professor Giancarlo Ghirard
The non-existence of the self-accelerating dipole, and related questions
We calculate the self-force of a constantly accelerating electric dipole,
showing, in particular, that classical electromagnetism does not predict that
an electric dipole could self-accelerate, nor could it levitate in a
gravitational field. We also resolve a paradox concerning the inertial mass of
a longitudinally accelerating dipole, showing that the combined system of
dipole plus field can be assigned a well-defined energy-momentum four-vector,
so that the Principle of Relativity is satisfied. We then present some general
features of electromagnetic phenomena in a gravitational field described by the
Rindler metric, showing in particular that an observer fixed in a gravitational
field described by the Rindler metric will find any charged object supported in
the gravitational field to possess an electromagnetic self-force equal to that
observed by an inertial observer relative to which the body undergoes rigid
hyperbolic motion. It follows that the Principle of Equivalence is satisfied by
these systems.Comment: 10 pages, 4 figures; improved discussion of pressure; added remarks
on simultaneity and Rindler fram
Matter-wave coherence limit owing to cosmic gravitational wave background
We study matter-wave interferometry in the presence of a stochastic
background of gravitational waves. It is shown that if the background has a
scale-invariant spectrum over a wide bandwidth (which is expected in a class of
inflationary models of Big Bang cosmology), then separated-path interference
cannot be observed for a lump of matter of size above a limit which is very
insensitive to the strength and bandwidth of the fluctuations, unless the
interferometer is servo-controlled or otherwise protected. For ordinary solid
matter this limit is of order 1--10 mm. A servo-controlled or cross-correlated
device would also exhibit limits to the observation of macroscopic
interference, which we estimate for ordinary matter moving at speeds small
compared to c.Comment: 8 pages; 3 figure
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