arXiv subjects

W. Unruh

Publications and source records attributed to W. Unruh.

3 recordsLinked to original sources

arXiv2002

Temporal Ordering in Quantum Mechanics

We examine the measurability of the temporal ordering of two events, as well as event coincidences. In classical mechanics, a measurement of the order-of-arrival of two particles is shown to be equivalent to a measurement involving only one particle (in higher dimensions). In quantum mechanics, we find that diffraction effects introduce a minimum inaccuracy to which the temporal order-of-arrival can be determined unambiguously. The minimum inaccuracy of the measurement is given by dt=1/E where E is the total kinetic energy of the two particles. Similar restrictions apply to the case of coincidence measurements. We show that these limitations are much weaker than limitations on measuring the time-of-arrival of a particle to a fixed location.

quant-ph↗

arXiv1998

Cosmological long wavelength perturbations

This paper presents an exact solution to the long wavelength perturbations for the scalar modes and for a scalar field theory with arbitrary potential. Locally these modes are coordinate transformations of the homogeneous background solutions (although non-locally they are not). These solutions are then used to discuss a couple of recent papers in which such perturbations play a role. Abramo, Brandenberger, and Mukhanov have recently argued that long wavelength perturbations have the effect of driving the cosmological constant to zero if the higher order perturbation equation are examined. I argue that this effect is invisible to any local observer, and thus does not constitute a relaxation of the cosmological constant in the normal sense of the term. Grishchuk has argued that the standard lore on the strength of the perturbations at the end of inflation is wrong. I discuss the disagreement in light of the exact long wavelength solutions, and emphasize the importance of the initial conditions in resolving the disagreement.

astro-ph↗

arXiv1998

On the Hawking Turok solution to the Open Universe wave function

Hawking and Turok have recently published a solution to the WKB "wave-function for the universe" which they claim leads in a natural way to an open universe as the end point of the evolution for a universe dominated by a scalar field. They furthermore argue that their solution a preferred solution under the rules of the game. This paper will, I hope, clarify their solution and the limits of validity of their argument.

gr-qc↗