W. G. Unruh

William George Unruh (born August 28, 1945) is a Canadian physicist at the University of British Columbia, Vancouver, who discovered the Unruh effect. Unruh was born in Winnipeg, Manitoba. He obtained his B.Sc. from the University of Manitoba in 1967, followed by an M.A. (1969) and Ph.D. (1971) from Princeton University, New Jersey, under the directions of Professor John Archibald Wheeler.

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Unruh has made seminal contributions to our understanding of gravity, black holes, cosmology, quantum fields in curved spaces, and the foundations of quantum mechanics, including the discovery of what is now known as the Unruh effect.

Unruh also appears to be interested in music and teaches the Physics of Music.

The Unruh effect

Main article: Unruh effect

The Unruh effect, which Unruh discovered in 1976, is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none. In other words, the accelerating observer will find himself or herself in a warm background. The quantum state which is seen as ground state for observers in inertial systems is seen as a thermodynamic equilibrium for the uniformly accelerated observer. The Unruh effect therefore means that the very notion of vacuum depends on the path of the observer through spacetime.

The Unruh effect can be expressed in a simple equation giving the equivalent energy kT of a uniformly accelerating particle (with a being the constant acceleration), as:

kT = \frac{\hbar a}{2\pi c}

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