William George "Bill" Unruh (; born August 28, 1945) is a
Canadian physicist at the
University of British Columbia,
Vancouver who described the hypothetical
Unruh effect in 1976.
Early life and education
Unruh was born into a
Mennonite family in
Winnipeg,
Manitoba. His parents were Benjamin Unruh, a refugee from
Russia, and Anna Janzen, who was born in Canada. 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 direction of
John Archibald Wheeler.
Areas of research
Unruh has made seminal contributions to our understanding of
gravity,
[
][
] black holes
A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can def ...
,
[
] cosmology, and quantum fields in curved spaces, including the discovery of what is now known as the
Unruh effect. Unruh has contributed to the foundations of
quantum mechanics in areas such as
decoherence[
] and the question of time in quantum mechanics. He has helped to clarify the meaning of nonlocality in a quantum context, in particular that
quantum nonlocality does not follow from
Bell's theorem and that ultimately quantum mechanics is a local theory.
[
] Unruh is also one of the main critics of the
Afshar experiment
The Afshar experiment is a variation of the double-slit experiment in quantum mechanics, devised and carried out by Shahriar Afshar while at the private, Boston-based Institute for Radiation-Induced Mass Studies (IRIMS). The results were presente ...
.
[
]
Unruh is also interested in music and teaches the Physics of Music.
The Unruh effect
The Unruh effect, described by Unruh in 1976, is the prediction that an accelerating observer will observe
black-body radiation
Black-body radiation is the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment, emitted by a black body (an idealized opaque, non-reflective body). It has a specific, continuous spect ...
where an inertial observer would observe none.
In other words, the accelerating observer will find itself in a warm background, the temperature of which is proportional to the acceleration. The same
quantum state of a field, which is taken to be the ground state for observers in inertial systems, is seen as a
thermal state
In the statistical mechanics of quantum mechanical systems and quantum field theory, the properties of a system in thermal equilibrium can be described by a mathematical object called a Kubo–Martin– Schwinger state or, more commonly, a KM ...
for the uniformly accelerated observer. The Unruh effect therefore means that the very notion of the
quantum 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:
:
References
External links
University of British Columbia Physics Dept. page*
ttp://www.theory.physics.ubc.ca/ UBC Theoretical Physics Homepage - a web server ran by Unruh
{{DEFAULTSORT:Unruh, William George
1945 births
Living people
Canadian physicists
Canadian Mennonites
Fellows of the Royal Society
People from Winnipeg
Princeton University alumni
Relativity theorists
University of British Columbia faculty
University of Manitoba alumni