Leonard Emanuel Parker (born Leonard Pearlman; in 1938) is a distinguished professor emeritus of physics and a former director of the Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee. During the late 1960s, Parker established a new area of physics—quantum field theory in curved spacetime. Specifically, by applying the technique of Bogoliubov transformations to quantum field theory with a changing gravitational field, he discovered the physical mechanism now known as cosmological particle production. His breakthrough discovery has a surprising consequence: the expansion of the universe can create particles out of the vacuum.^[1] His work inspired research by hundreds of physicists and has been cited in more than 2,000 research papers; it was credited in the memoirs of Soviet physicist Andrei Sakharov and helped Stephen Hawking discover the creation of particles by black holes.^{[citation needed]}

Along with David Toms of Newcastle University, Parker co-wrote a latest addition to graduate-level textbooks on quantum field theory in curved spacetime, entitled Quantum Field Theory in Curved Spacetime: Quantized Fields and Gravity (Cambridge University Press, 2009, ISBN 978-0-521-87787-9).

He received his PhD from Harvard University in 1967. His advisor was Sidney Coleman.

• 1984 Elected Fellow, American Physical Society
• 2000 The Parker symposium

• Parker's faculty page at University of Wisconsin–Milwaukee
• The Center for Gravitation and Cosmology
• Milwaukee Journal Sentinel article about Leonard Parker

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