William George Unruh (/ˈʌnruː/;[citation needed] born August 28, 1945) is a Canadian physicist at the University of British Columbia, Vancouver who described the hypothetical Unruh effect in 1976.

His parents were Benjamin Unruh, a refugee from Russia, and Anna Janzen, who was born in Canada.

(1969) and Ph.D. (1971) from Princeton University, New Jersey, under the direction of John Archibald Wheeler.

Unruh has made seminal contributions to our understanding of gravity,[1][2] black holes,[3] cosmology, and quantum fields in curved spaces, including the discovery of what is now known as the Unruh effect.

The Unruh effect therefore means that the very notion of the quantum vacuum depends on the path of the observer through spacetime.