Paul Charles William Davies AM (born 22 April 1946) is an English physicist, writer and broadcaster, currently a professor at Arizona State University as well as the Director of BEYOND: Center for Fundamental Concepts in Science. He has held previous academic appointments at the University of Cambridge, University of London, University of Newcastle upon Tyne, University of Adelaide and Macquarie University. His research interests are in the fields of cosmology, quantum field theory, and astrobiology. He has proposed that a one-way trip to Mars could be a viable option.

In 2005, he took up the chair of the SETI: Post-Detection Science and Technology Taskgroup of the International Academy of Astronautics.

Davies's inquiries have included theoretical physics, cosmology, and astrobiology; his research has been mainly in the area of quantum field theory in curved spacetime. Notable contributions are the so-called Fulling–Davies–Unruh effect, according to which an observer accelerating through empty space will perceive a bath of thermal radiation, and the Bunch–Davies vacuum state, often used as the basis for explaining the fluctuations in the cosmic background radiation left over from the big bang. A paper co-authored with Stephen Fulling and William Unruh was the first to suggest that black holes evaporating via the Hawking effect lose mass as a result of a flux of negative energy streaming into the hole from the surrounding space. Davies has had a longstanding association with the problem of time’s arrow, and was also a forerunner of the theory that life on Earth may have come from Mars cocooned in rocks ejected by asteroid and comet impacts. During his time in Australia he helped establish the Australian Centre for Astrobiology.

Some scientists are critical of what they see as Davies' theistic agenda. Davies' article in the New York Times, "Taking Science On Faith", was criticised by Jerry Coyne, Nathan Myhrvold, Lawrence Krauss, Scott Atran, Sean Carroll, Jeremy Bernstein, PZ Myers, Lee Smolin, John Horgan, Alan Sokal[1] Davies's response begins I was dismayed at how many of my detractors completely misunderstood what I had written. Indeed, their responses bore the hallmarks of a superficial knee-jerk reaction to the sight of the words "science" and "faith" juxtaposed.

Richard Dawkins (The God Delusion chapter 1) and Victor J Stenger (reviewing The Cosmic Blueprint) have also criticised Davies' public stance on science and religion