Paul S. Wesson

Paul S. Wesson, a Cambridge-educated Fellow of England’s Royal Astronomical Society who died on September 16, 2015 at the age of 66, was a prolific and influential physicist and astronomer whose contributions will leave a lasting impact, particularly in the fields of cosmology and unified-field theory.

Paul’s first papers, published while he was an undergraduate student at the University of London, were on geophysics; and he participated in a Cambridge-led geological expedition to the Kush mountains of Afghanistan in 1972. He switched to theoretical astrophysics by the time he began his doctoral studies at Cambridge, but his early interest in geology made itself felt in his first book, Cosmology and Geophysics in 1978.¹ His doctoral advisor was Martin Rees, but he also fell under the spell of Fred Hoyle, whose influence can be discerned in Paul’s science-fiction novels and short stories, and scientifically in his contributions to the ongoing Search for Extra- Terrestrial Intelligence (SETI); notably his rehabilitation of the idea (known as panspermia) that life --- at least in a limited form --- could have propagated through the vast reaches of interstellar space.²

Paul worked on numerous problems in theoretical astrophysics and cosmology as a postdoctoral research fellow with Richard Henriksen in Canada and Rolf Stabell in Norway, and took an initial faculty position at the University of Edmonton in 1980, where he published a second book, Gravity, Particles and Astrophysics.³ His innovative recalculation of the intensity of the optical extragalactic background light or EBL (with Stabell)⁴ received wide notice, dispelling lingering myths about the importance of cosmic expansion in resolving Olbers’ paradox, and replacing them with a renewed awareness of the profound link between the darkness of the night sky and the age of the Universe.⁵ Related calculations enabled Paul to set robust limits on any possible contributions to the EBL from various species of dark matter and energy, results that were eventually summed up in two more books (with James Overduin), Dark Sky, Dark Matter ⁶ and The Light/DarkUniverse.⁷

In 1984, Paul took up a permanent position at the University of Waterloo in Canada. It was here, and during the course of several visits abroad (mainly to Berkeley and Stanford) that he carried out what may prove his most lasting work, on the unification of gravitation and particle physics. It has been known since the 1920s that General Relativity (GR) with one additional compact space dimension reduces in four dimensions to Einstein’s theory plus Maxwell’s theory, thus “geometrizing” the electromagnetic field. String theorists and others have since shown that the other gauge fields of the standard model can be similarly incorporated into GR with additional space dimensions. But unification in this approach is no longer geometrization. Explicit higher- dimensional matter fields must be introduced in order to compactify the extra dimensions and explain why they are not observed. Steven Weinberg has aptly likened this compromise to the fable of “stone soup,” in which a miraculous stew supposedly made only out of rocks and water turns out to have been surreptiously flavoured by meats, vegetables and spices. What Paul discovered in about 1990 is that it may be possible to achieve unification without sacrificing geometrization, if one is willing to relax the requirement of compactification. All forms of matter and energy in the four-dimensional world can then be seen as manifestations of pure geometry in higher dimensions, a realization that forms the core of what has been known since 1996 as Space-Time- Matter theory.⁸ Paul’s ideas anticipated the boom in research on “large extra dimensions” beginning in 1998.

Their theoretical foundations and implications for cosmology, astrophysics and particle physics occupied 160 of Paul’s lifetime output of almost 300 publications with 20 collaborators, accounting for nearly 5000 of his more than 6500 career citations. Paul summed up this work over the course of five more books including Space-Time- Matter,⁹ Five-Dimensional Physics¹⁰ and Brave New Universe (with Paul Halpern).¹¹

Paul’s scientific outlook was influenced, not only by Einstein and Hoyle, but also by theorists such as Paul Dirac and Arthur Eddington. He remained unconvinced that the last word on physical reality belonged to quantum mechanics, hoping instead for a deeper underlying theory to emerge, one that would likely be based on higher-

dimensional geometry. His last book, Weaving the Universe (2010),¹² was an exploration of the ways in which his discoveries had led him toward the Eddingtonian view that “the stuff of the Universe is mind-stuff.” These attitudes were in no way reflexive, but rather the products of long and hard thought, as attested to by the copious margin notes in many of the books he owned on quantum and particle physics as well as relativity and cosmology. Although interested in philosophical implications, he was also instinctively uncomfortable with unfettered speculation. One inscription in a book on the string landscape reads: “After reading all of the wobble in this book, I feel redirected towards concrete, equation-based physics.” To those who raised metaphysical issues with extra dimensions, he was most likely to emphasize the need for more exact mathematical solutions with acceptable physical properties. And though he was a theorist first and foremost, he took great pains to remain personally involved with experiment and observation, particularly at Berkeley’s Center for Extreme Ultraviolet Astrophysics and Stanford’s Hansen Experimental Physics Laboratory, where he spent extended periods as a visiting scientist. He passed this attitude on to his students as well, urging them to look up at the stars, but always to keep one foot on the ground. In this, and in much else, Paul Wesson will be sorely missed by many, as a scientist, teacher, colleague and friend.

1. 1. P.S. Wesson, Cosmology and Geophysics (Oxford: Oxford University Press, 1978).
2. 2. P.S. Wesson, “Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space,” Sp. Sci. Rev. 156, 239-252 (2010).
3. 3. P.S. Wesson, Gravity, Particles, and Astrophysics (Dordrecht: Reidel, 1980).
4. 4. P.S. Wesson, K. Valle and R. Stabell, R., “The Extragalactic Background Light and a Definitive Resolution of Olbers’s Paradox,” Astrophys. J. 317, 601‑606 (1987).
5. 5. J.A. Peacock, Cosmological Physics (Cambridge: Cambridge University Press, 1998)
6. 6. J.M. Overduin and P.S. Wesson, Dark Sky, Dark Matter (Boca Raton, FL: CRC Press, 2002).
7. 7. J.M. Overduin and P.S. Wesson,The Light/Dark Universe (Singapore: World Scientific, 2008).
8. 8. P.S. Wesson, J. Ponce de Leon, H. Liu, B. Mashhoon, D. Kalligas, C.W.F. Everitt, A. Billyard, P. Lim and J.M. Overduin, “A Theory of Space, Time and Matter,” Int. J. Mod. Phys. A11, 3247-3255 (1996).
9. 9. P.S. Wesson, Space-Time-Matter (Singapore: World Scientific, 1999).
10. 10. P.S. Wesson, Five-Dimensional Physics (Singapore: World Scientific, 2006).
11. 11. P. Halpern and P.S. Wesson, Brave New Universe (Washington: Joseph Henry Press, 2006).
12. 12. P.S. Wesson, Weaving the Universe (Singapore: World Scientific, 2011).