REINVENTING GRAVITY

Canadian theoretical physicist Moffat describes efforts to explain several distressing new cosmological phenomena that don’t fit comfortably into the theory of relativity.

Readers will easily follow the first-time author’s lucid prose as he lays out the story of gravitation research from the time of Aristotle (who taught that objects fell to earth because they belonged there) through Newton to Einstein, whose theory of relativity explains a great deal but not everything. For 50 years astronomers have known that gravitational attraction from visible matter can’t explain the movements of stars and galaxies. For Einstein’s theory to work, 90 percent of matter in the universe must be invisible. (Gas and dust don’t qualify because astronomers can detect them.) This “dark matter” must consist of strange subatomic particles that no particle accelerator has yet produced. In 1998 more flies entered the ointment with the discovery that the expansion of the universe is accelerating, requiring an immense, hypothetical “dark energy.” Explaining these has led to Rube Goldberg–like theories featuring many so-far undetected particles (supersymmetry) or complex mathematical systems impossible to verify (string theory). Twenty years ago, Moffat and others began suggesting that gravity can vary. This violates relativity but eliminates the need for dark matter and perhaps even dark energy. After initially turning up its nose, the establishment softened, and now a respectable minority of physicists is working to modify the theory of gravity. Following in the nuts-and-bolts footsteps of Brian Greene (The Elegant Universe, 1999) and Dan Hooper (Nature’s Blueprint, 2008), Moffat does a fine job recounting his field’s history until well into the 20th century, but readers who have forgotten their first-year college physics may struggle to understand the controversies that disturb today’s theoretical physicists.

Solid, mainstream popular science.