The Cosmic Speed Limit

John Moffat, professor emeritus of physics, is not one to think small when looking for adversaries. He’s going after Albert Einstein himself, in particular what Einstein’s 1905 theory of relativity has to say about the absolute limit formed by the speed of light.

According to Einstein, the speed of light (300 million metres per second) is an absolute constant. It is the cosmic speed limit. Nothing can, did or ever will travel faster. If there ever was a holy writ in modern physics, this is it; every physics advance of the last century assumes that on this score, Einstein has the final word. But Moffat has questioned Einstein’s theory for years, and in the journal Physics Letters B he argued last year that while the speed of light may be the universal speed of light today, that doesn’t mean it hasn’t changed since the universe began.

Moffat’s paper, co-authored with former graduate student Michael Clayton (now teaching at Commonwealth University of Virginia), tries to find an answer to a paradox that bedevils our understanding of the early history of the universe. More and more measurements and theories indicate that if everything in the visible universe exploded outward from a single point (the so-called Big Bang), and if nothing moves faster than light, then our universe is impossibly big. In addition, a universe that expands impossibly fast and continues to accelerate implies some unknown gravitationally repulsive form of matter unlike anything currently known to exist. You can either assume such a scenario, say Moffat and Clayton, or you can assume the speed of light is much slower now than it was at the beginning of time. All you have to do is break Einstein’s rule that the speed of light has never varied, and all the big cosmological problems disappear.

Moffat may be on to something, according to John D. Barrow, professor of mathematical sciences at the University of Cambridge. “The simplicity of this new model and the striking nature of its predictions suggest that we should investigate it more seriously,” he wrote in an article in New Scientist magazine. “[It] should provoke us to take a wide-ranging look at the constancy of nature’s ‘constants.’ ”

Moffat expressed his doubts about general relativity in a letter to the great physicist in the early 1950s. Einstein, then at Princeton, kindly replied: “Every individual… has to retain his way of thinking if he does not want to get lost in the maze of possibilities. However, nobody is sure of having taken the right road – myself least of all.”

In that respect the two physicists agree. As Moffat says: “Shifting paradigms in science should never be easy. Scientists should stick with a theory that has been grounded in fact, until there’s a real reason for changing. But if you think your ideas are right, then you have to persist.”