IS TIME AN ILLUSION?

For decades, physicists have been searching for a quantum theory of gravity to reconcile Einstein's general relativity, which describes gravity at the largest scales, with quantum mechanics, which describes the behaviour of particles at the tiniest scales. One reason it has been so difficult to merge the two is that they are built on incompatible views of time. "I am more and more convinced that the problem of time is key both to quantum gravity and to issues in cosmology," says Lee Smolin of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada. ...

... Something has to give. The fact that the universe has no outside, by definition, suggests that quantum mechanics will be the one to surrender - and to many, this suggests that time is not fundamental. In the 1990s, for instance, physicist Julian Barbour proposed that time must not exist in a quantum theory of the universe. All the same, physicists are loath to throw out quantum theory, as it has proven capable of extraordinarily accurate predictions. What they need is a way to do quantum mechanics in the absence of time.

Single quantum event
Carlo Rovelli, a physicist at the University of Marseille in France, has found just that. In the past year, he and his colleagues have worked out a method to compress multiple quantum events in time into a single event that can be described without reference to time (Physical Review D, vol 75, p 084033).It is an intriguing achievement. While Rovelli's approach to dealing with time is one of many, and researchers working on other models of quantum gravity may have different opinions on the matter, nearly every physicist agrees that time is a key obstacle to finding an ultimate theory. Rovelli's approach seems tantalisingly close to surmounting that obstacle. His model builds upon research into generalising quantum mechanics by physicist James Hartle at the University of California, Santa Barbara, as well as Rovelli's earlier work on quantum systems. ...IS TIME AN ILLUSION? NEW SCIENTISTJanuary 19, 2009