What if time is real? If you’re not a theoretical physicist, the question being posed by Lee Smolin might sound as silly as if he’d asked: "What if your shoes and socks are real?" You experience them every day; so how could they not be?

Within the world of foundational physics, though, the notion that time might be real is practically radical. Yes, as human beings we experience time as a thing that flows; we mark a divide between the immutable past and the yet-to-be-written future; and we believe we live in a special moment that we call the present, which is constantly being refreshed. Yet according to conventional wisdom—or that peculiar brand of unconventional wisdom that governs quantum physics and cosmology—time is an illusion that emerges from some deeper physics.

In this view, time is a fictitious shorthand for the large-scale behavior of something more fundamental. "It is common in philosophy and science to presume that the things that are deepest and truest about the world are outside of time," summarizes Smolin, a theoretical physicist at the Perimeter Institute in Waterloo, Ontario. "The key question is, is time real or is it an illusion? We experience life as a sequence of moments, but is that the way the world really is?"

"There is no question that time exists—we use it everyday," adds Sean Carroll, a physicist at the California Institute of Technology and a prize winner in FQXi’s Nature of Time essay contest. "But we’re not sure whether time is really fundamental—whether it is a necessary part of a deep understanding of physics, or whether it is just a useful approximation."

Smolin wishes to hold on to the reality of time. But to do so, he must overcome a major hurdle: General and special relativity seem to imply the opposite. In the classical Newtonian view, physics operated according to the ticking of an invisible universal clock. But Einstein threw out that master clock when, in his theory of special relativity, he argued that no two events are truly simultaneous unless they are causally related. If simultaneity—the notion of "now"—is relative, the universal clock must be a fiction, and time itself a proxy for the movement and change of objects in the universe. Time is literally written out of the equation.

Although he has spent much of his career exploring the facets of a "timeless" universe, Smolin has become convinced that this is "deeply wrong," he says. He now believes that time is more than just a useful approximation, that it is as real as our guts tell us it is—more real, in fact, than space itself.

The notion of a "real and global time" is the starting hypothesis for Smolin’s new work, which he will undertake this year with two graduate students supported by a $47,500 grant from FQXi. Smolin hopes that this move will allow him to chip away at one of the biggest unsolved problems of physics and cosmology—uniting the laws of quantum physics with the laws of general relativity.

Quantum physics works wonderfully well when applied to atoms and their constituent parts; general relativity is a tried-and-true description of spacetime on the macro scale of planets, stars, and galaxies. When these two sets of laws meet, though, as they must to describe what happens inside a black hole and what the universe was like at the time of the Big Bang, they conflict and break down. Could time be the thread that can stitch them together?

The Cosmic Clock

Smolin hopes that taking time seriously will help to untangle what went on in the early cosmos. At the moment, it is tough to distinguish the laws of nature from the universe’s initial conditions. (By contrast, it’s easy to distinguish between the two in lab experiments because these tests can be repeated with different starting conditions. Cosmologists, however, cannot re-run the universe.)

If he can get a handle on the laws of physics with the help of a fundamental cosmic clock, Smolin can examine the possibility these laws may have been different in the past. The idea that physical laws can evolve over time only makes sense in a framework in which time is fundamental, Smolin argues. To understand why, imagine a soccer game in which the rules are programmed to change every minute. If the clock itself is not fundamental, but is also governed by those fluctuating rules, the poor players and referees would be stuck in an infinite logical loop.

Smolin’s ideas may be unconventional, but others admire his attempts to save time. "Not to do so is to deny the most fundamental data we get from life every day—which also underlies our ability to perform experiments and to analyze theories," says George Ellis, a mathematician at the University of Capetown in South Africa. (George Ellis’ prize-winning FQXi essay “On the Flow of Time” is here.)

However, Carlo Rovelli, a physicist at the University of Marseille, France takes the opposite view: "We must not force theories into our intuition: We change the intuition to understand the theory." (Carlo Rovelli’s prize-winning FQXi essay, "Forget Time" is here.)

Smolin is aware that his theories must be more than philosophically pleasing, if they are to be considered scientific. He notes that astronomers are already using gamma ray telescopes and cosmic ray observatories to probe whether the laws of special relativity still hold at extreme energies. (See "Journeying Through the Quantum Froth.") These experiments have yielded results that constrain some quantum gravity theories. "Though they won’t settle the question of whether time is real," says Smolin, "they do limit the options for theorizing about the nature of time."