This article is part of DISCOVER's 30th anniversary special section, including

11 eminent scientists'

predictions about the next 30 years. Share your thoughts on the future of science at the Science Not Fiction blog.

My great hope is that we will figure out how to meld gravity and quantum mechanics, realizing a dream that can be traced back to Einstein and that, in its more modern form, has captivated two generations of theoretical physicists. Such a theory might provide us the tools for gaining a clear understanding of the origin of the universe.

A vital part of such progress requires making contact between experiment and our theoretical attempts to quantize gravity and unify nature’s forces. For a long time we have been pursuing theoretical ideas like string theory without input from experiment or observation, and that is an unusual way for a science to evolve. In three decades—perhaps sooner with the help of the Large Hadron Collider and satellite-based astronomical observations—I would hope this changes. Should the observations support the theory, great; should they rule it out, that’s great too, because we’d be able to move on, full throttle, to other ideas. A big puzzle now facing string theory is that there are many possible forms for the extra dimensions that the mathematics requires. In the mid-1980s there were dozens. Today that number has soared, by some estimates to 10500 if not more. There’s no way theorists can possibly examine all of them; 10500 dwarfs the number of particles in the observable universe! So we will continue to search for some mathematical equation that pinpoints a handful or even one specific form for the extra dimensions, allowing us to determine a single universe that string theory predicts. Alternatively, we may establish that there is not a unique universe but many. Each universe would make use of a different form for the extra dimensions, with our universe being just one of many in a grand multiverse. That would be one of the most profound revolutions in thinking we have ever sustained.

I am confident that well before 2040 we will nail down what dark matter is. Identifying dark energy will be harder, but we might nail that, too. And if I allow my imagination to run wild, I would love it if we had some deep insight that let us understand what space and time actually are. We know a lot about the features of space and time, what they can do—but many of us believe these are not fundamental. Identifying the constituents of space and time would be a grand insight.

Brian Greene is a string theorist at Columbia University, author of the best seller The Elegant Universe, and cofounder of the World Science Festival in New York.