String theorists think the universe’s “hidden” dimensions take on these tiny shapes. Mirror symmetry helped rejuvenate the field, and this line of research is still going strong with regular international math conferences devoted to it.Ĭalabi-Yau spaces, six-dimensional objects represented here on the two-dimensional page, measure just 10-33 centimeter. Mathematicians jumped into the act, using mirror symmetry to tackle other unsolved problems in enumerative geometry, typically entailing counting lines and curves on complicated surfaces and three-dimensional spaces. In 1991, the physicist Philip Candelas and his colleagues used mirror symmetry to solve a century-old problem, in effect counting the number of spheres that could fit inside a Calabi-Yau space. Scientists quickly learned that this newfound symmetry could be harnessed to address various mathematical puzzles. The theorists dubbed the phenomenon “mirror symmetry.” The surprise was that these apparently disparate Calabi-Yau shapes had a hidden kinship, both giving rise to the same physics. By rotating a Calabi-Yau space in a special way, they could produce a mirror image of sorts, though one with a very different shape.
String theorists soon made a remarkable discovery. A particle’s mass, the strength of a given force and other fundamental quantities depend on the shape, or geometry, of this convoluted space. These minute dimensions have to be “compactified” in a specific way to reproduce the physics we observe, and Strominger and his colleagues determined what that scrunched-up shape had to be: a six-dimensional mathematical object known as a Calabi-Yau space.
STRINGS THEORY PLUS
The three familiar dimensions plus time make four, meaning six or seven “extra” spatial dimensions must lie hidden, shrunk down so small we can’t see them. In 1985, three years after getting his Ph.D., Strominger co-authored one of the field’s seminal papers - part of the so-called “first string revolution.”Ī central premise of string theory is that strings, the most basic unit of nature, vibrate in a 10- or 11-dimensional universe. As an MIT graduate student, Strominger was told to steer clear of risky subjects like string theory he ignored the advice. He dropped out of Harvard twice in the 1970s to live in communes in New Hampshire and China before returning to college, bent on probing the universe through theoretical physics. Strominger was never one for the beaten path.
Emerging from this diverse work is a new consensus: String theory may not be the fabled theory of everything, Strominger says, “but it is definitely a theory of something.” Hidden Depths Others still are relying on string theory for unexpected help with calculations relating to particle physics and exotic states of matter. Some practitioners are applying string theory techniques to problems in pure mathematics, while Strominger is working to secure a deeper conceptual grasp of black holes. Many of today’s string theorists have adopted a utilitarian approach, dwelling less on its all-embracing potential and more on the here and now. “The theory is still evolving and getting better - and better understood,” maintains Juan Maldacena of the Institute for Advanced Study at Princeton, New Jersey. But while string theory has receded from the spotlight, it has not gone away. The backlash may have peaked in 2006, when several high-profile books and articles attacked the theory. No one has yet conceived of an experiment that could definitively verify or refute string theory. And, sure enough, skepticism has seeped in over the years. Strominger knew, even in the euphoric ’80s, that such assertions were overblown. “At the time of its new popularity,” he says, “there was a declaration that we had solved all the problems in physics and had the final theory in hand.” Harvard University physicist Andrew Strominger, a leader in string theory for decades, remembers the early enthusiasm. Some physicists hailed string theory as the long-sought “theory of everything.” Arising from the notion that matter and energy are fundamentally composed of tiny, vibrating strings rather than pointlike particles, this theory attempted to unify all the known forces into a single, elegant package. In the 1980s and ’90s, it promised seemingly unlimited bounty.
String theory was once the hottest thing in physics.
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