Over the past 20 years, physicists have built up an imposing scientific orthodoxy around a compelling—and unproven—set of postulates they call the "Theory of Everything." Now, from the bottom floor, one mathematician is trying to shake the foundations.
If, as Carl Sagan contended, extraordinary claims require extraordinary evidence, string theory will require an unprecedented physical effort to prove (or refute) its remarkable suppositions.
Enter the Large Hadron Collider, an underground colossus of a particle accelerator, bestriding the border between France and Switzerland at CERN, the world’s largest particle physics laboratory. After an enormous effort by the scientific community, the first experiments in the LHC should be running by the end of next year, and physicists’ breath is decidedly bated. The collider, appropriately enough, collides beams of protons traveling in opposite directions around a circumference of nearly 20 miles, guided by coils exerting 100,000 times Earth’s magnetic field. With so much juice, the protons will travel at just about the speed of light, and will collide every 25 nanoseconds or so, releasing 14 trillion electron volts each.
So what does a giant, circular bumper-car course for subatomic particles in the middle of the Alps have to do with, well, everything?
The LHC’s five major experiments could give string theory an enormous boost, just as some critics are prophesying its downfall. The high-speed collisions will create conditions similar to the ones just seconds after the Big Bang; with careful measurements of the debris from such powerful collisions, CERN experimenters may be able to detect the as-yet-unseen “superparticles” that, according to the theory, complement the familiar subatomic building blocks. (Imagine crashing two SUVs into each other in order to study their engines. With protons, of course, you can’t just open the hood.)
The most optimistic experimenters are hoping for even more extraordinary finds. Tiny black holes—much smaller than an atomic nucleus and deteriorating harmlessly—could emit particles visible (so to speak) in our three-dimensional world but exhibiting characteristics of the extra dimensions that string theory predicts. In theory, observers might be able to count the number of dimensions in the universe from deep within the Alpine tunnels.
Of course, even experiments conforming to string theorists’ predictions are unlikely to quiet critics. In a New York Times op-ed published in October, string theory impresario Brian Greene acknowledged that no single experiment could prove string theory absolutely: “The bottom line is that it’s hard to test a theory that not only taxes the capacity of today’s technology but is also still very much under development.” Some have even argued that unless it were the size of the universe, a proton collider would be useless in a robust verification of the theory. Michio Kaku, physics professor and author of Hyperspace, one of the earliest popularizations of string theory, calls this argument “silly.” “Most science is done indirectly, not directly,” he says. “No one has been to the sun, but we know what the sun is made of by analyzing its sunlight.”
Meanwhile, a few Cassandras have even speculated about the possibility of a universe-liquidating black hole created by the concentration of energy involved in the Collider’s heavy-ion collisions. Similar concerns arose in 1999, with the completion of the Relativistic Ion Collider in Upton, N.Y.; physicists at CERN assure us that the collapse of the universe is no more likely to start outside Geneva than it was on Long Island.
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