Faster-than-light neutrino poses the ultimate cosmic brain teaser for physicists


Einstein posited that the speed of light is an integral part of the geometry of four-dimensional space-time. (Daily Herald Archive/SSPL VIA GETTY IMAGES)
November 14, 2011

It’s been an interesting and awkward autumn for physicists. They’ve been presented with an experimental finding that threatens to blow their vision of the universe to smithereens. A team of scientists in Europe announced in September that they’d clocked tiny particles called neutrinos traveling faster than the speed of light.

Which is heresy. Nothing goes faster than light. Einstein said so; a century of experiments have backed him up.

The theorists are now knotted up with conflicting emotions. As much as they support Einstein, they’d also love for the new finding to be true. It’d be weirdly thrilling. They’d get to rethink everything. If neutrinos violate the officially posted cosmic speed limit, the result will be the Full Employment Act for Physicists.

“Besides my wedding day and the birth of my kids, it would be the happiest day of my life,” says Brian Greene, the author of “The Fabric of the Cosmos” and a theoretical physicist at Columbia University. “That’s what we live for.”

The European experiment, named OPERA (which somehow comes from Oscillation Project with Emulsion-Tracking Apparatus), found that neutrinos traveled from a lab near Geneva to a detector in Gran Sasso, Italy, 60 nanoseconds faster than the speed of light.

The scientists have now tweaked their experiment using more discrete pulses of particles and are expected to submit new findings this month. They could well wind up reaffirming their original, shocking conclusion.

Lawrence Krauss, a best-selling author (“The Physics of Star Trek”) and professor at Arizona State University, believes the OPERA team made a public relations blunder by announcing its intial finding before it had been verified by outside experimenters. Krauss thinks this could wind up embarrassing the profession. But if it holds up, he said, the implications will be astounding.

“It’s not as if science is just a series of facts that are separate. Relativity is the basis of all of modern physics, all of particle physics, and astronomy,” Krauss said.

When a reporter suggested to Krauss that the neutrino report is like someone declaring that motherhood is bad, he said, “Actually, it’s like saying motherhood doesn’t exist.”

A crucial part of space-time

Lurking within the neutrino story is a grander question: How close are we to knowing everything about space, time, matter, energy, the origin of the universe? Are we still scratching the surface? Or are we starting to get vanishing returns as we use expensive gadgets to probe the margins of nature?

This debate goes back to the 1890s, when some physicists feared there was nothing left to do but tweak the established truths to the sixth decimal. A few years later, Einstein showed up, and next came the wonders of the atom and the development of the spooky theories of quantum mechanics. So the smart money is always on surprises.

But scientists also tend to be conservative. There’s an institutional preference for simple explanations consistent with previous experiment and theory. The simple explanation for the neutrino shocker is that the scientists made an error somewhere.

There is logic and beauty in a universe in which space, time, energy and matter are tightly associated with the speed of light. The special status of the speed of light isn’t like an Olympic record, something begging to be broken. Someone could come along who is faster than Usain Bolt, and it wouldn’t change the way we look at the world.

But the speed of light, according to Einstein, is an integral part of the geometry of four-dimensional space-time.

When we discuss the speed of light, we’re not talking about the characteristics of light so much as we’re describing the fabric of the universe. Light speed is the ultimate speed that anything (including things with zero mass, such as light or other electromagnetic radiation) can possibly go.

This also puts a limit on the speed of information, and, as such, helps enforce the fundamental law of causality. There’s an “arrow of time”: Splattered eggs on the kitchen floor don’t reassemble themselves in the shell and leap back onto the countertop.

“The melded nature of space and time is intimately woven with properties of light speed,” Greene says. “The inviolable nature of the speed of light is actually, in Einstein’s hands, talking about the inviolable nature of cause and effect.”

Michael Turner, a University of Chicago physicist, says the universe won’t seem as logical if there are particles that can move faster than light.

“In science we like surprises. We like big surprises. This one is too big to be true,” Turner said. “We really like things that rock the boat and turn us in a new direction, but this one turns the boat upside down and fills it with water.”

But Lisa Randall, a Harvard physicist and author of “Knocking on Heaven’s Door: How Physics and Scientific Thinking Illuminate the Universe and the Modern World,” sounds a less alarmist note, saying it might be possible to accommodate faster-than-light neutrinos without abandoning relativity: “It would mean that the underlying assumptions of Einstein’s theory are not precise, they’re just approximate.”

Science isn’t a democracy. A thousand tenured professors cannot overrule the hard facts of observation. So it is that even Einstein can be challenged. The reason his theory of relativity holds up is not because Einstein said so, but because it has been confirmed experimentally.

So the data ultimately can trump a theory. But if you’ve got conflicting data, you’ve just got a mess. That’s where we are now.

There’s a major hitch in the neutrino story: Neutrinos have been timed in the real world by astronomers. A supernova that was detected in 1987 sent streams of neutrinos to Earth, and they arrived at just about the same moment as the light of the exploding star. Had those neutrinos been traveling at OPERA speed, they would have arrived four years earlier. (There could be a way around this hitch: Maybe the high-energy neutrinos in the lab experiment go faster than the ones from the supernova.)

John Ellis, a theorist from the Geneva lab where the super-speed neutrinos originated, said by e-mail, “Deep in my heart, I do not expect the faster-than-light interpretation of the OPERA data to survive, but one must keep an open mind.”

He sent along a quotation from the late Carl Sagan:

“We are constantly prodding, challenging, seeking contradictions or small persistent residual errors, proposing alternative explanations, encouraging heresy.”

Sure, but Sagan had another saying: “Keep your mind open, but not so open that your brains fall out.”

Joel Achenbach writes on science and politics for the Post's national desk and on the "Achenblog."
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