frank wilczek on spotting tremors in space-time

In the year to come, plausibly, but almost certainly within the next few years, physicists will detect tremors in space-time—or, to use the scientific term, gravitational waves. Through gravitational waves we will be able, for the first time, to monitor some of the most violent, dramatic events the universe has to offer.

My prediction is inspired by an extraordinary instrument, the Laser Interferometer Gravitational-Wave Observatory, or LIGO, which is operated by Caltech and MIT. LIGO is designed to detect extremely tiny changes in the distances between a few pairs of mirrors. The numbers are mind-boggling. The mirrors are four kilometers apart, and the distances between them are expected to change by less than one thousandth of the diameter of a proton. All kinds of things can jiggle mirrors, but gravitational waves produce a unique pattern of changes, so their signal can emerge from the noise.

It is poetic that this first observation of gravitational waves will coincide with the centenary of Einstein’s prediction that they exist. They’re a logical consequence of his general theory of relativity. According to general relativity, space and time aren’t rigid structures but form a kind of elastic medium—an ubiquitous cosmic Jell-O.  Massive bodies cause stress in space-time, and the distortion they produce affects the motion of other bodies. This is how general relativity accounts for gravity.

But Einstein carried his reasoning a major step further. As massive bodies move, space-time tries to dance to their tune. But the cosmic Jell-O has inertia, so it can’t follow rapid motions perfectly. Some of its distortions break free, take on a life of their own and spread at the speed of light. This is the origin of gravitational waves.

Space-time Jell-O is far stiffer than steel, so it takes enormous forces to produce significant tremors. (Memo to wormhole and time-­travel fans: Bending space-­time is hard.) Even with LIGO, we can only hope to observe gravitational waves produced by extremely massive bodies in extremely rapid motion.   These waves signal spectacular events, like the death throes of binary systems involving white dwarfs, neutron stars or black holes.

LIGO eventually should be able to detect pulses that emerge from such catastrophes anywhere within our local group of galaxies. No doubt we’ll discover, once again, that the universe is a strange place.

Dr. Frank Wilczek, winner of the 2004 Nobel Prize in Physics, is a professor of physics at the Massachusetts Institute of Technology. His most recent book is “A Beautiful Question: Finding Nature’s Deep Design.”

This essay originally appeared in The Wall Street Journal


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