How an MIT professor helped confirm Einstein’s theory of relativity

After over 40 years of research, the work of MIT physics professor Rainer Weiss has been validated.

A computer simulation of two black holes colliding, an extremely powerful astronomic event detected for the first time ever by the Laser Interferometer Gravitational-Wave Observatory, or LIGO.

An MIT professor is at the center of what is being hailed as one of the most momentous discoveries in the world of physics, one that provides evidence validating a final part of Albert Einstein’s theory of relativity.

Scientists announced today that they have detected ripples in the fabric of space-time, known as gravitational waves, 100 years after Einstein originally predicted their existence. The waves were the result of two black holes colliding over a billion light-years away, and were detected when two giant antennas in Washington and Louisiana known as the Laser Interferometer Gravitational-Wave Observatory (LIGO) vibrated slightly, producing a small chirp of sound.

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On the other side of Cambridge, scientists at the Harvard-Smithsonian Center for Astrophysics who had gathered in an auditorium to watch a video feed of the announcement erupted in applause. Avi Loeb, the Chair of the Astronomy Department and the Frank B. Baird, Jr. Professor of Science at Harvard, called gravitational waves a once-in-a-lifetime discovery.

“This is the most exciting thing that I have witnessed during my career so far,’’ Loeb said. “We still have a lot of unanswered questions about black holes, especially involving the unification of quantum mechanics and gravity, so there’s a lot to do. But it really is exciting.’’

A computer simulation showing how Earth and our sun warp space and time, or spacetime. —LIGO Laboratory/Reuters

Prior to the publishing of Einstein’s theory of relativity, prevailing wisdom based on theories by Sir Isaac Newton said that the structure of the universe was static, with celestial bodies moving within it.

Einstein suggested the shape of the universe can be changed by the matter and energy residing in it, be it a small moon or two massive black holes merging together at half the speed of light to form a super black hole with a mass equivalent to 62 suns. The New York Times used the analogy of a heavy sleeper representing matter and energy, and a mattress representing the universe, which might sag or warp due to the matter inhabiting (or in the analogy, lying on top of) it.

A disturbance in the cosmos could cause space-time to stretch, collapse and even jiggle, like a mattress shaking when that sleeper rolls over, producing ripples of gravity: gravitational waves.

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LIGO’s observation of gravitational waves represents the culmination of over 40 years and $1.1 billion worth of research that originated in the 1970s as a partnership between the Massachusetts Institute of Technology and California Institute of Technology. But even before then, the first few thought bubbles that led to LIGO began as a classroom experiment by MIT Physics Professor Emeritus Rainer Weiss.

An aerial photo shows the LIGO Hanford laboratory detector site near Hanford, Washington. —LIGO Laboratory/Reuters

Weiss discussed the genesis of the LIGO experiment in a Q&A with MIT News this morning, detailing its origins as a theoretical exercise with his students at MIT and its crystallization after sharing a hotel room with Caltech physicist Kip Thorne.

“The obvious thing to me was, let’s take freely floating masses in space and measure the time it takes light to travel between them,’’ Weiss said, describing the physics course he was teaching on general relativity. “The presence of a gravitational wave would change that time. Using the time difference one could measure the amplitude of the wave. Equations for this process are simple to write and most of the students in the class could do it. Forget for a moment that this was a thought experiment requiring impossibly precise clocks. The principle was OK.’’

After thinking about the problem, Weiss began to determine whether current technology (in the late 1960s) could conceivably detect gravitational waves. It wasn’t until 1975 when Weiss allowed Thorne to crash in his Washington D.C. hotel (Thorne hadn’t booked one) that the two decided to propose a joint partnership between the two universities to build what eventually became LIGO.

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Thorne explained LIGO’s observation to The New York Times in an email using the analogy of the ocean instead of a mattress.

“Until now, we scientists have only seen warped space-time when it’s calm,’’ Dr. Thorne said in an email. “It’s as though we had only seen the ocean’s surface on a calm day but had never seen it roiled in a storm, with crashing waves.’’

The black holes that LIGO observed created a storm “in which the flow of time speeded, then slowed, then speeded,’’ he said. “A storm with space bending this way, then that.’’

As for what the discovery means to him, Weiss told MIT News that at 83 years old, the validation of his life’s work brought him more relief than joy.

“I feel an enormous sense of relief and some joy, but mostly relief,’’ Weiss said. “There’s a monkey that’s been sitting on my shoulder for 40 years, and he’s been nattering in my ear and saying, “Ehhh, how do you know this is really going to work? You’ve gotten a whole bunch of people involved. Suppose it never works right?’’ And suddenly, he’s jumped off. It’s a huge relief.’’

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