CMU physics professor hit by a gravitational wave of excitement
Entering the Carnegie Mellon University office of Ira Rothstein almost feels like walking onto the movie set for “A Beautiful Mind” or “Good Will Hunting.”
The expansive white board is filled with numbers and letters and equations, scrawled variously in green, blue, red and black marker, clearly the work of someone with a deep understanding of that which, for the layman, is difficult to understand.
Things like time and space and the universe.
Rothstein, who has called Pittsburgh home for the last 16 years, was a senior at Brown University and a computer science major, when he took a theoretical physics class for the first time.
Not only did taking that class change the trajectory of Rothstein’s own life, but its ripple effect was to aid the work of those scientists who announced last month that they finally had proof of the existence of gravitational waves, a theory postulated by Albert Einstein about 100 years ago.
Now a professor in the department of physics at CMU, Rothstein is energized by the discovery that has been 30 years in the making.
Not all theoretical physicists can communicate their work on a level within the grasp of the nonphysicist, but Rothstein, with his laid-back affability, can.
“Look at the sky,” he said. “You can see stars and planets that are coming from the light. But there’s a lot more stuff coming to us from outer space that we can’t see with our eyes.”
Included in that category are the effects of gravity.
“The stars are so far away,” said Rothstein. “They have a gravitational pull on us, but we couldn’t measure it.”
But when two objects in space collide, he said, they produce a gravitational wave that can be measured.
Rothstein illustrated that effect by using the hypothetical of two people sitting in a swimming pool at opposite ends. If one person slaps the water with his hand, little ripples will be created that may be felt by the person on the other side of the pool.
Similarly, if a star collides with something out in space, waves will be created by that collision. Those waves eventually will reach us on Earth, and in theory, we can measure them, and thus prove their existence.
Last month, David Reitze, executive director of LIGO, the Laser Interferometer Gravitational-Wave Observatory — which was developed 30 years ago to do such measuring — announced that scientists had done just that.
“We have detected gravitational waves,” Reitze announced to reporters. “We did it.”
In this case, the gravitational waves that were measured were created by two black holes that collided 1.8 billion years ago, Rothstein said. Those black holes were pretty far away — 80 megaparsecs, a distance which he described as 8, followed by 20 zeros miles.
The waves were detected through the LIGO, which is essentially two mirrors, four kilometers apart, with a light shining between them.
“When a ripple comes through,” Rothstein said, “it changes the distance between the mirrors.”
“These little ripples are in space and time,” he continued. “They are what Einstein predicted, and he was right.”
The mirrors are only moved a fraction of the length of an atom, so the sensitivity of the LIGO is critical in detecting the movement. Every five years since the LIGO has been in use, scientists have increased its sensitivity. The sensitivity most recently was increased in September 2015, Rothstein said, and immediately, the gravitational waves created by the collision of the two black holes were apparent.
“The rumor is [the scientists] have seen more [waves] since then, but they have not analyzed them yet,” he said.
There are two sets of LIGOs, Rothstein noted. One set is in Louisiana and the other is in Washington state. Both sets moved at the same time as a result of the gravitational waves created by the collision of the two giant black holes.
Rothstein’s contribution to the LIGO project is a mathematical formula to determine “when black holes spin, how that changes their ripples.”
Rothstein worked on that research five or six years ago, along with graduate student Rafael Porto, he said.
“In this case, they couldn’t use [the research] because the size of the black holes was too big,” he said. But his mathematical contribution could be applied to the measurement of other gravitational waves that may be detected by the LIGO.
“This is a very old subject,” he noted. “People have been working on it since Einstein postulated it. And there was a lot of debate as to whether gravitational waves were real.”
The significance of the discovery of gravitational waves is huge, he said.
“This has opened up a whole new window on the universe,” said Rothstein, a member of Congregation Beth Shalom. “It’s given us a new sense. We can’t see black holes, but we can feel the gravitational waves. The implications are that it’s a big universe out there, and it’s as if we’ve been blind. It’s like someone has taken off the blindfold. Who knows what else is out there.”
Anyone interested in more details about the discovery of gravitational waves can check out Rothstein’s interview on WESA, which can be found online.
Toby Tabachnick can be reached at tobyt@thejewishchronicle.net.
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