Alumnus lectures on gravitational wave detection

September 23, 2016

UT alumnus David Reitze, director of the Laser Interferometer Gravitational-Wave Observatory, began his presentation by telling a story that started 1.3 billion years ago with the collision of two black holes that caused ripples through space-time.

“Unfortunately, we’re going to skip most of that 1.3 billion years and move forward to about a hundred years ago,” he said. “This is where the story gets interesting from the human perspective.”

Gravitational Waves Public Lecture
Photo Credit: Thomas Negrete, The Daily Texan

Reitze, who spoke Wednesday evening in the Hogg Memorial Auditorium at a talk sponsored by the UT physics department, said gravitational waves were first theorized by Albert Einstein as part of his theory of general relativity. Gravitational waves can occur when two objects orbit each other quickly and cause waves to distort space-time. When Einstein wrote about the waves in the early 20th century, technology capable of detecting gravitational waves didn’t exist.

“[Einstein said] if you’re an experimentalist and you’re trying to measure this effect, you should just go home, because you’re not going to be able to see the effect,” Reitze said.

Between September 2015 and January 2016, however, scientists detected, for the first time, two confirmed signals of gravitational waves and a third possible signal that fell short of their statistical confirmation standards.

“I personally didn’t think we were going to detect a gravitational wave until 2017,” Reitze said. “Extraordinary claims require extraordinary evidence, and this was going to be an extraordinary claim.”

LIGO consists of two laser interferometers each of which can split a beam of light into two and send it four kilometers away to a mirror to reflect back and recombine. When the two light beams recombine, they should be at the same frequency and cancel each other out. If a gravitational wave changes the space-time around the light beams, however, it causes an interference wave.

Richard Matzner, a UT physics professor, said the first gravitational wave signal was detected almost exactly 100 years after Einstein wrote about them. Matzner said when this first wave was detected last September, he was ecstatic.

“I had been working on relativity for a long time, and I was certainly anticipating that we would detect [gravitational waves],” Matzner said.

Reitze shared examples of gravitational waves appearing in popular culture caused by the announcement of the discovery, such as science-themed dresses with gravitational wave patterns and scientific “baseball cards.”

“The announcement, quite frankly, it overwhelmed me,” he said. “I was not prepared for the amount of visibility that this got.”

Biology pre-med freshman Joy Liu said she was interested in the talk because she likes space and wanted to learn more about gravitational waves.

“I heard about [gravitational waves], but I wasn’t sure what was really going on, so I was hoping this would teach me more about it,” Liu said. “I want to go to more of these [talks] in the future, because these seem really cool. If I had my way, I would probably major in something like astrophysics.”

According to Matzner, LIGO will be upgraded to be about three times more sensitive and will be able to detect gravitational waves from a volume of space 27 times larger.

“I would expect that that will mean there will be a whole lot more actual detections, probably on the order of about one a week,” Matzner said.

Reitze said in the future, the two U.S. LIGO detectors, and a third that will soon be completed in Italy, can be used to find the location of collisions between neutron stars, the remnants of massive stars made completely of densely-packed neutrons. Astronomers can use this information to point traditional instruments, such as x-ray telescopes, at the location to record more information from the event.

“This is a very exciting scientific revolution that is taking place right now,” Reitze said. “This is really the dawn of a new kind of astronomy. The next 20 or 15 years should bring us great discoveries. Gravitational waves are here, it’s a really exciting time.”

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