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Thomas Carruthers speaks about LIGO and gravitational waves

The Outreach Committee for the Physics Department invited Thomas Carruthers to present four mini-lectures about black holes and gravitational waves this Spring semester. Carruthers is a senior member of the Laser Interferometer Gravitational-Wave Observatory, or LIGO, Scientific Collaboration, a large-scale physics experiment that observes gravitational waves by using twin detectors.

The senior physicist gave his first lecture on gravitational waves on Wednesday, March 28, 2018, where he introduced Isaac Newton’s theory of gravity. “Previously, scientists thought that gravity was a static force with no notion of traveling through space,” Carruthers said. “Gravity used to be thought of as instantaneous.”

He contrasted Newton’s theory with Albert Einstein’s theory of gravity. “[Einstein said] gravity is not a force, but a property of space and time. Because gravity can affect light, it must be a property of the universe rather than a force,” Carruthers said.

Carruthers explained how Einstein’s theory of gravity expanded the scope of physics. “It completely changed how scientists see the universe,” Carruthers said. “But how can scientists’ measure gravity?”

In the 1960s, physicist Joseph Weber used an aluminum bar, now known as a “Weber bar,” to record the movement of gravity. “During Weber’s first attempt, Weber heard a clear ringing tone from the aluminum bar that lasted for over a day. He announced that this was caused by gravitational waves bursting and striking the aluminum,” Carruthers said.

However, Carruthers explained that Weber’s evidence from his first attempt to detect gravitational waves in 1969 was incorrect. Carruthers said, “It turned out to be nothing but noise.”

Weber’s research made false claims about the detection of gravitational waves. “Even though Weber was incorrect, he pioneered the process of finding gravitational waves,” Carruthers said. “LIGO now carefully and conservatively releases observations after having been thoroughly tested.”

Throughout the lecture, Carruthers discussed black holes, neutron stars and the rubber sheet model. Additionally, he shared one of LIGO’s observations. “Pulsars are rapidly rotating stars. LIGO had observed mountains on pulsars,” Carruthers said. “Although they are only a few centimeters in height, the amount of energy it would take to climb the mountain would be equivalent to climbing Mount Everest about 100,000 times.”

Junior physics major Phoebe Sandhaus spoke about her impression of the lecture. She said, “[Carruthers] explained gravitational waves in a way that was easy for anyone to understand. I had no idea about pulsars having mountains; I thought they were completely smooth.”

Sandhaus described the experience as informative and enlightening. “The coolest thing about gravitational waves is that we could theoretically learn about things that happen inside the event horizon [of a black hole],” she said.

Carruthers spoke about LIGO’s potential contributions to science. “LIGO is searching for binary black holes, neutron star merges, binary neutron star collisions and more. They will pick up new revolutionary discoveries in the future, thanks to gravitational waves,” he said.

Carruthers’ lecture series is open to the public in Physics Building lecture hall 101. The dates and times of Carruthers’ future lectures are posted on the Physics Department News & Events section. Any individuals interested in science are welcome to attend the lectures.

“There are so many mysteries in science,” Sandhaus said. “There are many things we don’t already know and so many avenues to explore. I want to be a part of the discoveries scientists are making about the world we live in.”