May 5, 2016
From the moment Einstein hypothesized in his general theory of relativity that
gravitational waves exist, scientists have spent 100 years trying to prove it.
Now, students can finally follow the steps taken to prove a scientific breakthrough that
opened an entire new field of astronomical research.
Nergis Mavalvala, professor at MIT and member of Laser Interferometer Gravitational-
Wave Observatory, helped improve the project’s laser interferometers. On May 4,
Get The Daily Illini in your inbox!
Mavalvala will discuss the detection of these waves at the William D. Watson Memorial
Lecture.
The University will be the next academic institute where the quantum astrophysicist will
thoroughly explain the complex science behind LIGO’s findings.
“It’s really very rare that a scientific discovery makes it to the stages of major
newspapers worldwide,” Mavalvala said. “So what I plan to do is kind of unpack what’s
behind these new headlines.”
Mavalvala will focus on two main aspects: building an instrument that is capable of
measuring changes in distances that are 1,000 times smaller than a proton and
observing its signal.
The signal indicates a collision of two black holes in another galaxy more than a billion
light years away.
Stuart Shapiro, professor in physics at the University, theorized about black holes and
gravitational waves for decades. He said the discovery excited him because he has
spent a large portion of his career trying to validate Einstein’s theory.
“(LIGO) detected a gravitational wave source, and when it was analyzed, it was a
perfect, generic binary black hole merger — the kind you can only theorize about,”
Shapiro said. “This is the most important test ever in the theory of general relativity.”
Although this signal was detected in Sept. 14, 2015, several tests were needed to be
conducted before confirming its validity five months later.
“We had to confirm that the instrument was working correctly, and that it wasn’t just
some artifact from the instrument — something else that made the mirrors move,”
Mavalvala said.
The LIGO team also had to verify that a fake signal wasn’t already inserted into the
data, which was a common procedure used to check their searching techniques.
Once LIGO was confident that their findings implied the gravitational wave’s existence,
they began to examine the black holes more closely. From the signal, they were able to
determine the actual source parameters of the black holes.
With a team of 1,000 people, this data was collected and transposed into a research
paper over the course of three months. According to Mavalvala, many versions of this
paper — about 27 versions to be more specific — were written before the final product
was published.
Although these processes became timeconsuming, Mavalvala had a gut instinct that
she was dealing with genuine findings within the first day or two of obtaining the signal.
“One of the remarkable things about what LIGO measured is that the signal really looks
just as Einstein’s field equations would have predicted,” Mavalvala said.
LIGO had two detectors, located in Louisiana and in Washington, that both detected the
signal. Louisiana was the first to detect the signal, and Washington saw it seven
seconds later.
“So that time separation was important — the fact that the signal looked the same in the
tube detector,” Mavalvala said. “If it was some local artifact, like something bumping the
mirror, then it should be different in the two detectors.”
Once LIGO confirmed their observations on Feb. 11, Shapiro and his group of
University postdoctorates and undergraduates — known as the Illinois Relativity Group
— were able to simulate the cosmic scenario on their computers within a day or two.
“We get a plot of what is known as the ‘gravitational wave form signal’ that LIGO
detected,” Shapiro said. “One of these curves is the signal that LIGO detected; the other
curve is the signal we get in our computer simulation … We have two signals
overlapped. That means we nailed it — we know what happened.”
Abid Khan, senior in LAS and Engineering and member of the Illinois Relativity Group,
is ecstatic with the newest quantifiable evidence for black holes, but he is also curious
to hear about LIGO’s process.
“That was always something interesting to me,” Khan said. “How they were able to get
that precise to detect something that is (smaller than) an atom.”