LIGO founder Rainer Weiss talks gravitational waves at UW

There has been a great deal of talk about gravitational waves since scientists with the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced back in February that they had collected the first evidence of the phenomenon in September 2015. Dr. Rainer Weiss, professor emeritus of physics at MIT and one of the founders of LIGO, talked about the history, discovery, and future of LIGO Tuesday at the University of Washington. The event was part of the Frontiers of Physics lecture series of the University’s College of Arts and Sciences.

Was LIGO really the first?

Dr. Rainer Weiss, a co-founder of LIGO, gave a lecture this
week at the University of Washington about the detection
of gravitational waves. The logos represent the more
than 80 organizations involved in the LIGO
Scientific Collaboration. Photo: Greg Scheiderer.

Weiss said that it might not be totally accurate to say that LIGO was the first to spot gravitational waves. Joseph Weber at the University of Maryland claimed to have detected them way back in 1969, but no other scientists could duplicate his observation, and the claim was eventually discredited. Weiss said much credit should go to Russell Hulse and Joseph Taylor, Jr., of the University of Massachusetts. They used a radio telescope to study what is now called the Hulse–Taylor binary, and noticed that the orbits of these two neutron stars around each other have decayed since they were discovered in 1973. A graph of the decay matches up precisely with a plot of the loss of energy predicted due to gravitational waves.

“It’s a dead ringer,” Weiss said. “That was, as far as I’m concerned, the first real evidence that there were gravitational waves. It was a very important moment, because there had been endless discussions in the scientific community about whether the gravitational waves that Einstein had predicted were real or not.”

In a way the detection of gravitational waves is like the story of an “overnight sensation” who hits the big-time after decades toiling in obscurity. The first glimmerings of LIGO go back more than 40 years, and the basic design of the observatory was actually created well before Einstein dreamed up gravitational waves as part of the general theory of relativity.

The beginnings of LIGO

Back in 1967 MIT asked Weiss to teach a course about relativity. He didn’t tell them that he wasn’t really up on the math of relativity, and joked that it was all he could do to keep a day ahead of his students. Weber was doing his experiments at the time, and Weiss had his class do a thought experiment—what Einstein would call a Gendankenexperiment—about how to detect gravitational waves using light beams. Their solution was essentially a Michaelson Interferometer, a device developed in 1880s. (An animated view of a simple interferometer is below; also check our recent post about LIGO from an Astronomy on Tap Seattle event.) A few years later, after the Weber findings were dismissed, Weiss started to think about the detection of gravitational waves a little more seriously.

“I wanted to convert that Gedankenexperiment into a real apparatus,” he said.

An animation of how LIGO works. A laser beam is directed through a splitter into two
equal-length arms, and reflected back. If the length remains the same, the reflected beams
cancel each other out. But if a gravitational wave distorts the beams, they do not cancel and
light reaches a detector. Image credit: LIGO/T. Pyle.

This was easier said than done. As noted, many in the scientific community doubted that gravitational waves existed, and even Einstein had expressed doubt that they could ever be detected. This made getting funding for the work a challenge. The technical obstacles were greater still. The device had to detect preposterously small distortions in spacetime—along the order of a thousandth of the width of a proton—and it had to do so in an environment in which there is a tremendous amount of noise. The Earth itself is spinning and vibrating, ocean waves lap up on the shore, a train goes by. They had to figure out a way to get the interferometer mirrors to hold still. That problem was solved by suspending the mirrors from multiple pendula, which themselves hang from a noise-reducing feedback system. Even a little heat or a molecule of oxygen in the interferometer tube could distort the light beam.

“The way you get rid of it: you make a very good vacuum, and that costs a lot of money,” Weiss noted. They also added mirrors to the basic design that make the light path longer and keep more light in the system, both ways to amp up the sensitivity of the instrument.

It’s no wonder this “overnight” discovery was more than 40 years in the making, and didn’t happen until a century after Einstein first proposed gravitational waves. Weiss spent a lot of time recognizing the many scientists who contributed to LIGO over the years, and noted that today the LIGO Scientific Collaboration includes more than one thousand people from 83 different organizations.

More discovery to come

The future of gravitational wave astronomy is fascinating, according to Weiss. With the VIRGO interferometer in Italy and LIGO-India (INDIGO) joining the LIGO facilities at Hanford, Washington and Livingston, Louisiana, scientists will be able to triangulate to get a better idea about where detected gravitational waves originate. The eLISA mission of the European Space Agency would be a huge interferometer in space that could possibly spot gravitational waves with longer lengths, created by such events as the mergers of supermassive black holes. The LISA Pathfinder mission successfully tested some of the technology earlier this year, and the ESA just this week put out a call for concepts for the next phase of the project. Most interesting is the possibility to detect gravitational waves from almost the instant of the Big Bang, which could be spotted as density variations in the cosmic microwave background.

“I fully expect that if there are gravitational waves that come from inflation, in the next ten years they’ll be found,” Weiss predicted.

A full house at the UW enjoyed the engaging lecture by Weiss.

Brilliant blunders can be portals to discovery

Mario Livio takes comfort in the gaffes of the greatest scientific minds of all time.

“There is something very reassuring in the fact that even these giants made major blunders,” he said during a talk Wednesday in Seattle to promote his new book. “People would ask me what the book was about; I’d tell them it’s called Brilliant Blunders, and it’s not an autobiography.”

Mario Livio spoke about his latest
book, Brilliant Blunders, May 15 at Town
 Hall Seattle. Photo: Greg Scheiderer.

In Brilliant Blunders Livio, senior astrophysicist at the Space Telescope Science Institute, examines major mistakes by some of the greatest scientists ever: Albert Einstein, Charles Darwin, Linus Pauling, Lord Kelvin, and Fred Hoyle. He talked about three of the examples during his lecture at Town Hall Seattle.

First, Livio took on Darwin and evolution, which Livio called “the single best idea that anybody has ever had.” Darwin’s blunder, though, was adopting a theory of blended heredity, which was a fairly widely accepted viewpoint of the time. Blended heredity held that the characteristics of a mother and father would be mixed, as one might mix a gin and tonic.

“Darwin did not understand, at first at least, that with blended heredity there is no way natural selection would have ever worked,” Livio said, noting that if you bred black and white cats, within a few generations you would only have gray. “In your gin and tonic, if you mix it with lots of tonic, in the end there is no gin.”

In Darwin’s time Gregor Mendel was coming up with the correct model for genetics, but Livio said Darwin didn’t know of Mendel’s work, and if he had he probably would not have understood it—“Darwin was very weak in mathematics,” he noted—but somehow Darwin had nailed evolution.

“When you have somebody who is a real genius some of the steps along the way may be wrong, but somehow their insight leads them to the correct result,” Livio said.

The next big blunder considered was Linus Pauling’s attempt to come up with a structure for DNA.

“Pauling’s model for DNA had the wrong number of strands, it was built inside out, and there was nothing to hold it together. Worse yet, he tried to hold it together with hydrogens,” Livio marveled. The “A” in DNA stands for acid, which Livio explained means that when you put it in water it should release hydrogen. But in Pauling’s model hydrogen was holding the structure together, so it couldn’t release it.

“Here was the greatest chemist of the world proposing a model the violated the basic rules of chemistry!” Livio exclaimed. He discusses Pauling’s shortcoming at length in the book, but said it may have been a combination of a race to publish and a bit of egotism from previous successes.

“If I work out the basic structure,” Livio surmised Pauling may have been thinking, “all of the other details will work out.”

Finally Livio took on Einstein, whom he called “the embodiment of genius.” Livio noted that when Einstein developed the theory of relativity he assumed that the universe was standing still. But that couldn’t be, because its gravity would cause it to collapse on itself. So Einstein added what Livio called a “fudge factor”—the cosmological constant—to make things balance out.

Then, when Lemaître and Hubble found the universe to be expanding, Einstein concluded he didn’t need the constant and took the term out of his equation. Fast-forward to 1998 and the discovery that the expansion of the universe was accelerating—because of the constant.

“Einstein’s blunder was to take the term out, not to put it in!” Livio said. “If he left that term in he could have predicted that the universe should be accelerating.”

The conclusion Livio draws from these brilliant blunders is that science can be messy and that there’s no straight line to the truth. Goofs are good.

“When you think outside the box you’re likely to make mistakes every now and then,” he said. “If you want to be certain all the time, your progress will be so incremental that you actually may miss the real breakthroughs.”

“This is not to advocate for sloppy science,” Livio continued. “This is just to say that you have to allow for these things that I call brilliant blunders. You have to allow for the possibility of making breakthroughs through processes that occasionally will actually hit upon various obstacles.

“Scientific blunders can be portals to discovery.”