Tag Archives: Rainer Weiss

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?

Rainer Weiss at UW

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.

Share

LIGO, LSST, AOT set for alphabet soup week

A talk by a founder of LIGO and a closer look at the LSST are the highlights of our astronomy calendar for the week.

Wave of the future

Rainer Weiss

Dr. Rainer Weiss. MIT photo: Bryce Vickmark.

Gravitational waves have been all the rave since they were first and finally detected last year. Dr. Rainer Weiss, one of the founders of the Laser Interferometer Gravitational-wave Observatory (LIGO) will give a lecture titled, “Gravitational Wave Astronomy: A New Way to Explore the Universe” on Tuesday, October 25 at 7:30 p.m. in room 130 of Kane Hall on the University of Washington campus in Seattle. Weiss began his work on gravitational waves with a classroom exercise in a general relativity course given at MIT way back in 1967. He will discuss the history of gravitational waves proposed by Einstein, go over the results of the LIGO project, and look into the future of gravitational wave astronomy.

All sign-ups for the free lecture have been taken, but you can watch a live stream of the talk on Tuesday. You can also sign up for the waiting list should seating become available. The talk is part of the Frontiers of Physics public lecture series from the UW College of Arts and Sciences.

AOT goes LSST

AOT LSSTTwo University of Washington scientists involved in the Large Synoptic Survey Telescope (LSST) will talk about the project at a special Friday edition of Astronomy on Tap Seattle at 7 p.m. October 28 at Peddler Brewing Company in Ballard. Doctors John Parejko and David Reiss will explain the LSST, currently under construction in Chile and targeted for being fully operational by 2023. The LSST will image and catalogue tens of billions of galaxies and stars and find more than three million exploding stars and six million asteroids and comets over the next decade, effectively creating a 10-year, multi-color, ultra high-resolution movie of the night sky. It will collect an astounding 20 terabytes of data every night. Parejko and Reiss will talk about the LSST telescope and camera design, the software challenges associated with processing such a huge data set, and the science to be gained from mining the sky in 4-D.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the UW, this month in concert with TEDxSeattle and the LSST. It’s free. It’s always a good idea to bring a chair, as the combination of beer and astronomy is tremendously popular!

Star parties and planetarium shows

The Island County Astronomical Society will hold a free public star party on the evening of Friday, October 28 at Fort Nugent Park in Oak Harbor.

The Spokane Astronomical Society will hold a special Halloween star party beginning at 5:30 p.m. Saturday, October 29 at the club’s dark-sky observing site near Fishtrap Lake on Miller Ranch Road East near Sprague.

Haunted Night SkyIt’s Spook-tober at the Pierce College Science Dome, and this Saturday, October 29 will be the last day for its kids’ planetarium show called “Haunted Night Sky.” Participants will be able to find creatures in the night sky, build a Frankenstein satellite, and take a tour of the Sea of Serpents on the Moon, the Witch’s Head Nebula, and other spooky places in the universe. Best for kids ages 3-12. Shows are scheduled for 12:30 p.m. and 2 p.m. Cost is $3.

Futures file

You can scout out future astronomy events on our calendar. New additions to the calendar this week include:

Up in the sky

Venus flirts with Saturn and Jupiter has an encounter with the Moon this week. The Sky This Week from Astronomy magazine and This Week’s Sky at a Glance from Sky & Telescope have more observing highlights for the week.

Share