Arizona State University will celebrate the centennial of Albert Einstein's Theory of General Relativity on Friday. Meanwhile across the country, scientists are analyzing data attempting to prove the existence of gravitational waves, the last, most elusive prediction of Albert Einstein's theories.
Last week, ASU Professor Lawrence M. Krauss caused a furor when he tweeted "confirmation" of a rumor he'd heard that gravitational waves indeed had been discovered at the Laser Interferometer Gravitational-Wave Observatory (LIGO).
"If it were discovered in this centennial year of general relativity, it would be beautifully poetic," Krauss said. "It would open up a new window on the universe."
LIGO was begun by scientists at Caltech and MIT in 1992 and started operation 10 years later. It searched for eight years to no avail before shutting down in 2010 to upgrade equipment.
Joseph H. Taylor Jr. won a Nobel Prize in 1993 for discovering a pulsar in a binary star system allowing him to measure the frequency of its pulse. He subsequently was able to infer perturbations that suggested the existence of gravitational waves.
"Indirectly, we kind of know they exist, but we've never seen them directly," explained Krauss, who's written several popular books on astrophysics, including A Universe From Nothing. "This would be a profoundly important observation but more importantly to be able to use it to do the astronomy of the 21st century."
LIGO finished the five-year, $200 million upgrade early last year, improving the resolution of the equipment by more than 300 percent. Its scientists are trying to pick up the collisions of black holes and neutron stars (near-black holes).
Like dancers, they'll circle each other, drawing closer before merging. The objects are so massive that when they finally come together, it will send shock waves through space-time, like ripples across a pond. These gravitational waves are what LIGO is seeking.
As Krauss explained, the first-generation equipment wasn't sensitive enough. These collisions are pretty rare, particularly in the Milky Way, and many don't create a wave strong enough to reach us. The upgrade has made detection possible.
"The kinds of things that [LIGO] would be sensitive to happen very rarely, but if you have sensitivity to detect these events out to maybe 100 million light years, there are a lot of galaxies," he said. "If you have hundreds or thousands of galaxies or more, then presumably these things are occurring all the time. The wonderful thing about the universe is that it's big and it's old — so very rare events happen all the time."
LIGO has two detectors — one in Louisiana, the other in Washington. They consist of an L-shaped tunnel four kilometers (2.5 miles) long on its longest side, the other side half as long. These vacuum tunnels contain mirrors reflecting a laser.
Should a gravitational wave pass, it would disturb the laser's timing by a minuscule amount, and if both detectors pick it up (eliminating a local effect, such as a tremor), they should be able to triangulate its origin.
But it's not that cut-and-dried. Three members of the team have access to a special control that allows them to move the mirrors in a way that mimics an event. Known as a "blind injection," it's occurred on two occasions, in 2007 and 2010.
When one occurs, it isn't revealed to the team until after they've looked at the data and decided to submit an article
The rumor is that a measurement occurred during the engineering run, when a blind injection wasn't occurring. Krauss didn't specify his source on the matter.
"The only reason I am confident is that the people talking about it said that issue had been addressed, but I don't know for sure. I don't really know," Krauss said. "We'll wait and see until they come out with their results. I'm just excited by the possibility."
Krauss caught backlash for promoting a rumor, but he said: "I don't think it harms anyone.
"The only thing I do feel a little bit bad about is that the poor experimentalists are now getting inundated by reporters when they really should be working."
There was a suggestion a little more than a year ago that a group working at the South Pole had discovered gravitational waves that suggested proof for inflation in the Cosmic Microwave Background, the echo of the Big Bang that reverberates across the universe. In the end, they withdrew their claim, blaming the readings on galactic dust.
The gravitational waves picked up at LIGO "will probably be much more useful to understand the nature of general relativity," but success might create the kinds of tools that can isolate the telltale clues proving the Big Bang and Inflation, just like we're finishing up General Relativity now.
"It's the most exiting new window into the rest of the universe," Krauss said. "It means we'll be building more complicated and powerful instruments that will be the astronomy of the 21st century."
