Vuk Mandic and his colleagues made big headlines in scientific journals last week by finding nothing — nada, zilch, zippo — in their search for gravitational waves.
In order to comprehend why nothing can be something big in astrophysics, we need to look first at the stakes in this quest for gravitational waves.
These mysterious waves were predicted in Albert Einstein’s 1916 general theory of relativity. If mass accelerates in some way — say, you pick up a child or drive a car — you have these ripples in space and time, the theory goes. But we Earthlings are mere specks on a universal scale, so any waves we make are insignificant.
Instead, scientists are looking for the waves in connection with mega-scale cosmic events: collisions of black holes, shock waves from supernova explosions — and the granddaddy of all, the Big Bang.
Influence has been observed
The gravitational waves’ influence on stars has been observed. But the waves themselves never have been directly detected. If they were, it would set off a revolution in physics, opening an entirely new way of looking at the universe.
“Black holes, we can’t see at all at this point … super nova explosions are not understood yet,” Mandic said. “So we hope that gravitational waves would allow us to open another window into astronomy.”
Scientists also believe that the Big Bang created a flood of gravitational waves that still fill the universe and carry information about the immediate aftermath of that colossal explosion. No one has ever been able to study the full fiery nature of the physics at play in the moments following the Bang. In that sense, gravitational waves would have a unique tale to tell, Mandic said.
“Gravitational waves are the only way to directly probe the universe at the moment of its birth; they’re absolutely unique in that regard. We simply can’t get this information from any other type of astronomy,” said David Reitze, a physics professor at the University of Florida and spokesperson for the collaboration behind this research.
700 scientists, 60+ institutions
With those incentives in mind, scientists have tried for decades to directly detect the waves. In 1997, the National Science Foundation funded a project engaging 700 scientists from more than 60 institutions in 11 countries. Caltech and Massachusetts Institute of Technology designed and operated the project.
Mandic co-chairs a working group in that LIGO (Laser Interferometer Gravitational-Wave Observatory) collaboration. He was the lead author on the first major report of the collaboration’s findings, published last week in the journal Nature.
The report is based on data collected from 2005 to 2007 using instruments called interferometers. The main instruments are located in Hanford, Wash., and Livingston, La.
At those sites, scientists split a laser into two beams that travel back and forth down long interferometer arms. When a gravitational wave passes by, one arm should be slightly stretched while the other is compressed, according to Einstein’s theory, and the beams should reflect the difference.
Two years of research analyzed
In Minnesota, Mandic’s team analyzed data from the two years of research and explored the implications for different theoretical models.
As I said at the beginning of this post, they found nothing.
Now, finally, comes the question of why that is something.
Think of gravitational waves as if they were waves on a pond, coming in different sizes from different directions. Scientists had believed this metaphoric pond was stormy with large, crashing waves.
The findings don’t support that theory. They suggest smaller turbulence, calling for different rulers to measure gravitational waves. In other words, physicists can now rule out some models of the early universe.
“We can start learning what the universe is not like,” Mandic said.
New constraints, and parameters for future study
That in itself is a profound discovery, putting new constraints on the details of how the universe looked in its earliest moments.
And it suggests parameters for future phases of the research. Work is under way on an Advanced LIGO, which is to use instruments that are 10 times more sensitive than those available for this study.
At the end of the interview with Mandic, I said “Maybe I’ll call you back in a few years for the story of the actual detection of gravitational waves.”
Said Mandic, “That would be splendid.”
Sharon Schmickle writes about a wide range of subjects, including science, international affairs and Greater Minnesota.