Ryan Shannon has spent the last 11 years with his ear to the cosmos, but he still hasn’t heard what he’s been listening for.
Using the high-precision Parkes telescope, Dr. Shannon and a team of scientists have tried for more than a decade to detect the most elusive element of Albert Einstein’s general theory of relativity: gravitational waves. They revealed last week that they have so far come up empty in their search, casting doubt on our understanding of galaxies and black holes.
"We heard nothing. Not even a whimper," said Shannon, who works at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, in a news release. "It seems to be all quiet on the cosmic front – at least for the kind of waves we are looking for."
Since first proposed by Einstein a century ago, the general theory of relativity has withstood nearly every scientific test thrown at it. Its postulation of gravitational waves – which could help us look back into the very beginning of the universe – remains its only prediction that scientists have been unable to confirm.
In their search for proof of the existence of gravitational waves, Shannon and his team of researchers focused their attention on pairs of black holes circling around each other at the center of galaxies. Their theory is that as the black holes merge, they send ripples through space and time. The scientists have tried to detect these gravitational waves by using pulsars, dead stars that create regular pulses of light with such regularity that they’re used as cosmic clocks. As Space.com explains:
Scientists with the Parkes Pulsar Timing Array want to look for interruptions in the regular pulse of these pulsars caused by gravitational waves. Put simply, if a gravitational wave passed by a pulsar, it could warp the space-time between the pulsar and Earth. This could cause a hiccup in the timing of the otherwise extremely regular light pulses.
Theoretical work has suggested that the Parkes telescope should be sensitive enough to detect the waves. But Vikram Ravi, a postdoctoral fellow at the California Institute of Technology and member of the research team, said he and his colleagues reached that level of sensitivity but still found nothing. That means, if it waves do exist, they are quieter than scientists predicted.
"So what it means is that the theorists – including me – need to come up with better models," Mr. Ravi told Space.com. "They need to think a bit harder about what the gravitational wave signal may actually look like."
The team’s findings were published Wednesday in the journal Science.