Gravity: Making Waves

LIGO’s Extended Family

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An artist's depiction of LISA's three satellites orbiting Earth.

Jet Propulsion Laboratory

Because LISA will have little interference from outside noise, the low-frequency waves should show up as obvious spikes in the signal output. In addition, LISA should be able to pick up gravitational information from supermassive black holes, which radiate waves at frequencies ground-based interferometers can’t register. “If we haven’t detected a gravitational wave within a day or two of LISA starting operation,” says Cornish, “we’ll know that something’s gone horribly wrong.”

Probing Creation
As ambitious as LISA is, the search for gravitational waves won’t end there. Fast-forward 30 years into the future. At that time, Cornish anticipates being heavily involved in an even-more-next-generation interferometer that he describes as “LISA on steroids”: the Big Bang Observatory. Along with LISA, this observatory is a key component of the Beyond Einstein project, a collection of missions aiming to answer fundamental questions about the structure and evolution of the Universe. The space-based Big Bang Observatory could offer scientists an unprecedented view of the very earliest moments of our Universe’s expansion—one seen through gravitational waves.

Gravitational waves first started escaping from the Big Bang at about 10 ^–35 seconds after it began 14 billion years ago. It’s taken that long for the gravitational information to reach our cosmic doorstep, and to this day, waves from this event continue to pass by. Because gravitational waves are affected little by intervening space objects, these ancient signals are theorized to be intact, yet faint. They’ve had quite a journey, after all.

“We expect these gravitational waves from the Big Bang to be fairly weak,” explains Cornish, “so we have to up the sensitivity of the instrument.” This translates into two supersized interferometers for the Big Bang Observatory. Each will resemble LISA, but they will be equipped with lasers over a thousand times more powerful and they will have much larger mirrors, each a few meters wide.

The behemoth instrument is very much in the conceptual stages. Cornish is currently determining how the endless stream of competing signals from binary sources will be subtracted from the observatory’s anticipated readings in order to get the purest possible Big Bang signal.

With five ground-based interferometers in place and two space projects in the works, the science community is putting quite a lot of stock into a theoretical signal that hasn’t even been officially detected yet. But Cornish, like most physicists, isn’t worried. “The most spectacular discovery for gravitational-wave observatories would be an absence of waves,” he says. “That would be the most revolutionary discovery of science this century.”