Ripples in space-time, which were predicted by Albert Einstein as part of his theory of relativity. Here's a little primer on that, featuring the dreamy voice of David Tenant:
Massive objects in space really do warp it, not unlike a ball rolling around on a piece of stretchy fabric. If we could directly observe these ripples, we could see the signatures of events like the mergers of massive black holes.
"Virtually our entire knowledge about the Universe is based upon the observation of electromagnetic waves, such as visible light, infrared, ultraviolet, radio, X-rays and gamma rays," the ESA explained in a statement. "LISA Pathfinder will pave the way to a completely different method of observing the Universe: detecting gravitational waves. This will allow astrophysicists to address some of the most fundamental questions about the Universe and possibly raise new ones, such as the nature of binary black holes and their mergers, which are among the most powerful events in the Universe."
LISA Pathfinder itself won't look for these ripples. The probe carries two 4.4 pound cubes made of gold and platinum, and once the probe is about a million miles away from Earth, they'll be released into free-fall in vacuum chambers meant to protect them from any interference. Tiny thrusters will work tirelessly to correct the probe's position as the force of the sun's light pushes it out of place. In theory, the blocks will be kept in perfect suspension. LISA's lasers will try to detect minute movement between the blocks caused by space-time ripples, but scientists on the ground don't expect to witness any events of that sort this time around.
“We want to see whether we can create an environment in orbit that’s free of interference, and where we can conduct these high-precision measurements,” Michael Menking, senior vice president for Earth observation, navigation and science at Airbus Defense and Space -- the main technology contractor on the mission -- told the AP.
If all goes as planned, the real LISA mission could launch as soon as 2034. It's likely that ground-based detectors will have made our first observations of big, dramatic gravitational waves by then, but a space-based probe like LISA will be necessary to detect the ones hiding behind curtains of cosmic dust.