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Physics + MathPhysics & Math

Big Ideas of 2016: Gravitational Waves Rocked the World

ByAllison EckNOVA NextNOVA Next

Gravitational waves were the life of the party in 2016—at least, from a physicist’s point of view.

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Einstein famously predicted them as part of his general theory of relativity. The idea was that gravitational waves behave like electromagnetic waves except that the latter travel in spacetime; the former, however, is an actual disruption in spacetime itself. And unlike electromagnetic waves, gravitational waves emanate any time something moves—it’s just that most of the time, those movements aren’t extreme enough (nor do they involve enough mass) for the resulting gravitational waves to be visible to mere humans. But this year’s discovery changed that, and practically everyone was talking about it.

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LIGO scientists witnessed two black holes from 1.3 billion years ago collide and become one.

Advanced LIGO, an updated version of the initial observatory that started listening for gravitational waves in 2002, is made up of two L-shaped tubes called interferometers. If a gravitational wave passes through, one arm of the “L” expands and the other contracts. That’s what the LIGO team saw in the fall of 2015 (their results weren’t published until February 2016): the first direct evidence of gravity’s echo through spacetime, and the first dispatch from a black hole merger 1.3 billion light-years away. These black holes were 29 and 36 solar masses—substantial enough to generate gravitational waves that were still detectable (using incredibly sophisticated technology, of course) by the time they reached Earth.

In June, LIGO scientists announced that they’d observed a second signal from a separate pair of rapidly orbiting black holes. While this event was similar to the first, there were a few notable differences: the signal was weaker, but it shifted into higher frequencies—bringing it within LIGO’s sensitive range earlier on in the merger compared to the first detection. This allowed the team to record more orbits before the merger was complete—and in turn, access more precise data.

Both the first and the second detections aligned perfectly with Einstein’s theory. With that much confirmed, the LIGO team now hopes to analyze the rate of these black hole coalescences. Some scientists believe that gravitational waves could have other applications—for example, they could help prove string theory or solve the information paradox .

Despite that gravitational waves were a favorite contender for this year’s Nobel Prize, the LIGO team didn’t qualify because the results were announced after the deadline for nomination. So unless another incredible finding emerges, the team could have 2017 in the bag.

Meanwhile, LIGO’s top masterminds —Ronald P. Drever and Kip. S. Thorne of the California Institute of Technology, and Rainer Weiss of the Massachusetts Institute of Technology—will split $1 million awarded by Yuri Milner, a Russian Internet entrepreneur and philanthropist. Another $2 million (also from Milner) will go to the 1,012 other scientists who helped surmount this astronomical feat.

Image credit: Alain Riazuelo / IAP/UPMC/CNRS (CC BY-SA)

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