In the pantheon of yet to be directly detected astrophysics/physics exotic phenomenon—things like the Higgs boson or dark matter—gravitational waves probably get the least amount of attention. Surprising in part, considering that gravity is one of the oldest known forces. And it certainly isn’t for lack of oddness — a powerful gravitational wave has the potential to literally warp reality, stretching space before your eyes. But if a team of Princeton researchers is correct, the direct detection of these elusive waves could be “imminent.”
To understand gravitational waves, first posited by Einstein in 1916, we need to go back to general relativity and the idea that space is bent by objects within it, like heavy balls on a rubber sheet. As space bends, time has to bend with it because, of course, that stretching has created more distance to travel. Something with enough mass, the infinite mass of a black hole perhaps, would turn that dent in space-time’s fabric into a bottomless pit. Instead of just making the journey around the massive object take longer, the black hole makes it take forever.
This can lead to some strange funhouse effects in our universe. As a macro example, if the photo above were an outline of subatomic particles, we’d expect such a squishing and stretching. But compared to other forces, the effect of gravitational waves on Earth is super-diluted, which is why we have to do extreme things to detect them.
The gravitational waves of orbiting neutron stars (NASA)
That space-time fabric is a real material in the sense that waves propagate through it. If you could punch a sheet of space-time, the result would be a rippling outward across the sheet — like if you punched a surface of water. The task before researchers now is to find those ripples, created by the cosmic punches of colliding galaxies or orbiting black holes. Said events should send ripples through space-time that eventually reach Earth. But by the time they get here, gravitational waves from these distant powerful events should be pretty weak, like the ripples we’ve made with our water-punch reaching a distant shore, far, far away. Hence, detecting them isn’t easy.
Our best bet for detectable gravitational waves then are collisions between the heaviest things in the universe: giant galaxies sporting supermassive black holes. According to a paper by McWilliams posted today at the arVix pre-print server, Princeton astronomer Sean McWilliams and his co-authors think these cosmic mergers are much more common than previously thought, and that in the last 6 billion years, galaxies have roughly doubled in mass and quintupled in size. Specifically, the rate of these massive, gravitational-wave-emitting mergers is “10 to 30 times higher,” with gravitational waves “3 to 5 times” more powerful than previously expected. According to the paper, this means researchers are 95 percent certain to directly detect gravitational waves by 2016.
One way of looking for these waves is to very carefully monitor what’s basically a super-cooled, perfectly-machined metal rod, hoping to catch distortions in its resonant frequencies caused by gravitational wave interference. Another method would be via NASA’s abandoned LISA project: a network of spacecraft beam lasers at each other, and the waves cause distortions in the beams sizable enough for scientists to detect.
The route to a 2016 detection is a bit different: instead of listening to some rod or laser array here on Earth, they look at deep space pulsars, e.g. the rapidly rotating “lighthouses” of the cosmos. Pulsars are so regular in their rotation — shooting off radio waves on every go around — that it should be possible to detect any distortion in that rotation caused by the gravitational waves. The discovery that these pulsars’ signals are disturbed by gravitational waves earned two researchers the Nobel Prize in 1993.
Video: what’s gravity and how do we detect it?
With a project called the International Pulsar Timing Array, a worldwide crew of observers studying a collection of 30 pulsars, we’re already looking for these distortions. The researchers suggest that a PTA might’ve already revealed gravitational waves, and they’re just hanging out in the data. Technology Review goes as far as to say, the first direct observation of gravitational waves “will be one of the most important breakthroughs ever made in astronomy; the discoverer a shoe-in for a Nobel Prize.”
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