Astrophysicists may finally have discovered gravitational waves
In TechInsider, Dave Mosher writes:
Gravitational waves may have been detected for the first time, but we won’t know for sure until February 11, 2016 — when scientists will either confirm or dispel the rumors, sources close to the matter tell Tech Insider.
Detection of gravitational waves would be unprecedented. Whoever finds them is also likely to pick up a Nobel prize, since the phenomenon would confirm one of the last pieces of Albert Einstein’s famous 1915 theory of general relativity.
Confirming they exist would tell us we’re still on the right track to understanding how the universe works. Failing to find them after all these years might suggest we need to revisit our best explanation for gravity or rethink our most sensitive experiments, or that we simply haven’t looked long enough.
“Gravitational waves are ripples in the fabric of space-time, predicted by Einstein 100 years ago,” Szabi Marka, a physicist at Columbia University, told Tech Insider. “They can be created during the birth and collision of black holes, and can reach us from distant galaxies.”
Black holes are the densest, most gravitationally powerful objects in existence — so a rare yet violent collision of two should trigger a burst of gravitational waves that we could detect here on Earth.
Colliding neutron stars and huge exploding stars, called supernovas, are thought to generate detectable gravitational waves, too.
However, any sort of signal has eluded the planet’s brightest minds and the most advanced experiments for decades. Until now — maybe.
Columbia University in New York City is hosting a “major” event the morning of Thursday February 11, 2016, a source who is close to the matter, but asked not to be named, told Tech Insider.
Another source also confirmed the event but downplayed the significance of the event as anything “major.”
Regardless, several physicists and astronomers with expertise in gravitational wave science are scheduled to attend.
The topic? The latest data from the Laser Interferometer Gravitational-Wave Observatory (LIGO), a $1 billion experiment that has searched for signs of the phenomenon since 2002.
LIGO has two L-shaped detectors that are run and monitored by a collaboration of more than 1,000 researchers from 15 nations, and Marka is one of them.
Marka said that he and his colleagues have worked in the field for more than 15 years and that “these are very exciting and busy times for all of us.”
He also said that Advanced LIGO, an upgrade that went online in September 2015, finished a period of hunting for gravitational waves on January 12, 2016. (That was one day after we saw the first alluring rumors of detection.)
Both LIGO instruments are L-shaped arrays of lasers and mirrors that should be able to detect gravitational waves. Szabi Marka compared them to a pair of giant ears that can “hear” the spacetime ripples that result from black hole mergers, or some other catastrophic event in space. The closer a collision is to Earth, the “louder” the signal should be.
LIGO’s hearing is sensitive enough to detect mind-blowingly small disturbances of space, “much smaller than the size of the atoms the detector is built of,” he said. PhD Comics says LIGO’s level of sensitivity is “like being able to tell that a stick 1,000,000,000,000,000,000,000 meters long has shrunk by 5mm.”
Put another way, detecting a gravitational wave is like noticing the Milky Way — which is about 100,000 light-years wide — has stretched or shrunk by the width of a pencil eraser.
It would be no wonder why it has taken researchers so long to find gravitational waves; it’s terribly difficult work. (Even a truck driving on a nearby road can disturb LIGO, despite the instruments having state-of-the-art vibration-dampening equipment.)
It would also be no wonder why scientists might try to stay tight-lipped about the discovery yet “suck at keeping secrets just like everyone else,” as Jennifer Ouellette wrote at Gizmodo.
But at this point, there’s only one way to know for sure if the latest rumors are true: Wait until Thursday.
When Einstein’s General Relativity was first proposed, it was incredibly different from the concept of space and time that came before. Rather than being fixed, unchanging quantities that matter and energy traveled through, they are dependent quantities: dependent on one another, dependent on the matter and energy within them, and changeable over time. If all you have is a single mass, stationary in spacetime (or moving without any acceleration), your spacetime doesn’t change. But if you add a second mass, those two masses will move relative to one another, will accelerate one another, and will change the structure of your spacetime. In particular, because you have a massive particle moving through a gravitational field, the properties of General Relativity mean that your mass will get accelerated, and will emit a new type of radiation: gravitational radiation.
This gravitational radiation is unlike any other type of radiation we know. Sure, it travels through space at the speed of light, but it itself is a ripple in the fabric of space. It carries energy away from the accelerating masses, meaning that if the two masses orbit one another, that orbit will decay over time. And it’s that gravitational radiation — the waves that cause ripples through space — that carries the energy away. For a system like the Earth orbiting the Sun, the masses are so (relatively) small and the distances so large that the system will take more than 10^150 years to decay, or many, many times the current age of the Universe. (And many times the lifetime of even the longest-lived stars that are theoretically possible!) But for black holes or neutron stars that orbit each other, those orbital decays have already been observed.
We suspect there are even stronger systems out there that we simply haven’t been able to detect, like black holes that spiral into and merge with one another. These should exhibit characteristic signals, like an inspiral phase, a merger phase, and then a ringdown phase, all of which result in the emission of gravitational waves that Advanced LIGO should be able to detect. The way the Advanced LIGO system works is nothing short of brilliant, and it takes advantage of the unique radiation of these gravitational waves. In particular, it takes advantage of how they cause spacetime to respond.
Detection range of AdvLIGO