Awesome Astronomy Announcement: Gravitational Waves Detected
Physicists (who are also now astronomers) have announced the direct detection of gravitational waves produced by colliding black holes and predicted by Albert Einstein 100 years ago.
“We have detected gravitational waves. We did it,”
– David Reitze, executive director of LIGO at a press conference in Washington.
This news is just stupendous. We are witnessing an immense milestone in astronomy that is certain to be the science news of the year, if not the decade, and is almost a complete no-brainer for a Nobel prize.
But what are gravitational waves? Albert Einstein predicted them a century ago as part of his theory of General Relativity. In a nutshell, they are fluctuating waves of space-time itself traveling at the speed of light. When he published his Magnum Opus, General Relativity, in 1915, he introduced to the world many things, including the revolutionary idea that gravity can be interpreted as the curvature of space-time due to mass. A year later in 1916 he realized that if mass could curve space-time, it could also send ripples across it. This happens to an extraordinary degree when tremendous masses accelerate. What are the heaviest things and how fast can they go? How about 2 black-holes accelerating to a significant fraction of the speed of light. That would be the king of gravitational wave creators and that’s exactly what the Laser Interferometer Gravitational-Wave Observatory (LIGO) has apparently found.
It happened on September 14, 2015. Just hours after the system was turned on (and before it was even officially “ON”) some shocking squiggles appeared on the LIGO readout. I have to say that making such a find so soon after being turned on seems almost too fortuitous…just sayin. When it was all said and done, the scientists determined that the signal had to have come from a black hole merger, the first detection of one ever. All the gravitational wave hallmarks for such a merger were there. The signals matched General Relativity predictions precisely. Primarily, this included a distinctive “chirp” pattern that black-holes were thought to emit as they collide with titanic force. Solidifying their discovery even more, they also detected another pattern of expected gravitational waves called the Ringdown that newly formed black holes should make as they pop into their final spherical shape. As the signals were examined closely, they could even flesh out the major details of the event such as its 1.3 billion light year distance and the masses involved. Imagine two spheres, each roughly 150 km wide. Now cram 29 suns into one and 36 into the other. Then have them spiral around each other until they collide at 150,000 km per second. All that from just a chirp. Science rocks!
The real heroes of this story though are the twin LIGO installations on the opposite ends of the U.S. These “observatories” detect gravitational waves (GWs) by shooting laser beams down two 4 kilometer tubes which are at right angles to each other. These beams reflect off the far-end and come back to re-combine where the tubes meet. If the distances the light travels is exactly the same, the light waves align perfectly in such a way to cancel each other out. If GWs are passing by however, the tubes lengthen and contract in an asynchronous way since they’re 90 degrees to each other. Since one tube gets longer when the other gets shorter, the 2 laser beams will not travel the same distance. Therefore, when the beams are combined, the waves will no longer cancel each other out meaning that gravitational waves could have just done a hit and run.
Sounds easy doesn’t it? Well getting to that point was, in a word…Fucking hard as hell. I call this Isolation Frustration. Isolating just the GWs was a truly monumental task. This instrument is the most sensitive ever created ever. It can detect the minutest of distance discrepancies. Many news stories are claiming that LIGO can identify a distortion in spacetime that is one thousandth the diameter of a proton. Other descriptions are even more impressive-sounding such as…LIGO can detect a change in the distance between the Sun and Proxima Centauri, four light years away, that is the thickness of a human hair.
In other words, LIGO is really really really really really sensitive. The makers of LIGO had to, not only, make an instrument that was sensitive to something beyond belief, but also make it completely IN-sensitive to everything else. Here’s some of the things they had to identify and then eliminate or control over the many years of refinement:
- Tiny imperfections in the laser light due to minute fluctuations in the power grid
- The random movements of the individual atoms within the mirrors
- The nearby motions of the wind and ocean
- Distant lightning storms
- Passing cars or wolves
Ans this is only a small handful of the things that could either be mistaken for GWs or obscure the real ones. The father of LIGO, Rainer Weiss said
“There are ten thousand other tiny things, and I really mean ten thousand..And every single one needs to be working correctly so that nothing interferes with the signal”
You may think that if this happened way back in September, what took so long for the announcement? This is science baby. Reaching the gold standard of 5 sigma (1 in 3.5 million that the results are due to chance) takes time. Researchers had to verify that everything was calibrated properly, go through every damn line of code, review all possible environmental disturbances etc until the only reasonable conclusion was that two black holes merged and sent us their gravitational wave evidence. Another reason that they had to be so absolutely sure was that GW detection had gained something of a bad reputation over the years. The first primitive detectors decades ago seemed to find many signals, all the time in fact, all of which were not real. Then there was that debacle in 2015 when BICEP 2 scientists claimed to find primordial gravitational waves which turned out to be just space dust.
So why is this so damn important? It’s not just that Einstein’s prediction has finally been validated. That guy is lionized enough. It’s a little embarrassing at this point, isn’t it. Like his rep really needs another boost (just joking Al…love ya lots…mwaaah). It isn’t because we finally have solid evidence that gravitational waves exist after years of searching and researching. We kinda already knew they existed (see the first point above). Plus certain phenomena already indirectly pointed to their existence. The real reason is that we’ve finally been released from the tyranny of the electromagnetic spectrum. Ever since Galileo peered into the night sky we’ve been obsessed with these little ethereal waves of photons from space. First it was visible light then, one by one, we voluntarily put on the shackles of radio waves, x-rays, infrared, gamma, you name it.
The confirmation that we can detect gravitational waves opens a new window on the universe, creating a completely new branch of astronomy…Gravitational Wave Astronomy. With it we can interrogate the universe in a way impossible until now. We can seriously investigate the vast numbers of mysterious dark objects that don’t emit much light: black holes, neutron stars, maybe even cosmic strings. We’ll be able to see some of the inner workings of the most energetic events in the universe. My personal favorite is using primordial gravitational waves to find out what the big deal was with that mother of all bangs, The Big Bang.
Light is useless for looking at universe at its zygote stage and what created it. The oldest light, the Cosmic Microwave background radiation, was set free into the universe when it became transparent after 400,000 years (this is photon decoupling). To see deeper in the past than that we need to use something that was able to penetrate the haze of the early universe that light could not. These primordial waves could finally tell us details about the origin of everything that we could never find out otherwise.
And most importantly….I predicted this would be the year of gravitational waves on our podcast.
Image Credit: https://www.sciencenews.org/article/gravitational-waves-explained