As far as big deals in astronomy go, the confirmation of the existence of gravitational waves is likely to change our understanding of the universe in ways we never thought possible before.
After almost a century trying to prove Einstein’s theory of the existence of gravitational waves, the evidence turned out to be right under our noses.
Using the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), one of the most powerful of its kind in the world, the faint traces of the ripples caused in space-time from cataclysmic events were recorded for the first time in September 2015, with significant fanfare.
While we can hardly describe the astronomy we have conducted for hundreds of years as ‘being in the dark’ (despite the murky depths of space), the official confirmation of gravitational waves has been described by astronomers as the equivalent of us throwing open a curtain to see how the universe really works.
A new door opens
Until now, astronomers have only been able to view the cosmos either directly using space telescopes, or by analysing objects in deep space using instruments that measure ultraviolet light.
While you, me and everyone you know creates ripples in space-time simply by, say, dancing around with another person, this rippling is practically insignificant and undetectable.
However, with major cosmic events – like the collision of two black holes, or the birth of a supernova – huge ripples expand into the universe over vast distances that, eventually, strike our planet, but very faintly.
LIGO, the L-shaped telescope, consists of two 4km, highly-sensitive laser beams that can detect even the faintest of these changes.
When a gravitational wave hits Earth, LIGO and advanced monitoring systems can detect the smallest stretching or squeezing of space-time between two points of each laser.
And so it was in September last year that such a warping of space-time was detected at a frequency of 100Hz.
This discovery allows us to throw open the door and view the first one trillionth of a second of the Big Bang.
“In short, this is a really, really difficult experiment.” Those are the words of Dr David Reitze, the man who announced to the world last September: “Ladies and gentlemen, we have detected gravitational waves. We did it.”
First steps with LISA Pathfinder
A California Institute of Technology physicist and the executive director of LIGO, Reitze was at the heart of this major breakthrough, and is one of those who will help determine where we go from here in terms of actually using the phenomenon to unlock previously-kept secrets.
Speaking with Siliconrepublic.com, Reitze spoke of how surprising the breakthrough had been in the first place, not only because it was discovered earlier than he had anticipated (he had predicted 2017), but also by how ‘loud’ the signal was.
While the reading that preceded the discovery of gravitational waves was measured at this cosmic shot of 100Hz, a typical gravitational wave measures a much lower frequency of between 0.1MHz and 1Hz.
In order to find these more elusive frequencies, we needed a very special piece of equipment called the Laser Interferometer Space Antenna (LISA) Pathfinder.
Developed by the European Space Agency (ESA) LISA Pathfinder was a testbed for future gravitational wave observatories and, in June 2016, recorded gravitational wave measurements five-times more accurate than anyone anticipated.
Having reached its operational orbit 1.5m km from Earth, the experimental craft internally released a pair of identical, 2kg, 46mm gold–platinum cubes.
By monitoring the smallest of fluctuations in the relative positions of the cubes, LISA Pathfinder could detect gravitational waves free of the seismic, thermal and terrestrial gravity noises that limit ground-based detectors.
“Ground-based detectors are sensitive to certain classes of astrophysical objects, particularly stellar mass binary black holes or neutron stars,” Reitze said, “but eLISA will widen the gravitational wave spectrum to be able to probe more massive astronomical objects such as intermediate-mass black holes.”
eLISA: a space project like no other
What Reitze is referring to in eLISA – the ‘e’ standing for evolved – will be a full-scale working space-based gravitational wave observatory.
With a planned launch in 2034, eLISA will be the largest instrument ever built by humanity and will act as a space-based gravitational wave detector measuring the smallest of space-time distortions.
That’s not to say there won’t be other possibilities for those without access to such a powerful device.
Even now, new research is beginning at a number of other LIGO-like observatories, including Virgo in Europe, the Kamioka Gravitational Wave Detector (KAGRA) in Japan and the recently-approved Indian Initiative in Gravitational-wave Observations (INDIGO).
This will not only help us “better pinpoint in near real-time the location of gravitational wave events in the sky,” Reitze said, but “will enable an entire new field of transient astronomy in which joint gravitational wave and electromagnetic observations of the same event can reveal vastly more than independent observations”.
With multiple observatories trawling the night’s sky both on Earth and in space, Reitze and many of his colleagues will hope that we could soon answer one of the greatest questions of our time: how did it all begin?
“The big payoff will come when we see gravitational waves produced during the Big Bang for the first time,” Reitze said. “These primordial gravitational waves carry information from the moment of Big Bang and, in fact, are the only way we can derive information from the first moments of the universe. A detection of primordial gravitational waves will be huge for the field of cosmology.”
AI in gravitational waves’ future
This huge amount of astronomical data obtained from eLISA and all the other LIGO-like observatories on Earth will require a digital toothcomb like no other.
To give an example of the amounts of data astronomers can expect to deal with, the Large Synoptic Telescope (LSST) expected to begin operations in 2019 will map sections of the night’s sky on a daily basis.
During a night’s activity, it has been estimated that the LSST will generate 30TB of images, requiring a database capable of handling 150 petabytes of storage.
This is simply more than a whole team of astronomers can ever attempt to handle manually, but now and in the future, perhaps AI and machine-learning techniques can make the entire process much more efficient.
“With its wide field, LSST will collect an unprecedented amount of image data in a very short time. Millions of astronomical objects need to be identified and classified on timescales shorter than hours. That’s a problem that’s tailor-made for machine learning,” Reitze said.
Even now, early attempts are underway to use machine learning and the internet to help sift through huge amounts of astronomical data.
Perhaps the most famous example being SETI@Home, which allows thousands of people at home to bind together to form a supercomputer to search through data in the hope that one of its millions of users could find evidence of an extraterrestrial signal.
AI has already played a significant part in making the breakthrough that led to the recording of the September gravitational wave and will likely do so again in the future.
With so much ‘noise’ generated by the world around us, it was up to AI to help astronomers filter out irrelevant signals and hone in on the minute fluctuations that make up a gravitational wave.
This was achieved by comparing the signals in the gravitational wave channel with other channels, and the coupling of frequencies helped rule out irrelevant ones.
Author and computer scientist Michael Yuan said about the technology behind detecting gravitational waves: “With proper physics models in place, the AI could learn to fit the data against the models and quickly predict astronomical events associated with new signals.”
With another two decades before eLISA begins orbiting Earth, astronomers still have time to perfect that technology that will open a new window into the origins of the universe.