On Monday, theoretical physicist Laurence Krauss sent the scientific community on Twitter reeling when he suggested that researchers may have detected, for the first time, an astrophysical phenomenon called gravitational waves.
Discovering gravitational waves would be a huge deal for physics
Right now, the rumor is just that. The scientists to which the rumor refers work at the Laser Interferometer Gravitational-Wave Observatory (LIGO) and told Business Insider that there is no basis for such a discovery, yet.
Discovering gravitational waves would be a huge deal for physics, cosmology, and our understanding of the universe at large. But if you’re not a scientist studying one of the aforementioned fields, it’s possible you’ve never heard of these mysterious ripples. What the heck are gravitational waves, and why have physicists been struggling to find them for a century? Moreover, why should we care?
Simply put, gravitational waves are vibrations in the fabric of the universe—light-speed ripples in spacetime itself, caused by such epically violent events as exploding stars and black hole mergers. Thanks to inconceivably large, violent, and distant celestial happenings, the atoms that make up everything from the stars in the sky to the human beings on Earth are shaking a tiny bit, all the time.
Krauss does not work with the Advanced Laser Interferometer Gravitational Wave Observatory, or LIGO, which is searching for ripples in the fabric of space and time.
But he tweeted on Monday about the apparent shoring up of rumor he’d heard some months ago, that LIGO scientists were writing up a paper on gravitational waves they had discovered using US-based detectors.
“My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting,” Krauss tweeted.
His message has since between retweeted 1,800 times.
What are gravitational waves?
Gravitational waves are disturbances in the fabric of spacetime. If you drag your hand through a still pool of water, you’ll notice that waves follow in its path, and spread outward through the pool. According to Albert Einstein, the same thing happens when heavy objects move through spacetime.
But how can space ripple? According to Einstein’s general theory of relativity, spacetime isn’t a void, but rather a four-dimensional “fabric,” which can be pushed or pulled as objects move through it. These distortions are the real cause of gravitational attraction. One famous way of visualizing this is to take a taut rubber sheet and place a heavy object on it. That object will cause the sheet to sag around it. If you place a smaller object near the first one, it will fall toward the larger object. A star exerts a pull on planets and other celestial bodies in the same manner.
What are gravitational waves and why do they matter?
If gravitational waves have been discovered, astronomers could use them to observe the cosmos in a way that has been impossible to date. “We would have a new window on the universe,” Krauss said. “Gravitational waves are generated in the most exotic, strange locations in nature, such as at the edge of black holes at the beginning of time. We are pretty certain they exist, but we’ve not been able to use them to probe the universe.”
Einstein predicted that the waves would be produced in extremely violent events, such as collisions between two black holes. As gravitational waves spread out, they compress and stretch spacetime. The ripples could potentially be picked up by laser beams that measure minute changes in the lengths of two 4km-long pipes at the Ligo facilities.
Engineers occasionally add synthetic signals to the Ligo data to test the equipment. While these are designed to mimic gravitational wave signals, Krauss said he had heard explicitly that the signal had not been added artificially.
“I don’t know if the rumour is solid,” Krauss told the Guardian. “If I don’t hear anything in the next two months, I’ll conclude it was false.”
The discovery would open a new window on the universe by showing scientists for the first time that gravitational waves exist, in places such as the edge of black holes at the beginning of time, filling in a major gap in our understanding of how the universe was born.
A team of scientists on a project called BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) announced in 2014 that they had discovered these very ripples in space time, but soon admitted that their findings may have been just galactic dust.
However, scientists have yet to confirm this theory with observational evidence, which is why LIGO is so important.
“The detection of gravitational waves would be a game changer for astronomers in the field,” Clifford Will, a distinguished profess of physics at the University of Florida who studied under famed astrophysicist Kip Thorne told Business Insider in 2015. “We would be able to test aspects of general relativity that have not been tested.”
Not only that, the ability to observe gravitational waves would open a whole new frontier of astronomy. The same way that astronomers today use light waves to study the universe, they could also use gravitational waves to see cosmic objects — such as colliding black holes — like never before.
How to snag a gravitational wave
LIGO first began sniffing the skies for gravitational waves in 2002. And between 2002 and 2010, the $620 million experiment came up empty handed.
To better the odds, engineers began upgrading LIGO to make it 10 times more sensitive to gravitational waves. Last September, scientists turned the new-and-improved machine on and began taking data with, what is now called Advanced LIGO.
The way Advanced LIGO works is that it consists of two identical machines that are located 1,865 miles apart — one is in Livingston, Louisiana and the other is in Hanford, Washington.
At each detector, there are two equally-long tunnels that have a mirror at the end (one of the mirrors is shown in the image above). Scientists split a laser beam in two and then fire each half down one of the two tunnels. When the beams reflects off the mirror, the two beams should return at the same time, since they’re both traveling at the speed of light.
However, if a gravitational wave passes through the detector the same time the laser is traveling through the two tunnels, there will be a slight difference in time when the first half of the beam returns compared to the other half.
Compared to the length light waves we see with our eyes, which are micrometers in size (about the width of a human hair), gravitational waves are huge. This is why the distance between each LIGO detector is over 1800 miles, because that’s about how long astronomers think a gravitational wave should be.
Therefore, if one detector observes a gravitational wave, it should mean the other detector should measure the same signal, offering immediate confirmation that the observation at the first detector isn’t a fluke.
Scientists at LIGO aren’t taking any chances with this experiment. Before they announcing a discovery, the data will have been fully vetted twice-over by their expert peers.
But if they do succeed, it will revolutionize astronomy as we know it.