Update: Researchers today announced that gravitational waves have been detected for the first time. More information about this historic announcement is provided at the end of the article.
A group of scientists from Caltech and M.I.T. are making an announcement this afternoon (15:30 GMT) regarding the possible detection of gravitational waves. For years scientists have searched for the waves predicted by Einstein’s general theory of relativity but always come up short. Rumours have been rippling through social media for months but the wait will finally be over later today.
— LIGO (@LIGO) February 10, 2016
It’s all relative
I feel the strength of a scientific theory is in its ability to make predictions. Albert Einstein made incredibly bold predictions that have turned out to be right time and time again, sometimes taking almost a hundred years to confirm. His greatest contribution was undoubtedly the theory of general relativity. It can’t be overstated how incredible this work was. If aliens arrived today and said, “sure, you’ve got digital watches and selfie sticks, but how advanced are you really?” I’d tell them that we’ve figured out general relativity.
General relativity sounds a bit crazy and it’s easy to see how his ideas weren’t believed by many researchers at first. Einstein predicted that space and time actually exist together as one interwoven spacetime that can be stretched and distorted by massive objects like planets and stars. What we experience as gravity is just spacetime itself being warped.
A common analogy for explaining gravity involves simplifying the situation by imagining only 2 dimensions. Imagine placing balls of different weights on a bedsheet held taut. The balls will warp the material and the heaviest will create the biggest wells in the otherwise flat sheet. If you roll small marbles across the sheet and they get too close they can be pulled into a well created by a ball. Spacetime is warped by mass just as the bedsheet is. Large objects like planets bend spacetime itself and we call the effects gravity.
Spacetime is probably more fluid that you might imagine. Instead of a bedsheet, another 2D analogy could be the surface of coffee. If you stir it with a spoon it will create swirls. The spinning of planets swirls spacetime, a phenomena we call frame dragging. Our own satellites have their orbits affected by frame dragging as the Earth itself swirls spacetime around it.
As crazy as warping spacetime itself sounds, Einstein’s theory of general relativity has stood strong since 1915. In his own lifetime he saw many predictions confirmed. One of the most important involved a wobble in Mercury’s orbit around the sun. Astronomers had predicted an unseen planet influencing Mercury’s orbit, but Einstein claimed his theory could explain Mercury’s wobble. Spacetime is curved by the Sun’s mass and Mercury simply follows the shortest past through the distorted fabric of spacetime. Einstein also predicted that the Sun’s warping of spacetime would bend the incoming light of distant galaxies during a solar eclipse. In 1919, Arthur Eddington photographed a full eclipse and found that star clusters were stretched out to an extent predicted by Einstein’s theory.
It can be difficult to image how the time aspect of spacetime can be warped but we know it happens and it affects our daily lives. Engineers use general relativity calculations to correct GPS satellites so that we can use navigation on our smartphones. If ignored, the GPS coordinates would be off and get worse by several kilometers every day. This adjustment is required because the satellites experience time differently to us. A clock on one of these satellites would tick faster than an identical clock here on the Earth’s surface. It can be hard to imagine but Einstein’s theory holds true time and time again.
Ripples in spacetime
What we experience as gravity is the warping of spacetime. Employing the bedsheet analogy once more, being pulled into a planet’s orbit is just falling into a part of the fabric distorted by mass on it. Imagine suddenly dropping a heavy ball onto the sheet or causing one of the balls to explode. A ripple would travel across the whole sheet and be felt everywhere before returning to normal. Einstein predicted that epic events in space, such as black holes colliding, would send ripples through spacetime itself. We call these gravitational waves. Physicists are certain they exist but they have never been detected despite years of searching.
Scientists have searched for gravitational waves since 2002 using LIGO (Laser Interferometer Gravitational Wave Observatory), which consists of two L-shaped detectors in Washington and Louisiana. Using mirrors and lasers, the detectors should be able to measure changes in spacetime itself. LIGO ran from 2002 until 2010 and detected nothing. So does that mean gravitational waves don’t exist? Or are they just too difficult to detect? The waves are smaller than an atom by the time they arrive at Earth, so maybe our technology isn’t sensitive enough.
LIGO was recently upgraded with advanced technology and the search resumed last September. Immediately there were rumours from inside sources that something exciting had been discovered. Cosmologist Lawrence Krauss got Twitter users excited after tweeting that waves may have been discovered.
My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.
— Lawrence M. Krauss (@LKrauss1) January 11, 2016
Something has been found
It’s easy to get your hopes up when you work with LIGO. Fake detections are deliberately introduced to the data once in a while to keep the researchers on their toes. It would be unwise to announce the discovery of gravitational waves in September even if that’s what they believe they’ve found. The fact that we’re getting a major announcement several months later is a promising sign.
Why should we care about the detection of gravitational waves? Firstly, it’s further evidence that we’re on the right track when it comes to understanding how the universe works. We can be more confident than ever that Einstein was right. Perhaps more importantly, it’s hoped that someday we can use gravitational waves as a tool for probing previously unseen parts of the cosmos. Not everything emits light, so we might be able to use gravitational waves to study the darkest matter in the universe. We could even detect supernovae before they’re actually visible in telescopes as the gravitational waves would reach us before the light does (the ripple would set off when the collapse occurs, but the burst of light happens later). We could have an early warning system so we know where to point our telescopes.
This is an exciting day and we’ll update the article this afternoon to reflect on the press announcement.
News from LIGO sounds exciting. Not tweeting details before Thurs. Two days left before a new era in astronomy and physics could begin.
— Lawrence M. Krauss (@LKrauss1) February 10, 2016
Update: Gravitational waves have been detected!
— LIGO (@LIGO) February 11, 2016
The researchers have confirmed that LIGO has detected ripples in spacetime. The wave was caused by two black holes colliding over a billion miles away from Earth. When these black holes collided, multicellular life on Earth was only just beginning to evolve! This is a huge announcement and has big implications for astronomy. We’ve detected gravitational waves; we’ve directly detected black holes; and all of this further confirms the theory of general relativity. Now that we know we can detect the waves, all sorts of exciting techniques should be possible in the future. This could really be a new era for astronomy as it should lead to technology letting us directly observe previously hidden phenomena like black holes and neutron stars.
Dave Reitze: "This is the first time a #BinaryBlackHole system has been directly observed"
— LIGO (@LIGO) February 11, 2016
It’s incredible to think that we can detect the fabric of the universe itself being pulled and stretched at such a tiny scale. Congratulations to the international researchers!
Main image © LIGO Scientific Collaboration