In a remarkable coup, physicists have detected gravitational waves. This is the biggest science story of this century, so far. It has deep implications for the future of physics. It will affect our lives in ways we cannot yet conceive.
It was a long time coming. One hundred years ago, Albert Einstein predicted waves of gravity based on his math, but he said they were too small to detect. Sixty years later a slight slowdown in the clocklike signal from a spinning neutron star in binary orbit matched the predicted loss of energy by gravitational waves, a measurement that won a Nobel Prize. Soon most astrophysicists accepted that the waves exist, but nobody had observed them directly.
An international project did it with a billion-dollar budget and an apparatus known as LIGO that was dismissed as a waste of money. It bounces a laser beam off distant mirrors to see if they vibrate by a miniscule fraction of the size of an atom. Well, of course they do! On that scale, they thrash about wildly with vibrations from distant earthquakes, traffic noise or even an indiscreet cough. Its keepers use clever ways to eliminate such influences. Then they wait for some humungous event there to radiate a gravity-wave signal. They check a duplicate setup 3,000 kilometres away to see if it gets the same signal.
It worked. On Thursday, the LIGO team announced laconically in a prestigious peer-reviewed journal that, “On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal.” Convincingly they show this signal is the real thing. It matches the expected signature of an extraordinary event, two big black holes colliding a billion years ago. A billion light years away here on Earth, LIGO started listening just in time to catch its gravitational echo.
Observing this event reconfirms Einstein’s theory. It is a shoo-in for a Nobel Prize, but it means much more.
First, it opens up a whole new capability. Since the days of Galileo we’ve used different kinds of “eyes” to see what happens in the universe with electromagnetic waves. Now gravitational waves give us another cosmic sense. Who knows what we will see with it?
Second, until now black holes have been the subject of much cosmological theory backed up by indirect observations such as stars moving in tight orbits around nothing visible. Now we are observing black holes directly.
Third, we have discovered a new class of black holes. Black holes with multimillion solar masses may lie at the centres of galaxies. Black holes with up to 10 solar masses are thought to result from the collapse of stars. The two black holes LIGO observed colliding had masses about 30 times that of our sun. This is a size astrophysics says should not exist. The LIGO event shows they are so common that two of them could get together. As I predict on fundamental grounds, intermediate black holes such as these may be the universe’s missing dark matter.
And fourth, gravitational waves — now known to exist and to behave as theory expects — may let us see through the opaque hot plasma that blocks our view of the first 370,000 years after the universe began. They could address the ultimate question: what happened before the Big Bang? Several projects that could answer this are underway. When one succeeds, that may be the biggest science story ever.
Republished from the Winnipeg Free Press, February 13, 2016.