The First Measurement of Gravitational Waves
Written by Colin Devroe · 12 February 2016
One hundred years ago, in an apartment in Bern, Germany here on Earth, Albert Einstein had a theory that everything in the universe was rolling around on a fabric called spacetime and that objects with larger masses had larger affects on this fabric.
Picture the difference between a sumo wrestler and an infant child sitting in the middle of a trampoline. The infant child would naturally be “drawn” to the wrestler since the wrestler bends the fabric of the trampoline so much more.
Or, imagine the affects of throwing a pebble or a massive boulder into the middle of a placid lake. The more massive the object, the more waves.
Since Einstein’s work was published his theories have slowly been proven to be true by observations made in nature. What Einstein worked out on paper using letters and numbers has actually been observed through telescopes both here on Earth and those orbiting in space.
Image credit: NSA/ESA.
One example of this is gravitational lensing. If spacetime bends under the weight of massive objects, like our sun, then light itself would bend as it moved over this fabric. It turns out this isn’t easiest of things to observe (you know, since the sun is so bright) but during a solar eclipse it is a bit easier. After a few tries, and a lot of arguments, this affect was clearly documented in 1919 by Arthur Eddington and Frank Watson Dyson when they actually measured light from distant stars being bent around the sun.
This and other observations proved that Einstein’s theory regarding the fabric of spacetime was sound. But, did this mean that this fabric could have waves in it like the pond when a boulder is thrown into it? Do these gravitational waves move at the speed of light? Could massive gravitational events that happen in the universe be measured by these waves?
It turns out, this is far harder to measure than gravitational lensing. Massive gravitational events don’t happen very often close to home. And so the waves they produce end up being very small by the time they reach Earth. What is a massive gravitational event? Well, a star exploding would be one.
And over the years humans have seen a number of these events. The Crab Nebula, as an example, likely exists due to a supernova that was observed by Chinese astronomers in 1054 AD. This event is referred to as SN 1054. There have been many others like SN 185, SN 1006, and SN 1572.
Not only did Einstein’s theory not exist when these events occurred but there was also no instrumentation sensitive enough to measure the gravitational waves of spacetime — which at this distance from these events could only be referred to as a light wobble — brushing passed Earth at the speed of light.
Fifty years or so ago an instrument began to be constructed to attempt to measure these waves. LIGO, or Laser Interferometer Gravitational-Wave Observatory, is an instrument that detects slight wobbles of gravity. Very slight. Like, width-of-a-human-hair at millions of miles from Earth slight.
Once built all we needed to do was wait for a large enough gravitational event to happen that we can measure it with this new tool. Well, it turns out one already happened and the gravitational waves from it was just about to whoosh passed Earth.
One-point-three billion years ago two black holes merged after falling towards each other for billions of years. A black hole is massive. Not in its size but in its actual mass. But when the two black holes merged, an event that took only a few milliseconds to happen, the amount of gravitational power emitted was astronomical. Like two spheres of water splashing together mid-air this sent a bunch of “waves” out throughout the cosmos.
The initial wave is incredibly powerful. Calculations show that the power of this gravitational wave is greater than all of the gravitational power of all of the stars in the known universe. Multiplied by 50.
One of the waves from this event sped passed Earth last year and fortunately the team at LIGO was watching. It results in a blip that lasts less than a second. But in that short blip is an incredible amount of data and the ability to state that Einstein’s original theory of spacetime being bent in waves by larger gravitational events to be true yet again.
What effect will this have on astronomy? Reddit user Astronomer321 put it this way:
Finally, I can't emphasize how huge this is! We are literally going into a new era of astronomy right now, and I think that's no exaggeration. Think of it this way, most of astronomy right now has been done with light, ie. electromagnetic waves - with some exceptions, like cosmic rays or space missions - but pretty much all astronomy has only been with EM waves. Now we will literally have a new tool in our toolkit and will likely learn all sorts of new things we won't have even expected. I can't wait!
Light tells us a lot. Light from a distant star can tell us how far away it is, how large it is, how hot it is, whether or not it is moving towards us or away from us, what materials actually make up the star, and whether or not any other objects orbit the star. Among other things. So for decades we’ve been learning about the universe by looking at the different types of light rays coming from distant objects and events. And we’ve learned an awful lot.
Starting yesterday we can now begin to measure large gravitational events and learn even more than we could have otherwise. We do not even know what we can learn yet. And as LIGO and other instrumentation becomes even more sensitive we’ll be able to detect smaller and smaller events at greater distances.
In short, the LIGO announcement changes everything yet again.