By Bernie Hobbs
Scientists have finally found direct evidence of gravitational waves — a feat Albert Einstein never thought we would manage. But what does this discovery actually mean?
For starters, it opens a new field of astronomy — gravitational wave astronomy — that will let us see everything from the heart of a black hole, to the moments after the Big Bang.
What are gravitational waves?
Einstein’s general theory of relativity tells us that gravity is the curvature of space and time.
The stronger the gravity an object has, the greater the deformation of space and time it causes.
Gravitational waves are caused when objects with strong gravity accelerate. As they accelerate, ripples of space travel away from them at the speed of light.
They are not like light waves travelling through space, they are actual waves in space: rhythmic stretching and squeezing of space.
All objects sitting in the path of gravitational waves rhythmically move further apart and closer together as the space they exist in is stretched and squeezed.
The strongest gravitational waves — the only ones we have a hope of detecting — are formed when objects with enormous gravity undergo dramatic acceleration. Like when two black holes merge to form another.
If scientists have indeed detected the to and fro movement caused by passing gravitational waves it will be a monumental achievement.
These ripples are so small — only a fraction the size of an atom — that Einstein thought they had to be beyond our technology.
What does the discovery mean?
Being able to detect and measure gravitational waves opens up an entire new field of astronomy.
Gravitational wave astronomy would allow us to look further back in time and deeper inside the most extreme objects in the sky — to the earliest instant after the Big Bang.
All of our existing knowledge of the universe comes from telescopes, and all telescopes (optical, radio, X-ray etc) rely on light coming from distant objects.
Telescopes tell us a lot, but the light they detect has been absorbed and scattered by lots of gas and dust between the source and the telescope. At best, we are getting blurry images.
Like light waves, gravitational waves are imprinted with information about their source — but it is information that light could never provide.
Gravitational wave astronomy will reveal the insides of distant objects because it will let us “see” their mass.
The pattern of movement as black holes coalesce, the changes inside a supernova, the mechanisms of a gamma ray burst will all become visible to us.
And because gravitational waves only interact with gas and dust to a tiny extent, their signal is much cleaner than those from light.
Our picture of the universe will come into much sharper focus.
Why was it so hard to find gravitational waves?
While Einstein’s general theory of relativity predicted gravitational waves, he thought that if they did exist, they would be far too small to ever be detected.