Scientists have for the first time detected gravitational waves, ripples in space and time hypothesised by physicist Albert Einstein a century ago.
What is all the fuss about gravitational waves and why should I care? Am I in danger?
Astronomers and astrophysicists are over the moon with the news that gravitational waves have been directly detected. They had only indirect evidence but now have a direct detection of one of these things. There is no danger, the waves pass over us all the time and we don't feel them. The excitement is scientists now know they exist rather than just believe they exist.
But what are they?
Explaining what they are is easy, but convincing you why it is so important is more difficult. Imagine throwing a pebble into a pond. It hits the water kicking off small waves that radiate outwards. The waves appear because they use up the energy delivered by the pebble.
Now bring the pebble up to the size of a star or a black hole. Imagine the energy involved if two black holes smashed into one another, a common occurrence in deep space. The energy has to go somewhere and is given off in a number of ways including making gravitational waves.
These spread out in all directions travelling through spacetime as they go. This is the very fabric of the universe, a combination of space and time.
Anything that has gravity - for example planet Earth - can bend and distort spacetime but you need something cataclysmic to deliver the energy needed to kick off gravitational waves.
How did they manage to find them?
This was achieved by an international collaboration called LIGO. It uses two enormous L-shaped detectors based in Louisiana and Washington State. Each arm of the detectors is 4km long and laser beams are fired down these arms. If a wave passes by causing spacetime to distort then the beam in one arm will get shorter than the other by a tiny amount. This can be as small as one thousandth the diameter of a hydrogen atom so we are talking tiny. LIGO can detect this but can also predict what kind of event caused the wave, for example colliding black holes.
So what is the take home on this?
Being able to detect and study gravitational waves gives astronomers a whole new way to view the universe. It also proves the last big prediction made by Albert Einstein 100 years ago that gravitational waves must exist
It took all that time since to develop ways of detecting these invisible waves and then actually finding them after 14 years of effort by 1,000 scientists from 16 countries involved in LIGO.