Why Gravitational Waves are Relativily Amazing!

Today I'm going to write about gravity. And not the ironically scientifically inaccurate film of 2013, but the enormous scientific breakthrough that was announced earlier today.

For those of you who haven't heard yet, it was announced earlier today that gravitational waves have been picked up by the LIGO detector in The United States. I was originally intending to do a post on either how we learn or why plants are green today but lets face it, I'm not just going to sit around and write about biology while my favourite science has made what is debatably the biggest discovery since the Higgs boson.

So I guess I should start by explaining what gravitational waves are and why they are so important? Okay. 100 years ago a pretty smart guy called Einstein realised why nobody could detect variations in the speed of light no matter how hard they tried, because it was a universal constant. And he postulated that that in order to keep it constant, even time and space would bend. And so, the theory of general relativity was born.

The theory that says that space and time are one thing called space-time, like the fabric of the universe and we're all like little bugs wandering around on our speck of dirt. However space-time isn't constant, as I said its like a big piece of fabric, and as a result, it is able to stretch, contract and twist. The thing that causes it to stretch and contract is mass. Yeah that's right, anything with mass, even you, warps the space around it. When it warps this space, things around it are drawn towards it and so it gives the illusion of gravity.

So what has this got to do with gravitational waves? Einstein predicted a lot of amazing things with his theory of relativity, gravitational lensing, Frame dragging, time dilation etc. And amazingly each one of these has been tested and proven experimentally one by one. Except for gravitational waves.

Gravitational waves are when an enormous amount of mass disturbs the fabric of space-time enough to cause what are effectively ripples of physical space. This can only happen however, if the object moves in an uneven way. A circular object spinning doesn't produce them, but a non uniform supernova explosion does. They are in the form of what are known as quadrupole waves, waves which oscillate in a similar way to a slinky, except its in three dimensions and instead of a string stretching, its space. So gravitational waves are like ripples in a pond, but in the universe itself.

So why can't we detect them? Even the biggest gravitational collisions caused by neutron stars merging, super massive black holes and even hypernova explosions, produce waves which only change the size of our space on Earth by a factor of 10^-21. And such extreme events are enormously rare across the universe! So in order to detect these, we need an extremely long piece of space to measure, and something to measure it against which is smaller than the fluctuation in space, as well as a really rare powerful event to happen a long time ago in a galaxy far far away (they travel at the speed of light but still might take millions of years to reach us).

How did we do it then? We're physicists so lasers are the obvious go-to answer. So physicists in America built the LIGO (Laser Interferometer Gravitational-Wave Observatory) with two detectors, one in Washington, and one in Louisiana. In each one, a singular laser beam is split into two and travel down two tunnels which are perpendicular to each other. At the end of the tunnel they are reflected off a mirror and come straight back. As the waves have travelled equal distances, they should come back together to make a wave which  exactly the same as the initial one, however if a gravitational wave passed through the system, it would mean that the space would contract in one direction more than the other and so the resulting beam would be different to the one that set off to begin with.

On September 14th 2015, a signal was measured which, looked promising, and various observatories were consulted to look for astronomical events which could have been the cause. This signal is now known to coincide with  the collision of 2 super-massive black hole which produced more than 500 times the energy of the starts in the visible universe. The statistical evidence also shows that the chance of it being a fluke are roughly 1 in 6 million. So in summary well done them!

This marks a new age for astronomy, now that we know that gravitational waves exist and can be detected, it could pave the way towards gravitational telescopes which would let us image our universe in entirely new ways! In fact the LISA project is currently looking at how to build  gravitational wave detector in space because, although the eventual goal for these devices is astronomy, they have  long way to go yet.

It is a true demonstration of human perseverance and intelligence that, 100 years after we predict something, we are still searching for it until we find it. Personally my favourite quote is by Isaac Newton - "If I have seen further, it is by standing on the shoulders of giants." and this has never been more evident than now. The work we do today was inspired by Albert Einstein, a Giant, like Newton and Pythagoras before him, and we can only hope that one day, maybe even we may be held in such regard.

Once again thank you all so much for reading and see you next time :)