What are gravitational waves?

What are gravitational waves? And why was everyone talking about it?

If you happen to have any friends on Facebook who even remotely follow the physics world, or if you yourself are that friend, there is a very high chance that you heard about LIGO and their discovery of gravitational waves.

But it's hard to understand how truly revolutionary this discovery is, without really understanding what it means. And believe me when I say, it's a very big deal.

Let's go back, to when Newton first proposed his grand idea about what gravity was. Newtonian gravity is probably the type of gravity that you are most familiar with.

"A particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses but also inversely proportional to the square of the distance between them".

In short, it means that we everything exerts a force upon us, and the strength of the force is determined by how big the object is compared to us, and how far away we are from the object. Specifically, if the object is very large, then it will exert a very large force on us. But if it is very far away, it will exert a lesser force on us.

That's a given. But there are a multitude of problems with it. The predictions for mercury's orbit around the sun with newtonian gravity is wrong, the idea that two objects can communicate with each other instantaneously is ludicrous (as Newton himself said), and many more. (watch this video if you want more detail https://www.youtube.com/watch?v=d95I3ka6DXU)

A certain scientist, one that you've likely not heard of, realised the flaws in Newtonian gravity, and decided to come up with his own model. His name was Albert Einstein (very small scientist, you probably wouldn't know who he is).

His proposal was that objects in space bended space-time around it, as if space was some thing flexible and fabric-esque. Objects which were heavier bended space-time more, and thus attracted objects smaller than it. If you're having trouble visualising it, have a look at this: https://www.youtube.com/watch?v=MTY1Kje0yLg

Now, whenever there are disturbances in the fabric of space and time, it will cause a 'ripple' in space-time, as gravitational waves.

The reason this has all come about is as LIGO detected one of these gravitational waves, last month. The amazing part the gravitational wave was caused by the collision of 2 black holes, and that the ripples caused by it have been travelling through space time for 1.3 billion years.

So that is it! Gravitational waves are caused by disturbances in space-time, and LIGO has recently detected some that were caused by a collision of 2 black holes a very long time ago.