As no boffin has piped up with a detailed explanation, I'll offer the limited benefit of my fag packet science. Apologies in advance for inevitable errors that follow.
A century ago, Einstein published a paper that said things with mass actually bend the fabric of space and time, relative to how much mass they have. (This isn't the e=mc
2 one; it's his other famous theory)
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If you were really close to something massive (like a planet or a star), your watch would tick more slowly than it does now. This is because the very fabric of space and time is being bent by the huge thing next to you; the ordinary laws of physics change. It's actually true of little things, too, but it's obviously more apparent the bigger (the more
massive) the thing gets.
Gravity is how we describe the force created by one thing with mass has over another thing with mass. As I bend spacetime, I am pulling the TV remove towards me. It, in turn, is pulling me to it, only not quite as strongly.
One of the implications of Einstein's theory was that having a thing in space is a bit like dropping a stone in some water.
The water is space-time and the stone is anything with mass doing something.
The effect a thing has on spacetime if you drop it in then ripples out like the waves in the water - and that's exactly what they are: waves. Only the waves in our space example aren't water waves; they're the ripples in the fabric of spacetime caused by the lump that's disrupting it.
As with the stone in the pond, the further away the ripples get, the less obvious they are.
Gravitational waves have only been the playthings of the theoretical physicists, though, because no one has seen any actual evidence of them existing. The other scientists have spent the last century trying to join the theoretical physicists' club.
In reality, we need something absolutely enormous to cause a really big plop somewhere and then we could get a tiny, almost undetectable ripple our way. The explosion of an enormous star or something like a black hole would do. We need a massive thing doing something big to really give a big splash.
With improved sensors and smarter technology, this was accepted for publication today:
Waves!
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