Image: Mooc Summers / Wikimedia Commons

Science explained: Gravitational waves

Over the past couple of weeks you’ve no doubt heard a lot about gravitational waves. They’ve been everywhere: in the papers, on Facebook and, of course, here in the Boar. Everyone has been ranting about how amazing it is that they’ve been discovered, but there’s a simple question that a lot of people have been left with – what the hell are they?

To understand that, we need to go back to the basics and answer a fundamental question: what is gravity? Now you’ll probably remember that story about Isaac Newton and an apple falling from a tree – the big mass (Earth) pulling the small mass (the apple) down because it has a greater mass. Both of the masses exert a force upon the other mass, but because the Earth is pretty big in comparison to the apple, the Earth always wins the tug-of-war. Albert Einstein (a name you’ve probably heard before) came up with a different way of thinking about things, however, and it’s a bit… weird.

Imagine that the universe is all made out of a fabric a bit like a trampoline, and that it’s called spacetime

Imagine that the universe is all made out of a fabric a bit like a trampoline, and that it’s called spacetime. Now if you put a mass on it (like a tennis ball), the fabric sinks around where the mass rests. A bigger mass (like a bowling ball) sinks the fabric more than a smaller one, and that’s kind of the basics to Einstein’s ‘theory of general relativity’. As objects move around in the universe (and in spacetime), they get attracted into orbits around bigger objects because of the dimple in spacetime the bigger objects cause. When huge objects like black holes start orbiting, though, things get extreme.

Black holes have enormous masses – anything from ten to several billion times as massive as our sun – so when they move they disturb spacetime just like you do when you roll on a trampoline. This disturbance can stretch and compress the fabric that makes up the universe, and these stretches and compressions are known as gravitational waves. When you get two black holes orbiting each other, the gravitational waves produced are very energetic, meaning that when they reach Earth the entirety of space and time – including everything on our planet – momentarily stretches and compresses as the wave goes by.

Comments (1)

  • I enjoyed eavesdropping on Seti Astrophysicists having a text talk about these gravity waves about 10 years ago. They seem to have the distinction of being way in advance of these latest posers to discovery. 🙂
    The gist of the talk was about the effect these super dense, or heavy gravity waves will have on our little tennis ball when they arrive, a much more dire description of utter destruction, than the current descriptions of this eventual event, the one from our galactic core, and as yet unarrived. These massive distances take a long time to travel to our local orbit.
    Remember the movie 2012 ? Ya. Only worse. Complete destruction, add to these gravity waves, somewhat slower travelling monsters, the faster, and much more concentrated ultraviolet waves also emitted from our galactic core and we have a real life GW Bush scorched earth scenario, everyone dies, baked alive. Lets not forget those ugly gamma ray tsunamis as well, more of the same, heh, utter destruction.
    Add to this great news about the three suns (Seti talk) about to go supernova anytime between the next 10 seconds and 10 million years, all placed in a triurnal position around our little green pea planet and the inability to travel far enough nor fast enough to escape the crowning inglorious gob smacking we get sooner than later and life is indeed a precarious and short term existential blip on the infinity scale of things.
    If the blast from these fail safe suns doesn’t kill us all, the radiation shall. 🙂
    Perhaps this global warming cooling,volcano spewing, earth quaking, water evaporating, inevitable Dune scenario, phenomenon is due to the recent arrivals of the forerunners of the aforementioned waves and rays, supernova rumblings out there in the firmament of the recently discovered Flat Earth Theory. ??
    Do ya think ? 🙂 Have a nice day.

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