Have you ever tried meeting a friend somewhere without saying when? Or meeting them at a certain time but without saying where? No? Well, that’s because it’s impossible. Space and time are joined at the hip, that’s why it’s called spacetime.

It’s fairly straightforward to understand space. It comes in three dimensions, the one that goes up and down, the one that goes backwards and forwards, and the one that goes left and right. Spacetime simply adds in another, fourth dimension – time. Think of spacetime as a piece of fabric. Everyone and everything is somewhere on this piece of fabric, in a certain place at a certain time:

Massive objects cause space-time to curve.

Certain massive objects can actually stretch out the fabric we call spacetime. So if you were near a black hole, where spacetime is stretched out, you’ll experience time passing more slowly:

While you’re unlikely to ever find yourself next to a black hole, spacetime is known to get stretchy right here on Earth too.

Scientists used incredibly precise clocks called atomic clocks to figure this out. They put one clock on a mountaintop and one near sea level. When they brought the two clocks back together in the lab, the times they showed were different. The clock from the mountaintop was ahead of the clock near sea level. This is because the centre of the Earth is one of those things that stretches out spacetime. So the closer you are to the centre, the more slowly time passes. Not that we’d have noticed without those atomic clocks!

Teddy San Miguel

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