Why does nothing travel faster than light?

A ray of light travelling through space moves extremely quickly. After just one second, it’ll have whizzed 300,000 kilometres ahead. Light travels so fast, it can orbit the globe 7.5 times in one second!

That’s the universal speed limit – nothing can go faster than that. But why is that?

Space race

Imagine you’re in a rocket travelling through space. A ray of light flies past you, and you decide to chase it.

You switch on your engines and race behind the light. Your speed is going up and up. At one point, your rocket is travelling at 150,000 kilometres per second: half the speed of light.

You’d think the ray of light would be moving away from you at 150,000 kilometres per second. But in reality, it’s still speeding ahead at 300,000 kilometres per second!

Fast lane

That’s because light doesn’t behave how you’d expect. If you’re in a car on a motorway travelling at 50 kilometres hour and you’re following another car travelling at 100 kilometres per hour, the car in front of you will only speed away from you at 50 kilometres per hour.

But that’s not the case for light. It’d be pulling away from you at the same top speed: 300,000 kilometres per second!

Some strange things happen to make that possible. For instance, clocks start to behave differently as they approach the speed of light...

but that’s a topic for another day. The key point is: however fast you travel, light will always move away from you at the same speed. That’s why you can never, ever beat the speed of light.

Answered by Ans Hekkenberg