What happens when things move really fast.
Pushing things makes them go faster. People used to think that if you could keep pushing something hard enough for long enough you could make it move as fast as you want. So some people tried to make things go faster than anything else ever had, by pushing as hard as they could.
Thing is, it didn’t work.
Turns out that no matter how hard or how long you push something for, at least one thing will always be faster than it: light. Light is the fastest thing there is and you can never make anything go faster. In fact, however fast or slow you go, light always seems just as fast to you: it always moves away from you just as quickly!
So imagine this. You are holding a bright thing and pushed by a friend so hard for so long that it seems to her that you are nearly as fast as the light leaving the bright thing. To her, the light is moving just a little bit faster than you, so only getting away from you slowly. But to you, the light is still moving away from you faster than anything else can ever move. You and your friend don’t agree on how quickly you and the light are moving away from each other. What’s going on?
We need to think about what moving means. How fast something moves is how far it goes in a given time. If you and your friend don’t agree about how fast something’s moving, then in fact you don’t agree about either how FAR something goes or the TIME it took to get there.
This means something BIG. How someone sees time and space changes with how fast they are moving! A watch moving very fast will say the time is earlier than a watch standing still - this is because time goes more slowly for a moving thing.
I know what you’re thinking, though. You move about lots, and still everyone agrees what time it is. Thing is, because you are moving so much more slowly than light does, the change in time made by you moving is far too small for anyone to notice. It’s only when things move really, really, REALLY fast that the changes can be noticed.”—Euan.