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Time Dilation

According to Einstein's General Theory of Relativity, the closer an object's velocity (speed) approaches the speed of light (which scientists like to call c), the slower their time seems to pass.

» Exercising those imagination muscles:

Let's say you and your friend decide to do a little experiment. Before the experiment, both you and your friend syncronise your watches so that they show exactly the same time. Now your friend hops into an ultra-speedy rocket (with flames painted on it, of course) and flies away from you (who is still on Earth) at half the speed of light. After 12 seconds, you look through your telescope to see your friend's watch, which shows that only 10.4 seconds have passed! How bizzare!

As your friend accelerates to 3/4 of c, you decide to take another look at their watch. Another 12 seconds has passed since you last looked at your friend's watch. As you observe the reading for the second time, you see that only 8.8 seconds have passed on their watch since you last saw it! Holy cow!

» Your friend must be getting bored of that slow-moving time. Let's bring them back.

Your friend now comes back to meet you on Earth. You ask if they realised that time was moving slower.

"No," they say.

"Hmm," you think. Being the trusting friend that you are, you decide to repeat the experiment again - only this time you go on the rocket while your friend stays on Earth. But first, you syncronise your watches again.

After 12 seconds of flying at half the speed of light, you take a look at your friend's watch - it's only passed 10.4 seconds! You do the same as the previous experiment and accelerate to 75% of the speed of light - and the same thing happens.

» Wha- eh?

You and me both. But apparently, what happens is that we have to assign one of the points to be "stationary" and the other to be "moving". Remember relativity? You can't tell which one is moving and which one is stationary. We can only say that one is moving at a speed relative to the other. An animation from Wikipedia better explains this:

Animation of time dilation.

In the above animation, the green and red dots are spaceships, and the blue dots are pulses of light that the spaceships emit. Note that in the moving spaceships, light takes longer to get from one spaceship to the other, as it has to move longer distances.

» Awesome dilating machine thing

A dude called Walter Fendt has made an interactive java applet that shows time dilation at different speeds! You need Java to see it, though.