A Glimpse of Time Dilation

Before Reading This, see -
Chasing a Beam of Light (Nov. 1st, 2006)

Hey, all. I'm posting my first ever "sequel" post. This post can be thought of as a direct sequel to Chasing a Beam of Light, which is one of my favorite posts so far.

When confronted with the paradox of light's never-changing speed, Einstein decided to rethink exactly what time was. In this quest he completely redefined physics with something called Special Relativity.

Let's see each step of his reasoning in a simple, logical way.

(Note - this article is a bit more complex than the others. So if you can't handle it, try reading some of my other, simpler articles)

First, we'll be using the world's simplest and most impractical clock - the Light Clock. Basically, you have two mirrors facing each other, attached by a bracket, and a single photon (the stuff that Light is made out of) bouncing back and forth between the two mirrors. There's a detector that clicks whenever light makes one complete round trip.
So you have a piece of light bouncing back and forth between two mirrors, with a counter counting the amount of time it bounces.

Let's say that our two mirrors are far enough apart so that one second passes for every billion clicks of the timer. So when the light bounces back and forth one billion times, then a second has passed.
We can use this like a stopwatch. Say that after you run a track, thirty billion clicks have passed on the light clock. You can then deduce that you ran the track in thirty seconds.

Great clock, eh? And because light will always travel at the same speed, it seems to be perfect, never wavering.

So you're staring there, watching your little fancy light clock on the table. Then someone comes and gives you another one, and you decide to do a little experiment.
What would happen if you moved one around?

Here's the trick - it would take longer for a photon to make one complete trip on a moving clock!
Notice in the picture to the left (which, I am proud to say, I made myself). You can click it to make it larger, but you can kind of see the gist here.
As you can see, as the Light Clock moves, the light must travel a farther distance to keep up. It's no longer just going straight up and down...it's also going side-to-side as well.

To make one complete cycle, the light has to travel farther in a moving clock than a stationary clock.

Because light cannot speed up or slow down, then we can say that it takes longer for light to complete one cycle when the light clock is moving.
If there is a little digital counter on top of a moving and a stationary light clock, you can see that the moving light clock ticks a tiny bit slower than the stationary one.
You see why? Because it takes longer for light to complete a cycle on the moving clock, the moving clock "ticks" less often. As a result, its counter is slightly slower.


There you have it. The simplest proof of Time Dilation. Objects in relative motion travel slower through time than relatively stationary objects.


Let's say that you and the moving clock are moving at the same speed, the same direction. Here, you don't see the diagonal movement of the light as in the previous picture. We have shown that the for the moving light clock, 1 billion ticks is slightly greater than a second.
But if you don't see the diagonal movement of the light, then nothing is being delayed. Light doesn't "take longer to travel", because, well, to you, it's still bouncing straight up and down, without that side-to-side motion that you saw when you were stationary. So to you, 1 billion ticks still equals one second!

Someone looking at you from a stationary vantage point would see you moving in slow-motion. Because, you see, what is 1 second to you is actually a bit more than 1 second to him.

...Did I lose you?

Just to sum everything up -
Time passes slower for objects in (relative) motion.

Wow. Am I saying that when you're driving a car, you're going through time slower than someone who's walking? You're time traveling?
...Yes. But the difference is so tiny that you don't even notice.
But say, if you were traveling in a spaceship at 502,500,000 MPH (3/4ths the speed of light), then boy, the difference would be astounding! You'd be moving in slow motion compared to the rest of the world. One second for you would be 1.5 seconds for someone standing still. If you travel for two years at that speed and come back, then you'd find out that 3 years had passed on Earth. Time travel indeed.

The closer you are to the speed of light, the larger this delay is.

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All of that may seem too abstract. But let me give you a more concrete example.
A Muon is a special type of elementary particle. It's so rare because the instant that one is formed, it disintegrates after two millionths of a second. It's like a muon lives life with a suicide bomb strapped to its chest with a countdown set at two millionths of a second.

But scientists found that if they sent the muon flying nearly at the speed of light, the muon would live a lot longer.
What's happening here?
At, say, 667 million mph (about 99.5% of the speed of light), the "clock" on the suicide bomb slows down! Just like the moving light clock slows down. In fact, here it is moving so fast that the clock ticks about ten times as slow!
In fact, the muon's life expectancy is about ten times as high. When the muon finally dies, the lab clocks would say that ten times the life expectancy had passed since the muon was born...but in the muon's clock, only one time the life expectancy has passed.

Mind-boggling? It's supposed to be. Einstein completely shattered the world.

(Note - while this is supposed to be mind-blogging, it's not supposed to be mind-boggling so much that you don't understand a word I just said. So if you have any questions or comments, please leave...a comment. Thanks :) )