## Saturday, January 28, 2012

### Special Relativity Time Dilation

I recently had a conversation where I was explaining why time slows down as you travel near the speed of light.

The explanation is rather simple if you think of light as particles, like bullets, called photons. One beauty of light is that it moves at a constant rate when traveling through a vacuum or medium. It doesn't move faster or slower unless you change the medium it's traveling in.

Thought Experiment
Imagine that you're standing at a fixed distance from a clock. As light reflects off the clock, it strikes your eyes at a fixed rate such that the clock's second hand sweeps at the same rate. Time is ticking away like normal.

Now, imagine if you are moving away from the clock at near the speed of light. Since the photos (bullets) are moving at a fixed rate, it will take longer and longer for each particle, reflected off the clock, to catch up with you. Therefore, you'll experience the sweeping of the clock's second hand at a slower rate. Hence, time appears to slow down - the clock looks as if it's running slower.

But, time isn't really slowing down. The watch on your wrist will mark time normally from your point of view. From the point of view of the clock, which is also marking time normally, it will look as if you're slowing down, too.