Speed of Light

Though I don’t come from a physics background, the subject has always intrigued me. One of the more interesting constants to me has been the speed of light, which is roughly , which I’ll refer to as . That in itself isn’t too interesting, as it must have a speed, so any number is as good as any other.

The interesting fact, which has been verified experimentally, is that the speed of light appears constant to all observers. That is to say, if you’re in a very fast moving space ship moving at , and you shoot a ray of light out the front of the ship, you’d expect that a stationary observer would see the ray of light move at . To the contrary, it appears  to the stationary observer as it does for you on the ship!

This result is very counterintuitive, but what does it imply?

Say you’re on a space ship moving at , and you’ve installed two vertically opposing mirrors. You observe a photon of light bounce between the mirrors. A stationary observer would see that same photon of light moving along a diagonal path as it bounces back and forth, due to the forward trajectory of the ship.

  VS 

Say the observation period is one second. If the distance between the mirrors is  meters, I’ll have observed the photon bounce back and forth  times on the ship. The stationary observer sees the photon bouncing back and forth in a diagonal path of length . But because of the diagonal path is longer than , the photon will only bounces back and forth times in one second.

This implies that what I experienced as one second on the ship (seeing the photon bounce  times) is in fact more than one second to the stationary observer. Time slows down when you’re moving fast!

How can this possibly be? What you have to accept is that space and time are relative. Everything slows down when you’re moving fast: the clock, molecules, your brain! I can see light moving at . The stationary observer sees the same ray of light moving at .