Transcript:

The other thing that will happen is if I'm moving very fast, let's say I'm in a car moving at almost close to the speed of light—when you, as an observer, measure the length of my car, it will be contracted. It will not be the same length that you would have measured if I was standing still. This is a consequence of the speed of light being an absolute constant. And the third thing that happens is: for any mass that is being accelerated and becoming closer and closer to the speed of light, it becomes heavier and heavier. So mass also is not constant. It is a function of how fast something is moving.

So now I'm going to ask you a question for which there is only one answer. At what rate does time move for a photon? And the answer is zero. Time does not move for a photon. What is the length of a photon? The answer is zero. What is the mass of the photon? The answer is zero.

It's a very similar answer to the question, "Does this dress make me look fat?" The answer is no. You can't think about it. If you thought about, "Is this dress making me look fat?"—dude, you're done. Same thing for a photon. Mass of a photon is zero. Time passage for a photon is zero. Length of a photon is zero. This is all a consequence of Einstein's special theory of relativity. It's beautiful.

That's it for this episode. See you in the next one.