NOVA Online | Time Travel | Think Like Einstein (4)

Think Like Einstein
Part 4: The Solution

By now you probably understand the conflict: How is it possible that light always travels at the same speed, no matter how fast its source is moving? Einstein, when he was 16, thought about the same thing.

Are you familiar with the equation v=d/t? All it says is velocity (speed) equals distance travelled divided by time.

v = d/t

Here's an example of how it can be used...

And here are two more examples that show how speed can stay the same even though distance and time can change...

v=d/t

See the relationship between speed, distance and time?

If we use this equation in our first scenario—the one where you threw the ball—it works out fine. For you, within the train, as well as for someone standing by the tracks, we can calculate the speed of the ball by adding the distance the train travelled and the distance the ball travelled.

The equation does not work out so well in the second scenario, though, because we're dealing with the speed of light, so the "v" in the equation always has to be 186,000 miles per second.

Something has to give.

Question: What can we infer from what we've seen so far?