There's a great thought experiment to help understand how time dilation works.

Imagine you're standing beside a train track when a boxcar goes by. Hanging from the roof of the boxcar is a lamp that can be turned on an off.

Now, let's assume that you have super vision and can actually see the individual photons coming out of the lamp, streaming down and hitting the bottom of the boxcar.

First, imagine that the box car is stopped. You turn the light on and then measure the distance a photon travels before it hits the bottom. Obviously, this will be the height of the boxcar, let's say it's 3 metres.

You know that the photon was moving at 300,000 km/s and it traveled a total distance of 3 metres in a fraction of a second.

Next imagine the boxcar is hurtling past you at nearly the speed of light. The photon is emitted from the lamp and travels down to the floor of the boxcar. Now, since you're outside the boxcar, it actually travels diagonally down from your point of view (it moves from the lamp to the floor, and the boxcar is moving horizontally).

Now, if you measured the total path the photon took, it would actually be longer than the distance from the lamp to the floor.

We all know that the speed of light is a constant no matter what speed you're going, so the only way light could have traveled the extra distance is if it had more time to make the journey. In otherwords, time slowed down for the boxcar in relation to you.

That make sense?

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Fraser Cain
Publisher
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