relativity lesson #1

Since I cannot just ramble on about Relativity in a single post, I’ll give them in installments! Yey! Thank you trivia sections of my blog! For our first point under the Special Theory of Relativity (see my previous post for some ideas on it): time slows down in a moving vehicle.

One of the key instruments in Einstein’s thought-experiments for Relativity is the light clock. Imagine a point of light bouncing between two mirrors, say, 30 cm. apart. Each bounce is equivalent to a tick. Do remember that the speed of light is constant — it’s the same for everyone no matter how fast you’re going. Now, how will this explain time slowing down?

Imagine (yes, the key to Einstein’s theories is imagination. If you’re not much of an imaginative person then, start training) having a friend ‘hold’ the light clock in total darkness. This way, you are able to see the point of light bouncing its merry way up and down the two mirrors. Now ask your friend to run. You’ll then see the point of light as something like this:

Yey, another photograph. Please bear with my poor photographing skills. Anyways, that's how it should look in your head.

It’s like when you see someone running holding one of those fireworks-stick-thingies. A sparkler, right. It’s called lusis here in our country. Anyways, it’s supposed to be like that. The point is, the faster your friend goes, the further the distance the point of light has to travel in order to reach the bottom (or top) of the clock. But since light cannot speed up (because it’s speed is constant), then it takes longer for it to reach either mirror and make a tick. In short, time slows down.

Do note, however, that to your friend, the point of light isn’t zigzagging. It’s still doing the same old up-down tick that it used to. Which is why, the slowing down of time in a vehicle is only visible to an outside observer. This is so because everything inside the moving vehicle — all clocks, machines and bodies — slows down along with it. To those inside the the vehicle, the slowing down of time is imperceptible — just like how your friend sees the light clock the same way — because they are all affected by it.

(I’ll post lesson #2 in a while so take your time digesting this. Peace out.)


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A shy and quiet person who loves anime, books and Japanese food.

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