Why Does Time Slow Down?

The question was posed, “Would someone please explain further why time slows as speed increases?”

As an exercise, I make an imperfect attempt to explain.

This is an anal break down of a simple, everyday event.

If I throw a baseball back and forth with a friend, the ball goes between us with a certain speed.

  1. The distance traveled is fixed. Zero. We’re standing still.
  2. The passage of time is fixed. Every second that goes by is the same length.
  3. The speed of the ball is fixed. (For all intents and purposes. Keep it simple.)

Those things are obvious, and pointing them out anal. I get that.

Let’s change the situation slightly, and add motion.

If we get inside a big cargo airplane and it flies through the air, we can still play catch. The ball goes back and forth with the same speed between us as when we were on the ground.

Looking at it from the ground, the total speed of the ball changes because the moving airplane has to be taken into account. When the ball goes forward, it is going a little faster than the airplane. When the ball goes backward, it is going a little slower than the airplane.

In this situation, when we look at speed, distance traveled, and time…

  1. The distance traveled by the is fixed. We all go from LA to NY on the airplane.
  2. The passage of time is fixed. Every second that goes by is the same length.
  3. The speed of the ball is changing as it goes back and forth. It’s a little faster going forward, and a little slower going backwards.

The important part is that two things are fixed (distance, time) and one has to flex (speed).

Here’s a kink in the picture.

If my friend and I could throw light back and forth like we could a baseball, things would work differently. No matter the situation, light in space travels the same speed. This screws things up.

If we got on a space ship and sped up to tens of millions of miles per hour (seriously you have to go that fast), the effect can be seen. Here’s what happens:

Throwing a baseball on an airplane: Throwing light on a space ship:
The distance traveled by the is fixed. LA to NY on the airplane. The distance traveled is fixed, star A to star B.
The speed of the ball is changing as it goes back and forth. It’s a little faster going forward, and a little slower going backwards. Light’s speed is fixed in space. Nature’s a bugger about that.
Time is fixed; a second is a second. Time is … ?

The only part not nailed down is time. The amount of time to travel back and forth has to flex.

The effect is only seen at insane speeds, at tens of millions of miles per hour. If you’re not going that fast, the effect is so tiny Mother Nature doesn’t notice or care. In other words, time is fixed; a second is a second.

A short Japanese animation that plays with this idea (imperfectly) is Voices of a Distant Star (trailer). A 15 year-old girl goes to space while her 15 year-old boyfriend stays on Earth.

Her expedition goes the insane speeds, so time flexes for her. From her perspective only a short time has passed.

She is depressed by the fact that for her boyfriend, time has not flexed, and nine years have passed for him. She laments,

I want to be hit by the rain, I want to go to a convenience store and eat ice cream together… Noboru… Noboru, who’s become 24 years old! I am the 15 year old Mikako

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