ELIF: how is time relative?
In: Physics
Imagine a space ship is about to leave on a voyage. It sets its clock to Earth time and by magic (or via a radio transmitter) the captain can always see both the earth clock and the ship clock. As the ship gets further from earth the captains can tell the difference between the clocks since light travels at a finite speed. At slow speeds the clock on Earth lags a little behind the ship clock, but they still go at the same pace. So far so sensible. The captain can tell how far away the ship is from Earth too.
Now lets say the ship is travelling away from Earth at a reasonable fraction of the speed of light. Things are a bit different now. The time the light takes to travel from the earth clock to the captain is increasing as the ship gets further from earth. Not only is the Earth clock lagging behind the ship clock but the increase in lag (over time) is noticeable. To the captain Earth’s time has slowed down. The impossible limit is when the light from the Earth clock never catches up with ship because the ship is going at the speed of light. To the captain the earth clock has stopped.
And then there is general relativity to complement special relativity (above) when gravity slows time down (give or take)…
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