Thursday, August 30, 2007

Time and relativity

I was reminded today of the theory of relativity, and in particular the idea that funny things start to happen when you try to travel as fast as light. The idea is that in order to go as fast as light you need nearly infinitely large amounts of energy to get there and will suffer an effect known as time dilation.

For example, suppose you travel around the earth as fast or faster than the speed of light. In theory, you could move fast enough to get to the point where you started before the light you saw then had reached you, hence the effect of time travel.

What I often have to remind myself is that its not about where you're coming from, but where you are going to. The destination. Start a stopwatch on yourself and one at the destination at the same time (never mind the logistics of that) and when you get to the destination, they should show exactly the same time regardless of how quickly you got there. It's not about the time that you think the destination has from where you are, but their time (assuming you use the same type of clock).

So when someone looks at the stars and says the light we can see left there umpteen years ago, thats just a feature of the story light tells. If we traveled faster than radio waves, which is a good deal slower than light, the same effect occurs. It's just not true time travel.

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