Just finished The Elegant Universe, by Brian Greene. It’s about string theory. [Two branches of physics in a very brief nutshell: general relativity deals with the force of gravity and the movement of large bodies, quantum mechanics deals with electromagnetism and the interaction of subatomic particles. Both are very successful in experiment, but when used together lead to contradictions. String theory is an attempt to unite the two theories.]
This post is about a side issue. Stay with me now...

Imagine you’re standing to the west of a table that’s at eye level to you. I roll two marbles on the table at precisely the same speed; one going straight from north to south, one going slightly diagonal southwest. Because the table is at eye level you’re only able to discern the north-south movement of the marbles, not the east-west movement. So what happens? To you, the second marble appears to be going straight north-south, but at a slightly slower speed than the first.
The motion of the first marble is in one dimension only. The second, though, is moving in two dimensions, and some of its velocity bleeds off from one in order to feed the other (think vectors). So even though it’s moving at the same rate as the first marble, to someone viewing just the one dimension it appears to be slower.

One of the results of Einstein’s theory of relativity is that we’re all in constant motion through four dimensions – the three spatial dimensions plus time. And, this motion is constant at the speed of light. We’re all moving at the speed of light through time. When we move through the other three dimensions some of that velocity bleeds off to support it.
This has two consequences. One, the speed of light is the maximum velocity one can reach moving through space. Two, when in spatial motion our motion through time slows, so that a person attaining a significant percentage of lightspeed would age more slowly. If one were moving through space at the speed of light, one’s velocity through time would be zero.

Got all that? It gets more complicated when you consider that two people moving relative to each other have equally valid points of view; that is, each can claim to be motionless while the other is moving. Then, though, you have to figure in the effects of gravitational fields. That part gives me a headache.

- posted by Dactyl @ 10:38 AM