Speed, distance, time - Reply

Chris asked, and, unless the mail system here has gone nuts again,
no-one
has yet replied to it:

> I heard something about speed of light in relation to time That once

Yes. According to Special Relativity, at high sub-light speeds, your
mass increases and time slows down relative to a body moving more slowly.
Also, the universe seems to shrink in the direction that you're moving
(described delightfully by Larry Niven as having someone heavy sit on the
universe). I won't
quote the exact equations here -- mail me if you want them. The
important point that makes c the upper limit for speed is that your mass goes
to
infinity _at_ c.
Also, time stops and distances shrink to zero.

> And, the fourth dimension is? Could that be time? <

Again, yes, although it's important to realise just what people who blithely
talk
about the 4th dimension really mean (or _should_ mean). Most people are
familiar with the 3 spacial dimensions (call 'em x,y and z); but when you
introduce time into the equations (to deal with that thing we call
"space-time"),
there is the problem that time is a different quantity to length, which is how
we
quantify the 3 spacial dimensions. _But_, by introducing a fundamental
quantity (a constant) like the speed of light in a vacuum (our old friendly
enemy, c), you
can treat the mathematics of space-time as a problem in 4 similar
dimensions, all measured as lengths: x,y,z and "ct". Which is what Einstein
did, and what led to things like the Lorenz contraction (someone sitting on
the
universe) and other non-obvious results of relativity. The thing is, it
seems to work!

However, why we perceive time as a different quantity to length, and why
movement in time is not readily performed as it is in space (and all the
important results that follow from that, like the second law of
thermodynamics), is something that we still don't know.

It's interesting to note that it has been worked out that if you re-do
special
relativity in _5_ dimensions (and no, I don't know what the 5th could
be) for a charged particle, the maximum speed obtainable by said particle (or
larger
body) -- the equivalent to c in 4D SR -- depends on the charge-to-mass
ratio. For a "typical spaceship", anything up to about 1000c could be possible
(Warp Factor 10 from the original Star Trek, anyone?). Electrons can zip
around at 10^21 c, which should do for communications systems. All we have to
do is come up with this 5th dimension. Makes all the old SF versions of
hyperspace take on a whole new lease of life...

Phil