Previously Dominic Thomas said:
The BBC warp article says:-
"The time dilation effect means that anyone travelling to the stars at
speeds approaching that of light would experience a journey of a few
years. But when they came back to Earth they would find that thousands of
years had passed and all their friends were long dead. "
I was wondering just how true this was?
From what I recall from physics lessons, the basic tenet is that in this
universe the speed of light is a constant. Period. No matter how fast you
are actually travelling, it will be the case that any light you see will
seem to be travelling at c. Also, nothing can ever break the light barrier.
No, no no no, no. The only way to get round this (as has been utilised by
B5, Star Wars et al) is to drop out of this universe into one in which the
physical laws are different, and do allow you to travel faster than light.
But I digress.
Anyhoo, the way time dilation figures into this is as follows:
Say you travel in your starship at some high fraction of the speed of light
- 99% seems a popular number. You turn on the headlights. What happens?
Common sense (that is, not taking screwy physics stuff like time dilation
into account) dictates that the light would seem to crawl away from you at
1% the usual speed of light. This is like, "If you're in a car moving at 30
mph, how fast does a car moving at 40mph in the same direction seem to be
travelling relative (there's the "R" word - it had to figure in somewhere)
to you?" The obvious answer for that is "10mph, stupid." And so it was that
I answered my physics teacher's headlights question. He proceeded to mess
with my mind like so:
Your perception of time when moving quickly, by all measurable means you can
carry with you, is slowed so that the light seems to move away from you at
c, its normal speed. While it might really be only just pulling ahead of
you, you'd see the light from the headlights dashing away at the speed of
light. To stationary observers, you and the light beam zip past almost neck
and neck. So the observer might watch you travel 1 light year in just over a
year, but because of the slowing effect of high-speed travel to you it'd
seem to be much, much quicker. Unless you were in economy class, in which
case it'd seem an eternity. ;-) Of course, to any observer in front of you
your headlights would seem to be emitting hard X-rays due to doppler shift,
but that's neither here nor there.
There's also some gumph about objects approaching light speed getting really
heavy, but my brain was still hurting too much from time dilation stuff for
me to understand it. It's to do with the energy/mass relation of the
object, I think - you know, that "E=mc^2" thing. Someone else can explain
that one.
I'm sure any physicists out there will shout at me if I got it wrong, but
hey. I'm also uncertain what happens to light rays travelling in the
opposite direction to your 99% light speed starship - do they seem faster,
slower, what?
I need to go lie down now. My brain hurts.
Later,
Steve :-)
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(oO)
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