Posted by C2FThom at edutopia.mpsaz.org on March 11, 2004 at 14:08:38:
In Reply to: Hmmm posted by AshFan on March 11, 2004 at 13:29:55:
: So it IS possible to travel faster than the speed of light then?
No. Here's why:
: The way I understood relativistic speed was that the person on the trip would have had only 2 years gone round trip by while back at home 50 had gone by.
You're correct. As an object approaches the speed of light, it's "internal clock" so to speak, its own timeline, slows down relative to that of the rest of the universe. So a person in a "near-light ship" would experience only a year or two, maybe as little as six months, of existence while the rest of the universe would experience 50 or more. (Such numbers depend on the actual speeds and accellerations. Their values are arbitrary to this argument.)
I think you get that concept. What you've got to remember, however, is that speed is a measurement of distance OVER time, so if time is distorted, so will relative speed. Hence, you can travel at 3 mph onboard the ship, relative to the ship, but if you try to look at that motion with the universe as the frame of reference, that "ship-hour" could last days or even years. Since the ship itself is travelling at a tremendous speed relative to the universe, the added "slow-mo stroll" would make a miniscule difference, not enough to push your total speed, relative to the universe, beyond the speed of light.
If you could somehow build a vessel large enough to house another near-light vessel, and set it up so that the large vessel was travelling near-light, relative to the universe, and the small vessel was travelling near-light relative to the large ship, the small vessel would still be travelling at sub-light speeds relative to the universe. Think of it somewhat like Zeno's paradox, a.k.a. the half-distance paradox.