fatty_ashy "Erm, I was wondering if travelling at the speed of light actually means instant travel."
alternative-3 "- If I were moving at the speed of light through deep space or whatever, would I get squished into a near-2D line? Would I survive?"
1. You cannot move at the speed of light as long as you have mass, because as you approach the speed of light, your mass increases and the energy requred to accelerate you faster increases.
2. As you approach the speed of light your mass approaches an infinite mass. This is how it appears to an observer outside your inertial frame (at rest).
3. Your dimension in the direction of travel also appears to contract by any measurements made by such an observer. For non-relativistic speeds this contraction is very small.
The formula for the Lorenz contraction is: L = L'*sqrt(1-v2/c2) where L is the length measured by the observer and L' and v are the length measured by the subject, and the subjects velocity measured by the observer. You can see that L and L' are nearly equal unless v approaches a significant fraction of c (which is the speed of light.)
4. Time appears to slow down to an observer at rest relative to you also.
The formula for time contraction is: t' = t*sqrt(1-v2/c2), where t' is the observers time, t and v are the subjects time and velocity relative to the observer. You can see that unless v approaches a significant fraction of c (the speed of light) there is very little difference between t' and t.
5. You notice none of these things until you return from your trip. On your return, we will disagree on how long you were gone. Our time measurements of your trip will differ by a certain amount, depending on how fast you traveled and how far. And both of us will be correct.
6. If you could travel at the speed of light, it would appear instantaneous to you in your inertial frame, because time (for you) would have stopped for the period which you were traveling at the speed of light. But to me, you would appear to have traveled at the speed of light, not instantaneously. This is the opposite of what sardonyx247 said, but (s)he was correct in stating that time is relevant only to the observer. Observers who are in the same inertial frame measure time identically. If the inertial frames differ, then their measures of time also differ. Lucky for us the difference is very small at speeds we are likely to travel at.
7. Fatty_ashey had a question regarding the distance of the trip as it appears to the travelers. This is interesting because their meter-stick would have contracted in the direction of their travel, but because of time dilation, they would also think they had traveled for a shorter time (and they actually did in their inertial frame); but at a higher velocity (their meter-stick has contracted). But when they multiply the time by their measured rate of travel the two effects would cancel out and they would measure the distance of the trip to be the same as an observer in a more or less stationary inertial frame. This is contrary to the conclusion drawn in the second link below. I think the difficulty is because the author is using v as measured by someone outside the inertial frame of the travelers when he should have used v as measured by the travelers. I was wrong once before, this might be the second time. ;-)
(This note added later... There is something inconsistent in my explanation above, and I must admit, I am not sure what the answer is. As you travel at a constant velocity along the route, the route appears to be moving past you at some velocity in the opposite direction, and thus would appear contracted to you. I'm beginning to think that as you travel the route at a relativistic velocity it will actually seem to be a shorter route.)
check these liniks:
http://www.drphysics.com/syllabus/time/time.html
http://www.physics.umass.edu/gemsFol...ionexample.pdf
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