Yes, there are data that show that a massive body can't reach [imath]c[/imath].

A moving body has momentum

[math]p = \frac{mv}{\sqrt{ 1 - (\frac{v^2}{c^2})}}[/math]

Which is asymptotic approaching the speed of light. What this means is that it would take an infinite amount of energy to accelerate a body of finite mass to the speed of light. Even turning all the matter in the universe into energy, and using it to accelerate the body with 100% efficiency, we'd still only get close to [imath]c[/imath].

The only things that can travel at [imath]c[/imath] are massless particles, such as photons. And yeah, they are weird; time does stop for them.

afarnen wrote:however how would one "observe," in a way familiar to us, when one is still in the four dimension

If you think about it, we are existing in 4-space right now - we move freely in three of the dimensions, and are constrained in the fourth, time-like dimension. Like H G Wells said;

H G Wells wrote:Can an instantaneous cube exist?'

'Don't follow you,' said Filby.

'Can a cube that does not last for any time at all, have a real existence?'

Filby became pensive. 'Clearly,' the Time Traveller proceeded, 'any real body must have extension in four directions: it must have Length, Breadth, Thickness, and - Duration.

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afarnen wrote:What about when we cross over to the imaginary numbers, by going faster than c relative to a body? Would that mean that each body would observe the other body in backwards motion while they move forward through time? If backward/forward is relative in this way, does that mean that slower than c/faster than c is also relative? And again, what happens at c?

You can't go faster than [imath]c[/imath] relative to anything. To add velocities properly, you use the formula

[math]s = \frac{v+u}{1 + (\frac{vu}{c^2})}[/math]

Which again never gives an answer higher than [imath]c[/imath].

If you use the formulae correctly, it is probably easier than you are imagining. No imaginary numbers, nothing going backwards in time. Sure, you have to get used to space and time dimensions being a bit plastic, but once you've got your head round that it's actually OK.

Oh, and don't hold back. As long as it's not covered by the common questions, then feel free to ask anything (unless it's a homework assignment, then people tend to want to give hints rather than full answers).