Out of all of the replies I've read I agree with twomers the most, so I'm going to quote his comment:

It's true that as objects "move faster" they "move slower in time." That is why the speed of light with respect to *any* frame of reference is a constant. Two objects moving relative to each other, say 500 million miles *per hour,* will both measure the speed of photons emitted from an independent light source as traveling 670 miles *per hour.* It's the *per hour* part of the equation that changes.As things get faster I believe Einstein conjectured* that they move slower in time and get heavier. I agree with JaWiB, but I do not pretend to know much about this kind of stuff.

* I think he proved this, in fact, but I cannot fully remember.

Also, it's not that the object actually 'gets heavier' per se, it's that as you tend towards any extreme (as you mentioned) it takes more and more energy to get the same desired effect. For example, as you bring the temperature of a system closer and closer to 0K, it requires increasing amounts of work to extract heat from the system boundaries (therefore it seems as if the system has acquired an 'increased resistance to heat extraction').

aeghion-flux theory, pronounced 'aeon-flux' like the movie/show, tries to connect relativistic effects with the transfer of mass into energy. The theory basically states that if mass 'warps the fabric of spacetime,' then the energy 'synthesized' from that same mass may also create relativistic effects. A subset of the theory explains how a separate mass introduced to a changing aeghion-flux field can "gain the essential characteristics ... necessary to commence propagation at the speed of light."

A few notes on the theory:

- Note the use of the word 'propagation.' If you read on further through the material you realize that what's *really* happening is that the 'mass' is basically being turned into electromagnetic waves...photons! Somewhat of a killjoy.

- The theory claims that this is the only process (in the universe) which is both 'real' and reversible (in the 'thermodynamics' sense of the word).

- The mathematical representation used to show the 'spacetime' distortion is the outer product between two quaternions (before and after the mass transfer into energy).

- The process only operates under a 'changing' aeighon-flux (I guess similar to how only a changing magnetic flux can induce a current)

- The Hiroshima bombing of 1945 is said to have induced a 'spacetime deflection' of .00001 (the units and interpretation of this number are basically impossible to understand), and that 1*10^-4billion grams of matter could be made to travel at the speed of light (but, again, because the mass is really being turned into electro magnetic waves).