I'd like to bring up the topic of a theoretical, as yet undiscovered particle: the tachyon.
Tachyons are conceptually extremely cool. Theory (both general relativity and string) have equations that describe some tachyonic behavior:
1.) Tachyons move faster than light.
2.) Not only do tachyons travel at superluminal speeds, they actually CANNOT go slower than the speed of light.
Number 2 is interesting when one thinks of a curve showing the speed of light vs. required energy input to increase a mass' velocity. It's generally accepted that in order for a particle to attain light speed, an infinite amount of energy has to be put in. To put it in common sense terms (which I like), the faster you wanna go, the more energy you need. Eventually you'll reach a wall at which, no matter how much more energy you put in, you can go no faster.
Tachyons are completely opposite. In order to go faster, they actually LOSE energy. IOW, it costs a tachyon energy to slow down. That's somewhat like hitting the gas in your RBV to slow down.
Another cool concept that I haven't seen much about (and, honestly don't know where it fits into current theory) is quantum tunneling.
Instead of trying to lay it out in words, I'll steal someone else's graphic.
The top of the "mountain" in this picture is the unattainable speed of light. Tachyons from earlier would only exist in the right-side of the picture with normal known matter existing on the left.
Anywho, enough rambling...