I posted this one Turbofans thread on sound, but it applies here more as it was to do with faster than light travel etc. Bear in mind this is just my unserstanding of it so if I am wrong just let me know
"......that is where E=mc2 comes in. And also the rocket will reach a constant velocity when its forward speed is equal to the speed of the gases being emitted from the rocket, as it is newtons reaction (equal and opposite) that makes the rocket accelerate.
.....with reference to the speed of light, scientists have already found particles that travel faster than the speed of light, called quarks, but they only exist for microseconds, but I was theorising that maybe we can only detect them for microseconds because due to traveling faster than the speed of light, they are traveling through time, or maybe they are flicking in and out of sub either, or even existing in more than one place at a time due to traveling in the 4 th dimension....that being time........Just some food for thought
"
Gravity powered ships would be a good start, considering that balck holes are so strong that even light can't escape them!!!!