As I see it we would need to be able to control gravity and we would need a faster than light drive. Say we learnt how to nullify gravitational attraction (graviton field). In a car then, the earth's gravity could be nullified and it would effectively float. That gets you into orbit but what about interstellar travel? Wormholes have been theorized with black hole endpoints. Could the control of gravity be used to protect ourselves from the immense forces as we traversed them? A common military UFO sighting phenomenon seems to involve sudden high acceleration. If the craft contained a very dense mass, say a gravitationally shielded bit of a neutron star, could that be used to selectively generate force in regard to other large mass objects like the sun? The nice thing about this theory is that you could look for it. There are satellites that measure gravitational forces so any fleeting variations could be easily observed.