Nah it's because as you approach the speed of light energy is directly converted to mass, according to a theory I can't remember the name of. The work around is by moving the fabric of space, so essentially instead of having your ship push on space, space pushes a bubble of space around your ship and that carries you.
Sadly it requires negative energy, and the only form of negative energy we know of, is gravity.
Simply put, the space has to move around you and not the other way around. And gravity is not so hard to replicate, you just need to spin really really fast.