Einstein spoke of gravity but he never wrote the equation which unlocked it. Gravity is the last " frontier" for physics, well at least as far as we know. Einstein did start the train rolling on the understanding of its effects in space as well as time, see the satellite orbiting around the sun and the delay of its signal returning to Earth because of the Sun's gravity experiment. If and when gravity is "conquered" space travel as we now know it will more closely resemble the hollywood version aka Star Trek.