Probably more advances in nanotechnology, better batteries, quantum computing. The answer to more power over the macro scale is more power over the micro scale.
Throughout history, there is a general trend to make things smaller, which only makes them more powerful. Anti-gravity might even be possible by reversing the Casimir effect with a sort of nano-scale lens.
Even using our present-day knowledge of physics, the possibilities are almost endless if we can harness the engineering needed