The idea that speed and energy is all we need to traverse interstellar distances is preposterous. Debris - even hydrogen ions - would get in the way. At 10% cee the impact of a hydrogen ion with the hull of a starship would flood the interior with a shower of gamma rays, destoying both living and electronic things. We have to clear a path through space in order to traverse it at these speeds. Maybe speed isn't the answer.

I like the idea of wormholes: where nuclear particles are viewed not as matter or energy, but as a blister of spacetime. All such blisters are connected together with a tunnel, or wormhole, in a higher dimension with zero distance between them in the higher reality. But the wormhole is closed to us, and since there are no natural events that open them, there is no debris inside them. If we can trick spacetime blisters into expanding, we might step through and emerge on the other side of room, or the other side of the universe, unscathed. Timelag might not occur, neither would causality violation, because light would take multiple paths between two points: both via the long route and through the wormhole.

Say if a proton consists of 3 quarks, we might trick those quarks into higher orbits than are possible in nature, maybe orbiting several feet apart. Then we just step through to the other side...

Problems:
1. How to open a wormhole.
2. How to choose a destination.

(currently science fiction)