Actually he said you couldn't. He considered the speed of light the universal and ultimate speed limit. At relativistic speed we get into the concept of relativistic mass where γ m appears, where the gamma factor γ = (1–v2/c2)–1/2 What this boils down to is that any increase in propulsive energy doesn't increase speed but simply increases the realtivistic mass.
NASA has a theoretical model to make that work.
Not likely.
He said an object couldn’t break the speed of light. But he also said you could use gravity to condense the space the object is traveling through to create a functional travel speed higher than the speed of light without breaking it.
You can say not likely, but I’m going to believe Einstein and NASA.