The cosmic speed limit? - Maybe - But consider this:
Focus: The Birth of Wormholes
March 25, 2005• Phys. Rev. Focus 15, 11

"A 1935 idea from Albert Einstein and Nathan Rosen for unifying electromagnetism with gravity lives on in the minds of science fiction fans.

In honor of the World Year of Physics, which commemorates Einstein’s “miraculous year” in 1905, we’re presenting papers from the Physical Review archive related to Einstein’s accomplishments.

In the last decades of his life, Albert Einstein tried endlessly to unify electromagnetism with his own theory of gravity, general relativity. These efforts are mostly now regarded as quixotic, but a short proposal written in 1935 with a colleague has survived in unlikely fashion as the source of science-fiction ideas for speeding across the universe by means of “wormholes” through spacetime. From the modern perspective, the paper also illustrates how general relativity posed mathematical and conceptual difficulties that foxed even its creator......."
See whole article here:
http://physics.aps.org/story/v15/st11