And something tells me...
That collecting the relative abundance of antimatter in Saturn's rings
will be easier than trying to obtain dark energy for interstellar travel.
We CAN build Orion, though. It may be slow by comparison and it may be messy, but it is feasible and we can do it now, if we have the will
and the foresight. And I read somewhere that one type of Orion craft
could get a human crew to Alpha Centauri in about 150 years, which is
a heck of a lot better than the fastest interstellar craft we have now,
which would take 77,000 years to get to AC if they were going in that
direction - which they aren't. Plus they'll stop working a few eons
before then anyway.