Antimatter Engine
“Just one gram of antimatter could generate an explosion equivalent to a nuclear bomb. It's that kind of energy, some say, that could boldly take us where no one has gone before at record speed.”
It could also—and, if history has taught us anything, probably will—do other things.
“An antimatter engine could theoretically accelerate a spacecraft at 1g (9.8 meters per second squared) getting us to Proxima in just five years... That's 8,000 times faster than it would take Voyager 1 — one of the fastest spacecraft in history — to travel about half the distance, according to NASA.
“Even within our own solar system, an antimatter-powered spacecraft could reach Pluto in 3.5 weeks compared to the 9.5 years it took NASA's New Horizons probe to arrive.
“The engine system would first gather high-energy positrons from krypton-79 and then direct them toward a layer of regular matter, producing annihilation energy.”
Annihilation energy.
But apparently, this is all in fact pretty old science:
“In 1953, Austrian physicist Eugen Sänger proposed a “photon rocket” that would run on positron annihilation energy.”
The hurdle seems to be: (a) Funding, and (b) Testing. Regarding the latter, one has to be very careful where to go about testing “annihilation” energy apparently. One scientist has a remarkably bright idea though:
”'So we need an ability to test high energy density systems somewhere that don't threaten the biosphere, but still allow us to develop them,' said Howe, who thinks the moon would make a good testing base. 'And if something goes wrong, you melted a piece of the moon,' and not Earth, he added.”
Swell.