With all the recent press about the 4 billion mile, 10 year trip to a comet in the asteroid belt, and the release of Interstellar in the movie theatres, it seems appropriate to look at the way we do travel in space. Despite 50 years of invention, we appear to be pretty much stuck with rockets and flybys. However as detailed in this nice Gizmodo article, there are other options for traveling thru space. The article goes into some detail about three options that seem like science fiction, but that we’re currently working on.
The first option is thermonuclear fusion. At least we know it works – it powers the Sun after all. However, we’ve never been able to set up a successful fusion experiment. The problem has always been controlling the plasma in a usable fashion and keeping the fusion process alive. It could another 30 years before we reach the stage where this lets us travel cheaply through the solar system, but it could let us approach maybe one tenth the speed of light, where we could reach the nearest stars in 40 years or so.
The second option is a solar sail. We’ve actually launched one of these, although the rocket blew up and so it never got a chance to be deployed. The idea here is a large unfolded sail that could either harness the power of the (free) solar pressure or (more expensive) lasers directed into space. Although such a space-craft system would start off slow it could quickly get up to about 1/5 the speed of light. The technology exists for this one, we just need to get it launched.
The third option is the most exotic. You could, theoretically traverse the entire universe inside a few years of your own life by using a pair of black holes. In essence you go into a sling shot between the black holes and then fly off into space. As you get really close to the speed of light, your time slows down so you could get anywhere and back in a few years. Unfortunately a few billion years may have passed on Earth while you are gone. This one remains in the realms of science fiction, for now.