Once habitable planets are discovered and chemically fingerprinted around nearby stars, there will be a lot of interest in dispatching interstellar probes to check out the best candidates for life.

But dreams of star travel present an awfully steep slope when one calculates the energy needed to make the journey. Though exotic "massless" drives, somehow tapping the "vacuum energy" of space may eventually be realized, let's assume for this discussion only simple action/reaction engines based on good ol' Newtonian physics can be used.

If you assume that, you're never going anywhere. To read more, click here.