One of the mainstays of nearly all sic-fi si the idea that we will be able to travel outside our Solar System and eventually across the galaxy and perhaps even to other galaxies.
There is a little bit of a problem with that idea, however, and that is just how far away those stars are.
Let’s do a little (very little) math. Light travels at 300,000km a second, which means that it takes about 8 minutes for the light from our sun to reach the Earth. The nearest star is a little over 4 light years away. VoyagerI, launched in the 1970s, has only travelled a bit over 14 hours from earth. It is moving at 17km/s. A light year is, for simplicity sake, 10,000,000,000,000km (10 trillion km). Voyager 1 moves 530,000,000km in a year, so with some simple math, it will take Voyager 1 nearly 19,000 years to travel ONE light year. It will take nearly 40,000 years before Voyager I travels far enough to be free of the sun’s gravitational pull. If it were flying to Alpha Centauri, it would get there in about 85,000 years, but the star it is flying to is much further away, and it will not reach that star for nearly 400,000 years.
Without a drive capable of generating constant acceleration, you’re not going to be able to get to even the nearest star (and there’s no reason at all to go there) in under 10,000 years no matter what you do, and to provide constant acceleration you need a lot of mass to eject. The more mass you need, the more mass you need to move that mass. The math gets very complicated very quickly, but the upshot is that it cannot be done with rockets, solar sails, or ion engines. With the technology we know is possible, we are still looking at eons just to get to the nearest star.
Any interstellar travel is going to require something that may not be possible. That is to say, there is a very real possibility that the idea of interstellar flight is a complete non-starter and may never be possible.
Sure, we may discover we can warp space (Yes, NASSA is researching that), or that objects can be sent via wormholes, but at this point these are all fictions and there is no reason to think they will actually be possible, and many reasons to think they may not.
Even within our own Solar System, travel between the planets will take years, and that’s just to the inner planets. Flying to Jupiter might be done in a decade, but Saturn is twice as far away. The Asteroid belt is pretty close, and is filled with resources, but you’re still looking at 5 years to get there, and 5 years to get back.
Without a major breakthrough that challenges, if not changes, the model we have for how the universe works, traveling to the stars is never going to happen.