Humanity has been theorizing about the possibilities of
interstellar colonization long before it even qualified for Type I
civilization on Kardashev scale. Before we event sent our first
seed ship, it has been theorized that it will take several
generations before it even pass the half-way mark towards it's
destination. Some even suggested that by the time the first such
ship would arrive, the rest will already have developed faster and
more efficient ways of travel between interstellar bodies. Some
were putting their hopes in quantum computing, or even
self-teaching AI, but alas, our machines are still only as perfect
as their creators. Here we are, still floating around at sub-light
speeds, spending the first half of the journey speeding up and the
other half slowing down and praying for our calculations to be
correct. As fascinating as it may seem, even the stars move around.
We have to calculate the trajectory of our target and account for
the delay caused by the speed of light and the distance, because by
the time the star's light reaches our eyes, it might be already
long gone. In the better case, it merely moves from it's previous
position. Worst case, it's gone supernova and our ship will arrive
to a newly formed black hole...
Then there is this little annoying thing backed up by out
observations from our home planet - the universe (or at least it's
observable part at least) is expanding - we can tell, because the
stars are gradually changing their color spectrum towards red and
infra-red meaning the light itself is taking longer and longer to
travel all the way to our photoreceptors...
Sounds depressing doesn't it?