(Jeffery) wrote in
m:

Interstellar travel is impossible since it would take centuries or
millennia to reach other stars. Aliens are not going to spend 1000
years traveling to our star, doing nothing but making a B line to our
star, when from their point of view, it's very unlikely that there is
life on a planet orbiting our star.

If you are in suspended animation, who cares if it takes a long time to
travel? At least as long as you plan on one way colonization. Holiday
trips seems ruled out. It is likely to be expensive, yes, but far from
impossible. You could even hollow out an asteroid, build a city inside
and travel real slowly while living as ordinary.

Finding out that Earth harbors life isn't very difficult. We're planning
on sending up a telescope able to detect life on planets around nearby
stars within about a decade. You just need enough resolution to get a
spectrum of the atmosphere to see that Earth is not in equilibrium, and
as far as we understand chemistry life is the most plausible way of
generating an atmosphere with lots of oxygen. Any civilization with the
technology to attempt interstellar travel will have much better
equipment.

Since you can't travel faster that
light no matter what your technology, the impossibility of
interstellar trave is independent of technology. This is the proof of
the nonexistence of UFOs. To claim otherwise is the same as believing
in UFOs.

Certainly not. Just because interstellar travel is possible doesn't mean
anyone has been here. Would the non-existence of airplanes before 1903
have proved that heavier than air flight was impossible?

If you claim
that aliens can travel to other inhabited worlds, then why not say
that an alien space craft crashed in Roswell, New Mexico in 1947?

Because there is no evidence an alien space craft crashed in Roswell and
considerable evidence against it.