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. 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. No matter what our technology, we'll never travel to other
stars except maybe nearby stars like Alpha Centauri which you could
reach in a few decades. Otherwise the distances are just too vast. You
just have no comprehension of interstellar distances. 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?

Absolutely no one in their right mind would suggest that Earth was the
only world with life in the entire Universe. It is unlikely but there
could even be other worlds with life within our own solar system, such
as on Mars, Ganymede, or Europa. I say "world" to encompass terrestial
planets, gas giants, moons, asteroids, comets, etc. There are about
100 billion stars in the Milky Way galaxy. If there was one planet or
moon with life for every 1000 stars, and one planet or moon with
intelligent life for every 1000 with life, that would be 100,000
worlds with intelligent life in the Milky Way, which is an average
sized galaxy out of 100 billion galaxies in the observable universe,
so you multiply 100,000 by 100 billion to get 10^16 worlds with
intelligent life in the observable universe. If you took a more
skeptical view that there was only one world with life for every
10,000 stars, and only one world with intelligent life for every
10,000 with life, that would still give us 1000 worlds with
intelligent life in the Milky Way galaxy, and 10^14 worlds with
intelligent life in the observable universe. No one would ever suggest
that Earth was the only world with life in the entire Universe.

Why not just take it a step farther and say that you are the only
organism in the Universe, and all others are figments of your
imagination? That's a small step from suggesting Earth was the only
world with life in the Universe. I mean if you are denying the
existence of life on other planets because you haven't seen it, how
many people have you personally seen? Have you seen all one billion
people in China? Have you seen all 300 million people in the United
States? Of course not, yet you accept their existence without
question.

Jeffery Winkler

http://www.geocities.com/jefferywinkler