this conversation only works if we pretend that faster-than-light travel is actually possible.

are we allowed to pretend whatever we want? if so, i have some things to say about invisible emus and their plot to assassinate me (as predicted by the ancient mythology of the Kalahari)

There are actually particles theorized to travel faster than the speed of light, and the theory of special relativity does not disallow faster-than-light travel.

Besides, you do not necessarily need faster-than-light travel for space exploration. For example, with technology we have now we could reach Mars within about 210 - 250 days. With technology in, say, 100 years time that time could be drastically reduced. Because of this, it means that, rather than using faster-than-light travel, you could just colonized each planet in turn, slowly getting further out. This is one of the reasons why actual contact with other life is so unlikely.

Edit: In fact, Barack Obama has said:

So space travel without faster-than-light travel is certainly not impossible.

the nearest star is about 4.2 light years away.
the nearest extrasolar planet is 10.5 light years away.
the nearest earth-like planet orbiting within the habitable zone of its star is 20.3 light years away.

Mars, on the other hand, is a mere 2.4x10^-5 light years away.

so let's imagine that in 100 years we somehow reduce the time it takes to reach Mars form 230 days to just a week. 7 short days, traveling at about 1/800th the speed of light.

it would still take 3,340 years to reach Proxima Centauri, the nearest star. and a full 16,000 years to get to reach the closest known earth-like planet.

do you see the problem?

Yes I understand this, but what's to say they don't travel in a sort of space station in which they reproduce on board. I understand I'm getting a bit unrealisitic here but what I'm saying is it is possible, even if faster-than-light travel did not exist (which it could). But yes, I see what you mean.

wormholes.

It's easily possible that any other life in the universe has discovered a way to travel that we have not. Other life (especially a species that may be a hundred times older than humans) is not necessarily held down by what we see as possible/impossible. We shouldn't assume that they can't do something just because we can't. Does that make sense?

you're absolutely right.

in fact, it's possible to imagine anything you want if you choose to ignore all our knowledge of how the universe works. if we open ourselves up to all possibilities, however improbable, we can waste away our days dreaming up invisibility pills and flying cybernetic chimpanzee slaves and laser blaster tickle guns and mini dragon pocket pets.

but i'll tell you something - that sort of thinking isn't very practical. it might be fun to consider for a few minutes here or there, but there's no sense in taking it seriously...

Another problem with assuming or arguing aliens could visit us or have visited us is that then you also have to explain why they're not here right now. I've never seen an alien and I haven't seen proof that they exist. Why would they keep their presence a secret? And if they visited us way back then, why did they leave again? One might think that in the universe, a planet supporting life is like a rich oasis in a desert. Life and interest would congregate around them because of the wealth of resources they provide.

Well, we all may be able to talk rationally about seeing an alien on a forum or one on one, but I have no doubt an alien showing up in some downtown city would cause mass panic. We are still stupid creatures and I'm sure a species advanced enough to actually get to our planet would consider us lesser animals and would try to prevent that hysteria. Much like how we hide from animals when trying to film them in their natural habitats.

Like I said earlier, I try not to give much credence to the ancient alien theories and how they helped advance early civilizations, but I really do believe in aliens. I also believe they have visited our planet in some capacity. The universe is too large for intelligent life not to exist elsewhere, we have a very young sun compared to other solar systems with planets that could potentially support life, and I think a species that could travel space would be very interested in exploring all forms of life including our planet.

You exagerate every point. Imagining differences in our knowledge and the truth if not irrational in the slightest. In the past 100 years our scientific knowledge has changed immensely - who's to say we aren't completely wrong? Like Sljslj said, we shouldn't assume that they can't do something just because we can't.

And also, as zevokes said, if wormholes are a reality then that is your answer to how aliens could travel those distances in one lifetime.

Again, this depends on the frequency of life in the universe. If it's very frequent, then perhaps we are nothing special to them. There are many reasons why the aliens may have left - a distant war requiring them, not enough resources to stay, etc. As for proof, well, supporters of this theory would suggest that there's a lot of evidence, but over time many other explanations have also come about and more and more evidence is lost.

I certainly believe aliens exist, but I'm definately not too sure on whether or not they visited us. You say you don't give much credence to these theories and yet you say you believe that aliens have visited our planet in some capactiy?