[A.J.Armitage]

If no other life could exist anywhere in the universe would mean the universe is sterile. That we exists proves the universe is not sterile, but fertile. There would have to be overwhelming proof of the entire universe being sterile in order to completely negate the possibility of other life elsewhere. There is no such proof.

First, could exist and does exist aren't the same thing.

Second, if there are intelligent aliens, why aren't they here? That there are many civilizations but only one, us, with an urge to explore is as unlikely as many planets but only one, Earth, with native civilizations.

[mvpel]

Jewish tradition states that God created and destroyed many worlds before creating this one.

[judgeandjury]

Second, if there are intelligent aliens, why aren't they here.

They've probably already "been here, done that". Having vastly more intelligent and technologically advanced aliens watching us human beings go about our daily routines would probably be about as interesting to them as you or me watching some cows in a field going about their daily routines. The aliens probably visited us, took some notes, and then moved on to explore other worlds.

[yendu bwam]

Second, if there are intelligent aliens, why aren't they here?

Quite possibly for the same reason that we aren't spread out all over the galaxy ourselves. The speed of light limit, and the enormous energies or time needed to traverse the galaxy put an enormous barrier to its exploration. Those barriers may be untranscendable, making them as difficult for others as they are for us.

[Physicist]

Second, if there are intelligent aliens, why aren't they here?

'Cuz the trip is really, really, really, really long.

[TopQuark]

Second, if there are intelligent aliens, why aren't they here? Firstly, we may not be important. Secondly, do not forget that we are of any interest at all for just about 10,000 years. And another civilization may ve so far away that it takes light this many years to travel. IN other words, as they look NOW at our Earth, they see Neanderthal-like creatures from which that light was reflected. They will see us, with our TV, satellites, libraries, etc. only 10,000 years from now.

[Joe Hadenuf]

Second, if there are intelligent aliens, why aren't they here?

Do we really know they are not? Or have been already in the past?

We always seem to think that aliens would be similar to us in size etc.

Imagine an alien spacecraft the size if a shirt button, that held 2000 space travelers. It wouldn't even show up on radar, and the chances of actually seeing it would be very remote.

[Valin]

Second, if there are intelligent aliens, why aren't they here?

And what makes you think They're not? < /Art Bell> :-)

As far as life on other planets...sure why not. Maybe even intelligent life, maybe the fall didn't happen.

Not only is the universe stranger than you imagine, it's stranger than you can imagine
A Einstein (I believe)

[Vinnie_Vidi_Vici]

Second, if there are intelligent aliens, why aren't they here?

Probably because of that "Prime Directive" thingy!