I see no reason to doubt the existence of aliens. I believe pretty much the same thing that Carl Sagan used to go on about, that it's not just likely, but extremely likely.

Of course, there's also the very valid point to make, also in agreement with Sagan, that the chances of them ever finding us or vice versa is extremely slim.

So while I believe there is plenty of alien intelligence out there, I see no reason to believe that we've ever been visited, and plenty of reasons to believe that we haven't.

I wouldn't argue either way though really. Truth is, nobody knows, so the best we can do is speculate on the probability.

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