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Originally Posted by Knalus

I think we have evidence that gravity exists outside of our galaxy.

You've never been there, you don't know for sure. It could be some other phenomenon and it just looks similar to our galaxy.

Assuming that gravity works in other galaxies is exactly that; an assumption. It's a good assumption because every other observation we've ever made about the laws of physics and such support it, and there's nothing ever been observed to indicate that it's a bad assumption.. but it's still just an assumption, one that giving provisional support to makes sense.

Originally Posted by Knalus

Have you not noticed that discussing the existence of Alien life is one of those topics that serious scientists all seem to accept as not just plausible and probable, but move beyond that into likely?

They do? A biologist giving a talk about convergent evolution in the context of speculation about aliens to try and appeal to a lay-audience certainly doesn't do that, and that's where you started out.

But if I had to choose, I'd probably choose likely as well, at least given what we currently know.

From a simple probability point of view, given an infinite universe anything that isn't impossible will be duplicated.

And in a finite universe, the probability that things would turn out so that there'd only be exactly one planet where life arose is like walking on the edge of a knife (far more probably to have either no life, or lots of life), something to be very suspicious of and certainly not a place to start from. And since we know that we exist... We have no good reason to think we're in a unique situation here.

If you reach into a box filled with a trillion coloured marbles, and you know that the marbles can only be one of two colours, and you pull out a red one, the safe bet is to assume that the marbles are either all red, or a significant portion of them are. To bet that there's only one red one in the trillion and you just happened to get it isn't the safe bet. Without looking you can't know of course, and no one would make a definitive statement about the ratio of red marbles, but some possibilities are still preferred over others until more information is uncovered (like maybe red marbles and your hand attract each other).

Originally Posted by Knalus

Even in the face of a complete lack of evidence?

Absence of evidence is not evidence of absence.

Not that that constitutes evidence that there is alien life.

Originally Posted by Knalus

I wonder why that is. Can we not find wonder in our universe without conjuring up a multitude of imaginary beings flying all around the place? Does the universe really need dressing up in order to make it fun enough to involve the lay person? I personally don't think it does.

How do you go from not saying aliens and skeptic in the same breath to saying science conjures imaginary flying beings to create a sense wonder because they don't see enough already??

Life arose once, the universe is vast beyond imagining (maybe infinite), to think that the right circumstances for life arose exactly once (as opposed to zero or more than once) is the position that requires skepticism IMO.