Either way it's based upon assumptions for which there's no evidence at all. One scientists thinks it's an educated guess to think the galaxy must be crawling with life, another thinks we probably are the only planet on which there's life.

I tend to agree with the first group of scientists, but until we've found some actual proof, it's as good as either guess.

Also, don't forget those chance figures are incredibly arbitrary and no scientist thinks of exactly the same figure... there's no simple rule to determine the real chance of life, especially since we don't really know much about the earliest phase or at least what or how it started.



That's an assumption on your side as there are definitely also serious scientists that believe it's very possible that other civilizations have already overcome such obstacles. Problem with such theories is that we don't really know how they have managed to overcome those problems... But just because we don't understand how doesn't mean it's not possible at all or even unlikely for that matter.

It's the big issue when there's a lack of evidence... we can fantasize all day long, but it would still get us nowhere unless we actually solve those problems ourselves or capture and reverse-engineer one of their space craft.



Assuming there's at least more than just one planet on which life started / or spread to, it's still incredibly questionable whether there's advanced and intelligent life comparable or better than here. (Mind you a lot of this talk is based on our rules of statistics that could be far off anyways.)

Obviously a few cells on a distant planet won't be able to visit us and we won't be able to visit them either as they are likely way too far away.

Perhaps there are or have been conditions elsewhere in our universe good enough to support life, but until we find such a place it's still a huge step to assume there might be life comparable to us.