Re: Do you think it would be possible for extraterrestrials to live on Earth ?

It sounds as though you are properly skeptical of the idea that there are extra-
terrestials among us. Let me give you a few other problems I see with this idea. 
I would think that there are several other, more difficult problems for them to 
solve (such as how to traverse interstellar distances, developing suspended 
animation, maintaining a civilization across multicentury gaps imposed by star 
travel) than how to live in an oxygen rich, methane poor, one-g environment. If 
there are other planets and civilizations, then some of them will probably have 
similar atmospheres and environments to Earth's. I happen to think there 
probably are other Earth-like biosystems with sentient lifeforms, but physics as 
we know it today, would make interstellar travel very unlikely.

Then there are the problems of motivation and goals that the idea of "hidden 
extra-terrestials" poses. Why would a lifeform that put all that energy into 
travelling across interstellar distances then go and hide itself? I'm sure many 
people can come up with all sorts of conspiratorial theories, but none that I 
have heard have convinced me. 

I am by the way, a big reader of science fiction, but I try to remember what-is-
fiction and what-is-real. I know that the question of what-is-real is 
occasionally tricky, but we should do our best to use what we can repeatedly and 
reproducibly observe. I don't think the ETs are in that definition of reality. 
(Yet.)

Regards,
David Winsemius, MD