I'm a physiologist, not in anyway well-versed in physics beyond what I took as a pre-medical student. Forgive any lapses in proper vocabulary or wording of my inquiries. I have a question about the habitable zone theory. Not so much this: http://en.wikipedia.org/wiki/Circumstellar_habitable_zone in terms of an individual star and satellite but moreso about the galaxy in general. What do you think of the galactic "habitable zone" theory that postulates life can really only exist in a narrow band of the galaxy. As wikipedia says, "the galactic habitable zone is the region of a galaxy in which life is most likely to develop [...] For the Milky Way this region is commonly believed to be an annulus with an outer radius of about 10 kiloparsecs and an inner radius close to the Galactic Center, both of which lack hard boundaries." The reason I am asking is because I am writer of science fiction, and while I'm not qualified to write really hard sci-fi, I'd rather not create alien planets in regions of the galaxy that even amateur cosmologists will read about and promptly throw my writing into the trash.