-There are on the order of 100,000,000,000 (one hundred billion) galaxies in the universe, as far as our telescopes can detect.
-Some of these galaxies may hold up to 100,000,000,000 stars, but most galaxies probably contain at least 10,000,000,000 (ten billion) stars.
-Young galaxies may not have formed many solar systems yet, while very old galaxies may have very few solar systems left. For the galaxies of middle age, as many as 1/4 of the stars may possess solar systems.
Assuming for practical and computational purposes that 1/3 of galaxies are of "middle age" and full of stars, you get:
(3.33 x 10^10 galaxies) times (1.00 x 10^10 stars) times (1/4) = conservatively and roughly 8.325 x 10^19 stars with solar systems in our universe.
That's 83 billion billion (83 with eighteen zeros after it) other stars with solar systems in the universe. To me, it's a statistical inevitability that we are not the only intelligent life in the universe. Alien life is not something you "believe in", it's pretty much something that exists, but we have yet to discover.
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