...When confronted with the topic of stars and galaxies, a question that tantalizes most humans is, “Is there other intelligent life out there?”...http://waitbutwhy.com/2014/05/fermi-paradox.html
As many stars as there are in our galaxy (100 – 400 billion), there are roughly an equal number of galaxies in the observable universe—so for every star in the colossal Milky Way, there’s a whole galaxy out there. All together, that comes out to the typically quoted range of between 1022 and 1024 total stars...Moving back to just our galaxy, and doing the same math on the lowest estimate for stars in the Milky Way (100 billion), we’d estimate that there are 1 billion Earth-like planets and 100,000 intelligent civilizations in our galaxy.
...But it hasn’t. Not one. Ever.
Where is everybody?
See the link above for more.