If you hold up your thumb to the sky at night, you block the light from a trillion galaxies; If you hold up a grain of sand to the sky at night, you block the light from a billion galaxies.
How many thumbs does it take to completely block the night sky around the entire globe of the Earth? Compute the total number of galaxies in the universe. Hint: find a number above 70 billion trillion.
Multiply that number times the average number of stars in a galaxy (300,000,000) to get the total number of stars in the universe.
Assume each star has only 1 planet; assume that only 20% of all plants are in the carbon cycle habitable zone; assume that of those planets only 1 percent currently have intelligent life: how many planets is that?
Assume you have a starship capable, for arguments sake, of Warp Nine and can stop instantaneously: how long will it take the ship to visit all the planets which currently have intelligent life?
Discuss how the number of planets with intelligent life will change during the course of the trip. And discuss whether or not you will have to visit and revisit all the stars that exist by the time you finish visiting them all the first time.
There’s no intelligent life in the White House...