Are dolphins the only intelligent life in the universe? We don't know for sure, but this tutorial gives a framework for thinking about the problem.
10710_Detectable_civilizations_in_our_galaxy_2.html
10709_Detectable_civilizations_in_our_galaxy_1.html
10711_Detectable_civilizations_in_our_galaxy_3.html
All video content by Khan Academy is under their license: CC by NC SA
Website created using Khan Academy Static Downloader