We define ourselves as intelligent. That's odd, because we're doing the definition - We're creating our own definition and saying, 'We are intelligent!'

Carl Sagan spoke fluently between biology and geology and astrophysics and physics. If you move fluently across those boundaries, you realize that science is everywhere; science is not something you can step around or sweep under the rug.

Perhaps we've never been visited by aliens because they have looked upon Earth and decided there's no sign of intelligent life.

Neil deGrasse Tyson Quotes