The Big Picture: On the Origins of Life, Meaning, and the Universe Itself

by Sean Carroll

Now the basics have been well established. The Milky Way we see stretching across the dark night sky is a galaxy—a collection of stars orbiting under their mutual gravitational attraction. It’s hard to count precisely how many, but there are over 100 billion stars in the Milky Way. It’s not alone; scattered throughout observable space we find at least 100 billion galaxies, typically with sizes roughly comparable to that of our own. (By coincidence, the number 100 billion is also a very rough count of the number of neurons in a human brain.) Recent studies of relatively nearby stars suggest that most of them have planets of some sort, and perhaps one in six stars has an “Earth-like” planet orbiting around it.