Are We Alone?

For billions of years, life on this planet waffled in oceans in the simplest single-celled incarnation. Today, all complex life forms, no matter how disparate they seem, share common features. Trees, humans, squid, and lettuce are related. It is not known how the simple single-celled organisms finally transitioned to a multi-celled organism that seems to be the singular, original source of all complex life on Earth. So how rare is the emergence of life on any planet, let alone complex life forms?

We now estimate that there are tens of billions of planetary systems in our own galaxy and there are hundreds of billions of galaxies in the universe, each presumably stocked with the chemical blocks necessary for life. In the competition between such large numbers and such small numbers, which wins? Are we alone? Astrophysicist Janna Levin invites biochemist Nick Lane, author of The Vital Question, and astrobiologist Caleb Scharf, author of The Copernicus Complex, to discuss the origin of life on this planet, on other planets, and even in other universes. ♦

Scientific Controversies brings together two scientists in conversation to explore unsolved quandaries. The focus is on ideas and the unknown, the precipice between where we are now and where we imagine the future will bring us.