A Universe of Earths

Abstract

Planet Earth. The phrase trips lightly from our tongues. Yet planet Earth has been a concept for a mere fraction of recorded history. Until the mid-1600s, most humans thought of Earth as, well, just Earth—immobile, not (like the planets) participating in what Galileo called “the dance of the stars.” A Universe of Earths recounts how that all changed, and how the change augmented and enriched our understanding of where Earth and its inhabitants are in the Universe, how we fit into the Big Picture of the Cosmos. But almost as soon as humans started to grasp that Earth is a planet, many began wondering if perhaps the other planets might be earths. This bold conjecture ignited the whole history and literature of space travel, of extraterrestrials, of other worlds. Yet the thesis that the Universe is full of other worlds like our Earth has from the start been fueled much more by imagination than by evidence. For all its appeal, it has always been undermined by observations of the actual Universe. A Universe of Earths offers a surprising alternative to that “many worlds” tale, one that releases humans from the pre-Copernican view of Earth as low, lowly, dark, a cosmic sump—as well as from the persistent modern aspersion of Earth as cosmically ordinary, “mediocre.” Instead, the true Copernican picture offers the bracing realization that Earth is, in the classical sense, a star, a dynamically wandering one, and a bright, maybe even peerless participant in the dance of the stars.