Humans have always been fascinated by the possibility of extraterrestrial life, often wondering if we are alone in the universe. Drawing on nearly fifty years as a leader in planetary exploration, Louis Friedman brings into focus the subject of extraterrestrial life, separating knowledge from conjecture, fact from fiction, to draw scientific and technical conclusions that answer this enduring question.

Friedman argues that intelligent life is probably rare in the universe (maybe even uniquely on Earth) but that simple life is likely abundant on millions or billions of planets waiting now to be discovered. He asserts that studying and searching for extraterrestrial life cannot be done by interstellar probes—due to the vastness of space and the comparative brevity of human lifespans—but it can be done remotely by a new technique involving the solar gravity lens that can magnify exoplanets by tens of billions. This technique will allow humankind to explore exoplanets and open up an exciting new field of comparative astrobiology.

Wide-ranging in scope, this book discusses the history of searching for extraterrestrial life, the scientific evidence thereof, and finally his own conclusions on what’s next. Included in the book are three appendices: an explanation of interstellar messaging, a reprint of a debate between Carl Sagan and Ernst Mayr on extraterrestrial intelligence, and an opinion essay on the search for extraterrestrial intelligence.

Louis Friedman co-founded the Planetary Society with Carl Sagan and Bruce Murray and was its executive director for thirty years. A member of the NASA Innovative Advanced Concepts External Council, he is the author of Starsailing, Human Spaceflight, and Planetary Adventures. Friedman was a leader of JPL Advanced Programs, including Mars, Venus, and Jupiter missions studies.

"Dr. Friedman argues that we are alone, absolutely alone in the cosmos, and that this is a feature, not a bug. He acknowledges and celebrates the idea that there are almost certainly a great many bugs out there, that primitive life must be extant all over the cosmic place. Whereas intelligent life, life that can make its presence known in the cosmos, is so unlikely that we humans are, in Lou’s view, the absolute only example. Is it heartbreaking or a wonderful insight? It’s certainly something for intelligent beings to ponder. Read on."—Bill Nye, CEO of The Planetary Society

“In Alone but Not Lonely, Dr. Friedman takes a courageous dive into the mystery of the sky above us and endeavors to divine our place and future in this universe and whether we will ever meet our neighbors, face to face, in person.”—Mae Jemison, MD and former NASA astronaut

“From the birth of Earth through the emergence of AI, Friedman’s wide-ranging and incisive review of space exploration bursts a ton of bubbles—yet paints a galactic future abound with adventure.”—Greg Pass, founding chief entrepreneurial officer of Cornell Tech and former CTO of Twitter

“This is an important book by a true expert in the field. Lou Friedman has spent his life pondering the question of life in the universe and participated in many of the relevant space missions. Much has been written about alien civilizations, both in fiction and in fact. This book is an essential antidote to wild speculation.”—Simon P. Worden, Simon P. Worden, chairman of the Breakthrough Prize Foundation and former Director of NASA Ames Research Center

“Friedman draws a clear line between speculation and scientific probability. This book is for anyone interested in the quest for intelligent life in the universe.”—T. D. Oswalt, Embry-Riddle Aeronautical University, CHOICE Connect

“No human has devoted more lifespan to our future in space than Louis Friedman. Here he takes a bold stand on the giant question of intelligent life in the universe.”—David Brin, scientist and author of EARTH and The Postman

“Let’s think as Friedman does of a program of exploration that stretches out for centuries, with not one but numerous missions exploring through ever refined technologies the images that the bending of spacetime near the Sun creates. We keep hunting, in other words, for both life and intelligence, for we know that the cosmos seems to have embedded within it the factor of surprise.”—Paul Gilster, Centauri Dreams— -