New York Times Bestseller | Wall Street Journal Bestseller | Publishers Weekly Bestseller | Publishers Marketplace 2020 Buzz Book | Amazon Best Book of the Year | Longlisted for the 2022 PEN/E.O. Wilson Literary Science Writing Award Harvard's top astronomer lays out his controversial theory that our solar system was recently visited by advanced alien technology from a distant star. "Provocative and thrilling ... Loeb asks us to think big and to expect the unexpected."--Alan Lightman, New York Times bestselling author of Einstein's Dreams and Searching for Stars on an Island in Maine In late 2017, scientists at a Hawaiian observatory glimpsed an object soaring through our inner solar system, moving so quickly that it could only have come from another star. Avi Loeb, Harvard's top astronomer, showed it was not an asteroid; it was moving too fast along a strange orbit, and left no trail of gas or debris in its wake. There was only one conceivable explanation: the object was a piece of advanced technology created by a distant alien civilization. In Extraterrestrial, Loeb takes readers inside the thrilling story of the first interstellar visitor to be spotted in our solar system. He outlines his controversial theory and its profound implications: for science, for religion, and for the future of our species and our planet. A mind-bending journey through the furthest reaches of science, space-time, and the human imagination, Extraterrestrial challenges readers to aim for the stars--and to think critically about what's out there, no matter how strange it seems.

Kinetic Theory in the Expanding Universe is a self-contained exposition of the applications of kinetic theory to basic problems in modern cosmology, such as the role of stable and unstable massive neutrinos and the theory of cosmological helium production. There has been rapid development of the theory of the origin and evolution of the universe in recent years, stimulated, in large part, by new observations and theories in astrophysics and particle physics. Bernstein takes a different approach and studies what can be concluded from the application of kinetic theory, and in particular the Boltzmann equation and its solutions, to cosmological problems. He begins with a brief survey of the necessary relativity, cosmodynamics, and kinetic theory, before going on to discuss specific problems, such as the role of stable and unstable massive neutrinos, electron-positron annihilation and the theory of cosomological helium production. The focus is in obtaining both a theoretical understanding and concrete numerical results.