In How the Universe Got Its Spots, physicist Janna Levin takes aim at a question that has been puzzling humankind for at least as long as there have been teenagers and pot: Is the universe infinite? And, if so, what does that mean? Levin approaches this daunting topic with a blend of audacity (“Before I reject infinity, I want to admire it”) and reverence (“Some of the great mathematicians killed themselves”); unfazed, she sets out to challenge the assumption that the universe is infinite. “No infinity has ever been observed in nature. Nor is infinity tolerated in a scientific theory—except we keep assuming the universe itself is infinite,” she writes. Levin compares this assumption with the long-held view that the world was flat—which, of course it wasn’t: Explorers could sail around the globe and arrive in the same spot where they started. “If the universe is finite,” writes Levin, “explorations of space may end where they began.” Far out, man. Throughout the book—which began as a series of unsent letters to her mother— Levin describes her theories about the topology and geology of the universe in accessible prose and simple diagrams. Inevitably, she fails at answering all of the universe’s unanswerable questions, but she succeeds in smoking out the wonder lust of our minds. Puff, puff, pass at 7 p.m. Tuesday, May 7, at Olsson’s Books & Records, 1200 F St. NW. (202) 347-3686. Free. (Felix Gillette)