The author of Einstein's Dice and Schrödinger's Cat returns with another examination of difficult scientific concepts.Halpern, a Guggenheim fellow and professor of physics at Saint Joseph's University, begins by introducing the James Webb Space Telescope, launched in late 2021, whose instruments reach "faint, distant galaxies from the nascent era of the universe" and send back "vivid photo evidence." By definition, our universe includes everything, so an "alternative" universe makes no sense; no one will ever see one. Yet multiverse models offer enticing mathematical and theoretical ideas. Such concepts were no secret to 19th-century mathematicians, but they entered the mainstream in the 20th when the physics community reluctantly accepted a fourth dimension to make sense of Einstein's relativity. Then, scientists confronted quantum theory, which works so brilliantly, at least theoretically, that the traditional view (propounded by quantum pioneer Niels Bohr) requires physicists to accept that quantum phenomena occur in a "black box." Although this remains the standard interpretation, plenty of geniuses yearn to look inside the box. A dedicated teacher, Halpern explores half a dozen relevant topics including string theory, supergravity, and M-theory. Readers anxious to plunge ahead may want to reserve their decision until they sample the author's explanation of a simple high school physics term: the vector. Halpern's analysis is not for the innumerate, but dedicated readers will be rewarded by illuminating discussions of a host of complex concepts, a penultimate chapter on the physics of time travel, and a conclusion that describes alternate universes portrayed in movies and TV. Halpern's 2021 book, Flashes of Creation: George Gamow, Fred Hoyle, and the Great Big Bang Debate, is a delightful and accessible popular science book. This follow-up is an ingenious slog that may enlighten those with college courses in relativity and quantum theory under their belts.Cutting-edge physics for the educated layperson.

Halpern (Flashes of Creation), a physics professor at Saint Joseph’s University, delves into the multiverse in this thought-provoking if challenging offering. He opens with a superb introduction to the concept of the multiverse, explaining that it stems from physicist Hugh Everett’s hypothesis that measuring quantum states “splits” reality, with every possible outcome constituting its own world. The idea is not without its critics, Halpern notes, observing that because there’s no agreed upon method for detecting or measuring alternate universes’ existence, some scientists decry the multiverse as unfalsifiable. The bulk of the book consists of a broad scientific and philosophical history of the ideas underlying the multiverse, covering Albert Einstein and Niels Bohr’s disagreements over observers’ role in quantum mechanics and physicist Paul Steinhardt’s 1980s work suggesting the early cosmos might have been “a bubbling froth of multiple expanding universes.”Halpern sometimes loses focus, however, as when he takes a lengthy detour examining Friedrich Nietzsche’s belief in the “endless repetition of events throughout the eons.” Though Halpern does his best to make the science accessible (he likens Everett’s understanding of the multiverse to “an ever-flowing river with many persistent branches”), his valiant efforts come up short when faced with the complexity of string theory and a proposed “eleven-dimensional brane world.” Still, the curious will find much to ponder. Photos. (Jan.)