What makes Carroll's new project so worthwhile...is that...he offers us a cogent, clear and compelling guide to the subject while letting his passion for the scientific questions shine through every page ... in straight-forward language, Carroll keeps his justification for the Many Worlds view grounded in principles like simplicity and economy of description that scientists should all agree on. As his previous books have demonstrated, Carroll is an excellent guide through the frontiers of physics for interested laypeople. Those skills are on ample display in the new book as well. Carroll expertly takes his readers through the conundrum quantum mechanics dumps into the laps of scientists ... It is worth noting, however, that this book does not seem aimed at folks who are entirely new to the subject. It works at a slightly higher level and might prove challenging for those who've never seen the topic at all. I'd like to be able to say that I came away convinced of Carroll's argument that the Many Worlds interpretation is the right way to view the world. But that didn't happen ... convincing people is not Carroll's only intention—which is the books' greatest charm. In a remarkable chapter, Carroll presents a number of the Many World's competitor interpretations (including QBIsm) in a wonderfully fair and balanced way ... Most important, though, Carroll wants readers to see how remarkable the questions quantum mechanics poses are in-and-of-themselves.

In Something Deeply Hidden, the equation Schrödinger developed...rules the discussion (the book helpfully provides a stripped-down layman’s version of this equation, which will thoroughly baffle most of those laymen) ... Carroll’s book is so comprehensive, and he’s such a fantastic teacher ... As a smart and intensely readable undergraduate class in the history of quantum theory and the nature of quantum mechanics, Something Deeply Hidden could scarcely be improved. Carroll has a natural teacher’s knack for democratizing the conversation without sacrificing his own authority. I don’t believe for one femtosecond that possibility is the same thing as actuality; I don’t believe in ghost worlds and don’t think there’s a single word in Carroll’s book that should make anybody else believe in them ... [but] it sure is fun to imagine.

Readers will recognize the attractiveness of Everett’s quantum paradigm, offering a clear picture of reality, not merely a blur of probabilities. They will appreciate, too, the conceptual parsimony of a quantum science distilling its entire framework in a single wave formula ... Carroll argues persuasively that every available alternative to Everett’s formulation entangles scientists in inconsistencies likely to foreclose progress in developing a much-needed quantum explanation of gravity. Readers in this universe (and others?) will relish the opportunity to explore the frontiers of science in the company of titans.

Readers unfamiliar with quantum physics may have difficulty grasping the concepts, but after some rereading of more advanced ideas (such as the wave function), they should begin to understand the hypotheses provided ... Fans of popular science authors such as Neil deGrasse Tyson and John Gribbin will find great joy while exploring these groundbreaking concepts.

Theoretical physicist Carroll...explores holes in the foundation of modern physics in this challenging, provocative book ... Carroll gives a sense of both the frustration and the wonder that the many-worlds theory inspires, and what it implies about free will and human consciousness. Moving smoothly through different topics and from objects as small as particles to those as enormous as black holes, Carroll’s exploration of quantum theory introduces readers to some of the most groundbreaking ideas in physics today.

Although in theory it works brilliantly, no one fully understands quantum mechanics. However, Carroll...works hard—and somewhat successfully—to deliver an accessible explanation ... Eschewing mathematics, Carroll labors mightily to reveal the meaning behind quantum mechanics with a major detour into general relativity, both of which might benefit from at least a little math. Readers who remember freshman college physics will be intrigued; others will struggle.