In a very positive review, Clive Cookson in The Financial Times wrote that "physics could do with more characters like Tegmark" and that his book "should engage any reader interested in the infinite variety of nature.

[7] Brian Rotman, writing for The Guardian, was unconvinced by Tegmark's conclusions but also wrote that the book is "at the cutting edge of cosmology and quantum theory in friendly and relaxed prose, full of entertaining anecdotes and down-to-earth analogies.

"[8] Similarly, cosmologist Andrew Liddle, in Nature, summarized:[4] This is a valuable book, written in a deceptively simple style but not afraid to make significant demands on its readers, especially once the multiverse level gets turned up to four.

[10] In a review written for The Wall Street Journal, physicist Peter Woit said that the problem with Tegmark's proposal is "not that it's wrong but that it's empty" and "radically untestable.

[12] In New Scientist, Mark Buchanan contrasted what he saw as the "uninhibited speculation" in parts of Tegmark's book with his earlier "hard, empirical" work which established him as a physicist.