This is a book review of The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes by Paul Halpern.
The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes, by Paul Halpern (Basic Books), 2024. Pp. 311, 23.5 × 15 cm. Price $30 (about £25) (hardback, ISBN 978 1540602182). (about £24) (hardback, ISBN 978 154160217 5).
The book covers various types of Multiverses and their historical context. The first three of Tegmark's(1) four Levels of Multiverses are all discussed: the part of our Universe beyond our horizon, different universes of which ours is but one example, and the many worlds of the many-worlds interpretation of quantum mechanics. The idea of a universe splitting due to the actions of travellers in time is a new aspect. However, the emphasis is not so much on different types of Multiverses but rather on different ideas which can lead one to the concept. On the other hand, Tegmark's Level II Multiverse — which is probably the one (apart from the trivial Level I) most are most willing to accept — is discussed mostly in the context of eternal inflation, although the general idea is much older (e.g. ref 10). In general, the title is a good description of the book: it is about the allure of the Multiverse, i.e. what makes it an attractive idea in various contexts, rather than more technical aspects. Towards the end, is a good summary, emphasizing the fact that in many other contexts most are content to accept things which are not directly observable (i.e. the interior of black holes, the inflaton, the `dark ages' of the Universe), even though they might use the lack of direct detectability as an objection to the Multiverse.