The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes

The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes by Paul Halpern

The Allure of the Multiverse by Paul Halpern delves into the scientific history of the theory that seems to have taken over pop culture. Admittedly difficult at time thanks to the relatively esoteric nature of some of the theories such as string theory or M-brane theory, and also perhaps a bit mistitled, it remains a mostly clear exploration of 20^th and 21st century physics.

The book opens with what might come as a surprise to some readers who have steeped in the multiverse concept via film, TV, and books for some time now: the theory is far from universally accepted by scientists thanks to “the stark disadvantage of a lack of direct detectability.” Scientists prefer theories that can be tested, and so, as Halpern puts it, while “many theorists are willing to accept unobservable components … if it supports a promising way of explaining the basic facts of the reality we experience … there is a wide range of opinions and tastes about how seriously to take multiverse schemes.” Halpern’s own stance is to “remain cautiously open-minded about various multiverse schemes — rather than dismissing them outright,” pointing out how “what is fringe sometimes slips into vogue”, such as the concept of the fourth dimension which was once considered mystical nonsense and now is “standardly applied” in space-time calculations.

From there it’s a relatively deep dive into classical physics, particle physics and the weird world of quantum physics, with all the usual stop-offs at Newton, Einstein, Schrödinger’s Cat, the Standard Model, Bohr, Heisenberg’s Uncertainty Principle, the Big Bang, Hawking, String theory, black holes, the Higgs boson, and more. Halpern methodically lays out the questions all these are supposed to answer, then more importantly for the book’s subject, all the questions they don’t answer, which leads to the origination of Hugh Everett’s Many Worlds Interpretation, one of several multiverse theories.

One of the better elements of the book is in fact how Halpern makes clear there is more than one way to skin Schrödinger’s Cat and get to the multiverse: there’s Everett’s theory, the argument that in an infinite universe filled with finite material it’s inevitable to have multiple Earths, the theory of eternal inflation (meant to explain things like the uniformity of the observable universe), and even Nietzsche’s concept of a never-ending cycle of repeating lives and events. Another point I appreciated was how he made clear that the pop culture view of Everett’s theory doesn’t actually align with the actuality of the theory, which is far more prosaic than the idea that every decision creates another “you” out there somewhere. As Halpern notes, “the MWI would not produce dueling Kirks, bearded versus clean-shaven Spocks … battling Lokis … Rather it might distinguish between near-identical versions of a scientist witnessing one type of blip versus another type of blip.” Hardly “Avengers Assemble!”

For the most part Halpern does a good job of making this all understandable, employing the usual tools of popular science: analogy, metaphor, and of course clear, easy-to-follow language and syntax. That said, it does at times get a little hard to follow, as with this passage:

The Randall-Sundrum model attempts to resolve the cosmological constant problem by adding a large positive value to a slightly smaller negative value to produce a tiny positive value for the overall cosmological constant. The large positive value is the vacuum energy of our brane due to the baseline of quantum interactions in the Standard Model. The slightly smaller negative value is the negative cosmological constant of the higher dimensional anti-de Sitter space in which our brane resides.

The reality of course is these are abstruse concepts and lots of times writers will go too far in oversimplifying them. So this is less a criticism than simply an observation that readers may face some difficulties. That said, passages like this one are rare; for the most part the book simply requires some readerly attention.

A bit more of a criticism is the titling, which I’d say implies a more far-ranging, in-depth exploration of the multiverse in pop culture than what we get, which is mostly limited to a single chapter. So those coming for that book may be a bit disappointed. But as an exploration of modern-day physics, Halpern more than satisfies.