Universe or Multiverse?

by Bernard Carr (Editor)

Recent developments in cosmology and particle physics, such as the string landscape picture, have led to the remarkable realization that our universe - rather than being unique - could be just one of many universes. The multiverse proposal helps to explain the origin of the universe and some of its observational features. Since the physical constants can be different in other universes, the fine-tunings which appear necessary for the emergence of life may also be explained. Nevertheless, many physicists remain uncomfortable with the multiverse proposal, since it is highly speculative and perhaps untestable. In this volume, a number of active and eminent researchers in the field - mainly cosmologists and particle physicists but also some philosophers - address these issues and describe recent developments. The articles represent the full spectrum of views, providing for the first time an overview of the subject. They are written at different academic levels, engaging lay-readers and researchers alike.

Genres: Science, Physics, Nonfiction, Philosophy

Hardcover

First published June 21, 2007

About the author

Bernard J. Carr is a professor of mathematics and astronomy at Queen Mary University of London (QMUL). His research interests include the early universe, dark matter, general relativity, primordial black holes, and the anthropic principle.

Reviews

[Paige McLoughlin · Rating 5 out of 5]

A collection of articles on the borderlands of Physics, Cosmology, and Philosophy. It is science-oriented written by practicing physicists and cosmologists on the topic of the multiverse which happens when one bumps up against the horizon of Cosmic Background radiation surrounding us like a spherical plasma screen 44 billion lightyears away surrounding us in all directions. What lies beyond this barrier does it go on forever outside of what we can see with telescopes and radio dishes. Or it may crop up at the atomic level in Quantum Mechanics with the Many world interpretation which like the movie premise of "sliding doors" starring Gweneth Paltrow multiple outcomes happen from diverging branches of the wavefunction of probabilities in the outcomes of multiple histories made myriad at the atomic level (the premise of many sci-fi stories). Or at the level of the big bang with may have started with a rapid inflationary expansion in the first instances after the singularity of the big bang before the (nearly steady and more relaxed paced and more stately expansion of the current universe). According to this model, inflation stops in some places with normal Hubble expansion in small pockets while inflation continues in rapidly expanding spaces outside these small pocket or bubble universes. A whole new road to infinity and that is just to name three ways our universe could potentially be infinite.
This raises a conundrum for physicists. What is typical in an infinite multiverse with (maybe near-infinite or infinite variety) are we run of the mill in such a situation of infinite examples or are we exceedingly rare. How do you put a measure to that. This in fact has been dubbed "the Measure Problem" (not to be confused with the "measurement problem of Quantum Mechanics"). Some approaches with statistical thinking in this problem of typicality among a possibly infinite number of cases. It also touches lightly on the metaphysical problems of such a multiverse. Recommended.

The Measure problem part one
https://www.youtube.com/watch?v=F1Z_A...

The Measure problem part two
https://www.youtube.com/watch?v=JocAe...

[Paige McLoughlin · Rating 4 out of 5]

A very good book on the state of the multiverse, probably circa 2015. It is a good book on the growing consensus at the time from many different areas of cosmology that pointed to the idea of a multiverse. Physicists don't like the idea, but many various lines of evidence forced them to embrace it. Some still don't, and many are uneasy about taking it on and are reluctant to hold it. Now there is a crisis of cosmology shaking things up in the current field. This book came out before this cropped up, and maybe a new resolution will change the picture and the prospects of the multiverse. Being a metaphysically speculative person, I am inclined to like the idea of a multiverse (I am in love with those infinite spaces that Pascal feared and find infinity exhilarating instead), but I share some of the misgivings of the theory. It is way too meta and has falsifiability problems. We will see where it goes.

Reread on 11/19/2025. Deals with the physics and cosmology of the possible multiverse. Max Tegmark does a good job of talking about the multiverse. Level I: The quilted multiverse is just more of the same outside our cosmological horizon. The Level II multiverse is the string Landscape of possibly different constants and physics brought about via Chaotic Inflationary Cosmology. Level III multiverse is the Everettian Many Worlds of Quantum mechanics, which exists in a branching Hilbert space, and Level IV is essentially the existence of all consistent mathematical forms in a Platonic Plenum or Plato's Heaven (very old idea). The book debates whether these ideas make sense, and there is a way to test or falsify these claims or if they are simply made plausible by extending principles that explain physics in our own universe. Also, look for ways of figuring out fine-tuning and anthropic selection or whether some deeper physical principle will eliminate the need for fine-tuning and anthropic arguments simply because it will be manifest that things could be no other way. Anyway, it is a good book on a topic that lives rent-free in my head.

[Reader · Rating 5 out of 5]

"Universe or Multiverse?" is an appealing book.

Our universe is a multiverse. I don't see how it couldn't be. On this planet we call Earth, we have various generations in one household, making it possible for someone from 1906 to occupy the same house as someone from 1966, then someone else from 1976, then someone else from 1986, and then 1996.

Another example of how our universe is a multiverse... we have history (tragedies in particular) that repeat themselves; something like that could never happen in a strictly singular universe because there would no supporting articulation of a time-sequenced pattern of supportable hypotheses.

[Stephen Cranney · Rating 4 out of 5]

Nonspecialists like me can get a surprising amount from this book from reading in between the lines. Addresses "whether there be one [universe] or many," a pretty fundamental question that I'm surprised doesn't get as much popular attention as the latest transitory details about the presidential race.