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Universe or Multiverse? Hardcover – 21 Jun 2007

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Product details

  • Hardcover: 544 pages
  • Publisher: Cambridge University Press; 1 edition (21 Jun. 2007)
  • Language: English
  • ISBN-10: 0521848415
  • ISBN-13: 978-0521848411
  • Product Dimensions: 17.4 x 2.9 x 24.7 cm
  • Average Customer Review: 5.0 out of 5 stars  See all reviews (1 customer review)
  • Amazon Bestsellers Rank: 2,409,417 in Books (See Top 100 in Books)
  • See Complete Table of Contents

Product Description


'… probably the most comprehensive tome on the subject around at the moment and, like the others, I imagine it will have a long shelf-life … this well-constructed collection of writings is the best we can possibly hope for in the era of this new great debate.' Pedro Ferreira, Physics World

'This book really does lie at the frontier of cosmology, philosophy and possibly even theology. It is essential reading for anyone who wants to consider these ideas in depth.' Martin Redfern, Science, People and Politics

'Reading this book is a complex and rich experience. I find it useful as recommended reading as an introduction for undergraduate students.' Luca Valenziano, CERN Courier

'… an essential acquisition for those requiring an up to date account of the various physical proposals and their problems.' Science and Christian Belief

Book Description

Is our universe unique or just one of many? Eminent physicists explain how recent scientific developments lead to the 'multiverse' proposal. Suitable for professional physicists and scientifically-minded lay people, the articles reflect the full diversity of views on this highly speculative and untestable theory.

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Most Helpful Customer Reviews

Format: Hardcover Verified Purchase
Excellent compilation of papers on cosmology, with an emphasis on the Anthropic Principle. After all the opinions are aired, I'm left doubting whether the multiverse is the right answer. Still, the relationship between cosmology and string theory is fascinating --- even though it may always remain debatable.
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Most Helpful Customer Reviews on (beta) 5 reviews
22 of 24 people found the following review helpful
An excellent book on a very interesting topic 1 Nov. 2007
By Jill Malter - Published on
Format: Hardcover
This is a wonderful and highly readable book about the question of whether or not our universe is part of a multiverse. The more than two dozen contributors all do a fine job.

We see plenty about the Anthropic Principle and about the Copernican Principle (also known as the Principle of Mediocrity). The Anthropic Principle merely points out that given that we exist in this universe, our universe must be habitable. But this argument can be extended. Steven Weinberg shows how he was able to use the Principle of Mediocrity and the Anthropic Principle to put some interesting probable bounds on a cosmological constant. A universe with such a constant being less than 0.6 would be relatively unlikely for humans to be in, so his guess was that this constant was over 0.6. At the time, most guesses for the cosmological constant were 0.0, but soon after this, studies of supernovae showed that this constant is around 0.7. Several of the contributors discuss this argument. It's an unusual type of argument, and Weinberg makes an analogy to Einstein's use of a symmetry principle argument to come up with the Special Theory of Relativity (nowadays, symmetry principle arguments are commonplace, but Einstein's, in 1905, was the first major successful one).

Several contributors also discuss Hoyle's use of the Anthropic Principle to claim that there must be an excited state of Carbon-12 with the right energy to produce carbon in stars. This excited state is no big surprise, given the general properties of alpha-particle couplings, so Weinberg and others are unimpressed. However, I side with Hoyle here.

Weinberg explains that we now have a vast number of possible values of physical parameters provided by the "string landscape." By the Anthropic Principle, we can guess that we must be in a universe that permits us to exist. The reader is left to guess that therefore, there are probably many other universes where we can not and do not exist.

Weinberg also points out that the Anthropic Principle shows how the universe can appear to be fine-tuned to allow our existence without requiring some sort of Intelligent Creator or Creators.

Frank Wilcek shows how in the case of inflationary cosmology, we see that universal laws need not be multiversal.

Stephen Hawking says that the reason we live in four dimensions (three of which are spatial) is not due to any anthropic principle (maybe there could be intelligent life in eleven dimensions) but simply because we can see that we live in four dimensions. He does, however, say that it may be significant that we live in the interior of anthropically allowed regions of omega-space. By not being at the edge of such a region, we wind up in a universe with many galaxies, not just one galaxy. That implies that variations in omega are fairly flat. One galaxy ought to suffice for life to exist, and since there are many, Hawking does not conclude that we need many galaxies, but that there are in fact many sites which contain life. Max Tegmark also indicates that there may be plenty of life in the Galaxy, as well as as many as 10 to the 20 "habitable planets in our Hubble volume alone." Our Hubble volume is, of course, what many of us would call the Universe.

Craig Hogan discusses the difference between the down quark mass and the up quark mass, in relation to the electron mass. Well, that's obviously critical for life: it causes the neutrons to be a little heavier than the protons. If we change that mass difference, we can quickly get into regimes in which chemistry does not exist.

Let me give an example of the Principle of Mediocrity, which says that in the absence of evidence to the contrary, we ought not treat ourselves (or our position in the universe) as special. Suppose there is a big lottery with a hundred winners. The winners are congratulated, but they are not told in what order they were selected. They are then told that they will double their winnings if they guess correctly whether they were in the first 25 or last 75 to be chosen. Invoking the Principle of Mediocrity, they all guess that they were in the final 75. At the awards ceremony the winners are presented in the order they were chosen. We note that the first few all guessed wrong! Does that show a problem with the Principle of Mediocrity? Of course not, and we see that when the final 75 all guess right.

Incredibly, in his chapter, Lee Smolin steps out of character and makes a big logical error. He gives the case in which the population of the world increases exponentially. Many people realize that there may be a population crash, and using the Principle of Mediocrity, they guess that they have a relatively high chance to be in the final few generations before that crash. Smolin boasts that someone 1000 years ago would have been incorrect to make such an argument. But he's totally wrong here: he's ignoring the fact that in his example, the majority of those who make this argument will be right. That means that everyone was right to make that argument, even the minority who get the wrong answer thereby.

I think that the Principle of Mediocrity is indeed a very good default that can spare us from making wild arbitrary politically correct guesses, but it is still just a default.

I truly enjoyed this book, and I highly recommend it.
4 of 4 people found the following review helpful
Superb multiverse compendium by the experts in the field 21 Oct. 2011
By Robert Adler - Published on
Format: Paperback Verified Purchase
Popular science outlets have been covering the possibility that our universe is just one among a potentially infinite number of universes--the multiverse--for years now, but in bits and pieces. If you are seriously interested in the science behind the various multiverse concepts, read this book. It's a compendium of 28 invited articles on every aspect of the multiverse field by the theoreticians and researchers who invented and are advancing this very active area. I found Bernard Carr's essay on the anthropic principle very helpful, along with Max Tegmark's multiverse hierarchy,Leonard Susskind's discussion of the anthropic landscape of string theory, Lee Smolin's essay on alternatives to the anthropic approach, and John Barrow's "Living in a simulated universe." However, readers will find definitive essays on every aspect of the multiverse, inclouding many that don't get covered in the popular science press.

A caveat, however, don't turn to this book for an easy read. On the whole, these are essays by scientists writing for other scientists or for readers who are, for example, comfortable with equations, technical terminology, and densely reasoned arguments. For a less technical survey of the field, I'd recommend Brian Greene's _The Hidden Reality: Parallel Universes nd the Deep Laws of the Cosmos_.
3 of 4 people found the following review helpful
The state of knowledge as it stands now 15 Feb. 2010
By John Matlock - Published on
Format: Paperback
One answer to the question about us being the only intelligent life in the cosmos is answered by the multiverse theory of multiple universes. This is a subject that has received a lot of thinking and mathematical analysis in recent years. Recent developments in cosmology and particle physics, such as the string landscape picture, have led to some serious thinking that ours is not the only universe.

This book has papers from a number of active and eminent researchers in the field, mainly from cosmologists and particle physicists, but also from such diverse fields as philosophy. The papers cover the complete spectrum from enthusiastic support to outright scepticism. There is very little advanced mathematics in the book when compared with some other texts on the subject.
6 of 9 people found the following review helpful
An excess of speculation 2 Jun. 2013
By Dr. Lee D. Carlson - Published on
Format: Paperback Verified Purchase
When reading the articles in this book, one can easily be astounded at the enormous level of speculation and lack of scientific evidence that is included in them. If the authors insisted on using the fundamental physical theory that many of them had a hand in making, the contents of this articles would be very different, and much more palatable to those readers who insist on a more fundamental approach to current issues in cosmology and the controversies behind the multiverse hypothesis. Most of the articles in this book reflect an avoidance of solving the bound state problem in quantum field theory, which is the fundamental theory governing elementary particle interactions, and as a result, the authors resort to hand-waving arguments and back-of-the-envelope calculations. In addition to that, many of the authors display a discomfort in being confronted with large numbers such as 10^56, and this discomfort causes them it seems to make hypotheses that would not be made by someone who works with such large numbers on a daily basis.

For example, S. Weinberg, in the opening article of the book takes it as unacceptable that the cancellation by quantum fluctuations of the vacuum energy would have to be exact to 56 decimals places. But many who work in fields such as cryptography deal with much larger numbers than 10^56 in everyday practice, and therefore they would probably not be concerned so much with the purported delicacy in this cancellation. Weinberg's objection also reflects his insistence on explaining everything using symmetry arguments, which as the first part of the article is clear evidence of. He does not want to face up to solving the bound state problem (via the Schwinger-Dyson equations or some other approach). This is also manifested in his totally unsubstantiated claim that galaxies and stars would not form if the vacuum energy density was too large. No explicit calculation is done to support this claim in the context of quantum field theory, which is the proper framework in which to discuss the interactions of elementary particles which of course make up stars and galaxies. Showing explicitly that stars and galaxies would not form would be an enormously difficult calculation in quantum field theory, requiring extensive numerical calculation (possibly within the lattice gauge theory framework). Weinberg does not do this, or reference articles that do. Instead readers are given only a rudimentary hand-waiving argument.

The next article by F. Wilczek will be more palatable to the skeptical reader, for in it he discusses the role that symmetry principles have had in determining the values of the fundamental parameters, and argues that they have not been able to. If one is to accept fine-tuning, even though the evidence is weak and the definition of it not really stated explicitly in any of the literature, there is much to find plausible in Wilczek's statement that some parameters could be understood dynamically while others anthropically.

Some other parts of the book that might annoy the skeptical reader who insists on evidence supported by explicit calculations in quantum field theory include:
- The article by M. J. Rees wherein he claims that different values of the "fluctuation parameter" Q may prohibit clusters of galaxies from forming, and that galaxies would form later than they did in our universe. He admits though that some researchers have attempted to derive the value of Q using the detailed physics of an inflationary era. I better idea would be to face up to solving the bound state problem in quantum field theory in order to determine just what is possible for star and galaxy formation, etc.
- The article by B. Carr, wherein he states that "in order for life to exist, there must be carbon". This is true of course, but this does not support any evidence for the anthropic principle. How about explicitly showing how carbon atoms form using basic principles of quantum field theory? This would be a formidable undertaking, one that the author may not be prepared to do.
- The article by R. Kallosh, wherein it is claimed that the probability of the emergence of life would be "appreciably suppressed" for certain values of the cosmological constant. But how is this outlandish claim for the probability to be calculated? Life depends on carbon atoms of course, but it also depends on a complicated process of folding of protein molecules. The computational difficulties behind protein folding are well known, but these difficulties, along with a complete omission of any estimates from quantum field theory of how carbon atoms themselves can form, make this article absolutely worthless from a scientific viewpoint.
- The article by C. J. Hogan, which asserts that "the world would disappear" if there were only a few per cent fractional change in the quark mass difference. A diagram is given that is supposed to justify this assertion, but it does not. Showing that the "world would disappear" using the formalism of quantum field theory would again entail an understanding of how to solve the bound state problem.

There are many other examples in the book of handwaving, unjustified claims but space prohibits a detailed listing. Speculative discussions about fine-tuning and the multiverse abound, with the rhetoric of a type that usually accompanies debates in religion and philosophy. And indeed the silliness of the claims is only exceeded by the last articles in the book which attempt to give a religious "theistic" justification of the universe/multiverse. When reading these articles, one can easily wonder if some of the authors ever even calculated a cross-section or transition amplitude in quantum field theory, let alone have the expertise to approach the bound state problem. Fine-tuning may seem like a constraint on the values of the parameters that "allow life", but the values of these parameters do not seem to "optimize life" in the sense that living organisms face an uphill battle when it comes to sustaining themselves. Indeed, the conditions on Earth itself versus what is found in the rest of the solar system lead to the impression that reality is not conducive in general to the sustainment of living organisms. Not only that, but the authors of those articles that support theistic perspectives never seem to entertain the possibility that the creator of the universe is a temporary, finite being itself. These articles were written before the discussion of "Boltzmann brains" in inflationary scenarios, and a generalization of these "brains" would open up the possibility of an entity that could come into existence, create (a portion of) the universe, and then die off. This is extreme speculation of course, but no different than the other extreme speculations found in this book, and it would also be a kind of twist on the words put on the title of a popular weekly newsmagazine back in the 1960's, namely that God is dead.
8 of 13 people found the following review helpful
A very good book but something lacking 21 Mar. 2009
By T. Schumann - Published on
Format: Hardcover Verified Purchase
This is a book of essays by very prominent and knowledgeable scientists and philosophers who discuss the reason that our universe has the very special characteristics that allow life and conscious observers to exist. Primarily they discuss this in terms of the anthropic principle. Most of the authors assume an infinite variety of universes, mostly without life. Only a tiny fraction of these universes have the characteristics that enable life and observers to exist and of course we can only exist and observe a universe with the very special characteristics that enable us to exist. The book omits another argument to "explain" those special characteristics. According to quantum physics, a system may not have real, definite characteristics, having only a superposition of possibilities, until those characteristics are observed. Extending this to the whole universe, the universe cannot become real unless it is observed. Thus, for self-consistency, it must have the characteristics which enable observers to evolve, thus eliminating the need for an infinity of universes without observers.
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