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on 19 March 2011
Brian Green's fascinating book "The Hidden Reality: Parallel Universes and the Deep laws of the Cosmos" is about a growing body of work that is steadily converging around a proposal that our universe is actually one of many universes. He admits that the subject of parallel universes is highly speculative. No experimentation or observation has been established. The point of the book is not to convince us. Its intention is to lay out the intellectual steps and the chain of theoretical insights that led physicists from a range of perspectives to consider the possibility that ours is one of many universes.
He says some people recoil at the notion of parallel worlds. They feel it marginalizes our place and importance in the cosmos. Green's take is different. What matters is whether there exists exciting realms that challenge convention by suggesting what we thought to be the universe is only one component of a far grander mostly hidden reality. The journey so far takes us through nine variations of the multiverse theme - the Quilted, Inflationary, Brane, Cyclic, Landscape, Quantum, Simulated and Ultimate. Each envisions our universe as part of an unexpectedly larger whole, but the complexion of the whole and the nature of the member universes differ sharply. Some are separated by enormous stretches of space and time, other hover millimeters away, in others the very notion of their location proves parochial, devoid of meaning.
Over the course of five centuries we've had to give up our belief in the earth's centrality among our cosmic neighbors, the sun's centrality in the galaxy, the Milky Way's centrality among the galaxies, and even the centrality of protons, neurons and electron in the cosmic recipe.
Greene says, "It's at once humbling and stirring to imagine just how expansive reality may be. If we're part of a multiverse, at best we can learn about our universe, our corner of the cosmos...I don't know how it will turn out. But it's only through fearless engagement that we can learn our own limits."
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on 12 January 2013
Following up his two previous bestsellers, The Elegant Universe and The Fabric of the Cosmos, Columbia University Professor of Physics and Mathematics Brian Greene has carried on in his attempt to enlighten the lay reader to leading edge developments in scientific research into the deepest mysteries of both the micro-world and the macro-world of not only our own universe, but other universes that may exist beyond our current ability to contact them.

Including 30 pages of notes, mostly for the more technically inclined, an extensive index, and using metaphor, analogy, historical anecdotes, and a touch of humour, Professor Greene looks at the latest theoretical thinking and experimental analyses to give, as he says in the Preface, "...a broadly accessible account of some of the strangest and, should they prove correct, most revealing insights of modern physics. Many of the concepts require the reader to abandon comfortable modes of thought and to embrace unanticipated realms of reality."

What spurred Greene to give us an up-to-date account of developments in fundamental theoretical physics is that they have led investigators to the serious consideration of different types of parallel universes. In the book, he identifies 9 varieties of what are called "multiverses." And, what is so amazing to Greene and to his colleagues around the world is that "...all of the parallel-universe proposals that we will take seriously (in the book) emerge unbidden from the mathematics of theories developed to explain conventional data and observation."

Proceeding like a class in the conceptual, non-technical overview of contemporary physics, displaying his knack for making difficult concepts easy to understand by relating them to common, everyday examples from life, and ascribing nomenclature generally used in the field of cosmology, Dr. Greene first examines what is known as the Quilted Multiverse. He begins the discussion with a review of the Big Bang and Einsteinian relativity to illustrate "...that basic physical principles establish that if the cosmos is infinitely large, it is home to infinitely many parallel worlds - some identical to ours, some differing from ours, many bearing no resemblance to our world at all."

Because astronomers have calculated that we can only see out from earth about 41 billion light-years (called the cosmic horizon - an enormous distance, but certainly less than infinite), if the universe itself is infinite, there must be an infinite amount of other regions of space that have their own cosmic horizons. If those regions are sufficiently distant from each other, such an array would look like a patchwork quilt of an infinite number of finite regions that are individual universes themselves. Such a scenario is called a Patchwork or Quilted Multiverse. In such a multiverse, there would be endless doppelgangers - exact, repetitive reproductions of everything we experience, even ourselves.

Greene's second type of multiverse is called the Inflationary Multiverse. This one is based on the continual expansion of our universe that would eternally produce bubble universes, and only one of those would be the one we see. We can think of the bubble universes in the Inflationary Multiverse as the holes in an ever-expanding Swiss cheese cosmos.

Professor Greene's third and fourth types of multiverses derive from String theory and from the braneworlds of M-theory. In Chapter 4, he reiterates from his previous books a clear explanation of various aspects of quantum mechanics resulting in String theory, extra spatial dimensions, singularities, and black holes that lead us into Chapter 5's discussion of the Brane Multiverse and the Cyclic Multiverse. The former consists of three-dimensional branes (don't worry - Greene explains what branes are) that float in higher dimensions with other branes, and the latter derives from the collisions of those braneworlds that result in new universes with their own big bangs.

We are next introduced to something called the Landscape Multiverse. It derives from a combination of the Inflationary Multiverse and String theory.

In 1998, two separate teams of astronomers measured a positive but tiny number for Einstein's cosmological constant - a value that gives us the amount of dark, invisible energy thought to be existing uniformly throughout space. Dark energy governs the repulsive gravitational force that drives our universe's inflation. Contrary to what we would expect - that after the Big Bang the inflation of the universe would gradually slow down - the measurements indicated that for approximately the past half of our universe's life its rate of expansion has been accelerating.

String theory tells us that each of the ever-increasing number of bubble universes in an Inflationary Multiverse contains a different configuration of extra dimensions "...providing a cosmological framework that realises all possibilities." It also tells us that different values of the cosmological constant in each bubble universe give rise to "...bubbles inside of bubbles inside of bubbles..." When combined with accelerating expansion, this bubble tunnelling process provides an entire "landscape" of different universes. Hence, the totality is called a Landscape Multiverse.

50-page long, Chapter 8 describes what's called the Quantum Multiverse - a multiverse that emerges directly from quantum mechanics. Greene reminds us of the double-slit experiment and its consequential interference pattern in order to guide us through his explanations of a particle's probability wave and Niels Bohr's Copenhagen Interpretation which dictate that the act of measurement/observation results in the collapse of the wave function locating only one position for a given particle - one definite, observed reality outcome.

Professor Greene then takes us to the realm of the Holographic Multiverse where reality takes place on a universe's distant boundary surface and projects its information into the 3D world we know and experience as a kind of holographic movie. We can think of this as we would think of the information in an architect's blueprints being translated into the actual physical realisation of a building. In other words, the boundary surface of a universe can be thought of as a physically equivalent parallel universe.

Greene adds, "That familiar reality may be mirrored, or perhaps even produced, by phenomena taking place on a faraway, lower-dimensional surface ranks among the most unexpected developments in all of theoretical physics.... Looking to the future, I suspect that the holographic principle will be a beacon for physicists well into the twenty-first century."

The 8th and 9th multiverses identified in the book involve both actual and computer simulations. The 8th variety is called a Simulated Multiverse. Here, Greene takes a bold step in contemplating universe creation by future humans in the possession of very advanced technologies. There are two types of these we can think of: (1) usual, physical universes, and (2) virtual, computer-generated universes. The first involves artificially producing a white hole that spews out matter. The second is akin to the conceptual presentation in movies like The Matrix, The Thirteenth Floor, and Vanilla Sky.

The 9th and final multiverse discussed is what Professor Greene calls the Ultimate Multiverse. It is his own rationalisation for the existence of a multiverse, independent of being a by-product of quantum mechanics, inflationary cosmology, String theory, or any other such applications that led indirectly to the previous 8 types of multiverses. He surmises, "Maybe math is more than just a description of reality. Maybe math is reality." Perhaps, "Different collections of mathematical equations are different universes. The Ultimate Multiverse is thus the by-product of this perspective on mathematics." (M.I.T.'s Max Tegmark calls this the Mathematical Universe Hypothesis.)

Greene further posits, "Mathematical existence is synonymous with physical existence. And since this would be true for any and all math, this provides another road leading us to the Ultimate Multiverse." It's another way of saying that every possible universe we can imagine, and therefore describe with a mathematical equation, is, somewhere and at some time, a real universe.

Greene ends with questions like, "Can scientific theories that invoke a multiverse be tested?" And, "Should we believe mathematics?" In fact, he admits that math is central to all he discusses. The multiverse theories examined in his book "rely on a belief that mathematics is tightly stitched into the fabric of reality."

He adds in conclusion, "It's only through the rational pursuit of theories, even those that whisk us into strange and unfamiliar domains, that we stand a chance of revealing the expanse of reality."

- This review first appeared in New Dawn magazine issue #132
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"When we hand over the steering wheel to the mathematical underpinnings of the major proposed physical laws, we're driven time and again to some version of parallel worlds." - from THE HIDDEN REALITY

When I entered college and foolishly took over the wheel of the vessel "Engineering Major" that would presumably steer me towards my life's profession and gainful employment, I soon ran hard aground on the reef of Differential Calculus. It wasn't until I abandoned the wreck and transferred to the good ship "Life Sciences Major" that I safely arrived at where I am today. I've never gotten over that perilous time on the rocks. So, it was with some trepidation that I picked up THE HIDDEN REALITY by physicist Brian Greene. As an occasional buff of sci-fi lit, the concept of parallel worlds has always been of casual interest, but perhaps, with Greene's book, I was setting sail into dodgy waters once again.

Over the course of his discourse, the author discusses nine parallel universe, or "multiverse", concepts derived from the mathematics (as opposed to direct observations) of the Relativity, Quantum and String Theories: Quilted, Inflationary, Brane, Cyclic, Landscape, Quantum, Holographic, Simulated, and Ultimate. I'm not even going to attempt a further summary of the material as it would only invite ridicule and cause my subsequent humiliation.

The surprising fact is that I managed to make it through to the end, albeit clinging desperately by my fingernails to the edge of an event horizon such that I didn't fall screaming into the Black Hole of Total Bewilderment. This ultimate survival I attribute solely to Greene's skill at conveying the concepts without resorting to descriptive (to some) mathematical formulae. (Ok, ok, he threw out an E = mc2 equation once or twice, but anything heavier he relegated to the Notes at the end for interested numbers geeks. Suffice it to say, I didn't even glance at that section.) Rather, he illustrated key points with drawings and examples that can likely be appreciated by math-challenged readers such as me. Perhaps this is what makes him a best-selling author.

Now that I've finished THE HIDDEN REALITY, to say that I've a comprehensive grasp of the topic would be a mind-boggling overstatement. Were I to take a test on the volume's contents, I might manage a C-, and that's if it was multiple choice format and not essay. I consider this passing grade, rather than an F, to be a solid accomplishment attributable mostly to Greene's teaching skills. And though I've not read any other expert on the subject to whom I can make comparison, I suspect he's a much better teacher than most. Therefore, five stars for the didactic quality of his book. Don't look for any cheeky humor, though; Greene is no Bill Bryson of A Short History Of Nearly Everything.

Now, if I go outside and gaze at the night sky perhaps visible through the Greater Los Angeles light reflected off the haze and/or smoke, I'll most certainly think to myself, "Wow, could there be more than one those?" One must always be open to a sense of wonderment.

And, in case you're curious, a "flop singularity" is a spherical portion of space compressed to an infinitesimal size.
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on 15 May 2013
The strength of this fine book lies in the meticulous manner in which the author systematically builds the evidence necessary to convince even the most sceptical reader to at least think seriously about the concept of parallel universes. Just as Copernicus overturned the anthropic solar-centric universe model, Greene draws upon the mathematics of the most recent developments in physics, all of which support the existence of a multiverse of which our own is far from unique.

In citing: quantum mechanics, string theory and M theory the reader is drawn ever closer to the probable conclusion that our universe is merely one of many. In so doing Greene brilliantly raises questions about the empirical basis of science and proposes a paradigm shift from the classical physics approach of using equations describing physical laws, knowledge of the constants of nature and initial conditions to predict future outcomes with certainty.

Perhaps the most compelling argument for parallel universes, besides the fact almost all the most recently developed theories support it, is the manner in which it can potentially reconcile that most thorny issue of contemporary physics- how to reconcile the inherent weakness of gravity and its relationship with the quantum world. The extra dimensions implicit in M theory and the possibilities of string theory offer an exciting future solution to the gravity problem which has so far stood in the way of the holy grail of a theory of everything. Indeed so powerful are the arguments proffered by Greene here, the multiverse hypothesis is set to make the pursuit of such a theory obsolete. If ours is just one of many universes, the need to understand its constants becomes less significant. In a multiverse all possible universes exist with all possible ranges of cosmological constant, Higgs field strengths and atomic particle masses.

Greene uses metaphor and illustrations to great effect and is forensic in the piecing together of evidence to support his theories. For example he convincingly reconciles quantum wave theory with string theory in support of the holographic multiverse arguably the most perplexing of all the multiverse hypotheses.

Memorable discussions about simulated universes and whether we are currently part of such a reality also feature- enough to entertain P.K.Dick officianados. Greene latterly also reflects upon the consequences of multiverse theories for science as an empirical investigative discipline based on observations. He also cogently explores the power of mathematics as the basis of reality and its role in multiverse theory.
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on 17 April 2012
If you ever wonder what possessed the medieval world to defend and embrace the Ptolemaic view of the cosmos against all comers until the time of Copernicus and for some time thereafter, then this book should provide many people with that same level of discomfort that the defenders of Ptolemy must have felt when faced with the idea of a heliocentric cosmos. It is relatively easy to be wise after the event and scorn the ignorance and stubborness of Ptolemy's guard; even Einstein found the idea of an expanding universe (which is what his original equations told him was happening) to be unacceptable; at least until Hubble provided him with the proof. In a similar vein, Brian Greene's The Hidden Reality takes one on a mind-expanding journey through contemporary versions of Parallel Universes held within the community of astrophysicists and mathematicians who spend their time delving into such matters. At first blush, one might be foregiven for thinking that such concepts are to be taken no more seriously than the world of Alice in Wonderland; at least in terms of their representing our 'Hidden Reality.' However, Greene leads us through each proposal in a clear and concise manner to reveal such concepts as:
The Quilted Multiverse
The Inflationary Multiverse
The Brane Multiverse
The Cyclic Multiverse
The Landscape Multiverse
The Quantum Multiverse
The Holographic Multiverse
The Simulated Multiverse
The Ultimate Multiverse
Along the way, ideas from quantum mechanics and string theory are addressed, along with consideration in the final chapter to the question of the Limits to scientific enquiry about these concepts; most of which might prove impossible to ever actually 'test' in a scientific manner.
This book is not an easy read, although given the nature of the concepts under discussion this is hardly surprising. However, Greene manages to provide a relatively clear explanation of the concepts, without resorting to the need to drown the reader in complex equations and mathematics. At the same time, anyone with a reasonable grasp of scientific methodology and some background in physics and mathematics will probably find this a fascintating read. To really get to grips with the subject matter would involve a more careful rereading and study of the contents, but for an overview of the ideas an initial diligent read will suffice.
Certainly, I should recommend this book to anyone interested in finding out about current thinking and ideas around this subject. I totally disagree that this book could have been reduced to 20 pages and that the remaining 95% is waffle as suggested by one other reviewer. This is not light reading, but nor is it waffle. Indeed, it is impressive precisely because it keeps focused throughout and ties the various ideas together in a coherent and meaningful manner. Above all, even if you regularly read books about philosopy of mind, metaphysics, epistemology, science fiction relating to parallel universes, newtonian and quantum mechanics the ideas in this book will certainly provide some stimulating and entertaining food for thought.
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on 7 March 2013
I'm not an academic, just a regular Joe interested in reading about ideas being considered by those who are, and enjoyed the book very much.
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on 12 June 2011
The quote on the back of the book lauds Greene as "The new Hawking, only better", aside from his being American this is fairly accurate, if you consider "better" to mean `a more accessible and enjoyable read'. Greene brings cutting-edge physics and cosmology to life and his previous two efforts have been highly enjoyable.

Perhaps what I took pleasure from most about Elegant and Cosmos was the intertwining explanations of established physics through to the more cutting-edge (and dare I say 'speculative') areas of the field: primarily String and M-Theory. As I've worked my way through explanations of the Uncertainty Principle, Super-Symmetry, and Relativity I've really felt a sense of achievement, learning of something considered fairly immutable - at least in my lifetime. The Hidden Reality does not follow this pattern, nods are given to The Double Slit Experiment and some other fundamental areas and questions (counting infinity anyone?) that will always remain as they are; but in percentage terms the mass majority of the book remains very hypothetical - it postulates nine distinct theories of the multiverse. I did enjoy the explanation of the Many Worlds theory which helped to explain a phrase I'd heard in pop culture and other literature - and for many of us is the best explanation we will ever receive on this.

Rightly or wrongly I cannot bring myself to give 5 stars to a book that could ultimately prove (or more likely we'll never truly know) to be totally incorrect. The content, at times, requires some very abstract thinking and towards the end it descends into drunken conversation you had with a friend after the first time you both watched The Matrix - "what if we're all in a computer man?". I do appreciate that the reader may not want further `reference' material and in this respect this really does feel like a book that brings the layman right up to the forefront of current cosmological and scientific endeavour. However, it offers no concrete assertions and each multiverse option appears equally as likely as the next.

In short, I think my problem with this book is that it's so cutting edge that it could all be wrong, none of the nine multiverses could be right, hell, we may not even live in a multiverse. This sounds fickle on my behalf, it is fickle, "so what if it's not right, you read fiction books and they aren't real, you watch Sci-Fi and that's not life as we know it". Exactly. This is where the book redeems itself. No matter how you read it, one of things I enjoy most about Greene's books is they are so easy to read that I don't think you really need to understand everything fully to get sucked into the grandeur. You can almost read it as a work of Sci-Fi, fiction, or general reference. No matter what level of understanding you possess you can still romanticise the contents and have your mind blown by the concepts involved. Undeniably there are some areas that you will understand, you will follow, and you will subsequently think about for days. Conversely, some areas of this book are more challenging than others; brane multiverses for example lost me for the most part, but comprehending the principle of inflationary universes is a lot easier and more rewarding.

Greene clearly signposts his prose (including the more complex areas), if you've read his other two books the same analogies and explanations are there, explaining things more clearly than any other author covering this material the guy could probably convince me to hand my wallet over to him with a series of logical and well founded arguments. A particular favourite of mine was the `Cartman' analogy from South Park - although I'm not quite sure what percentage of readers would have got that one (I'd love to know).

This is fascinating and intriguing stuff to anyone with even a passing interest in the subject matter. I will look forward to his next offering: perhaps something a little more tangible Brian.
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on 2 April 2011
Brian Greene must have enjoyed Max Tegmark's May 2003 Scientific American article on parallel universes, since he recycled the concept for the third book in his physics trilogy. After covering string theory in The Elegant Universe: Superstrings, Hidden Dimensions and the Quest for the Ultimate Theory and inflationary cosmology in The Fabric of the Cosmos: Space, Time and the Texture of Reality (Penguin Press Science), Greene covers alternative, possible, and parallel worlds and universes in this new book. He does so with a light touch and an easy manner, honed by years now of delivering such highly theoretical and speculative content to popular audiences. Whether he succeeds in whetting your appetite is another matter. Personally, I loved his first book, really liked his second one, and felt a slight ennui over the third one.

The fact is that the science of all these possible worlds is hardly science at all in the traditional sense, and there's a lot of hand-waving and vague philosophizing in Greene's account of it all. Like Steven Pinker, who wrote several big popular books in quick succession and found his content thinning out accordingly, Greene has found that the physics on show in his new parade is less meaty than most physics buffs will hunger for. Indeed, when string theorists admit that they need five hundred zeroes just to write out the number of possible universes on their recent estimations and when Greene admits that we might just as well be living inside a giant simulation in an alien supercomputer, à la Matrix, we are right to sigh and lose heart for the new physics.

Physics has had a great run in the last hundred years. From the Newtonian world of colliding particles in absolute space and time, perfused with electromagnetic waves, we have moved on to the weird world that Greene has presented as well as any physicist since Heinz Pagels, who published a fine trilogy on quantum physics, big bang cosmology, and the emerging science of complexity a quarter of a century ago. We need these popular prophets for physics even in times like these when the theory has navigated into a fog bank. Perhaps a bright kid somewhere will be inspired by Greene's books to find a way out of the fog.

Note added in proof: For a physics buff, the notes in Greene's new book are the best part. It's a pity that most readers, me included, will probably never read them all. Greene should have the courage of his professorial salary and put the good stuff in the main book where it belongs, and forget about trying to reach the top of the bestseller lists with a book that without the notes is too bland.
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on 28 March 2012
I've read his two previous books and if anyone can explain String theory to a numpty lorry driver this man has taught me a heck of a lot.I really enjoyed it and I've read quite a few popular quantum theory books now including Feynman, Gribbin, lovely Lisa Randall and even had a bash with L.Susskind. This book (and his others) are definitly worth the time, I would soon get bored and dump it if it was "95 per cent waffle"
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on 26 April 2012
Personally, I found this to be a clear and carefully presented explanation of what actually leads researchers to these apparently bizarre 'universes', and the main message seems to be to trust good results without worrying TOO much about the implications of, eg 'many-worlds', models. After all, scientists have been in this boat for decades over the peculiar implications of quantum physics - some ponder the 'real' meaning of it all, while others accept it as giving the most accurate results and predictions to date, and 'get on with the job'. Maybe one day we'll find out!

The care Brian Greene takes in explaining the various models may appear a bit tedious for those already well in the know, but they are necessary, and very helpful for those enquiring into unfamiliar topics. I think he does a very good job of encouraging his reader not to give up with a 'what complete rubbish' conclusion, but to be prepared to take the ideas for their own merit. He makes it fairly clear what is more or less main-stream or outlandish, and he gives the option to skip ahead of some detailed passages. It is also interesting to read his current assessment (still reasonably positive, but none the less measured) of string theory which is/was dear to his heart. He does make a plea to trust that the maths may still represent reality even though it is very reluctant to become an experimental testable theory - then he throws in a very interesting section or two about possible ways coming up of verifying or rebutting it, after all.

The only thing that slightly worries me is the sense of deja-vu I got from a couple of the 'state of the theory' tables and the many-worlds diagrams of the probabilities of where a particle may be found in Manhatton (was it?). They felt quite familiar yet the book is apparently a new release (copyright 2011), so I can't have read it already and forgotten (that has happened!) yet I couldn't find them in his other two main books I have read.

Quite stimulating, I thought.
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