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The Hidden Reality by Brian Greene

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The Hidden Reality by Brian Greene

The cover of Brian Greene's book The Hidden Reality

Alfred A. Knopf/Random House

The Bottom Line

This is one of the clearest books available about the multiverse, laying out each type of parallel universe in a way that's well organized. There is a lot of background physics needed to make sense of parallel universes, but Greene is able to delve into these topics without losing the nuance of why one type of parallel reality is different from another.
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  • Clear descriptions of different types of parallel universes.
  • Fundamental physics concepts are explained in accessible language.


  • Has to lay a lot of complex groundwork before getting to each type of parallel universe.


  • Originally published January 2011 by Alfed A. Knopf Books/Random House.
  • 384 pages, 11 chapters + Endnotes + Suggestions for Further Reading
  • Available in paperback November 2011.
  • This review is based on a Kindle edition of the book, read on the iPad Kindle application, in spring/summer of 2011.
  • Full title: The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos

Guide Review - The Hidden Reality by Brian Greene

Many physicists believe that our "universe" is actually a vast multiverse. In this book, Brian Greene tackles the reasoning behind these parallel universes, which spring up in many different ways in physics. While other books have tackled of these topics, the distinctions tend to get lost in the overall spectacle of the underlying science.

Greene's approach doesn't suffer from this (too much), with a clear methodology of breaking down the different ways parallel universes show up in physics:

  • Quilted Multiverse - Space is infinite, therefore somewhere there are regions of space that will exactly mimic our own region of space. There is another world "out there" somewhere in which everything is unfolding exactly as it unfolds on Earth.
  • Inflationary Multiverse - Inflationary theory in cosmology predicts an expansive universe filled with "bubble universes," of which our universe is just one.
  • Brane Multiverse - String theory leaves open the possibility that our universe is on just one 3-dimensional brane, while other branes of other number of dimensions could have whole other universes on them.
  • Cyclic Multiverse - One possible result from string theory is that branes could collide with each other, resulting in universe-spawning big bangs that not only created our universe, but possibly other ones.
  • Landscape Multiverse - String theory leaves open a lot of different fundamental properties of the universe which, combined with the inflationary multiverse, means there could be many bubble universes out there which have fundamentally different physical laws than the universe we inhabit.
  • Quantum Multiverse - This is essentially the Many Worlds Intepretation (MWI) of quantum mechanics: anything that can happen does ... in some universe.
  • Holographic Multiverse - According to the holographic principle, there is a physically-equivalent parallel universe that would exist on a distant bounding surface (the edge of the universe), in which everything about our universe is precisely mirrored.
  • Simulated Multiverse - Technology will possibly advance to the point where computers could simulate each and every detail of the universe, thus creating a simulated multiverse whose reality is nearly as complex as our own.
  • Ultimate Multiverse - In the most extreme version of looking at parallel universes, every single theory which could possibly exist would have to exist in some form somewhere.

That's a lot to take in, and there's a lot of background physics needed to grasp it all. When the reader does begin to lose track of exactly what type of parallel universe Greene is talking about, he re-iterates things clearly enough that back on track. The concepts themselves are kind of slippery, so it's imperfect in places, but I think a reader would get through the book with a clear understanding of the basic arguments in favor of each type of parallel universe.

Note: In the Kindle app, the tables in this book are kind of clunky. I assume the print edition has better formatting.

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