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In 1998, Stephen Hawking laid 50-50 odds that the holy grail of physics, the elusive "theory of everything," was less than 20 years away.
Around the same time, Hawking's renowned peer, collaborator and sometime-disputant, Roger Penrose of Oxford University, set out to write a book detailing just how distant the odds actually are of unifying all the laws of physics.
"We are nowhere close to an accurate, purely physical theory of everything," Penrose told Nature earlier this year.
Indeed, Penrose's newly published 1,099-page treatise -- The Road to Reality: A Complete Guide to the Laws of the Universe -- expends little ink ruminating over what is not known. Rather, The Road to Reality is as rigorous and exhaustive a map to the "theory of nearly everything" as a reader could hope to find today.
Penrose makes a unique tour guide, overhauling components of big-bang cosmology and quantum mechanics as some tinkerers might take out and reinstall their car's transmission. And Penrose's tendency to pepper the discussion with mathematical equations and terminology (he spends nearly 400 pages on calculus, number theory and advanced geometry before decamping into the physical universe) will undoubtedly limit the book's readership to those not easily intimidated by section titles such as "frequency splitting on the Riemann sphere" or "Hamiltonian dynamics and symplectic geometry."
Yet, according to professor Seth Lloyd of MIT, those willing to invest the energy to work through this mathematical Finnegans Wake will be rewarded for their efforts.
The Road to Reality, Lloyd says, "shows (Penrose's) brilliant and unique grasp of mathematics as it applies to the physical world. That is evidenced in the first part. The second part of the book shows his courageousness in going on to propose fundamental physical effects even in the absence of an explicit theory, which he thinks intuitively to be true. So he's very bold as well as original and insightful."
Those fundamental physical effects that Penrose proposes in Road, some of which were first covered in his 1989 best-selling book, The Emperor's New Mind: Concerning Computers, Minds and the Laws of Physics, are as controversial as they are bold.
For instance, despite the stampede of physicists today seeking to unify all physical theories under the aegis of string theory, Penrose thinks his colleagues are on a wild goose chase.
In 2002, Penrose spoke at Stephen Hawking's 60th birthday celebration. Penrose argued that the underlying assumption of string theory -- that space-time consists of anywhere from 10 to 26 dimensions -- is simply wrongheaded and unmotivated by either intuition or evidence. (Penrose devotes much of the last four chapters of his book to this same argument and to an alternative model he sets up in string theory's absence, using a mathematical formalism Penrose invented called "twistors.")
One colleague, Penrose said, responded during the conference's lunch break with the observation, "You're completely right, of course ... but totally misguided."
Such has been the nature of the brickbats Penrose has faced. His genius is unquestioned. No individual save Albert Einstein has contributed more to relativity theory. But Penrose's sometimes-iconoclastic notions can cause colleagues to close their eyes and ears.
At the top of the list of his unpopular departures from convention is Penrose's theory of quantum mechanical "state reduction." Standard quantum theory holds that submicroscopic particles exist in a nearly continual state of blur: An electron is not so much here or there but rather a little bit here and a little bit there. The longer an electron, or an ensemble of particles, is allowed to evolve in isolation from the rest of the universe, the more distended and blurry the quantum state of the particle(s) become. Only the act of an observation -- or, alternately, the noisy and jostling environment surrounding it -- forces the quantum state into a precise location and energy level.
But what exactly constitutes an "observation"? Is it just an arbitrary threshold separating the classical macroscopic world from the submicroscopic quantum regime? Does a conscious mind actually need to observe a system physically to cause its quantum state to collapse?
In part because of the precise agreement between quantum theory's predictions and experimental evidence, many physicists are content to leave well enough alone: Quantum mechanics works -- it's beautiful in its own way, and our expectations, not the theory's inner workings, are what need to be modified.
Penrose, however, has proposed that the missing link between macroscopic and submicroscopic is gravity. Aggregations of particles exist in their blurry quantum mechanical states until so many particles are both here and there that space-time itself -- which is warped by the presence of matter and therefore is warped in multiple simultaneous ways by matter that is both here and there -- ultimately can no longer support so much indeterminacy. Heisenberg's uncertainty principle wins every time.
The problem with this theory -- which Penrose first proposed in The Emperor's New Mind and revisits in Chapter 30 of The Road to Reality -- is that observational evidence is still wanting. Penrose proposes an experiment that would put his model of quantum state reduction to the test. A team led by Dirk Bouwmeester of the University of California at Santa Barbara is now working on Penrose's proposed experiment. However, the results are still years away.
"Penrose's place in history is secure," Lloyd said. "But I would add the caveat, in this case, that I think he's bold and wrong."
One of Penrose's collaborators, Stuart Hameroff of the University of Arizona, has applied Penrose's unconventional quantum models to develop a theory of the conscious mind rooted in hypothesized quantum mechanical forces inside the neuron.
"Roger is not just spinning yarn," Hameroff said. "He's doing this work from a knowledge base that is unsurpassed. Then he uses his intuition and imagination and thinks big.... My first thought was, 'This is just crazy.' But looking back, it's just obvious. I see that it couldn't be any other way."
