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Roger Penrose is a highly original andcreative mathematical physicist. Hepioneered the development of global

methods in general relativity, which trans-formed and greatly deepened our under-standing of black holes, revealing them to bedynamic entities rather than dead, frozenashes. Overturning long-accepted dogmas,

he also discovered thepossibility of quasi-periodic tilings, whichhave turned out todescribe actual mate-rials (quasicrystals).

In recent years,Penrose has become asuccessful author ofpopular books on sci-ence. In this too, hisapproach has beenhighly original. TheEmperor’s New Mind

(1) and Shadows of the Mind (2) are long,demanding books that include brilliant anduncompromising exposition of difficult mate-rial. For example, they provide honest, self-contained accounts of universal Turingmachines, Gödel’s theorem, and the founda-tions of quantum mechanics that are models oflucid exposition. But these books also makeconnections and propound scientific thesesthat are, to say the least, controversial. Theyculminate in claims that quantum coherenceand quantum gravity are implicated in normalbrain function and consciousness, claims thathave not won wide acceptance.

The Road to Reality resembles those ear-lier books in its eclectic style, and itincludes consideration of some of the samethemes. But it comes at them from a differ-ent perspective and develops them in quitedifferent directions. Here the emphasis is onphysics, not biology.

The first thing to say about The Road toReality is that it is a big, sprawling book. Asthe text progresses, the level of sophistica-tion expected of the reader ascends frommodest beginnings to truly dizzyingheights. The exposition might be self-contained at some formal level, but in anyrealistic sense it is not. I don’t imagine thatthere are many readers who will first learn

from the book both what a complex numberis and what a holomorphic line bundle ontwistor space is.

Nor need they try. For despite the title,the second thing to say about what’s insidethe book is that Penrose does not presentanything like a well-ordered, sequentialpath leading to the Holy Grail “reality.”Rather, one f inds a series of intellectualtreks, toward the end quite strenuous, with abrilliant and engaging, if not entirely reli-able, guide into some wild frontiers of fun-damental physics and cosmology. The Grailis never espied; too bad. But because read-ers are liberated from the obligation to fol-low a single road, they can feel free to pickand choose from among the treks on offer—and to turn back, without a deep sense ofloss, when the going gets too rough.

Because The Road to Reality is sodiverse and multi-tiered, I find it useful todiscuss the book from three different per-spectives: as a survey for novices, as stimu-lation for sophisticates, and as a scientifictreatise.

I imagine that a bright and ambitiousteenager contemplating a career in mathe-matics or physics would find much to enjoyand to savor in the book. Its first half (runningfor over 500 pages) presents a smorgasbordof essentially mathematical ideas, includingunusual perspectives on complex variables,Fourier analysis, and connections betweenthese that motivate the concept of hyperfunc-tions. The discussions of the conformalgeometry of special relativity and of spinorsare real gems. This part would suit beginnerswell, as a stimulus to their imaginations. Thesecond half of the book enters into essentiallyphysical material. Here, I think failure toground the discussion adequately in empiri-cal facts renders it quite unsuitable for thosenew to the field. They will not obtain from thebook a sound knowledge of the basics of thesubjects under discussion, nor will they be ina position to judge the relative credibility ofconventional ideas and Penrose’s alternatives.It is as if in a trial one were exposed only tothe prosecution’s summation, without thepresentation of physical evidence or the testi-mony of witnesses (much less the defense’sarguments).

Sophisticated physicists will pass overthe book’s first half rapidly, enjoying thegems. In the second half, they will find sev-eral provocative ideas. Specifically, Penroseargues that there must be a genuine physi-

cal process, involving non-unitary evolution, that imple-ments the “collapse of thewave function” in quantumtheory. He speculates that this“R-Process” will emergefrom a quantum theory ofgravity. He also argues force-fully that the standard initialstate assumed in big bangcosmology, which posits ther-mal equilibrium for matterbut near-perfect order in thegravity f ield (i.e., uniform-ity), is highly unlikely—inthe precise sense of havingextremely low entropy rela-tive to the maximum avail-able. He speculates that anintrinsic time asymmetry ofphysical law, perhaps relatedto the R-Process, will explainthis anomaly. He expresses atlength his frustration withstring theory and sketchesloop variable, spin network,and twistor alternatives. Thelast of these I found particu-larly interesting, in its intro-duction of beautiful mathe-matics and a controlled form

The reviewer is in the Department of Physics,Massachusetts Institute of Technology, Cambridge,MA 02139–4307, USA. E-mail: wilczek@mit.edu

P H Y S I C S

Treks of ImaginationFrank Wilczek

The Road to RealityA Complete Guide

to the Lawsof the Universeby Roger Penrose

Jonathan Cape, London,2004. 1122 pp. £30,C$85. ISBN 0-224-04447-8. Knopf, NewYork, 2005. $40. ISBN 0-679-45443-8.

BOOKS et al.

Dante astray in the Dusky Woods. The first of Gustave Doré’sillustrations (1861) of Dante’s Inferno.

11 FEBRUARY 2005 VOL 307 SCIENCE www.sciencemag.orgPublished by AAAS

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of non-locality, but at present twistor ideasappear more as the desire for a physical the-ory than the embodiment of one.

Regarded as a scientif ic treatise, TheRoad to Reality is in many ways problematic.By nominally addressing a substantive dis-cussion of frontier issues in theoreticalphysics and cosmology to a popular audi-ence, an author deprives himself of the disci-pline of having to provide details, to addressconcrete experimental issues, or to pitch thelevel of his argumentation to peers capable ofjudging them critically. Galileo pulled this offbrilliantly, but times were much simpler then!The worst parts of the book are the chapterson high-energy physics and quantum fieldtheory, which in spite of their brevity containseveral serious blunders: The Cabibbo angledoes not govern the mixing of K0 and K

– 0

mesons to make the long- and short-lived Ks.There are not alternative directions of elec-troweak symmetry breaking. And no associ-ated disorder arises at that symmetry-break-ing transition, any more than at the analogoustransition in ordinary superconductors.

To summarize, there’s much to admireand profit from in this remarkable book, butjudged by the highest standards The Roadto Reality is deeply flawed.

References1. R. Penrose, The Emperor’s New Mind: Concerning

Computers, Minds, and the Laws of Physics (OxfordUniv. Press, Oxford, 1989).

2. R. Penrose, Shadows of the Mind: An Approach to theMissing Science of Consciousness (Oxford Univ. Press,Oxford, 1994).

10.1126/science.1106081

A D AY O U T : B I O G R A P H Y

Refuge fromBerlin’s Bustle

John Bohannon

The sailing ship, the distant view, thelonely walks in autumn, the relativesilence, it is paradise.” This is how

Albert Einstein described his summer homejust outside Berlin in the villageof Caputh, where he lived from1929 to 1932. He could not haveknown these would be the lastcarefree years of his life. Whenthe Nazis seized power in 1933,he was visiting the United Statesand he settled there. Soon, help-less, he would witness his wifeElsa’s death from a painful illness and laterthe application of his revolutionary theoriesin the creation of the most destructiveweapons ever known.

Einstein is receiving evengreater attention than usual in thispleasingly symmetric year, 50years after his death and 100 yearsafter the publication of his world-changing trio of publications onthe quantum theory of light,Brownian motion, and special rel-ativity. For those seeking a moreprivate glimpse into his life, a tripto Berlin would be timely. Inpreparation for visitors, theEinstein Forum (an interdiscipli-nary institution formed in 1993 topromote innovative thinking andengage the public) is renovatingthe Caputh summer house andplans to offer tours starting in May.

Walking along the damp paththrough the birch trees, slipping through theback door of the house, and opening thewide windows to gaze out over the graciouscurve of Templiner Lake, one immediatelysees what Einstein meant by paradise. Thehouse was an escape from the intrudingouter world.

By 1929, Einstein was already a house-hold name. Ten years earlier, his general theory of relativity had been triumphantlyconfirmed by the observation of starlightbending around the eclipsed sun, and he hadreceived the 1921 Nobel Prize in physics(although the citation mentioned the photo-electric effect, not relativity). As word spreadof his 50th birthday, Einstein was inundatedwith letters and presents from around theworld. But what he most wanted was a quietrefuge where he could entertain friends,spend time with his wife and two stepdaugh-ters, and think about the unified field theory,which he would pursue for the rest of his lifeand which still eludes physicists today. Andso, using most of his savings to buy the landand build a house, he got his retreat.

Einstein’s desire for a wooden houseattracted the architect Konrad Wachsmann,who designed the block house at Caputh andbecame a dear friend. Acting fromPrinceton, Einstein later helped him flee

Nazi Germany for the UnitedStates. There, in the 1940s,Wachsmann worked withWalter Gropius. Together theydeveloped a system for produc-ing prefabricated wood housesthat would gain him an interna-tional reputation and help radi-cally alter the suburban land-

scape. As one of his earliest designs usingwood, the Caputh house has an added histor-ical significance.

As Einstein no doubt would havewanted, the house has not been turned into ashrine. Instead, it continues to be used forthe annual Nobel lectures held by the

Forum and for academic retreats. Ratherthan rummaging for furniture in antiqueshops to match the original contents (whichwere lost in the years of first Nazi and thencommunist East German control), theForum is fitting the house with functional,tasteful equivalents. As the Forum’s RüdigerZill puts it, this is the “honest” approach.

A 15-minute drive away in Potsdam,black-and-white photographs from Ein-stein’s Caputh years are on display at theEinstein Forum. One can’t help but smileseeing these images; some are iconic, suchas Einstein setting off in Tümmler, thebeloved sailboat he kept moored on theTempliner. But many others are intimate andspontaneous: His stepdaughters recline insunchairs with obvious pleasure. Einsteinemerges serenely from the door in rumplyclothes or gazes out the window with a lookof utter peace. These reveal Einstein at hismost unguarded and, perhaps, optimistic.

10.1126/science.1110157

B R O W S I N G S

Einstein 1905. The Standard of Greatness.John S. Rigden. Harvard University Press,Cambridge, MA, 2005. 185 pp. $21.95,£14.95. ISBN 0-674-01544-4.

Between March and September 1905,Einstein wrote five Annalen der Physikpapers that would greatly influence 20th-century physics.These present the argument,from considerations of entropy, that lightconsists of quanta; Einstein’s dissertation onthe determination of molecular dimensions;his theory of Brownian motion; the theory ofspecial relativity; and the derivation of m = E/c2. For each paper, Rigden discussesthe background, underlying ideas, content,and organization before surveying its recep-tion and impact. General readers who wish to understand the magnitude of what Ein-stein accomplished during his annusmirabilis will find this lucid, nonmathemati-cal account ideal.C

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Einstein’s SummerHouse in Caputh

Einstein Forum, AmNeuen Markt 7, 14467Potsdam, Germany.www.einsteinforum.de

The reviewer is at Choriner Strasse 74, 10119 Berlin,Germany.Web site: www.johnbohannon.org

“

www.sciencemag.org SCIENCE VOL 307 11 FEBRUARY 2005

B O O K S E T A L .

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