US theoretical John Wheeler helped to bring into the mainstream.

PHYSICS Einstein’s curve ball enjoys a ‘biography’ of the general .

he mathematical physicist penetration, physical Ferreira describes, one of the most eminent remarked in 1955 that although his late intuition and mathe- of the who brought the general friend ’s general theory matical skill”, Einstein theory back into the limelight was US theo- Tof relativity was a peerless scientific achieve- developed his general retician John Wheeler. Wheeler was at first ment, “its connections with experience [are] theory of relativity — deeply uneasy about the theory’s mathemati- slender”. The appeal of the theory for Born a new theory of grav- cal singularities — the point at which the was similar to that of “a great work of art, to be ity — and published it quantities used to measure the strength of enjoyed and admired at a distance”. eight years later. In the gravitational fields become infinite — and Today, Born’s comments seem quaint. In final straight, the Ger- even wanted to remove them. In December an age of precision astronomy, it is now pos- man mathematician The Perfect 1963, he was one of the speakers at the first sible to study consequences of the theory; was hot Theory: A Century Texas Symposium on Relativistic Astrophys- of and the existence of gravitational , for on his heels. the Battle over ics, where the audience excitedly discussed instance, can be inferred from studying Ferreira outlines General Relativity the recently identified “quasi stellar radio . With the theory’s centenary only a the theory, but I wish PEDRO G. FERREIRA sources”, neatly dubbed by one of year away, this is an opportune to look that he had tried a Houghton Mifflin the attendees. It seemed likely that general back on its inception and its achievements, little harder to con- Harcourt: 2014. relativity might well be needed to under- as astrophysicist Pedro Ferreira does in The vey the surpassing stand this and other astronomical discover- Perfect Theory, a ‘biography’ of Einstein’s beauty of Einstein’s equations. As the great ies. Sure enough, the theory became a much brainchild for those with a smattering of theoretician has stressed, more popular subject of study soon after, and and next to no . this was the quality that persuaded his col- several extremely strong research groups — Einstein recalled that his crucial epiph- leagues to take relativity seriously. I suspect notably in Moscow; Princeton, New Jersey; any occurred in 1907. Sitting in the Swiss that many readers would have tolerated a and Cambridge, UK — began to catch the patent office in , he realized that “if a few moments’ perplexity for a sense of its eye of the community. person falls freely he will not feel his own mathematical glory. At the symposium was the British math- weight”. Using what Born described as “the The theory was past its fiftieth birthday ematical physicist , who went most amazing combination of philosophical when it entered mainstream physics. As on to work with to make

614 | | VOL 505 | 30 JANUARY 2014 © 2014 Macmillan Publishers Limited. All rights reserved BOOKS & ARTS COMMENT pioneering contributions to our under- standing of the origins of the , and of black holes, a term adopted by Wheeler after an audience member sug- gested it. Later, astronomers observed these exotic objects — regions of - SCIEPRO/SPL/CORBIS time where is so strong that it appears can escape. Einstein would surely have been delighted to see this and other demonstrations of the surprising consequences of his theory. His equations were smarter than he was, to paraphrase the physicist . Yet general relativity is not quite per- fect. It takes no account of theory and is extremely difficult to combine with “General the well-tested relativity is now account of the framework nature’s other for planning fundamental and interpreting interactions — many weak, electro- astronomical magnetic and experiments.” strong — in the standard model of . Ferreira lucidly sketches several attempts to generalize Einstein’s theory, including , which both describes gravity and offers Joined-up thinking an explanation of why it exists. Although enormously promising and mathemati- Chris Frith explores a masterful model of how cally rich, string theory is unpopular consciousness plays out in the theatre of the brain. among some physicists in part because of the extreme difficulty of putting it to test, at least in the foreseeable . n 1874, Thomas Henry Huxley gave a Consciousness that such technologies Meanwhile, good old general relativ- prescient lecture on mind and brain. The and the Brain: have made possible. ity — once regarded as too recondite to biologist argued that subjective experience Deciphering How For Dehaene, con- the Brain Codes be worth studying — is now the frame- Idepends on the brain’s “anterior divisions”, sciousness is simply Our Thoughts work for planning and interpreting many and that consciousness has as little effect on STANISLAS DEHAENE this: we are conscious astronomical experiments, as Ferreira behaviour as a steam whistle has on a loco- Viking Books: 2014. of whatever we choose describes in a moving coda. motive’s progress — rendering humans little to focus our attention When the sculptor Henry Moore vis- more than “conscious automata”. He raised on. He details many experiments, and pre- ited Chicago, Illinois, in the late 1960s, two questions that remain key in contem- sents the best attempt yet to answer the two the brilliant theoretical astrophysicist porary studies of the neural of con- questions raised by Huxley. Subrahmanyan Chandrasekhar asked sciousness: what is special about the neural Regarding the first, on neural processes, him how best to view a work of sculp- processes that underlie consciousness, and the brain does a lot of work before we ture. Moore replied that the greatest of what, if anything, is consciousness for? become conscious of a stimulus, as Helm- these works should be viewed from all The 1870s seemed a likely time for a con- holtz pointed out. When you read these distances, as new aspects of their beauty certed research effort to answer those ques- words, you are rarely aware of the individual are revealed on every scale. Likewise, tions. Herman von Helmholtz had made the letters — yet you must have analysed them 50 years later, the mathematical aes- distinction between conscious and uncon- to have understood the meaning. How much thetic of relativity has been enhanced by scious brain processes, and Gustav Theodor unconscious analysis happens before what the beautiful demonstrations of its verac- Fechner’s ‘psychophysics’ had begun to allow we are looking at emerges into conscious- ity that Ferreira describes. These would the experimental study of the relationship ness? Dehaene relates how clever techniques probably have made Born ponder why he between subjective experience and physical have been developed to answer this question. and his peers did not spend more time stimulation. But it was not until the 1970s In backward masking, for example, a word developing a deeper appreciation of the that three-dimensional imaging of the liv- (such as ‘five’) is presented, followed by a mask theory soon after Einstein first presented ing human brain became possible through (a meaningless series of letters, for example). it. Maybe there’s a lesson here for some of physicist Peter Mansfield’s work in magnetic It has been found that the brain begins to ana- today’s string-theory sceptics? ■ resonance imaging. Among the first to realize lyse the word as soon as it appears, but that the importance of this breakthrough for the this analysis ceases when the mask appears. Graham Farmelo is a by-fellow at study of mind and brain was cognitive neuro­ If the switch from word to mask is very rapid, Churchill College, Cambridge, and Stanislas Dehaene. In his brilliant there is no consciousness that the word was author of Churchill’s Bomb. Consciousness and the Brain, Dehaene con- presented. Yet, as Dehaene has shown, the e-mail: [email protected] veys the excitement of developing unconscious neural processing that goes

30 JANUARY 2014 | VOL 505 | NATURE | 615 © 2014 Macmillan Publishers Limited. All rights reserved