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they are two forms of the same thing： energy is liberated matter； matter is energy waiting tohappen。 since c2（the speed of light times itself） is a truly enormous number； what theequation is saying is that there is a huge amount鈥攁 really huge amount鈥攐f energy bound upin every material thing。
4you may not feel outstandingly robust； but if you are an average…sized adult you willcontain within your modest frame no less than 7 x 1018joules of potential energy鈥攅nough toexplode with the force of thirty very large hydrogen bombs； assuming you knew how toliberate it and really wished to make a point。 everything has this kind of energy trappedwithin it。 we鈥檙e just not very good at getting it out。 even a uranium bomb鈥攖he mostenergetic thing we have produced yet鈥攔eleases less than 1 percent of the energy it couldrelease if only we were more cunning。
among much else； einstein鈥檚 theory explained how radiation worked： how a lump ofuranium could throw out constant streams of high…level energy without melting away like anice cube。 （it could do it by converting mass to energy extremely efficiently 脿 lae =mc2。） itexplained how stars could burn for billions of years without racing through their fuel。 （ditto。）at a stroke； in a simple formula； einstein endowed geologists and astronomers with theluxury of billions of years。 above all； the special theory showed that the speed of light wasconstant and supreme。 nothing could overtake it。 it brought light （no pun intended； exactly） tothe very heart of our understanding of the nature of the universe。 not incidentally； it alsosolved the problem of the luminiferous ether by making it clear that it didn鈥檛 exist。 einsteingave us a universe that didn鈥檛 need it。
physicists as a rule are not overattentive to the pronouncements of swiss patent officeclerks； and so； despite the abundance of useful tidings； einstein鈥檚 papers attracted little notice。
having just solved several of the deepest mysteries of the universe； einstein applied for a jobas a university lecturer and was rejected； and then as a high school teacher and was rejectedthere as well。 so he went back to his job as an examiner third class； but of course he keptthinking。 he hadn鈥檛 even e close to finishing yet。
when the poet paul val茅ry once asked einstein if he kept a notebook to record his ideas；einstein looked at him with mild but genuine surprise。 鈥渙h； that鈥檚 not necessary；鈥潯e replied。
鈥渋t鈥檚 so seldom i have one。鈥潯 need hardly point out that when he did get one it tended to begood。 einstein鈥檚 next idea was one of the greatest that anyone has ever had鈥攊ndeed； the verygreatest； according to boorse； motz； and weaver in their thoughtful history of atomic science。
4how c came to be the symbol for the speed of light is something of a mystery； but david bodanis suggests itprobably came from the latin celeritas； meaning swiftness。 the relevant volume of the oxford englishdictionary； piled a decade before einsteins theory； recognizes c as a symbol for many things； from carbonto cricket； but makes no mention of it as a symbol for light or swiftness。
鈥渁s the creation of a single mind；鈥潯hey write； 鈥渋t is undoubtedly the highest intellectualachievement of humanity；鈥潯hich is of course as good as a pliment can get。
in 1907； or so it has sometimes been written； albert einstein saw a workman fall off a roofand began to think about gravity。 alas； like many good stories this one appears to beapocryphal。 according to einstein himself； he was simply sitting in a chair when the problemof gravity occurred to him。
actually； what occurred to einstein was something more like the beginning of a solution tothe problem of gravity； since it had been evident to him from the outset that one thing missingfrom the special theory was gravity。 what was 鈥渟pecial鈥潯bout the special theory was that itdealt with things moving in an essentially unimpeded state。 but what happened when a thingin motion鈥攍ight； above all鈥攅ncountered an obstacle such as gravity？ it was a question thatwould occupy his thoughts for most of the next decade and lead to the publication in early1917 of a paper entitled 鈥渃osmological considerations on the general theory of relativity。鈥�
the special theory of relativity of 1905 was a profound and important piece of work； ofcourse； but as c。 p。 snow once observed； if einstein hadn鈥檛 thought of it when he did someoneelse would have； probably within five years； it was an idea waiting to happen。 but the generaltheory was something else altogether。 鈥渨ithout it；鈥潯rote snow in 1979； 鈥渋t is likely that weshould still be waiting for the theory today。鈥�
with his pipe； genially self…effacing manner； and electrified hair； einstein was too splendida figure to remain permanently obscure； and in 1919； the war over； the world suddenlydiscovered him。 almost at once his theories of relativity developed a reputation for beingimpossible for an ordinary person to grasp。 matters were not helped； as david bodanis pointsout in his superb book e=mc2； when the new york times decided to do a story； and鈥攆orreasons that can never fail to excite wonder鈥攕ent the paper鈥檚 golfing correspondent； onehenry crouch； to conduct the interview。
crouch was hopelessly out of his depth； and got nearly everything wrong。 among the morelasting errors in his report was the assertion that einstein had found a publisher daring enoughto publish a book that only twelve men 鈥渋n all the world could prehend。鈥潯here was nosuch book； no such publisher； no such circle of learned men； but the notion stuck anyway。
soon the number of people who could grasp relativity had been reduced even further in thepopular imagination鈥攁nd the scientific establishment； it must be said； did little to disturb themyth。
when a journalist asked the british astronomer sir arthur eddington if it was true that hewas one of only three people in the world who could understand einstein鈥檚 relativity theories；eddington considered deeply for a moment and replied： 鈥渋 am trying to think who the thirdperson is。鈥潯n fact； the problem with relativity wasn鈥檛 that it involved a lot of differentialequations； lorentz transformations； and other plicated mathematics （though it did鈥攅veneinstein needed help with some of it）； but that it was just so thoroughly nonintuitive。
in essence what relativity says is that space and time are not absolute； but relative to boththe observer and to the thing being observed； and the faster one moves the more pronouncedthese effects bee。 we can never accelerate ourselves to the speed of light； and the harderwe try （and faster we go） the more distorted we will bee； relative to an outside observer。
almost at once popularizers of science tried to e up with ways to make these conceptsaccessible to a general audience。 one of the more successful attempts鈥攎ercially at least鈥攚as the abc of relativity by the mathematician and philosopher bertrand russell。 init； russell employed an image that has been used many times since。 he asked the reader toenvision a train one hundred yards long moving at 60 percent of the speed of light。 tosomeone standing on a platform watching it pass； the train would appear to be only eightyyards long and everything on it would be similarly pressed。 if we could hear thepassengers on the train speak； their voices would sound slurred and sluggish； like a recordplayed at too slow a speed； and their movements would appear similarly ponderous。 even theclocks on the train would seem to be running at only four…fifths of their normal speed。
however鈥攁nd here鈥檚 the thing鈥攑eople on the train would have no sense of thesedistortions。 to them； everything on the train would seem quite normal。 it would be we on theplatform who looked weirdly pressed and slowed down。 it is all to do； you see； with yourposition relative to the moving object。
this effect actually happens every time you move。 fly across the united states； and youwill step from the plane a quinzillionth of a second； or something； younger than those you leftbehind。 even in walking across the room you will very slightly alter your own experience oftime and space。 it has been calculated that a baseball thrown at a hundre