按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
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 hundred miles an hour willpick up 0。000000000002 grams of mass on its way to home plate。 so the effects of relativityare real and have been measured。 the problem is that such changes are much too small tomake the tiniest detectable difference to us。 but for other things in the universe鈥攍ight；gravity； the universe itself鈥攖hese are matters of consequence。
so if the ideas of relativity seem weird； it is only because we don鈥檛 experience these sorts ofinteractions in normal life。 however； to turn to bodanis again； we all monly encounterother kinds of relativity鈥攆or instance with regard to sound。 if you are in a park and someoneis playing annoying music； you know that if you move to a more distant spot the music willseem quieter。 that鈥檚 not because the musicis quieter； of course； but simply that your positionrelative to it has changed。 to something too small or sluggish to duplicate this experience鈥攁snail； say鈥攖he idea that a boom box could seem to two observers to produce two differentvolumes of music simultaneously might seem incredible。
the most challenging and nonintuitive of all the concepts in the general theory of relativityis the idea that time is part of space。 our instinct is to regard time as eternal； absolute；immutable鈥攏othing can disturb its steady tick。 in fact； according to einstein； time is variableand ever changing。 it even has shape。 it is bound up鈥斺�渋nextricably interconnected；鈥潯nstephen hawking鈥檚 expression鈥攚ith the three dimensions of space in a curious dimensionknown as spacetime。
spacetime is usually explained by asking you to imagine something flat but pliant鈥攁mattress； say； or a sheet of stretched rubber鈥攐n which is resting a heavy round object； suchas an iron ball。 the weight of the iron ball causes the material on which it is sitting to stretchand sag slightly。 this is roughly analogous to the effect that a massive object such as the sun（the iron ball） has on spacetime （the material）： it stretches and curves and warps it。 now ifyou roll a smaller ball across the sheet； it tries to go in a straight line as required by newton鈥檚laws of motion； but as it nears the massive object and the slope of the sagging fabric； it rollsdownward； ineluctably drawn to the more massive object。 this is gravity鈥攁 product of thebending of spacetime。
every object that has mass creates a little depression in the fabric of the cosmos。 thus theuniverse； as dennis overbye has put it； is 鈥渢he ultimate sagging mattress。鈥潯ravity on this view is no longer so much a thing as an oute鈥斺�渘ot a 鈥榝orce鈥櫋ut a byproduct of thewarping of spacetime；鈥潯n the words of the physicist michio kaku； who goes on： 鈥渋n somesense； gravity does not exist； what moves the planets and stars is the distortion of space andtime。鈥�
of course the sagging mattress analogy can take us only so far because it doesn鈥檛incorporate the effect of time。 but then our brains can take us only so far because it is sonearly impossible to envision a dimension prising three parts space to one part time； allinterwoven like the threads in a plaid fabric。 at all events； i think we can agree that this wasan awfully big thought for a young man staring out the window of a patent office in thecapital of switzerland。
among much else； einstein鈥檚 general theory of relativity suggested that the universe mustbe either expanding or contracting。 but einstein was not a cosmologist； and he accepted theprevailing wisdom that the universe was fixed and eternal。 more or less reflexively； hedropped into his equations something called the cosmological constant； which arbitrarilycounterbalanced the effects of gravity； serving as a kind of mathematical pause button。 bookson the history of science always forgive einstein this lapse； but it was actually a fairlyappalling piece of science and he knew it。 he called it 鈥渢he biggest blunder of my life。鈥�
coincidentally； at about the time that einstein was affixing a cosmological constant to histheory； at the lowell observatory in arizona； an astronomer with the cheerily intergalacticname of vesto slipher （who was in fact from indiana） was taking spectrographic readings ofdistant stars and discovering that they appeared to be moving away from us。 the universewasn鈥檛 static。 the stars slipher looked at showed unmistakable signs of a doppler shift5鈥攖hesame mechanism behind that distinctive stretched…out yee…yummm sound cars make as theyflash past on a racetrack。 the phenomenon also applies to light； and in the case of recedinggalaxies it is known as a red shift （because light moving away from us shifts toward the redend of the spectrum； approaching light shifts to blue）。
slipher was the first to notice this effect with light and to realize its potential importancefor understanding the motions of the cosmos。 unfortunately no one much noticed him。 thelowell observatory； as you will recall； was a bit of an oddity thanks to percival lowell鈥檚obsession with martian canals； which in the 1910s made it； in every sense； an outpost ofastronomical endeavor。 slipher was unaware of einstein鈥檚 theory of relativity； and the w