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—a really huge amount—of energy bound upin every material thing.
respect to an observer depending on whether the observer was moving toward the source oflight or away from it, but no one had figured out a way to measure this. It occurred toMichelson that for half the year the Earth is traveling toward the Sun and for half the year it ismoving away from it, and he reasoned that if you took careful enough measurements atopposite seasons and compared light’s travel time between the two, you would have youranswer.
(Just to put these insights into perspective, it is perhaps worth noting that at the time Leavittand Cannon were inferring fundamental properties of the cosmos from dim smudges onphotographic plates, the Harvard astronomer William H. Pickering, who could of course peerinto a first-class telescope as often as he wanted, was developing his seminal theory that darkpatches on the Moon were caused by swarms of seasonally migrating insects.)Combining Leavitt’s cosmic yardstick with Vesto Slipher’s handy red shifts, Edwin Hubblenow began to measure selected points in space with a fresh eye. In 1923 he showed that a puffof distant gossamer in the Andromeda constellation known as M31 wasn’t a gas cloud at allbut a blaze of stars, a galaxy in its own right, a hundred thousand light-years across and atleast nine hundred thousand light-years away. The universe was vaster—vastly vaster—thananyone had ever supposed. In 1924 he produced a landmark paper, “Cepheids in SpiralNebulae” (nebulae,from the Latin for “clouds,” was his word for galaxies), showing that theuniverse consisted not just of the Milky Way but of lots of independent galaxies—“islanduniverses”—many of them bigger than the Milky Way and much more distant.
When the poet Paul Valéry once asked Einstein if he kept a notebook to record his ideas,Einstein looked at him with mild but genuine surprise. “Oh, that’s not necessary,” he replied.
1In 1891 he produced his results and learned to his dismay that the important work on entropyhad in fact been done already, in this instance by a retiring scholar at Yale University namedJ. Willard Gibbs.
At the same time he had fallen in love with a fellow student, a Hungarian named MilevaMaric. In 1901 they had a child out of wedlock, a daughter, who was discreetly put up foradoption. Einstein never saw his child. Two years later, he and Maric were married. Inbetween these events, in 1902, Einstein took a job with the Swiss patent office, where hestayed for the next seven years. He enjoyed the work: it was challenging enough to engage hismind, but not so challenging as to distract him from his physics. This was the backgroundagainst which he produced the special theory of relativity in 1905.
Einstein was born in Ulm, in southern Germany, in 1879, but grew up in Munich. Little inhis early life suggested the greatness to come. Famously he didn’t learn to speak until he wasthree. In the 1890s, his father’s electrical business failing, the family moved to Milan, butAlbert, by now a teenager, went to Switzerland to continue his education—though he failedhis college entrance exams on the first try. In 1896 he gave up his German citizenship toavoid military conscription and entered the Zurich Polytechnic Institute on a four-year coursedesigned to churn out high school science teachers. He was a bright but not outstandingstudent.
colleague at the patent office named Michele Besso. It was, wrote C. P. Snow, as if Einstein“had reached the conclusions by pure thought, unaided, without listening to the opinions ofothers. To a surprisingly large extent, that is precisely what he had done.”
Every object that has mass creates a little depression in the fabric of the cosmos. Thus theuniverse, as Dennis Overbye has put it, is “the ultimate sagging mattress.” Gravity on thisview is no longer so much a thing as an outcome—“not a ‘force’ but a byproduct of thewarping of spacetime,” in the words of the physicist Michio Kaku, who goes on: “In somesense, gravity does not exist; what moves the planets and stars is the distortion of space andtime.”
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 “in all the world could comprehend.” There was nosuch book, no such publisher, no such circle of learned men, but the notion stuck anyway.
Ten years later, by now a professor at the Case School in Cleveland, Michelson becameinterested in trying to measure something called the ether drift—a kind of head windproduced by moving objects as they plowed through space. One of the predictions ofNewtonian physics was that the speed of light as it pushed through the ether should vary with2Planck was often unlucky in life. His beloved first wife died early, in 1909, and the younger of his two sonswas killed in the First World War. He also had twin daughters whom he adored. One died giving birth. Thesurviving twin went to look after the baby and fell in love with her sisters husband. They married and two yearslater she died in childbirth. In 1944, when Planck was eighty-five, an Allied bomb fell on his house and he losteverything-papers, diaries, a lifetime of accumulations. The following year his surviving son was caught in aconspiracy to assassinate Hitler and executed.
We now know that Cepheids throb as they do because they are elderly stars that havemoved past their “main sequence phase,” in the parlance of astronomers, and become redgiants. The chemistry of red giants is a little weighty for our purposes here (it requires anappreciation for the properties of singly ionized helium atoms, among quite a lot else), but putsimply it means that they burn their remaining fuel in a way that produces a very rhythmic,very reliable brightening and dimming. Leavitt’s genius was to realize that by comparing therelative magnitudes of Cepheids at different points in the sky you could work out where theywere in relation to each other. They could be used as “standard candles”—a term she coinedand still in universal use. The method provided only relative distances, not absolute distances,but even so it was the first time that anyone had come up with a usable way to measure thelarge-scale universe.
For all his gifts, Hubble was also an inveterate liar.
Over the next decade, Hubble tackled two of the most fundamental questions of theuniverse: how old is it, and how big? To answer both it is necessary to know two things—howfar away certain galaxies are and how fast they are flying away from us (what is known astheir recessional velocity). The red shift gives the speed at which galaxies are retiring, butdoesn’t tell us how far away they are to begin with. For that you need what are known as“standard candles”—stars whose brightness can be reliably calculated and used asbenchmarks to measure the brightness (and hence relative distance) of other stars.
But the landmark event—the dawn of a new age—came in 1905, when there appeared inthe German physics journal Annalen der Physik a series of papers by a young Swissbureaucrat who had no university affiliation, no access to a laboratory, and the regular use ofno library greater than that of the national patent office in Bern, where he was employed as atechnical examiner third class. (An application to be promoted to technical examiner secondclass had recently been rejected.)His name was Albert Einstein, and in that one eventful year he submitted to Annalen derPhysik five papers, of which three, according to C. P. Snow, “were among the greatest in thehistory of physics”—one examining the photoelectric effect by means of Planck’s newquantum theory, one on the behavior of small particles in suspension (what is known asBrownian motion), and one outlining a special theory of relativity.
Glory instead would pass to a large mass of ego named Edwin Hubble. Hubble was born in1889, ten years after Einstein, in a small Missouri town on the edge of the Ozarks and grewup there and in Wheaton, Illinois, a suburb of Chicago. His father was a successful insuranceexecutive, so life was always comfortable, and Edwin enjoyed a wealth of physicalendowments, too. He was a strong and gifted athlete, charming, smart, and immensely good-looking—“handsome almost to a fault,” in the description of William H. Cropper, “an5Named for Johann Christian Doppler, an Austrian physicist, who first noticed the effect in 1842. Briefly, whathappens is that as a moving object approaches a stationary one its sound waves become bunched up as they cramup against whatever device is receiving them (your ears, say), just as you would expect of anything that is beingpushed from behind toward an immobile object. This bunching is perceived by the listener as a kind of pinchedand elevated sound (the yee). As the sound source passes, the sound waves spread out and lengthen, causing thepitch to drop abruptly (the yummm).
Hubble quickly demonstrated how wrong that belief was.
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—forreasons that can never fail to excite wonder—sent the paper’s golfing correspondent, oneHenry Crouch, to conduct the interview.
Among much else, Einstein’s 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 à 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’t exist. Einsteingave us a universe that didn’t need it.
Michelson talked Alexander Graham Bell, newly enriched inventor of the telephone, intoproviding the funds to build an ingenious and sensitive instrument of Michelson’s owndevising called an interferometer, which could measure the velocity of light with greatprecision. Then, assisted by the genial but shadowy Morley, Michelson embarked on years offastidious measurements. The work was delicate and exhausting, and had to be suspended fora time to permit Michelson a brief but comprehensive nervous breakdown, but by 1887 theyhad their results. They were not at all what the two scientists had expected to find.
In 1875–78, Gibbs produced a series of papers, collectively titledOn the Equilibrium ofHeterogeneous Substances , that dazzlingly elucidated the thermodynamic principles of, well,1Specifically it is a measure of randomness or disorder in a system. Darrell Ebbing, in the textbook GeneralChemistry, very usefully suggests thinking of a deck of cards. A new pack fresh out of the box, arranged by suitand in sequence from ace to king, can be said to be in its ordered state. Shuffle the cards and you put them in adisordered state. Entropy is a way of measuring just how disordered that state is and of determining thelikelihood of particular outcomes with further shuffles. Of course, if you wish to have any observationspublished in a respectable journal you will need also to understand additional concepts such as thermalnonuniformities, lattice distances, and stoichiometric relationships, but thats the general idea.
THE NINETEENTH century drew to a close, scientists could reflect with satisfaction thatthey had pinned down most of the mysteries of the physical world: electricity, magnetism,gases, optics, acoustics, kinetics, and statistical mechanics, to name just a few, all had falleninto order before them. They had discovered the X ray, the cathode ray, the electron, andradioactivity, invented the ohm, the watt, the Kelvin, the joule, the amp, and the little erg.
This finding alone would have ensured Hubble’s reputation, but he now turned to thequestion of working out just how much vaster the universe was, and made an even morestriking discovery. Hubble began to measure the spectra of distant galaxies—the business thatSlipher had begun in Arizona. Using Mount Wilson’s new hundred-inch Hooker telescopeand some clever inferences, he worked out that all the galaxies in the sky (except for our ownlocal cluster) are moving away from us. Moreover, their speed and distance were neatlyproportional: the further away the galaxy, the faster it was moving.
In 1875, when a young German in Kiel named Max Planck was deciding whether to devotehis life to mathematics or to physics, he was urged most heartily not to choose physicsbecause the breakthroughs had all been made there. The coming century, he was assured,would be one of consolidation and refinement, not revolution. Planck didn’t listen. He studiedtheoretical physics and threw himself body and soul into work on entropy, a process at theheart of thermodynamics, which seemed to hold much promise for an ambitious young man.
This was truly startling. The universe was expanding, swiftly and evenly in all directions. Itdidn’t take a huge amount of imagination to read backwards from this and realize that it musttherefore have started from some central point. Far from being the stable, fixed, eternal voidthat everyone had always assumed, this was a universe that had a beginning. It mighttherefore also have an end.
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’sobsession with Martian canals, which in the 1910s made it,in every sense, an outpost ofastronomical endeavor. Slipher was unaware of Einstein’s theory of relativity, and the worldwas equally unaware of Slipher. So his finding had no impact.
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, compiled 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.
2We shall turnto these ourselves in a moment, but first we must make a slight (but relevant!) detour toCleveland, Ohio, and an institution then known as the Case School of Applied Science. There,in the 1880s, a physicist of early middle years named Albert Michelson, assisted by his friendthe chemist Edward Morley, embarked on a series of experiments that produced curious anddisturbing results that would have great ramifications for much of what followed.
That’s a huge number, much bigger than merely saying it would lead you to suppose. Ifgalaxies were frozen peas, it would be enough to fill a large auditorium—the old BostonGarden, say, or the Royal Albert Hall. (An astrophysicist named Bruce Gregory has actuallycomputed this.) In 1919, when Hubble first put his head to the eyepiece, the number of thesegalaxies that were known to us was exactly one: the Milky Way. Everything else was thoughtto be either part of the Milky Way itself or one of many distant, peripheral puffs of gas.
So if the ideas of relativity seem weird, it is only because we don’t experience these sorts ofinteractions in normal life. However, to turn to Bodanis again, we all commonly encounterother kinds of relativity—for 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’s 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—asnail, say—the idea that a boom box could seem to two observers to produce two differentvolumes of music simultaneously might seem incredible.
In fact, of course, the world was about to enter a century of science where many peoplewouldn’t understand anything and none would understand everything. Scientists would soonfind themselves adrift in a bewildering realm of particles and antiparticles, where things popin and out of existence in spans of time that make nanoseconds look plodding and uneventful,where everything is strange. Science was moving from a world of macrophysics, whereobjects could be seen and held and measured, to one of microphysics, where events transpirewith unimaginable swiftness on scales far below the limits of imagining. We were about toenter the quantum age, and the first person to push on the door was the so-far unfortunateMax Planck.
This was more than a little odd, for Hubble’s life was filled from an early age with a levelof distinction that was at times almost ludicrously golden. At a single high school track meetin 1906, he won the pole vault, shot put, discus, hammer throw, standing high jump, andrunning high jump, and was on the winning mile-relay team—that is seven first places in onemeet—and came in third in the broad jump. In the same year, he set a state record for the highjump in Illinois.
“As the creation of a single mind,” they write, “it is undoubtedly the highest intellectualachievement of humanity,” which is of course as good as a compliment can get.
Hubble was a much better observer than a thinker and didn’t immediately appreciate thefull implications of what he had found. Partly this was because he was woefully ignorant ofEinstein’s General Theory of Relativity. This was quite remarkable because, for one thing,Einstein and his theory were world famous by now. Moreover, in 1929 Albert Michelson—now in his twilight years but still one of the world’s most alert and esteemed scientists—accepted a position at Mount Wilson to measure the velocity of light with his trustyinterferometer, and must surely have at least mentioned to him the applicability of Einstein’stheory to his own findings.
If a thing could be oscillated, accelerated, perturbed, distilled, combined, weighed, or madegaseous they had done it, and in the process produced a body of universal laws so weightyand majestic that we still tend to write them out in capitals: the Electromagnetic Field Theoryof Light, Richter’s Law of Reciprocal Proportions, Charles’s Law of Gases, the Law ofCombining Volumes, the Zeroth Law, the Valence Concept, the Laws of Mass Actions, andothers beyond counting. The whole world clanged and chuffed with the machinery andinstruments that their ingenuity had produced. Many wise people believed that there wasnothing much left for science to do.
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 become. We can never accelerate ourselves to the speed of light, and the harderwe try (and faster we go) the more distorted we will become, relative to an outside observer.
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—nothing can disturb its steady tick. In fact, according to Einstein, time is variableand ever changing. It even has shape. It is bound up—“inextricably interconnected,” inStephen Hawking’s expression—with the three dimensions of space in a curious dimensionknown as spacetime.
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—enough 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’re just not very good at getting it out. Even a uranium bomb—the mostenergetic thing we have produced yet—releases less than 1 percent of the energy it couldrelease if only we were more cunning.
Hubble died of a heart attack in 1953. One last small oddity awaited him. For reasonscloaked in mystery, his wife declined to have a funeral and never revealed what she did withhis body. Half a century later the whereabouts of the century’s greatest astronomer remainunknown. For a memorial you must look to the sky and the Hubble Space Telescope,launched in 1990 and named in his honor.
Physicists as a rule are not overattentive to the pronouncements of Swiss patent officeclerks, and so, despite the abundance of useful tidings, Einstein’s papers attracted little notice.
It is worth pausing for a moment to consider just how little was known of the cosmos at thistime. Astronomers today believe there are perhaps 140 billion galaxies in the visible universe.
In 1900 he graduated and within a few months was beginning to contribute papers toAnnalen der Physik. His very first paper, on the physics of fluids in drinking straws (of allthings), appeared in the same issue as Planck’s quantum theory. From 1902 to 1904 heproduced a series of papers on statistical mechanics only to discover that the quietlyproductive J. Willard Gibbs in Connecticut had done that work as well, in his ElementaryPrinciples of Statistical Mechanics of 1901.
Undaunted—well, perhaps mildly daunted—Planck turned to other matters.
As Caltech astrophysicist Kip S. Thorne has written: “The speed of light turned out to bethe same inall directions and at all seasons.” It was the first hint in two hundred years—inexactly two hundred years, in fact—that Newton’s laws might not apply all the timeeverywhere. The Michelson-Morley outcome became, in the words of William H. Cropper,“probably the most famous negative result in the history of physics.” Michelson was awardeda Nobel Prize in physics for the work—the first American so honored—but not for twentyyears. Meanwhile, the Michelson-Morley experiments would hover unpleasantly, like a mustysmell, in the background of scientific thought.
Gibbs is perhaps the most brilliant person that most people have never heard of. Modest tothe point of near invisibility, he passed virtually the whole of his life, apart from three yearsspent studying in Europe, within a three-block area bounded by his house and the Yalecampus in New Haven, Connecticut. For his first ten years at Yale he didn’t even bother todraw a salary. (He had independent means.) From 1871, when he joined the university as aprofessor, to his death in 1903, his courses attracted an average of slightly over one student asemester. His written work was difficult to follow and employed a private form of notationthat many found incomprehensible. But buried among his arcane formulations were insightsof the loftiest brilliance.
At all events, Hubble failed to make theoretical hay when the chance was there. Instead, itwas left to a Belgian priest-scholar (with a Ph.D. from MIT) named Georges Lema?tre tobring together the two strands in his own “fireworks theory,” which suggested that theuniverse began as a geometrical point, a “primeval atom,” which burst into glory and hadbeen moving apart ever since. It was an idea that very neatly anticipated the modernconception of the Big Bang but was so far ahead of its time that Lema?tre seldom gets morethan the sentence or two that we have given him here. The world would need additionaldecades, and the inadvertent discovery of cosmic background radiation by Penzias and Wilsonat their hissing antenna in New Jersey, before the Big Bang would begin to move frominteresting idea to established theory.
In 1900, now a theoretical physicist at the University of Berlin and at the somewhatadvanced age of forty-two, Planck unveiled a new “quantum theory,” which posited thatenergy is not a continuous thing like flowing water but comes in individualized packets,which he called quanta. This was a novel concept, and a good one. In the short term it wouldhelp to provide a solution to the puzzle of the Michelson-Morley experiments in that itdemonstrated that light needn’t be a wave after all. In the longer term it would lay thefoundation for the whole of modern physics. It was, at all events, the first clue that the worldwas about to change.
Soon the number of people who could grasp relativity had been reduced even further in thepopular imagination—and the scientific establishment, it must be said, did little to disturb themyth.
Though he later claimed to have passed most of the second decade of the century practicinglaw in Kentucky, in fact he worked as a high school teacher and basketball coach in NewAlbany, Indiana, before belatedly attaining his doctorate and passing briefly through theArmy. (He arrived in France one month before the Armistice and almost certainly never hearda shot fired in anger.)In 1919, now aged thirty, he moved to California and took up a position at the MountWilson Observatory near Los Angeles. Swiftly, and more than a little unexpectedly, hebecame the most outstanding astronomer of the twentieth century.
One Harvard computer, Annie Jump Cannon, used her repetitive acquaintance with thestars to devise a system of stellar classifications so practical that it is still in use today.
Remarkably, and despite his findings, when the twentieth century dawned Michelsoncounted himself among those who believed that the work of science was nearly at an end,with “only a few turrets and pinnacles to be added, a few roof bosses to be carved,” in thewords of a writer in Nature.
Called “On the Electrodynamics of Moving Bodies,” it is one of the most extraordinaryscientific papers ever published, as much for how it was presented as for what it said. It hadno footnotes or citations, contained almost no mathematics, made no mention of any workthat had influenced or preceded it, and acknowledged the help of just one individual, a3Einstein was honored, somewhat vaguely, "for services to theoretical physics." He had to wait sixteen years, till1921, to receive the award-quite a long time, all things considered, but nothing at all compared with FrederickReines, who detected the neutrino in 1957 but wasnt honored with a Nobel until 1995, thirty-eight years later, orthe German Ernst Ruska, who invented the electron microscope in 1932 and received his Nobel Prize in 1986,more than half a century after the fact. Since Nobel Prizes are never awarded posthumously, longevity can be asimportant a factor as ingenuity for prizewinners.
In simplest terms, what the equation says is that mass and energy have an equivalence.
What Michelson and Morley did, without actually intending to, was undermine alongstanding belief in something called the luminiferous ether, a stable, invisible, weightless,frictionless, and unfortunately wholly imaginary medium that was thought to permeate theuniverse. Conceived by Descartes, embraced by Newton, and venerated by nearly everyoneever since, the ether held a position of absolute centrality in nineteenth-century physics as away of explaining how light traveled across the emptiness of space. It was especially neededin the 1800s because light and electromagnetism were now seen as waves, which is to saytypes of vibrations. Vibrations must occur in something; hence the need for, and lastingdevotion to, an ether. As late as 1909, the great British physicist J. J. Thomson was insisting:
Hubble’s luck was to come along soon after an ingenious woman named Henrietta SwanLeavitt had figured out a way to do so. Leavitt worked at the Harvard College Observatory asa computer, as they were known. Computers spent their lives studying photographic plates ofstars and making computations—hence the name. It was little more than drudgery by anothername, but it was as close as women could get to real astronomy at Harvard—or indeed prettymuch anywhere—in those days. The system, however unfair, did have certain unexpectedbenefits: it meant that half the finest minds available were directed to work that wouldotherwise have attracted little reflective attention, and it ensured that women ended up with anappreciation of the fine structure of the cosmos that often eluded their male counterparts.
However—and here’s the thing—people 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 compressed and slowed down. It is all to do, you see, with yourposition relative to the moving object.
His famous equation, E =mc2, did not appear with the paper, but came in a brief supplementthat followed a few months later. As you will recall from school days, E in the equation standsfor energy, m for mass, and c2for the speed of light squared.
Among much else, Einstein’s 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 “the biggest blunder of my life.”
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’t static. The stars Slipher looked at showed unmistakable signs of a Doppler shift5—thesame 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).
nearly everything—“gases, mixtures, surfaces, solids, phase changes . . . chemical reactions,electrochemical cells, sedimentation, and osmosis,” to quote William H. Cropper. In essencewhat Gibbs did was show that thermodynamics didn’t apply simply toheat and energy at thesort of large and noisy scale of the steam engine, but was also present and influential at theatomic level of chemical reactions. Gibbs’s Equilibrium has been called “the Principia ofthermodynamics,” but for reasons that defy speculation Gibbs chose to publish theselandmark observations in the Transactions of the Connecticut Academy of Arts and Sciences,a journal that managed to be obscure even in Connecticut, which is why Planck did not hearof him until too late.
The first won its author a Nobel Prize and explained the nature of light (and also helped tomake television possible, among other things).
The wonder, as Stephen Hawking has noted, is that no one had hit on the idea of theexpanding universe before. A static universe, as should have been obvious to Newton andevery thinking astronomer since, would collapse in upon itself. There was also the problemthat if stars had been burning indefinitely in a static universe they’d have made the wholeintolerably hot—certainly much too hot for the likes of us. An expanding universe resolvedmuch of this at a stroke.
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—light,gravity, the universe itself—these are matters of consequence.
“The ether is not a fantastic creation of the speculative philosopher; it is as essential to us asthe air we breathe”—this more than four years after it was pretty incontestably establishedthat it didn’t exist. People, in short, were really attached to the ether.
In 1936 Hubble produced a popular book called The Realm of the Nebulae, whichexplained in flattering style his own considerable achievements. Here at last he showed thathe had acquainted himself with Einstein’s theory—up to a point anyway: he gave it four pagesout of about two hundred.
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 “special” about the special theory was that itdealt with things moving in an essentially unimpeded state. But what happened when a thingin motion—light, above all—encountered 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 “Cosmological Considerations on the General Theory of Relativity.”
“It’s so seldom I have one.” I need hardly point out that when he did get one it tended to begood. Einstein’s next idea was one of the greatest that anyone has ever had—indeed, the verygreatest, according to Boorse, Motz, and Weaver in their thoughtful history of atomic science.
Adonis” in the words of another admirer. According to his own accounts, he also managed tofit into his life more or less constant acts of valor—rescuing drowning swimmers, leadingfrightened men to safety across the battlefields of France, embarrassing world-championboxers with knockdown punches in exhibition bouts. It all seemed too good to be true. It was.
As a scholar he was equally proficient, and had no trouble gaining admission to studyphysics and astronomy at the University of Chicago (where, coincidentally, the head of thedepartment was now Albert Michelson). There he was selected to be one of the first Rhodesscholars at Oxford. Three years of English life evidently turned his head, for he returned toWheaton in 1913 wearing an Inverness cape, smoking a pipe, and talking with a peculiarlyorotund accent—not quite British but not quite not—that would remain with him for life.
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’t even come close to finishing yet.
If you needed to illustrate the idea of nineteenth-century America as a land of opportunity,you could hardly improve on the life of Albert Michelson. Born in 1852 on the German–Polish border to a family of poor Jewish merchants, he came to the United States with hisfamily as an infant and grew up in a mining camp in California’s gold rush country, where hisfather ran a dry goods business. Too poor to pay for college, he traveled to Washington, D.C.,and took to loitering by the front door of the White House so that he could fall in besidePresident Ulysses S. Grant when the President emerged for his daily constitutional. (It wasclearly a more innocent age.) In the course of these walks, Michelson so ingratiated himself tothe President that Grant agreed to secure for him a free place at the U.S. Naval Academy. Itwas there that Michelson learned his physics.
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’t 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. “Without it,” wrote Snow in 1979, “it is likely that weshould still be waiting for the theory today.”
3The second provided proof that atoms doindeed exist—a fact that had, surprisingly, been in some dispute. The third merely changedthe world.
Almost at once popularizers of science tried to come up with ways to make these conceptsaccessible to a general audience. One of the more successful attempts—commercially atleast—was 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 compressed. 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.
Neither Hubble nor Einstein would be much of a part of that big story. Though no onewould have guessed it at the time, both men had done about as much as they were ever goingto do.
Leavitt’s contribution was even more profound. She noticed that a type of star known as aCepheid variable (after the constellation Cepheus, where it first was identified) pulsated witha regular rhythm—a kind of stellar heartbeat. Cepheids are quite rare, but at least one of themis well known to most of us. Polaris, the Pole Star, is a Cepheid.
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’s relativity theories,Eddington considered deeply for a moment and replied: “I am trying to think who the thirdperson is.” In fact, the problem with relativity wasn’t that it involved a lot of differentialequations, Lorentz transformations, and other complicated mathematics (though it did—evenEinstein needed help with some of it), but that it was just so thoroughly nonintuitive.
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.
Of course the sagging mattress analogy can take us only so far because it doesn’tincorporate the effect of time. But then our brains can take us only so far because it is sonearly impossible to envision a dimension comprising 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.
Spacetime is usually explained by asking you to imagine something flat but pliant—amattress, say, or a sheet of stretched rubber—on 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’slaws 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—a product of thebending of spacetime.
