galison and burnett - niels bohr...

Newton, forgive me . . .

–Albert Einstein, Autobiographical Notes

d. graham burnett: Peter, in 1997you gave a plenary session lecture at theHistory of Science Society meeting in LaJolla entitled “Relentless Historicism:Machines and Metaphysics.” I have avivid memory of the presentation, whichwas, I think, the ½rst time you sharedwith the wider community of historiansand philosophers of science your re-search on Einstein, relativity, and the

material culture of time in the ½n de siè-cle. And you turned a lot of heads. Yourargument went something like this: Atthe heart of Einstein’s watershed 1905paper on special relativity–the paperthat shook the foundations of Newton-ian physics–lies a ‘thought experiment’about clock synchronization and the‘problem’ of simultaneity; there, talkingabout trains arriving in stations andobservers watching their watches, Ein-stein posed what turn out to be insur-mountable challenges to Newton’snotion of absolute time (and absolutespace). This we knew. But then the talkgot juicy: you went on to point out thatthis thought experiment might not bemerely a thought experiment, since thebusiness of synchronizing time framesthrough space was more than justabstruse theoretical physics in the latenineteenth and early twentieth cen-turies. It was a perfectly real, quotidian,and central preoccupation of railwaycompanies, nation-states, and militaryplanners. The increasing speed of rail-way travel in the second half of the nine-teenth century had made it necessary tocodify ‘time zones’ around the world–zones of conventionalized simultaneity,where people would ignore local time(say, the ‘noon’ of the sun), and go bythe noon on their clocks: a subtlechange, but an important one, since it

Dædalus Spring 2003 1

Peter L. Galison & D. Graham Burnett

Einstein, Poincaré & modernity:a conversation

Peter L. Galison has just completed a new book,“Einstein’s Clocks, Poincaré’s Maps,” that formsthe basis of this dialogue. A Fellow of the Ameri-can Academy since 1992, Galison is the Mallin-ckrodt Professor of the History of Science and ofPhysics at Harvard University. Galison’s otherbooks, including “Image and Logic” (1997) and“How Experiments End” (1987), explore theinteraction between the principal subcultures oftwentieth-century physics–experimentation, in-strumentation, and theory–and also the cross-currents between physics and other ½elds.

D. Graham Burnett is an assistant professor ofhistory in the Program in History of Science atPrinceton University. He is the author of “Mas-ters of All They Surveyed”(2000) and “A TrialBy Jury” (2001), and a co-editor of “The Historyof Cartography” (1987–).

© 2003 by Peter L. Galison & D. GrahamBurnett

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put people across the globe in temporalstep. There was no other way to run arailroad. Moreover, the design and man-ufacture of electromechanical systemsthat ‘distributed’ this new coordinatedtime–networks of clocks running insync–was a major precision industry.Looked at in the right way, Einstein’sthought experiment bore an uncannyresemblance to a set of wholly practicalexperiments going on all around him–even under his very nose, as he earnedhis living in the Berne Patent Of½cereviewing exactly these sorts of time-distribution devices. That day in La Jollayou left us with a question: Could wereally understand Einstein’s 1905 paperwithout understanding the rise of inter-national time conventions and the tech-nologies of industrial time-synchroniza-tion? Now you have written a book, Ein-stein’s Clocks, Poincaré’s Maps: Empires ofTime, which delivers on this questionand expands your original insight. Forreaders to whom all this is new, wouldyou start by describing how trains andclocks ½gure in Einstein’s landmark pub-lication?

peter l. galison: Certainly. Perhapsthe greatest success of nineteenth-centu-ry physics was the prediction (and sub-sequent demonstration) of the existenceof ‘electric waves.’ Light was nothingother than such a wave. Suddenly theancient science of optics became nomore than a sub½eld of electromagnet-ism. At the same time, this thrilling ½nd-ing brought with it a puzzle: Physicistsof the late nineteenth century, very rea-sonably, thought that a wave had to be awave in something. After all, waves at thebeach are waves in water, sound wavesare waves in air, and so on. But lightcould travel in a vacuum–that is, appar-ently through empty space. This ledmost everyone to suppose that there hadto be a special all-pervading (and as yet

undiscovered) substance–the ‘ether’–permeating everything, everywhere,present even in a vacuum. But experi-mentalists had no luck ½nding this elu-sive medium. Einstein’s famous 1905paper on relativity begins here. General-izing from failed attempts to ‘see’ theether (or, more correctly, to see any evi-dence that the earth was moving‘through’ it), Einstein decided to scrapthe ether altogether, and to go after theproblem of the propagation of light in adifferent way. First, he stipulated that allthe laws of physics–including electricityand magnetism–were the same in anyconstantly moving frame of reference.Then he added a seemingly simple (andmodest) second assumption: Light trav-els at the same speed no matter how fastits source is moving. To anyone thinkingof ether this was not so strange: Moveyour hands at any reasonable speedthrough a room of still air; once you clapyour hands the sound waves propagatethrough the room at the same speed–independent of the original motion ofyour hands. Maybe light was like that: alamp moving in the ether simply excitedlight waves that radiated out at a singlespeed independent of the motion of thelamp. Yet these two reasonable startingassumptions appeared to contradict oneanother. Suppose lamps were flying thisway and that at various speeds, but thatin some frame the light beams fromthose lamps were all traveling at 186,000miles per second, just the speed predict-ed by the equations of electrodynamics.Wouldn’t those same beams of lightappear to be traveling at different speedswhen seen from a different, movingframe of reference? If that was so, thenthe equations of electrodynamics wouldonly be valid in one frame of reference,violating Einstein’s ½rst principle. It wasto resolve this apparent contradictionthat Einstein made his single most dra-matic move: he criticized the very idea

2 Dædalus Spring 2003

Peter L.Galison &D. GrahamBurnettontime


of time as it was usually understood. Inparticular, he relentlessly pursued themeaning of ‘simultaneity.’ Only by criti-cizing the foundational notions of timeand space could one bring the pieces ofthe theory–that the laws of physicswere the same in all constantly movingframes; that light traveled at the samespeed regardless of its source–into har-mony. And this is where the trains andclocks enter. Suppose, Einstein rea-soned, that you wanted to know whattime a train arrived in a train station.Easy enough: you see where the hand ofyour watch is at the time the engine pullsup alongside you. But what if you want-ed to know when a train was pulling intoa distant station? How do you knowwhether an event here is simultaneouswith an event there? Einstein insistedthat we need a simultaneity-½xing pro-cedure, a de½nite system of exchangingsignals between the stations that wouldtake into account the time it took for thesignal to get from one station to another.By pursuing this insight, Einstein discov-ered that two events that were simulta-neous in one frame of reference wouldnot be simultaneous in another. More-over, since a length measurement in-volves determining the position of thefront and back of an object at the sametime, the relativity of simultaneity meantthat length was relative as well. By remov-ing the absolutes of space and time, Ein-stein restructured modern physics.

dgb: So what was at stake here was notonly the universal ether, the substrate ofthe cosmos, but also time–that absolute,ever-unrolling, eternally immutableflowing, the Platonic time of which allworldly clocks were mere dilapidations.It was this time that Newton had under-stood was a necessary condition of hisphysics, and that he had placed beyondthe realm of merely human investiga-

tion; it flowed in the “Sensorium ofGod.”

plg: Just by demanding a conventionalclock-and-signal based procedure to ½xsimultaneity, Einstein was breaking withthe Newtonian idea of time. For New-ton, there was absolute, true, mathemat-ical time that ticked ever-constantly thesame way for all observers. Clocks–allkinds–were only pale reflections, ap-proximations to this metaphysical tem-porality. But Einstein’s departure fromNewtonian time went further, since onceEinstein’s starting points are accepteddramatic consequences follow. For in-stance, if a train travels through our sta-tion and the engineer and caboose driverflash their lanterns towards the center ofthe train (at what we in the station judgeto be simultaneous moments), we canask what happens in the train. We on thestation platform say: The mid-train con-ductor moves towards the site where theengine driver had flashed his lantern andaway from the site where the caboosetender had flashed her lamp. So (say westation-based observers) the middleconductor receives the engine flash ½rst.Since by assumption the middle conduc-tor measures the two flashes as movingat equal velocities from equally separat-ed points of origin, he concludes–asnight follows day–that the two flasheswere not sent simultaneously. So the twoflashes that were simultaneous in thestation frame are not simultaneous in themoving one. Simultaneity is relative to aframe of reference; it is not absolute.From an apparently prosaic startingpoint about clocks, trains, and light sig-nals, Einstein had smashed one of thevery centerpieces of classical physics.

dgb: This is perhaps the Einstein ofmyth and legend, the knight-errant inthe borderlands of metaphysics who


Einstein,Poincaré &modernity


slays the last chimera of the crystallinespheres. A searcher in the realm of puremind, he reconnoiters the Sensorium ofGod and ½nds it empty. But this image,you would remind us, is a distortion ofEinstein’s character, of what he thoughthe had done, and of his approach toproblems as well, no?

plg: Einstein, without any doubt, is thebest-known scientist ever, and he occu-pies an astonishingly robust culturalplace. He doesn’t seem to come into andfall out of fashion as much as he is sim-ply appropriated for new purposes witheach generation. But one of the perenni-al features of Einstein-the-icon is the½gure of the great mind living in a worldapart, the ultimate loner. No doubt Ein-stein himself is in some measure respon-sible for this image, since, in later life, hereflected nostalgically on solitude, isola-tion, and creativity. For instance, hewrote wistfully of the lighthouse atten-dant, whose world could be that of un-distracted thought. So we think of himas the person who could not quite navi-gate the physical world, and associatethat incapacity with a romantic pictureof scienti½c genius. This in turn leads toan odd rewriting of the way he lived hislife and did his work.

dgb: Was the patent of½ce Einstein’s‘lighthouse’?

plg: This has generally been the story–Einstein at the patent of½ce is the geniusat his day job: at best a source of breadand butter, at worst a distraction, but insome deep way irrelevant to understand-ing his science.

dgb: When did you begin to get a differ-ent idea of how the story might be told?

plg: I was standing at a train station innorthern Europe admiring a line ofclocks that went along the platform. AndI noticed that the minute hands were allat the same point–I could just see themall lined up. I thought, “These are won-derful clocks; isn’t that impressive thatthey can make them to hold such regu-larity?” Then I noticed that the secondhands were clicking in synchrony too,which was startling, and I thought,“These can’t be that accurate–you can’thave clocks running like this that are notsynchronized in some way, or else they’dget out of phase.” Suddenly I wonderedif Einstein had paid attention to syn-chronized clocks in train stations. If hehad it would give a very tangible senseto that most famous of all scienti½cthought experiments in his 1905 paper. Itwould make his move towards a criti-cism of absolute time both ½gurative andliteral. So I went back and I started pok-ing around–and found myself in themidst of an absolutely immense litera-ture on ½n-de-siècle timekeeping andclocks. As you know, there was at thetime an urgent technological problem ofcoordinating time along train tracks.More than that: in Europe the center ofprecision-coordinated timekeeping wasSwitzerland, and if all this industry wasbased in Switzerland they must havebeen processing patents right and left. Iwent to the patent of½ce, and foundmyself surrounded by a huge number ofpatents with diagrams of clocks linkedby signals. There were even proposalsfor patents and articles in the technicaljournals about clocks linked by radiowaves. All this seemed extremely closeto the kind of materialization of timethat preoccupied Einstein. Of course,the clock factories and inventors had nointerest in ‘frames of reference’ or in all




the ‘physics of the ether.’ But the impor-tance of distributing simultaneity byelectromagnetic means was clear toeveryone. Here was a technical problemlocated in Switzerland, centered inBerne, and with ideas coming to a pointin Einstein’s patent of½ce. It all seemedremarkable; and it is there that I beganthis work.

dgb: And yet Einstein certainly wasn’tthe only physicist at the turn of the cen-tury preoccupied with time . . .

plg: Not at all. In fact, even as I workedon “Einstein in the Patent Of½ce” (andprepared the paper you mentioned), Ikept wondering, “Who else would have,should have, been in this mix? And whoelse from the physics community wouldhave been concerned with ideas of si-multaneity?” There is one other personwho cared about simultaneity at least asmuch as Einstein–and earlier–and thatwas Henri Poincaré. He certainly sawthat clock coordination was essential forde½ning what we mean by simultaneity.

dgb: Einstein may be a householdname, but the same cannot be said forPoincaré.

plg: I suppose household name, liketime and simultaneity, is a relative con-cept. In France, Poincaré has long been ahero. Known for his innovations in thequalitative studies of chaotic systems,for his invention of the mathematicaltheory of topology, for his contributionsto mathematical physics, and for his phi-losophy of conventionalism, Poincaréwas without any question the most re-nowned French scientist of the late nine-teenth and early twentieth century. Andthat, in France, meant he was an extraor-

dinarily visible ½gure whose booksabout science, philosophy, and moralitywere best-sellers. He also wrote dramati-cally and often about the new theory ofrelativity to which he contributed im-portantly. Crucially for our understand-ing of his ideas of simultaneity, Poincaréwas, beginning in the early 1890s, deeplyinvolved in time-distribution networks.

dgb: At the Bureau des Longitudes?

plg: Yes, where he would serve severalterms as president. And this was crucial,because the astronomers and geogra-phers of the Bureau were working inten-sively with the telegraphic transmissionof time. This was not for domestic rail-road use–or at least not in the ½rst in-stance. Rather, these engineers and sci-entists were working at a much higherlevel of precision. They needed to deter-mine simultaneity so distant observerscould determine their relative longitude.

dgb: For cartographic purposes, sincelongitude measurements are measure-ments of time?1

plg: Precisely. Their goal was to mapthe nation, the empire, and then muchof the world. Speci½cally, they aimed to½nd points of reference–for instance, inNorth Africa, Senegal, Ecuador, andVietnam–from which the further map-ping of the interiors could proceed.Maps were important for extraction of



1 The earth rotates once on its axis each day,or 360 degrees every 24 hours, or 15 degreesevery hour. Longitude is measured with respectto some arbitrary zero line–say, the meridianof Paris. So if we know that the sun is directlyover our heads (it is noon where we are) andwe get a telegraph message from Paris saying itwas noon there an hour before, we know weare 15 degrees west of Paris.


ores, for military domination, for thecutting of roads, and the laying of rail-road lines. Railroad lines brought inmore cable, and therefore more map-ping, and so on. All of this constituted amajor technical program, a great nation-al moment. And the timing is fascinat-ing. Poincaré really became a public ½g-ure starting in 1887 or so. And by 1892 hewas involved with the Bureau of Longi-tude, where he tackled problems of timeconventions–from the decimalizationof the hour to reconciling the longitudeof the Paris and Greenwich observato-ries. I remember staring at these reportsfrom the 1890s, trying to ½gure out whatthe Bureau’s telegraphic time-½nderswere doing, and expecting that I’d ½ndthat–as in the case of Einstein’s patentof½ce–the ½xing of simultaneity was afairly crude affair. But this work wasanything but crude! Instead, I saw thatby the 1890s it was altogether routine forthe astronomer-engineers to take intoaccount the time the electrical signal took to gofrom one place to another. That, I thought–I had assumed–was exclusively a pre-occupation of physicists and their ‘rela-tivity.’ But it turned out that Poincaré’scolleagues at the Bureau were preciselyworried about this, and their concern isplain as day once you look at their data.Columns in the of½cial reports arelabeled: “time of transmission.” Theengineers even sent their time signals onround-trips to compensate for errors.The more I looked at it, the more speci½cthe connections seemed. So in January1898, when Poincaré wrote his famousphilosophical article “The Measure ofTime,” introducing the simultaneityconvention via the metaphor of tele-graphic longitude ½nders, he had inmind an abstraction but also a concreteprocedure. A procedure from next door.

dgb: So here, in a real material networkof telegraphic transmissions (assembled

for geodetic purposes), lies the wholeschematic of ‘relativistic’ physics: Asyou put it in the book, “simultaneity is aconvention, nothing more than the coordina-tion of clocks by a crossed exchange of electro-magnetic signals, taking into account thetransit time of the signal.” This is physics,but it is also technology at the turn ofthe century. And yet, in a way, Poincaréisn’t the guy who ‘gets’ the physics ofrelativity. Or at least this is how he isusually remembered: He was so close,but he turned away from the more radi-cal interpretation of his thinking, andthe real discovery was left to Einstein,no?

plg: What Poincaré ½rst publishes, inJanuary 1898, is the idea that in principlesimultaneity is nothing other than theexchange of signals between clocks, tak-ing into account the time of transfer be-tween the clocks of the electric signal orof light. It is a philosophical point (pub-lished in the Review of Metaphysics andMorals) that is, on my reading, alsodeeply technological. Between 1898 and1900 he doesn’t apply the scheme to thephysics–he thinks of the correction toNewtonian physics as being too small,just another longitude-½nder’s ½x. Andthe reason that he says it’s just anothererror is because that was how it wasbeing treated by his colleagues in theBureau of Longitude. Then, in late 1900,Poincaré was invited to speak at a gath-ering to honor H. A. Lorentz, perhapsthe leading theoretical physicist of theday, and an innovator in the electrody-namics of moving bodies. He was also anadmired friend of Poincaré’s and a father½gure to Einstein–so Lorentz was alooming ½gure in late nineteenth-centu-ry physics. Poincaré, preparing for thisevent during a period when he was in-volved with the details of the Bureau(and still actively presenting the timecoordination idea to philosophers), sud-




denly sees that he can reinterpret a pure-ly mathematical idea of time in Lor-entz’s physics as a physical coordinationprocedure. In other words, Poincaré looksat the formal way that Lorentz has dealtwith the problem, and he says to him-self: “No! Really, this is just the tele-graph problem that I had written aboutphilosophically two years before!” FromDecember of 1900, Poincaré put thetime coordination procedure into hisphysics. He writes about it, and he lec-tures about the philosophical signi½-cance of the physics of time coordina-tion. So it works out that both Poincaréand Einstein were interested in the prob-lem of the philosophical nature of time,the technical ways in which clocks couldbe set to distribute time, and the physicsof how time should enter the theory ofelectrodynamics of moving bodies.

dgb: Still, physicists and historians ofphysics have spilled much ink on whyPoincaré ‘missed’ being the ½rst to de-velop Einstein’s version of relativity–Poincaré was too conservative, he wastoo much the mathematician. In yourbook you try to put this question aside,and having situated both physicists in abroader story–a story about how simul-taneity was actually produced at the turnof the century, as well as its technicaland cultural resonance–you then returnto their different perspectives in the con-clusion. For there is still a question, isn’tthere? Given that they’re both in thismix that you describe–both preoccu-pied with the “empires of time” in therealms of technology, physics, and evenmetaphysics–how is it that they comeout of it with such different ‘takes’? As Iunderstand it, your answer would haveus put aside the idea that Einstein wasthe ‘modern’ and Poincaré fell ‘behindthe times.’ In fact, you even suggest atone point that we can hold them next to

each other as representatives of “twomodernities.” Would you say a littlemore about this tempting idea?

plg: In the years following 1905, Ein-stein and Poincaré were working onmany of the same problems, both at theabsolute top of the profession, bothmaintaining massive correspondencewith many of the same colleagues andfriends (including Lorentz). Both weredeeply interested in the philosophy ofscience, both were writing on the sidefor popular audiences. These were scien-tists who in many ways were very simi-lar, and yet they did not exchange a sin-gle postcard through the entirety of theirlives–and neither ever even footnotedthe other’s work on space and time. Itputs one in mind of the way that Freudtreated Nietzsche: in some ways theywere too close and too alien at the sametime. It became unbearable for Freud toapproach the work of his predecessor.On special relativity neither Poincarénor Einstein ever argued with the other;they simply acted as if they lived in par-allel but nonintersecting universes. NowPoincaré is often depicted as the reac-tionary who was too backward to absorbfully the radical thoughts of Einstein.That, I believe, is absolutely the wrongway of thinking about it. Both Einsteinand Poincaré were concerned with a newand modern physics and a new andmodern world. Poincaré wrote essaysand gave many lectures about the newmechanics, always emphasizing theenormous novelty of these changes inphysics. It simply is not possible to de-scribe him as simply trying to conserve,to reinstate an older physics. But his ideaof what needed to be changed was dif-ferent. It was not Einstein’s.

dgb: You characterize Poincaré as an‘ameliorist’ at one point.




plg: Yes, I think he is. In another con-text his nephew once said of Poincaréthat he wanted to “½ll in the whitespaces on the maps.” That really gets atsomething important. In much of hiswork, whether it was in mathematics(for instance in his discovery of chaos,where he literally made a new kind ofmap for mathematics, ‘Poincaré maps’),or administration (for instance in hiswork trying to map and track the detailsof a mining accident), or geodetics (forinstance in his directing the surveyorswho were representing the surface of theearth), he was always trying to ½x things,to ½ll things in, with a great faith in sci-ence. He was the ultimate Third Repub-lic French savant–a believer in progress,a believer in using reason to make tech-nical things work, a believer in improv-ing the world and solving its crises.Poincaré saw himself as ‘reforming’ timeto save Lorentz’s extraordinary new the-ory.

dgb: And this comes out of his trainingas an engineer, no? Which is so impor-tant to the way you depict him . . .

plg: Yes, Poincaré’s modernism isexactly the modernism of the progres-sive, late-nineteenth-century engineer–somebody who faced all problems assolvable, from the social and political tothe scienti½c and technical. He evenplayed an important technical role in ab-solving Dreyfus when he reanalyzed the‘proof’ that Dreyfus had authored an in-criminating sheet of paper known as the‘bordereau.’ Poincaré’s modernism fa-vored scienti½c-intuitive understanding(in mathematics as in the physics of theether) and utterly avoided all referenceto the spiritual or mystical. It was a mod-ernism that expected the French to leada rational and ultimately internationalistreformation of all manner of things from

the standard meter on up. As far as Poin-caré was concerned, physics had oftenfaced crises–and in each instance had orcould solve the dif½culty by an applica-tion of a reparative reason. So it waswith space and time. These concepts hadto be ½xed for physics to survive. Poin-caré’s own ideas about changing thetime concept would, he hoped, repairthe theory, just as space had been re-paired by Lorentz’s assumption thatmoving objects contracted in their direc-tion of motion. But Poincaré kept thefundamental distinctions between ‘truetime’ (in the frame of the ether) and ‘ap-parent time’ as measured in any otherframe of reference. And of course hekept the ether–which he thought heneeded for a productive, intuitivephysics. So, for Poincaré, the reinterpre-tation of time was a necessary patch tokeep Lorentz’s theory working, onemore idea in the kit of ideas that would½x the broken engine of physics.

dgb: And Einstein?

plg: Well, Einstein had a different pic-ture of what modern physics should be.Einstein had as his ideal neither a ma-chine on which we would do repairs, nora set of assumptions that would maxi-mize our human convenience in assem-bling a theory. Instead, Einstein aimedfor a reformulation of physics in whichthe order of theory itself would mirrorthe order of the world. If the world ofphenomena showed no observable dis-tinction between frames of referencethen (so Einstein believed) neithershould the theory: a symmetry in thephenomena should show up as a symme-try in the theory. ‘Apparent time’ and‘true time’ were terms he would neverutter. Einstein’s ideal of a physical theo-ry was thermodynamics, which beganwith two simple assumptions: ½rst, that




energy was the same; and second, thatthe disorder of a system, the ‘entropy,’always increased. From these startingpoints you went to town, deriving every-thing else from them. There was (as faras Einstein was concerned) a classicalsimplicity to thermodynamics: its twopillars supporting all the other elementsof the edi½ce. And Einstein wanted, hereand in many of his other works, to buildhis theories out of principles in this way.He too chose two starting assumptionsfor relativity theory: ½rst, any observermoving at a constant speed would havethe same laws of physics; second, thespeed of light is always constant no mat-ter how fast or in what direction thelight source was moving. In order to rec-oncile these two ideas, he argued, it wasnecessary to put basic ideas of space andtime on a defensible and nonarbitraryfooting. So Einstein’s idea of time reallybegins at the beginning of the theory,and is necessary to get off the ground atall–in the service of simplifying, unify-ing, and streamlining the theory. Poin-caré’s theory was differently epistemo-logical, less concerned with “What canwe know of an external Nature, and howcan we secure that knowledge?” thanwith his aim of ½xing the theory suchthat it correctly predicted phenomenawhile maximizing convenience. Poin-caré’s modernism aimed at an aggressiveprogram of technical repair; Einstein’sat a purifying reformulation. Poincaréfastened on simplicity-for-us, assiduous-ly avoiding reference beyond the human.Einstein’s modernism aimed for a kindof depth, a matching between represen-tation and the world not just in predic-tions but deeper in the theory itself. Ein-stein, after all, in his later years loved totalk about how much choice God had atthe beginning of the universe (not a per-sonal God but an underlying order).Poincaré never even grazed that kind ofmetaphysics. All that said, it would be

gross distortion to treat Poincaré as areactionary or a failed Einstein. Themodernism of Picasso is not the mod-ernism of Pollock; and to force the verydifferent breaks with the past into a sin-gle line of progression is to lose sight ofhistory.

dgb: The irony here is that, far frombeing the wild-haired radical, Einstein isrevealed to be, if anything, deeply ‘clas-sical’ in his conception of physics.

plg: Well, in some ways, Einstein is themost classical of classical physicists. Heis somebody who saw himself in a wayas purifying, simplifying, symmetriz-ing–bringing out elements of a lessbaroque physics. There are many mo-ments, famous moments, in his career,when he objects to the way physics hasturned–notably in quantum mechanics.By exploring the relationships of classi-cal physics, by deepening them, and byconnecting different domains of thoughtpreviously held to be disjunct, Einstein, Ibelieve, saw himself as a kind of radicalclassicist.

dgb: And yet he was, perhaps despitehimself, a kind of time bomb in thatclassical tradition.

plg: I think here that Einstein’s extraor-dinary apology to Newton–where Ein-stein writes, in this odd and intimateway, “Newton, verzeih’ mir’”–is, in asense, his coming to terms with the factthat in his pursuit of this purifying clas-sical vision he disrupted it. In a way it isa note to himself–a note about his ownlife trajectory, a note on the transforma-tion that resulted from an attempt todeepen and streamline a classical vision.

dgb: One reading of your book wouldbe that you think you have discovered




the ‘smoking gun’ for this very transfor-mation, the smoking gun for nothingless than the theory of relativity itself:Einstein is at his patent desk, looking atdiagrams of electromechanical networksfor time distribution along railway lines.“Eureka!” he shouts, and he sits down todemolish the idea of absolute time andspace. I know that you don’t care for thisreading, and you don’t think this is yourstory, but it will be tempting for manyreaders . . .

plg: It is absolutely not how I think ofthe problem–not for Poincaré, not forEinstein. Almost all of my work stemsfrom a concern with the strange juxtapo-sition of the very abstract and the veryconcrete. This is not a question that is byany means restricted to physics, but phy-sics makes it abruptly clear how sudden-ly we pass from symbols to materiality.In Einstein’s Clocks, Poincaré’s Maps I wantto get away from two widespread ideas:½rst, a notion that science proceeds by akind of Platonic ascension, an evapora-tive or sublimating process that takes thematerial into the abstract. Material rela-tions do not eject ideas or produce ideaslike ripples on the surface of deep-flow-ing currents. And here coordinatedclocks did not cause Einstein to introducethe synchronizing procedure. Telegraph-ic longitude mapping did not force Poin-caré to the simultaneity procedure. Con-versely, physics does not advance bypure condensation–it would be a terri-ble distortion to see physics beginning ina realm of pure ideas, and then graduallyacquiring the weight of materiality untilthey stand in corporeal form as the ob-jects of everyday life. So the reason that I½nd this moment of late-nineteenth andearly-twentieth-century contemplationof time so interesting is that it representsneither of these unilateral directions(concrete-to-abstract or abstract-to-con-

crete). Instead there is an extraordinaryoscillation back and forth between ab-straction and concreteness. I like thismix–this high-pressure interaction ofmaterial technologies, philosophy, andphysics. Each was in play, in differentways, and ‘simultaneity’ was at stake ineach domain: in Lorentz’s mathematical‘local time,’ in the technological ex-change of time signals, in the philosoph-ical critique of absolute time. In theirown ways, Poincaré and Einstein werereading philosophy, working at techno-logical projects, grappling with electro-dynamics. Einstein certainly knewpieces of what Poincaré had done (howmuch and exactly when is a longer sto-ry). Then came Poincaré’s moment inDecember 1900 (and Einstein’s in May1905) when a statement about what si-multaneity is suddenly participated in allthree arcs–the crossing point.

dgb: Technology, metaphysics, physics.

plg: What interests me about this storyis precisely that you can’t start to tell it ifyou think that it’s all on one scale, or allis really grounded in only one of thesedomains. Or rather you see very limitedpieces of it while vast blocks of the storybecome unmotivated, even incompre-hensible. So if you tell the story of timecoordination as a pure history of ideasthen Poincaré’s references to telegraphyand telegraphic longitude remain . . .

dgb: incoherent . . .

plg: Incoherent, or, more precisely, theyappear as fully abstract thought experi-ments, with the subject (the ground ofthe metaphor) chosen arbitrarily. Butwhat is interesting to me about it is thatas you start to tell the story, no matterwhere you start–and in some ways youhave a choice about where to begin–you




need the other levels. Otherwise thestory contains arbitrary elements: Why,for example, is Poincaré publishingabout the same procedure for coordinat-ing time in a journal of philosophy ofmetaphysics and morals, in the Annalsof the Bureau of Longitude, and in thephysics publications? I think that thevery quick back and forth between scalesactually points to a dimensionality ofhistory that simply is wiped out if youtry to narrate it from a single line. This isa theme of my work, that the metaphori-cal and the literal are inextricable: thatthe literal is always referring outwardsmetaphorically and the metaphoricalflickers back into the literal. Askingabout the history of physics leads atsome key moments both to very materi-al circumstances and to the ethereal lay-ers of metaphysics as well. In the book, Iam constantly trying to avoid the histo-riography of both sublimation and con-densation. Instead, I ½nd a peculiar stateof vapor and water known as ‘criticalopalescence’ to be a better metaphor forthe relationship between the abstractand the concrete. For under particularpressure and temperature, vapor flashesback into liquid and liquid into vapor atevery scale, from a few molecules to thewhole system. The light that we shine onthe opalescent mixture reflects back inevery color, at every scale. In the latenineteenth century synchronized timewas more like that: debates over syn-chronizing time–debates over the con-ventionality of time itself–took place atthe scale of buildings, blocks, cities,countries, and the planet, while at thesame time arguments came fast and furi-ous about the philosophical and physicalbasis of time. What I wanted to know–very speci½cally–was how a simpleproposition, “time–simultaneity–isnothing other than the coordination ofclocks, taking into account the electrical

signal-time between them,” could func-tion jointly in this multiplicity of trajec-tories: physics, metaphysics, technology.

dgb: Where somebody was actuallymaking that notion real by creating syn-chronized zones, by creating coordinat-ed clocks, even as the same propositionwas transforming our understanding ofthe physical world, and, perhaps, ourplace in it.

plg: Exactly. In 1899, Poincaré was ar-guing with Greenwich astronomersabout how to get their astronomicalclocks synchronized, giving a lecture inwhich he reinterpreted Lorentz’s timeconcept, and presenting to the philoso-phers his arguments against absolutespace and time. All of this occurred es-sentially at once–no one domain drovethe others. Precisely the simultaneity ofall this presents the historian with twogreat challenges. One is to show how thedomains come together. But the other isto exhibit the quasi-stability of each ofthese discourses, games, or traditions.

dgb: And to do this we must, as you say,“look up to see down, and down to seeup.”

plg: The juxtapositions, the links–allthis is historical. It is now a commonplacefor string theorists to think of physicsand algebraic geometry ‘going together’;twenty-½ve years ago that wasn’t obvi-ous at all. For those turn-of-the-centurydecades it made perfect sense to minglemachines and metaphysics. For us,perhaps, the nearness of things andthoughts seems to have vanished, atleast where time is concerned. WhenPoincaré and Einstein looked into thedetails of electrical engineering, whenthey stared at generators, radios, andcables, they saw in them critical prob-




lems of physics and philosophy. Con-versely, they could hardly considerphilosophical questions of time andspace without asking about central fea-tures of physics–or technology.

dgb: With hindsight, we will surely dis-cover that we now have our own “philo-sophical machines.” It is tempting to saythat the computer is for us what theclock was for much of the history of sci-ence: a machine to think with.

plg: Moments of critical opalescence inthe history of science–moments when ahuge variety of scales are implicated–are not frequent. But the development ofthe modern computer is such a moment–as was the late-nineteenth-centurydeployment of synchronized clocks. Itsimply isn’t possible to tell the story ofinformation theory, for example, with-out invoking the history of computation.Conversely, there can be no coherenthistory of electronic computation with-out showing in detail how the hardwarestory crossed with the development oftheories of information–or theories ofbrain function.

dgb: But let’s pull back for a moment.How does the story you tell in this book½t with larger narratives in the history ofclocks and timekeeping? Is Einstein’srelativistic time ‘just’ time? Is it the apo-theosis of the classic history of technolo-gy story about time, that wonderfulstory of progressive human efforts topush time up out of the dirt and thegrass, the pulse of the blood and the or-ganic cycles of days and seasons, and tocreate instead an abstract, disembodied,‘pure’ time–a flowing that would bemonitored with fantastically precisedevices, devices so precise that theywould become critical tools of investiga-tion of nature, and reveal and measure,

through time, the myriad quirks andwobbles of the cosmos? With Einstein’stime, perhaps, that abstraction outreach-es itself, in a way, and collapses backonto us, onto the earth, onto the contin-gencies of here and there. Does thatmake sense?

plg: You can tell that story of the earlierphysics of time, as you suggest: Timepassed from a world in which the sublu-nary sphere was thought of as corruptand material to another realm, beyondthe superlunary, to the inaccessiblereaches of Newton’s pure, mathematicaltime. The story of the late nineteenthcentury, though, is one in which the ab-straction and concreteness of time areboth present. Conventionalizing timethrough the exchange of signals forcedthe made-ness of time into the domainof the visible: time zones imprinted thetechnical fabrication of simultaneity ineveryday life. Physicists, philosophers,psychologists, astronomers–all weredebating how to make time, how to mea-sure it precisely and ship it from place toplace. As Poincaré and Einstein insertedtechnical, engineered time into the phy-sics of electrodynamics, they very delib-erately set aside reference to Newtonianabsolutes. They brought the abstractinto the concrete–not by jettisoning therealm of the ideas for the sun and sea-sons, but by joining the material to theabstract. We could say that the moderni-ty of time is made visible by the absenceof time-in-itself, by the absence of time-as-absolute.

dgb: In a way, that traditional history oftime and timekeeping, particularly ascultivated by historians of science andtechnology, has been a story of the ‘de-mythologizing’ of time. Sure, peoplewent on using time imagery for didacticor symbolic functions–from vanitas




paintings of skulls to devotional hour-glasses. But the history of time in sci-ence and technology has been the storyof abstracting that pure and preciselymetered flow from such accretions of‘meaning.’ And yet, the products of suchprogressive puri½cations are alwaysthemselves reintegrated into the realmof human meaning-making. For in-stance, the emerging concept of ‘geolog-ical time’ in the eighteenth and nine-teenth centuries rapidly came to be en-tangled with systematic theology anddeist notions of natural law–were rocksa particular lesson in eternity? This sortof endless ‘folding’ between science andsigni½cation makes me wonder: Wasthere–is there–a didactic or symbolicsigni½cance in Einstein’s time?

plg: You might approach this in twoways. One would be to look at the speci-½city of the way Einstein and his physi-cist interlocutors treated time, and theother would be to explore how time wastaken up in the wider cultural sphere.For example, Einstein was very amusedby the ‘twin paradox’ in which one twintravels out and back at relativistic speedsand ends up much younger than his stay-at-home sibling (he called this “thething at its funniest”). But Einstein’sheart was always elsewhere–his real in-vestment was in the invariants he found(for example, the absolute speed of light,or the identity of the laws of physics forall inertial reference frame observers).He was consistently more interested inthese aspects of the theory than he wasin the differing perspectives of each ob-server on space and time. But clearly thewider public was, and has remained, fas-cinated precisely with the relativity oftime. From jokes to art and ethics, Ein-stein has been invoked to justify thetenet that the most basic of conceptswere ‘just relative.’

dgb: And yet–and this is so easy for thelay reader to overlook–‘relativity’ ispredicated on a cosmic and universalabsolute.

plg: Indeed–there is a great irony heresince Einstein referred to his work as‘Invariant Theory’ until he could nolonger buck the worldwide trend tolabel it ‘Relativity Theory.’

dgb: So while the public seized on therelativity of time, what did physiciststake from Einstein’s intervention?

plg: The critical gaze that Einstein caston the notion of time promptly putother concepts under the microscope.Einstein had made time and simultane-ity stand with, not behind, experienceand procedure. Now physicists wantedto know how this rebuilding of a con-cept could be extended into quantumtheory: What was causality? What did itmean for a particle to have a momentumand a position? Over the decades thatfollowed, physical concepts fell one afteranother from a priori metaphysicalheights to the ground where they (cou-pled to other concepts) met experimen-tal inquiry. Time invariance–that amovie of the physical world should beplayable backwards and forwards–wasnot, it seemed, the rule of a priori law.Nor was parity invariance (that the mir-ror reflection of phenomena shouldalways be physically possible). Nowfrom a distant philosophical perspectiveone might say that the criticism ofcausality, for example, was even moredramatic than Einstein’s and Poincaré’scritique of Newtonian absolute time.But the critique of time came ½rst, andin a deep and abiding sense it guided therebuilding of physical knowledge forgenerations after 1905. This, I believe, isbecause the reformation of time was not




just a change in a particular doctrine(“time is better measured this way thanthat way”). At stake was what it meantto have a physical concept at all.

dgb: And at stake too was how onegains access to such a concept, no? Since‘abstraction’–or, as you call it, ‘sublima-tion’–is not merely a way to tell histori-cal stories; it is also a way to think aboutnature, it is a way to think about whatscience itself is and how it should bedone. And yet Einstein’s pursuit of timeleads to a simultaneous apotheosis andinversion in the larger history of time inscience and technology. His is an exer-cise in abstraction that is also, improba-bly, a kind of rei½cation.

plg: Understanding the history of timealways involves examining exactly thatrelationship between the abstract andthe concrete, and, for Einstein, under-standing time itself demanded this aswell. What I ½nd so remarkable aboutthe ½n de siècle is that not just in relativ-ity theory, but in the whole cultural sur-round, the categories of time and spaceexhibit a kind of abstract concreteness(or concrete abstraction). When theFrench ½nally persuaded the interna-tional community to ‘sanction’ themeter in 1889, they held an elaborate cer-emony, and a ritualized ‘burial’ of thestandard. At the moment the assembleddignitaries and scientists sealed theiridium-platinum rod in its triple-lockedchamber (and shared out the keys), thisprecisely engineered rod rose to become‘M’–the object that could measure butnot be measured. Practical? Of course;industrialists desperately needed a refer-ence meter. But symbolic? How couldone say no?

dgb: When people start playing withabsolutes, when they start to conjure

them–they do, we do, the strangestthings. It takes strange activity to bringabsolutes into the contingencies andlocalities of human life. You can be surethat people are going to start makingsome very unusual gestures, and bringout keys and locks and boxes and burythings in the ground and make funnynoises . . .

plg: And particularly in the Third Re-public, where religious iconology mor-phed into scienti½c-technical procedure.Time, too, was similarly concrete-abstract. In the 1890s, for example, Poin-caré joined a commission on the deci-malization of time. On one reading, thiswas entirely a practical affair–railroadadministrators argued passionately forthe simplicity that 9.56 or 22.34 o’clockwould afford by allowing travelers to cal-culate time differences by simple sub-traction. On another, though, it was en-tirely symbolic: a reanimation of thedream of rationality so passionately ad-vocated during the French Revolutionand brought to international promi-nence through the Convention of theMeter in the 1880s. Reflections on timeare so often like this–practical and morethan practical, utterly utilitarian andhighly symbolic.

dgb: Hence, the practical utility, forNewton, of a ‘physics time’ that lived in,of all places, the Sensorium of God. Talkabout practical and more than practical!But I still wonder: Did Einstein andPoincaré bring time back to earth? Re-move it from the realm of ½rst and ½nalthings?

plg: Yes and no. True, they grasp timefrom the domain of the pure absolute.True, they rope it into procedure of elec-tro-chronological coordination. But theysurely do not sever time from its wide




and deep bonds with modernity. Bothscientists’ writings on the ‘new mechan-ics’ (with its non-absolute time) werewidely read by artists, philosophers, andwriters. Both–though in different ways–saw the relativity of time as a funda-mental piece of the new physics.

dgb: The meaning of the clock wouldnever be the same.

plg: And yet, of course, clocks havenever been just gears and pointers. Somewere mounted in late-medieval towers,establishing dominion of property andfaith. In paintings they stood as harbin-gers of death. By the late nineteenth cen-tury, mounted in factories, observato-ries, and trading rooms, they stood forthe modern ambitions of regulated life,precision-mapped territory, and the in-stantaneity of contemporary life. It isagainst this seven-hundred-year clockhistory that relativity entered, and whenit did, there were certain to be no smalleffects.

dgb: ‘Grand narrative’ historians havelong talked about the conflict between‘church time’ and ‘merchant time’ in thelate-medieval period: the steeple clockversus the factory clock. On the onehand the time of God, on the other thetime of labor and money. Your story ofEinstein and Poincaré, of clocks andmaps in the ½n de siècle, could be read–playfully, I admit–as the ½nal con-frontation of these two chronometriesof European civilization: in 1905 theSensorium of God gets tied to the tracksof railway time . . .

plg: But modernity is not–or perhapsshould I say ‘not just’–a train wreck! In-stead, what we see in this story is thatthe great metaphors of time–trains andmaps–chosen by Einstein and Poincaréare both the most imaginative of allthought experiments, and, at the sametime, the most everyday technologies ofthe modern world.




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