This is the text of "Einstein, Poincaré &
Modernity: a Conversation,"
by Peter L. Galison & D. Graham Burnett, from Daedalus
The dialogue is based on Galison's book Einstein's
Clocks, Poincaré's Maps (2003).
Newton, forgive me . . .
–Albert Einstein, Autobiographical Notes
D. GRAHAM BURNETT: Peter, in 1997 you gave a plenary
session lecture at the History of Science Society meeting in La
Jolla entitled "Relentless Historicism: Machines and Metaphysics."
I have a vivid memory of the presentation, which was, I think, the
first time you shared with the wider community of historians and
philosophers of science your research on Einstein, relativity, and
the material culture of time in the fin de siècle. And you
turned a lot of heads. Your argument went something like this: At
the heart of Einstein's watershed 1905 paper on special relativity
- the paper that shook the foundations of Newtonian physics - lies
a "thought experiment' about clock synchronization and the "problem"
of simultaneity; there, talking about trains arriving in stations
and observers watching their watches, Einstein posed what turn out
to be insurmountable challenges to Newton's notion of absolute time
(and absolute space). This we knew. But then the talk got juicy:
you went on to point out that this thought experiment might not
be merely a thought experiment, since the business of synchronizing
time frames through space was more than just abstruse theoretical
physics in the late nineteenth and early twentieth centuries. It
was a perfectly real, quotidian, and central preoccupation of railway
companies, nation-states, and military planners. The increasing
speed of railway travel in the second half of the nineteenth century
had made it necessary to codify "time zones" around the world -
zones of conventionalized simultaneity, where people would ignore
local time (say, the "noon" of the sun), and go by the noon on their
clocks: a subtle change, but an important one, since it put people
across the globe in temporal step. There was no other way to run
a railroad. Moreover, the design and manufacture of electrotechnical
systems that "distributed" this new coordinated time - networks
of clocks running in sync - was a major precision industry. Looked
at in the right way, Einstein's thought experiment bore an uncanny
resemblance to a set of wholly practical experiments going on all
around him - even under his very nose, as he earned his living in
the Berne Patent Office reviewing exactly these sorts of time distribution
devices. That day in La Jolla you left us with a question: Could
we really understand Einstein's 1905 paper without understanding
the rise of international time conventions and the technologies
of industrial time - synchronization? Now you have written a book,
Einstein's Clocks, Poincaré's Maps: Empires of Time,
which delivers on this question and expands your original insight.
For readers to whom all this is new, would you start by describing
how trains and clocks figure in Einstein's landmark publication?
PETER L. GALISON: Certainly. Perhaps the greatest
success of nineteenth-century physics was the prediction (and subsequent
demonstration) of the existence of "electric waves." Light was nothing
other than such a wave. Suddenly the ancient science of optics became
no more than a subfield of electromagnetism. At the same time, this
thrilling finding brought with it a puzzle: Physicists of the late
nineteenth century, very reasonably, thought that a wave had to
be a wave in something. After all, waves at the beach are
waves in water, sound waves are waves in air, and so on. But light
could travel in a vacuum - that is, apparently through empty space.
This led most everyone to suppose that there had to be a special
all - pervading (and as yet undiscovered) substance - the "ether"
- permeating everything, everywhere, present even in a vacuum. But
experimentalists had no luck finding this elusive medium. Einstein's
famous 1905 paper on relativity begins here. Generalizing from failed
attempts to "see" the ether (or, more correctly, to see any evidence
that the earth was moving "through" it), Einstein decided to scrap
the ether altogether, and to go after the problem of the propagation
of light in a different way. First, he stipulated that all the
laws of physics - including electricity and magnetism - were the
same in any constantly moving frame of reference. Then he added
a seemingly simple (and modest) second assumption: Light travels
at the same speed no matter how fast its source is moving. To anyone
thinking of ether this was not so strange: Move your hands at any
reasonable speed through a room of still air; once you clap your
hands the sound waves propagate through the room at the same speed
- independent of the original motion of your hands. Maybe light
was like that: a lamp moving in the ether simply excited light waves
that radiated out at a single speed independent of the motion of
the lamp. Yet these two reasonable starting assumptions appeared
to contradict one another. Suppose lamps were flying this way and
that at various speeds, but that in some frame the light beams from
those lamps were all traveling at 186,000 miles per second, just
the speed predicted by the equations of electrodynamics. Wouldn't
those same beams of light appear to be traveling at different
speeds when seen from a different, moving frame of reference?
If that was so, then the equations of electrodynamics would only
be valid in one frame of reference, violating Einstein's first principle.
It was to resolve this apparent contradiction that Einstein made
his single most dramatic move: he criticized the very idea of time
as it was usually understood. In particular, he relentlessly pursued
the meaning of "simultaneity." Only by criticizing the foundational
notions of time and space could one bring the pieces of the theory
- that the laws of physics were the same in all constantly moving
frames; that light traveled at the same speed regardless of its
source - into harmony. And this is where the trains and clocks enter.
Suppose, Einstein reasoned, that you wanted to know what time a
train arrived in a train station. Easy enough: you see where the
hand of your watch is at the time the engine pulls up alongside
you. But what if you wanted to know when a train was pulling into
a distant station? How do you know whether an event here
is simultaneous with an event there? Einstein insisted that we need
a simultaneity - fixing procedure, a definite system of exchanging
signals between the stations that would take into account the time
it took for the signal to get from one station to another. By pursuing
this insight, Einstein discovered that two events that were simultaneous
in one frame of reference would not be simultaneous in another.
Moreover, since a length measurement involves determining the position
of the front and back of an object at the same time, the
relativity of simultaneity meant that length was relative
as well. By removing the absolutes of space and time, Einstein restructured
DGB: So what was at stake here was not only the
universal ether, the substrate of the cosmos, but also time
- that absolute, ever - unrolling, eternally immutable flowing,
the Platonic time of which all worldly clocks were mere dilapidations.
It was this time that Newton had understood was a necessary condition
of his physics, and that he had placed beyond the realm of merely
human investigation; it flowed in the "Sensorium of God."
PLG: Just by demanding a conventional clock-and-signal
based procedure to fix simultaneity, Einstein was breaking
with the Newtonian idea of time. For Newton, there was absolute,
true, mathematical time that ticked ever - constantly the same way
for all observers. Clocks - all kinds - were only pale reflections,
approximations to this metaphysical temporality. But Einstein's
departure from Newtonian time went further, since once Einstein's
starting points are accepted dramatic consequences follow. For instance,
if a train travels through our station and the engineer and caboose
driver flash their lanterns towards the center of the train (at
what we in the station judge to be simultaneous moments), we can
ask what happens in the train. We on the station platform say: The
mid-train conductor moves towards the site where the engine
driver had flashed his lantern and away from the site where
the caboose tender had flashed her lamp. So (say we station-based
observers) the middle conductor receives the engine flash first.
Since by assumption the middle conductor measures the two flashes
as moving at equal velocities from equally separated points of origin,
he concludes - as night follows day - that the two flashes were
not sent simultaneously. So the two flashes that were simultaneous
in the station frame are not simultaneous in the moving
one. Simultaneity is relative to a frame of reference; it is not
absolute. From an apparently prosaic starting point about clocks,
trains, and light signals, Einstein had smashed one of the very
centerpieces of classical physics.
DGB: This is perhaps the Einstein of myth and
legend, the knight-errant in the borderlands of metaphysics who
slays the last chimera of the crystalline spheres. A searcher in
the realm of pure mind, he reconnoiters the Sensorium of God and
finds it empty. But this image, you would remind us, is a distortion
of Einstein's character, of what he thought he had done, and of
his approach to problems as well, no?
PLG: Einstein, without any doubt, is the best-known
scientist ever, and he occupies an astonishingly robust cultural
place. He doesn't seem to come into and fall out of fashion as much
as he is simply appropriated for new purposes with each generation.
But one of the perennial features of Einstein-the-icon is the figure
of the great mind living in a world apart, the ultimate loner. No
doubt Einstein himself is in some measure responsible for this image,
since, in later life, he reflected nostalgically on solitude, isolation,
and creativity. For instance, he wrote wistfully of the lighthouse
attendant, whose world could be that of undistracted thought. So
we think of him as the person who could not quite navigate the physical
world, and associate that incapacity with a romantic picture of
scientific genius. This in turn leads to an odd rewriting of the
way he lived his life and did his work.
DGB: Was the patent office Einstein's "lighthouse"?
PLG: This has generally been the story - Einstein
at the patent office is the genius at his day job: at best a source
of bread and butter, at worst a distraction, but in some deep way
irrelevant to understanding his science.
DGB: When did you begin to get a different idea
of how the story might be told?
PLG: I was standing at a train station in northern
Europe admiring a line of clocks that went along the platform. And
I noticed that the minute hands were all at the same point - I could
just see them all lined up. I thought, "These are wonderful clocks;
isn't that impressive that they can make them to hold such regularity?"
Then I noticed that the second hands were clicking in synchrony
too, which was startling, and I thought, "These can't be that accurate
- you can't have clocks running like this that are not synchronized
in some way, or else they'd get out of phase." Suddenly I wondered
if Einstein had paid attention to synchronized clocks in train stations.
If he had it would give a very tangible sense to that most famous
of all scientific thought experiments in his 1905 paper. It would
make his move towards a criticism of absolute time both figurative
and literal. So I went back and I started poking around
- and found myself in the midst of an absolutely immense literature
on fin-de-siècle timekeeping and clocks. As you know, there
was at the time an urgent technological problem of coordinating
time along train tracks. More than that: in Europe the center of
precision-coordinated timekeeping was Switzerland, and if all this
industry was based in Switzerland they must have been processing
patents right and left. I went to the patent office, and found myself
surrounded by a huge number of patents with diagrams of clocks linked
by signals. There were even proposals for patents and articles in
the technical journals about clocks linked by radio waves. All this
seemed extremely close to the kind of materialization of time that
preoccupied Einstein. Of course, the clock factories and inventors
had no interest in "frames of reference" or in all the "physics
of the ether." But the importance of distributing simultaneity by
electromagnetic means was clear to everyone. Here was a technical
problem located in Switzerland, centered in Berne, and with ideas
coming to a point in Einstein's patent office. It all seemed remarkable;
and it is there that I began this work.
DGB: And yet Einstein certainly wasn't the only
physicist at the turn of the century preoccupied with time ...
PLG: Not at all. In fact, even as I worked on
"Einstein in the Patent Office" (and prepared the paper you mentioned),
I kept wondering, "Who else would have, should have, been in this
mix? And who else from the physics community would have been concerned
with ideas of simultaneity?" There is one other person who cared
about simultaneity at least as much as Einstein - and earlier -
and that was Henri Poincaré. He certainly saw that clock
coordination was essential for defining what we mean by simultaneity.
DGB: Einstein may be a household name, but the
same cannot be said for Poincaré.
PLG: I suppose household name, like time and simultaneity,
is a relative concept. In France, Poincaré has long been
a hero. Known for his innovations in the qualitative studies of
chaotic systems, for his invention of the mathematical theory of
topology, for his contributions to mathematical physics, and for
his philosophy of conventionalism, Poincaré was without any
question the most renowned French scientist of the late nineteenth
and early twentieth century. And that, in France, meant he was an
extraordinarily visible figure whose books about science, philosophy,
and morality were best-sellers. He also wrote dramatically and often
about the new theory of relativity to which he contributed importantly.
Crucially for our understanding of his ideas of simultaneity, Poincaré
was, beginning in the early 1890s, deeply involved in time-distribution
DGB: At the Bureau des Longitudes?
PLG: Yes, where he would serve several terms as
president. And this was crucial, because the astronomers and geographers
of the Bureau were working intensively with the telegraphic transmission
of time. This was not for domestic railroad use - or at least not
in the first instance. Rather, these engineers and scientists were
working at a much higher level of precision. They needed to determine
simultaneity so distant observers could determine their relative
DGB: For cartographic purposes, since longitude
measurements are measurements of time?1
PLG: Precisely. Their goal was to map the nation,
the empire, and then much of the world. Specifically, they aimed
to find points of reference - for instance, in North Africa, Senegal,
Ecuador, and Vietnam - from which the further mapping of the interiors
could proceed. Maps were important for extraction of ores, for military
domination, for the cutting of roads, and the laying of railroad
lines. Railroad lines brought in more cable, and therefore more
mapping, and so on. All of this constituted a major technical program,
a great national moment. And the timing is fascinating. Poincaré
really became a public figure starting in 1887 or so. And by 1892
he was involved with the Bureau of Longitude, where he tackled problems
of time conventions - from the decimalization of the hour to reconciling
the longitude of the Paris and Greenwich observatories. I remember
staring at these reports from the 1890s, trying to figure out what
the Bureau's telegraphic time-finders were doing, and expecting
that I'd find that - as in the case of Einstein's patent office
- the fixing of simultaneity was a fairly crude affair. But this
work was anything but crude! Instead, I saw that by the 1890s it
was altogether routine for the astronomer-engineers to take
into account the time the electrical signal took to go from one
place to another. That, I thought - I had assumed - was exclusively
a preoccupation of physicists and their "relativity." But it turned
out that Poincaré's colleagues at the Bureau were precisely
worried about this, and their concern is plain as day once you look
at their data. Columns in the official reports are labeled: "time
of transmission." The engineers even sent their time signals on
round-trips to compensate for errors. The more I looked at it, the
more specific the connections seemed. So in January 1898, when Poincaré
wrote his famous philosophical article "The Measure of Time," introducing
the simultaneity convention via the metaphor of telegraphic longitude
finders, he had in mind an abstraction but also a concrete procedure.
A procedure from next door.
DGB: So here, in a real material network of telegraphic
transmissions (assembled for geodetic purposes), lies the whole
schematic of "relativistic" physics: As you put it in the book,
"simultaneity is a convention, nothing more than the coordination
of clocks by a crossed exchange of electromagnetic signals, taking
into account the transit time of the signal." This is physics,
but it is also technology at the turn of the century. And yet, in
a way, Poincaré isn't the guy who "gets" the physics of relativity.
Or at least this is how he is usually remembered: He was so close,
but he turned away from the more radical interpretation of his thinking,
and the real discovery was left to Einstein, no?
PLG: What Poincaré first publishes, in
January 1898, is the idea that in principle simultaneity is nothing
other than the exchange of signals between clocks, taking into account
the time of transfer between the clocks of the electric signal or
of light. It is a philosophical point (published in the Review
of Metaphysics and Morals) that is, on my reading, also deeply
technological. Between 1898 and 1900 he doesn't apply the scheme
to the physics - he thinks of the correction to Newtonian physics
as being too small, just another longitude-finder's fix. And the
reason that he says it's just another error is because that was
how it was being treated by his colleagues in the Bureau of Longitude.
Then, in late 1900, Poincaré was invited to speak at a gathering
to honor H. A. Lorentz, perhaps the leading theoretical physicist
of the day, and an innovator in the electrodynamics of moving bodies.
He was also an admired friend of Poincaré's and a father
figure to Einstein - so Lorentz was a looming figure in late nineteenth-century
physics. Poincaré, preparing for this event during a period
when he was involved with the details of the Bureau (and still actively
presenting the time coordination idea to philosophers), suddenly
sees that he can reinterpret a purely mathematical idea of time
in Lorentz's physics as a physical coordination procedure. In
other words, Poincaré looks at the formal way that Lorentz
has dealt with the problem, and he says to himself: "No! Really,
this is just the telegraph problem that I had written about philosophically
two years before!" From December of 1900, Poincaré put the
time coordination procedure into his physics. He writes
about it, and he lectures about the philosophical significance of
the physics of time coordination. So it works out that both Poincaré
and Einstein were interested in the problem of the philosophical
nature of time, the technical ways in which clocks could be set
to distribute time, and the physics of how time should enter the
theory of electrodynamics of moving bodies.
DGB: Still, physicists and historians of physics
have spilled much ink on why Poincaré "missed" being the
first to develop Einstein's version of relativity - Poincaré
was too conservative, he was too much the mathematician. In your
book you try to put this question aside, and having situated both
physicists in a broader story - a story about how simultaneity was
actually produced at the turn of the century, as well as
its technical and cultural resonance - you then return to their
different perspectives in the conclusion. For there is still a question,
isn't there? Given that they're both in this mix that you describe
- both preoccupied with the "empires of time" in the realms of technology,
physics, and even metaphysics - how is it that they come out of
it with such different "takes"? As I understand it, your answer
would have us put aside the idea that Einstein was the "modern"
and Poincaré fell "behind the times." In fact, you even suggest
at one point that we can hold them next to each other as representatives
of "two modernities." Would you say a little more about this tempting
PLG: In the years following 1905, Einstein and
Poincaré were working on many of the same problems, both
at the absolute top of the profession, both maintaining massive
correspondence with many of the same colleagues and friends (including
Lorentz). Both were deeply interested in the philosophy of science,
both were writing on the side for popular audiences. These were
scientists who in many ways were very similar, and yet they did
not exchange a single postcard through the entirety of their lives
- and neither ever even footnoted the other's work on space and
time. It puts one in mind of the way that Freud treated Nietzsche:
in some ways they were too close and too alien at the same time.
It became unbearable for Freud to approach the work of his predecessor.
On special relativity neither Poincaré nor Einstein ever
argued with the other; they simply acted as if they lived in parallel
but nonintersecting universes. Now Poincaré is often depicted
as the reactionary who was too backward to absorb fully the radical
thoughts of Einstein. That, I believe, is absolutely the wrong way
of thinking about it. Both Einstein and Poincaré were concerned
with a new and modern physics and a new and modern world. Poincaré
wrote essays and gave many lectures about the new mechanics, always
emphasizing the enormous novelty of these changes in physics. It
simply is not possible to describe him as simply trying to conserve,
to reinstate an older physics. But his idea of what needed to be
changed was different. It was not Einstein's.
DGB: You characterize Poincaré as an "ameliorist"
at one point.
PLG: Yes, I think he is. In another context his
nephew once said of Poincaré that he wanted to "fill in the
white spaces on the maps." That really gets at something important.
In much of his work, whether it was in mathematics (for instance
in his discovery of chaos, where he literally made a new kind of
map for mathematics, "Poincaré maps"), or administration
(for instance in his work trying to map and track the details of
a mining accident), or geodetics (for instance in his directing
the surveyors who were representing the surface of the earth), he
was always trying to fix things, to fill things in, with a great
faith in science. He was the ultimate Third Republic French savant
- a believer in progress, a believer in using reason to make technical
things work, a believer in improving the world and solving its crises.
Poincaré saw himself as "reforming" time to save Lorentz's
extraordinary new theory.
DGB: And this comes out of his training as an
engineer, no? Which is so important to the way you depict him...
PLG: Yes, Poincaré's modernism is exactly
the modernism of the progressive, late-nineteenth-century engineer
- somebody who faced all problems as solvable, from the social and
political to the scientific and technical. He even played an important
technical role in absolving Dreyfus when he reanalyzed
the "proof" that Dreyfus had authored an incriminating sheet of
paper known as the "bordereau." Poincaré's modernism favored
scientific-intuitive understanding (in mathematics as in the physics
of the ether) and utterly avoided all reference to the spiritual
or mystical. It was a modernism that expected the French to lead
a rational and ultimately internationalist reformation of all manner
of things from the standard meter on up. As far as Poincaré
was concerned, physics had often faced crises - and in each instance
had or could solve the difficulty by an application of a reparative
reason. So it was with space and time. These concepts had to be
fixed for physics to survive. Poincaré's own ideas about
changing the time concept would, he hoped, repair the theory, just
as space had been repaired by Lorentz's assumption that moving objects
contracted in their direction of motion. But Poincaré kept
the fundamental distinctions between "true time" (in the frame of
the ether) and "apparent time" as measured in any other frame of
reference. And of course he kept the ether - which he thought he
needed for a productive, intuitive physics. So, for Poincaré,
the reinterpretation of time was a necessary patch to keep Lorentz's
theory working, one more idea in the kit of ideas that would fix
the broken engine of physics.
DGB: And Einstein?
PLG: Well, Einstein had a different picture of
what modern physics should be. Einstein had as his ideal neither
a machine on which we would do repairs, nor a set of assumptions
that would maximize our human convenience in assembling a theory.
Instead, Einstein aimed for a reformulation of physics in which
the order of theory itself would mirror the order of the world.
If the world of phenomena showed no observable distinction between
frames of reference then (so Einstein believed) neither should the
theory: a symmetry in the phenomena should show up as a symmetry
in the theory. "Apparent time" and "true time" were terms he would
never utter. Einstein's ideal of a physical theory was thermodynamics,
which began with two simple assumptions: first, that the disorder
of a system, the "entropy," always increased. From these starting
points you went to town, deriving everything else from them. There
was (as far as Einstein was concerned) a classical simplicity to
thermodynamics: its two pillars supporting all the other elements
of the edifice. And Einstein wanted, here and in many of his other
works, to build his theories out of principles in this way. He too
chose two starting assumptions for relativity theory: first, any
observer moving at a constant speed would have the same laws of
physics; second, the speed of light is always constant no matter
how fast or in what direction the light source was moving. In order
to reconcile these two ideas, he argued, it was necessary to put
basic ideas of space and time on a defensible and nonarbitrary footing.
So Einstein's idea of time really begins at the beginning of the
theory, and is necessary to get off the ground at all - in the service
of simplifying, unifying, and streamlining the theory. Poincaré's
theory was differently epistemological, less concerned with "What
can we know of an external Nature, and how can we secure that knowledge?"
than with his aim of fixing the theory such that it correctly predicted
phenomena while maximizing convenience. Poincaré's modernism
aimed at an aggressive program of technical repair; Einstein's at
a purifying reformulation. Poincaré fastened on simplicity-for-us,
assiduously avoiding reference beyond the human. Einstein's modernism
aimed for a kind of depth, a matching between representation and
the world not just in predictions but deeper in the theory itself.
Einstein, after all, in his later years loved to talk about how
much choice God had at the beginning of the universe (not a personal
God but an underlying order). Poincaré never even grazed
that kind of metaphysics. All that said, it would be gross distortion
to treat Poincaré as a reactionary or a failed Einstein.
The modernism of Picasso is not the modernism of Pollock; and to
force the very different breaks with the past into a single line
of progression is to lose sight of history.
DGB: The irony here is that, far from being the
wild-haired radical, Einstein is revealed to be, if anything, deeply
"classical" in his conception of physics.
PLG: Well, in some ways, Einstein is the most
classical of classical physicists. He is somebody who saw himself
in a way as purifying, simplifying, symmetrizing - bringing out
elements of a less baroque physics. There are many moments, famous
moments, in his career, when he objects to the way physics has turned
- notably in quantum mechanics. By exploring the relationships of
classical physics, by deepening them, and by connecting different
domains of thought previously held to be disjunct, Einstein, I believe,
saw himself as a kind of radical classicist.
DGB: And yet he was, perhaps despite himself,
a kind of time bomb in that classical tradition.
PLG: I think here that Einstein's extraordinary
apology to Newton - where Einstein writes, in this odd and intimate
way, "Newton, verzeih' mir' " [Newton, forgive me] - is, in a sense,
his coming to terms with the fact that in his pursuit of this purifying
classical vision he disrupted it. In a way it is a note to himself
- a note about his own life trajectory, a note on the transformation
that resulted from an attempt to deepen and streamline a classical
DGB: One reading of your book would be that you
think you have discovered the "smoking gun" for this very transformation,
the smoking gun for nothing less than the theory of relativity itself:
Einstein is at his patent desk, looking at diagrams of electromechanical
networks for time distribution along railway lines. "Eureka!" he
shouts, and he sits down to demolish the idea of absolute time and
space. I know that you don't care for this reading, and you don't
think this is your story, but it will be tempting for many readers
PLG: It is absolutely not how I think
of the problem - not for Poincaré, not for Einstein. Almost
all of my work stems from a concern with the strange juxtaposition
of the very abstract and the very concrete. This is not a question
that is by any means restricted to physics, but physics makes it
abruptly clear how suddenly we pass from symbols to materiality.
In Einstein's Clocks, Poincaré's Maps, I want to
get away from two widespread ideas: first, a notion that science
proceeds by a kind of Platonic ascension, an evaporative or sublimating
process that takes the material into the abstract. Material relations
do not eject ideas or produce ideas like ripples on the surface
of deep-flowing currents. And here coordinated clocks did not cause
Einstein to introduce the synchronizing procedure. Telegraphic
longitude mapping did not force Poincaré to the simultaneity
procedure. Conversely, physics does not advance by pure condensation
- it would be a terrible distortion to see physics beginning in
a realm of pure ideas, and then gradually acquiring the weight of
materiality until they stand in corporeal form as the objects of
everyday life. So the reason that I find this moment of late-nineteenth
and early-twentieth-century contemplation of time so interesting
is that it represents neither of these unilateral directions
(concrete- to-abstract or abstract-to-concrete). Instead there is
an extraordinary oscillation back and forth between abstraction
and concreteness. I like this mix - this high-pressure interaction
of material technologies, philosophy, and physics. Each was in play,
in different ways, and "simultaneity" was at stake in each domain:
in Lorentz's mathematical "local time," in the technological exchange
of time signals, in the philosophical critique of absolute time.
In their own ways, Poincaré and Einstein were reading philosophy,
working at technological projects, grappling with electrodynamics.
Einstein certainly knew pieces of what Poincaré had done
(how much and exactly when is a longer story). Then came Poincaré's
moment in December 1900 (and Einstein's in May 1905) when a statement
about what simultaneity is suddenly participated in all
three arcs - the crossing point.
DGB: Technology, metaphysics, physics.
PLG: What interests me about this story is precisely
that you can't start to tell it if you think that it's all on one
scale, or all is really grounded in only one of these domains. Or
rather you see very limited pieces of it while vast blocks of the
story become unmotivated, even incomprehensible. So if you tell
the story of time coordination as a pure history of ideas then Poincaré's
references to telegraphy and telegraphic longitude remain...
PLG: Incoherent, or, more precisely, they appear
as fully abstract thought experiments, with the subject (the ground
of the metaphor) chosen arbitrarily. But what is interesting to
me about it is that as you start to tell the story, no matter where
you start - and in some ways you have a choice about where to begin
- you need the other levels. Otherwise the story contains arbitrary
elements: Why, for example, is Poincaré publishing about
the same procedure for coordinating time in a journal of philosophy
of metaphysics and morals, in the Annals of the Bureau of Longitude,
and in the physics publications? I think that the very quick back
and forth between scales actually points to a dimensionality of
history that simply is wiped out if you try to narrate it from a
single line. This is a theme of my work, that the metaphorical and
the literal are inextricable: that the literal is always referring
outwards metaphorically and the metaphorical flickers back into
the literal. Asking about the history of physics leads at some key
moments both to very material circumstances and to the ethereal
layers of metaphysics as well. In the book, I am constantly trying
to avoid the historiography of both sublimation and condensation.
Instead, I find a peculiar state of vapor and water known as "critical
opalescence" to be a better metaphor for the relationship between
the abstract and the concrete. For under particular pressure and
temperature, vapor flashes back into liquid and liquid into vapor
at every scale, from a few molecules to the whole system. The light
that we shine on the opalescent mixture reflects back in every color,
at every scale. In the late nineteenth century synchronized time
was more like that: debates over synchronizing time - debates over
the conventionality of time itself - took place at the scale of
buildings, blocks, cities, countries, and the planet, while at the
same time arguments came fast and furious about the philosophical
and physical basis of time. What I wanted to know - very specifically
- was how a simple proposition, "time - simultaneity - is nothing
other than the coordination of clocks, taking into account the electrical
signal-time between them," could function jointly in this multiplicity
of trajectories: physics, metaphysics, technology.
DGB: Where somebody was actually making that
notion real by creating synchronized zones, by creating coordinated
clocks, even as the same proposition was transforming our understanding
of the physical world, and, perhaps, our place in it.
PLG: Exactly. In 1899, Poincaré was arguing
with Greenwich astronomers about how to get their astronomical clocks
synchronized, giving a lecture in which he reinterpreted Lorentz's
time concept, and presenting to the philosophers his arguments against
absolute space and time. All of this occurred essentially at once
- no one domain drove the others. Precisely the simultaneity
of all this presents the historian with two great challenges. One
is to show how the domains come together. But the other is to exhibit
the quasi-stability of each of these discourses, games, or traditions.
DGB: And to do this we must, as you say, "look
up to see down, and down to see up."
PLG: The juxtapositions, the links - all this
is historical. It is now a commonplace for string theorists
to think of physics and algebraic geometry "going together"; twenty-five
years ago that wasn't obvious at all. For those turn-of-the-century
decades it made perfect sense to mingle machines and metaphysics.
For us, perhaps, the nearness of things and thoughts seems to have
vanished, at least where time is concerned. When Poincaré
and Einstein looked into the details of electrical engineering,
when they stared at generators, radios, and cables, they saw in
them critical problems of physics and philosophy. Conversley, they
could hardly consider philosophical questions of time and space
without asking about central features of physics - or technology.
DGB: With hindsight, we will surely discover that
we now have our own "philosophical machines." It is tempting to
say that the computer is for us what the clock was for much of the
history of science: a machine to think with.
PLG: Moments of critical opalescence in the history
of science - moments when a huge variety of scales are implicated
- are not frequent. But the development of the modern computer is
such a moment - as was the late-nineteenth-century deployment of
synchronized clocks. It simply isn't possible to tell the story
of information theory, for example, without invoking the history
of computation. Conversely, there can be no coherent history of
electronic computation without showing in detail how the hardware
story crossed with the development of theories of information -
or theories of brain function.
DGB: But let's pull back for a moment. How does
the story you tell in this book fit with larger narratives in the
history of clocks and timekeeping? Is Einstein's relativistic time
"just" time? Is it the apotheosis of the classic history of technology
story about time, that wonderful story of progressive human efforts
to push time up out of the dirt and the grass, the pulse of the
blood and the organic cycles of days and seasons, and to create
instead an abstract, disembodied, "pure" time - a flowing that would
be monitored with fantastically precise devices, devices so precise
that they would become critical tools of investigation of nature,
and reveal and measure, through time, the myriad quirks and wobbles
of the cosmos? With Einstein's time, perhaps, that abstraction outreaches
itself, in a way, and collapses back onto us, onto the earth, onto
the contingencies of here and there. Does that make sense?
PLG: You can tell that story of the earlier physics
of time, as you suggest: Time passed from a world in which the sublunary
sphere was thought of as corrupt and material to another realm,
beyond the superlunary, to the inaccessible reaches of Newton's
pure, mathematical time. The story of the late nineteenth century,
though, is one in which the abstraction and concreteness of time
are both present. Conventionalizing time through the exchange of
signals forced the made-ness of time into the domain of the visible:
time zones imprinted the technical fabrication of simultaneity in
everyday life. Physicists, philosophers, psychologists, astronomers
- all were debating how to make time, how to measure it
precisely and ship it from place to place. As Poincaré and
Einstein inserted technical, engineered time into the physics of
electrodynamics, they very deliberately set aside reference to Newtonian
absolutes. They brought the abstract into the concrete - not by
jettisoning the realm of the ideas for the sun and seasons, but
by joining the material to the abstract. We could say that the modernity
of time is made visible by the absence of time-in-itself, by the
absence of time-as-absolute.
DGB: In a way, that traditional history of time
and timekeeping, particularly as cultivated by historians of science
and technology, has been a story of the "demythologizing" of time.
Sure, people went on using time imagery for didactic or symbolic
functions - from vanitas paintings of skulls to devotional
hour - glasses. But the history of time in science and technology
has been the story of abstracting that pure and precisely
metered flow from such accretions of "meaning." And yet, the products
of such progressive purifications are always themselves reintegrated
into the realm of human meaning - making. For instance, the emerging
concept of "geological time" in the eighteenth and nineteenth centuries
rapidly came to be entangled with systematic theology and deist
notions of natural law - were rocks a particular lesson in eternity?
This sort of endless "folding" between science and signification
makes me wonder: Was there - is there - a didactic or symbolic significance
in Einstein's time?
PLG: You might approach this in two ways. One
would be to look at the specificity of the way Einstein and his
physicist interlocutors treated time, and the other would be to
explore how time was taken up in the wider cultural sphere. For
example, Einstein was very amused by the "twin paradox" in which
one twin travels out and back at relativistic speeds and ends up
much younger than his stay-at-home sibling (he called this "the
thing at its funniest"). But Einstein's heart was always elsewhere
- his real investment was in the invariants he found (for
example, the absolute speed of light, or the identity of the laws
of physics for all inertial reference frame observers). He was consistently
more interested in these aspects of the theory than he was in the
differing perspectives of each observer on space and time. But clearly
the wider public was, and has remained, fascinated precisely with
the relativity of time. From jokes to art and ethics, Einstein has
been invoked to justify the tenet that the most basic of concepts
were "just relative."
DGB: And yet - and this is so easy for the lay
reader to overlook - "relativity" is predicated on a cosmic and
PLG: Indeed - there is a great irony here since
Einstein referred to his work as "Invariant Theory" until he could
no longer buck the worldwide trend to label it "Relativity Theory."
DGB: So while the public seized on the relativity
of time, what did physicists take from Einstein's intervention?
PLG: The critical gaze that Einstein cast on the
notion of time promptly put other concepts under the microscope.
Einstein had made time and simultaneity stand with, not behind,
experience and procedure. Now physicists wanted to know how this
rebuilding of a concept could be extended into quantum theory: What
was causality? What did it mean for a particle to have a momentum
and a position? Over the decades that followed, physical concepts
fell one after another from a priori metaphysical heights to the
ground where they (coupled to other concepts) met experimental inquiry.
Time invariance - that a movie of the physical world should be playable
backwards and forwards - was not, it seemed, the rule of a priori
law. Nor was parity invariance (that the mirror reflection of phenomena
should always be physically possible). Now from a distant philosophical
perspective one might say that the criticism of causality, for example,
was even more dramatic than Einstein's and Poincaré's critique
of Newtonian absolute time. But the critique of time came first,
and in a deep and abiding sense it guided the rebuilding of physical
knowledge for generations after 1905. This, I believe, is because
the reformation of time was not a change of doctrine ("time is better
measured this way than that way"). At stake was what it meant to
have a physical concept at all.
DGB: And at stake too was how one gains access
to such a concept, no? Since "abstraction" - or, as you call it,
"sublimation" - is not merely a way to tell historical stories;
it is also a way to think about nature, it is a way to think about
what science itself is and how it should be done. And yet Einstein's
pursuit of time leads to a simultaneous apotheosis and inversion
in the larger history of time in science and technology. His is
an exercise in abstraction that is also, improbably, a kind of reification.
PLG: Understanding the history of time always
involves examining exactly that relationship between the abstract
and the concrete, and, for Einstein, understanding time itself demanded
this as well. What I find so remarkable about the fin de siècle
is that not just in relativity theory, but in the whole cultural
surround, the categories of time and space exhibit a kind of abstract
concreteness (or concrete abstraction). When the French finally
persuaded the international community to "sanction" the meter in
1889, they held an elaborate ceremony, and a ritualized "burial"
of the standard. At the moment the assembled dignitaries and scientists
sealed the iridium-platinum rod in its triple-locked chamber (and
shared out the keys), this precisely engineered rod rose to become
"M" - the object that could measure but not be measured. Practical?
Of course; industrialists desperately needed a reference meter.
But symbolic? How could one say no?
DGB: When people start playing with absolutes,
when they start to conjure them - they do, we do, the strangest
things. It takes strange activity to bring absolutes into the contingencies
and localities of human life. You can be sure that people are going
to start making some very unusual gestures, and bring out keys and
locks and boxes and bury things in the ground and make funny noises
. . .
PLG: And particularly in the Third Republic, where
religious iconology morphed into scientific-technical procedure.
Time, too, was similarly concrete - abstract. In the 1890s, for
example, Poincaré joined a commission on the decimalization
of time. On one reading, this was entirely a practical affair -
railroad administrators argued passionately for the simplicity that
9.56 or 22.34 o'clock would afford by allowing travelers to calculate
time differences by simple subtraction. On another, though, it was
entirely symbolic: a reanimation of the dream of rationality so
passionately advocated during the French Revolution and brought
to international prominence through the Convention of the Meter
in the 1880s. Reflections on time are so often like this - practical
and more than practical, utterly utilitarian and highly symbolic.
PLG: Yes and no. True, they grasp time from the
domain of the pure absolute. True, they rope it into procedure of
electro-chronological coordination. But they surely do not sever
time from its wide and deep bonds with modernity. Both scientists'
writings on the "new mechanics" (with its non-absolute time) were
widely read by artists, philosophers, and writers. Both - though
in different ways - saw the relativity of time as a fundamental
piece of the new physics.
DGB: The meaning of the clock would never be the
PLG: And yet, of course, clocks have never been
just gears and pointers. Some were mounted in late - medieval towers,
establishing dominion of property and faith. In paintings they stood
as harbingers of death. By the late nineteenth century, mounted
in factories, observatories, and trading rooms, they stood for the
modern ambitions of regulated life, precision-mapped territory,
and the instantaneity of contemporary life. It is against this seven-hundred-year
clock history that relativity entered, and when it did, there were
certain to be no small effects.
DGB: "Grand narrative" historians have long talked
about the conflict between "church time" and "merchant time" in
the late-medieval period: the steeple clock versus the factory clock.
On the one hand the time of God, on the other the time of labor
and money. Your story of Einstein and Poincaré, of clocks
and maps in the fin de siècle, could be read - playfully,
I admit - as the final confrontation of these two chronometries
of European civilization: in 1905 the Sensorium of God gets tied
to the tracks of railway time...
PLG: But modernity is not - or perhaps should
I say "not just" - a train wreck! Instead, what we see in this story
is that the great metaphors of time - trains and maps - chosen by
Einstein and Poincaré are both the most imaginative of all
thought experiments, and, at the same time, the most everyday technologies
of the modern world.
1. The earth rotates
once on its axis each day, or 360 degrees every 24 hours, or 15
degrees every hour. Longitude is measured with respect to some arbitrary
zero line - say, the meridian of Paris. So if we know that the sun
is directly over our heads (it is noon where we are) and we get
a telegraph message from Paris saying it was noon there an hour
before, we know we are 15 degrees west of Paris. BACK
This is the text of the essay, "Einstein,
Poincaré & Modernity: a Conversation," by Peter
L. Galison & D. Graham Burnett, which appeared in the journal
(Spring 2003) pp. 1-15. Copyright � 2003 by Peter L. Galison &
D. Graham Burnett.
Peter L. Galison's book Einstein's
Clocks, Poincaré's Maps (2003), forms the basis of
this dialogue. A Fellow of the American Academy since 1992, Galison
is the Mallinckrodt Professor of the History of Science and of Physics
at Harvard University. Galison's other books, including Image
and Logic (1997) and How Experiments End (1987), explore
the interaction between the principal subcultures of twentieth-century
physics - experimentation, instrumentation, and theory - and also
the crosscurrents between physics and other fields.
D. Graham Burnett is an assistant
professor of history in the Program in History of Science at Princeton
University. He is the author of Masters of All They Surveyed
(2000) and A Trial By Jury (2001), and a co-editor of The
History of Cartography (1987-).