Einstein's 1905 Revolution: New Physics, New Century

— Ansar Fayyazuddin

ALBERT EINSTEIN HARDLY needs an introduction.  A popular culture icon, his name, his disheveled appearance in late life, his theory of relativity are synonymous with genius.  It may be hard to imagine a physicist as a popular culture icon, Time's Person of the Century (for heaven's sake); yet no other figure of the 20th Century comes to my mind, with the possible exception of Picasso, whose legacy is so indisputable as to qualify for the position of something so improbable as Person of the Century.

As a culture we are very much taken with Einstein whether we understand him or not. It may very well be that the supposed inscrutability of his body of work confirms Einstein's status as genius as it does, mutatis mutandis, for Picasso.

This year marks the 100th anniversary of Einstein's most revolutionary year of scientific research.

The end of the 19th Century brought to a close a century of incredible discovery.  The basis for what is known as "classical Physics" was laid in the 19th Century.  Physics seemed to be a finished subject then.  There were still unsolved puzzles but none of them appeared to be beyond the reach of already known Physics.

Little did anyone suspect that these puzzling details were the seeds leading to the complete transformation of what came to be known as "classical Physics."  Einstein's work contributed directly to the 20th Century revolution that was about to take place.

Physics at the turn of the century was a combination of Newton's laws of mechanics, his theory of gravity, a theory of electricity and magnetism unified in Maxwell's equations, and thermodynamics.  Light was understood to be an electromagnetic wave described by Maxwell's equations—the corpuscular (or particle) theory of light no longer in vogue.

Conservation of energy between different forms—chemical, electrical, mechanical—was firmly established and encoded in the First Law of Thermodynamics.

1905 was a remarkable year.  In many ways we all long for that year.  It was in a period of incredible optimism in Europe—the center of industrialization.  What we might call the modern viewpoint matured during these early years of the 20th Century.  Changes brought about by the second industrial revolution transformed everyday life completely, especially in the cities.

Electrification, the network of railroads connecting far-flung places, the birth of photography and cinema all contributed to an ethos of progress.  All of this occurred at the cost of the constants of traditional life.  But at the beginning of the century the fruits of the sacrifices of industrialization seemed at hand and a new, better world seemed just a breath away.

This optimism was embedded in a culture of uprootedness.  The "constant revolutionizing of the means of production" that Marx and Engels talked about, and its jarring effects on the psyche described so lyrically in the Communist Manifesto, were much more true then than sixty years earlier when the Manifesto was written.  These dislocations, physical and mental, found expression in a variety of forms including the art of the early 20th Century.

The revolution that was just starting to take place in Physics contributed to the modernist ethos of the time.  On the one hand the bold steps that Physics took seemed to leave the old world far behind.  On the other, Physics turned its attention to phenomena not directly observable by the unaided eye.

In so doing, Physics was no longer concerned with the experiences of everyday life.  The shift away from everyday experiences to the nether world of atoms, and of objects traveling close to the speed of light, established a rupture between the concerns of traditional and modern Physics.  This rupture mirrored the one experienced by the European working class from its traditional and secure place in the feudal economy to a new ever-changing one over which no one seemed to have any control.

In the year 1905 Einstein published five papers.  Each one of them was a landmark.  They touched on three distinct areas of Physics.  Two of his papers dealt with the atomic nature of matter; another two concerned what came to be known as the "special theory of relativity;" and his fifth paper contributed directly to the Quantum Revolution whose groundwork was being laid then.

Brownian Motion and Atomism

At the end of the 19th Century, while a section of the Physics community accepted the possibility of matter being built out of atoms, it was not a generally accepted point of view.  There were still many who thought that matter was continuous and not made up of discrete atoms. (See note 1)

Even by the turn of the century, the atomist conception of matter had met with a number of successes.  Most notably the kinetic theory of gases was able to account for thermodynamic properties of gases.  In this view heat was conceived as the energy associated with the motion of the constituent atoms, while the thermodynamic (or macroscopic) properties of gases (such as pressure) were due to the collective behavior of their atomic constituents.

Despite these successes, a positivist philosophical inclination held sway in some influential circles denying any reality to the atomic hypothesis in the kinetic theory of gases.  Thus atoms in this model were thought of as convenient mathematical fictions, which allowed one to calculate interesting quantities but did not refer to real physical objects.

Brownian motion is the random motion of small particles suspended in liquid that can be observed with the help of a microscope.  This motion was a well studied phenomenon, but lacked a convincing theoretical explanation.

Einstein in one of his papers from 1905 provided a theoretical explanation.  He showed that using the atomic hypothesis one can show that the random jiggling of a suspended particle can be attributed to it being kicked in random directions by the atoms in the suspending liquid.  The main significance of Einstein's work is that he provided a concrete test of the atomic hypothesis.

What is particularly interesting about Brownian motion, as a test of the atomic hypothesis, is that Brownian motion concerns the motion of particles visible under a microscope (such as pollen), with sizes of the order of one thousandth of a millimeter—whereas atoms themselves are unobservable under a microscope since their size is considerably smaller at about 10 billionths of a centimeter.

Special Theory of Relativity

According to Newtonian mechanics, forces are responsible for acceleration.  In the absence of forces all bodies continue to either be at rest or move at a constant speed along a straight line.  Observers on which no forces are acting are called inertial observers.

Newton's dynamical laws are the same for all inertial observers.  Clearly inertial observers moving with respect to each other do not agree on velocities.  For instance, each of two such observers will think of themselves as at rest while the other as in motion.

Maxwell's theory of electricity and magnetism provides a successful framework with which to study light.  In this theory light is an electromagnetic wave.  Using Maxwell's equations one can compute the speed of light.  One finds that the speed of light is 300,000,000 meters (186,000 miles) per second.

The question arises: which inertial observer is this speed of light relative to?  As in the previous paragraph, two inertial observers traveling relative to each other should observe different speeds for the same light wave.

The 19th Century answer to this question relied on the belief that all waves travel in a medium.  Light waves were supposed to be ripples in a ubiquitous "ether."  The speed of light computed using Maxwell's equations was believed to be what a particular inertial observer—one who is at rest with respect to the ether—would measure.

Einstein worked out the consequences of what at first sight seem to be two contradictory propositions: 1) that all inertial observers are equivalent (i.e. there is nothing special about any particular inertial observer) and 2) that the speed of light is constant and the same for all inertial observers.

He found that the two principles are not in conflict with each other—but that their consistency leads to counterintuitive results.  By dissecting our naively accepted notions of synchronizing clocks and agreeing on measures of distance, Einstein discovered that two inertial observers moving relative to each other would not agree on measures of time or distance.

They may also not agree on the order in which events take place.  Thus two events that appear to be simultaneous to one observer may not be simultaneous according to another who is moving relative to the first observer.  These effects are observable only when the relative velocities of the observers are close to the speed of light.

Although the conceptual ideas behind Einstein's investigation are easy to state, the consequences are far-reaching and revolutionary.  For example, the absolute nature of time implicit in Newtonian mechanics is overthrown and replaced by the idea of space-time, making time into another coordinate—"the fourth dimension."  Points in space-time are then events.

A consequence of Einstein's hypotheses is that one can associate energy with the mass of an object.  The equation E = mc2, justly famous, captures this equivalence and the possibility of converting mass into energy and vice versa.

In particular, the energy that binds nuclei together is quite large.  The conversion of mass into energy in nuclear processes is responsible for the way the sun produces energy as well as how nuclear weapons explode.  Without Einstein's equation we would not be able to make sense of any of the phenomena involving the conversion of mass into energy, since they do not conserve our pre-relativity notions of energy.

Einstein's theory of special relativity has been experimentally confirmed in many situations.  A particularly dramatic test is the "lengthening" of the lifetime of unstable particles traveling close to the speed of light observed in cosmic ray experiments. Another, perhaps even more dramatic, consequence of relativity was arrived at theoretically by P.A.M. Dirac in the late 1920s when he discovered that requiring quantum physics (the theory of atomic and sub-atomic physics) to be compatible with special relativity requires the existence of anti-matter.  This was experimentally established when the anti-particle of the electron—the so-called positron—was observed in 1933.

The Quantum Hypothesis

In his fifth paper of 1905, Einstein proposed that while Maxwell's equations describe optical phenomena very well, there are phenomena involving light for which a particle theory of light provides a more natural explanation.  This was arguably Einstein's most revolutionary hypothesis.

Einstein proposed that a light beam should be thought of as a collection of particles—now called photons.  These photons can be thought of as light quanta—discrete packets of energy each carrying an amount of energy given by E=hf. (Here f denotes the frequency of the light beam and h is a universal constant known as Planck's constant.) (See note 2)

Einstein's quantum hypothesis immediately explained phenomena for which there was no existing theoretical explanation as well as clarifying the theoretical underpinnings of earlier work.  Einstein explained the meaning of Planck's theoretical assumption that radiation is produced with discrete energy in his derivation of the formula for how hot bodies radiate.

In addition, Einstein explained a completely new phenomenon—the photoelectric effect.  The photoelectric effect is the ability of light to produce electrical currents in a system.  Although classical electromagnetic theory could explain how light could produce currents in materials, it could not explain the experimental observation that the currents are independent of the intensity of light.

Einstein predicted that electrons absorb light quanta whole, thus getting discrete increases in their energy and escaping the material if their energy is large enough.  Consistent with his discrete energy quantum hypothesis, he argued that the energy of the electrons increases with the frequency of the incident light, not its intensity.

This reasoning also gave a new way of measuring Planck's constant, a crucial ingredient in the yet to be formulated quantum mechanics.  For his theoretical explanation of the photoelectric effect Einstein won the Nobel Prize in 1921.

1905 in Context

Einstein's three major contributions to Physics in 1905 were monumental.  What makes them even more remarkable is that during 1905 Einstein worked not as a Physicist at an academic institution but as a patent officer in Bern, Switzerland.  He had been unable to secure a position at a university and was not to find a job at an academic institution until 1908.

The image of the misunderstood genius working in isolation who manages to transform the intellectual landscape is so compelling, seductive and heroic that it is no surprise that Einstein occupies such an important iconic space in our culture.  Yet to say that Einstein worked in an intellectual vacuum would be to misunderstand his importance completely.

Einstein addressed questions that were thrown up by the preoccupations of 19th Century Physics.  The puzzles were there and he was one of the many who tried to address them.  Had a person completely out of synch with the time written the five papers that made Einstein a household name, s/he would have lived a life of obscurity or, worse, notoriety.  Einstein's contributions had the impact that they did because they were very much in synch with their time.

Einstein's theory of relativity formulated during 1905 was the first one to really solve the problem of the ether by boldly embracing the two principles mentioned above.  However, some of Einstein's mathematical results were known to Lorentz and others who had studied the symmetries of Maxwell's equations.  In addition, experiments performed by Michelson and Morley had shown that the speed of light is the same in all directions, independently of the direction of motion of the putative "ether," thus seriously undermining the ether hypothesis.

While Einstein indisputably was the first to pose the problem "correctly" and understand how to circumvent the problem of the ether in a compelling way, with very clearly observable experimental consequences, his ideas nevertheless had the impact they did because they were presented to a world grappling with the same urgent problems.

The heroic image of Einstein in 1905 as patent clerk, isolated yet intellectually fertile whose genius is yet to be recognized, has impacted both popular culture and the culture within Physics.  The popular culture idea of dilettante as potential genius is very much rooted in the mythical image of Einstein.

A manifestation of this is the notion of theoretical Physics as an amateur field that can be practiced in isolation as a hobby.  Professional physicists regularly receive self-proclaimed revolutionary contributions to Physics from non-physicists.  These people, often employed in completely unrelated fields, model themselves on Einstein.

The mythological Einstein has influenced the culture within Physics as well.  In Physics the privileging of theory over experiment often misunderstands the crucial role experiments have historically played in formulating universal principles, including the role they played in Einstein's own life.

The image of Einstein as ahistorical actor, able to conjure up universal principles in isolation from experiment, is one that has had tremendous influence within Physics.  The culmination of this view is the present day theoretical attempts at finding the "ultimate" theory from aesthetically pleasing principles alone.  In this view, there must be a compellingly unique theory, which inescapably must describe our universe.  The formulations, often theological in their fervor, fail to acknowledge their own historically specific and subjective criteria for the litmus test of an "ultimate" theory.

Beyond 1905

Although 1905 was a watershed for Einstein and Physics, Einstein's contributions to Physics continued beyond that year.  Perhaps the most important of these many contributions is the theory of General Relativity.  More than any of his other ideas, General Relativity is the most difficult to explain historically.  It seems to come out of nowhere, although it is a generalization of some of the ideas inherent in Special Relativity.

General Relativity is a radical theory of gravity.  According to this theory, energy curves space-time in such a way that what we call motion under the influence of gravity can be thought of as motion not due to a force, but simply motion as a result of living in a warped space-time.

Much as Newton needed new mathematics—the calculus—to formulate his mechanics, Einstein needed curved space geometry, or Riemannian geometry, to formulate his general theory of relativity.  Unlike Newton, who had to invent the Calculus himself, Einstein had the relative advantage of Riemannian geometry (a form of non-Euclidean geometry) already existing, albeit as an infant science.

The successes of the general theory started to accumulate almost immediately after its publication in 1915.  It predicted the bending of light due to gravity and famously observed by a 1919 expedition led by Eddington.  It also explained a property of the planet Mercury's orbit that could not be accounted for by Newtonian gravity.

Despite relativity's ability to explain astronomical facts we are yet to find an experimentally viable theory that includes both general relativity and quantum mechanics. (See note 3)  This inability has had few practical consequences since relativity and quantum mechanics are usually important over entirely different distance scales—relativity being relevant at astronomical distances while quantum mechanics at the atomic scale.

Nevertheless, an intellectual unease with this seemingly arbitrary separation of domains of validity, and the discovery of the simultaneous relevance of quantum mechanics and general relativity in the physics of black holes as well as the existence of other conundrums, has created a fertile atmosphere for the exploration of possible theories of "quantum gravity," an active area of research today.

Humanist and Socialist

So far I have focused exclusively on Einstein as scientist and icon.  Einstein was a considerably more complex historical figure than this.  His humanism and identification with socialist ideas are important aspects of the real Einstein.  His status as the leading intellectual of the 20th Century means that his legacy on political and ethical questions is hotly debated.

No matter what the particular spin one might be confronted with in this regard, it is hard to escape the fact that Einstein identified with values very much in line with socialist ideas.  Einstein believed increasingly in the need for a world government and planning that would rid the world of war, inequality and injustice.  He was a pacifist (even during World War I), he opposed the use of atomic weapons and believed in the urgent need of ethnic equality.

The clearest statement of his belief in Socialism that I am aware of is his piece for the first issue of the American socialist magazine Monthly Review in 1949.  In this article he summarizes a view of capitalist society practically identical to the one of Marxists.  He extols the need for democratic socialist planning while outlining the limitations of planning alone—implicitly criticizing Stalinism.

Given these beliefs, it is hard to understand how Einstein could support the "Jewish State" of Israel.  In fact, Einstein had a very troubled relationship to the Zionist idea.

Anti-Semitism in Europe, which Einstein experienced first hand, and its culmination in the Nazi holocaust led many to accept the Zionist belief that European anti-Semitism could not be defeated, only escaped.  A long moral distance had to be traveled between this idea and accepting the colonial project and dispossession of the Palestinian Arab people, based on ethnicity, that this meant in practice.

Einstein struggled with the real-life Israel and took stands against many of the practices of the Zionist state, including the very idea of a closed nationalist state, and particularly and openly against anti-Arab terrorism carried out by the fascist Jabotinsky wing of Zionism.

His towering intellect, humanist values, socialist political commitments and belief in our ability to rationally understand the world through science, make Einstein a truly worthy hero of our times.


  1. I am simplifying here a much more nuanced and intricate landscape and history of atomist vs. non-atomist ideas.  Please consult the references on page 26 for a more complete treatment.
    (back to text)
  2. Frequency corresponds to color for the visible part of the light spectrum and is analogous to pitch for sound waves.  Higher frequencies correspond to bluer colors and smaller to redder ones.
    (back to text)
  3. There is a candidate theory of quantum gravity known as "string theory."  At this stage at least, it is far from able to make experimental predictions about our world.  Nevertheless, string theory has given us important insights into many of the puzzles surrounding relativity and quantum mechanics.
    (back to text)

Sources and Further Reading:

There is a considerable literature on Einstein.  In preparing this article, I relied on the superb biography Subtle is the Lord by Abraham Pais, as well as the excellent volume of edited papers by Einstein from 1905 titled Einstein's Miraculous Year, which contains commentary by the Einstein scholar John Stachel.  I am told that the Ronald Clark's biography Einstein: Life and Times is an eminently readable book.  In addition, Purrington's Physics in the Nineteenth Century is an indispensable history of the last century of "classical" physics.  A general sense of this period in time can be gleaned by reading Eric Hobsbawm's The Age of Empire, but in my opinion the volume by John Berger, The Success and Failure of Picasso, as well as his seminal essay the "The moment of cubism" makes the zeitgeist and vibrancy of the time much more palpable.

More information about Einstein can be found at the American Institute of Physics website.  For the person interested in exploring Einstein's theory of special relativity, I can think of no clearer book than N. David Mermin's Space and Time in Special Relativity. —A.F.

ATC 116, May-June 2005