Einstein's Genius Club (20 page)

The word “relativity” eventually weighed upon Einstein like an albatross of imprecision. It implies opposition to “absolute”—yet Einstein's relativity theories are anchored to the absolute of absolutes: the speed of light. That speed alone remains absolute; time and space are relative to it. In later years, when Einstein fought his rearguard action against the relativism of quantum mechanics, his early discoveries came back to haunt him. “God does not play dice with the universe,” he said. But a devil's advocate might say, with Banesh Hoffmann, that Einstein had loosed the demons himself. His quantification of light via Planck is often deemed the inaugural
leap into quantum theory. His special theory, with its equivalences of mass and energy, has as its legacy particle physics, the arena for quantum mechanics. Einstein died believing quantum physics to be incomplete in its description.

It is the blessing of youth that its energy is greater than its foresight. Einstein's miracle year produced four extraordinary papers: the first on light quanta, the second on the size of molecules, the third on Brownian motion and the existence of the atom, and the fourth on moving bodies—“special relativity.”

In 1896, the discovery of radioactivity inaugurated a search for the nucleus. In 1898, Marie Curie found two radioactive elements, and Ernest Rutherford started sorting out the alpha, beta, and gamma rays from radiation. In 1903, with Frederick Soddy, Rutherford explained radioactive decay, and, in 1911, he finally discovered the atomic nucleus. This set off the next wave of discoveries: Bohr's quantum theory of the atom in 1913; Chadwick's discovery of the neutron in 1932; artificial fission by the Joliot-Curies; and the explanation of nuclear fission by Hahn in 1939.

In 1905, the young Einstein had launched both relativity and quantum physics. (Planck had discovered the quantum phenomenon, but Einstein started quantum physics by applying the concept to light quanta.) Relativity, special and general, were Einstein's singlehanded achievement. But very few physicists specialized in that until after Einstein's death. Einstein worked on it by himself.

Quantum physics, however, attracted a crowd and needed them: The implications went in every direction. Einstein himself remained a most important contributor, continuing to publish important work on quantum problems even while laboring away at general relativity. In March 1916, he finally published the complete gravitational theory; in July, he began to publish three papers on quantum theory. Late in life, he told a friend that he had thought a hundred times more about quantum physics than about relativity. As usual, his thinking took a quite individual turn.

Accounts of Einstein's work usually pass quickly over this
longest and, in some ways, most ambitious part of his career. For one thing, this period can be dismissed as evidence of his decline in genius. Indeed, this last effort turned out to be a failure, having added little to the progress of physics. It opened no paths for the future. Recent unifying attempts go in an entirely different direction.

But the question of what happened in Einstein's search for unity may cast light on a neglected side of science. Science is collective and cumulative. Its processes ensure that even its surpassing contributions will ultimately “fail.” We rarely see this side of science. Instead, science is presented as a series of dramatic breakthroughs, new pathways, inventions, new frontiers. True, the biologist Robert Hooke and the chemist Robert Boyle were once in the vanguard of discovery; now they have moved back into the fabric of the grand design. Historians of science know that Boyle discovered the relationship between pressure and volume (Boyle's law), but how many working physicists could fairly describe the achievements of the Swedish physicist Svante Arrhenius, whose work on ions predicted the greenhouse effect? Does it matter? Physics is in many ways a self-erasing discipline, concerned only with the latest leading edge of research.

In later life, Einstein was overtaken by history twice. First, by his personal history: In his forties and fifties, his gifts, quickness, and prowess inevitably faded. This happens to everyone. His extraordinary discovery of general relativity may well have made him too confident that he could then master the intricacies of a unified theory. But scientists are overtaken by history in the special way just noted: Sooner or later, the most surpassing achievements will be modified, supplanted, or rebuilt. Newton's gravitational theory eventually became a special case of Einstein's general relativity. If that could happen to Newton, it could happen to Einstein—and indeed, Einstein predicted that it would.

In the world of drama, only Shakespeare can be said to rival Sophocles. Literary works are unique and their truths timeless. But
the same cannot be said of science. If Einstein had not modified Newton, someone else would have sooner or later, with whatever variations. Science guarantees that all its members will be challenged and essentially usurped—though it might be more accurate to say superseded, displaced, corrected, or improved. Einstein was challenged in just this way when quantum mechanics emerged in 1925, for its view of the universe contradicted Einstein's most fervent beliefs. If gravity is ever joined successfully to quantum mechanics, even the theory of relativity may well be modified.

Are we to imagine that if Einstein at fifty had retained his youthful powers of imagination, he would have been able to find a unifying theory? That does not seem realistic. No matter how much genius was applied, the time was not ripe: Too little was known about electromagnetism and the fundamental forces of the atom. Strong and weak nuclear forces had yet to be discovered. Yet Einstein, trusting to his formalisms and intuition, dismissed the new evidences of quantum mechanics.

In 1905, Einstein, working on a problem called the “photoelectric effect,” wrote a paper that some say gave birth to the quantum revolution.
²³
This paper, modestly titled “On a Heuristic Viewpoint Concerning the Production and Transformation of Light,” offered to solve problems rather than build theory. Still, its language portended radical change:

It seems to me that the observations associated with black-body radiation, fluorescence, the production of cathode rays by ultraviolet light, and other related phenomena connected with the emission or transformation of light are more readily understood if one assumes that the energy of light is
discontinuously
distributed in space. In accordance with the assumption to be considered here, the energy of a light ray spreading out from a point source
is not continuously distributed
over an
increasing space but consists of a
finite number of energy quanta
which are
localized at points
in space, which move without dividing, and which can only be produced and absorbed as
complete units
.
²⁴
[emphasis added]

“Discontinuously… not continuously distributed… quanta”—these are words that fly in the face of Newton and his classical world. It was as if, in his most productive year, Einstein spoke what much later he would, like Shelley's Prometheus, “re-pent me.”

Like all science, quantum physics was built on the shoulders of history. As we have seen, by 1900, the world of physics had split into warring camps or worldviews, each still under the sway of classical Newtonian physics. On one side was the Enlightenment faction, which believed the world a clockwork mechanism. On the other side were the converts to electromagnetic theory, which under Maxwell had wedded electricity and magnetism into a unified theory. Yet problems remained that could not be explained by either side. Among them were three bedeviling conundrums: black-body radiation, the photoelectric effect, and bright-light spectra, which could neither be explained by classical physics nor ignored (certainly not by young physicists out to make their name). Solving them led inexorably to the quantum revolution.
²⁵

The first inkling of quantum theory came from a lab in Berlin. In 1900, Max Planck was a forty-year-old physicist with expertise in chemistry and thermodynamics. He was also a fervent believer in the second law of thermodynamics, which states that in a closed system, entropy (loosely translated as “disorder,” but also meaning heat loss) increases and, once achieved, cannot be reversed. It was Planck's appreciation of this law and his refusal to give it up that led him to the black-body solution.

Planck was one of the few theoretical physicists amid the cadres of experimental scientists populating German universities.
He was to some extent off the academic radar, and thus had the freedom to contemplate problems that spanned disciplines. Although focused on thermodynamics, he knew of electromagnetism. Maxwell, remember, had demonstrated that light is an electromagnetic wave. Planck believed in Maxwell's findings. More obviously, he noted in the black-body question the intersection of heat (his field), light, and electromagnetism.

Planck set out to examine black-body radiation in the context of the second law. Again, the black-body problem had resisted explanation by classical physics, but held out much practical promise. The reason is that radiation is emitted from the black body in the form of light—specifically, color. For centuries, potters had observed that heat within their kilns turned colors, like a spectrum. From blue through white, each successive color indicates hotter temperature. What can black-body radiation tell us about the behavior of radiation?

As was their wont, German physicists tackled the problem experimentally. They created a black body—an enclosure that would absorb all the electromagnetic radiation it could—with a small hole through which electromagnetic waves could escape. Then they observed the color distribution of radiation coming through the hole. They hoped in this way to study the electromagnetic waves within, just as Maxwell had studied heated gases. To be sure, the question was of more than theoretical interest. Electricity was big business at the turn of the century. If a means for measuring emitted energy could be discovered, electrical companies would be able to quantify their product and provide the greatest amount of power using the least energy.

Two formulas emerged. Unfortunately, one worked well for high frequencies, but not for low frequencies; the other worked only for low frequencies. In fact, at higher frequencies, the second formula produced an impossible result. Light, as had been established, comes in waves, and waves, unlike particles, can multiply
infinitely—they just get closer and closer together. As the waves moved closer and closer at higher frequencies, the power (or temperature) would, theoretically, enter the ultraviolet zone and beyond, to infinity. It would become an “ultraviolet catastrophe,” emitting radiation with infinite power! Fortunately, nothing like that happens in real life. The black-body heat finds equilibrium, just as Maxwell's gas had. The problem was how to formulate an equation that would explain what was happening.

Planck tried formulae that were tied to the second law of thermodynamics, using standard theories of radiation. Nothing worked. At last, he tried a thought experiment. What if, instead of waves, the black-body chamber was full of oscillating and discrete charges? As the interior heats up, the charges would continue to oscillate at all of the possible frequencies. Planck reworked his formula to fit the experimental results, using a constant to make the equation work. With great consternation, he pondered the result. Only by imagining the electromagnetic waves as discrete elements, using statistics, as Maxwell had with heated gas, and ascribing to the resulting discontinuity a constant (
h
), could he fit the formula to reality. Planck, forever the enemy of what would become quantum physics, had “quantized” radiation, at least within the black body. At the time, however, he preferred to think of his “constant” as a useful trick rather than a key to atomic architecture.

Ironically, it was Einstein, implacable foe of later quantum theory, who established a theoretical basis for Planck's constant. In essence, he quantized light. He also solved a second conundrum: the photoelectric effect. As Planck was pondering the black-body problem, another German, Philipp Lenard, was experimenting with cathode rays and light beams. He tried shining a light of a single frequency onto a thin metal foil. The result was startling, to say the least. Out of the foil came electrons. The light had somehow ejected electrons. If light were a wave and the electrons were ejecting because they were being disturbed by the energy of the light, then it follows that if the light were of greater intensity, the electrons
would carry more energy when they were ejected. But Lenard found otherwise: At low frequencies, even with a very bright beam, no electrons were ejected; at increasingly higher frequencies, the energy of the ejected electrons remained the same. Nothing in classical physics explained Lenard's findings.

The explanation came in Einstein's second paper published in 1905. If, Einstein argued, we consider light not as waves but as photons, we can then explain the photoelectric effect—the emission of electrons that occurs when light is shined on metal. If light acts not as a continuous wave, but as a collection of particles, then the photoelectric effect is nothing more than photons colliding with electrons—tiny particle colliding with tiny particle. His idea of photons explained another problem: that of cooling bodies, which gave off heat not in a neat, continuous way, but discontinuously, “jumping” from temperature to temperature. Newtonian physics could not account for this phenomenon. Quantum physics did. For his discovery of photons—not for relativity—Einstein won the Nobel Prize.

It was not long before someone—it turned out to be the French aristocrat turned experimental physicist Louis de Broglie—asked the obvious question: If light waves behaved like particles, could particles of matter behave like waves?

Before we hear de Broglie's answer, we must take a detour into the atom itself. As Einstein was investigating the large story of gravity and the universe, others searched in the opposite direction, trying to understand the architecture and behavior of invisible particles.