Джеймс Глик - Genius - The Life and Science of Richard Feynman

“Space of itself and time of itself wil sink into mere shadows, and only a kind of union between them shal survive.”

Later, quantum mechanics suffused into the lay culture as a mystical fog. It was uncertainty, it was acausality, it was the Tao updated, it was the century’s richest fount of paradoxes, it was the permeable membrane between the observer and the observed, it was the funny business sending shudders up science’s al -too-deterministic scaffolding. For now, however, it was merely a necessary and useful contrivance for accurately describing the behavior of nature at the tiny scales now accessible to experimenters.

Nature had seemed so continuous. Technology, however, made discreteness and discontinuity a part of everyday experience: gears and ratchets creating movement in tiny jumps; telegraphs that digitized information in dashes and dots. What about the light emitted by matter? At everyday temperatures the light is infrared, its wavelengths too long to be visible to the eye. At higher

temperatures,

matter

radiates

at

shorter

wavelengths: thus an iron bar heated in a forge glows red, yel ow, and white. By the turn of the century, scientists were

struggling to explain this relationship between temperature and wavelength. If heat was to be understood as the motion of molecules, perhaps this precisely tuned radiant energy suggested an internal oscil ation, a vibration with the resonant tonality of a violin string. The German physicist Max Planck pursued this idea to its logical conclusion and announced in 1900 that it required an awkward adjustment to the conventional way of thinking about energy. His equations produced the desired results only if one supposed that radiation was emitted in lumps, discrete packets cal ed quanta. He calculated a new constant of nature, the indivisible unit underlying these lumps. It was a unit, not of energy, but of the product of energy and time—

the quantity cal ed action.

Five years later Einstein used Planck’s constant to explain another puzzle, the photoelectric effect, in which light absorbed by a metal knocks electrons free and creates an electric current. He, too, fol owed the relationship between wavelength and current to an inevitable mathematical conclusion: that light itself behaves not as a continuous wave but as a broken succession of lumps when it interacts with electrons.

These were dubious claims. Most physicists found Einstein’s theory of special relativity, published the same year, more palatable. But in 1913 Niels Bohr, a young Dane working in Ernest Rutherford’s laboratory in Manchester, England, proposed a new model of the atom built on these quantum underpinnings. Rutherford had recently imagined the atom as a solar system in miniature,

with electrons orbiting the nucleus. Without a quantum theory, physicists would have to accept the notion of electrons gradual y spiraling inward as they radiated some of their energy away. The result would be continuous radiation and the eventual col apse of the atom in on itself.

Bohr instead described an atom whose electrons could inhabit only certain orbits, prescribed by Planck’s indivisible constant. When an electron absorbed a light quantum, it meant that in that instant it jumped to a higher orbit: the soon-to-be-proverbial quantum jump. When the electron jumped to a lower orbit, it emitted a light quantum at a certain frequency. Everything else was simply forbidden. What happened to the electron “between”

orbits? One learned not to ask.

These new kinds of lumpiness in the way science conceived of energy were the essence of quantum mechanics. It remained to create a theory, a mathematical framework that would accommodate the working out of these ideas. Classical intuitions had to be abandoned.

New meanings had to be assigned to the notions of probability and cause. Much later, when most of the early quantum physicists were already dead, Dirac, himself chalky-haired and gaunt, with just a trace of white mustache, made the birth of quantum mechanics into a smal fable. By then many scientists and writers had done so, but rarely with such unabashed stick-figure simplicity.

There were heroes and almost heroes, those who reached the brink of discovery and those whose courage and faith in the equation led them to plunge onward.

Dirac’s simple morality play began with LORENTZ. This Dutch physicist realized that light shines from the oscil ating charges within the atom, and he found a way of rearranging the algebra of space and time that produced a strange contraction of matter near the speed of light. As Dirac said,

“Lorentz succeeded in getting correctly al the basic equations needed to establish the relativity of space and time, but he just was not able to make the final step.” Fear held him back.

Next came a bolder man, EINSTEIN. He was not so inhibited. He was able to move ahead and declare space and time to be joined.

HEISENBERG started quantum mechanics with “a bril iant idea”: “one should try to construct a theory in terms of quantities which are provided by experiment, rather than building it up, as people had done previously, from an atomic model which involved many quantities which could not be observed.” This amounted to a new philosophy, Dirac said.

(Conspicuously a noncharacter in Dirac’s fable was Bohr, whose 1913 model of the hydrogen atom now represented the old philosophy. Electrons whirling about a nucleus? Heisenberg wrote privately that this made no sense: “My whole effort is to destroy without a trace the idea of orbits.” One could observe light of different frequencies shining from within the atom. One could not observe electrons circling in miniature planetary orbits, nor any other atomic structure.)

It was 1925. Heisenberg set out to pursue his conception

wherever it might lead, and it led to an idea so foreign and surprising that “he was real y scared.” It seemed that Heisenberg’s quantities, numbers arranged in matrices, violated the usual commutative law of multiplication that says a times b equals b times a. Heisenberg’s quantities did not commute. There were consequences. Equations in this form could not specify both momentum and position with definite precision. A measure of uncertainty had to be built in.

A manuscript of Heisenberg’s paper made its way to DIRAC himself. He studied it. “You see,” he said, “I had an advantage over Heisenberg because I did not have his fears.”

Meanwhile, SCHRÖDINGER was taking a different route.

He had been struck by an idea of DE BROGLIE two years before: that electrons, those pointlike carriers of electric charge, are neither particles nor waves but a mysterious combination. Schrödinger set out to make a wave equation, “a very neat and beautiful equation,” that would al ow one to calculate electrons tugged by fields, as they are in atoms.

Then he tested his equation by calculating the spectrum of light emitted by a hydrogen atom. The result: failure.

Theory and experiment did not agree. Eventual y, however, he found that if he compromised and ignored the effects of relativity his theory agreed more closely with observations.

He published this less ambitious version of his equation.

Thus fear triumphed again. “Schrödinger had been too timid,” Dirac said. Two other men, KLEIN and GORDON,

rediscovered the more complete version of the theory and published it. Because they were “sufficiently bold” not to worry too much about experiment, the first relativistic wave equation now bears their names.

Yet the Klein-Gordon equation stil produced mismatches with experiments when calculations were carried out careful y. It also had what seemed to Dirac a painful logical flaw. It implied that the probability of certain events must be negative, less than zero. Negative probabilities, Dirac said,