einstein

he really does deserve it,” she wrote in another letter. “I only hope that fame does not exert a detrimental influence on his human side.” 42
In one sense, Mari ’s worries proved unwarranted. Even as his fame increased exponentially, Einstein would retain a personal simplicity, an
unaffected style, and at least a veneer of genial humility. But viewed from a different reference frame, there were transformations to his human side.
Sometime around 1909, he began drifting apart from his wife. His resistance to chains and bonds increasingly led him to escape into his work
while taking a detached approach to the realm he dismissed as “the merely personal.”
On one of his last days working at the patent office, he received a large envelope with an elegant sheet covered in what seemed to be Latin
calligraphy. Because it seemed odd and impersonal, he threw it in the wastebasket. It was, in fact, an invitation to be one of those receiving an
honorary doctorate at the July 1909 commemoration of the founding of Geneva’s university, and authorities there finally got a friend of Einstein to
persuade him to attend. Einstein brought only a straw hat and an informal suit, so he stood out rather strangely, both in the parade and at the
opulent formal dinner that night. Amused by the whole situation, he turned to the patrician seated next to him and speculated about the austere
Protestant Reformation leader who had founded the university: “Do you know what Calvin would have done had he been here?” The gentleman,
befuddled, said no. Einstein replied, “He would have erected an enormous stake and had us all burnt for our sinful extravagance.” As Einstein later
recalled,“The man never addressed another word to me.” 43
Light Can Be Wave and Particle
Also at the end of the summer of 1909, Einstein was invited to address the annual Naturforscher conference, the preeminent meeting of
German-speaking scientists, which was held that year in Salzburg. Organizers had put both relativity and the quantum nature of light on the agenda,
and they expected him to speak on the former. Instead, Einstein decided that he preferred to emphasize what he considered the more pressing
issue: how to interpret quantum theory and reconcile it with the wave theory of light that Maxwell had so elegantly formulated.
After his “happiest thought” at the end of 1907 about how the equivalence of gravity and acceleration might lead to a generalization of relativity
theory, Einstein had put that subject aside to focus instead on what he called “the radiation problem” (i.e., quantum theory). The more he thought
about his “heuristic” notion that light was made up of quanta, or indivisible packets, the more he worried that he and Planck had wrought a
revolution that would destroy the classical foundations of physics, especially Maxwell’s equations. “I have come to this pessimistic view mainly as a
result of endless, vain efforts to interpret . . . Planck’s constant in an intuitive way,” he wrote a fellow physicist early in 1908. “I even seriously doubt
that it will be possible to maintain the general validity of Maxwell’s equations.” 44 (As it turned out, his love of Maxwell’s equations was well placed.
They are among the few elements of theoretical physics to remain unchanged by both the relativity and quantum revolutions that Einstein helped
launch.)
When Einstein, still not officially a professor, arrived at the Salzburg conference in September 1909, he finally met Max Planck and other giants
that he had known only through letters. On the afternoon of the third day, he stepped in front of more than a hundred famed scientists and delivered
a speech that Wolfgang Pauli, who was to become a pioneer of quantum mechanics, later pronounced “one of the landmarks in the development of
theoretical physics.”
Einstein began by explaining how the wave theory of light was no longer complete. Light (or any radiation) could also be regarded, he said, as a
beam of particles or packets of energy, which he said was akin to what Newton had posited. “Light has certain basic properties that can be
understood more readily from the standpoint of the Newtonian emission theory than from the standpoint of the wave theory,” he declared. “I thus
believe that the next phase of theoretical physics will bring us a theory of light that can be interpreted as a kind of fusion of the wave and of the
emission theories of light.”
Combining particle theory with wave theory, he warned, would bring “a profound change.” This was not a good thing, he feared. It could
undermine the certainties and determinism inherent in classical physics.
For a moment, Einstein mused that perhaps such a fate could be avoided by accepting Planck’s more limited interpretation of quanta: that they
were features only of how radiation was emitted and absorbed by a surface rather than a feature of the actual light wave as it propagated through
space. “Would it not be possible,” he asked, “to retain at least the equations for the propagation of radiation and conceive only the processes of
emission and absorption differently?” But after comparing the behavior of light to the behavior of gas molecules, as he had done in his 1905 light
quanta paper, Einstein concluded that, alas, this was not possible.
As a result, Einstein said, light must be regarded as behaving like both an undulating wave and a stream of particles. “These two structural
properties simultaneously displayed by radiation,” he declared at the end of his talk, “should not be considered as mutually incompatible.” 45
It was the first well-conceived promulgation of the wave-particle duality of light, and it had implications as profound as Einstein’s earlier
theoretical breakthroughs. “Is it possible to combine energy quanta and the wave principles of radiation?” he merrily wrote to a physicist friend.
“Appearances are against it, but the Almighty—it seems—managed the trick.” 46
A vibrant discussion followed Einstein’s speech, led by Planck himself. Still unwilling to embrace the physical reality underlying the mathematical
constant that he had devised nine years earlier, or to accept the revolutionary ramifications envisioned by Einstein, Planck now played protector of
the old order. He admitted that radiation involved discrete “quanta, which are to be conceived as atoms of action.” But he insisted that these quanta
existed only as part of the process of radiation being emitted or absorbed. “The question is where to look for these quanta,” he said. “According to
Mr. Einstein, it would be necessary to conceive that free radiation in a vacuum, and thus the light waves themselves consist of atomistic quanta, and
hence force us to give up Maxwell’s equations. This seems to me a step that is not yet necessary.” 47
Within two decades, Einstein would assume a similar role as protector of the old order. Indeed, he was already looking for ways out of the eerie
dilemmas raised by quantum theory. “I am very hopeful that I will solve the radiation problem, and that I will do so without light quanta,” he wrote a
young physicist he was working with. 48
It was all too mystifying, at least for the time being. So as he moved up the professorial ranks in the German-speaking universities of Europe, he
turned his attention back to the topic that was uniquely his own, relativity, and for a while became a refugee from the wonderland of the quanta. As
he lamented to a friend, “The more successes the quantum theory enjoys, the sillier it looks.” 49