Though Planck spent much of his time after the war on
administrative matters, he still turned a great deal of attention
to the new field in physics: quantum mechanics. And there was certainly
a lot to think about, as the best and brightest of European physics
worked to figure out the quantum puzzle. And, with German scientists
at the forefront, this exciting new field seemed the best way for
Germany to regain its former position as the leader of physics communities.
In the years just after World War
I the central issue confronting physicists was one
that stretched back to the startling results of Planck's work on
blackbody radiation: was light a particle or a wave? Scientists
in Copenhagen and at the University of Göttingen worked diligently
at the problem, and, by combining their efforts, they were eventually
able to reach a workable solution.
In 1926, physicist Erwin Schrödinger came up with a theory
that seemed to reconcile the bizarre data of quantum theory with
the classical understanding of wave mechanics. He discovered an
equation for a wave, which he thought of as a wave function showing
the distribution of electricity in an atom. This direction of thinking greatly
pleased old guard physicists such as Albert Einstein, who were
reluctant to throw out a century's worth of beliefs about light and
energy. But the other quantum physicists were less impressed.
They put forward a new theory about Schrödinger's wave
function, describing it as a probability wave – a wave measuring
the probability that an electron will occupy a certain place and
certain state at any given time. Planck despised the idea, and
he refused to accept a worldview that involved never knowing anything
for certain about the makeup of atoms. For Planck, the entire goal
of physics was to completely dissect the workings of the universe,
and the idea that some things were just unknowable was completely
repugnant to him, and reminiscent of the positivism that he had
attacked so passionately in years past.
To Planck's dismay, the quantum physicists continued their
inexorable march toward the concept that the universe was, at its
core, unknowable. Things came to a head when the quantum physicists working
in Copenhagen put forward what would come to be known as the Copenhagen
interpretation of quantum physics; by 1927, it had become the definitive
response to the wave/particle question.
As formulated by Werner Heisenberg and Niels Bohr, the Cophenhagen
interpretation had two parts. The first was Heisenberg's uncertainty
principle, which dictated that it was impossible for an observer
to know both the exact position and the exact momentum of a subatomic
particle. The more exact your measurement was of one, the less
exact it would be of the other. Bohr's contribution of the principle
of complementarity, which sidestepped the question of whether light
was a particle or a wave. According to Bohr, it was both: light
was a particle or a wave, depending on how the observer measured
it.
Basically, Bohr argued that the experimenter was an inextricable part
of the experiment and that the method he chose for measuring a
phenomenon would determine the results. Asking whether light "is"
a particle or a wave is a useless question–physics, Bohr claimed,
is about the results of experiments, not about the way things really
"are." This philosophy represented everything Planck had always
stood against in physics; if Bohr was right, there was no such
thing as an objective reality independent of the observer. Planck
felt that the Copenhagen interpretation was nothing more than a
way of giving up on the real questions and, essentially, was a scientific
expression of the pessimism rampant in German life.
Planck was not the only one to dislike the new trend in
physics. Einstein detested the Copenhagen interpretation, calling
it "the Heisenberg-Bohr tranquilizing philosophy, or religion."
Indeed, scientists like Einstein, Schrödinger, and Planck hoped
that the Copenhagen interpretation was just a detour on the way
to a true understanding of quantum mechanics. But because they
had hope for the future, none of these scientists gave up on quantum
mechanics. And though he disagreed with their results, Planck held
fast to his belief that supporting the quantum physicists would
bring prestige to German science and to Germany itself.
For a time, he was right. No one could deny the remarkable
contributions that German scientists had made to the new field.
German science seemed to be on the right track. But once again,
politics was about to overtake science. Once again, Planck would
have to fight for his field's survival, though it would no longer
be so clear, to him or to anyone else, whom he was fighting and
whom he was protecting. In 1933, the Nazi party came to power,
and Germany turned against itself.
