384 THE QUANTUM THEORY
tization applied to matter, to his material oscillators. He was unaware of the fact
that his proposal implied the need for a revision of the classical radiation field
itself. His reasoning alleged to involve only a modification of the interaction
between matter and radiation. This did not seem too outlandish, since the inter-
action problem was full of obscurities in any event. By contrast, when Einstein
proposed the light-quantum he had dared to tamper with the Maxwell equations
for free fields, which were believed (with good reason) to be much better under-
stood. Therefore, it seemed less repugnant to accept Planck's extravaganzas than
Einstein's.
This difference in assessment of the two theoretical issues, one raised by Planck,
one by Einstein, is quite evident in the writings of the leading theorists of the day.
Planck himself had grave reservations about light-quanta. In 1907 he wrote to
Einstein:
I am not seeking the meaning of the quantum of action [light-quanta] in the
vacuum but rather in places where absorption and emission occur, and [I]
assume that what happens in the vacuum is rigorously described by Maxwell's
equations. [Pll]
A remark by Planck at a physics meeting in 1909 vividly illustrates his and others'
predilections for 'leaving alone' the radiation field and for seeking the resolution
of the quantum paradoxes in the interactions:
I believe one should first try to move the whole difficulty of the quantum theory
to the domain of the interaction between matter and radiation. [PI2]
In that same year, Lorentz expressed his belief in 'Planck's hypothesis of the
energy elements' but also his strong reservations regarding 'light-quanta which
retain their individuality in propagation' [L9].
Thus by the end of the first decade of the twentieth century, many leading
theorists were prepared to accept the fact that the quantum theory was here to
stay. However, the Maxwell theory of the free radiation field, pure and simple,
provided neither room for modification (it seemed) nor a place to hide one's igno-
rance, in contrast with the less transparent situation concerning the interaction
between matter and radiation. This position did not change much until the 1920s
and remained one of the deepest roots of resistance to Einstein's ideas.
- The Impact of Experiment. The first three revolutionary papers on the
old quantum theory were those by Planck [P4], Einstein [E5], and Bohr [B2]. All
three contained proposals that flouted classical concepts. Yet the resistance to the
ideas of Planck and Bohr—while certainly not absent—was much less pro-
nounced and vehement than in the case of Einstein. Why? The answer: because
of the impact of experiment.
Physicists—good physicists—enjoy scientific speculation in private but tend to
frown upon it when done in public. They are conservative revolutionaries, resist-
ing innovation as long as possible and at all intellectual cost, but embracing it
