28 INTRODUCTORY
on the subject by Henry Bergson written as late as 1922 [B2]. Nevertheless, senior
men like Planck, as well as a new generation of theorists, readily recognized spe-
cial relativity to be fully specified by the two principles stated by Einstein in his
1905 paper (7a). All the rest was application of these theoretical principles. When
special relativity appeared, it was at once 'all there.' There never was an 'old'
theory of relativity.
By contrast, the 'old' quantum theory, developed in the years from 1900 to
1925, progressed by unprincipled—but tasteful—invention and application of ad
hoc rules rather than by a systematic investigation of the implications of a set of
axioms. This is not to say that relativity developed in a 'better' or 'healthier' way
than did quantum physics, but rather to stress the deep-seated differences between
the evolution of the two. Nor should one underestimate the tremendous, highly
concrete, and lasting contributions of the conquistadores, Einstein among them,
who created the old quantum theory. The following four equations illustrate bet-
ter than any long dissertation what they achieved:
V,T) = ^ I (2.1)Planck's formula for the spectral density p of blackbody radiation in thermal equi-
librium as a function of frequency v and temperature T (h = Planck's constant,
k = Boltzmann's constant, c = velocity of light), the oldest equation in the quan-
tum theory of radiation. It is remarkable that the old quantum theory would orig-
inate from the analysis of a problem as complex as blackbody radiation. From
1859 until 1926, this problem remained at the frontier of theoretical physics, first
in thermodynamics, then in electromagnetism, then in the old quantum theory,
and finally in quantum statistics;
Einstein's 1905 equation for the energy E of photoelectrons liberated from a
metallic surface irradiated by light of frequency v (19e), the oldest equation in the
quantum theory of the interaction between radiation and matter;
Einstein's 1906 equation for the specific heat c, of one gram-atom of an idealized
crystalline solid, in which all lattice points vibrate harmonically with a unique
frequency v around their equilibrium positions (R is the gas constant) (20), the
oldest equation in the quantum theory of the solid state; and
the equation given in 1913 by Niels Bohr, the oldest equation in the quantum
theory of atomic structure. Long before anyone knew what the principles of the