DOC.
33
SCHWARZSCHILD
211
Doc.
33
Einstein's Memorial Lecture
on
Karl
Schwarzschild
Not translated for this volume.
212
DOC. 34 EMISSION
&
ABSORPTION OF RADIATION
Doc.
34
Emission and
Absorption
of Radiation in
Quantum Theory
by
A. Einstein
(Received
on
July
17, 1916)
[p.
318]
Sixteen
years ago,
when
Planck
created
quantum theory
by deriving
his radiation
[1]
formula,
he took the
following approach.
He calculated the
mean
energy
E of
a
resonator
as a
function of
temperature according
to
his
newly
found
quantum-
theoretic basic
principles,
and determined from this the radiation
density
p as a
function of
frequency v
and
temperature.
He
accomplished
this
by
deriving-based
upon electromagnetic
considerations-a
relation between radiation
density
and
[2]
resonator
energy
E:
E
=
-^£-.
(1)
87tv2
His derivation
was
of
unparalleled
boldness,
but found
brilliant confirmation. Not
only
the radiation formula
proper
and
the calculated
value
of
the
elementary quantum
[3]
in it
was
confirmed,
but
also
the
quantum-theoretically
calculated value
of
E
was
[4]
confirmed
by
later
investigations
on
specific
heat. In this
manner, equation (1),
originally
found
by electromagnetic
reasoning, was
also confirmed.
However,
it
remained
unsatisfactory
that the
electromagnetic-mechanical analysis,
which led
to
[5]
(1),
is
incompatible
with
quantum theory,
and
it is
not
surprising
that Planck
himself
and all theoreticians
who
work
on
this
topic incessantly
tried to
modify
the
theory
[6]
such
as
to
base it
on
noncontradictory
foundations.
[7]
Since
Bohr's
theory
of
spectra
has achieved its
great
successes,
it
seems
no
longer
doubtful
that the basic idea
of
quantum
theory
must be maintained. It
so
appears
that
the
uniformity
of
the
theory
must be established such that the
electromagneto-mechanical
considerations,
which led
Planck
to
equation (1), are
to
be
replaced by quantum-theoretical contemplations
on
the interaction between
matter
[p. 319]
and radiation.
In
this
endeavor I feel
galvanized by
the
following
consideration,
[8]
which
is
attractive both for its
simplicity
and
generality.
§1.
Planck's Resonator
in
a
Field
of Radiation
The behavior
of
a
monochromatic resonator in
a
field
of
radiation,
according
to the
classical
theory, can
be
easily
understood
if
one
recalls the
manner
of
treatment that
[9] was
first used in the
theory
of
BROWNian
movement. Let
E
be the
energy
of
the
