DOC.
61
395
Doc.
61
"Discussion"
following
lecture version of
"On
the
Development
of
our
Views Concerning
the Nature
and
Constitution of Radiation"
[Doc. 60]
[Physikalische
Zeitschrift
10
(1909):
825-826]
Planck:
While I
am
taking the
liberty
to
say
a
few
words
of
comment
on
the
lecture, I
will
begin
by
joining in
the thanks of the
entire audience,
which
listened with the
greatest
of interest
to Mr.
Einstein's
presentation
and
was
stimulated
to
further reflection
even
where perhaps opposition
may
have
emerged.
Naturally, I
will restrict
myself
to
the
things
in
which
my
opinion
differs
from
that of the lecturer. After
all,
most
of
what the
lecturer has
been
saying
will
not
meet
with
any
disagreement.
I,
too,
emphasize
the
necessity of
introducing
certain
quanta.
We
cannot
progress
with
the
radiation
theory
unless
we
divide,
in
a
certain
sense,
the
energy
into
quanta, which
are
to be
conceived
as
atoms
of action.
The
question
is
now
where
to
look
for these
quanta.
According
to
the latest considerations of
Mr.
Einstein,
it
would
be
necessary
to
conceive the free radiation in
vacuum,
and
thus the light
waves
themselves,
as
atomistically
constituted,
and hence
to give
up
Maxwell's
equations.
This
seems
to
me a
step which
in
my
opinion
is
not
yet
necessary.
I
will
not
go
into details, but
will
rather
note
the [1]
following.
In the latest consideration
by
Mr.
Einstein
he inferred the
fluctuations of free radiation in
pure
vacuum
from
the
motion
of
matter.
This
inference
seems
to
me
absolutely
irreproachable
only
in the
case
that the
interactions
between
the radiation in
vacuum
and
the
motion
of
matter
are
completely
known;
if this is
not
the
case,
then the
bridge necessary
to
cross
from
the
motion
of the mirror
to
the
intensity
of the incident light is miss-
ing. However,
it
seems
to
me
that
we
know very
little about
this interaction
between
the free electrical
energy
in
vacuum
and
the
motion of
the
atoms
of
matter.
This interaction is essentially
based
on
the emission
and
absorption
of light.
Essentially
this is also the
case
for radiation
pressure, at
least
according to
the
generally accepted theory
of dispersion,
which also
reduces
reflection
to
absorption
and
emission.
However,
it is just emission
and
absorption
which
are
the obscure points about
which
we
know
very
little.
We