DOC.
56
357
Doc. 56
ON
THE
PRESENT
STATUS OF THE
RADIATION
PROBLEM
by
A.
Einstein
[Physikalische
Zeitschrift
10
(1909):
185-193]
This
journal has recently published expressions of opinion
by
Messrs.
H. A.
Lorentz1,
Jeans2, and
Ritz3
which
offer
good
insight
into the
[4]
present status
of this
extremely important
problem.
In the belief that it
would
be
of benefit if all those
who
have seriously
thought
about
this
matter
would communicate
their
views,
even
if
they
have
not
been
able
to
arrive
at
a
final
result, I
would
like
to
communicate
the
following.
1.
The simplest
form in which
we can
express
the
laws of
electro-
dynamics
established
so
far is that
presented
by
the
Maxwell-Lorentz
partial
differential
equations.
In
contrast to
Mr.
Ritz3, I
regard
the
forms
containing
retarded functions
as merely
auxiliary
mathematical forms.
The
[5]
reason
I
see myself
compelled
to
take this
view
is first
of
all that those
forms
do
not
subsume
the
energy
principle,
while
I
believe that
we
should
adhere
to
the strict validity of the
energy
principle
until
we
shall
have
found
important
reasons
for
renouncing
this
guiding star.
It is
certainly
true
that Maxwell's
equations
for
empty
space,
taken
by
themselves,
do not say
anything,
that
they only represent
an
intermediary construct;
but,
as
is well
known,
exactly
the
same
could
be
said
about Newton's equations
of motion,
as
well
as
about
any
theory
that
needs to be
supplemented
by
other theories in
order
to yield
a
picture for
a
complex
of
phenomena.
What
distinguishes
the
Maxwell-Lorentz differential
equations from
the
forms
that contain retarded
functions is the circumstance that
they
yield
an
expression
for the
energy
and
the
momentum
of the
system
under
consideration for
any
instant of time,
relative
to
any
unaccelerated
coordinate
system. With
a
theory
that
operates
with retarded forces it is
not
possible
to
describe the instantaneous
state
of
a
system
at
all without
using
earlier
states
of the
system
for this
description.
1H.
A.
Lorentz,
Phys.
Zeit.
9 (1908): 562-563.
2J.
H.
Jeans,
Phys.
Zeit.
9
(1908):
853-855.
3W.
Ritz,
Phys.
Zeit.
9
(1908): 903-907.
[1]
[2]
[3]