DOCUMENT 347 JUNE
1917 461
potential.
In
1913,
in the second
part
of
his
critique
of
the
“Entwurf”
theory,
Mie had
argued
that the
invariance
of
Einstein’s
theory
under
general
linear transformations should
likewise be
understood
in
terms
of
the
principle
of
the
relativity
of
the
gravitational
potential
and
not,
as
Einstein
did,
in
terms
of
a generalization
of
the
principle
of
the
relativity
of
motion
(Mie
1914b,
pp.
169-172).
The metric
tensor and invariance
under
general
linear
transformations,
Mie
argued, play
the
same
role
in
the
“Entwurf”
theory as
the scalar
potential
and invariance
under
rescaling
of
the units
of
measurement
in
his
own
theory, pointing
out
that
he did not
see
the
advantage
of
Einstein’s
complicated
tensor
theory over
his
own
simpler
scalar
theory (Mie 1915, p. 252).
In
his Wolfskehl
lectures, however,
Mie
recognized
that in the
generally
covariant version
of
the tensor
theory developed
in the meantime
by
Einstein
and
Hilbert,
all effects
of
gravitation on physical
phenomena
can
be treated in
a way
similar
to
that in which the effect
of
a
constant
gravitational
potential had been treated in Mie’s
earlier
theory
(see
Mie
1917b,
pp.
576-578).
He
formulated the “axiom
of
the
general relativity
of
the
gravitational
field”
(“Axiom von
der
allgemeinen
Relativität des
Gravitationsfeldes,”
Mie
1917c,
p.
597),
a gener-
alization
of
the
principle
of
the
relativity
of
the
gravitational potential,
which
applies
to
any region
of
space-time no
matter
whether the
potential (represented by
the
metric
field)
is
constant
or
not. Essen-
tially,
this
generalized principle
states that
one
obtains
an
accurate
description
of
a physical
system
in
the
presence
of
a gravitational
field from the
description,
in
some
inertial
frame,
of
the
correspond-
ing
system
in the absence
of
a gravitational
field
by changing,
in
an appropriate
manner,
the coordi-
nates
and,
in
general,
the
space-time geometry.
The
general
covariance
of
general relativity,
Mie
argued (as
he had done
for
the covariance
under
general
linear
transformations of
the
“Entwurf”
theory),
should be understood
in
terms
of this
principle
and not in terms
of
a general relativity
of
motion
(Mie 1917c,
p.
598).
For
a
concise
statement
of
Mie’s
position, see
Mie
1920b, pp.
651-653.
The ideas
are explained
for
a more
general
audience in Mie 1921.
[4]The
“uncertainty”
refers
to
the
complete
freedom in
choosing
coordinates.
[5]Mie
had left the
University
of
Greifswald
earlier
in the
year
to
accept an appointment
at the Uni-
versity
of
Halle.
347. From Wilhelm Wien
Würzburg Pleicherring
8,
den
1.
Juni 1917
Herrn
Prof.
Dr.
Einstein Berlin Wittelsbacherstraße
13
Sehr
geehrter
Herr
Kollege!
Beim
Lesen Ihrer interessanten
Abhandlung
über
die
Quantentheorie (P.
Z. 1917
S.121)[1]
ist mir ein Bedenken
gekommen,
das ich Ihnen mitteilen möchte.
Sie betrachten das
Gleichgewicht
zwischen
Molekülen
und
Strahlung
und
kom-
men
zu
dem
Ergebnis,
daß das
Gleichgewicht nur
bestehen
kann,
wenn
die Strah-
lung
in
einer bestimmten
Richtung ausgesandt
wird und
auf
das aussendende Mo-
lekül ein
Bewegungsmoment überträgt.[2]
Nun kann aber dieses
System
niemals
vollständig
sein,
weil die auftreffende
Strahlung
licht-elektrische
Elektronen
aus-
löst und diese wiederum
Strahlung erregen.
Beim
Aussenden eines Elektrons wird
2
hv
ein
Bewegungsmoment
übertragen
von
der Größe
--
wenn
die
Beziehung
171-v2
=
hv
gilt.
Andrerseits wird das
ausgesandte
Elektron beim Zusammenstoß
wieder
Bewegungsmomente
übertragen,
deren Größe unbekannt
bleibt,
da das
Elektron
nicht
notwendigerweise
durch
nur
einen
einzigen
unelastischen
Stoß
zur
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