DOCUMENT 527 APRIL 1918 743
pp.
478-480,
Weyl argued
that the notion
on
which Einstein’s
objection was
based,
namely
that rods
and clocks
directly measure
the line
element,
is
problematic even
in
ordinary general relativity.
In
par-
ticular,
he
argued,
it is not at all
clear
whether
a
clock continues
to
measure
the
length
of
its
worldline
when
it
is not
moving on a geodesic,
such
as
in the
presence
of
a strong
and
fluctuating
electromag-
netic field.
Citing
both
Weyl
1918c,
pp.
182-184, and Kretschmann
1917,
he added that clocks and
rods
can
be
dispensed
with
altogether
in the formulation
of
general relativity
and that
light signals
suffice
as
the
means
of
measuring
the line
element
and the
components
of
the metric
tensor
up
to
a
constant factor
reflecting
the freedom
to
choose
a (global)
unit
of
length. Weyl
then
pointed
out that
to
a very good approximation
the line element in his
theory
would almost
always
be
equal
to
the line
element
in
general relativity.
Even
if
it
is
assumed,
he
continued,
that clocks
measure
the
integral
of
the line
element
along
their
worldlines
(which
in
Weyl’s theory, as
Einstein had
pointed
out,
would
make the
rate
of
a
clock
path dependent),
the
theory
would still be
compatible
with the existence
of
identifiable
spectral
lines
(the empirical
evidence
Einstein
had cited
against
the
theory),
because,
as
Weyl claimed,
"the influence
of
any stormy prehistory
will
quickly
fade
away"
("der
Einfluß einer
etwaigen
stürmischen
Vorgeschichte
wird rasch
abklingen,"
Weyl
1918b, pp.
479-480).
Einstein’s
response
to
Weyl’s argument can
be found in
a
letter
to
Walter Dällenbach about six weeks later
(see
Doc.
565).
[2]See
Doc.
512 for
an
account
of
the difficulties that Einstein’s
objection
to
Weyl’s theory
had
caused two
weeks
earlier in
getting
Weyl’s
paper
accepted
for
publication
in the
proceedings
of
the
Prussian
Academy.
In the
end,
both
Einstein’s
objection (in
the formulation
given
in Doc.
512)
and
Weyl’s
rejoinder
were appended
to the
paper (Einstein
1918h
[Vol.
7,
Doc.
8],
Weyl
1918b, pp.
478-
480).
[3]Walther
Nernst
had
protested
in the Prussian
Academy against
silent
acceptance
of
Weyl’s
theory (see
Doc.
512).
[4]The
phrase
that Einstein had used
more
than
a
week
earlier
to
express
his admiration for
Weyl’s
theory
from
a
purely
theoretical
point
of
view while
rejecting
it
as a description
of
physical reality
(see
Doc.
512).
527. From Marga
Planck[1]
[Berlin,]
30.
April
1918.
Sehr
geehrter
Herr
Professor!
Haben Sie
herzlichen
Dank
für
die
Zusendung
Ihrer
"Predigt",
die wir
uns ge-
stern
nochmals
vorgelesen
haben.[2]
Wir
freuten
uns
wieder
an
Ihren
Gedanken;
und sie
nun
als
Erinnerung
an
den schönen
Abend
zu
besitzen.[3]
Und ich
selbst
freue mich noch
ganz
besonders-das möchte
ich Ihnen heut
zum
Ausdruck brin-
gen-,
daß mein Mann in Ihnen einen
so warmen
Freund
gefunden
hat!
Mit
bestem
Gruß Ihre
Marga
Planck.
ALS.
[19
274].
[1]Planck,
née
von
Hoesslin.
[2]Einstein
1918e
(Vol. 7,
Doc.
7),
delivered at
a special meeting
of
the Deutsche
Physikalische
Gesellschaft
on
26
April
in
honor of
Planck’s sixtieth
birthday
(on
23
April).
For
a published
account
of
the
festivities, see
Swinne
1918.
[3]The
participants
assembled in
a
restaurant
in the Friedrichstraße after the celebration
(see
Moritz
Schlick
to
Gerda
T.,
4
May
1918,
excerpt
in
Stargardt
auction
catalogue
659 [16-17 March
1995],
lot
496).
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