EARLY WORK ON QUANTUM HYPOTHESIS 145
was an important turning point leading
to the
general recognition
that
Planck's
law
implies
fundamental
changes
in the foundations
of
physics.[76]
Even those who
accepted
the need for
some
form
of
energy quantization
objected
to
the
concept
of
light quanta,
since
numerous optical phenomena seem
to
require a wave
theory
for
their
explanation.[77]
In 1907 Planck wrote Einstein:
"I
am
not
looking
for the
meaning
of
the
elementary quantum
of
action
(light quantum)
in the
vacuum,
but at the
places
of
absorption
and
emission,
and
assume
that
vacuum processes are exactly
described
by
Max-
well's
equations"
("ich
suche die
Bedeutung
des elementaren
Wirkungsquantums
(Lichtquants)
nicht im
Vakuum,
sondern
an
der Stelle der
Absorption u.
Emission, und
nehme
an,
daß die
Vorgänge
im Vakuum durch die Maxwellsche
Gleichungen genau
dargestellt werden").[78]
Of Einstein's
German-speaking colleagues, only
the
experimentalist
Johannes
Stark
supported
the idea
of
an
atomistic structure
of
radiation in
1909.[79]
He
argued
for the
existence
of
localized
energy
quanta
in
X-rays,
in
opposition
to the
prevailing electromag-
netic
wave-pulse interpretation.[80]
He observed that the
absorption
of
X-rays by a
metal
results in the
ejection
of
electrons
of
almost
the
same energy as
the cathode
rays
producing
the
X-rays,
no
matter how
great
the distance traveled
by
the
X-rays
between
production
and
absorption.[81]
Although
Einstein
was
familiar with Lorentz 1908b and the discussion
papers
of
Jeans
and
Ritz,
he had not read Lorentz 1908a before
publication
of
Einstein 1909b
(Doc.
56),
his contribution to the discussion initiated
by
Lorentz's
paper.[82]
Shortly
afterwards, he
sent Lorentz
a copy
of
his
paper, describing
the work
as
"the
insignificant
result
of
years
of reflection"
("das
geringfügige Ergebnis von
jahrelangem Nachdenken"),
adding:
"I
have not been able to attain
a
real
grasp
of
the
matter" ("Zu
einem wirklichen Erfassen
der Sache habe ich nicht
vordringen
können").[83]
The
paper presents
Lorentz
to
Wilhelm
Wien, 6
June
1908,
quoted
in
part
in Kuhn
1978,
p.
302, note 19.
[76]
For further discussion of
Lorentz 1908a
and its
aftermath,
see
Kuhn
1978,
pp.
189-205.
[77]
Of
particular concern were
observations of
interference effects with radiation
of
even
the
weakest
intensity
(see,
e.g.,
Taylor 1909).
For
this
argument against light quanta,
see
Hendrik
Lorentz
to Einstein, 6 May
1909. For
a summary
of
the views
of
several German theorists
on
this
question, see
Jungnickel
and
McCormmach
1986b, pp.305-306.
[78]
Max Planck to
Einstein,
6
July
1907. See
also
Planck's
comment
on
Einstein 1909c
(Doc.
60),
in Einstein
et
al.
1909c
(Doc. 61).
Laue
wrote Einstein
in
a
similar vein
a year
earlier
(see
Max
Laue to
Einstein, 2
June
1906).
Planck's
struggle
with the foundations
of
his
ra-
diation formula
throughout
this
period are ex-
amined
in
Needell
1980.
[79]
See Stark
1909a,
and Johannes Stark to
Einstein,
8 April
1909. For
a
discussion
of
Stark's
research
on X-rays, including
his
sup-
port
of
the
quantum hypothesis, see
Wheaton
1978a, pp.125-143.
[80]
For
a
discussion
of
the
"pulse theory,"
see
Wheaton 1978a.
[81]
Einstein referred
to
this
phenomenon
in
support
of
the
light quantum hypothesis during
his
Salzburg
lecture,
and Stark reviewed his
findings during
the discussion
of Einstein's
lec-
ture (see
Einstein
1909c
[Doc. 60],
p.
492, and
Stark's
comment
in Einstein
et
al.
1909c
[Doc.
61]).
Einstein continued the discussion
of
X–
rays
in
a
letter to Arnold Sommerfeld
of
19
Jan-
uary
1910.
[82]
This
paper was published on
15
March
1909. He wrote Lorentz
on
13
April
1909 that
he had
just
read Lorentz
1909a-a
slight
revi-
sion
of
Lorentz
1908a-in
terms
indicating
that
he had
not
previously
read Lorentz 1908a.
[83]
Einstein to Hendrik
Lorentz, 30 March