INTRODUCTION
TO VOLUME
3
xxvii
been thrown
on
the
problems involving
quanta
had been
provided by
the
use
of Boltzmann's
principle.
Yet there
were
still
conflicting
views
of
just
what this
principle
said
and
when it
was
valid.
Einstein had been
using
Boltzmann's
principle
for
more
than
six
years by
this
time;
it
had been his
major
heuristic
guide
in
his
exploration
of
quanta.[58]
He
had written
about
its
general significance
several
times,
most
recently
in
his
paper
on
critical
opalescence.[59]
(The
first part
of
this
paper might
be
described
as setting
forth
the
beginning
of
statistical
thermodynamics, a
statis-
tical
theory
of
macroscopic systems
that
does not
call
upon an underlying
mechanics.)
In
his
Solvay
discussion remarks Einstein
analyzed
the
connec-
tion between
Boltzmann's
principle
and
irreversibility,
and then showed how
the
principle
could be
given
precise physical meaning
as a
relationship
be-
tween
measurable
quantities.
The
Solvay Congress brought
the
problems
associated with the
hypothesis
of
quanta
to
the attention of
some
who had
never previously
concerned them-
selves
with
such
matters.[60]
The
inescapability
of
some
kind of
quanta,
some
discreteness in the
natural
world,
seems
to have
been
impressed
on
practically
all
of those
present.
Marcel Brillouin
expressed
the
conclusion he had drawn
from the
reports
and
discussions,
a
conclusion
which,
as
he
recognized, might
seem
"rather
timid"
to
the
younger participants:
"It
seems
from
now on
quite
certain
that
we
will
have
to
introduce into
our
physical
and chemical
concepts
a
discontinuity,
an
element that
changes
by jumps, something
of
which
we
had
no
idea
at all
a
few
years
ago."[61]
What the
Solvay
Congress
meant to Einstein is
harder
to
evaluate. His
note
to
Solvay, thanking
him
for "the
extremely
beautiful week" in
Brussels, pro-
claimed
that
the
Congress
would
always
be
"one
of
the
most
beautiful
mem-
ories" of
his
life.[62]
To
his
friends, however,
Einstein reacted
quite
differently.
"The whole
story
would have been
a
delight
for diabolical
Jesuits,"
he wrote
[58]See
Einstein
1905i
(Vol. 2,
Doc.
52),
Einstein
1907b
(Vol. 2,
Doc.
39),
Einstein
1909b
(Vol.
2,
Doc.
56),
and Einstein
1909c
(Vol. 2,
Doc.
60).
[59]Einstein
1910d
(Doc.
9).
[60]This
was
the
case
for Henri
Poincare. See Poincare 1912 and also McCormmach
1967.
[61]"Peut-etre
ma
conclusion semblera-t-elle bien timide
aux plus jeunes
d'entre
nous
...
Il
semble desormais bien certain
qu'il
faudra introduire dans
nos conceptions physiques
et
chimi-
ques une
discontinuite,
un
element variant
par
sauts,
dont
nous
n'avions
aucune
idee
il
y
a
quelques
annees." Marcel Brillouin in
Rapports
1912,
p.
451. Brillouin,
then
a fifty-six-year-old
professor
of mathematical
physics at
the
College
de
France,
had worked
on
the kinetic
theory
of
gases,
but not
on
any
problems
related
to
quanta.
[62]"die
überaus schöne Woche"
...
"Der
Solvay-Kongress
wird
stets
eine der schönsten
Erinnerungen
meines Lebens bilden." Einstein to Ernest
Solvay,
22
November
1911.