DOC.
19
JULY
1914 31
19. To
Paul
Ehrenfest
[Berlin,]
8 July
[1914][1]
Dear
Ehrenfest,
Despite
all
the
assurances lately,
it
is
now
unfortunately
impossible
for
me
to
take the
trip
with
you.[2]
One
of
these
days my
mother must endure
a
serious
operation
(cancer)[3]
which has
upset
all
my plans.
But
even
if
it does
not
work
out
this
year:
I
hope
to
go
with all of
you on my
next
walking
excursion.
The
hydrogen
affair
is
very interesting.
It
seems
to
prove finally
that
quanta
without
zero
point
energy
do not conform with
experience.[4]
The
specific
heat
of
heavily compressed gases
also clamors for
zero
point
energy.
But
now we
must
try
it
with
quanta
and
zero
p[oint]
energy:[5]
w=(o+1)e-eo/kTEo=h2/32/n4J(o+1/2)2
E
=
Kr2¿{lgf
+
1e"S}'
The
expressions only differ,
of
course,
by
the
1/2
in
(o+1/2)2
in
Eo.
Would
you
not want to consider
this
case
as
well?
If it
also did
not
conform
with
experience,
it would
get
the
adiabatic
theorem in
trouble
and
surely
also
quantum theory
in
general.
If
you do,
write
me
how
the
matter
stands.-
I
have
considered Nernst’s theorem at
length
and find
that
it should be valid
if
all
solid
phases
at absolute
zero are
unmixed
(chemical individuals)
and
are
crystallized
in
space
lattices.[6]
It
is
simply
S=KlgZ,
where Z is
the
number of
possible
realizations of
the
thermodynamic state.
In
unmixed
space lattices, only
atoms
of
the
same
type
can
be
exchanged
without
leaving
the
thermodynamically
defined
state.
If the
system nv
has
v-type
atoms,
it
is
then
simply
z=II(nv!)
But
if mixed
crystals occur,
then Z
is
larger,
because states allowed
by
the
exchange
of dissimilar atoms result.
With
cordial
greetings
to
you, your
wife,
and
your
little
ones, yours,
Einstein.
Amicable
greetings
also to
your
aunt.
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