194
DOCS.
191,
192 FEBRUARY
1916
e-e/kT
for
T
=
0
dizzyingly
small. Hence
the
statement: The
pencil
cannot
stand
at absolute
zero!
Corresponding
assertion. Solid carbon and solid
oxygen
cannot be
contiguous
to
one
another
at
T
=
0. Only CO2
exists.
Proof
e-E/kT
is
frightfully
small! You
stuntman![1]
General
relativity is
now,
almost
exactly
since
we
last
saw
each
other,
finally
resolved. General covariance of
the
field
equations.
Perihelion motion of
Mercury
explained exactly. Theory very
transparent
and
fine.
Lorentz, Ehrenfest, Planck,
and
Born
are
convinced
adherents,
likewise
Hilbert.
Reflect
on
the
objection;
you
will
surely
come
to
the
conviction that it
is
justified.
Cordial
greetings, yours,
A.
Einstein.
192. To Otto Stern
[Berlin,
after
15 February
1916][1]
Dear Mr.
Stern,
I
remain
with the
example
of
the
pencil.[2]
I
assert: The fact
that
we
may
apply thermodynamics
to
chemical
systems
at
all,
ultimately
rests
on
that
we
do
treat
a
change, happening
so quickly
that Brownian
motion
does
not have
time
to
knock
down the
standing
pencil,
as
an
infinitely
slowly
reversible
change,
in the
thermodynamic
sense.
On
the
basis of
your reasoning you
can
propose
at
most
one
of two statements:
a)
The mixed crystal (in the sense
of
your correctly given
definition)[3]
does
not
exist
at T =
0.
b) Although it exists, you cannot speak
about
its entropy, because
the state
cannot
be produced by reversing the process.
Now, (a)
could be asserted
with
the
same
justification (mutatis
mutandis)
of
any
chemical
system
that
is not at
the absolute
entropy
maximum
(system
C
|
O2).
With
(b),
if it
were
correct,
you
could
slaughter
almost all
of
physical chemistry.
But
for
the
statement: