118
DOCS.
103,
104 AUGUST
1915
There
are
serious
doubts about the
assumption
of
zero-point energy
existing
in
elastic
oscillations.
For
if at
falling
temperatures
the
(thermal)
elastic
vibrational
energy
does not
drop
to
zero
but
only drops
to
a finite positive value,
then
an
analogous
behavior
must
be
expected
of all
temperature-dependent properties
of
solids, i.e.,
the
approach
toward constant
finite
values
at low temperatures.
But
this contradicts
Kamerlingh
Onnes’s
important
discovery, according
to which
pure
metals
become
“superconductors” on approaching
absolute
zero.[8]
It
is
very
good
of
you
to take such
trouble
with
the
conference
proceedings.
If
I
can
relieve
you
of
some
of
it,
I
shall do
so
gladly
(e.g., correcting
the
discussion
contributions
by
the
German
speakers).
With
cordial
greetings, yours,
A.
Einstein.
[6]Recipient’s
appended
note: “If
we
want to
introduce
zero-point energy
in Planck’s
sense,
in
my
view
we
may
not
deny
that
it consists in
motions, i.e.,
here
specifically
in
elastic oscillations in
Debye’s
sense.
Thus
it
is
furthermore
inevitable
that
we
attribute
to
that
energy
an
influence
on
the
intensity
of Laue’s interference
points.”
104. To Wander de
Haas
[Berlin,]
7 August 1915
Dear de
Haas,
I just
received
the
offer
from
the
mover
(Schur).[1]
He asserts
that the
price
of removals has
risen
greatly
as a
result
of
the
war;
he
asks for
a
total of
590 M.
I
am going
to
have
a
second cost estimate made
by
another
mover
and shall
take
Schur if the second
is not cheaper.-
Lots of
luck
on
your
work.[2] I
am now
trying
resonance-free
alternating
current
through
a
refinement
of
the
optical
method,
but
I
fear effects
at
double
the
frequency.
Affectionate
greetings
to
you
&
yours,
from
your
Einstein.