### TL;DR
Bohr's paper is a direct response to the famous 1935 pap...
Further reading: [J. S. Bell: On the Einstein Podolsky Rosen parado...
Bohr's response to the EPR paradox was essential in defending the i...
Bohr points out that the act of measurement in quantum mechanics fu...
© 1935 Nature Publishing Group
JULY
13,
1935
NATURE
65
Letters
to
the Editor
The
Editor
does
not
hold
himself
responsible
for
opinions
expressed
by
his
correspondents.
J:Ie
cannot undertake to return, or to correspond
with
the writers of,
rej"ected
manuscripts
mtendedfor
this or
any
other
part
of
NATURE.
No
notice
is
taken
of
anonymous
communications.
NOTES
ON
POINTS
IN
SOME
OF
THIS
WEEK'S
LETTERS
APPEAR
ON
P. 71.
CORRESPONDENTS
ARE
INVITED
TO
ATTACH
SIMILAR
SUMMARIES
TO
THEIR
COMMUNICATIONS.
Quantum
Mechanics
and
Physical Reality
IN a
recent
article
by
A.
Einstein,
B.
Podolsky
and
N.
Rosen,
which
appeared
in
the
Physical
Review
of
May
15,
and
was
reviewed
in
NATURE
of
June
22,
the
question
of
the
completeness
of
quantum
me-
chanical
description
has
been
discussed
on
the
basis
of
a
"criterion
of
physical
reality",
which
the
authors
formulate
as
follows :
"If,
without
in
any
way
disturbing
a
system,
we
can
predict
with
certainty
the
value
of
a
physical
quantity,
then
there
exists
an
element
of
physical
reality
corresponding
to
this
physical
quantity".
Since,
as
the
authors
show,
it
is
always
possible
in
quantum
theory,
just
as
in
classical
theory,
to
predict
the
value
of
any
variable
involved
in
the
description
of
a
mechanical
system
from
measurements
per-
formed
on
other
systems,
which
have
only
tem-
porarily
been
in
interaction
with
the
system
under
investigation
;
and
since
in
contrast
to
classical
mechanics
it
is
never
possible
in
quantum
mechanics
to
assign definite
values
to
both
of
two
conjugate
variables,
the
authors
conclude
from
their
criterion
that
quantum
mechanical
description
of
physical
reality
is
incomplete.
I
should
like
to
point
out,
however,
that
the
named
criterion
contains
an
essential
ambiguity
when
it
is
applied
to
problems
of
quantum
mechanics.
It
is
true
that
in
the
measurements
under
considera-
tion
any
direct
mechanical
interaction
of
the
system
and
the
measuring
agencies is
excluded,
but
a closer
examination
reveals
that
the
procedure
of
measure-
ments
has
an
essential
influence
on
the
conditions
on
which
the
very
definition
of
the
physical
quantities
in
question
rests.
Since
these
conditions
must
be
considered
as
an
inherent
element
of
any
phenomenon
to
which
the
term
"physical
reality"
can
be
un-
ambiguously
applied,
the
conclusion
of
the
above-
mentioned
authors
would
not
appear
to
be
justified.
A fuller
development
of
this
argument
will
be
given
in
an
article
to
be
published
shortly
in
the
Physical
Review.
Institute
of
Theoretical
Physics,
Copenhagen.
June
29.
N.
BoHR.
Isotopic
Constitution
of
Palladium
and
Gold
THESE
two
elements
are
among
the
few
from
which
positively
charged
atoms
have
not
been
obtained
by
means
of
volatile
compounds
introduced
into
the
electrical
discharge
or
by
means
of
anode
rays.
In
a
letter
in
NATURE\
the
possibility
of
using
the
ions
from a
high-frequency
spark
was
pointed
out.
With
the
mass-spectrograph
[recently
described
in
NATURE
2
]
it
was
found
that
palladium
consists
of
six
isotopes
with
atomic
masses
102, 104, 105, 106,
108,
llO.
They
could
be
compared
with
doubly-
charged
platinum
and
gold
atoms
which
were
present
as
a
slight
impurity.
The
four
middle
components
are
about
equally
strong;
the
one
at
llO
is
weaker,
and
the
lightest
at
102 is
the
faintest.
From
its
atomic
weight
197·2
and
the
behaviour
of
other
elements
of
odd
atomic
number,
it
was
anticipated
that
gold
would
have
two
isotopes
at
197
and
199,
one
about
ten
times
the
intensity
of
the
other.
It
was
somewhat
of
a
surprise
to
find
that
no
second
component
could
be
found.
Ex-
posures
were
made
with
300
and
500
times
the
time
required
to
show
the
main
line,
and
failed
to
show
any
trace
of
a
heavier
isotope.
It
is
thus
very
prob-
able
that
gold
has
only
one
component,
and
that
the
accepted
atomic
weight
is
too
high.
University
of
Chicago.
June
12.
1
NATURE,
135, 542 ; 1935.
1
NATURE,
135, 993 ; 1935.
A.
J.
DEMPSTER.
Platinum
Isotopes and their Nuclear
Spin
Using
a
water-cooled
hollow
cathode
of
a
new
design,
the
hyperfine
structure
of
the
arc
lines
of
platinum
AA
3408
and
3042 A.
have
been
studied.
These
two
lines
have
a
common
lower
level 5d
8
6s2as
F,
;
and
the
similarity
of
their
structure
patterns
leads
to
the
conclusion
that
in
neither
case is
the
upper
level
split.
The
lines
have
the
following
structure
:
Wave-
length
Classification
1
Structure
(in I.A.)
(In
em.·')
3408·13
5d'6s'
a'F,
- 5d
8
6s6p
z'D',
+
0·161
(5),
0·000
(18),
-
0·086
(7), -
0·176
(1),
3042·75
5d
8
6s'
a'F,-
5d'6s6p z•G•,
-
0·314
(4). (vide Fig. 1)
+
0·162
(5),
0·000
(18)
-
0·087
(7),-
0·174
(1),
-
0·314
(4).
An
examination
of
the
structure
leads
to
the
unique
inference
that
the
three
central
components
0·000
(18), -
0·086
(7)
and
-
0·176
(1)
have
to
be
ascribed
to
the
even
isotopes
196, 194
and
192
respectively,
the
remaining
two
components
being
due
to
the
odd
isotope
195
with
a.
nuclear
spin
of
ih/2rt.
The
centre
of
gravity
of
the
latter
com-
ponents
falls
at
-
0·050
cm.-
1
between
the
bright
components
due
to
196
and
194.
The
deeper
level
5d
8
6sa
3
D
2
shows
no
measurable
isotopic
displacement.
The
hyperfine
levels
in
platinum
are
inverted.
These
results
are
confirmed
by
the
analysis
of
eight
other
arc
lines
of
platinum,
namely,
2998, 2929, 2734,
2719, 2705, 2702, 2659
and
2650 A.
Neglecting
Further reading: [J. S. Bell: On the Einstein Podolsky Rosen paradox](https://fermatslibrary.com/p/083d72a6)
Bohr points out that the act of measurement in quantum mechanics fundamentally alters the conditions under which physical quantities are defined. This perspective reinforced the idea that quantum mechanics does not provide definite values for conjugate variables (ex: position and momentum) simultaneously, due to the observer's role in defining reality.
Bohr's response to the EPR paradox was essential in defending the idea that quantum mechanics despite its counterintuitive nature is a complete theory for describing physical phenomena.
This response from Bohr laid the groundwork for future generations of physicists and helped solidify the Copenhagen interpretation of quantum mechanics. This interpretation became one of the most widely accepted frameworks for understanding quantum mechanics and still informs much of modern physics today.
Read on: [Copenhagen interpretation](https://en.wikipedia.org/wiki/Copenhagen_interpretation)
### TL;DR
Bohr's paper is a direct response to the famous 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen - the so called EPR paper. EPR argued that quantum mechanic was an incomplete theory because it could not describe all elements of physical reality simultaneously, as demonstrated by EPR's proposed "criterion of physical reality."
Bohr's response challenges their conclusions and highlights the philosophical and interpretative issues within quantum mechanics. The paper significantly contributed to the philosophical debate about the nature of reality and how it is described in physics. Bohr's insistence that the conditions of measurement are part of defining what is real in a quantum system challenged classical assumptions about objectivity and determinism.