Albert Einstein
Physics & reality
Editor’s Note: There is probably no modern
scientist as famous as Albert Einstein. Born in
Germany in 1879 and educated in physics and
mathematics at the Swiss Federal Polytechnic
School in Zurich, he was at ½rst unable to ½nd
a teaching post, working instead as a technical
assistant in the Swiss Patent Of½ce from 1901
until 1908.
Early in 1905, Einstein published “A New
Determination of Molecular Dimensions,"
a paper that earned him a Ph.D. from the
University of Zurich. More papers followed,
and Einstein returned to teaching, in Zurich,
in Prague, and eventually in Berlin, where an
appointment in 1914 to the Prussian Academy
of Sciences allowed him to concentrate on re-
search.
In November of 1919, the Royal Society of
London announced that a scienti½c expedition
had photographed a solar eclipse and com-
pleted calculations that veri½ed the predictions
that Einstein had made in a paper published
three years before on the general theory of rel-
ativity. Virtually overnight, Einstein was
hailed as the world’s greatest genius, instantly
recognizable, thanks to “his great mane of
crispy, frizzled and very black hair, sprinkled
with gray and rising high from a lofty brow”
(as Romain Rolland described in his diary).
Permission to reprint Physics & reality grant-
ed by the Albert Einstein Archives, the Jew-
ish National & University Library, the He-
brew University of Jerusalem, Israel.
22
Dædalus Fall 2003
In the essay excerpted here, and ½rst pub-
lished in 1936, Einstein demonstrates his sub-
stantial interest in philosophy as well as sci-
ence. He is pragmatic, in insisting that the
only test ofconcepts is their usefulness in de-
scribing the physical world, yet also idealistic,
in aiming for the minimum number of con-
cepts to achieve that description.
In 1933, Einstein renounced his German
citizenship and moved to the United States,
where he lived until his death in 1955. A recipi-
ent of the Nobel Prize in physics in 1921, he
was elected a member of the American Acad-
emy of Arts & Sciences in 1924.
general consideration con-
cerning the method of science
It has often been said, and certainly not
without justi½cation, that the man of
science is a poor philosopher. Why, Poi,
should it not be the right thing for the
physicist to let the philosopher do the
philosophizing? Such might indeed be
the right thing at a time when the physi-
cist believes he has at his disposal a rigid
system of fundamental concepts and
fundamental laws which are so well es-
tablished that waves of doubt cannot
reach them; Ma, it cannot be right at a
time when the very foundations of phys-
ics itself have become problematic as
they are now. At a time like the present,
when experience forces us to seek a new-
er and more solid foundation, the physi-
cist cannot simply surrender to the phi-
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Physics
& reality
losopher the critical contemplation of
the theoretical foundations; for, he him-
self knows best, and feels more surely
where the shoe pinches. In looking for
a new foundation, he must try to make
clear in his own mind just how far the
concepts which he uses are justi½ed, E
are necessities.
The whole of science is nothing more
than a re½nement of everyday think-
ing. It is for this reason that the critical
thinking of the physicist cannot possibly
be restricted to the examination of the
concepts of his own speci½c ½eld. Lui
cannot proceed without considering
critically a much more dif½cult problem,
the problem of analyzing the nature of
everyday thinking.
Our psychological experience con-
tains, in colorful succession, sense expe-
riences, memory pictures of them, io sono-
ages, and feelings. In contrast to psy-
chology, physics treats directly only of
sense experiences and of the “under-
standing” of their connection; but even
the concept of the “real external world”
of everyday thinking rests exclusively on
sense impressions.
Now we must ½rst remark that the dif-
ferentiation between sense impressions
and images is not possible; O, at least it
is not possible with absolute certainty.
With the discussion of this problem,
which affects also the notion of reality,
we will not concern ourselves but we
shall take the existence of sense experi-
ences as given, that is to say, as psychic
experiences of a special kind.
I believe that the ½rst step in the set-
ting of a “real external world” is the for-
mation of the concept of bodily objects
and of bodily objects of various kinds.
Out of the multitude of our sense experi-
ences we take, mentally and arbitrarily,
certain repeatedly occurring complexes
of sense impressions (partly in conjunc-
tion with sense impressions which are
interpreted as signs for sense experi-
ences of others), and we correlate to
them a concept–the concept of the bod-
ily object. Considered logically this con-
cept is not identical with the totality of
sense impressions referred to; but it is a
free creation of the human (or animal)
mente. D'altra parte, this concept
owes its meaning and its justi½cation
exclusively to the totality of the sense
impressions which we associate with it.
The second step is to be found in the
fact that, in our thinking (which deter-
mines our expectation), we attribute to
this concept of the bodily object a sig-
ni½cance, which is to a high degree inde-
pendent of the sense impressions which
originally give rise to it. This is what we
mean when we attribute to the bodily
object “a real existence.” The justi½ca-
tion of such a setting rests exclusively on
the fact that, by means of such concepts
and mental relations between them, we
are able to orient ourselves in the laby-
rinth of sense impressions. These no-
tions and relations, although free mental
creations, appear to us as stronger and
more unalterable than the individual
sense experience itself, the character of
which as anything other than the result
of an illusion or hallucination is never
completely guaranteed. On the other
hand, these concepts and relations, E
indeed the postulation of real objects
E, generally speaking, of the existence
of “the real world,” have justi½cation
only in so far as they are connected with
sense impressions between which they
form a mental connection.
The very fact that the totality of our
sense experiences is such that by means
of thinking (operations with concepts,
and the creation and use of de½nite func-
tional relations between them, and the
coordination of sense experiences to
these concepts) it can be put in order,
this fact is one which leaves us in awe,
but which we shall never understand.
One may say “the eternal mystery of the
Dædalus Fall 2003
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Albert
Einstein
SU
science
world is its comprehensibility.” It is one
of the great realizations of Immanuel
Kant that the postulation of a real exter-
nal world would be senseless without
this comprehensibility.
In speaking here of “comprehensibili-
ty,” the expression is used in its most
modest sense. It implies: the production
of some sort of order among sense im-
pressions, this order being produced by
the creation of general concepts, rela-
tions between these concepts, e da
de½nite relations of some kind between
the concepts and sense experience. È
in this sense that the world of our sense
experiences is comprehensible. The fact
that it is comprehensible is a miracle.
In my opinion, nothing can be said a
priori concerning the manner in which
the concepts are to be formed and con-
nected, and how we are to coordinate
them to sense experiences. In guiding us
in the creation of such an order of sense
experiences, success alone is the deter-
mining factor. All that is necessary is to
½x a set of rules, since without such rules
the acquisition of knowledge in the de-
sired sense would be impossible. One
may compare these rules with the rules
of a game in which, while the rules
themselves are arbitrary, it is their ri-
gidity alone which makes the game pos-
sible. Tuttavia, the ½xation will never be
½nal. It will have validity only for a spe-
cial ½eld of application (cioè., there are no
½nal categories in the sense of Kant).
The connection of the elementary
concepts of everyday thinking with com-
plexes of sense experiences can only be
comprehended intuitively and it is un-
adaptable to scienti½cally logical ½xa-
zione. The totality of these connections–
none of which is expressible in concep-
tual terms–is the only thing which dif-
ferentiates the great building which is
science from a logical but empty scheme
of concepts. By means of these connec-
zioni, the purely conceptual proposi-
tions of science become general state-
ments about complexes of sense experi-
enze.
We shall call “primary concepts” such
concepts as are directly and intuitively
connected with typical complexes of
sense experiences. All other notions
are–from the physical point of view–
possessed of meaning only in so far as
they are connected, by propositions,
with the primary notions. These propo-
sitions are partially de½nitions of the
concepts (and of the statements derived
logically from them) and partially prop-
ositions not derivable from the de½ni-
zioni, which express at least indirect re-
lations between the “primary concepts,"
and in this way between sense experi-
enze. Propositions of the latter kind are
“statements about reality” or laws of
natura, cioè., propositions which have to
show their validity when applied to
sense experiences covered by primary
concepts. The question as to which of
the propositions shall be considered as
de½nitions and which as natural laws
will depend largely upon the chosen rep-
resentation. It really becomes absolutely
necessary to make this differentiation
only when one examines the degree to
which the whole system of concepts
considered is not empty from the physi-
cal point of view.
stratification of
the scientific system
The aim of science is, on the one hand, UN
comprehension, as complete as possible,
of the connection between the sense ex-
periences in their totality, E, on the
other hand, the accomplishment of this
aim by the use of a minimum of primary
concepts and relations. (Seeking, as far as
possible, logical unity in the world pic-
ture, cioè., paucity in logical elements.)
Science uses the totality of the primary
concepts, cioè., concepts directly connect-
ed with sense experiences, and proposi-
24
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Physics
& reality
tions connecting them. In its ½rst stage
of development, science does not con-
tain anything else. Our everyday think-
ing is satis½ed on the whole with this
level. Such a state of affairs cannot, how-
ever, satisfy a spirit which is really scien-
ti½cally minded; because the totality of
concepts and relations obtained in this
manner is utterly lacking in logical unity.
In order to supplement this de½ciency,
one invents a system poorer in concepts
and relations, a system retaining the pri-
mary concepts and relations of the “½rst
layer” as logically derived concepts and
relations. This new “secondary system”
pays for its higher logical unity by having
elementary concepts (concepts of the
second layer), which are no longer di-
rectly connected with complexes of
sense experiences. Further striving for
logical unity brings us to a tertiary sys-
tem, still poorer in concepts and rela-
zioni, for the deduction of the concepts
and relations of the secondary (and so
indirectly of the primary) layer. Thus the
story goes on until we have arrived at a
system of the greatest conceivable unity,
and of the greatest poverty of concepts
of the logical foundations, which is still
compatible with the observations made
by our senses. We do not know whether
or not this ambition will ever result in a
de½nitive system. If one is asked for his
opinion, he is inclined to answer no.
While wrestling with the problems,
Tuttavia, one will never give up hope
that this greatest of all aims can really
be attained to a very high degree.
An adherent to the theory of abstrac-
tion or induction might call our layers
“degrees of abstraction”; but I do not
consider it justi½able to veil the logical
independence of the concept from the
sense experiences. The relation is not
analogous to that of soup to beef but
rather of check number to overcoat.
The layers are furthermore not clearly
separated. It is not even absolutely clear
which concepts belong to the primary
layer. As a matter of fact, we are dealing
with freely formed concepts, Quale,
with a certainty suf½cient for practical
use, are intuitively connected with com-
plexes of sense experiences in such a
manner that, in any given case of experi-
ence, there is no uncertainty as to the
validity of an assertion. The essential
thing is the aim to represent the multi-
tude of concepts and propositions, close
to experience, as propositions, logically
deduced from a basis, as narrow as pos-
sible, of fundamental concepts and fun-
damental relations which themselves
can be chosen freely (axioms). The liber-
ty of choice, Tuttavia, is of a special
kind; it is not in any way similar to the
liberty of a writer of ½ction. Piuttosto, it is
similar to that of a man engaged in solv-
ing a well-designed word puzzle. Lui
may, it is true, propose any word as the
solution; Ma, there is only one word
which really solves the puzzle in all its
parts. It is a matter of faith that nature–
as she is perceptible to our ½ve senses–
takes the character of such a well-
formulated puzzle. The successes reaped
up to now by science do, it is true, give a
certain encouragement for this faith.
The multitude of layers discussed
above corresponds to the several stages
of progress which have resulted from the
struggle for unity in the course of devel-
opment. As regards the ½nal aim, inter-
mediary layers are only of temporary
natura. They must eventually disappear
as irrelevant. We have to deal, Tuttavia,
with the science of today, in which these
strata represent problematic partial suc-
cesses which support one another but
which also threaten one another, be-
cause today’s system of concepts con-
tains deep-seated incongruities.
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