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jeudi 11 septembre 2014

Mach, Poincaré and Einstein as ennemies of materialism and campaigning against the heirs of Isaac Newton

by Yanick Toutain

under construction


Un de leur thuriféraires, un relativiste partisan de Einstein, successeur de Einstein à Vienne, le principal biographe (avec l'auteur de Créateur et rebelle) de Albert Einstein – Philippe Frank – a la franchise de nous le révéler :

L'idée de Mach que les lois générales de la science sont simples résumés de faits expérimentaux, et l'idée de Poincaré que ce sont libres créations de l'esprit semblent s'opposer diamétralement l'une de l'autre. Mais si 1'on considère les courants intellectuels du dernier quart du 19° siècle, on peut voir qu'elles étaient seulement deux ailes du même mouvement intellectuel, généralement connu sous le nom de mouvement positiviste.» (Einstein, sa vie et son temps P.84 10- MOUVEMENTS POSITIVISTES ET PRAGMATISTES. LE MONDE PHYSIQUE AVANT EINSTEIN)


8 Ernst Mach: The General Laws of Physics Are Summaries of Observations Organized in Simple Forms 38
9 Henri Polncarl: The General Laws of Physics Are Free Creations of the Human Mind 40
10 Positivistic and Pragmatic Movements 42

7. Critics of the Mechanistic Philosophy Toward the end of the nineteenth century more and more physical phenomena were discovered that could be explained
only with great difficulty and in a very involved way
Conceptions of the Physical World before Einstein by the principles of Newtonian mechanics. As a consequence new thories appeared in which it was not clear whether they
could be derived from Newtonian mechanics, but which were accepted as temporary representations of the observed phenomena.
Was this true knowledge of nature or only a "mathematical description/
as the Copernican system was considered in medieval physics ? These doubts could not be resolved so long
as it was believed that there were philosophical proofs according to which reduction to Newtonian mechanics provided the
only possibility for the true understanding of nature.
During the last quarter of the nineteenth century a critical attitude toward this mechanistic philosophy became more and
more evident. An understanding of this criticism is an essential prerequisite for the understanding of Einstein's theory and its
position in the development of our knowledge of nature. As long as it was believed that Newtonian mechanics was based
ultimately on human reason and could not be shaken by scientific advance, every attempt such as that of Einstein, to establish
a theory of motion not founded on Newton's theory necessarily appeared absurd. The critics of mechanistic philosophy plowed
the soil in which Einstein was then able to plant his seeds.
As the first of these critics, we may mention Gustav Kirchhoff, the discoverer of spectral analysis. In 1876 he stated that the task
of mechanics was "to describe completely and as simply as possible motions occurring in nature." This meant that Newtonian
mechanics is itself only a convenient scheme for a simple presentation of the phenomena of motion that we observe in daily
experience. It does not give us an "understanding" of these occurrences in any other philosophical sense. By thus contravening
the general opinion that Newton's principles of mechanics are self-evident to the human mind, he created something of a sensation
among natural scientists and philosophers.
Furthermore, with KirchhofFs conception that mechanics is only a description of the phenomena of motion, the mechanical
explanations of the phenomena in optics, electricity, heat, etc.
the aim of mechanistic physics became simply descriptions of these results in terms of a pattern that had been found to be
most suitable for mechanics. Why should one describe by this roundabout method of using mechanics instead of trying to find
directly the most suitable scheme for the description of various phenomena? Newtonian mechanics was thus deprived of its
special philosophical status.
In 1888 Heinrich Hertz discovered the electromagnetic waves,
Einstein: His Life and Times
which form the basis of our modem wireless telegraphy and radio, and he then set out to explain these phenomena in terms
of a physical theory. He took as his starting-point Maxwell's theory of electromagnetic fields. James Clerk Maxwell had derived
his fundamental equation from mechanistic physics by assuming that electromagnetic phenomena are actually mechanical
oscillations in the ether. Hertz noticed that in doing this Maxwell had been compelled to invent mechanisms that were
very difficult to calculate, and found it was simpler to represent electromagnetic phenomena directly by means of Maxwell's
equation between electric and magnetic fields and charges. Since it was also evident to him, however, that these relations could
not be derived directly from experience, he was led to a consideration of the logical character of these equations. In 1889 he
made a remark that can be regarded as the program for the new approach to physics, a conception that was eventually to replace
the mechanistic view. Hertz said:
"But in no way can a direct proof of Maxwell's equations be deduced from experience. It appears most logical, therefore, to regard
them independently of the way in which they had been arrived at, and consider them as hypothetical assumptions and let their plausibility
depend upon the very large number of natural laws which they embrace. If we take up this point of view we can dispense with a
number of auxiliary ideas which render the understanding of Maxwell's theory more difficult."
Thus Hertz consciously abandoned that which during both the organismic and the mechanistic period was described as the
"philosophical" foundation of physics. He maintained that it was sufficient to have a knowledge of laws from which phenomena
could be calculated and predicted without raising any question of whether these laws were intrinsically evident to the
human mind.

8. Ernst Mack: The General Laws of Physics Arc Summaries of Observations Organized in Simple Forms
The criticisms of the mechanistic philosophy by physicists such as Kirchhoff and Hertz were only occasional and
aphoristic. There were others, however,, whose criticisms were
Conceptions of the Physical World before Einstein based on a very precise conception of nature and of the task of
science. The French philosopher Auguste Comte advanced the sociological theory that the "metaphysical" stage in the development
of a science is already succeeded by a "positivistic" one. This means that the demand for the use of a specific analogy such
as the organismic and mechanistic views is abandoned and after that a theory is judged only as to whether it presents "positive"
experience in a simple, logically unobjectionable form.
This approach was most widely and profoundly developed by the Austrian physicist Ernst Mach, who became one of Einstein's
immediate forerunners. Mach carried out a thorough historical, and logical analysis of Newtonian mechanics and showed
that it contains no principle that is in any way self-evident to the human mind. All that Newton did was to organize his
observations of motion under several simple principles from which movements in individual cases can be predicted. But all
these predictions are correct only so long as the experiences upon which Newton based his principles are true.
Mach emphasized, in particular, the demand for simplicity and economy of thought in a physical theory: the greatest possible
number of observable facts should be organized under the fewest possible principles. Mach compared this requirement to
the demand for economy in practical life and spoke of the "economic" nature of scientific theories. Thus Mach, instead of
demanding the use of a specified analogy, insisted that science be "economical."
Furthermore, not only did Mach criticize the attempts of philosophers to make a philosophical system out of Newton's
mechanics, but he also criticized the remains of medieval physics that it still retained. He pointed out that Newton's theory contained
such expressions as "absolute space" and "absolute time," which cannot be defined in terms of observable quantities or
processes. In order to eliminate such expressions from the fundamental laws of mechanics, Mach raised the demand which is now frequently described as the positivistic criterion of science:
namely, that only those propositions should be employed from which statements regarding observable phenomena can
be deduced.
This demand is very aptly elucidated by his criticism of Newton's law of inertia. If we wish to test this law experimentally,
we can never formulate a question such as this : Does a body tend to maintain the direction of its initial velocity relative to absolute
space ? The question is meaningless since absolute space is
Einstein: His Life and Times
unobservable. If we perform, say, Foucault's pendulum experiment, which gives an experimental proof of the rotation of the
earth, we observe actually that the pendulum maintains its plane of oscillation relative, not to absolute space, but rather to the fixed
stars in the sky.
Consequently, according to Mack, all mention of absolute space should be removed from the law of inertia, and it would
then be expressed as follows: Every body maintains its velocity, both in magnitude and in direction, relative to the fixed stars
as long as no forces act upon it. This means that the fixed stars exert an observable influence on every moving body, an effect
that is in addition to and independent of the law of gravitation.
For the motion of terrestrial objects this latter influence is hardly observable in practice, since the force of gravity decreases with
the square of the distance between the attracting bodies, but the laws of inertia will determine all terrestrial motion if the framework
of the fixed stars is declared as an inertial system.

9. Henri Poincare: The General Laws of Physics Are Free Creations of the Human Mind
In consequence of the criticisms of Mach and others, it had become clear that the laws of Newtonian mechanics and the
understanding of all physical phenomena in terms of it are not demanded by human reason. However, Mach's assertion that the
general laws of physics are only simple economical summaries of observed facts was not satisfactory to many scientists. Particularly
for physicists who thought along mathematical lines and had a greater formal imagination, the assertion, for example, that
Newton's law of gravitation is only a simple summary of observation on the positions of the planets did not seem adequate. Between
the actual observation of the position of the planets by a telescope and the statement that the gravitational force between
two bodies is inversely proportional to the square of the distance there seemed to be a wide gap.
Criticism of nineteenth-century physics in this direction was carried on chiefly by the French mathematician Henri Poincare.
His writings on the logical character of the general laws of nature probably exerted more influence on mathematicians and
physicists toward the end of the nineteenth century than any other similar writings. He paved the way for a new, logically
Conceptions of the Physical World before Einstein satisfying conception of nature, and his ideas also played an
outstanding part in the reception and discussion of Einstein's theories.
Poincare's view is often described as "conventionalism." According to him,, the general propositions of science, such as the
theorem about the sum of the angles of a triangle, the law of inertia in mechanics, the law of conservation of energy, and so
on, are not statements about reality, but arbitrary stipulations about how words, such as "straight lines," "force," "energy," are
to be employed in the propositions of geometry, mechanics, and physics. Consequently one can never say whether one of those
propositions is true or false; they are free creations of the human mind and one can only question whether these stipulations or
conventions have been expedient or not.
This conception may be elucidated by means of two examples.
Let us first consider the geometrical theorem referred to above: namely, that the sum of the angles of a triangle is equal to two
right angles. According to nineteenth-century tradition this is an unshakable proposition, which is a product of human reasoning
and at the same time a statement concerning what is actually observed in nature. On the one hand, we can derive this proposition
from the axioms of geometry, which are "directly evident to the mind"; on the other hand, by measuring the angle of an
actual material triangle, we can corroborate this relationship.
Poincare, however, says: if an actual triangle is formed from,
say, three iron rods, and the measurement shows that the sum of the angles is not exactly equal to two right angles, one of two
different conclusions can be drawn: either that the geometrical theorem is not valid, or that the rods forming the triangle are
not straight lines. We have the two alternatives, and we can never decide by experiments the validity of geometrical theorems.
Consequently we can say that the propositions of geometry are arbitrary stipulations or definitions and not statements about
empirical facts. They establish under what circumstances we wish to call a rod a "straight line." Thus geometrical theorems
are not statements about the nature of space, as it is often expressed,
but rather definitions of such words as "straight lines."
According to Poincare, the laws of mechanics are of somewhat similar character to the propositions of geometry. Let us, therefore,
consider the law of inertia as the second example. The possibility of verification of the law rests on our ability to determine
whether or not a body moves with uniform velocity in a straight line. As long as we cannot do this, the law of inertia can only
Einstein: His Life and Times
be characterized in some such statement as this: "When a body moves without being influenced by forces,, we call this state a
uniform motion along a straight line." It is simply a definition of the expression "uniform motion in a straight line/' or, according
to our discussions in sections 3 and 4, a definition of the term "inertial system."
Thus the general principles, such as the theorem about the sum of the angles of a triangle or the law of inertia, do not
describe observable phenomena, but are rather definitions of expressions such as "straight line" or "uniform motion along a
straight line." One has to add definitions by which one recognizes whether a given rod is straight or the motion of a ball
is uniform and along a straight line and which have been named "operational definitions" by P. W. Bridgman. These, together
with the physical laws (e.g., the law of inertia), constitute a a system of propositions that can be verified by experience.
One of the chief consequences of this conception is that it makes no sense in science to inquire into the philosophical significance
or the "nature" of such physical expressions as "force," "matter," "electric charge," "duration of time," etc. The use of
such concepts is always justified if statements permitting experimental verification can be derived from the propositions in which these expressions occur. Apart from this they have no
meaning. Because Newtonian mechanics was able to describe very complex phenomena such as the motion of the planets in
simple statements with the aid of the words "force" and "mass,"
these terms have scientific meaning. There is no need to puzzle one's brain over whether "force" can be explained from a "mechanistic"
standpoint or "matter" from an "organismic" one.
"Force" and "matter" are constructions of the human mind.
10. Positivistic and Pragmatic Movements
The idea of Mach that the general laws of science are simple summaries of experimental facts, and the idea of Poincare
that they are free creations of the human mind, appear to
be diametrically opposed to each other; but when we consider
the intellectual currents of the last quarter of the nineteenth century,
we can see that they were only two wings of the same
intellectual movement, generally known as the positivistic movement.
It was directed chiefly against the metaphysical founda-
Conceptions of the Physical World before Einstein
tions of science. The proponents of this view asserted that the
validity of the general principles of science cannot be proved by
showing that they are in agreement with some eternal philosophical
truths, and they set out to investigate how the validity
can be judged within science itself. They found that two criteria
are possible, an empirical and a logical. In the former the observable
facts that follow from the general principles must have
experimental confirmation, and in the latter the principles and
operational definitions must form a practical and consistent system.
The emphasis put on the empirical or the logical criterion
determined one's position in one or the other wing of the
movement. Mach was on the extreme empirical wing, while
Poincare was on the extreme logical side. There was therefore
no conflict between them; it was only that two different aspects
of the same scientific method were being emphasized.
The positivistic movement exerted a great influence in central
and western Europe during the last quarter of the nineteenth
century. The central European positivism, chiefly centered in the
Austrian Ernst Mach, was to be found in the universities of
Vienna and Prague. It had but little influence and few followers
in the universities of the German Reich. At this time Germany
was completely under the influence of various versions of Kantian
philosophy, whose status was almost that of a state religion.
Since German was also the chief language of science in Austria,
Central European positivism developed largely as the critic and
rival of Kantian philosophy. For this reason it was more militant
than French positivism, led by Poincare.
About this time there appeared independently in the United
States a movement that is related to European positivism in its
chief line of thought. In 1878 C. S. Peirce published an essay
on the logical character of scientific statements. Like Mach and
Poincare, he pointed out that the meaning of general statements
cannot be derived from agreement with still more general metaphysical
truths, but must be drawn from the observed facts that
follow from them. In contrast to the European positivists, however,
Peirce emphasized particularly the role of propositions as
the basis for our actions. He therefore called his doctrine "pragmatism."
"The essence of a belief/' he said, "is the establishment
of a habit, and different beliefs are distinguished by different
modes of action to which they give rise." Like Mach, Peirce alsc
warned against the trivial metaphysics that we have imbibed
with our education since childhood. He said: "The truth is that
common sense or thought as it first emerges above the level oJ
Einstein: His Life and Times
the narrowly practical is deeply imbued with that bad logical
quality to which the epithet metaphysical is commonly applied."
He also emphasized that words such as "force" are only expedients
for the representation of facts and that every question as
to their "actual nature" is superfluous and useless. In the same
article he said:
"Whether we ought to say that a force is an acceleration or that it
causes an acceleration is a mere question of propriety of language
which has no more to do with the real meaning than the difference between
the French idiom *il fait froid* and the English equivalent
'it is cold.'"
An approach very similar to that of Mach was manifested by
John Dewey in his first scientific article: "The Metaphysical
Assumptions of Materialism/' published in 1882. Dismissing the
opinion that the reduction of all phenomena to the motions of
material bodies is an explanation of nature, he said:
"First, it assumes the possibility of ontological knowledge, by which
we mean knowledge of being or substance apart from a mere succession
of phenomena. . . . Secondly, it assumes the reality of causal
nexus and the possibility of real causation. In declaring that matter
causes mind it declares that the relation is one of dependency and
not one of succession."
The struggle against materialism here is not carried on in the
service of an idealistic philosophy, as with the average professors
of philosophy in European and American universities, but entirely
along the lines of central European positivism, which opposed
mechanistic physics on the ground that it is not a sufficiently
broad basis of science.
American pragmatism since then has developed into a powerful
movement, finding its most characteristic expression in John
Dewey and William James. It has devoted itself more to the
problems of human life than to the logic of the physical sciences,
in contrast to the development of positivism in Europe, Considered
from the purely logical point of view, however, the basic
tendency was the same on both sides of the Atlantic, The medieval
idea of a philosophical explanation in contrast to a practical
representation of facts vital to life lost prestige to an ever increasing
degree. From a logical basis of science, metaphysics
developed into a means of satisfying emotional needs.
Conceptions of the Physical World before Einstein

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