[Paleopsych] SW: Einstein on Physics and Progress
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History of Science: Einstein on Physics and Progress
http://scienceweek.com/2005/sw050708-5.htm
The following points are made by Albert Einstein (Physics Today 2005
June):
1) If philosophy is interpreted as a quest for the most general and
comprehensive knowledge, it obviously becomes the mother of all
scientific inquiry. But it is just as true that the various branches
of science have, in their turn, exercised a strong influence on the
scientists concerned and, beyond that, have affected the philosophical
thinking of each generation. Let us glance, from this point of view,
at the development of physics and its influence on the conceptual
framework of the other natural sciences during the last hundred years.
2) Since the Renaissance, physics has endeavored to find the general
laws governing the behavior of material objects in space and time. To
consider the existence of these objects as a problem was left to
philosophy. To the scientist, the celestial bodies, the objects on
Earth, and their chemical peculiarities, simply existed as real
objects in space and time, and his task consisted solely in
abstracting these laws from experience by way of hypothetical
generalizations.
3) The laws were supposed to hold without exceptions. A law was
considered invalidated if, in a single case, any one of its properly
deduced conclusions was disproved by experience. In addition, the laws
of the external world were also considered to be complete, in the
following sense: If the state of the objects is completely given at a
certain time, then their state at any other time is completely
determined by the laws of nature. This is just what we mean when we
speak of "causality." Such was approximately the framework of the
physical thinking a hundred years ago.
4) As a matter of fact, the framework was even more restrictive than
it has been sketched. The objects of the external world were
considered to consist of immutable mass points, acting upon each other
with well-defined forces eternally attached to them and, under the
influence of these forces, carrying out incessant motions to which, in
the last analysis, all observable processes could be reduced.
5) From a philosophical point of view, the conception of the world, as
it appears to those physicists, is closely related to naive realism,
since they looked upon the objects in space as directly given by our
sense perceptions. The introduction of immutable mass points, however,
represented a step in the direction of a more sophisticated realism.
For it was obvious from the beginning that the introduction of these
atomistic elements was not induced by direct observation.
6) With the Faraday-Maxwell theory of the electromagnetic field, a
further refinement of the realistic conception was unavoidable. It
became necessary to ascribe the same irreducible reality to the
electromagnetic field, continually distributed in space, as formerly
to ponderable matter. But sense experiences certainly do not lead
inevitably to the field concept. There was even a trend to represent
physical reality entirely by the continuous field, without introducing
mass points as independent entities into the theory.
7) Summing up, we may characterize the framework of physical thinking
up to a quarter of a century ago as follows: There exists a physical
reality independent of substantiation and perception. It can be
completely comprehended by a theoretical construction which describes
phenomena in space and time -- a construction whose justification,
however, lies in its empirical confirmation. The laws of nature are
mathematical laws connecting the mathematically describable elements
of this construction. They imply complete reality in the sense
mentioned before.
8) Under the pressure of overwhelming experimental evidence concerning
atomistic phenomena, almost all of today's physicists are now
convinced that this conceptual framework --notwithstanding its
apparently wide scope -- cannot be retained. What appears untenable to
physicists of our times is not only the requirement of complete
causality but also the postulate of a reality which is independent of
any measurement or observation.
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
HISTORY OF PHYSICS: EINSTEIN AND BROWNIAN MOTION
The following points are made by Giorgio Parisi (Nature 2005 433:221):
1) On 30 April 1905, Einstein completed his doctoral thesis on osmotic
pressure, in which he developed a statistical theory of liquid
behavior based on the existence of molecules. This work, together with
his subsequent paper on "brownian motion", constitutes one of the most
important, but often overlooked, contributions that Einstein made to
physics.
2) In the closing decades of the 19th century, theoretical physics was
in a state of turmoil. The big outstanding questions of that time have
been much discussed. Such questions culminated in relativity and
quantum mechanics -- theoretical developments in which Einstein's key
role is being justly celebrated this year. But it should not be
forgotten that the seemingly innocuous observations of Robert Brown
(1773-1858) of the irregular motions of a suspension of pollen grains
in water -- now known as brownian motion -- also heralded a revolution
in physical thought.
3) Although the concepts of atoms and molecules are now universally
accepted, this was not the case at the turn of the 20th century. The
statistical interpretation by Ludwig Boltzmann ((1844-1906) of the
laws of thermodynamics -- a body of work deeply rooted in the ensemble
dynamical motion of material atoms -- had many adherents. But there
were also many heavyweight dissenters (for a time including Max Planck
(1858-1947)), who did not accept that thermodynamics had its origins
in the reversible motion of invisible hypothetical particles. And many
distinguished physicists of the time (among them Wilhelm Roentgen
(1845-1923)) suspected that brownian motion indicated a clear failure
of Boltzmann's formulation of the second law of thermodynamics.
4) It was in this context that Einstein's explanation for brownian
motion made an initial impression. In particular, Einstein showed that
the irregular motion of the suspended particles could be understood as
arising from the random thermal agitation of the molecules in the
surrounding liquid: these smaller entities act both as the driving
force for the brownian fluctuations (through the impact of the liquid
molecules on the larger particles), and as a means of damping these
motions (through the viscosity experienced by the larger particles).
This connection between displacement and the viscosity can be
quantitatively expressed in one dimension as a relationship between
displacement, viscosity, the universal gas constant, Avogadro's
number, the Boltzmann constant, the temperature, and the radius of the
suspended particles. This finding went beyond simply confirming the
existence of atoms and molecules, and provided a new way of
determining Avogadro's number. As Einstein himself remarked, the
consequence of this relation is that one can see, directly through a
microscope, a fraction of the thermal energy manifest as mechanical
energy. By proving that a statistical mechanics description could
explain quantitatively brownian motion, all doubts concerning
Boltzmann's statistical interpretation of the thermodynamic laws
suddenly faded.(1-3)
References (abridged):
1. Pais, A. Subtle is the Lord... (Oxford Univ. Press, 1982)
2. Kuhn, T. S. Black Body Theory and the Quantum Discontinuity
1894-1911 (Oxford Univ. Press, 1978)
3. Mezard, M., Parisi, G. & Virasoro, M. A. Spin Glass Theory and
Beyond (World Scientific, Singapore, 1987)
Nature http://www.nature.com/nature
--------------------------------
Related Material:
HISTORY OF PHYSICS: EINSTEIN AND RADIATION
The following points are made by Daniel Kleppner (Physics Today 2005
February):
1) Albert Einstein had a genius for extracting revolutionary theory
from simple considerations: From the postulate of a universal velocity
he created special relativity; from the equivalence principle he
created general relativity; from elementary arguments based on
statistics he discovered energy quanta. His 1905 paper on quantization
of the radiation field (often referred to, inaccurately, as the
photoelectric-effect paper) was built on simple statistical arguments,
and in subsequent years he returned repeatedly to questions centered
on statistics and thermal fluctuations.
2) In 1909, Einstein showed that statistical fluctuations in thermal
radiation fields display both particle-like and wave-like behavior.
His was the first demonstration of what would later become the
principle of complementarity. In 1916, when he turned to the interplay
of matter and radiation to create a quantum theory of radiation, he
once again based his arguments on statistics and fluctuations.
3) Einstein's theory of radiation is a treasure trove of physics, for
in it one can discern the seeds of quantum electrodynamics and quantum
optics, the invention of masers and lasers, and later developments
such as atom-cooling, Bose-Einstein condensation, and cavity quantum
electrodynamics. Our understanding of the Cosmos comes almost entirely
from images brought to us by radiation across the electromagnetic
spectrum. Einstein's theory of radiation describes the fundamental
processes by which those images are created.
4) Einstein's 1905 paper on quantization endowed Max Planck's quantum
hypothesis with physical reality. The oscillators for which Planck
proposed energy quantization were fictitious, and his theory for
blackbody radiation lacked obvious physical consequences. But the
radiation field for which Einstein proposed energy quantization was
real, and his theory had immediate physical consequences. His paper,
published in March 1905, was the first of his wonder year. In rapid
succession he published papers on Brownian motion, special relativity,
and his quantum theory of the specific heat of solids.
5) In 1907, his interest shifted to gravity, and he took the first
tentative steps toward the theory of general relativity. His struggle
with gravitational theory became all-consuming until November 1915,
when he finally obtained satisfactory gravitational field equations.
During those years of struggle, however, Einstein apparently had a
simmering discontent with his understanding of thermal radiation, for
in July 1916, he turned to the problem of how matter and radiation can
achieve thermal equilibrium. One could argue that 1916 was too soon to
deal with that problem because there were serious conceptual obstacles
to the creation of a consistent theory. Einstein, in his Olympian
fashion, simply ignored them. In the next eight months, he wrote three
papers on the subject, publishing the third, and best known, in
1917.[1,2]
References (abridged):
1. A. Einstein, Phys. Z. 18, 121 (1917); English translation On the
Quantum Theory of Radiation, by D. ter Haar, The Old Quantum Theory,
Pergamon Press, New York (1967), p. 167
2. A. Pais, Rev. Mod. Phys. 49, 925 (1977)
Physics Today http://www.physicstoday.org
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