[Paleopsych] Science Week: Einstein, Lorentz, and the Ether
Premise Checker
checker at panix.com
Mon May 23 19:46:29 UTC 2005
History of Science: Einstein, Lorentz, and the Ether
http://scienceweek.com/2005/sa050304-1.htm
The following points are made by John Stachel (Nature 2005 433:215):
1) During the 19th century, the mechanistic world-view -- based on
Isaac Newton's formulation in the Principia (1687) of the kinematics
and dynamics of corpuscles of matter, and crowned by his stunningly
successful theory of gravitation -- was challenged first by the
optics, then by the electrodynamics of moving bodies. By the mid 1800s
Newton's corpuscular theory of light was no longer tenable. To explain
Snell's law of refraction, this theory assumed that light corpuscles
speed up on encountering a medium of higher refractive index. But in
1849, Leon Foucault (1819-1868) and Hippolyte Fizeau (1819-1896)
showed that, in fact, light slowed down, as predicted by the rival
wave theory espoused by Newton's contemporary Christiaan Huygens
(1629-1695). The problem now was to fit the wave theory of light into
the newtonian picture of the world.
2) Indeed, the ether -- the medium through which light waves were
assumed to propagate in the absence of ordinary, ponderable matter --
seemed to provide a physical embodiment of Newton's absolute space.
But elucidating the relation between ether and ponderable matter
presented grave problems: did moving matter drag the ether with it --
either totally or partially -- or did the ether remain immobile? It
proved impossible to reconcile the consequences of any of these
hypotheses with all the experimental results on the optics of moving
bodies. By the last third of the nineteenth century, many physicists
were acutely aware of this problem.
3) By 1865, James Clerk Maxwell (1831-1879) had demonstrated that
light could be interpreted as wave-like oscillations of the electric
and magnetic fields, obeying what we now call the Maxwell equations
for these fields. It was realized that the optical problems were only
a special case of similar problems in reconciling the electrodynamics
of moving bodies with newtonian kinematics and dynamics. Towards the
end of the century, however, Hendrik Antoon Lorentz (1853-1928) seemed
to overcome all these problems through his interpretation of Maxwell's
equations. Lorentz assumed that the electromagnetic ether is entirely
immobile, in which case there would be no dragging of the ether.
4) Although in newtonian mechanics it is impossible to distinguish any
preferred inertial frame (this result is often referred to as the
galileian principle of relativity), at first the situation seemed
different for electrodynamics and optics. The rest frame of the ether
provided a preferred inertial frame, and motion through it should have
been detectable. Yet all attempts to detect the translational motion
of the Earth through the ether by means of optical, electrical or
magnetic effects consistently failed. Lorentz succeeded in explaining
why: according to his theory, no such effect should be detectable by
any experiment sensitive to first order in (v/c), where v is the speed
of the moving object through the ether and c is the speed of light in
that medium. Until the 1880s, no experiment with greater sensitivity
had been performed, and Lorentz's explanation of the failure of all
previous experiments was a crowning achievement of his theory.
5) Newton's mechanics now seemed to have successfully met the
challenge of optics and electrodynamics. But the seeds of its downfall
had already been planted. Lorentz's explanation led him to introduce a
transformation from newtonian absolute time to a new time variable in
each inertial frame moving through the ether. As the relation between
absolute time and this time varied from place to place in each
inertial frame, Lorentz called this new variable the "local time" of
that frame, regarding the local time as a purely formal expression.
But Henri Poincare (1854-1912), the great mathematician who concerned
himself extensively with problems of physics, was able to give a
physical interpretation of this time variable within the context of
newtonian kinematics: it is the time that clocks at rest in a frame
moving through the ether would read if they were synchronized using
light signals, without taking into account the motion of that frame.
This was an important hint that the problems of the electrodynamics
and optics of moving bodies were connected with the concept of time.
But it was Einstein who made the final break with the concept of
absolute time by asserting that the local time of any inertial frame
is as physically meaningful as that of any other, because there is no
absolute time with which they can be compared.[1-5]
References (abridged):
1. Einstein, A. Ann. Phys. (Leipz.) 17, 132-148 (1905)
2. Einstein, A. Ann. Phys. (Leipz.) 17, 549-560 (1905)
3. Einstein, A. Ann. Phys. (Leipz.) 17, 891-921 (1905)
4. Einstein, A. Ann. Phys. (Leipz.) 18, 639-641 (1905)
5. Einstein, A. Ann. Phys. (Leipz.) 19, 289-306 (1906)
Nature http://www.nature.com/nature
--------------------------------
Related Material:
EINSTEIN ON PHYSICS AND REALITY
The following points are made by A. Einstein and L. Infeld (citation
below):
1) What are the general conclusions which can be drawn from the
development of physics? Science is not just a collection of laws, a
catalogue of unrelated facts. It is a creation of the human mind, with
its freely invented ideas and concepts. Physical theories try to form
a picture of reality and to establish its connection with the wide
world of sense impressions. Thus the only justification for our mental
structures is whether and in what way our theories form such a link.
2) We have seen new realities created by the advance of physics. But
this chain of creation can be traced back far beyond the starting
point of physics. One of the most primitive concepts is that of an
object. The concepts of a tree, a horse, any material body, are
creations gained on the basis of experience, though the impressions
from which they arise are primitive in comparison with the world of
physical phenomena. A cat teasing a mouse also creates, by thought,
its own primitive reality. The fact that the cat reacts in a similar
way toward any mouse it meets shows that it forms concepts and
theories which are its guide through its own world of sense
impressions.
3) "Three trees" is something different from "two trees." Again "two
trees" is different from "two stones." The concepts of the pure
numbers 2, 3, 4..., freed from the objects from which they arose, are
creations of the thinking mind which describe the reality of our
world.
4) The psychological subjective feeling of time enables us to order
our impressions, to state that one event precedes another. But to
connect every instant of time with a number, by the use of a clock, to
regard time as a one-dimensional continuum, is already an invention.
So also are the concepts of Euclidean and non-Euclidean geometry, and
our space understood as a three-dimensional continuum.
5) Physics really began with the invention of mass, force, and an
inertial system. These concepts are all free inventions. They led to
the formulation of the mechanical point of view. For the physicist of
the early 19th century, the reality of our outer world consisted of
particles with simple forces acting between them and depending only on
the distance. He tried to retain as long as possible his belief that
he would succeed in explaining all events in nature by these
fundamental concepts of reality. The difficulties connected with the
deflection of the magnetic needle, the difficulties connected with the
structure of the ether, induced us to create a more subtle reality.
The important invention of the electromagnetic field appears. A
courageous scientific imagination was needed to realize fully that not
the behavior of bodies, but the behavior of something between them.
that is, the field, may be essential for ordering and understanding
events.
6) Later developments both destroyed old concepts and created new
ones. Absolute time and the inertial coordinate system were abandoned
by the relativity theory. The background for all events was no longer
the one-dimensional time and the three-dimensional space continuum,
but the four-dimensional time-space continuum, another free invention,
with new transformation properties. The inertial coordinate system was
no longer needed. Every coordinate system is equally suited for the
description of events in nature.
7) The quantum theory again created new and essential features of our
reality. Discontinuity replaced continuity. Instead of laws governing
individuals, probability laws appeared.
8) The reality created by modern physics is, indeed, far removed from
the reality of the early days. But the aim of every physical theory
still remains the same. With the help of physical theories we try to
find our way through the maze of observed facts, to order and
understand the world of our sense impressions. We want the observed
facts to follow logically from our concept of reality. Without the
belief that it is possible to grasp the reality with our theoretical
constructions, without the belief in the inner harmony of our world,
there could be no science. This belief is and always will remain the
fundamental motive for all scientific creation. Throughout all our
efforts, in every dramatic struggle between old and new views, we
recognize the eternal longing for understanding, the ever-firm belief
in the harmony of our world, continually strengthened by the
increasing obstacles to comprehension.
Adapted from: The Evolution of Physics: From Early Concepts to
Relativity and Quanta. A. Einstein and L. Infeld. Simon and Schuster
1938, p.254.
--------------------------------
Related Material:
THE YEAR 1905: EINSTEIN'S ANNUS MIRABILIS
The following points are made by Arthur I. Miller (citation below):
1) By the spring of 1905, the 26-year-old Einstein had decided that
physicists were "out of their depth". From calculations based on
Planck's radiation law, Einstein drew the astounding "general
conclusion" that light can be a particle and a wave, and in fact both
at once, a wave/particle duality. Therefore the electromagnetic
world-picture could not succeed, because Lorentz's theory could
represent radiation, or light, only as a wave, and so could never
provide a way to explain how the electron's mass is generated by its
own radiation.
2) Whereas Planck had discovered certain peculiarities about the
energy of radiation, Einstein set out to explore the structure of
radiation itself. Einstein's particles of light differed fundamentally
from Newton's in ways that even he did not yet fully realize. Around
the third week of May 1905, Einstein sent his friend Habicht what are
surely some of the greatest understatements in the history of science.
He wrote that he had only some "inconsequential babble" for his
friend, whom he lambasted for neither writing nor visiting him during
Easter:
"So what are you up to, you frozen whale, you smoked, dried, canned
piece of soul... I promise you four papers."
3) The first paper is the light quantum paper that Einstein referred
to as "very revolutionary". The second suggested a means to measure
the size of atoms using diffusion and viscosity of liquids. The third
paper explored Brownian motion using methods of the molecular theory
of heat. Einstein wrote: "The fourth paper is only a draft at this
point, and is an electrodynamics of moving bodies which employs a
modification of the theory of space and time; the purely kinematic
part of this paper will surely interest you."
4) What is so incredible about this outburst of creativity is that by
late May two papers were completed and the third was in draft form."
[Editor's note: The fourth paper, the so-called relativity paper, was
completed a few weeks later in June 1905.]
Adapted from: Arthur I. Miller: Einstein, Picasso: Space, Time, and
the Beauty That Causes Havoc. Basic Books, New York 2001, p.189.
More information about the paleopsych
mailing list