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The Classical Vacuum - by Timothy H. Boyer

The Classical Vacuum - by Timothy H. Boyer - Physics Forum

The Classical Vacuum - by Timothy H. Boyer - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

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Old 01-07-2004, 03:56 PM
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Default The Classical Vacuum - by Timothy H. Boyer

The Classical Vacuum

[From Scientific American, August 1985, pp 70-78.]

It is not empty. Even when all matter and heat radiation have
been removed from a region of space, the vacuum of classical
physics remains filled with a distinctive pattern of
electromagnetic fields

by Timothy H. Boyer

Aristotle and his followers believed no region of space could
be totally empty: This notion that "nature abhors a vacuum" was
rejected in the scientific revolution of the 17th century;
ironically, though, modern physics has come to hold a similar
view. Today there is no doubt that a region of space can be
emptied of ordinary matter, at least in principle. In the
modern view, however, a region of vacuum is far from being
empty or featureless. It has a complex structure, which cannot
be eliminated by any conceivable means.

This use of words may seem puzzling. If the vacuum is not
empty, how can it be called a vacuum? Physicists today define
the vacuum as whatever is left in a region of space when it has
been emptied of everything that can possibly be removed from it
by experimental means. The vacuum is the experimentally
attainable void. Obviously a first step in creating a region of
vacuum is to eliminate all visible matter, such as solids and
liquids. Gases must also be removed. When all matter has been
excluded, however, space is not empty; it remains filled with
electromagnetic radiation. A part of the radiation is thermal,
and it can be removed by cooling, but another component of the
radiation has a subtler origin. Even if the temperature of a
vacuum could be reduced to absolute zero, a pattern of
fluctuating electromagnetic waves would persist. This residual
radiation, which has been analyzed only in recent years, is an
inherent feature of the vacuum, and it cannot be suppressed.

A full account of the contemporary theory of the vacuum would
have to include the ideas of quantum mechanics, which are
curious indeed. For example, it would be necessary to describe
the spontaneous creation of matter and antimatter from the
vacuum. Nevertheless, some of the remarkable properties of the
vacuum do not depend at all on the peculiar logic of the
quantum theory, and they can best be understood in a classical
description (one that ignores quantum effects). Accordingly I
shall discuss the vacuum entirely in terms of classical ideas.
Even in the comparatively simple world of classical physics the
vacuum is amply strange.

The Discovery of the Vacuum

Aristotle's doctrine that a vacuum is physically impossible was
overthrown in the 17th century. The crucial development was the
invention of the barometer in 1644 by Evangelista Torricelli,
who had been secretary to Galileo. Torricelli poured mercury
into a glass tube closed at one end and then inverted the tube,
with the open end in a vessel filled with mercury. The column
of liquid fell to a height of about 30 inches above the level
of the mercury in the vessel, leaving a space at the top of the
tube. The space was clearly empty of any visible matter;
Torricelli proposed that it was also free of gas and so was a
region of vacuum. A lively controversy ensued between
supporters of the Aristotelian view and those who believed
Torricelli had indeed created a vacuum. A few years later
Blaise Pascal supervised a series of ingenious experiments, all
tending to confirm Torricelli's hypothesis.

In the following decades experiments with the vacuum had a
great vogue. The best-remembered of these demonstrations is one
conducted by Otto von Guericke, the burgomaster of Magdeburg,
who made a globe from two copper hemispheres and evacuated the
space within. Two teams of eight draft horses were unable to
separate the hemispheres. Other experiments of the era were
less spectacular but perhaps more informative. For example,
they led to the discovery that a vacuum transmits light but not

MAGDEBURG HEMISPHERES made in 1654 by Otto von Guericke
demonstrated the existence of the vacuum, When the hemispheres
were put together and the air was pulled out, two teams of
eight draft horses could not separate them. The apparatus is
now in the Deutsches Museum in Munich.

The understanding of the vacuum changed again in the 19th
century. The nature of the change can be illustrated by a
thought experiment to be done with imaginary ideal apparatus.

Suppose one had a piston and cylinder machined so perfectly
that the piston could move freely and yet nothing could leak
past it. Initially the piston is at the closed end of the
cylinder and there is no vacant space at all. When a steady
force is applied to withdraw the piston against the pressure of
the air outside, the space developed between the piston and
the end of the cylinder is a region of vacuum. If the piston is
immediately released, it moves back into the cylinder,
eliminating the vacuum space. If the piston is withdrawn and
held for some time at room temperature, however, the result is
quite different. External air pressure pushes on the piston,
tending to restore the original configuration. Nevertheless, the
piston does not go all the way back into the cylinder, even if
additional force is applied. Evidently something is inside the
cylinder. What appeared to be an empty space is not empty
after the wait.

The physicists of the 19th century were able to explain this
curious result. During the period when the piston was withdrawn
the walls of the cylinder were emitting heat radiation into the
vacuum region. When the piston was forced back in, the
radiation was compressed. Thermal radiation responds to
compression much as a gas does: both the pressure and the
temperature rise. Thus the compressed radiation exerts a force
opposing the reinsertion of the piston. The piston and cylinder
could be closed again only if one waited long enough for the
higher-temperature radiation to be reabsorbed by the walls of
the cylinder.

The form of thermal radiation is intimately connected with the
structure of the vacuum in classical physics. Nothing in my
discussion so far has indicated that this should be so, and
indeed the physicists of the 19th century were unaware of the

The Thermal Spectrum

Thermal radiation consists of electromagnetic fields that
fluctuate in the most random way possible. Paradoxically this
maximum randomness gives the radiation great statistical
regularity. Under conditions of thermal equilibrium, in which
the temperature is uniform everywhere, the radiation is both
homogeneous and isotropic: its properties are the same at every
point in space and in every direction. An instrument capable of
measuring any property of the radiation would give the same
reading no matter where it was placed and what direction it was
pointed in.

The one physical quantity that determines the character of
thermal radiation is its temperature. In 1879 the Austrian
physicist Josef Stefan investigated the total energy density
(or energy per unit volume) of thermal radiation and, on the
basis of some preliminary experiments suggested that the energy
density varies as the fourth power of the absolute temperature.
Five years later Stefan's student Ludwig Boltzmann found the
same relation through a theoretical analysis.

The temperature of thermal radiation determines not only its
total energy density but also its spectrum, that is, the curve
defining the amount of radiant energy at each frequency. The
effect of temperature on the thermal spectrum is familiar from
everyday experience; as an object is heated it first glows red
and then white or even blue as the spectrum comes to be
dominated by progressively higher frequencies. The thermal
spectrum is not a monochromatic one, however; a red-hot poker
emits radiation most strongly at frequencies corresponding to
red light, but it also gives off lesser quantities of radiation
at all higher and lower frequencies.

The shape of the thermal spectrum and its relation to
temperature were explored experimentally in the last years of
the 19th century, but the attempt to formulate a consistent
theoretical explanation met with only limited success. The aim
was to find a mathematical expression that would give the
intensity of the radiation as a function of the frequency and the
temperature. In other words, given some specified temperature,
the expression had to predict the intensity of radiation that
would be measured at any chosen frequency.

A sophisticated classical analysis of the thermal spectrum was
given by the German physicist Wilhelm Wien in 1893. Wien based
his analysis on a thought experiment much like the one
described above, but with the added provision that the cylinder
be perfectly insulated so that no heat could be gained or lost.
Wien calculated the change in the spectrum that would be
brought about by an infinitesimal change in the internal volume
of the cylinder. From this calculation he was able to deduce
that the mathematical expression describing the spectrum must
have two factors, which are multiplied to yield the intensity
at a given frequency and temperature. One factor is the cube of
the frequency. The second factor is a function of the absolute
temperature divided by the frequency, but Wien was not able to
determine the correct form of the function. (He made a
proposal, but it was soon shown to be wrong.)

CREATION OF A VACUUM proceeds in stages that parallel the
historical development of ideas about the vacuum. In the 17th
century (a) it was thought a totally empty volume of space
could be created by removing all matter, and in particular all
gases. Late in the 19th century (6) it became apparent that
such a region still contains thermal radiation, but it seemed
the radiation might be eliminated by cooling. Since then both
theory and experiment have shown there is nonthermal radiation
in the vacuum (c), and it would persist even if the temperature
could be lowered to absolute zero. It is called zero-point

Classical Electron Theory

The mathematical function needed to describe the thermal
spectrum was suggested by Max Planck in 1900. Planck emphasized
that an understanding of thermal radiation required the
introduction of a new fundamental constant, now called Planck's
constant, with a value of 6.26 x 10**(-27) erg-second. In the
course of his struggle to explain his function for the thermal
spectrum Planck launched the quantum theory. The start of
quantum physics, however, did not mark the end of the story of
classical physics.

Stefan's and Boltzmann's proposal that the total energy density
of the thermal radiation is proportional to the fourth power of
the temperature implies that the energy density falls to zero
at a temperature of absolute zero. The thermal radiation simply
disappears at zero temperature. The possibility of eliminating
all thermal radiation led to a conception of the classical
vacuum that was an extension of the 17th-century view. A
perfect vacuum was still a totally empty region of space, but
to attain this state one had to remove not only all visible
matter and all gas but also all electromagnetic radiation. The
last requirement could be met in principle by cooling the
region to absolute zero.

This conception of the vacuum within classical physics was
embodied in the fundamental physical theory of the time, which
has since come to be known as classical electron theory. It
views electrons as pointlike particles whose only properties
are mass and electric charge. They can be set in motion by
electric and magnetic fields, and their motion in turn gives
rise to such fields. (An electron in steady oscillation, for
example, radiates electromagnetic waves at the frequency of
oscillation.) The interactions between particles and fields are
accounted for by Newton's laws of motion and by James Clerk
Maxwell's equations of electromagnetism. In addition certain
boundary conditions must be specified if the theory is to make
definite predictions. Maxwell's equations describe how an
electromagnetic field changes from place to place and from
moment to moment, but to calculate the actual value of the
field one must know the initial, or boundary, values of the
field, which provide a baseline for all subsequent changes.

It is through the choice of initial conditions that the nature
of the vacuum enters classical electron theory. Since in the
19th-century view the vacuum was empty of all radiation, the
initial conditions set on Maxwell's equations were the absence
of electric and magnetic radiation. Roughly speaking, the
19th-century version of classical electron theory assumed that
at some time in the distant past the universe contained matter
(electrons) but no radiation. All electromagnetic radiation
evolved from the acceleration of electric charges.

The Casimir Effect

Classical electron theory remains a viable field of
investigation today, but it has taken a new form in the 20th
century. The need for a revision is easily seen from an
experiment proposed in 1948 by Hendrik B. G. Casimir of the
Philips Research Laboratories in the Netherlands. Casimir
analyzed the forces that would act on two electrically
conducting, parallel plates mounted a small distance apart in a
vacuum. If the plates carry an electric charge, the laws of
elementary electrostatics predict a force between them, but
Casimir considered the case in which the plates are uncharged.
Even then a force can arise from electromagnetic radiation
surrounding the plates. The origin of this force is not
immediately obvious, but a mechanical analogy serves to make it

Suppose a smooth cord is threaded snuggly through holes in two
wood blocks, as in the upper illustration on the next page. The
cord is not tied to the blocks, and so at rest it neither
pushes them apart nor pulls them together. Nevertheless, if the
part of the cord between the blocks is made to vibrate
transversely, a force acts on the blocks and they tend to slide
along the cord away from each other. The force arises because
transverse motion of the cord is not possible where it passes
through a block, and so waves in the cord are reflected there.
When a wave is reflected, some of its momentum is transferred
to the reflector

The situation in Casimir's proposed experiment is similar. The
metal plates are analogous to the wood blocks, and the
fluctuating electric and magnetic radiation fields represent
the vibrating cord. The analogue of the hole in the wood block
is the conducting quality of the metal plates; just as waves on
the cord are reflected by the block, so electromagnetic waves
are reflected by a conductor. In this case there is radiation
on both sides of each plate, and thus the forces tend to
cancel. The cancellation is not exact, however; a small
residual force remains. The force is directly proportional to
the area of the plates and also depends on both the separation
between the plates and the spectrum of the fluctuating
electromagnetic radiation.

IDEAL PISTON AND CYLINDER provide the apparatus for a thought
experiment revealing the presence of thermal radiation. The
piston is initially at the closed end of the cylinder, leaving
no free space; then it is withdrawn partway and held in this
position for some time at room temperature. The space enclosed
would seem to be a vacuum, and yet when the piston is released,
it does not return to its initial position; indeed, it cannot
be pushed all tile way back into the cylinder even with
additional force. While the piston was held in the open
position tile walls of the cavity emitted thermal radiation
with a spectrum determined by the temperature. An attempt to
reinsert the piston compresses the radiation, raising its
temperature and tiles altering its spectrum. The hotter
radiation opposes the compression.

So far this analysis is wholly consistent with the 19th-century
view of the vacuum. The force acting on the plates is
attributed to fluctuating thermal radiation. When the
temperatures reduced to absolute zero, both the thermal
radiation and the force between. the plates should disappear.

Experiment contradicts this prediction. In 1958 the Dutch
physicist M. J Sparnaay carried out a series of experiments
based on Casimir's proposal and found that the force did not
approach zero when the thermal radiation was reduced to low
intensity. Instead there was a residual attractive force that
would persist even at absolute zero.

The residual force is directly proportional to the area of the
plates and inversely proportional to the fourth power of their
separation; the constant of proportionality is 1.3 x 10**(-18)
erg-centimeter. Although such a force is small, it is
measurable if the plates are sufficiently close together. For
plates with an area of one square centimeter separated by 0.5
micrometer the Casimir force is equivalent to the weight of 0.2

Whatever the magnitude of the Casimir effect, its very
existence indicates that there is something fundamentally wrong
with the 19th-century idea of the classical vacuum. If one is
to fit classical theory with experiment, then even at zero
temperature the classical vacuum cannot be completely empty; it
must be filled with the classical electromagnetic fields
responsible for the attractive force Sparnaay measured. Those
vacum fields are now referred to as classical electromagnetic
zero-point radiation.

CASIMIR EFFECT demonstrates the existence of electromagnetic
fields in the vacuum. Two metal plates in a vacuum chamber are
mounted parallel to each other and a small distance apart.
Because the plates are conducting, they reflect electromagnetic
waves; for a wave to be reflected there must be a node of the
electric field - a point of zero electric amplitude - at the
surface of the plate. The resulting arrangement of the waves
gives rise to a force of attraction. The origin of the force
can be understood in part through a mechanical analogy. If a
cord threaded through holes in two wood blocks is made to
vibrate, waves is the cord are reflected at tire holes and
generate forces on the blocks. The forces on a single block act
in opposite directions, but a small net force remains. Its
magnitude and direction depend on the separation between the
blocks and the spectrum of waves along the cord.

high temperature thermal radiation gives rise to a force
directly proportional to the temperature and inversely
proportional to the cube of the distance between the plates.
This force disappears at absolute zero, as the thermal
radiation itself does. The force associated with the zero-point
radiation is independent of temperature and inversely
proportional to the fourth power of the distance between the
plates. The forces shown are for plates with an area of one
square centimeter; the thermal force is an approximation valid
at high temperature.

The Zero-Point Spectrum

What are the characteristics of the zero-point radiation in the
classical vacuum? Much can be deduced from the fact that it
exists in a vacuum: it must conform to accepted basic ideas
about the nature of the vacuum. For example, it seems essential
that the vacuum define no special places or directions, no
landmarks in space or time; it should look the same at all
positions and in all directions. Hence the zero-point
radiation, like thermal radiation, must be homogeneous and
isotropic. Furthermore, the vacuum should not define any
special velocity through space; it. should look the same to any
two observers no matter what their velocity is with respect to
each other, provided the velocity is constant. This last
requirement is expressed by saying the zero-point radiation
must be invariant with respect to Lorentz transformation. (The
Lorentz transformation, named for the Dutch physicist H. A.
Lorentz, is a conversion from one constant-velocity frame of
reference to another, taking into account that the speed of
light is the same in all frames of reference.)

The requirement of Lorentz invariance is a serious constraint.
A railroad passenger may be momentarily unsure whether his
own train or the one on the next track is moving relative to
the earth, but the ambiguity can be resolved simply by
looking at some landmark known to be fixed. Lorentz invariance
implies that there are no such landmarks in the vacuum and
that no experiment could ever reveal an observer's velocity with
respect to the background of zero-point radiation. To meet this
condition the spectrum of the radiation must have quite
specific properties.

Suppose for the moment that the zero-point radiation, as
perceived by some observer, were all in the region of the
electromagnetic spectrum corresponding to green light. No
matter where the observer stood and no matter in what direction
he looked, the vacuum would appear to be filled with uniform
green radiation. Such a spectrum satisfies the requirements of
homogeneity and isotropy for this one observer, but now suppose
there is another observer moving toward the first one at a
constant speed. Because of the Doppler effect, the moving
observer would see the radiation in front of him shifted toward
the blue end of the spectrum and the radiation behind him
shifted toward the red end. The Lorentz transformation also
alters the intensity of the radiation: it would be brighter in
front and dimmer behind. Thus the radiation does not look the
same to both observers; it is isotropic to one but not to the

It turns out that the zero-point spectrum can have only one
possible shape if the radiation is to be Lorentz-invariant. The
intensity of the radiation at any frequency must be
proportional to the cube of that frequency. A spectrum defined
by such a cubic curve is the same for all unaccelerated
observers, no matter what their velocity; moreover, it is the
only spectrum that has this property.

ZERO-POINT SPECTRUM is independent of the observer's velocity
because of compensating changes in frequency and intensity.
When an observer is approaching a source of radiation, all
frequencies are shifted to higher values and all intensities
are increased; moving away from the source has the opposite
effect. Thus a spectrum that has a peak in the green region for
a stationary observer has a larger blue peak for so approaching
observer and a smaller red peak for a receding observer. The
cubic curve that defines the zero-point spectrum balances the
shifts in frequency and intensity. Light that appears green in
the stationary frame of reference becomes blue to an
approaching observer, but its intensity matches that of the
blue light seen by an observer at rest. By the same token,
green light is shifted to red frequencies for a receding
observer, but its intensity is diminished correspondingly.

One immediate objection might be made to the cubic form of the
zero-point spectrum: because the intensity of the radiation
increases steadily at higher frequencies, the spectrum predicts
an infinite energy density for the vacuum. In the 19th century
such a prediction might well have been considered a fatal flaw,
but since the 1940's infinities have turned up in several areas
of physics, and methods have been developed for dealing with
them. In this case the infinite energy is confronted directly
only in the realm of gravitational forces. All other
calculations are based on changes or differences in energy,
which are invariably finite.

If the universe is permeated by classical zero-point radiation,
one might suppose it would make its presence known in phenomena
less subtle than the Casimir effect. For example, one might
think it would alter the outcome of the piston-and-cylinder
experiment by resisting the insertion of the piston even after
all thermal radiation had been eliminated.

Analysis indicates otherwise. Under equilibrium conditions,
when no external force is applied to the piston, there is
radiation both inside and outside the cylinder, and the
radiation pressures acting on the piston are balanced. This
balance holds for both thermal and zero-point radiation. When
the piston is pushed into the cylinder, the radiation is
compressed. Wien's calculation of the change in the spectrum as
a result of a change in volume indicates that the thermal
radiation resists such compression; it increases in temperature
and exerts a greater pressure against the piston. When the
same analysis is made for the zero-point radiation, however,
the result is different: the zero-point spectrum does not change
at all in response to compression. Indeed, a spectrum described
by a cubic curve is the only one that has this remarkable property.

The other experiment in which the cubic zero-point spectrum
should be checked is the Casimir effect itself. A theoretical
calculation based on the spectrum predicts a force between the
plates directly proportional to their area and inversely
proportional to the fourth power of their separation, in
agreement with Sparnaay's results. Again it can be shown that
the spectrum is unique in supporting this prediction; no other
spectral curve yields an inverse-fourth-power dependence on

The New Classical Electron Theory

The statement that a spectrum described by a cubic curve is
unique refers only to the shape of the curve; actually there
are infinitely many curves with the same shape but different
scales. In all the curves the intensity of the radiation is
proportional to the cube of the frequency, but the magnitude of
the intensity in each spectrum depends on a constant, which
sets the scale of the curve.

The value of the constant cannot be calculated theoretically,
but Sparnaay's measurement of the force in the Casimir effect
allows the value to be determined from experiment. After some
preliminary algebraic manipulation it is found that the
constant is equal to 3.3 x 10**(-27) erg-second, a magnitude
corresponding to one-half of Planck's constant. Thus Planck's
constant, the hallmark of all quantum physics, appears in a
purely classical context.

The introduction of classical zero-point radiation in the
vacuum mandates an important change in classical electron
theory. The revised version of the theory is still based on
Newton's laws of motion for the electrons and Maxwell's
equations for the electromagnetic field, but the boundary
conditions imposed on Maxwell's equations must be altered. No
longer is the vacuum empty of all electromagnetic fields; it is
now filled with randomly fluctuating fields having the
zero-point spectrum. The modified theory is called classical
electron theory with classical electromagnetic zero-point
radiation, a name often shortened to stochastic

The altered boundary conditions change the predictions of the
theory. The changes can be understood by considering one of the
favorite models of modern physics: a harmonic oscillator made
up of an electron attached to a perfectly elastic and
frictionless spring. This imaginary mechanical system is to be
set up in the classical vacuum. If the spring is stretched and
then released, the electron oscillates about its equilibrium
position and gives off electromagnetic radiation at the
frequency of oscillation.

HARMONIC OSCILLATOR reveals the effects of zero-point radiation
on matter. The oscillator consists of all electron attached to
an ideal, frictionless spring. When the electron is set in
motion, it oscillates about its point of equilibrium, emitting
electromagnetic radiation at the frequency of oscillation. The
radiation dissipates energy, and so in the absence of
zero-point radiation and at a temperature of absolute zero the
electron eventually comes to rest. Actually zero-point
radiation continually imparts random impulses to the electron,
so that it never comes to a complete stop. Zero-point radiation
gives the oscillator an average energy equal to the frequency
of oscillation multiplied by one-half of Planck's constant.

The harmonic oscillator is a convenient model because the
motion of the electron is readily calculated. Under the older
version of classical electron theory just two forces act on the
electron: the restoring force from the spring and a reaction
force arising from the emission of radiation. Because the
reaction force is directed opposite to the electron's motion,
the theory predicts that the oscillations will be steadily
damped and the electron will eventually come to rest. In the
new version of classical electron theory, however, the
zero-point radiation provides an additional force on the
electron. The charged particle is continually buffeted by the
randomly fluctuating fields of the zero-point radiation, so
that it never comes to rest. It turns out the harmonic
oscillator retains an average energy related to the zero-point
spectrum, namely one-half of Planck's constant multiplied by
the frequency of oscillation.

Up to now the classical vacuum has been described from the
point of view of an observer at rest or moving with constant
velocity. The consequences of zero-point radiation are even
more remarkable for an accelerated observer, that is, one whose
velocity is changing in magnitude or direction.

Effects of Acceleration

Consider an observer in a rocket continuously accelerating with
respect to some frame of reference that can be regarded as
fixed, such as the background of distant stars. What does the
classical vacuum look like to the rocket-borne observer? To
find out, one must perform a mathematical transformation from
the fixed frame of reference to the accelerated one. The
Lorentz transformation mediates between frames that differ in
velocity, but the situation is more complex here because the
velocity of the accelerated observer is continuously changing.
By carrying out Lorentz transformations over some time
interval, however, the vacuum observed from the rocket can be

One might guess that the spectrum for an accelerated observer
would no longer be isotropic, and in particular that some
difference would be detected between the forward and the
backward directions. The spectrum might also, be predicted to
change as the acceleration continued. In fact the spectrum
remains homogeneous and isotropic, and no change is observed
as long as the rate of acceleration itself does not change.
Nevertheless, the spectrum is not the one seen by an
unaccelerated observer. At any given frequency the intensity of
the radiation is greater in the accelerated frame than it is in the
frame at rest.

The form of the classical electromagnetic spectrum seen by an
accelerated observer is not one immediately familiar to
physicists, but it can be interpreted by analyzing the motion
of a harmonic oscillator carried along in the rocket. The
equation of motion for the accelerated oscillator is much like
the one valid in a fixed frame of reference. There are two
differences: the radiation-reaction force has a new term
proportional to the square of the acceleration, and the
oscillator is exposed to a new spectrum of random radiation
associated with the acceleration. The effect of these changes
is to increase the average energy above the energy associated
with the zero-point motion. In other words, when an oscillator
is accelerated, it jiggles more vigorously than it would if it
were at rest in the vacuum.

One way of understanding the effect of acceleration on the
harmonic oscillator is to ask what additional electromagnetic
spectrum could be added to the zero-point radiation to cause
the extra motion. To answer this question one can turn to the
equivalence principle on which Einstein founded his theory of
gravitation. The principle states that an observer in a small
laboratory supported in a gravitational field makes exactly the
same measurements as an observer in a small accelerating
rocket. The laws of thermodynamics are found to hold in a
gravitational field. From the equivalence principle one
therefore expects the laws of thermodynamics to hold in an
accelerating rocket. There is then only one possible
equilibrium spectrum that can be added to the zero-point
radiation: the additional radiation must have a thermal
spectrum. With any other spectrum the oscillator would not be
in thermal equilibrium with its surroundings, and so it could
serve as the basis of a perpetual-motion machine. By this route
one is led to a remarkable conclusion: a physical system
accelerated through the vacuum has the same equilibrium
properties as an unaccelerated system immersed in thermal
radiation at a temperature above absolute zero.

The mathematical relation connecting acceleration and
temperature was found in about 1976 by William G. Unruh of the
University of British Columbia and P. C W Davies of the
University of Newcastle upon Tyne. The effective spectrum seen
by an observer accelerated through the vacuum is the sum of two
parts. One part is the zero-point radiation; the other is the
spectrum of thermal radiation deduced by Planck in 1900. Planck
was able to explain the form of that curve only by introducing
quantum-mechanical ideas, which he did with some reluctance; it
now turns out the curve can be derived from an entirely
classical analysis of radiation in the vacuum.

At least one more intriguing result arises from this line of
inquiry. If one again invokes the equivalence principle
relating an observer in a gravitational field with an
accelerating observer, one concludes that there is a minimum
attainable temperature in a gravitational field. This limit is
an absolute one, quite apart from any practical difficulties of
reaching low temperatures. At the surface of the earth the
limit is 4 x 10**(-20) degree Kelvin, far beyond the
capabilities of real refrigerators but nonetheless greater than

The discovery of a connection between thermal radiation and the
structure of the classical vacuum reveals an unexpected unity
in the laws of physics, but it also complicates our view of
what was once considered mere empty space. Even with its
pattern of electric and magnetic fields in continual
fluctuation, the vacuum remains the simplest state of nature.
But perhaps this statement reflects more on the subtlety of
nature than it does on the simplicity of the vacuum.

EFFECT OF ACCELERATION through tire vacuum is to change the
spectrum of observed radiation. At a temperature of absolute
zero a harmonic oscillator in a frame of reference at rest or
moving with constant velocity is subject only to zero-point
oscillations. In an accelerated frame the oscillator responds
as if it were at a temperature greater than zero.

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Old 01-07-2004, 05:34 PM
Uncle Al
Posts: n/a
Default The Classical Vacuum - by Timothy H. Boyer

Laurent wrote:

Hey stooopid - that's 20 years old in a lay publication. Try visiting
an academic library and ask a janitor for the Library of Congress
number for Physical Review. Or get a Head Start slum bunny to punch

[Only registered users see links. ]


Uncle Al
[Only registered users see links. ]
[Only registered users see links. ]
(Do something naughty to physics)
Reply With Quote
Old 01-07-2004, 11:26 PM
Posts: n/a
Default The Classical Vacuum - by Timothy H. Boyer

"Uncle Al" <[Only registered users see links. ].net> wrote in message
news:[Only registered users see links. ].net...

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Old 01-08-2004, 04:59 AM
The Ghost In The Machine
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Default The Classical Vacuum - by Timothy H. Boyer

In sci.physics, Laurent
<[Only registered users see links. ]>
on Wed, 7 Jan 2004 18:26:46 -0500
<[Only registered users see links. ]>:

Was he supposed to?

The luminiferous aether has been nicely disproven, although I
would have to look up the details. MMX in particular
disproved the notion of a rigid aether everywhere. While it
may be barely possible to have a fluid aether, the SR/GR
time expansion/space contraction methods seem to me far
more straightforward -- and physics has to be inertial-frame-
invariant, anyway, otherwise things make no sense, unless one
can actually find the Origin Of It All, which doesn't appear
horribly likely.

I can live with c = constant and v' = (v+w)/(1+vw/c^2).
There's also the "ultraviolet catastrophe", which was
nicely solved by QM.

[rest snipped]

#191, [Only registered users see links. ]
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Old 01-08-2004, 04:59 PM
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Default The Classical Vacuum - by Timothy H. Boyer

"The Ghost In The Machine" <[Only registered users see links. ]> wrote
in message news:[Only registered users see links. ]...

The only thing proven was that they didn't understand the aether's

You want to measure drag caused by the aether? Just measure a moving
object's momentum... or measure the force needed to accelerate that
same object... that's it, that's aether caused drag.



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Old 01-09-2004, 03:57 AM
Gerald L. O'Barr
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Default The Classical Vacuum - by Timothy H. Boyer

in message news:<[Only registered users see links. ]>
"Laurent" <[Only registered users see links. ]> wrote:

<deletes by O'Barr>

Gerald L. O'Barr <[Only registered users see links. ]> comments:
In the at theory, the ether is a very dynamic collection of
particles in a simple 3-D space, moving with simple mass,
momentum, and kinetic energy. Collisions are simple spalls.
In such a collection of dynamic particles, exchanges of momentum
can occur between any one particle with the background (ether.)
As it does this, there can be all kinds of fun things that can
occur, to include one type of particle that chases after another,
but it pushes the other away faster than it can chase it. Some
particles, or combination of particles, can reach stable motion
by going into a self sustaining spin.
Your statement here that there is a connection between mometum and
drag is most excellent. Stable particles, like what we have in
our world, have a neat balance between drag and their locomotion in
the ether. And to change their locomotion in the ether, requires
time and force to get them re-arranged to a new equilibrium state.
How did you know all this? Now not all inertial action is contained
in this act, but it is an important part of what is going on. Please
comment some more on this interesting concept!

Gerald L. O'Barr <[Only registered users see links. ]>

P.S. I hope it wasn't just wild guesses!
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Old 01-10-2004, 12:56 AM
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Default The Classical Vacuum - by Timothy H. Boyer

"Gerald L. O'Barr" <[Only registered users see links. ]> wrote in message
news:e9b03d3c.0401081957.4e2dbac3@posting.google.c om...

Read more at -

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Old 01-10-2004, 01:43 AM
Sam Wormley
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Default The Classical Vacuum - by Timothy H. Boyer

Laurent wrote:

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Crank Information
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Old 01-14-2004, 03:49 PM
John Sefton
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Default The Classical Vacuum - by Timothy H. Boyer

Laurent wrote:

MMX tried to pin down
the Aether while having no idea
of its properties.
Suppose it doesn't act by transfering
Suppose increasing speed *doesn't* mean
an increase in the number of 'raindrops'
but, like light, means blue-shifting
everything coming towards you?
Then suppose that each atom of you
interacts with gravity by absorbing a
certain frequency of that aether.
Do you see that it doesn't care which
way you are going in space?
There is no bow wind.
There is no tail wind.
It is not 'raindrops'.


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