[Paleopsych] SW: On the Aether and Broken Symmetry
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Wed Jul 6 00:32:36 UTC 2005
Theoretical Physics: On the Aether and Broken Symmetry
The following points are made by Frank Wilczek (Nature 2005 435:152):
1) The concept that what we ordinarily perceive as empty space is in
fact a complicated medium is a profound and pervasive theme in modern
physics. This invisible inescapable medium alters the behavior of the
matter that we do see. Just as Earth's gravitational field allows us
to select a unique direction as up, and thereby locally reduces the
symmetry of the underlying equations of physics, so cosmic fields in
"empty" space lower the symmetry of these fundamental equations
everywhere. Or so theory has it. For although this concept of a
symmetry-breaking aether has been extremely fruitful (and has been
demonstrated indirectly in many ways), the ultimate demonstration of
its validity --cleaning out the medium and restoring the pristine
symmetry of the equations -- has never been achieved: that is,
perhaps, until now.
2) In new work, Cramer et al. claim to have found evidence that --
for very brief moments, and over a very small volume
--experimentalists working at the Relativistic Heavy Ion Collider
(RHIC) at Brookhaven National Laboratory in New York have vaporized
one symmetry-breaking aether, and produced a more perfect emptiness.
This pioneering attempt to decode the richly detailed (in other words,
complicated and messy) data emerging from the RHIC experiments is
intricate, and it remains to be seen whether the interpretation
Cramer et al. propose evolves into a consensus. In any case, they've
put a challenge on the agenda, and suggested some concrete ways to
3) But what exactly is this underlying symmetry of nature that is
broken by the aether? How is it broken, and how might it be restored?
The symmetry in question is called chiral symmetry, and it involves
the behavior of quarks, the principal constituents of the protons and
neutrons in atomic nuclei (among other things). Chiral symmetry is
easiest to describe if we adopt the slight idealization that the
lightest quarks, the up quark (u) and down quark (d), are massless.
(In reality their masses are small, on the scale of the energies in
play, but not quite zero.) According to the equations of quantum
chromodynamics (QCD), the theory that describes quarks and their
interactions via the strong nuclear force, the possible
transformations among quarks are very restricted. One rule is that
u-quarks and d-quarks retain their "flavor" -- that is, a (u) never
converts into a (d), nor a (d) into a (u).
4) Quarks also, like the more familiar photons, have an intrinsic
spin. If the spin axis is aligned with the direction of motion, then
the sense of the rotation defines a handedness, known as chirality,
rather like a left- or right-handed screw. The two possible states of
chirality of a quark, left and right, are essentially the same concept
as left and right circular polarization for photons. The fundamental
interaction between quarks and gluons, to which we ultimately trace
the strong nuclear force, conserves chirality as well as flavor. Thus
a u-quark with left-handed chirality (written uL) never converts into
a right-handed uR, and so on. But these extra conservation laws, which
follow from the symmetry of QCD's equations, are too good to be true.
In reality, one finds that although the rule forbidding changes of
flavor holds true, there is no additional conservation law for
chirality -- chiral symmetry is broken.
5) The accepted explanation for this mismatch blames a form of aether.
The idea is that there is such a powerful attractive interaction
between uL-quarks and R-antiquarks (every quark has an antiquark with
the opposite charge), and likewise between dL-quarks and R-antiquarks,
that the energy gained from their attraction outweighs the cost of
creating the particles in the first place. Thus, perfectly empty
space, devoid of quarks, is unstable. One can lower the energy of the
vacuum by filling it with bound uL-R and dL-R pairs (and their
antiparticles, L-uR, L-dR). Physicists call this process the formation
of the chiral condensate. In the stable state that finally results,
the conservation of chirality is rendered ineffective, as space itself
has become a reservoir containing, for example, an indefinite number
1. Cramer, J., Miller, G., Wu, J. & Yoon, J. -H. preprint at
2. Kolb, P. F. & Heinz, U. in Quark Gluon Plasma Vol. 3 (eds Hwa, R.
C. & Wang, X.-N.) (World Scientific, Singapore, 2004); preprint at
3. Adcox, K. et al. (The PHENIX collaboration) Nucl. Phys. A
(submitted); preprint at http://arxiv.org/nucl-ex/0410003 (2005)
4. Adams, J. et al. (The STAR collaboration) Nucl. Phys. A
(submitted); preprint at http://arxiv.org/nucl-ex/05010095 (2005)
5. Back, B. B. et al. (The PHOBOS collaboration) Nucl. Phys. A (in the
press); doi:10.1016/j.nuclphysa.2005.03.084 (2005)
ON THE ETHER CONCEPT IN PHYSICS
Notes by ScienceWeek:
In the late 19th century, what we now call "classical" physics
incorporated the assumed existence of the "ether", a hypothetical
medium believed to be necessary to support the propagation of
electromagnetic radiation. The famous *Michelson-Morley experiment of
1887 was interpreted as demonstrating the nonexistence of the ether,
and this experiment became a significant prelude to the subsequent
formulation of Einstein's *special theory of relativity. Although it
is often stated outside the physics community that the ether concept
was abandoned after the Michelson-Morley experiment, this is not quite
true, since the classical ether concept has been essentially
reformulated into several modern *field concepts.
The following points are made by Frank Wilczek (Physics Today January
1) Isaac Newton (1642-1727) believed in a continuous medium filling
all space, but his equations did not require any such medium, and by
the early 19th century the generally accepted ideal for fundamental
physical theory was to discover mathematical equations for forces
between indestructible atoms moving through empty space.
2) It was Michael Faraday (1791-1867) who revived the idea that space
was filled with a medium having physical effects in itself... To
summarize Faraday's results, James Clerk Maxwell (1831-1879) adapted
and developed the mathematics used to describe fluids and elastic
solids, and Maxwell postulated an elaborate mechanical model of
electrical and magnetic fields.
3) The achievement of Einstein (1879-1955) in his paper on special
relativity was to highlight and interpret the hidden symmetry of
Maxwell's equations, not to change them. The Faraday-Maxwell concept
of electric and magnetic fields, as media or ethers filling all space,
was retained by Einstein. Later, Einstein was dissatisfied with the
particle-field dualism inherent in the early atomic theory, and
Einstein sought, without success, a unified field theory in which all
fundamental particles would emerge as special solutions to the field
4) Following Einstein, Paul Dirac (1902-1984) then showed that photons
emerged as a logical consequence of applying the rules of quantum
mechanics to Maxwell's electromagnetic ether. This connection was soon
generalized so that particles of any sort could be represented as the
small-amplitude excitations of quantum fields. Electrons, for example,
can be regarded as excitations of an electron field, an ether that
pervades all space and time uniformly. Our current and extremely
successful theories of the *strong, electromagnetic, and weak forces
are formulated as *relativistic quantum field theories with *local
5) The author states: "Einstein first purified, and then enthroned,
the ether concept. As the 20th century has progressed, its role in
fundamental physics has only expanded. At present, renamed and thinly
disguised, it dominates the accepted laws of physics."
Physics Today http://www.physicstoday.org
Notes by ScienceWeek:
Michelson-Morley experiment of 1887: Conducted by Albert Michelson
(1852-1931) and Edward Morley (1838-1923), the experiment attempted to
measure the velocity of the Earth through the "ether" by using an
interferometer to detect a difference in the speed of light in the
direction of Earth's rotation from the speed perpendicular to this
direction. No difference was observed, indicating the absence of an
special theory of relativity: Proposed by Einstein in 1905, the
special theory refers to inertial (non-accelerated) frames of
reference. It assumes physical laws are identical in all frames of
reference and that the speed of light in a vacuum is constant
throughout the Universe and is independent of the speed of the
observer. In general, the special theory gives a unified account of
the laws of mechanics and electromagnetism (including optics). The
companion theory, the general theory of relativity (1915), deals with
general relative motion between accelerated frames of reference, and
it is the general theory that led to Einstein's analysis of
field: In this context, in general, the term "field" refers to a
physical quantity (e.g., electric or magnetic field) that varies from
point to point in space.
strong, electromagnetic, and weak forces: The fundamental forces
currently identified in physics are the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear weak
force. The nuclear strong force is the dominant force that acts
between hadrons (e.g., the force that binds neutrons and protons in
nuclei). (A "hadron" is any object made of *quarks and/or antiquarks).
The weak force occurs between leptons (particles without internal
structure, e.g., electrons, neutrinos) and hadrons (particles with
internal structure, e.g., neutrons and protons); In general, the weak
force is responsible for radioactivity.
quarks and antiquarks: A quark is a hypothetical fundamental particle,
having charges whose magnitudes are one-third or two-thirds of the
electron charge, and from which the elementary particles may in theory
be constructed. The antiquark is the antimatter quark entity. In
general, antiparticles are homologs of elementary particles but with
opposite charge. The positron, for example, is the antimatter particle
homologous to the electron. Matter composed entirely of antiparticles
is called "antimatter".
relativistic quantum field theories: In general, a "quantum field
theory" is any quantum mechanical theory in which particles are
represented by fields whose normal modes of oscillation are quantized.
The term is also used to refer to a quantum mechanical theory applied
to systems having an infinite number of *degrees of freedom. Quantum
electrodynamics, for example, is a particular quantum field theory
describing the emission or absorption of photons by charged particles.
"Relativistic quantum field theories" are used to describe fundamental
interactions between elementary particles (which exhibit relativistic
velocities, i.e., velocities approaching the speed of light).
local interactions: In this context, a local interaction is an
interaction between particles whose quantum mechanical wave functions
are confined to a small region of a large system rather than being
extended throughout the system.
ON FIELD THEORY IN PHYSICS
Notes by ScienceWeek:
In physics, a field is an entity that acts as intermediary in
interactions between particles, and which is distributed over part or
all of space, and whose properties are functions of space coordinates,
and except for static fields, also functions of time. There is also a
quantum-mechanical analog of this entity, in which the function of
space and time is replaced by an operator at each point in space-time.
The following points are made by Roman Jackiw (Proc. Natl. Acad. Sci.
1) Present-day theory for fundamental processes (i.e., descriptions of
elementary particles and forces) is phenomenally successful.
Experimental data confirms theoretical prediction, and where accurate
calculation and experiments are attainable, agreement is achieved to 6
or 7 figures. Two examples: a) The helium atom ground state energy
(*Rydbergs) is experimentally measured as -5.8071394 and theoretically
calculated as -5.8071380. b) The muon magnetic dipole moment is
experimentally measured as 2.00233184600 and theoretically calculated
2) The theoretical structure within which this success has been
achieved is *local field theory, which offers a wide variety of
applications, and which provides a model for fundamental physical
reality as described by our theories of *strong, electroweak, and
gravitational processes. No other framework exists in which one can
calculate so many phenomena with such ease and accuracy.
3) But is spite of these successes, today there is little confidence
that field theory will advance our understanding of nature at its
fundamental workings beyond what has already been achieved. Although
in principle all observed phenomena can be explained by present-day
field theory, these accounts are still imperfect, requiring ad hoc
inputs. Moreover, because of conceptual and technical obstacles,
classical gravity theory has not been integrated into the *quantum
field description of nongravitational forces: *quantizing the *metric
tensor of Einstein's theory produces a quantum field theory beset by
infinities that apparently cannot be controlled.
4) These shortcomings are actually symptoms of a deeper lack of
understanding concerning *symmetry and symmetry breaking... Physicists
are happy in the belief that Nature in its fundamental workings is
essentially simple, but observed physical phenomena rarely exhibit
overwhelming regularity. Therefore, at the very same time that we
construct a physical theory with intrinsic symmetry, we must find a
way to break the symmetry in physical consequences of the model.
5) These problems have produced a theoretical impasse for over two
decades, and in the absence of new experiments to channel theoretical
speculation, some physicists have concluded that it will not be
possible to make progress on these questions within field theory, and
they have turned to a new structure, "*string theory". In field
theory, the quantized excitations are point particles with point
interactions, and this gives rise to the infinities. In string theory,
the excitations are extended objects -- strings -- with nonlocal
interactions; there are no infinities in string theory, and that
enormous defect of field theory is absent.
6) Yet in spite of its positive features, until now string theory has
provided a framework rather than a definite structure, and a precise
derivation of the *Standard Model has yet to be given. The author
concludes: "On previous occasions when it appeared that quantum field
theory was incapable of advancing our understanding of fundamental
physics, new ideas and new approaches to the subject dispelled the
pessimism. Today we do not know whether the impasse within field
theory is due to a failure of imagination or whether indeed we have to
present fundamental physical laws in a new framework, thereby
replacing the field theoretic one, which has served us well for over
Proc. Nat. Acad. Sci. http://www.pnas.org
Notes by ScienceWeek:
Rydbergs: A unit of energy used in atomic physics, value = 13.605698
local field theory: In this context, "locality" is the condition that
two events at spatially separated locations are entirely independent
of each other, provided that the time interval between the events is
less than that required for a light signal to travel from one location
to the other. For example, the quantum mechanical wave function is a
strong, electroweak, and gravitational processes: The fundamental
forces comprise the gravitational force, the electromagnetic force,
the nuclear strong force, and the nuclear weak force. The
"electroweak" interactions are a unification of the electromagnetic
and nuclear weak interactions, and are described by the Weinberg-Salam
theory (sometimes called "quantum flavordynamics"; also called the
quantum field description: In general, a quantum field theory is a
quantum mechanical theory applied to systems having an infinite number
of *degrees of freedom. The term is also used to refer to any quantum
mechanical theory in which particles are represented by fields whose
normal modes of oscillation are quantized (see below).
degrees of freedom: In general, the number of independent parameters
required to specify the configuration of a system.
quantizing: In experimental physics, a quantized variable is a
variable taking only discrete multiple values of a quantum mechanical
constant. In theoretical physics, "quantizing" means the consistent
application of certain rules that lead from classical to quantum
mechanics. In general, "quantization" is a transition from a classical
theory or a classical quantity to a quantum theory or the
corresponding quantity in quantum mechanics.
metric tensor: The mathematical statement (involving a set of
quantities) that describes the deviation of the Pythagoras theorem in
a curved space.
symmetry and symmetry breaking: If a theory or process does not change
when certain operations are performed on it, the theory or process is
said to possess a symmetry with respect to those operations. For
example, a circle remains unchanged under rotation or reflection, and
a circle therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry breaking
encompasses both "explicit" symmetry breaking and "spontaneous"
symmetry breaking. Explicit symmetry breaking is a phenomenon in which
a system is not quite, but almost, the same for two configurations
related by exact symmetry. Spontaneous symmetry breaking refers to a
situation in which the solution of a set of physical equations fails
to exhibit a symmetry possessed by the equations themselves.
string theory: In particle physics, string theory is a theory of
elementary particles based on the idea that the fundamental entities
are not point-like particles but finite lines (strings), or closed
loops formed by strings, the strings one-dimensional curves with zero
thickness and lengths (or loop diameters) of the order of the Planck
length of 10^(-35) meters.
Standard Model: In particle physics, the Standard Model is a
theoretical framework whose basic idea is that all the visible matter
in the universe can be described in terms of the elementary particles
leptons and quarks and the forces acting between them. Leptons are a
class of point-like fundamental particles showing no internal
structure and no involvement with the strong forces. A quark is a
hypothetical fundamental particle, having charges whose magnitudes are
one-third or two-thirds of the electron charge, and from which the
elementary particles may in theory be constructed.
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