84,860 research outputs found
The Superposition Principle of Waves Not Fulfilled under M. W. Evans' O(3) Hypothesis
In 1992 M.W. Evans proposed a so-called O(3) symmetry of electromagnetic
fields by adding a constant longitudinal "ghost field" to the well-known
transversal plane em waves. He considered this symmetry as a new law of
electromagnetics. Later on, since 2002, this O(3) symmetry became the center of
his Generally Covariant Unified Field Theory which he recently renamed as ECE
Theory. One of the best-checked laws of electrodynamics is the principle of
linear superposition of electromagnetic waves, manifesting itself in
interference phenomena. Its mathematical equivalent is the representation of
electric and magnetic fields as vectors. By considering the superposition of
two phase-shifted waves we show that the superposition principle is
incompatible with M.W. Evans' O(3) hypothesis.Comment: 5 pages, no figure
Quantum causal models, faithfulness and retrocausality
Wood and Spekkens (2015) argue that any causal model explaining the EPRB
correlations and satisfying no-signalling must also violate the assumption that
the model faithfully reproduces the statistical dependences and
independences---a so-called "fine-tuning" of the causal parameters; this
includes, in particular, retrocausal explanations of the EPRB correlations. I
consider this analysis with a view to enumerating the possible responses an
advocate of retrocausal explanations might propose. I focus on the response of
N\"{a}ger (2015), who argues that the central ideas of causal explanations can
be saved if one accepts the possibility of a stable fine-tuning of the causal
parameters. I argue that, in light of this view, a violation of faithfulness
does not necessarily rule out retrocausal explanations of the EPRB
correlations, although it certainly constrains such explanations. I conclude by
considering some possible consequences of this type of response for retrocausal
explanations
Lensing Properties of Cored Galaxy Models
A method is developed to evaluate the magnifications of the images of
galaxies with lensing potentials stratified on similar concentric ellipses. A
simple contour integral is provided which enables the sums of the
magnifications of even parity or odd parity or the central image to be easily
calculated. The sums for pairs of images vary considerably with source
position, while the signed sums can be remarkably uniform inside the tangential
caustic in the absence of naked cusps. For a family of models in which the
potential is a power-law of the elliptic radius, the number of visible images
is found as a function of flattening, external shear and core radius. The
magnification of the central image depends on the core radius and the slope of
the potential. For typical source and lens redshifts, the missing central image
leads to strong constraints; the mass distribution in the lensing galaxy must
be nearly cusped, and the cusp must be isothermal or stronger. This is in
accord with the cuspy cores seen in high resolution photometry of nearby,
massive, early-type galaxies, which typically have the surface density falling
like distance^{-1.3} outside a break radius of a few hundred parsecs. Cuspy
cores by themselves can provide an explanation of the missing central images.
Dark matter at large radii may alter the slope of the projected density;
provided the slope remains isothermal or steeper and the break radius remains
small, then the central image remains unobservable. The sensitivity of the
radio maps must be increased fifty-fold to find the central images in
abundance.Comment: 42 pages, 11 figures, ApJ in pres
Relativistic Constraints for a Naturalistic Metaphysics of Time
The traditional metaphysical debate between static and dynamic views in the
philosophy of time is examined in light of considerations concerning the nature
of time in physical theory. Adapting the formalism of Rovelli (1995, 2004), I
set out a precise framework in which to characterise the formal structure of
time that we find in physical theory. This framework is used to provide a new
perspective on the relationship between the metaphysics of time and the special
theory of relativity by emphasising the dual representations of time that we
find in special relativity. I extend this analysis to the general theory of
relativity with a view to prescribing the constraints that must be heeded for a
metaphysical theory of time to remain within the bounds of a naturalistic
metaphysics
No Need for Dark Matter in Galaxies?
Unhappily, there has been a maelstrom of problems for dark matter theories
over the last few years and many serious difficulties still have no resolution
in sight. This article reviews the evidence for dark matter in galaxies. The
haloes built up by hierarchical merging in dark matter cosmogonies are cusped
and dominated by dark matter at the center. Evidence from the microlensing
optical depth towards Baade's Window and from dynamical modelling of the
Galactic bar already suggests that the Galactic halo is not cusped. Similarly,
evidence from the stability of unbarred disk galaxies, as well as the survival
of fast bars in barred galaxies, suggests that the this result holds good more
generally. Judged on the data from galactic scales alone, the case for dark
matter is weak and non-standard theories of gravity provide a better
description. Of course, non-standard theories of gravity have their own
problems, but not on galactic scales.Comment: 8 pages, invited review for "IDM 2000: Third International Workshop
on the Identification of Dark Matter", ed. N. Spooner (World Scientific
Microlensing Maps for the Galactic Bulge
Microlensing maps -- that is, contours of equal numbers of events per
source stars -- are provided for the inner Galaxy under two alternative
hypotheses : (1) the bulge is an oblate axisymmetric spheroid or (2) the bulge
is a prolate bar. Oblate spheroids yield a total of events per year
per stars at Baade's Window ( events if the disk is maximal).
The event rate is slightly lower for prolate bars viewed at and
the maps have a characteristic asymmetry between positive and negative
longitudes. Prolate bars can yield mild amplifications of the event rate if
viewed almost down the long axis. The disk provides the dominant lensing
population on the bulge major axis for |\ell | \gta 6^\circ. Measurements of
the rate at major axis windows can test for disk dark matter or maximal disk
models.Comment: 12 pages, Late
Axisymmetric Self-Similar Equilibria of Self-Gravitating Isothermal Systems
All axisymmetric self-similar equilibria of self-gravitating, rotating,
isothermal systems are identified by solving the nonlinear Poisson equation
analytically. There are two families of equilibria: (1) Cylindrically symmetric
solutions in which the density varies with cylindrical radius as R^(-alpha),
with 0 <= alpha <= 2. (2) Axially symmetric solutions in which the density
varies as f(theta)/r^2, where `r' is the spherical radius and `theta' is the
co-latitude. The singular isothermal sphere is a special case of the latter
class with f(theta)=constant. The axially symmetric equilibrium configurations
form a two-parameter family of solutions and include equilibria which are
surprisingly asymmetric with respect to the equatorial plane. The asymmetric
equilibria are, however, not force-free at the singular points r=0, infinity,
and their relevance to real systems is unclear. For each hydrodynamic
equilibrium, we determine the phase-space distribution of the collisionless
analog.Comment: 13 pages, 7 figures, uses emulateapj.sty. Submitted to Ap
On the Non-Lorentz Invariance of M.W. Evans O(3)-Symmetry Law
Correcting a former proof of M.W. Evans it is shown that his O(3) hypothesis
is not Lorentz invariant and hence no law of Physics.Comment: 5 page
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