16,639 research outputs found
Isotropy of the velocity of light and the Sagnac effect
In this paper, it is shown, using a geometrical approach, the isotropy of the
velocity of light measured in a rotating frame in Minkowski space-time, and it
is verified that this result is compatible with the Sagnac effect. Furthermore,
we find that this problem can be reduced to the solution of geodesic triangles
in a Minkowskian cylinder. A relationship between the problems established on
the cylinder and on the Minkowskian plane is obtained through a local isometry.Comment: LaTeX, 13 pages, 3 eps figures; typos corrected, added references,
minor changes; to appear in "Relativity in Rotating Frames", ed. G. Rizzi G.
and M.L. Ruggiero, Kluwer Academic Publishers, Dordrecht (2003
Astrophysical Probes of the Constancy of the Velocity of Light
We discuss possible tests of the constancy of the velocity of light using
distant astrophysical sources such as gamma-ray bursters (GRBs), Active
Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by
some models of quantum fluctuations in the space-time background, and we
discuss explicitly how an energy-dependent variation in photon velocity \delta
c/ c \sim - E / M arises in one particular quantum-gravitational model. We then
discuss how data on GRBs may be used to set limits on variations in the
velocity of light, which we illustrate using BATSE and OSSE observations of the
GRBs that have recently been identified optically and for which precise
redshifts are available. We show how a regression analysis can be performed to
look for an energy-dependent effect that should correlate with redshift. The
present data yield a limit M \gsim 10^{15} GeV for the quantum gravity scale.
We discuss the prospects for improving this analysis using future data, and how
one might hope to distinguish any positive signal from astrophysical effects
associated with the sources.Comment: 37 pages LaTeX, 9 eps figures included, uses aasms4.st
Velocity of Light in Dark Matter with Charge
We propose an interesting mechanism to reconcile the recent experiments of
the Michelson-Morley type and slowdown of the velocity of light in dark matter
with a fractional electric charge when the index of refraction of dark matter
depends on the frequency of a photon. After deriving the formula for the
velocity of light in a medium with the index of refraction in a
relativistic regime, it is shown that the local anisotropy of the light speed
is proportional to the second order in . This result implies
that the experiments of the Michelson-Morley type do not give rise to a
stringent constraint on the slowdown of the velocity of light in dark matter
with electric charge.Comment: 10 page
On the Velocity of Light Signals in the Deep Underwater Neutrino Experiments
During the last few years deep underwater neutrino telescopes of a new
generation with dimensions close to 100 m or more were taken into operation.
For the correct track reconstruction and for the interpretation of light pulses
from calibration lasers one has to use the group velocity for light signals.
The difference between group velocity leads to an additional delay of about 10
ns for a distance of 100 m between light source and photjmultiplier. From the
time of the appearance of the first projects of deep underwater neutrino
telescopes in the middle of 70th this fact was never mentioned in the
literature.Comment: 4 pages, 2 figure
D-Foam Phenomenology: Dark Energy, the Velocity of Light and a Possible D-Void
In a D-brane model of space-time foam, there are contributions to the dark
energy that depend on the D-brane velocities and on the density of D-particle
defects. The latter may also reduce the speeds of photons linearly with their
energies, establishing a phenomenological connection with astrophysical probes
of the universality of the velocity of light. Specifically, the cosmological
dark energy density measured at the present epoch may be linked to the apparent
retardation of energetic photons propagating from nearby AGNs. However, this
nascent field of `D-foam phenomenology' may be complicated by a dependence of
the D-particle density on the cosmological epoch. A reduced density of
D-particles at redshifts z ~ 1 - a `D-void' - would increase the dark energy
while suppressing the vacuum refractive index, and thereby might reconcile the
AGN measurements with the relatively small retardation seen for the energetic
photons propagating from GRB 090510, as measured by the Fermi satellite.Comment: 10 pages, 3 figure
On the Ultrarelativistic Limit of General Relativity
As is well-known, Newton's gravitational theory can be formulated as a
four-dimensional space-time theory and follows as singular limit from
Einstein's theory, if the velocity of light tends to the infinity. Here
'singular' stands for the fact, that the limiting geometrical structure differs
from a regular Riemannian space-time. Geometrically, the transition Einstein to
Newton can be viewed as an 'opening' of the light cones. This picture suggests
that there might be other singular limits of Einstein's theory: Let all light
cones shrink and ultimately become part of a congruence of singular world
lines. The limiting structure may be considered as a nullhypersurface embedded
in a five-dimensional spacetime. While the velocity of light tends to zero
here, all other velocities tend to the velocity of light. Thus one may speak of
an ultrarelativistic limit of General Relativity. The resulting theory is as
simple as Newton's gravitational theory, with the basic difference, that
Newton's elliptic differential equation is replaced by essentially ordinary
differential equations, with derivatives tangent to the generators of the
singular congruence. The Galilei group is replaced by the Carroll group
introduced by L\'evy-Leblond. We suggest to study near ultrarelativistic
situations with a perturbational approach starting from the singular structure,
similar to post-Newtonian expansions in the case.Comment: 9 pages, Latex, submitted to Acta Physica Polonica (Jadwisin
Conference Proceedings
- …