[1] Cosmologies with varying light speed
We analyze a generalization of general relativity that incorporates a cosmic
time variation of the velocity of light in vacuum, c, and the
Newtonian gravitation “constant” G proposed by Albrecht and Magueijo.
We find exact solutions for Friedmann universes and determine the rate of
variation of c required to solve the flatness and classical
cosmological constant problems. Potential problems with this approach to the
resolution of the flatness and classical cosmological constant problems are
highlighted. Reformulations are suggested which give the theory a more
desirable limit as a theory of varying G in the limit of
constant c and its relationship to theories with varying electron
charge and constant c are discussed.
[2] Light speed reduction to 17 metres per second in an ultracold
atomic gas
Techniques that use quantum interference effects are being actively
investigated to manipulate the optical properties of quantum systems1. One such example is
electromagnetically induced transparency, a quantum effect that permits the
propagation of light pulses through an otherwise opaque medium2,3,4,5. Here we report an
experimental demonstration of electromagnetically induced transparency in an
ultracold gas of sodium atoms, in which the optical pulses propagate at twenty
million times slower than the speed of light in a vacuum. The gas is cooled to
nanokelvin temperatures by laser and evaporative cooling6,7,8,9,10. The quantum
interference controlling the optical properties of the medium is set up by a
‘coupling’ laser beam propagating at a right angle to the pulsed ‘probe’ beam.
At nanokelvin temperatures, the variation of refractive index with probe
frequency can be made very steep. In conjunction with the high atomic density,
this results in the exceptionally low light speeds observed. By cooling the
cloud below the transition temperature for Bose–Einstein condensation11,12,13 (causing a
macroscopic population of alkali atoms in the quantum ground state of the
confining potential), we observe even lower pulse propagation velocities
(17?m?s−1) owing to the increased atom density. We report an inferred nonlinear
refractive index of 0.18?cm2?W−1 and find that the system shows
exceptionally large optical nonlinearities, which are of potential fundamental
and technological interest for quantum optics.
[3] Light speed variation from gamma-ray bursts
The effect of quantum gravity can bring a tiny light speed variation which
is detectable through energetic photons propagating from gamma ray bursts
(GRBs) to an observer such as the space observatory. Through an analysis of the
energetic photon data of the GRBs observed by the Fermi Gamma-ray Space
Telescope (FGST), we reveal a surprising regularity of the observed time lags
between photons of different energies with respect to the Lorentz violation
factor due to the light speed energy dependence. Such regularity suggests a
linear form correction of the light
speed v(E)=c(1−E/ELV), where E is the photon energy
and ELV=(3.60±0.26)×1017GeV is the Lorentz violation scale measured
by the energetic photon data of GRBs. The results support an energy dependence
of the light speed in cosmological space.
[4] Method for Constraining Light Speed Anisotropy by Using Fiber
Optics Gyroscope Experiments
The Mansouri-Sexl theory is a well known test theory of relativity. Mansouri
and Sexl dealt with the theory of the Michelson-Morley, Kennedy-Thorndike and
Ives-Stilwell experiments but left out the very interesting Sagnac experiment.
In the following paper we will present a novel way of detecting anisotropy
effects in via a reenactment of the Sagnac experiment using fiber
optic gyroscopes (FOG) where is the length of the fiber and is the
angular speed of the FOG. We show how the fiber optics gyroscopes are used for
constraining light speed anisotropy in the framework of the Mansouri-Sexl test
theory. We also show an interesting amplification effect due to the use
of the Mansouri-Sexl slow clock transport equations in conjunction with FOGs.
Our paper is divided into four main sections: in the first one we give an
overview of the Mansouri-Sexl test theory of special relativity, in the second
one we give a historical perspective of the Sagnac experiment, in the third
section we formulate the Mansouri-Sexl theory for the Sagnac experiment and we
conclude with experimental setup and results.
[5] One-way Speed of Light Using Interplanetary Tracking Technology
Light transmission in the Sun-Centered Inertial (SCI) frame is considered
within a flat space-time metric of relativity theory. It is shown that this
metric which is used to derive the Langevin metric that generates the accurate
clock synchronization algorithm used in the Global Positioning System (GPS),
also predicts one-way light speed anisotropy in an inertial frame that
contradicts the principle of light speed constancy. This finding is tested and
confirmed in the SCI frame using the range equations employed in the tracking
of planets and spacecrafts moving within our solar system. These equations are
based on the observation that light travels in the SCI frame at a constant
speed c and have been extensively tested and rigorously verified. The
results suggest a modification of the Lorentz Transformations that yields new
transformations that are consistent with the observed light speed anisotropy
and which better accord with the physical world.
Reference
[1] Barrow, J.D., 1999. Cosmologies with varying light
speed. Physical Review D, 59(4), p.043515.
[2] Hau, L.V., Harris, S.E., Dutton, Z. and Behroozi, C.H.,
1999. Light speed reduction to 17 metres per second in an ultracold atomic
gas. Nature, 397(6720), pp.594-598.
[3] Xu, H. and Ma, B.Q., 2016. Light speed variation from
gamma-ray bursts. Astroparticle Physics, 82,
pp.72-76.
[4] Sfarti, A., 2013. Method for constraining light speed
anisotropy by using fiber optics gyroscope experiments. Physical
Science International Journal, pp.161-175.
[5] Gift, S.J., 2014. One-way Speed of Light Using
Interplanetary Tracking Technology. Physical Science International
Journal, pp.780-796.
