Light Cosmology Research Articles

Redshift in varying speed of light cosmology

ABSTRACT In standard cosmology, redshift is related to scale factor by z = a−1 − 1. Varying speed of light cosmologies have also applied this relationship, in which c does not explicitly appear, with the assumption that ℏ ∝ c. Measured redshift is not a comparison of an observed spectrum with the spectrum as it was emitted at a distant location, but a comparison with a reference spectrum generated more locally. This distinction suggests decomposition into two parts: (a) change during the flight of a photon and (b) difference in physics at the time of emission and at the time of observation of a photon associated with an electron transition between specific bound states of an atom. Based on atomic units consistent with data and a relativistic atomic model, redshift is given by z = β(θ)θa−1 − 1, where θ = c/c0, with c0 the present value of c, and β is a function of the atomic parameters describing the transition. The modified form appears to have a modest effect (a difference in scale factor <2 per cent) for redshifts that are not much greater than 10. However, the modification can have a major effect for an early universe with c significantly larger than the present. The simplified form z = θa−1 − 1, which results from a non-relativistic model, provides an approximation for redshift that is not transition-specific.

A Brief History of Primordial Light from the Perspectives of Sufi and Modern Science

The primordial light is fundamental in the creation of the universe from the Sufi cosmology. In particular of the Sufi tradition, the Ishrāqἱ (illumination) school serves as a major School of thought in the Islamic intellectual history with the knowledge of the Muhammadan Light (Nūr Muhammad) becoming the most prominent cosmological point of debate among of Muslim scholars. To date, discussions and reviews on the understanding of the Muhammadan Light from the perspective of theology, literature, philosophy and the cosmological view in comparison to modern cosmology are still lacking. In modern cosmology, the Big Bang theory which is directly related to the light cosmology has been significantly discussed. The present study provides additional evidence with respect to the cosmological perspective highlighting the importance of light cosmology aspects with the insights of combining both cosmological postulates by evidence of direct connection with current modern and Sufi cosmology (worldviews). The present study renders the understanding of the gnosis of God and His Prophet Muhammad PBUH through the light cosmology perspective.

Statistical Hierarchy of Varying Speed of Light Cosmologies

Abstract Many varying speed of light (VSL) theories have been developed recently. Here we address the issue of their observational verification in a fully comprehensive way. By using the most updated cosmological probes, we test three different candidates for a VSL theory (Barrow & Magueijo, Avelino & Martins, and Moffat). We consider many different Ansätze for both the functional form of c(z) and the dark energy dynamics. We compare these results using a reliable statistical tool such as the Bayesian evidence. We find that the present cosmological data are perfectly compatible with any of these VSL scenarios, but for the Moffat model there is a higher Bayesian evidence ratio in favor of VSL rather than the c = constant ΛCDM scenario. Moreover, in such a scenario, the VSL signal can help to strengthen constraints on the spatial curvature (with indication toward an open universe), to clarify some properties of dark energy (exclusion of a cosmological constant at level), and is also falsifiable in the near future owing to peculiar issues that differentiate this model from the standard one. Finally, we apply an information prior and entropy prior in order to put physical constraints on the models, though still in favor Moffat’s proposal.

Normal DGP in varying speed of light cosmology

Varying speed of light (VSL) has been used in cosmological models in which the physical constants vary over time. On the other hand, the Dvali, Gabadadze and Porrati (DGP) brane world model, especially its normal branch, has been extensively discussed to justify the current cosmic acceleration. In this article we show that the normal branch of DGP in VSL cosmology leads to a self-accelerating behavior and therefore can interpret cosmic acceleration. Applying statefinder diagnostics demonstrates that our result slightly deviates from the ΛCDM model.

Bayesian evidence and predictivity of the inflationary paradigm

In this paper we consider the issue of paradigm evaluation by applying Bayes' theorem along the following nested hierarchy of progressively more complex structures: i) parameter estimation (within a model), ii) model selection and comparison (within a paradigm), iii) paradigm evaluation. In such a hierarchy the Bayesian evidence works both as the posterior's normalization at a given level and as the likelihood function at the next level up. Whilst raising no objections to the standard application of the procedure at the two lowest levels, we argue that it should receive a considerable modification when evaluating paradigms, when testability and fitting data are equally important. By considering toy models we illustrate how models and paradigms that are difficult to falsify are always favoured by the Bayes factor. We argue that the evidence for a paradigm should not only be high for a given dataset, but exceptional with respect to what it would have been, had the data been different. With this motivation we propose a measure which we term predictivity, as well as a prior to be incorporated into the Bayesian framework, penalising unpredictivity as much as not fitting data. We apply this measure to inflation seen as a whole, and to a scenario where a specific inflationary model is hypothetically deemed as the only one viable as a result of information alien to cosmology (e.g. Solar System gravity experiments, or particle physics input). We conclude that cosmic inflation is currently hard to falsify, but that this could change were external/additional information to cosmology to select one of its many models. We also compare this state of affairs to bimetric varying speed of light cosmology.

Variable speed of light cosmology, primordial fluctuations and gravitational waves

A variable speed of light (VSL) cosmology is described in which the causal mechanism of generating primordial perturbations is achieved by varying the speed of light in a primordial epoch. This yields an alternative to inflation for explaining the formation of the cosmic microwave background (CMB) and the large scale structure (LSS) of the universe. The initial value horizon and flatness problems in cosmology are solved. The model predicts primordial scalar and tensor fluctuation spectral indices $n_s=0.96$ and $n_t=- 0.04$, respectively. We make use of the $\delta{\cal N}$ formalism to identify signatures of primordial nonlinear fluctuations, and this allows the VSL model to be distinguished from inflationary models. In particular, we find that the parameter $f_{\rm NL}=5$ in the variable speed of light cosmology. The value of the parameter $g_{\rm NL}$ evolves during the primordial era and shows a running behavior.

New tests of variability of the speed of light.

We present basic ideas of the varying speed of light cosmology, its formulation, benefits and problems. We relate it to the theories of varying fine structure constants and discuss some new tests (redshift drift and angular diameter distance maximum) which may allow measuring timely and spatial change of the speed of light by using the future missions such as Euclid, SKA (Square Kilometer Array) or others.

SNe data analysis in variable speed of light cosmologies without cosmological constant

In this work, we aim to show the possibilities of the variable speed of light (VSL) theory in explaining the type Ia supernovae (SNe) observations without introducing dark energy. The speed of light is assumed to be scale factor-dependent, which is the most popular assumption in VSL theory. We show the modified calculation of the distance modulus and the validity of the redshift-scale factor relation in VSL theory. Three different models of VSL are tested SNe data-sets with proper constraints on the model parameters. The comparison of the three models and flat ΛCDM in distance modulus is showed. Some basic problems and the difficulties of the confirmation of the VSL theory are also discussed.

A statefinder luminosity distance formula in varying speed of light cosmology

We derive a luminosity distance formula for the varying speed of light (VSL) theory which involves higher order characteristics of expansion such as jerk, snap and lerk which can test the impact of varying c onto the evolution of the universe. We show that the effect of varying c is possible to be isolated due to the relations connecting observational parameters already by measuring the second-order term in redshift z unless there is a redundancy between the curvature and an exotic fluid of cosmic strings scaling the same way as the curvature.

Redshift drift in varying speed of light cosmology

We derive a redshift drift formula within the framework of varying speed of light (VSL) theory using the specific ansatz for the variability of c(t)=c0an(t). We show that negative values of the parameter n, which correspond to diminishing value of the speed of light during the evolution of the universe, effectively rescale dust matter to become little negative pressure matter, and the cosmological constant to became phantom. Positive values of n (growing c(t)) make VSL model to become more like Cold Dark Matter (CDM) model. Observationally, there is a distinction between the VSL model and the ΛCDM model for the admissible values of the parameter n∼−10−5, though it will be rather difficult to detect by planned extremely large telescopes (EELT, TMT, GMT) within their accuracy.

Variable speed of light cosmology as a solution to the Pioneer anomaly

It is shown that the Pioneer anomaly is a natural consequence of variable speed of light cosmological models wherein the speed of light is assumed to be a power-law function of the scale factor (or cosmic time). In other words, the Pioneer anomaly can be regarded as a non-gravitational effect of the continuously decreasing speed of light which indicates itself as an anomalous light propagation time delay in local frames. This time delay is accordingly interpreted as an additional Doppler blue shift.

Note on varying speed of light cosmologies

The various requirements on a consistent varying speed of light (‘VSL’) theory are surveyed, giving a short check-list that needs to be satisfied by such theories.

HOW MATTER IS CREATED IN VSL THEORY?

In this work we investigate matter creation in the context of two types of varying speed of light (VSL) cosmologies. We write the energy conservation law arising from Einstein equations for a Friedmann–Robertson–Walker (FRW) line element in a flat universe, solve the field equations and study how particles are created as c changes with cosmic epoch. We calculate the "adiabatic" particle creation rate, the total number of particle as a function of time and find the constrains imposed by the second law of thermodynamics upon the models.

Unusual features of varying speed of light cosmologies

We contrast features of simple varying speed of light (VSL) cosmologies with inflationary universe models. We present new features of VSL cosmologies and show that they face problems explaining the cosmological isotropy problem. We also find that if c falls fast enough to solve the flatness and horizon problems then the quantum wavelengths of massive particle states and the radii of primordial black holes can grow to exceed the scale of the particle horizon. This may provide VSL cosmologies with a self-reproduction property. The constraint of entropy increase is also discussed. The new problems described in the this Letter provide a set of bench tests for more sophisticated VSL theories to pass.

Varying speed of light cosmology from a stringy short distance cutoff

It is shown that varying speed of light cosmology follows from a string-inspired minimal length uncertainty relation. Because of the reduction of the available phase space volume per quantum mode at short wavelengths, the equation of state of ultrarelativistic particles stiffens at very high densities. This causes a stronger than usual deceleration of the scale factor which competes with a higher than usual propagation speed of the particles. Various measures for the effective propagation speed are analyzed: the group and phase velocity in the high energy tail, the thermal average of the group and phase velocity, and the speed of sound. Of these three groups, only the first provides a possible solution to the cosmological horizon problem.

Varying speed of light cosmologies as two-dimensional dynamical systems

Varying speed of light cosmologies as two-dimensional dynamical systems

Varying- α theories and solutions to the cosmological problems

If the fine structure constant α= e 2/(ℏ c) were to change, then a number of interpretations would be possible, attributing this change either to variations in the electron charge, the dielectric constant of the vacuum, the speed of light, or Planck's constant. All these variations should be operationally equivalent and can be related by changes of standard units. We show how the varying speed of light cosmology recently proposed can be rephrased as a dielectric vacuum theory, similar to the one proposed by Bekenstein. The cosmological problems will therefore also be solved in such a theory.