No Arabic abstract
We investigate the impact of singularities occurring at future times in solutions of the Friedmann equations expressed in conformal coordinates. We focus on the consequences of extending the time coordinate through the singularity for the physics of matter and radiation occupying just one side. Mostly this involves investigation of the relationship between the metric with line element ds^2 = a^2(t) * (dt^2 - dx^2) and time reversal symmetry within electrodynamics. It turns out compatibility between these two is possible only if there is a singular physical event at the time of the singularity or if the topology is not trivial. In both cases the singularity takes on the appearance of a time-like mirror. We are able to demonstrate a relationship between the broken time symmetry in electrodynamics characterized by retarded radiation and radiation reaction and the absolute conformal time relative to the time of the singularity, i.e. between the Electromagnetic and Cosmological arrows of time. It is determined that the Wheeler-Feynman reasoning but with the future absorber replaced by the Cosmological mirror leads to a conflict with observation unless matter is electromagnetically strongly bound to the environment.
In this work, we propose a non-interacting model of Barrow holographic dark energy (BHDE) using Barrow entropy in a spatially flat FLRW Universe considering the IR cutoff as the Hubble horizon. We study the evolutionary history of important cosmological parameters, in particular, EoS $(omega_{B})$, deceleration parameter and, the BHDE and matter density parameter and also observe satisfactory behaviours in the BHDE the model. In addition, to describe the accelerated expansion of the Universe the correspondence of the BHDE model with the quintessence scalar field has been reconstructed.
Gauge invariance, a core principle in electrodynamics, has two separate meanings, only one of which is robust. The reliable concept treats the photon as the gauge field for electrodynamics. It is based on symmetries of the Lagrangian, and requires no mention of electric or magnetic fields. The other depends directly on the electric and magnetic fields, and how they can be represented by potential functions that are not unique. The first gauge concept has been fruitful, whereas the second has the defect that there exist gauge transformations from physical to unphysical states. The fields are unchanged by the gauge transformation, so that potentials are the necessary guides to correctness.
The ether concept -- abandoned for a long time but reinstated by Dirac in 1951-1953 -- has in recent years emerged into a fashionable subject in theoretical physics, now usually with the name of the Einstein-Dirac ether. It means that one special inertial frame is singled out, as the rest frame. What is emphasized in the present note, is that the idea is a natural example of the covariant theory of quantum electrodynamics in media if the refractive index is set equal to unity. A treatise on this case of quantum electrodynamics was given by the present author back in 1971, published then only within a preprint series. The present version is a brief summary of that formalism, with a link to the original paper. We think it is one of the first treatises on modern ether theory.
In this paper, a formulation, which is completely established on a quantum ground, is presented for basic contents of quantum electrodynamics (QED). This is done by moving away, from the fundamental level, the assumption that the spin space of bare photons should (effectively) possess the same properties as those of free photons observed experimentally. Within this formulation, bare photons with zero momentum can not be neglected when constructing the photon field; and an explicit expression for the related part of the photon field is derived. When a local gauge transformation is performed on the electron field, this expression predicts a change that turns out to be equal to what the gauge symmetry requires for the gauge field. This gives an explicit mechanism, by which the photon field may change under gauge transformations in QED.
In this paper we consider a special case of vacuum non-linear electrodynamics with a stress-energy tensor conformal to the Maxwell theory. Distinctive features of this model are: the absence of dimensional parameter for non-linearity description and a very simple form of the dominant energy condition, which can be easily verified in an arbitrary pseudo-riemannian space-time with the consequent constrains on the model parameters. In this paper we analyse some properties of astrophysical compact objects coupled to conformal vacuum non-linear electrodynamics.