Superstrings Encounters of the Second, Third or Fourth Types?

Strings and their evolutions as superstrings and M-theory have been one of the main focus of theoretical Physics for the last 40 years. In fact some have characterized superstrings and M-theory as the best candidates at explaining quantum gravity and providing a Theory of Everything. Others have claimed that it is “Physics of the next century provided for our exploration this century”. Yet not much has come out of it in terms of actual predictions or observation of anything about anything.In the context of explaining gravity with entanglement with multi-fold mechanisms, we encountered traces of superstrings and may have met some of them or their impacts. It qualifies for an alien encounter of the third type. Dualities between spacetime and superstrings were derived, yet nobody embarked or will ever embark on a superstring spacetime trip, at least. So no encounter of the fourth type. This paper summarizes what we have determined about strings, superstrings and M-theory as part of the multi-fold universe models. The observations and lessons learned are telling signs for superstring investigators.

Anisotropic universe models with magnetized strange quark matter in f(R) gravity theory

In this study, we have investigated generalized anisotropic universe models for magnetized strange quark matter (MSQM) distribution in the framework of [Formula: see text] gravitation theory. For this aim, we have used linearly varying deceleration parameter suggested by Akarsu and Dereli (2012) and equation of state for strange quark matter. For LRS Bianchi I universe model, the magnetic field was obtained as zero. But it was found to be different from zero for other universe models. Also, the geometric and physical aspects of the model are discussed in the conclusion.

Scalar field solutions for anisotropic universe models in various gravitation theories

In this study, we have investigated homogeneous and anisotropic Marder and Bianchi type I universe models filled with normal and phantom scalar field matter distributions with [Formula: see text] in [Formula: see text] gravitation theory (T. Harko et al., Phys. Rev. D 84 (2011) 024020). In this model, [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. To obtain exact solutions of modified field equations, we have used anisotropy feature of the universe and different scalar potential models with [Formula: see text] function. Also, we have obtained general relativity (GR) solutions for normal and phantom scalar field matter distributions in Marder and Bianchi type I universes. Additionally, we obtained the same scalar function values by using different scalar field potentials for Marder and Bianchi type I universe models with constant difference in [Formula: see text] gravity and GR theory. From obtained solutions, we get negative cosmological term value for [Formula: see text] constant scalar potential model with Marder and Bianchi type I universes in GR theory. These results agree with the studies of Maeda and Ohta, Aktaş et al. also Biswas and Mazumdar. Finally, we have discussed and compared our results in gravitation theories.

THE UNIFICATION OF RELATIVITY AND QUANTUM THEORIES

CONSTANCY OF NATURAL CONSTANTS AND THE UNIVERSE MODELS

Cosmology

The term ’cosmology’ has three main uses. At its most general, it designates a worldview, for example, the Mayan cosmology. In the early eighteenth century, shortly after the term made its first appearance, Christian Wolff used it to draw a distinction between physics, the empirical study of the material world, and cosmology, the branch of metaphysics dealing with material nature in its most general aspects. This usage remained popular into the twentieth century, especially among Kantian and neo-scholastic philosophers. But recent developments in science that allow the construction of plausible universe models have, effectively, pre-empted the use of the term in order to designate the science that deals with the origins and structure of the physical universe as a whole. Cosmology may be said to have gone through three major phases, each associated with a single major figure – Aristotle, Newton and Einstein. The ancient Greeks were the first to attempt to give a reasoned account of the cosmos. Aristotle constructed a complex interlocking set of spheres centred on an immovable central earth to account for the motions of the heavenly bodies. Newton formulated a theory of gravitational force that required space and time to be both absolute and infinite. Though the laws of nature could, in principle, be specified, nothing could be said about the origins or overall structure of the cosmos. In 1915, Einstein proposed a general theory of relativity whose field-equations could be satisfied by numerous universe-models. Hubble’s discovery of the galactic red shift in 1929 led Lemaître in 1931 to choose from among these alternatives an expanding-universe model, which, though challenged in the 1950s by a rival steady-state theory, became the ‘standard’ view after the cosmic microwave background radiation it had predicted was observed in 1964. The ‘Big Bang’ theory has since been modified in one important respect by the addition of an inflationary episode in the first fraction of a second of cosmic expansion. As a ‘cosmic’ theory, it continues to raise issues of special interest to philosophers.

Exact solutions, finite time singularities and non-singular universe models from a variety of Λ(t) cosmologies

Cosmological models with time-dependent [Formula: see text] (read as [Formula: see text]) have been investigated widely in the literature. Models that solve background dynamics analytically are of special interest. Additionally, the allowance of past or future singularities at finite cosmic time in a specific model signals for a generic test on its viabilities with the current observations. Following these, in this work we consider a variety of [Formula: see text] models focusing on their evolutions and singular behavior. We found that a series of models in this class can be exactly solved when the background universe is described by a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) line element. The solutions in terms of the scale factor of the FLRW universe offer different universe models, such as power-law expansion, oscillating, and the singularity free universe. However, we also noticed that a large number of the models in this series permit past or future cosmological singularities at finite cosmic time. At last we close the work with a note that the avoidance of future singularities is possible for certain models under some specific restrictions.