Sharif Digital Repository

Many physicists believed that all four forces were once unified at high energy levels but as the universe reduced into a lower-energy states the inherent symmetry between the forces began to break down.this broken symmetry caused the creation of four distinct forces of nature. The goal of the unified theory is an attempt to look back in time to when these forces where unified as one. In this thesis I tried to give an overview of the challenges which is againsted theorists in the way of unification. In the first chapter explores the theory that try to unify the electromagnetic and weak forces are investigated.it is done by considering guage principle and spontaneous symmetry breaking.in the... 

The search for an empirically proven quantum theory of gravity is one of the greatest open problems of fundamental physics. Obstacles are formal and conceptual in nature. Our goal is to find a theory that somehow unites general relativity (Einstein's classical field gravity theory) and quantum field theory. In this research work, the problem of quantum gravity and the reason for its importance are investigated, as well as the proposed solutions; and what philosophical issues do these approaches and the issue itself create. Research has been carefully selected to remain managed in terms of size and content, however, some basic formalism is introduced to enter physics and the philosophy of... 

In the framework of quantum field theory, countless consistent theories can be constructed. However, it is understood that only a small subset of these theories can be consistently embedded in a theory of quantum gravity (QG). In string theory, as the best candidate for quantum gravity, there is a landscape of effective field theories (EFTs) which are descended from some compactification of extra dimensions. EFTs which are not derived from a compactification is said to belong to swampland. From a bottom-up point of view, the aim of the swampland program is to find a list of criteria which an EFT must respect so that it survives the swampland. The trans-Planckian censorship conjecture (TCC)... 

Bonding gravity with Quantum mechanics has always been a challenging issue. So that, accomplishing a theory of quantum gravity is one of the most important research topics in High-Energy Physics.Information paradox in black holes is among such issues which connect quantum mechanics with gravity. Black holes as a natural solution of Einstein equations have a distinction, with other solutions, since there exists an event horizon that imparts space-time into two causally disconnected regions.According to Hawking’s calculations, black holes would evaporate over time by the thermal radiation. This resulting thermal radiation has less information than the initial collapsed matter in a pure state.... 

Multiverse scenario has been recently addressed by physicists and they have found it useful in many areas of physics. In this dissertation, I have treated some issues about multiverse such as the kinds of multiverses, the arguments for or against multiverse, areas in which multiverse is introduced, etc. This dissertation has six chapters and an appendix. In the chapter one, some classifications of multiverse is introduced, and also some definitions of the concept of a world is presented. Then, my classification and definition of a multiverse and a world is introduced. In the chapter two, the concept of possible worlds in philosophy and its relationship with multiverse hypothesis is examined.... 

Swampland conjectures are set of conditions that must be satisfied in a quantum field theory in order to be compatible with a theory of quantum gravity. These conditions have been deduced from the features of field theories, which are derived from the compactification of the additional dimensions of the string theory. However, it is thought that the mpatibility of these conditions with the theory of quantum gravity is independent of string theory. One of the important reasons is that the swampland conjectures can be obtained by examining the physics of black holes. Black hole is one of the quantum states of any quantum gravity theory. In this thesis, first we will have an overview of the... 

According to Penrose-Hameroff's theory, Consciousness as an undeniable reality can, in some cases, be explained by a kind of orchestrated objective reduction of the wave function in the cytoskeleton of the brain neurons. Here, I have presented the subject, problem, and claim of this theory, as well as its argument, which consists of three main premises. In the first premise, first by rejecting the opposing theories and then by presenting reasons, it is shown that human thinking is, in some manner, sound but non-computable, and at the same time, accepting the Non-computability of human thinking requires believing in the objects in the universe that are non-computable, but They can be...