Sharif Digital Repository

The goal of this thesis is to evaluate the strengths and weaknesses of the two existing formulations of Bohmian mechanics. The first one was proposed by Bohm, and emphasizes on the dynamics being second-order, and in which, the key tool for explaining the quantum phenomena is a non-classical potential, called "the quantum potential". In this approach, the postulates of de Broglie's "pilot-wave" theory, which now is known as Bohmian mechanics, are non-fundamental and are special to the atomic level. The possibility is proposed that these postulates become subjected to some modifications at the nuclear or lower levels, but no particular way for performing such modifications is suggested. The... 

In the special theory of relativity, it is not necessary to propose that there is no privileged frame of reference but because this formalism is of the epistemological level, we can not deduce this ontological conclusion. On the other hand, there are different physical motivations for a privileged frame of reference and also there is an alternative physical model for special relativity called inertial transformations which is similar to the special theory of relativity at the observational level, but there is a privileged frame of reference in that theory. In this paper, I have tried to collect motivations for a privileged frame of reference in physics, in order to prepare a source for those... 

Natural sciences have philosophical and ideological fundamentals. "The attitude towards human", is one of these philosophic or metaphysical fundamentals of science so that scientists and researchers, attentive or not, take it as a basis for their scientific activities. In the other hand, "the science" also affects "The attitude towards human", and different scientific theories caused various attitudes towards human to take shape. "Renaissance" is one of the most important and sophisticated historical periods of the west`s history, and the changes in this period are among the main basics of entering the modern age. In this thesis, first of all some issues about the fundamentals of the science... 

Non-locality was taken into account, in the first place by Bell’s inequalities in Quantum Mechanics. With the emergence of non-locality, it seems that there is a fundamental conflict between the two basic theories of the 20th century, Quantum Mechanics and Relativity. Relativity is constructed upon local descriptions, but there are some hidden non-local features in Quantum Mechanics .Thus, superluminal signaling, which is in conflict with Relativity, has attracted a lot of attention and some ideas were proposed , using this non-local feature, to send superluminal signal. But, the no-signaling theorems claim that none of these features can be used to send superluminal signal. On the other... 

The measurement problem is one of the issues that is still under debate about the Quantum theory. A significant part of literature during the recent years includes the standard point of view about this problem (including the separation of microscopic and macroscopic domains) and the criticisms of some major physicists in this context. Among these, alternative theories and interpretations have been getting more attention. Experimental tests of Quantum Mechanics in the macroscopic domain and their comparison with alternative theories have always encountered various difficulties (in particular the decoherence phenomenon). Anyway, towards the end of the last century, with the advances in... 

For more than a century, physicists have recognized the contrast between the asymmetry of thermodynamic phenomena and T-symmetry of the fundamental laws, and they have referred to it as the arrow of time. In this thesis we tried to give an overview of the past and present status of this problem, using various theories. It is shown that the problem becomes a question about the boundary conditions of thermodynamic systems, and then a question about cosmology, and finally it becomes the problem of initial conditions of universe. An analysis of initial condition theories is presented for knowing how each of them tries to solve the problem of arrow of time. Different views about the relationship... 

Inflationary Cosmology is the prevailing paradigm of Early Universe Cosmology. In these models, by considering that in the first moments after the Big Bang, there has been a scalar field which has dominated the energy of the universe, we can create a an era called inflation in which the scale factor has a positive acceleration. By such an era, we can solve some of the problems of the Standard Big Bang (SBB) theory such as the horizon problem and the flatness problem, which are in relation with the initial conditions. In addition, this paradigm creates a suitable context for explaining the creation of the inhomogeneities in the universe. Therefore, these models have a predictability feature... 

Quantum Mechanics, as the most famous physical theory was founded about 85 years ago; but still there are a lot of debates about its interpretation. In this work, we review some basic concepts of Quantum Mechanics in form of questions about uncertainty principle, measurement problem and complementarily. We also review Bell inequality which has great philosophical and recently technological results. Bell derived his inequality regardless of modeling the measuring apparatus; we show, by take a realistic model for measuring apparatus, Bell inequality would be deduced. Finally we review a mathematical language which was used to show the duality of wave and particle. Quantum... 

Quantum mechanics is very succesful in the description and prediction of the microphysical world. So nowadays very few doubt its authenticity. Nevertheless, there are some conceptual issues that are still under debate, such as action at a distance. It took a while after the introduction of the EPR paradox in 1935 until John Stewart Bell derived an inequality, using local hidden variables. This inequality was in contrast with predictions of quantum mechanics. Experiments also contradicted this inequality. This implies that there is action at distance which, in turn suggests, the violation of the special relativity. In this thesis, we consider this issue and shall see that on the one hand we... 

One of the important issues in the fundamental physics is the arrow of time. According to the fundamental theories, motion is symmetry with respect to the passage of time while on a macroscopic level time has direction. In the macroscopic models the arrow of time is provided by the Second Law of Thermodynamics.The thermodynamic arrow is often linked to the cosmological arrow of time, because it is ultimately about the boundary conditions of the early universe.Recently people have tried to suppose this challenge as a fundamental issue and use this as fundamental assumption in their theories.A number of models have attempted to solve the problem based on the concept of information.... 

Although the origin of matter-antimatter asymmetry remains unknown, continuing advances in theory and improved experimental limits have ruled out some scenarios for baryogenesis: for example, the sphaleron baryogenesis at the electroweak phase transition in the standard model. In this thesis, we give an introduction to some of the ideas and attempts to understand the origin of the matte -antimatter asymmetry of the universe. After the discussion of some basic issues of cosmology and particle theory, the scenarios of electroweak baryogenesis, GUT baryogenesis, and leptogenesis are outlined  

The worldview and value system can use a cognitive-normative framework to select and shape science and technology. Of course, this framework is not the sole factor in shaping and selecting science and technology. The context in which science and technology flourish is also an important factor. Thus a religious science and technology is possible. Furthermore one can find many examples in the contemporary science and technology which are rooted in a secular and naturalistic outlook., but one can shape a science and technology which are rooted in religious worldview and value system. These examples show that one can generate a religious type of science and technology ,but in order to do this... 

The influences of metaphysics in physical science in contemporary philosophy of science have the main place. In this article we consideration the scientific experiment and model for understanding of metaphysic influence .we answer the epistemological and metaphysical question about scientific experiment. We notice in the approximation in the scientific experiment and modeling. In this line we inference the exponential radiation law and consider approximation in this inference and conclude that from approximation, metaphysics of individual scientist influence in the future of physical sciences. We consider the role of model in scientific explanation and with this study we understand that... 

Nucleosynthesis and CMB data clearly indicate that most of the matter
in the universe is dark and non-baryonic. There’s no shortage of particle
physics candidates for this dark matter. This candidates can be classified
according to whether the dark matter particles originated via decoupling
from thermal bath or were created in some non thermal process. Thermal relics can be categorized further as to whether they were relatvistic or nonrelativistic at the moment of decoupling. The relics which were relatvistic at this time constitute hot dark matter, while those which where nonrelativistic constitute cold dark matter. The goal of this thesis is reviewing hot dark matter... 

This thesis seeks to demonstrate the importance (important status) of “subject” and “question” in science and also wants to show that choosing this issue is affected by values. There are various values, especially outside of science, which play role in subject choices made by scientists, scientific institutions and scientific policies, and therefore influence science by this way. So after giving an account of the term “scientific choice”, which has been proposed by Alvin Weinberg in 1963, we try to examine the impact of values on scientific choices and then the impact of these choices on science itself. In order to do this, we introduced choices in science and Weinberg’s index for them in... 

Isn’t our universe ,which includes everything that is causally connected to us, a tiny and negligible part of wider and diverse “multiple universes”? Although the multiverse idea has been considered by scientists recently, it had been discussed by philosophers and theologians in the past.
Many of our physical theories,whether being accepted like General Relativity, or speculative like string theory, lead naturally to the multiverse idea .The idea of multiverse is also brought forth to take care of the fine tuning observed in cosmology, in connection with the so – called anthropic principle.
This idea appeared in order to answer to some problems of quantum mechanics, string theory... 

In this dissertation we study the derivation of the second law of thermodynamics from an underlying physics. After discussing different methods for this derivation, we conclude that the only way to fulfill this, is to use a probabilistic mechanics which has probability as an inherent concept in itself, not as a supplementary one like statistical mechanics. This mechanics in contrary to the Newtonian mechanics, should be indeterministic  

In the early time of the discovery of the quantum mechanics and some decades after that, various interpretations of quantum mechanics were proposed. However, many years after that, the “indetermenistic” perspective well-known for Copenhagen perspective which was proposed mostly by Bohr and his colleagues became the dominant attitude among physicists. But nearly two decades after the fixation point of the Copenhagen perspective, a new interpretation of quantum mechanics was proposed by Bohm which was nonlocal but deterministic and it could reproduce all the predictions of quantum mechanics.Bohm’s theory responded to the many theoretical and philosophical objections assumed to the Copenhagen... 

The term “scientific naturalism” is the invention of Thomas H. Huxley. He used it to describe a philosophical outlook that shunned the supernatural and adopted empirical science as the only reliable basis of knowledge about the physical, social, and moral worlds. Recent decades have witnessed a flurry of philosophical activity in the name of naturalism. Most contemporary philosophers identify themselves as naturalist, and much recent work in philosophy can be seen as part of general trend toward conducting philosophical inquiry under the umbrella of naturalistic assumptions. Today the label “naturalism” refers to a particular worldview. Nevertheless, naturalism is not a clearly defined... 

The1935 EPR thought experiment, introduced the concept of entanglement of quantum states, and this brought up the problems of faster than light signaling and faster than light influencing.The quantum entanglement has becomeone of the most important aspects of quantum information in the last thirty years.But the standard quantum theory has not been able to solve the dilemma of quantum entanglement and has confined itselfto deny faster than light signaling, but admitting faster than light influencing.But the followers of Bohmian mechanics,which have appealed to hidden variables,see no problem with quantum entanglement.The aim of this thesis is to compare the status of the standard quantum...