ره يافت هاي متفاوت به تانسور انرژي‑تكانه

It can be said that few concepts hold a place as central as energy an‎d momentum, both in describing nature an‎d in a wide range of practical applications. The concept of momentum an‎d, by extension, force an‎d related quantities such as angular momentum, is used to explain systems across nature, from very simple cases like levers an‎d torque to the motion of planets an‎d celestial bodies in Newtonian descriptions. Of course, the limitations of these descriptions have themselves led to the development of more complete theories. In terms of applications, everything from launching satellites to constructing monumental structures an‎d even producing specialized materials is grounded in these concepts. While momentum may be relatively easy for some to grasp, energy is often less intuitive an‎d requires a greater level of abstraction to understan‎d. Nevertheless, its importance is no less than that of momentum. Many natural phenomena can be explained in terms of energy. In introductory treatments, however, various forms of energy are introduced, such as kinetic, thermal, gravitational potential, chemical potential, an‎d electrical potential, which can sometimes make the concept feel less intuitive an‎d even somewhat confusing. Alongside these concepts, conservation laws are also introduced. These laws are so highly regarded among scientists that, in some cases, other principles have been set aside in order to preserve them within theoretical frameworks. Because of the close relationship between momentum an‎d energy in certain formulations, these two quantities are often expressed together as a single entity known as the energy–momentum tensor. From a theoreticalperspective, Noether’s theorem reveals a deep connection between the intrinsic properties of the physical world an‎d these conservation laws, an‎d it can itself lead to definitions of energy an‎d momentum. As science has progressed, various definitions of these quantities have been proposed. While they all share a commitment to conservation laws, each comes with its own challenges that complicate their acceptance. In this thesis, we aim to examine these different definitions of the energy–momentum tensor, along with their associated issues an‎d the proposed solutions to address them. In Chapter 1, we begin with an introduction, discussing the energy–momentum tensor itself an‎d some of its general properties. In Chapter 2, we present Noether’s first theorem an‎d the definition of the energy–momentum tensor that arises from it, along with the desirable properties identified through this approach. In Chapter 3, we explore ways to refine this definition an‎d reconcile it with the more conventional one derived from general relativity. In Chapter 4, we study Maxwell’s electrodynamics as an example. Finally, in the last chapter, we summarize the results of this comparison an‎d discuss possible resolutions to the issues involved.

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بهروز ميرزا , مسلم زارعي