We know that the theory of general relativity has proved to be a major breakthrough to understand the spacetime continuum, but we also know that this theory couldn’t be able to answer some questions regarding it. But there is a theory called Quantum Field Theory by which we could able to answer those question. Still, we are not able to find all the answers but in near future, we will able to find all of that. In this article, we will discuss Quantum Field Theory and its possibilities. So, let’s get started.
Introduction to Quantum Field Theory?
Quantum Field Theory is the mathematical and conceptual framework for contemporary elementary particle physics. In an informal sense, it is the extension of Quantum Mechanics, dealing with particles, over to fields, i.e. systems with an infinite number of degrees of freedom. We live in a threedimensional world, but there can be more of that.
In the last few years, it has become a more widely discussed topic in the philosophy of science, with questions ranging from methodology and semantics to ontology. It taken seriously in its metaphysical implications seems to give a picture of the world which is at variance with central classical conceptions of particles and fields, and even with some features of QM.
Complications in Quantum Field Theory
Possibly the best and most comprehensive understanding of it is gained by dwelling on its relation to other physical theories, foremost with respect to QM, but also with respect to classical electrodynamics, Special Relativity Theory and Solid State Physics or more generally Statistical Physics. However, the connection between QFT and these theories is also complex and cannot be neatly described step by step.
There are several reasons for using Quantum Field Theory.
 It is a natural generalization of classical field theories, which are our most successful (nonquantum) theories of Nature.
 A QFT can account for the (observed, wellstudied) creation and annihilation of particles, processes that do not exist in QM.
 QFT is inherently relativistic, and magically (just mathematics) resolves issues of causality that plague even relativistic quantum particle theories.
Quantum Fields do not interact with matter. In a QFT, what we perceive as particles are excitations of the Quantum Field itself.
Evolution of Quantum Field Theory
The simplest “practical” QFT is quantum electromagnetism. In it, two fields are the electromagnetic field and the electron field. These two fields continuously interact with each other, energy and momentum are transferred, and excitations are created or destroyed. So for instance, what we picture intuitively as an electron absorbing a photon is, in quantum electrodynamics, a specific interaction between the electromagnetic field and the electron field, in which the electromagnetic field loses one excitation quantum, and the electron field gains its energy, momentum and angular momentum.
Some interesting originated theories from Quantum Field Theory

Quantum Gravity
The current understanding of gravity is based on Albert Einstein’s general theory of relativity, which is formulated within the framework of classical physics. On the other hand, the other three fundamental forces of physics are described within the framework of quantum mechanics and quantum field theory.
The standard model of particle physics covers the electromagnetic, the weak and the strong interaction. However, the fourth fundamental force in nature, gravitation, has defied quantization so far. Although numerous attempts have been made in the last 80 years, and in particular very recently, there is no commonly accepted solution up to the present day. One basic problem is that the mass, length and time scales quantum gravity theories are dealing with are so extremely small that it is almost impossible to test the different proposals.
Frankly speaking, the purpose of Quantum Gravity is only to describe the quantum behavior of the gravitational field and should not be confused with the objective of unifying all fundamental interactions into a single mathematical framework. We can say that the theory of quantum gravity is also a grand unification of all known interactions is sometimes referred to as The Theory of Everything.

String Theory
String theory is a theoretical framework in which the fundamental particles (i.e. electrons, protons etc.) are replaced by onedimensional objects called strings. It describes how these strings propagate through space and interact with each other. A string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string.
String Theory is one of the most promising theories for bridging the gap between QFT and General Relativity Theory by supplying a unified theory of all natural forces, including gravitation. The basic idea of string theory is not to take particles as fundamental objects but strings that are very small but extended in one dimension. This assumption has the pivotal consequence that strings interact on an extended distance and not at a point. This difference between string theory and standard QFT is essential because it is the reason why string theory also embraces the gravitational force which is very difficult to deal with in the framework of QFT.
Note: According to String Theory spacetime is a 10dimensional entity.
We can say that the Quantum Field Theory would prove crucial in understanding the all our unanswered question in near future. Possibly, it would also prove crucial to fill the gap between QFT and GRT as well. So we could find a unified theory to understand the mystique universe.
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