sign in sign up
<<
Home , Grand Unified Theory, Progress, Unification (physics), Unified field theory

Unified Theory Parashu Ram Poudel Department of , Prithvi Narayan Campus, Pokhara [email protected]

Abstract: is the long-sought means of tying together all known phenomena to explain the and behaviour of all and in . The quest for unification has been the perennial theme of . The that all physical phenomena can be reduced to simple and explained by a smaller number of is the central tenet of physics. Such a theory could potentially unlock all the secrets of nature and make a myriad of wonders possible, including such benefits as travel and an inexhaustible source of clean energy, among many others. This paper aims to explain unified theory and its development towards the unification of four in brief. Keywords: , , , theory of , super 1. INTRODUCTION nuclei made of . At each stage, the laws of Unified field theory is the physical theory that physics are more unified explaining a larger class combines the treatment of two or more types of of phenomena and reducing to of previous in fields in order to deduce previously unrecognized appropriate circumstances. Typically, the more interrelationships, especially such a theory unifying unified theories exhibit more symmetry, are more the theories of nuclear, electromagnetic, and predictive and less arbitrary. gravitational . In physics, a field refers to an area under the influence of some , such as 2. FUNDAMENTAL FORCES gravity or , for example. A unified field According to the current of physics, theory would reconcile seemingly incompatible forces are not transmitted directly between objects, aspects of various field theories to create a single but instead are described by intermediary entities comprehensive of equations. It is an attempt to called fields. All four of the known fundamental describe all fundamental forces and the relationships forces are mediated by fields, which in the Standard between elementary particles in terms of a single Model of result from exchange of theoretical framework. The term ‘Unified Field gauge bosons. Specifically the four interactions Theory’ was coined by Einstein. Einstein spent the to be unified are: Gravitation, , latter part of his life searching for such a unified Weak and . They are field theory, but was unsuccessful. described briefly as follows:

Physicists believe that laws of classical mechanics are 2.1 Gravitational Force a good approximation to the quantum mechanical laws Gravitational force is a purely attractive force which that govern the interaction of atoms, that the structure reaches through even the "empty" void of space to of atoms can be explained by the laws of interaction draw two masses toward each other. It keeps the of nuclei and , that the structure of nuclei can planets in orbit around the sun and the moon in orbit be explain by the theory of quarks and gluons, and around the Earth. finally that these are consequences of an even more comprehensive unified theory to be developed. Gravitation is described under the theory of , which defines it as the curvature of space Each stage in this development has required exploring time around an object of mass. This curvature, in natural phenomena at shorter and shorter distance, turn, creates a situation where the path of least explaining complex macroscopic constituents in energy is toward the other object of mass. This terms of simple microscopic constituents. Ordinary interaction acts on all particles. The postulated matter is made of atoms; atoms are made of nuclei, exchange particle has been named the graviton

87 Parashu Ram ... Unified ... 2.4 Strong Force or Interaction The strong interaction is responsible for holding quarks together to form and , and holding neutrons and protons together to form nuclei. In the helium atom, for example, it is strong enough to bind two protons together despite the that their positive electrical charges cause them to repulse each other. In essence, the strong interaction allows particles called gluons to bind quarks together to create the nucleons in the first place. Gluons can also interact with other gluons, which give the strong interaction a theoretically infinite distance; although it's major manifestations are all at the subatomic level. Fig 1: Illustration of the realm of four types of interaction. Modern unified field theory attempts to bring these four interactions together into a single framework 2.2 Electromagnetism as shown in figure. Electromagnetism is the interaction of particles with an electrical charge. Charged particles at rest interact through electrostatic forces, while in motion they interact through both electrical and magnetic forces. The is the exchange particle for this force. For a long time, the electric and magnetic forces were considered to be different forces, but they were finally unified by in 1864, under Maxwell's equations. In the 1940s, consolidated electromagnetism with quantum physics. Electromagnetism is perhaps the most obviously Fig 2: Unification of four forces/interactions prevalent force in our world, as it can affect things at a reasonable distance and with a fair amount of force. 3. HISTORICAL BACKGROUND AND IN UNIFIED FIELD THEORY 2.3 Weak Force or Interaction The first unifying scientific was the atomic The is a very powerful force hypothesis expressed by in 400 BC. that acts on the scale of the . This Sir 's theory of gravity was the first repulsive short-range interaction is responsible for grand success to unifying in a precise mathematical some forms of radioactivity, that acts on electrons, framework of the laws that govern the motion of , and quarks. It causes phenomena apples and planet. It incites the search for similar such as beta decay. It has been consolidated with unifying theories that would explain ordinary matter. electromagnetism as a single interaction called the "." The weak interaction is The next major step in the quest for unification mediated by the W boson (there are actually two of electricity and was developed types, the W+ and W- bosons) and also by the Z by Maxwell. In 1820 Hans Christian Oersted boson. discovered that electric currents exerted forces on , while in 1831, made 88 The Himalayan Physics, Vol.4, No.4, July 2013 the that time-varying magnetic fields attempt to explain in a classical could induce electric currents. Until then, electricity field theory was unsuccessful, many believe that the and magnetism had been thought of as unrelated goal of unification is achievable. phenomena. In 1864, Maxwell published his famous paper on a dynamical theory of the electromagnetic The development of quantum mechanics in the 1920s field. This was the first example of a theory that was and throughout the twentieth century enabled the able to encompass previous separate field theories completion of the atomic program, unifying chemistry (namely electricity and magnetism) to provide a and atomic physics. All the properties of ordinary unifying theory of electromagnetism. It explained matter, in all of its variety of forms, can be explained many electric and magnetic phenomena that had in terms of atoms and the electromagnetic forces been discovered over the years as manifestations of between them, realizing Democritus's vision. Quantum a single entity, the electromagnetic field. It also had mechanics also provides for a theory of the structure of many consequences. The most important of these was atoms in terms of the electromagnetic forces between the prediction of the existence of electro-magnetic the atomic nucleus and the electrons orbiting them. wave and demonstration that was such a wave. Thus optics was unified with electro-magnetism. In 1963 Sheldon Glashow proposed that the weak Hertz in 1888 presented the decisive experimental nuclear force and electricity and magnetism could confirmation for Maxwell theory. By 1900, the three arise from a partially unified electroweak theory. great branches of physics, electricity, magnetism In 1967, and and optics had merged into a single unified theory. independently revised Glashow's theory by having the masses for the W particle and Z particle arise in 1916 successfully formulated through spontaneous symmetry breaking with general theory of relativity which explained gravity the . This unified theory was as consequences of dynamic of the metric field of governed by the exchange of four particles: the space time and unifying structure of geometry of the photon for electromagnetic interactions, a neutral space time with gravitation, dreaming of a unified Z particle and two charged W particles for weak theory of all the forces of the nature and of all interaction. As a result of the spontaneous symmetry forms of matter. In the years following the creation breaking, the weak force becomes short range and of the general theory, a large number of physicists the Z and W bosons acquire masses of 80.4 and and mathematicians enthusiastically participated in 91.2 GeV/c2, respectively. Their theory was first the attempt to unify the then-known fundamental given experimental support by the discovery of interactions. In view of later developments in this weak neutral currents in 1973. In 1983, the Z and domain, of particular interest are the theories of W bosons were first produced at CERN by Carlo of 1919, who introduced the Rubbia's team. For their insights, Salam, Glashow of an (electromagnetic) gauge field in a classical and Weinberg were awarded the Nobel Prize in field theory and, two years later, that of Theodor Physics in 1979. and Simon van der Kaluza, who extended General Relativity to five Meer received the Prize in 1984. In 1974, Sheldon dimensions. Continuing in this latter direction, Glashow and proposed unifying the Oscar Klein proposed in 1926 that the fourth spatial strong and electroweak interactions into Georgi- dimension be curled up into a small, unobserved Glashow model, the first Grand Unified Theory, circle. In Kaluza-Klein theory, the gravitational which would have observable effects for curvature of the extra spatial direction behaves as an much above 100 GeV. additional force similar to electromagnetism. These and other models of electromagnetism and gravity In the latter half of the twentieth century, Physicists were pursued by Albert Einstein in his attempts at successfully unified the strong nuclear interaction a theory. Although it is now believed that Einstein’s and weak nuclear interaction with quantum 89 Parashu Ram ... Unified ... electrodynamics to form the of included in a . Although physics. This quantum theory of field identified the electromagnetism the strong and weak nuclear basic constituents of matter. They are the quarks forces have long been explained by a single theory that make up the nuclei at the centre of atoms known as the Standard Model; gravitation does not and the (such as the ) that revolve fit into the equation. Some theoretical physicists about the nuclei. The standard Model also explains currently believe that a quantum theory of general the forces that act on the elementary particles (the relativity may require frameworks other than electromagnetic, the weak, and the strong or nuclear field theory itself, such as or gravity. forces) as consequences of local gauge symmetries. Physicist are finding that certain depth and abstract mathmatical symmetries underling the world of Beyond the standard model, theories called ‘Grand subatomic particles and the force that act on them. Unified Theories’ have been proposed to unify the Experiences teaches that each stage of unification electroweak force with the strong force. The theory leaves many questions unanswered and reveals new of super symmetry requires a whole new set of mysteries that only find their at the particles beyond the standard model complements; next stage of unification a heavy partner of each , and gauge bosons of old set together all of them making up REFERENCES one great superfamily of particles. The three forces [1] Alan Isaacs, 1996, Dictionary of Physics,Oxford strong, electromagnetic and weak all have exactly University Press New York equal strength in this theory at a very high energy. [2] Arthur Beiser, 1999, Concept of Modern Meanwhile theoretical studies range far and wide Physics, Fifth Edition, Mc GRAW Hill New York in a search for the theory of everything (TOE). [3] The most familiar is string theory which pictures David J. Griffith, 1989, Introduction to particles as infinitesimal little vibrating loop of Electrody-namics, second Edition : Prentice strings in 10 dimensions. Further refinement lead Hall of India Private Limited, New Delhi to Membrane Theory, with the entire [4] Encyclopedia Britanica, 2010 regarded as existing on multidimensional sheets [5] John S. Rigden, 2000, Building Blocks of or membranes, with particles as loops anchored on matter, McGrow hill, Newyork. our sheet and graviton ranging into the continuum [6] Microsoft corporation, Encarta, 2009, Microsoft between sheets corporation [7] Nari Mistry, 2000, A brief introduction to 4. CONCLUSION particle physics, Cornell University,USA Unified field theory, an attempt to unify the [8] Niel Walet, 2003, Nuclear and Particle Physics, fundamental forces between the elementary UMIST, Manchester UK particles into a single theoretical framework, is [9] Poudel P., Gautam A., Adhikari B., Thapa M., highly theoretical, and to date there is no absolute Khatry M., 2010, of Physics for Class that it is possible to unify gravity with the XI and XII,Ayam Publication Kathmandu, Nepal other forces. has shown that other forces [10] Roger J Blin Stoyle, 1997, EUREKA ! Physics could be combined, and many physicists are willing to devote their lives, careers, and reputations to the of particles, matter and the universe:Institute of attempt to show that gravity, too, can be expressed physics publishing, Bristol Philadelphia, USA quantum mechanically. The consequences of such a [11] Wikipedia, the free encyclopedia, , en.wikipedia. discovery, of course, cannot be fully known until a org/wiki(obtained:2013.07) viable theory is proven by experimental evidence. [12] Young and Freedman, 2009, University The current quest for a unified field theory is largely Physics,12th Edition, Pearson , New focused on the theory which has to be successfully Delhi, India 90