Theoretical physicist Michio Kaku explains the basics of String Theory in this clip from his Floating University lecture. (Video Below)
The article below is a basic overview of String Theory contributed by Dr B.Sathyanarayanan
Basically, Superstring theory is a unified theory of fundamental interactions. It involves super symmetry, in which the basic objects are one dimensional and are known as Super strings. Since the distances between them are very small the energy associated with them is very high. Features of super strings are compatible with the experimental facts of elementary particles. Hence, study of Super strings essentially involves study of four fundamental interactions, forces associated with them and elementary particles which we shall see in this article in a simple manner.
2. The Four Fundamental Interactions:
-1. The Gravitational Interaction.
-2. The Weak Interaction.
-3. The Electromagnetic Interaction
-4. The Strong Interaction.
-1. Gravitational Interaction.
This is the weakest of all the four, which is 10power 40times weaker than electromagnetic interaction. We all know that it is an attractive force between bodies which have mass. This interaction can be visualised as a field of attraction which is proportional to the product of the masses of the interacting bodies but reduces as per square of the distance between them. In other words, Newton's Law of Gravitation states that any two objects in this Universe having masses of m1 and m2, separated by a distance of d are attracted with a force equal to G m1.m2/d2 where G is the Universal Gravitational constant. In Microcosm (atomic scale), the force is negligible giving prominence to other forces whereas in Macrocosm (Cosmological scale), the masses are enormous and the gravitational force is very important and holds the components of the Universe together.
General theory of relativity gives a consistent theory of gravitation, defining the four dimensions of space and time as 'curved' (Please refer to the article on General Theory of Relativity). But as such, Superstring theory will be able to give a consistent quantum theory of Gravitation as well, connecting it with other three fundamental forces. For this, a hypothetical concept of 'Graviton', the Gravitation particle is useful in some contexts.
Graviton: Gravitons are hypothetical particles for exchange of gravitational energies, postulated to make gravitational forces consistent with electromagnetic forces. (Inasmuch Photon is the particle carrying energy in Electromagnetic Energy; Graviton is the particle carrying energy in Gravitational force.) It is expected to have zero mass and travel with speed of light like photons and have a spin of 2. The graviton is the mediator in gravitational interactions functioning like exchange particle.
-2: The Weak Interaction:
The weak interaction occurs between leptons and in the decay of Hadrons. Leptons are elementary particles of very small mass (compared to nucleons) like electrons, muons, tau particles, and neutrinos. (Readers are recommended to go through any simple book on Elementary particles). For any lepton there is an equivalent anti particle. Anti leptons have equivalent anti charges whereas neutrinos do not possess any charge. These three particles differ only in masses Keeping the electron mass as the standard, muon is 200 times massive than electron and tau particle is 3500 times more massive than electron, yet much lighter than the nucleons (Protons and neutron).
Leptons interact with weak interaction and electromagnetic interaction thus making their unification possible.
-3 The electromagnetic interaction:
If a question is put to determine two important discoveries in Physics which have changed Science History, the answer can be easily said as discovery of Gravitation and Electromagnetic spectrum. As pointed out in this article elsewhere, Gravitation deals mainly with bodies in macrocosm whereas electromagnetic spectrum deals with particles in macrocosm. Electromagnetic interaction is responsible for the forces that control atomic structure, chemical reactions and all electromagnetic phenomena. It accounts for the forces between charged particles, but unlike gravitational interaction this force is either attractive or repulsive. It is also true that some neutral particles decay by electromagnetic interaction.
There are two viewpoints in visualizing this interaction.
The first viewpoint is visualizing this as a classical field of force which is characterised by coulomb's law. Coulomb's states that the force between two charged particles with charges q1 and q2 separated by a distance d is q1q2/4pi e d2 where e is the absolute permittivity of the intervening medium.
The second viewpoint is considering this force as virtual exchange of photons carrying an energy E= hf where f is the frequency of oscillation and h is Plank's constant.
They are long ranged interactions and are well defined by Maxwell's equations. The quantum theory of electromagnetic interactions is described by quantum thermodynamics which is a simple form of gauge theory. Photon is the mediator functioning as the energy carrier in this type of interactions.
What is a photon?
Photon is a particle with zero rest mass consisting of a quantum of energy hf. Photons travel with speed of light. It defines light and other electromagnetic radiations as particles.
Radio frequencies with less frequency and long wavelengths, Infrared radiation ( a form of heat radiation), Visible light, Ultra violet radiations, X-rays and Gamma rays with the highest frequency constitute the energy spectrum of Electromagnetic radiation.
-4: Strong Interactions:
Strong interaction is 100 times stronger than electromagnetic radiation and functions between Hadrons, and is responsible for the nuclear stability. Hadrons include protons, neutrons and pions. They are considered to have internal structure known as quarks.
Strong interactions are close ranged reactions since they take place inside the nucleus. Strong interactions are defined by quantum chromo dynamics. Here, the mediators are Gluons which act as the energy carriers.
4. The Super String Theory as the Connecting Link between the Four Fundamental Forces:
The super symmetry among the four fundamental interactions is visualised as a super string or as a one dimensional object. Super strings are supposed to have a length scale of 10 power -35 meter and energy scales about 10 power 19 GeV. Strings associated with Bosons particles which follow Bose-Einstein statistics having integral spin) are consistent in 26 dimensional space-time and with fermions (particles which follow Fermi-Dirac statistics, having half-spin) are consistent in 10 dimensional space -time. Kaluza-Klein theory is the one which unifies gravitation with other four interactions. The higher dimensions are rolled up to become microscopically small through a process called Spontaneous Compactification, finally ending in four macroscopic dimensions which we observe in General Theory of Relativity.
There is no direct evidence for super strings. But some features of super strings are compatible with the experimental facts of elementary particles which do not obey Parity.
5: Thought Force:
Science does not recognise thought force as the fifth force. But as per Holistic Philosophy Thought force is the mightiest of all which governs the entire Universe.
Readers are referred to earlier articles by the author on the topics 'What is life?' and 'What is Intelligence?' They will give an idea about the role Gravitation plays in forming life. In Macroscopic level, Physical life is formed using Gravitational force and the same life is sustained by opposing Gravitation, using other three fundamental forces in microscopic level. The concept of Negative entropy was introduced to highlight the truth behind sustenance of life.
Thought is Intelligence converted to material level and it uses all the forces to its benefit. Thus, study of thought force will help furtherance of fundamental forces.
In this article, a brief account of four fundamental forces is given. Finally, a brief account of Super string theory as the unified theory of all the four forces is given. A philosophical approach using thought force is also given.
The purpose of this article is to highlight the entire realm of Physics. If one has a good knowledge of all the known fundamental forces, he/she is construed to have an idea of entire physics because, Gravitation covers all the objects at Macro level and the weak, strong and the electromagnetic forces cover the entire microscopic and energy fields. Of course, readers are advised to consult prescribed text books and have update knowledge of fundamental forces and the Super string theory. However a reference can be made to this article which will give elementary clarification on any topic or title related to super string theory. The purpose of this article is to create that awareness.
The author wishes the readers all the best.
Dr B.Sathyanarayanan (65) is an experienced administrator, teacher and writer. He is M.Sc(Physics) from Annamalai University. He studied Psychology and Philosophy as two additional subjects for graduation. He worked as a PHYSICS LECTURER for 2 years (1969-1971). Later, he had to take up a bank job and continued Physics and Philosophy research privately. At the age of 50, he got voluntary retirement from banking service to devote more time for social,educational and research activities. In 2005, he took up Physics teaching once again and is continuously teaching for the past 8 years as a regular professor of Physics.
He continued his interest in Psychology and got his PhD in Psychological counselling in 2000 and is counselling on HIV/AIDS matters. He conducted several intervention programmes. He is a well known writer in English in fiction and article writing. His writing is recognised internationally by listing in the directory of World Philosophers, Bowling Green State University, U.S.A.
All along his life so far, he remained a scientific philosopher in thought and deeds. He considers Albert Einstein as his role model in Science and J.Krishnamurti, in Philosophy. His first book 'The Simple Truth", a comparative study of Religion and Science, was published in 1987. He is publishing the annual magazine 'Philosophy of Science' (since re-started). He founded Holistic Philosophy Society for the study of Physics and Philosophy. His latest book 'Glimpses of Holistic Philosophy' has been widely acclaimed. He conducts regular meetings on various topics on Physics and Philosophy in Chennai. He recently conducted a "Two days seminar on Religion, Science and Social Services" in Chennai, India which was attended by senior Professors of Physics and Philosophy. As an experienced author, he is glad to present the above article for the kind attention of readers.
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