Quantum Theory a brief overview
The various phenomena viz., Spectroscopy and heat capacities, black body radiation and the photoelectric effect, which were discoverd cannot be explained in terms of Classical Mechanics. This shook the basic theories which were in existance and shook the basic understanding of nature. A drastic turn happend to the modern view of physics, when Max Plank boldly introduced the quantum nature of light and Einstein's equally impressive explanation of the photoelectric effect in quantum terms. Neils Bhor who was working with Ernest Rutherford on the Nuclear Scattering experiments, took another step and developed a mathematical framework to explain the spectroscopy of Hydrogen atom. He introduced the idea of standing waves to justify the Quantal stability of certain levels in the atom. This provided proper explanation with good results. This theory is known by the name Old Quantum Theory. It was Prince Louis De Broglie who challenged the scientific world with his Phd Thesis that it the if light can behave as both particles and waves, matter too can. Every body among scientific community was shocked with the new developments. Many tried to prove that it is wrong. Same was the case with Erwin shrodinger. Ultimately he recognised this remarkable new idea and proposed the wave equation of matter. Werner Heisenberg also did calculate but with a different approach following matrix mechanics methods. The new Theory of Quantum Mechanics took final shape when Dirac wrote the relativistic wave equation. This alltogether became the great Quantum Theory. Check out the chart on the Quantum Theory Time line to know how science developed in the last 5 decades of the century. De Broglie equation contd... Quantum Theory Contd....
Special and General Theory of Relativity A revolutionary thought from a Great Mind..
The Greatness of this theory, The Special Theory Of Relativity, lies in the way it is presented to the world. It is a deviation from the classical mechanics which Newton introduced in 1700's. This theory when introduced in 1905 created ripples among the scientific community. Most intellectuals present on scene took the theory as just rubbish. In the coming years people were mostly involved in proving the theory worng. But as people started to prove the theory wrong, it began to show the worthness of the proposal. After more than 10 years he put forward the second theory of relativity which gave account for the universe as a whole.      The Special Theory of Relativity when first published, the article didn't include the now-famous equation E=mc2, but later in 1905, he added it to another publication. The theory stated that the speed of light is constant and absolute -- it always goes the same speed, and nothing can go faster than that. In fact, as things travel at speeds approaching the speed of light, strange things happen to them. They get shorter in the direction of travel, their mass increases, and time passes more slowly for them.     The implications of Einstein's theory were strange, but proved true mathematically and in the real world. Experimenters have carried extremely accurate atomic clocks on high-speed jets on around-the-world journeys. And when they compared these clocks to the extremely accurate clocks they left at home, the traveling clock had indeed gone slower and lost time. But by very little. Researchers calculated that going about a quarter of the speed of light would only change mass, length, and time measurements by 1 percent. That means that Newton's ideas and "laws" still work well for local measurements at ordinary speeds.This changes drastically the closer one goes to the speed of light: For an object moving at 6/7 the speed of light, its mass would be doubled. Thus giving credible information.      In Classical physics we have three system coordinates called the cartesian coordinates.or X, Y, Z coordinate system. Time is not considered at all. But Special theory took time also as a coordinate and made a revolutionary approach. The mathematical proof of time as a coordinate was given by Minkowski.. one of great intellectual brains. But he couldnt live long to see the greatness of the theory revealed. In his death bed he had only one sorrow that he couldnt live long to see the theory getting revealed. His work only saved Einstein from the burden to prove that the time as a coordinate.     The theory of relativity says that, any body at any instant of time can be depicted on a four dimensional space with coordinates X, Y, Z and T(time) as axis, and no body will take no two same point at an instant of time. To understand this more clearly lets take an example of a fly flying in a corner of a room. Now we all know that a room corner as a place where three lines or say three walls intersect. So it can be considered as the three of the four dimensions involved and we say it as X, Y and Z. Now say the fly started flying from rest. So if we draw a path in which the fly flies, we can see that the fly will never take two points at an instant of time. This is show in the Figure. This is the basic thought of the Special theory of relativity with respect to time. . For more information on Special and General Theory please click here. This site give you ample details on the subject.     In the General Theory of Relativity which Einstein proposed in 1915 considered gravity as not a force as Newton considered but as due to curvature of space time continuum. He used a thought experiment to compare the force felt from gravity with acceleration. Imagine you are in an elevator and feel what you believe is the force of gravity, holding you to the floor. According to Einstein, since you cannot see outside the elevator, you cannot tell if you are feeling the force of gravity or if the elevator is being pushed toward your feet. Einstein stated that the two forces are actually identical. Furthermore, if you were in the elevator accelerating upward and a beam of light entered the elevator parallel to the floor, the light beam would appear to bend downward. This meant that light, which ordinarily traveled in straight lines, could curve if it traveled across a gravitational field. This curving path of light meant that that "field" was really a curving of space, which Einstein found was inseparable from time. The curvature would be caused by bodies with great mass.     A weak gravitational field indicates nearly flat space-time, and there Newton's theories seem to apply. But a strong gravitational field throws classical predictions off. Einstein postulated three ways this theory could be proved. One was by observing the stars during a total solar eclipse. The sun is our closest strong gravitational field. Light traveling from a star through space and passing the sun's field would be bent, if Einstein's theory were true. If you could see the star during the day, he predicted, it would be in a different place than at night. The only chance to see it during the day would be during an eclipse.     On March 29, 1919, that opportunity came. British Astronomer Sir Arthur Eddington traveled to Pr�ncipe Island off the western coast of Africa. His team photographed starfields during the eclipse and compared the photos with those of the same starfield taken when the sun was not present. Eddington found the apparent location of the stars had shifted, just as Einstein predicted. General Theory deals mostly with all the macro items that we see in universe. During the development of this theory Einstein was stuck up with mathematical proof which was later taken from reinman's theorems, which he invented about a century earlier led to the completion of the project. It surmises about the existence of black holes and other phenomenon which scientific community was unaware at that time. Later after the advancements in the field of astronomy, the existence of black holes were discovered which led to further strengthening of the theory.     The most interesting part of the theory is the deduction of the famous E=mc2 equation. This famous equation is an outcome of the special theory of relativity. Einstein put the three spatial and time dimensions together in one four-dimensional system where space and time cannot be separated or viewed independently. In that system, energy and mass are really the same. And that is the fundamental point of E=mc2: Energy equals matter times the speed of light squared. You only need a minute amount of matter, say, an atom, to create a tremendous amount of energy. This led to the development and deployment of nuclear weapons. The massive destruction of the Japanese cities Hiroshima and Nagasaki by atomic weapons, made Einstein one of the major opponent of Nuclear Weapons. Personally i have some apprehentions on this theory espicially the axiom that nothing can travel beyond the speed of light. But it was inevitable. If this axiom is not presented the theory lacks the strength to prove the phenomenas which we see in nature.

KK Theory (Klauza-Klein Theory): The First Step in to a theory with extra dimensions
A new theory was introduced by Theodor Klauza in 1919. This was further enhanced by Oscar Klien in 1926. This theory makes use of the thought that the universe can contain more than three spatial dimensions. The basic premise is that the dimensions can be directly observable as our three dimensional world, or will be curled up in space and will be very minute and invisible. An analogy can be made with a garden hose. Say consider a garden hose and you are viewing it from a distance. It looks like a long one dimensional object lying on the ground. Now if you come closer, the circular dimension winding will become visible. Now depending on the scale of sensitivity of the observer the hose will either appear as one or two dimensional. The same is implied in the K-K theory. There were lots of experiments being conducted in particle physics. No experiments conducted have ruled out the possibility of additional spatial dimensions curled up on scales smaller than 10e-16 cm ( 10e-17 inches), the limit which our experiments can prove. This theory was originally introduced for point particles and later extended for strings. For K-K theory to be mathematically feasible the number of dimensions to be added was more than 10 spatial dimensions and the theory becomes absolute when the added dimensions approaches 26. This theory got forgotten in time, until it was reborn as the exciting String Theory.

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Super String Theory: In search for unification of theories. A bold move
Introduction     Through out the 20th century there were two theories, the Quantum Thoery and the Theory of Relativity, to explain the forces of nature. Quantum theory explained the macro force gravity in a simple way, where as Quantum Theory explained the other three forces of nature viz., weak forces, strong forces and the electromagnetic forces which we encounter in this universe. These two theories disagree each other when they try for a unification. Quantum mechanics is a part which describes the forces that act on microscopic particles. These microscopic forces are very different from what we see in nature. Even there is a notion that gravity when comes to microscopic level it becomes repulsive. Where as General Relativity, as i explained earlier, explains gravity as due to the curvature in spacetime.     Super String Theory or the String Theory as it is often called is not a predetermined creation. It was an accidental outcome from Abdus Salam and Steven Weinberg in the 1980's. String theory is an attempt by physicists to explain the mathematical incompatibility of Quantum theory and the Theory of relativity to a single theory. This theory modifies our understanding of the space time and the force of gravity. One recently discovered consequence is that the space time can undergo remarkable arrangements of its basic structure requiring the fabric of space time to tear apart and subsequently reconnect. String theory modifies the thought of particles as two or three dimensional with strings which are one dimensional with connects and interconnects which vibrates giving the charecteristics of the particle, like the charge, mass, spin etc. The vibrations are of the same type as acoustic vibrations.     As per the string theory the force of gravity itself is due to the vibration of strings of space. The beauty of this theory lies in the thought that every thing emnates from vibrations of the string and all the particles are made up of the same material.     The mathematics of the strings are very complex. For the theory to be correct the strings should vibrate in ten dimensions, which cannot be visulaized by thought. ( Since our brain cannot visualize more than 3 dimensional space, say 4 dimensional not more through thought (our brains fault)). The world we live in is a four dimensional world (special Theory of Relativity), then where the other 6 dimensions went. As per String Theorists the 6 dimensional space can be curled up and it may be so minute of the order of plank length, ie., 10e-33 cm. which cannot be visualized at all. Theorists believe that when the big bang occured,at that instant, our universe was broken in to two universes one with 4 dimensions and the other with 6 dimensions. The four dimensional space expanded while the 6 dimensional space contracted way beyond recognition. This theory gets thrust since more than 90% of the mass of the universe is seemed to be hidden some where. (may be black holes or new dimensions with in our universe itself).     It is assumed that every point in one-dimensional space would be connected to a tiny circle of the second dimension.ie., Every point in 4 dimensional space is imagined to connect to a very tiny ten-dimensional space, known as Calabi-Yau space. These forms have a ten dimensional surfaces. As a sphere has a two dimensional surface even though its three dimensional. It is the shape of this Clalab-Yau space that determines what vibrations the strings can express. If this theory is successful in its attempt no one knows what we can do with the nature. Click here for more. In this site i have tried to simplify information so that general public, espicially children, can understand the greatness of these theories. Please provide valuable suggestions so that i can improve the worthiness. !! Thank you !!