Einstein Theory of Relativity

Einstein Theory of Relativity
In 1905 Einstein suggested that the new source of energy was none other than matter itself. The route by which he reached this conclusion deserves to be traced. Early in 1905 Einstein published his great paper “On the Electrodynamics of Moving Bodies’” which laid the a foundations of what came to be called the special theory of relativity.

The cardinal notion of the special theory is that light always travels at the same speed regardless of the speed of its source. If you toss a pebble forward from a moving automobile, then the speed or the pebble equals the speed of the automobile plus the speed with which the pebble was thrown. But with light situation is different. If you turn on the headlights of a speeding car, the velocity of the light from the headlights relative to the ground does not consist of the speed of the light plus the speed of the car. According to the special theory of relativity, the speed of the light from the moving headlight is exactly the same as it would have been if the car had not been moving at all. This simple idea that the speed of light is constant relative to very (un-accelerated) frame of reference changed physics and changed the world.

In late 1905 Einstein published three page meditation on the relationship between the mass of an object and energy contained in it. He reasoned that if the expenditure of energy needed to accelerate an object resulted in an increase in the mass of an object, then a decrease in velocity must produce a decrease in the mass of an object. The exact mathematical relationship between the mass of an object and the energy it contained flowed directly from the equations of the special theory, and was expressed in the famous formula:

E=mc2

that is, that the energy of a body is proportional to the mass of the body multiplied by the square of the speed of light. In 1908 physics and chemistry joined hands when Max Planck took note of Einstein’s equation and suggested that the phenomenon of radioactivity could be explained as the direct transformation of matter into energy.

In the years immediately following Einstein’s proposal, physicist and journalist amused themselves with calculations that a teaspoon of matter contained enough energy to power an ocean liner around the world. But even in the relatively pacific years before World War 1 the military implications of radioactivity and atomic energy did not go unnoticed.
Einstein Theory of Relativity

History of Quantum Mechanics

History of Quantum Mechanics
Quantum mechanics is the study of mechanical systems whose dimensions are close to the atomic scale, such as molecules, atoms, electrons, protons and other subatomic particles. Quantum mechanics is a most intriguing theory, the empirical success of which is as great as its departure from the basic intuitions of previous theories.

It is a fundamental branch of physics with wide applications. The foundations of quantum mechanics were established during the first half of the twentieth century by Werner Heisenberg, Max Planck, Louis de Broglie, Albert Einstein, Niels Bohr, Erwin Schrödinger, Max Born, John von Neumann, Paul Dirac, Wolfgang Pauli and others.

The history of quantum mechanics began essentially with the 1838 discovery of cathode rays by Michael Faraday, the 1859 statement of the black body radiation problem by Gustav Kirchhoff, the 1877 suggestion by Ludwig Boltzmann that the energy states of a physical system could be discrete, and the 1900 quantum hypothesis by Max Planck that any energy is radiated and absorbed in quantities.

According to the theorem proved by Gustav Kirchhoff in 1859 on the basis of the second principle of thermodynamics, the blackbody spectrum has a very remarkable property: It is a universal function of temperature only. In the 1877, Ludwig Boltzmann and Willy Wien restricted the form of this function by combining electromagnetism and thermodynamics. In the 1890s, spectroscopists working at Berlin measured it with the aim of determining an absolute standard for high temperature measurement. At the same time, the Berlin theorist Max Planck attempted a complete theoretical determination of the blackbody spectrum.

In 1905, Einstein computed the entropy of dilute thermal radiation from the high frequency limit of Planck’s law.

In 1913, Niels Bohr emphasized that mathematical symbols from classical mechanics permitted visualization of the atom as a minuscule Copernican system. Although suitably quantized laws of classical mechanics are used to calculate the electron’s allowed orbits, or stationary states, classical mechanics can neither depict nor describe the electron in transit.

In 1932 von Neumann put quantum theory on a firm theoretical basis. Some of the earlier work had lacked mathematical rigour, but von Neumann put the whole theory into the setting of operator algebra.

In 1933 Fermi develops a successful quantum field theory of beta decay. It describes how neutrons spontaneously change into protons and emit electrons and neutrinos.
History of Quantum Mechanics