Reference: Disturbance Theory
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The Fundamentals
In 1900 when Planck was trying to find a relationship between the intensity of the electromagnetic radiation emitted by a black body and the frequency of the radiation, he could not come up with a theory using the classical approach that explained the experimentally observed blackbody spectrum. In desperation he took a statistical approach, making an arbitrary postulate that energy of the emitted radiation is proportional to its frequency. This provided a curve that fitted the experimental data. [See Blackbody radiation (Notes)]. Since frequency has a discrete nature, it meant that energy was discontinuous for radiation. This went against the classical notion of Maxwell’s theory that electromagnetic energy is a continuous function in space. Planck looked at his proportionality postulate as a mathematical convenience. He did not believe in the quantum interpretation of his postulate.
About this time Einstein was investigating the factors underlying the atomic phenomena. He was impressed by the success of statistical mechanics in this area, especially with kinetic theory of gases. He decided to apply statistical approach to the atomic theory to derive other material properties. Einstein estimated the accuracy of his assumptions by using them to calculate the Avogadro’s number. He thus verified his theoretical approach to the determination of viscosity (molecular attraction) and distribution coefficient in liquids. This approach has since been found very useful by molecular physicists and chemists.
Einstein was thus testing his assumptions as they applied to the yet theoretical domain of atoms and molecules through the calculation of Avogadro’s number. He then analyzed the Brownian motion of microscopic particles suspended in liquid, which appeared to be “selfinduced”. He developed an original statistical approach to determine the relationship between the mean square fluctuation of suspended particles and the distribution coefficient of liquid. Once again, Einstein confirmed his assumptions by calculating the Avogadro’s number. This time his work was immediately verified experimentally. This helped establish the physical reality of atoms and molecules for scientists who were very skeptical before.
Simultaneously, Einstein looked into the distribution of energy density in the blackbody radiation. He analyzed the work of Planck and Wien and showed mathematically that the energy density of radiation, which appeared to be continuous at lower frequencies, became particlelike at higher frequencies. The postulate of Maxwell’s theory that the energy of radiation was a continuous function in space was valid at lower frequencies only. At higher frequencies the behavior of energy density of radiation could be compared to the results from kinetic theory of gases. Einstein thus verified Planck’s postulate that energy of radiation was proportional to its frequency. But Einstein then did something more. He proposed the idea of “light quanta” based on Planck’s postulate and used it to explain the photoelectric effect. He proposed an energy equation for the photoelectric effect that could determine the Planck’s constant experimentally. (See Einstein’s Conception of Light Quanta).
Robert A. Millikan, who vehemently disagreed with the idea of “light quanta”, spent some ten years testing Einstein equation and he did the most exacting experiments. He found that “Einstein’s photoelectric equation · · · appears in every case to predict exactly the observed results.” This turned Planck’s theoretical idea of “energy quanta” into the physical reality of “light quanta”, which came to be known later as “photon”. Einstein also established equivalence between energy and matter that later gave rise to the harvesting of nuclear energy.
In 1905 Einstein published these researches in four different papers. He basically established a relationship between energy and matter. It showed that energy of electromagnetic radiation coagulated with increasing frequency. Thus light became particlelike at higher frequencies, and at the upper reaches of frequency spectrum the limiting condition appeared to be matter. This conclusion supported the idea of particles, such as electrons, in the Gamma range of the electromagnetic spectrum. Thus electromagnetic field was a more fundamental substance than matter. Einstein thus established the fundamentals of the quantum theory.
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The Theory of Relativity
It was the increasing frequency that coagulated energy into matter. Therefore, Einstein’s fifth paper in 1905 investigated the fundamentals of motion. The obvious questions were, “Is there an absolute rest point? What happens to electromagnetic radiation as frequency reduces to zero? What is the limiting condition then?”
In Newtonian Mechanics the absolute rest point was assumed to be the stars fixed in the firmament. Maxwell’s theory also declared the velocity of light to be absolute, and this was confirmed by most exacting experimental evidence. Material velocities did not seem to add or subtract to the velocity of light. When the velocity of light was taken to be an absolute constant, the Lorentz transformations showed that the very characteristics of space and time were affected.
Einstein observed that the simultaneity of time could not be maintained when there were vast differences in the velocities, such as those between light and matter. In his view time could not be treated as absolute. He gave up on the idea of an absolute rest point and advance a theory of relativity based on the following postulates.

All physical laws have the same form in all inertial frames (i.e. frames of references which move rectilinearly with a constant velocity with respect to each other);

The velocity of light is same in all inertial frames.
With these postulates Einstein could derive the Lorentz transformations newly. He then showed that as the difference in velocities between two inertial frames increased, the characteristics of space and time changed in the form of “length contraction” and “time dilation”.
In other words, space and time become “diluted” with increase in relative velocity.
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The Glitch
Einstein’s theory of relativity was extremely successful in explaining previously unexplained phenomena in the cosmological realm where light interacted with matter. But, when it came to the quantum realm, where light interacted with atomic structure, Einstein could not apply his theory of relativity successfully in spite of a lifelong of efforts. Einstein was very troubled by this failure.
Thus, a new subject of Quantum Mechanics came about that lacked a theoretical basis of physical explanations, and which was based entirely on mathematical relationships.
Theoretical physics seems to be stuck at the postulates that Einstein made to derive his theory of relativity. These postulates must be examined closely.
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