• In 1900, Planck made the assumption that energy was made of individual units, or quanta.
• In 1905, Albert Einstein theorized that not just the energy, but the radiation itself was quantized in the same manner.
• In 1924, Louis de Broglie proposed that there is no fundamental difference in the makeup and behavior of energy and matter; on the atomic and subatomic level either may behave as if made of either particles or waves. This theory became known as the principle of wave-particle duality: elementary particles of both energy and matter behave, depending on the conditions, like either particles or waves.

In 1927, Werner Heisenberg proposed that precise, simultaneous measurement of two complementary values – such as the position and momentum of a subatomic particle – is impossible. Contrary to the principles of classical physics, their simultaneous measurement is inescapably flawed; the more precisely one value is measured, the more flawed will be the measurement of the other value. This theory became known as the uncertainty principle, which prompted Albert Einstein’s famous comment, “God does not play dice.”

In 1900, physicist Max Planck presented his quantum theory to the German Physical Society. Planck had sought to discover the reason that radiation from a glowing body changes in color from red, to orange, and, finally, to blue as its temperature rises. He found that by making the assumption that energy existed in individual units in the same way that matter does, rather than just as a constant electromagnetic wave – as had been formerly assumed – and was therefore quantifiable, he could find the answer to his question. The existence of these units became the first assumption of quantum theory.

Planck wrote a mathematical equation involving a figure to represent these individual units of energy, which he called quanta. The equation explained the phenomenon very well; Planck found that at certain discrete temperature levels (exact multiples of a basic minimum value), energy from a glowing body will occupy different areas of the color spectrum. Planck assumed there was a theory yet to emerge from the discovery of quanta, but, in fact, their very existence implied a completely new and fundamental understanding of the laws of nature. Planck won the Nobel Prize in Physics for his theory in 1918, but developments by various scientists over a thirty-year period all contributed to the modern understanding of quantum theory.

Reference: https://www.youtube.com/watch?v=CejaM4NeSLE

Evolution of Quantum Theory

Early Developments

While the theory of relativity was largely the work of one man, Albert Einstein , the quantum theory was developed principally over a period of thirty years through the efforts of many scientists. The first contribution was the explanation of blackbody radiation in 1900 by Max Planck , who proposed that the energies of any harmonic oscillator (see harmonic motion ), such as the atoms of a blackbody radiator, are restricted to certain values, each of which is an integral (whole number) multiple of a basic, minimum value. The energy E of this basic quantum is directly proportional to the frequency ν of the oscillator, or E = h ν, where h is a constant, now called Planck’s constant, having the value 6.62607×10 ⁻³⁴ joule-second. In 1905, Einstein proposed that the radiation itself is also quantized according to this same formula, and he used the new theory to explain the photoelectric effect . Following the discovery of the nuclear atom by Rutherford (1911), Bohr used the quantum theory in 1913 to explain both atomic structure and atomic spectra, showing the connection between the electrons’ energy levels and the frequencies of light given off and absorbed.

Quantum Mechanics and Later Developments

Quantum mechanics is the foundation of chemistry, because it deals with subatomic particles, as well as atoms, molecules, elements, compounds, and much larger systems. The quantum theory does much more than explaining the structure of the simplest atom, it rationalizes the existence of the chemical elements.

The quantum theory has many mathematical approaches, but the philosophy is essentially the same. Quantum mechanics is the foundation of chemistry, because it deals with subatomic particles, as well as atoms, molecules, elements, compounds, and much larger systems.

At the sub-atomic scale, there is no boundary between particles and waves. In fact, both particles and wave properties must be considered simultaneously for a system. The study of quantum mechanics lead us to understand the material and the universe beyond the general perception of matter by our ordinary senses of tasting, seeing, hearing, feeling, and sensing.

Furthermore, when coupled with the theory of relativity developed by Einstein, there is no boundary between material and energy. Energy and mass are equivalent, and they can convert into each other.

Reference: https://www.youtube.com/watch?v=e5_V78SWGF0

Quantum mechanics is an essential development of modern physics progress. The quantum mechanics started with different inventions and discoveries. Cathode rays were discovered by Michael Faraday.

Gustav Kirchhoff in about 1860 had development the concept of black – body radiation. About ten years later about 1877, Ludwig Boltzmann suggested that any physical system can be discrete. This had led to the development of the photoelectric effect by Heinrich Hertz in 1887. Later in 1900, Max Planck postulated a hypothesis that stated that the atomic system when radiating energy into a number of discrete energy elements ε (epsilon) which direct proportional to the frequency ν:

ε  = h ν ε = h ν

h is a numerical value called Planck’s constant.

P. Dirac in 1928 had combined both the relativity theory with the quantum mechanics. This approach had led to the prediction of the antiparticle’s existence. In 1927, Heisenberg used the quantum mechanics to discover the uncertainty principle which had put theoretical limitation of the accuracy of specific measurements. In the past, it was thought that the measurements have to yield absolute values and data.

Einstein and Bose had developed the Bose – Einstein Statistics which put the limitation on the absolute’s values of the measurements. This development had similar approach in the Fermi – Dirac – Statistics.

So What Is Quantum Mechanics?

Quantum Mechanics is one of the branches of physics dealing small scale of the atoms and electrons. The classical mechanics deals with the matter and its studies at specific time and place.

Classical mechanics deals also with everyday size and not small subatomic sizes.

Three revolutionary principles

1. Quantized properties:

A quantized property: is definite size and the property which may be found in a multiple of that definite size.

• Particles of light: It was demonstrated experimentally that the light has a dual character: wave and particle.

• Waves of matter: Electron was also demonstrated experimentally that the light has a dual character.

Quantized properties?

Specific physical properties, such as position, speed and color, can sometimes only occur in specific, set of similar amounts.

Particles of light?

Light particles are called photons by Einstein which means that the light is made of flow of photons. Energy of these photons has specific oscillation frequency. The intensity of the light is the quantity of its photons

Waves of matter?

Matter waves are essential section of the quantum mechanics theory. All matter show wave – particle duality behavior. The dual character of the matter is referred to as the de Broglie hypothesis. Matter waves are known as de Broglie waves.

The uncertainty principle

The uncertainty principle is known as Heisenberg’s uncertainty principle which states that there fundamental limitations occur for the accuracy values of physical quantities of particles such as momentum and position. The position and the momentum are known complementary variables The uncertainty principles will limit to what extent other properties will main their relative and approximate values.

In 1927, Werner Heisenberg proposed that certain pairs of properties of a particle cannot simultaneously have exact values. In particular, the position and the momentum of a particle have associated with them uncertainties 

As with the de Broglie particle wavelength, this has practical consequences only for electrons and other particles of very small mass. It is very important to understand that these “uncertainties” are not merely limitations related to experimental error or observational technique, but instead they express an underlying fact that Nature does not allow a particle to possess definite values of position and momentum at the same time. This principle (which would be better described by the term “indeterminacy” than “uncertainty”) has been thoroughly verified and has far-reaching practical consequences which extend to chemical bonding and molecular structure.