The History of Quantum Mechanics J P SINGH ASSOCIATE PROFESSOR PHYSICS PGGC-11

1940: Pauli proves Spin-Statistic Theorem 1905: This Timeline has much Entropy. 1925: Heisenberg developed the Heisenberg Uncertainty principle Wolfgang Pauli developed the fourth quantum number- the spin number 1922: Neils Bohr won Nobel Prize in physics Stern-Gerlach Experiment (Verified the space quantization theory) 1940: Pauli proves Spin-Statistic Theorem 1905: Albert Einstein wrote the paper, "On a Heuristic Viewpoint Concerning the Production and Transformation of Light“; proposed the idea of energy quanta dealing with the photoelectric effect. 1936: Publishes paper on Wave Mechanics and Schrödinger's Equation 1932: Werner Heisenberg won Nobel Prize in physics 1944: Wolfgang Pauli won Nobel Prize in physics 1918: Max Planck won Nobel prize in physics 1924: Louis De Broglie published his doctoral thesis, “Recherches sur la théorie des quanta”, which introduced his theory of electron waves. 1929: Louis De Broglie won the Nobel Prize in Physics for hypothesis. 1933: Otto Stern measures the magnetic moment of the proton Schrodinger wins Nobel prize for his Schrodinger Equation 1943: Otto Stern receives Nobel prize in Physics 1921: Won the Nobel Prize in Physics for his discovery and explanation of the law of the photoelectric effect. 1900: Max Planck proposed theory about black-body radiation 1913: Neils Bohr proposed atomic structure theory

Erwin Schrödinger In 1926, at the University of Zurich, published a series of 4 papers Wave Mechanics & Schrodinger’s Equation Solved Quantum Harmonic Oscillation, the Rigid rotor, diatomic molecules and rederived his equation Compared his approaches to Heisenerg Showed how to work with time

Schrödinger’s Equation While this appears to be a rather complicated equation, it is. means at time t i is the square root of –1 Planck’s constant divided by 2π Derivative with respect to time ψ(t) = Wave Function H(t) = Quantum Hamiltonian

Erwin Schrödinger First paper has been universally celebrated as one of the most important achievements of the twentieth century, and created a revolution in quantum mechanics, and indeed of all physics and chemistry Nobel Prize 1933 Schrödinger’s Cat Thought Experiment - 1935

Schrödinger’s Cat Decay of gas kills cat 50% chance of decay 50% dead cat?

Otto Stern & Walter Gerlach Otto Stern and Walter Gerlach are famous for their Stern-Gerlach experiment, in which they shot a beam of silver atoms through a non-uniform magnetic field, showing that the atoms split up into only 2 bands This verified the space quantization theory, and tested whether particles had intrinsic angular momentum

Stern-Gerlach Experiment

More on Otto Stern Developed Molecular Ray Method Demonstrated the wave nature of atoms and molecules Measured atomic magnetic moments Corrected the proton’s magnetic moment Nobel Prize in Physics in 1943

Werner Heisenberg Won Nobel Prize in 1932 in Physics "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen". Heisenberg pointed out that it is impossible to know both the exact position and the exact momentum of an object at the same time.  Applying this concept to the electron we realize that in order to get a fix on an electron's position at any time, we would alter its momentum.  Any attempt to study the velocity of an electron will alter its position.  This concept, called the Heisenberg Uncertainty principle, effectively destroys the idea of electrons traveling around in neat orbits.  Any electron that is subjected to photons will have its momentum and position affected.

More on Heisenberg Invented Matrix Mechanics Formulated the Copenhagen Interpretation of Quantum Mechanics with Bohr Proposed Proton-Neutron model of atomic nucleus

Heisenberg's Experiment

Wolfgang Ernst Pauli Nobel Prize in Physics in 1945 The exclusion principle (No two electrons may exist in the same quantum state) provided the reason for electrons in atoms being arranged in shells with the maximum number of electrons being 2, 8, 18, 32… etc, from the first to the nth shell. This principle is significant for the fact that it explains why matter occupies space exclusively for itself and does not allow other material objects to pass through it, at the same time allowing lights and radiations to pass. It states that no two identical fermions may occupy the same quantum state simultaneously. A more rigorous statement of this principle is that for two identical fermions, the total wave function is anti-symmetric

More on Pauli Derived observed spectrum of H2, supporting Heisenberg Proved Spin-Statistics Theorem First named Neutrinos

Max Planck and Black Body Radiation Emission of light from hot objects (objects appear black before heating) How does the intensity of the electromagnetic radiation emitted by a black body depend on the frequency of the radiation and the temperature of the body? Interpolated between the laws of Wien and Rayleigh-Jeans Assumed that energy exists in individual units (discrete bundles) First proposed in a meeting on October 19, 1900

Planck’s Contributions Formula predicts the spectral intensity of electromagnetic radiation at all wavelengths from a black body at temperature T h is Planck’s constant which is measured in J.s 6.63x 10-34 Energy is always emitted or absorbed as a whole number multiple of h (2hv, 3hv…)

Planck Walk the Later simplified this to E=hv in which E is energy, h is Planck’s constant, and v is frequency

More stuff on Planck Basically states that energy is always emitted or absorbed in discrete units, called quanta (quantized) Gave the name “quantum”, which means “fixed amount,” to the smallest quantity of energy that can be emitted/absorbed as electromagnetic radiation Awarded Nobel Prize in Physics in 1918 for this *No major flaws or errors This is regarded as the start of quantum physics

Neils Bohr Introduced his concepts by borrowing ideas from quantum physics (Max Planck) in 1913 Presented a model of atomic structure that still stands true today Started by assuming that electrons move in circular orbits around the nucleus Determined that chemical properties of an element are determined by the number of electrons in its outer shell

More Bohring Information Idea that an electron can drop from a higher-energy level to a lower one, emitting a photon Also determined that: Electron exists a certain distance from the nucleus Electrons have circular orbits No energy is given off if an electron stays in one location Received Nobel prize in 1922 for physics

Flaws His assumptions about the energy given off when an electron drops to a lower-energy level only stands true for hydrogen (other elements are too large) Problem with describing an electron merely as a small particle circling the nucleus

Prince Louis-Victor de Broglie Won the Nobel Prize in Physics in 1929 Professor at the Faculty of Sciences at Paris University Elected a member of the Academy of Sciences of the French Institute in 1933 Broglie stated that all matter has a wave-like nature States that any moving particle or object had an associated wave Created a new field in physics, called wave mechanics, uniting the physics of light and matter

Broglie’s Equation λ= the particle's wavelength h= Planck's constant p= the particle's momentum m= the particle's rest mass v= the particle's velocity c= the speed of light in a vacuum

More on de Broglie Equation used to describe the wave properties of matter, specifically, the wave nature of the electron The de Broglie relation shows that the wavelength is inversely proportional to the momentum of a particle and that the frequency is directly proportional to the kinetic energy of the particle

Albert Einstein Won the Nobel Prize in Physics in 1921 for his discovery and explanation of the law of the photoelectric effect Widely regarded as one of the greatest physicists of all time Formulated the theory of relativity and made significant contributions to quantum mechanics and statistical mechanics Also famous for formulating E = mc2

The Photoelectric Effect The photoelectric effect is the emission of electrons from matter upon the absorption of electromagnetic radiation, such as ultraviolet radiation or x-rays

The Photoelectric Effect When light shines on a metal surface, the surface emits electrons A polished, negatively charged piece of metal such as zinc will lose its charge if it is exposed to ultraviolet light. This phenomenon is called the photoelectric effect

The Photoelectric Effect The photoelectric effect can be modeled by the equation: Ekin = h f – W Ekin = maximal kinetic energy of an emitted electron h = Planck constant (6.626 x 10-34 Js) f = frequency W = work function (the energy required to free an electron from the material)

The Photoelectric Effect In 1905, Einstein's work predicted that the energy of the ejected electrons would increase linearly with the frequency of the light At this time his idea could not be proven but, in 1915, it was found to be accurate when Robert Andrews Millikan experimentally determined the relationship to be linear

Summary All of these men are interrelated in their discoveries; some proved the discoveries of others, others borrowed ideas and concepts