Thread by @PhysInHistory

The Pioneers of Quantum Physics: A Brief History of one of the most successful theories in Modern Physics ✍️

Quantum physics is the branch of physics that deals with the behavior and properties of matter and energy at the smallest scales, where the classical laws of physics break down and new phenomena emerge.

In 1900, Max Planck proposed that the energy of electromagnetic radiation, such as light, is not continuous but discrete, meaning that it comes in packets or quanta. He derived a formula, known as Planck’s law, that describes the spectrum of blackbody radiation, which is the radiation emitted by a perfect absorber of heat. Planck’s law was the first quantum theory in physics, and Planck won the Nobel Prize in 1918 “in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta”.

In 1905, Albert Einstein used Planck’s hypothesis to explain the photoelectric effect, which is the emission of electrons from a metal surface when light shines on it. He showed that light behaves as a stream of particles, called photons, whose energy depends on their frequency. Einstein also proposed the special theory of relativity, which relates space and time in a new way and shows that mass and energy are equivalent. Einstein won the Nobel Prize in 1921 “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect”.

In 1913, Niels Bohr introduced a quantum model of the atom, in which electrons orbit around a nucleus only at certain distances and can jump between them by absorbing or emitting photons. Bohr also proposed the correspondence principle, which states that quantum phenomena must agree with classical physics in the limit of large numbers. Bohr won the Nobel Prize in 1922 “for his services in the investigation of the structure of atoms and of the radiation emanating from them”.

In 1923, Louis de Broglie suggested that matter, like light, has both particle and wave properties, and that the wavelength of a particle is inversely proportional to its momentum. This idea was confirmed by experiments that showed the diffraction and interference patterns of electrons and other particles.

In 1925, Werner Heisenberg formulated the matrix mechanics, which is a mathematical framework for quantum physics that uses matrices to represent physical quantities and operators. Heisenberg also discovered the uncertainty principle, which states that there is a fundamental limit to how precisely one can measure certain pairs of physical quantities, such as position and momentum. Heisenberg won the Nobel Prize in 1932 “for the creation of quantum mechanics”.

In 1926, Erwin Schrödinger developed the wave mechanics, which is another mathematical framework for quantum physics that uses differential equations to describe the evolution of wave functions. Schrödinger also introduced the concept of superposition, which means that a quantum system can exist in a combination of two or more states until an observation collapses it into one definite state. Schrödinger won the Nobel Prize in 1933 “for the discovery of new productive forms of atomic theory”.

In 1927, Paul Dirac unified quantum mechanics and special relativity in a single equation, known as the Dirac equation, which describes the behavior of electrons and other spin -1/2 particles. Dirac also predicted the existence of antimatter, which are particles with opposite charge and spin to their normal counterparts. Dirac won the Nobel Prize in 1933 “for the discovery of new productive forms of atomic theory”.

In 1928, Wolfgang Pauli proposed the exclusion principle, which states that no two identical fermions (such as electrons) can occupy the same quantum state in an atom or a molecule. Pauli also introduced the concept of spin, which is a quantum property that gives particles a magnetic moment. Pauli won the Nobel Prize in 1945 “for the discovery of the Exclusion Principle”.

In 1935, Albert Einstein, Boris Podolsky, and Nathan Rosen published a paper that challenged the completeness and consistency of quantum mechanics. They proposed a thought experiment, known as the EPR paradox, that involved two entangled particles that share a quantum state and can affect each other instantaneously over any distance. They argued that this implied either hidden variables or spooky action at a distance, both of which contradicted classical physics.

In 1948, Richard Feynman developed a graphical method for calculating quantum effects using diagrams that represent interactions between particles and fields. These diagrams are called Feynman diagrams and are widely used in quantum field theory and particle physics. Feynman also contributed to the development of quantum electrodynamics (QED), which is a quantum theory of electromagnetism that explains phenomena such as light scattering and electron-positron annihilation. Feynman won the Nobel Prize in 1965 “for their fundamental work in quantum electrodynamics”.

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"Atoms, Stars, and Everything in Between", 30 Collected Essays Illuminating The World Of Physics and Beyond 👇

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