” The Heisenberg-Bohr concepts leave us all breathless, and have made a deep impression on all theoretically oriented people.”           -Albert Einstein, 1926

The period 1905 to 1925 was a great time for the world’s leading physicists in the race to understand the quantum nature of matter. To explain so many curious and undigestible phenomena about radiation, atoms, molecules and solid materials, some groups worked together and sometimes compete with another. The climax happened around 1925 when the structure of quantum mechanics was finally laid down.

Louis de Broglie

This started with Louis de Broglie’s conjecture in 1924 that particle-like objects such as electrons should display wave properties. Indeed if light which is initially thought to be a wave can behave as a particle or quantum, why not those objects which we normally conceive of as particles display wave-like properties? Why not indeed?

Erwin Schrodinger

Shortly after de Broglie introduced his concept of matter waves, Erwin Schrodinger proposed an answer to the question of what happens to the matter waves when a force acts on it. He came up with a wave equation now known as Schrodinger’s Equation that lies at the heart of quantum mechanics.

Given a particle and the force that acts on it, Schrodinger’s equation  gives the possible waves associated with this particle at a given position and time. And this is designated by the hardest working symbol in modern physics: the wave function .

Max Born

That Schrodinger would be mistaken in the physical interepretation of the wave function is only one of  the many curious twists in this very interesting and engaging conversation.  What took Max Born to interpret the absolute square of as probability density for finding electrons and not  matter density as  Schrodinger intimated?

Werner Heisenberg

Pascual Jordan

Months before Schrodinger was to write down his famous equation, Max Born, with his young students Werner Heisenberg and Pascual Jordan, already created  an entirely different approach from that of Schrodinger.  The matrix formulation of quantum mechanics developed by Born’s group in Gottingen, Germany described matter  and radiation as discrete particles.

The two formulations of quantum mechanics were thought to be different but they were quickly proved to be equivalent by Schrodinger himself.  Soon thereafter, Paul Dirac incorporated the special  theory of  relativity with quantum mechanics and the ‘quantum field theory’ was born.

Paul Dirac

The physical world that was opening up in  1900 was revealed and seen in a radical light. Max Planck’s bold hypothesis that light was emitted in  bundles or  quanta of energy where each quantum’s energy is determined by the frequency was completely  without  precedence. Planck tried for a number of years to fit his quantum hypothesis into the fabric of  classical  physics but failed.

In 1905, Albert Einstein published a paper proposing that light was not only emitted in integral units or bundles of energy but it was also absorbed in such bundles – bundles that came to be known as photons. Again the energy of absorption was equal to the mysterious, h, Planck’s constant multiplied by the light’s frequency, f. Indeed this is the same equation of Max Planck where the quantum of action, h, was introduced for the first time in 1095: E= hf. This is the single equation that changed the world of physics.

Albert Einstein

Nothing could have been more contrary to the prevailing ideas at that time concerning the transfer of energy of a wave. Since light is in the form of waves, it has to got transfer its energy and be absorbed through its intensity and not by units of its frequency. Einstein in this 1905 paper also provided an explanation for a well-known phenomenon known as photoelectric effect which is associated with the absorption and emission of electromagnetic radiation by matter. It was this work that earned Einstein in 1921  the Nobel Prize in physics  not his special theory of relativity  which was also published that same year.

The Rutherford-type model of the atom proposed by Niels Bohr in 1913 was an extraordinary success in accounting for the spectrum, stability and other aspects of the hydrogen atom. Its success hinged on the Einstein-Planck quantum relation. However Bohr’s theory failed when applied to helium and other atoms. Plus the fact that the theory contained inconsistencies that could not been resolved.