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The early years of quantum mechanics and Heisenberg’s contributions (to 1927)
Points to ponder:
What tools do we have for understanding phenomena that we can't observe, like the atom?
What's the language of physics?
Why were quantum effects not noticed before 1900?
There was a great deal of discussion and controversy during the development of quantum mechanics about visualizability ("Anschaulichkeit"). Do we have a need for models to visualize what's going on at the atomic level?
Einstein in conversation with Heisenberg said: “Only the theory decides what one can observe”. Do you agree?
The state of physics after 1900 leading to Heisenberg's ground-breaking developments, namely, the first mathematical formulation of quantum mechanics (1925), and the Uncertainty Principle (1927).
The main discoveries and developments were:
Natural radioactivity (Henri Becquerel, Marie Curie).
Max Planck determines that energy comes in tiny units (later called quanta).
Einstein's explanation of the photoelectric effect (light as particles), although many phenomena are explained by light as waves.
The nuclear atom (Ernest Rutherford).
The planetary model of the atom (Niels Bohr).
Max Planck in 1918
Ernest Rutherford
Niels Bohr
Werner Heisenberg (1901 - 1976), the early years
His time as a youth in the Pathfinder (Pfadfinder) group (excerpt from a longer article); for the pdf, click here (2 pages).
Excerpt from the Mott-Peierls biography; for the pdf, click here (2 pages).
Heisenberg's 1925 ground-breaking paper about a reinterpretation of quantum theory based on observable quantities (translated):
On the quantum reinterpretation of kinematical and mechanical relationships
["Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen"]
Abstract: "The aim of the work is to gain the basis for quantum theoretical mechanics that is based exclusively on relationships between fundamentally observable quantities."
:
Excerpt of introduction: "... even with the simplest quantum theoretical problems it is simply impossible to think about the validity of classical mechanics. In this situation, it seems more advisable to completely abandon the hope of observing the previously unobservable quantities (such as the position and orbital period of the electron), at the same time admitting that the partial agreement of the quantum rules mentioned with experience is more or less fortuitous, and to try to develop a quantum theoretical mechanics analogous to classical mechanics."
Werner Heisenberg's breakthrough on Helgoland, in his own words (translated):
Werner Heisenberg's breakthrough on Helgoland, in his own words (translated):
"When the first terms [of the calculations] seemed to accord with the energy principle, I became rather excited, and I began to make countless arithmetical errors. As a result, it was almost three o'clock in the morning before the final result of my computations lay before me. The energy principle had held for all the terms, and I could no longer doubt the mathematical consistency and coherence of the kind of quantum mechanics to which my calculations pointed. At first, I was deeply alarmed. I had the feeling that, through the surface of the atomic phenomena, I was looking at a strangely beautiful interior, and felt almost giddy at the thought that I now had to probe this wealth of mathematical structures nature had so generously spread out before me. I was far too excited to sleep,and so, as a new day dawned, I made for the southern tip of the island, where I had been longing to climb a rock jutting out into the sea. "
– Werner Heisenberg: Physics and Beyond – Encounters and Conversations
– Werner Heisenberg: Physics and Beyond – Encounters and Conversations
(Der Teil und das Ganze – Gespräche im Umkreis der Atomphysik)
Werner Heisenberg (1901 - 1976)
The Memorial Inscription
"In June of 1925 the 23-year-old Werner Heisenberg succeeded here on Helgoland with the breakthrough in the formulation of quantum mechanics, the underlying theory of the laws of nature at the atomic level, which profoundly influenced human thought far beyond physics."
(My translation of the inscription)
Helgoland in the North Sea
Erwin Schrödinger on the sub-atomic world
Erwin Schrödinger on the sub-atomic world
"As our mental eye penetrates into smaller and smaller distances and shorter and shorter times, we find nature behaving so entirely differently from what we observe in visible and palpable bodies of our surroundings that no model shaped after our large-scale experiences can ever be “true.” A completely satisfactory model of this type is not only practically inaccessible, but not even thinkable. "
Schrödinger wave equation, an alternative mathematical formulation of quantum mechanics (Jan. 1926 paper):
Schrödinger wave equation with wave Ψ
Schrödinger wave equation with wave Ψ
“Erwin with his psi can do
Calculations quite a few.
But one thing has not been seen:
Just what does psi really mean?”
"Gar Manches rechnet Erwin schon
Mit seiner Wellenfunktion.
Nur wissen möcht’ man gerne wohl
Was man sich dabei vorstell’n soll.”
I knew of [Heisenberg's] theory, of course, but I felt discouraged, not to say repelled, by the methods of transcendental algebra, which appeared difficult to me, and by the lack of visualizability.
– Schrödinger in 1926
The more I think about the physical portion of Schrödinger's theory, the more repulsive I find it ... What Schrödinger writes about the visualizability of his theory 'is probably not quite right,' in other words it's crap.
– Heisenberg, writing to Pauli, 1926
1927 Solvay Conference
Supplementary:
Max Planck and Quantum Physics, Biography of the 1918 Nobel Physics Prize Winner: YouTube video (14:29) with a bit of docudrama, and some nice old photos.
Max Planck - Original Interview (1942) with English Subtitles: YouTube video (21:49)
The 84-year-old Planck talks about his life and work in the form of a self-portrait. The film was made on Dec. 15, 1942, by order of the Reich Ministry of Propaganda, but never used. The film was only rediscovered in 1983.
A quote (translated): "The happiness of the scientist lies not in possessing the truth, but in discovering the truth."
The size of Planck's constant:
h = 6.626 x 10 -27 erg seconds (with units of energy x time, or momentum x distance)
= 6.626 / 10 27 = 6.626 / 1,000,000,000,000,000,000,000,000,000 erg seconds
where 1 erg = 1 gram (cm / sec) 2
How small is this? Compared to a 1 gram mass moving a distance of 1 cm in 1 second => 1 erg second, it's extremely tiny.
Updated Oct. 19, 2023
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