In 1894, electricity companies commissioned Planck to discover how to generate the greatest luminosity from light bulbs with the minimum energy. To get to a solution, Planck turned his attention to the black-body radiation problem.
In 1900, Planck had a theoretical answer. With great distaste, he had borrowed ideas from statistical mechanics that had been introduced earlier by Austrian physicist Ludwig Boltzmann.
Planck had a strong aversion to treating thermodynamics’ laws as statistical rather than absolute gospel. Being compelled to apply statistics to get an agreeable solution he considered “an act of despair.”
Planck achieved concordance with experimental results via a simple formula: E = hv, where E is the energy of a wave, v is the frequency of the radiation, and h is a very small number that came to be known as Planck’s constant (aka Planck’s action quantum).
To his consternation, what Planck found was that energy absorption and radiation was not continuous. Energetic work instead happens in discrete amounts: quanta of energy, with the Planck constant (h) as the quantum. What was supposedly entirely wavelike manifested in particulate form.
(The elementary quantum of action, known as Planck’s constant, is 6.626 × 10–34 joule/second in meter/kilogram/second units, with just a bit of uncertainty.)
“It seemed so incompatible with the traditional view of the universe provided by physics.” ~ Max Planck
At first, Planck considered quantization only “a purely formal assumption” which he “did not think much about.” But then he tried to stuff the quantum genie back into the bottle and found that he could not.
“My unavailing attempts to somehow reintegrate the action quantum into classical theory extended over several years and caused me much trouble.” ~ Max Planck
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Statistical classical mechanics requires the existence of the Planck constant, but does not define its value. Planck ushered the recognition that physical action cannot take an arbitrary value. In other words, there is a fundamental order to Nature, which begins with the infinitesimal.
Phenomena must be a multiple of the Planck constant. Planck’s quantum of action essentially states that only certain energy levels may manifest, while values in between are forbidden to do so. Physics cannot explain why.
(Planck’s constant represents the limit of empirical existence. The least possible distance is Planck length. Minimal matter has Planck mass. The shortest duration is measured in Planck time.)
Existence consists of interacting fields which necessarily manifest in particulate form. Even thermal energy (heat) quantizes. We’ll see that this duality is both illusory and necessary for existence.
The dynamics of quantum systems are encoded in the amplitude and phase of wave packets. ~ French quantum physicist V. Gruson et al
The science of the quantum world is alternately called quantum mechanics (accenting the statistical nature of the study), quantum field theory (QFT) (emphasizing that quanta are merely manifest fields), or simply quantum theory (which points out that all the packets under discussion are entirely theoretical, and not to be confused with reality).