Reference: Essays on Substance
The History of Quanta
The concept of quantum emerged in the late 19th and early 20th centuries, revolutionizing our understanding of physics at the atomic and subatomic levels.
The idea of energy quanta was introduced by Planck in 1900 to explain blackbody radiation. Planck had been working on black-body radiation for years, trying to derive a law based on thermodynamics and electromagnetic theory. In October 1900, new experimental results showed that the existing Wien’s law was invalid for certain wavelengths. Planck presented a new radiation law that fit the experimental data well. This formula was initially derived through mathematical curve fitting rather than from first principles. Within two months, Planck worked to provide a theoretical explanation for why his formula worked. This led him to introduce the revolutionary concept of energy quanta.
Planck proposed that energy could only be emitted or absorbed in discrete “packets” or quanta. The energy of these quanta was directly proportional to the frequency of the radiation, expressed as E = hf, where h is Planck’s constant. Planck himself viewed this as a “act of desperation” and did not fully understand the implications of his own theory at first. The presentation of Planck’s quantum hypothesis on December 14, 1900, is often considered the birth of quantum theory. Albert Einstein’s work on the photoelectric effect in 1905 further corroborated and expanded on Planck’s findings.
As light moves out from its source in all directions in space, it spreads over an ever increasing volume. Following the inverse square law. The light thins out but it maintains its frequency. Ultimately, it reduces to photons that have the minimum energy possible for that frequency. This minimum energy is determined by E = hf.
These photons are like drops of a fluid and not point particles. When photons of the same frequency come together they coalesce into a larger body of light. Photons of different frequencies do not coalesce together.
The quantized states within the atom introduced by Niels Bohr is a very different phenomenon. These energy states are closely related to the resonance phenomenon. Atoms exhibit resonant behavior in their interactions with electromagnetic radiation, which is fundamental to their energy structure. The idea of “quantization” should not be confused with the concept of quanta.
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