The History of Quanta in Physics

Since human brains first experienced the process of cognitive contemplation, men have pondered the question, what is the world made of? We still don’t have all the pieces of the puzzle representative of the theory of everything, but during the past two hundred years of the quest to find answers, some very profound realizations have been manifest. One of the most prodigious of these is the theory of quanta emerging in the opening decades of the twentieth century.

A hundred years before quantum theory jelled in the mind of Max Planck, John Dalton confirmed the error of the Aristotelian affirmation of Empedocles notion that everything was composed of air water fire and earth. In place of the Aristotelian notion, which had prevailed for 2 millennia, Dalton favored Democritus’ theory of atomicity, that everything was composed of minute, indivisible and indestructible particles. Dalton was on the right track with respect to scientific truth and established empirical methods of classifying elements by their atomic weights. This can be seen as the beginnings of atomic theory. But Dalton and Democritus, as it would turn out, were wrong about two aspects of atomic theory, atoms were neither indestructible nor were they the smallest particles of matter. Nevertheless, Dalton’s atomic conception remained unchallenged and even bolstered by subsequent discoveries throughout the 19th century, that is to say with the exception of two emerging realizations which at very least and in terms of Daltononian atomic theory presented some paradoxical perplexities.

The first of these perplexities effervesced from the astute investigation and profound realizations about electromagnetism by James Clerk Maxwell, later to be codified by Heinrich Hertz through experimental intrinsic observations leading to the notion that there was something else in the universe which could not be considered in material terms. The basic theory evolving around this premise in terms of traditional perspectives of physics was that the energy Hertz had observed traveled through space in the same way a ripple caused by a pebble thrown in a pond radiates across the surface of the water. Ever since 1676 when Danish Astronomer Ole Romer quashed the notion that light, rather than instantaneously apparent was propagated at a constant temporal velocity, physicist considered, light too was a form of wave radiation. The conclusion was thereby drawn that space was not empty but filled with some ethereal medium to afford wave propagation. Thus the fundamental precepts of wave theory were codified becoming irrefutable and unanimously accepted as the status quo in the physics discipline.

In 1895, the German physicist Wilhelm Röntgen employing a cathode ray tube apparatus, discovered the second perplexity to Daltonian atomic theory, a new kind of waves he termed “x-rays.” A year later, repeating and expanding on Röntgen experimentation, French physicist Henri Becquerel made an even more radical and accidental discovery that a material known as pitchblende spontaneously emitted the same x-rays. Using an instrument developed by her husband Pierre called an electrometer, Marie Curie made the most important discovery of her career, although she and nobody else at the time realized it.  What she noted was, that the radiation emitted by elements was not the result of any chemical reaction, but some factor actually given off by atoms of the element itself. As we know today this radiation is the effect of transmutation of the element and conversion of matter into energy. This discovery would underwrite the beginnings of what can be characterized as the most prolific epoch of advancement of human understanding since humanity emerged on the planet.  

As physicists go, Max Planck could be considered a traditionalist and subscriber to Maxwellian principle. His own field of study was in the area of thermal dynamics and it was from this vane that new thought would emerge center stage in the theater of theoretical physics, and Planck would be the actor who played the part of its introduction. But what Planck discovered, rather than anything congruent with the physics of the day, was something that would expose a whole new and theretofore unimagined dimension of it. Moreover, it was a dimension which once entertained in Planck’s mind became quite disconcerting for him. It all had to do with how molecules reacted in terms of thermal radiation in response to an increase in applied temperature.

Traditional statistical mechanics analysis based on Boltzmann’s constant and confirmed by empirical  experimentation conducted by Maxwell, predicted a linear increase of both frequency and intensity of electromagnetic radiation and equal distribution of energy throughout a material body when heated. This is demonstrated when a piece of iron is heated in a furnace, first beginning to glow in the infrared, then red to orange to yellow and finally brilliant and intense white. Maxwell used these statistics to generate a graph denoted as the Maxwell-Boltzmann distribution and embodied by the Equipartition Principle.

Around 1900, a couple  of British physicists Lord Rayleigh and Sir James Jeans developed a theorem considering spectral radiance across the electromagnetic spectrum for a blackbody at a given temperature. Known as the Rayleigh-Jeans  Law the statistic indeed remains consistent across the electromagnetic spectrum and should remain so, taken in either spectral direction to infinity. Herein lies a paradox which would become known as the ultraviolet catastrophe. Under Rayleigh-Jeans Law, an infinite or unlimited increase in frequency of a blackbody substance would lead to a subsequent infinite increase in energy. While this may have seemed a theoretical possibility it didn’t fit with the Equapartition Principle because as infinity with respect to frequency is approached the energy of a single atom of matter could theoretically eclipse the total energy of the entire universe. This of course is a practical impossibility in terms of classical physics, although, as would later be learned has potential ramification in terms of gravitational singularities.

Max Planck, being as mentioned very much a classical physicist, took immediate exception to the apparent nonlinear status and ultraviolet catastrophe paradox of the Rayleigh-Jeans Law, setting out on his own course of investigation and thought experiment. In the process he came up with a postulate which reinforces the proportional distribution curve of the frequency to energy relationship across the electromagnetic spectrum and onwards towards infinity. He expressed this linear distribution with the mathematical formula E=hv, where “E” represents energy, “v,” frequency, and “h” a numerical constant of 6.77 X 10-27. Originally known as Planck’s Constant, today it is generally referred to as the Quantum Constant, and continues as the fundamental cornerstone of quantum mechanics.

Even to Planck, there was an immediate problem with his new formula when thinking of radiation in terms of waves. It was more practical and consistent to deal with the quantities of energy at any given frequency as discrete packages or bundles of it, and Planck termed these nice infinitesimally small bundles as “quanta” (from Latin meaning “how much”). The problem of dealing with energy in discrete packages (quanta), however, was it suggested the traditional notion of the propagation of radiation as waves could not possibly be right in the traditional sense of  physics. Planck himself an ardent subscriber to such tradition was clearly unnerved by this necessary rebuke of conventional thinking, and equally perplex by the fact that his quanta theory proved true beyond all scientific rigor applied and scrutiny  thrown at it. In simple terms, quantum theory worked, and you can’t argue with success.

When Planck first unveiled his quantum theory to a symposium of the German Physical Society on December 14, 1900, the father of quantum theory had little more confidence in it than any of those in attendance. After all, the quantum constant was a numerical value of no more significance than the fact it worked. It turns out that quantum theory was equally unnerving to a young Albert Einstein who first heard of Planck’s quantum theory in 1901. One of the most perplexing issues to Einstein and others, was how Planck had come up with the infinitesimally small number he used for his constant. Planck could do little better in explanation of how he came up with the number than to state that it was “a fortuitous guess.” Planck seem to have little interest in expounding or even considering the implications of quantum mechanics, but the younger Einstein would take up the task as his own.

In 1905, Albert Einstein formally quantified what Planck had invented or discovered— however one wishes to look at it. Einstein renamed Planck’s quanta packages as photons and used Planck’s quantum theory to describe the photoelectric effect, for which he would receive his Nobel Prize in 1921. Incidentally, Planck, not Einstein, received the 1918 Nobel in physics for discovery of the “quantum of energy.” Some Latter-day word smiths may attempt to beguile the reader into believing, through wordy dissertations of equally related and unrelated banter interleaved with seemingly endless quotations, that Einstein and not Planck was the true father of quantum theory. Consider in rebuttal to such distortions simply the words of professor Einstein as espoused in his 1914 Inaugural Address To The Prussian Academy:

“Then Planck showed that in order to establish a heat and radiation constant with experience, it is necessary to employ a method of calculation the incompatibility of which with the principles of classical physics became clearer and clearer. For with this method of calculation Planck introduced the quantum hypothesis into physics, which has since received brilliant conformation. With this quantum hypothesis he dethroned classical physics to the point where sufficiently small masses are moved at low speeds and high rates of acceleration, so that today the laws of motion propounded by Galileo and Newton can only be allowed validity as limiting laws.”

Yes, it’s true that Einstein used and embellished upon Planck’s quantum theory to extend it, but the question begs to be asked whether Einstein would ever have pondered the more bizarre implications of the quantum reality had he not received impetus to do so by Planck’s pioneering breech into the quantum dimension of the universe. Yes, Neils Bohr’s parlay of quantum mechanics in practical application to explain electron orbital energy levels was profound, but would he have been able to develop his own hypotheses were it not for the fact Planck and Einstein had blazed a trail into the wilderness of quantum mechanics. Likewise we can rest assured that Heisenberg would never have formulated the wave/particle duality relationship of photons were it not for those who built the foundations of quantum mechanics before him. 

Thus we conclude, if one wants to consider “The history of ‘quanta’ in physics” one needs begin with a clear and true perspective of who is responsible for its incipience and then take it from there to wherever one wants to go with it. In this case, while there are apparently some differing opinions as to whom the legacy of quantum theory truly belongs to, and which can only be derived through a distortion of the facts in the historical record, the notion of quanta and quantum theory first emerged in the mind of Max Planck.  To this day his hypothesis has withstood all scientific rigor and scrutiny it has faced, even as other models, including those of the Rutherford/Bohr atom, have been relegated to the scrap heap of misconceptions.  The rest of the history of quanta in physics has yet to be written as we delve further and further into the quantum nanouniverse of subatomic particles in search of the ultimate, the infinite, the unifying quanta.