Faraday's Fields
The word “field” appears for the first time in “On new magnetic actions” by Michael Faraday in 1846. Faraday was referring to a region in the vicinity of a magnet affected by some force. Forces, in mechanics, are actions that tend to maintain or alter the motion of a body or distort it. Faraday spent his life grappling with the mechanism by which the magnet supplied this apparent force at a distance.
Field-like regions of influence were an old idea by the time of Faraday. Abu Ma’shar published Kitab al-madkhal al-kabir around 850 A.D., effectively outlining the manner in which the moon tidally affected the oceans. Mechanistic explanations were absent for this action, in many ways up to the present. Robert Grosseteste suggested in 1227 that the light of the moon was in some way responsible for the apparent attraction. By the 1600s, with the arrival of Kepler’s Celestial Physics, scientists understood that a body’s influence extends outward into the space. Kepler proposed invisible carrier spheres responsible for transmitting the attraction, but this led to more problems than it solved.
The Greeks may have been the first to recognize that in order to apprehend certain mechanisms in nature, it is necessary to assume that there are invisible actors. Originally, these early thinkers proposed that invisible atoms could explain the properties of a material. Later, when enlightenment investigators sought to comprehend the mechanism that caused electricity to align iron filings, or move the needle on a compass, they once more assumed an invisible actor: the aether. While the concept of atoms has held up under strict scrutiny for thousands of years and unto the present day, the aether fell out of favor with the advent of Einsteinian Relativism in the Early 20th century (later we’ll look at why this was). The fields of Faraday persist.
The great electromagneticists of the 19th century, adopted Faraday’s term, field, to refer to the patterns of attractive and repulsive activity within the aether. Faraday, for most of his life believed these patterns, the lines of force within the field, were not merely places of activity but were actual physical materials themselves. Faraday referred to the lines of force as “tentacles” and would have gone to his grave believing that these force-carrying materials were themselves the building blocks of reality had he not been persuaded by the prevailing philosophy of the day, the experimental philosophy, that only the observable is scientifically known.
Lines of force are apparent in the form of iron filings around a current carrying wire. Image credit.
Without being able to observe the materials-in-action responsible for invisibly aligning the iron filings, the concept of “field” was adopted and eventually generalized up to the present day. This introduction of activity-as-actor was in alterative to the traditional natural philosophy approach where materials, even hypothetical structures like the atoms of the Greeks, were the basis for an explanation. Though the Cartesians on the other side of the English Channel still promoted this speculative method of scientific inquiry, they were eventually overrun by experimental philosophers insistent on evidence-based testimony. The triumph of experimental philosophy should come as no surprise since the experimentalists were beginning to provide serious technology for an increasingly industrialized age.
There were, however, critics of the new experimental philosophy, which had truly been gaining steam since Newton published his Principia in 1687. Gottfried Liebnitz and George Berkeley loudly protested that although Newton was able to use terms like “force” and “attraction” to seem explanatory, as if there is a cause for why planets move as they do, there is actually no hint as to how the physical materials involved promote this attraction. Newton defended that his work was only intended to prescribe mathematical, not physical, principles for natural philosophy. This approach held sway in part because of its humility. Science, it seemed, would rather describe what it can detect than overstep its authority and claim untouchable hypothetical mediators. In order to include invisible mediators in physical testimony, they must be evaluated experimentally.
With no way to touch the invisible fields, Faraday begrudgingly relinquished his physicalist perspective on the lines of force but left the caveat that if transmission of force through the fields were to take time, he would retreat to his original recalcitrant position. In “On the physical character of the lines of magnetic force” in June of 1852, he draws a line between actions at a distance such as gravity for which there is no convincing evidence of mediation, and other clearly mediated invisible process like light for which there is bending and polarization. Faraday wished to include magnetism in the latter category, although he could not definitively do so. Had he lived to see the recent discovery of gravitational waves, with measurable propagation speed, he would have likely removed the phenomenon from his list of true actions-at-a-distance and remained in protest of the field-as-actor approach popular today.
Physics has clearly moved forward without characterization of any hypothetical mediators and the concept of field reigns supreme today. In part this is because physics became primarily concerned with producing quantitative laws of behavior governing dynamics, rather than uncovering the true nature of fundamental reality. The 20th century astronomer and science personality, Arthur Eddington, once said “A physical quantity is defined by the series of operations and calculations of which it is the result.” This reinforced the the formal definition of a field as “some quantity which can vary continuously in some domain (usually the domain of space and time).”
Later, the entirety of physical existence became conceived of exclusively through relationships between physical quantities. For instance, Paul Dirac described relativistic particles quantum mechanically in order to produce the photon and electron. From these quantum electrodynamics, field operators are introduced, which provide for creation or annihilation of various particles. Today, physical reality is entirely conceived of in this quantitative fashion. But the tendency toward this paradigm was already in motion by the mid 1800s. Thermodynamics, a way of treating systems in terms of their ability to do work, was becoming popular for its practical applications. The concept of fields fit right in, as fields could account for energy transmission. Perhaps this quantitative lens explains why Michael Faraday was in many ways a loner in his uneasiness with the field– a term he coined and later came to loathe.
Although perhaps one of the greatest scientists of all time, Faraday was not a quantitatively oriented mind. His discovery of magnetic induction was only later quantified by Maxwell and the relationship that bears his name stands as one of the four great Maxwellian equations. Faraday had little formal education, although he spent seven years from the age of 14 in a bookstore gleaning all the knowledge made available to him in print. He was particularly attracted to chemistry, a science that involves spatial re-combination of physical structures, molecules. Ever the dedicated experimentalist, Faraday would become known for debunking mystical demonstrations such as seances, and other forms of mesmerism.
For Faraday, the concept of the field represented a sort of compromise on the behalf of science. Though we could not know what was truly occurring within some continuous region, we could effectively and reproducibly describe how the process unfolded: the field’s energetics and effects upon other bodies could be measured and catalogued and that is close enough for jazz. Still, we can confidently say that Faraday went to his grave believing that field effects described some action by physical actors within the now forgotten aether. Next time, we’ll dig into the death of the aether and see how the wake of that defeat ostensibly left physics with little choice but to carry on to the present treating fields as actor-less activity.
Note, 6/20/2020:
One of my readers pointed out that Faraday, though normally credited with the idea of fields-as-actors, may have received some of his insight from Roger Joseph Boscovich. I have not made my way to Boscovich’s original text, Philosophiæ naturalis theoria redacta ad unicam legem virium in natura existentium, but will report back when I have more insight.
