In this blog post, we will look at how the perspective of physics has changed, from Newton’s particle theory to Maxwell’s electromagnetic field theory.
According to the classical mechanics system established by Isaac Newton in the 17th century, physical reality consists of three basic elements. These are “absolute space,” in which nothing exists; “mass points,” which move according to certain laws within that space; and “forces” that act between these mass points. These three elements exist independently, but they interact closely with each other as the fundamental framework that constitutes the physical world. Based on this system, Newton attempted to explain various aspects of natural phenomena mathematically, and his theory became the basic way of thinking in Western natural science for centuries.
In this system, a physical event refers to the process of a mass moving in space under the influence of universal gravitation and certain laws of motion. In other words, events are not simply phenomena that occur, but are considered to be predictable and explainable movements based on strict mathematical principles. These movements can be accurately described by Newton’s laws of motion and theory of gravity, and the physical world came to be understood as a precisely designed machine.
Newton’s theory adopted a method of simplifying complex natural phenomena by removing unnecessary elements and focusing only on two elements: mass and translational motion. The color, shape, internal structure, and texture of objects were excluded from the explanation, and only characteristics that could be quantified mathematically were considered subjects of physics. Here, the concept of “remote action” was introduced, which allows forces to act between masses without direct contact. This remote action refers to the principle that forces are transmitted according to certain laws even though there is nothing physically present between two particles, and Newton’s theory of gravity was developed based on this concept of remote action.
This theoretical structure can be described as “particle theory” in that it explains the natural world as the motion and interaction of particles, and as “mechanics” in that the particles operate according to certain laws. In this way, Newton’s physics regarded the entire universe as a giant machine and justified attempts to reduce all natural phenomena to mechanical principles.
However, there were limitations that could not be resolved theoretically, and the most unsatisfactory aspect was the question of the nature of light. Newton argued that light was also composed of tiny particles, based on his particle-centered theoretical system. However, this claim was questioned even among scientists at the time. For example, when attempting to explain the phenomenon of light being absorbed by objects using particle theory, the question “How do the absorbed light particles disappear?” inevitably arose, and there was no clear answer.
Furthermore, unlike the particles that make up matter, light was believed to have no mass, so the attempt to explain these two types of particles in the same way was theoretically problematic. Treating particles with mass and particles without mass within the same framework undermined physical consistency, and this became an academic issue.
The introduction of the concept of electricity into the scientific community further complicated the issue. This was because electrically charged particles had properties that were completely different from those of existing material particles and light. Electrically charged particles appeared to have little or no mass, but at the same time, they interacted with other electrically charged particles and exhibited peculiar behavior, such as pushing and pulling each other. This behavior was a new phenomenon that could not be explained by simple particle collisions or gravitational forces, forcing physicists to reconsider particle theory.
Nevertheless, attempts to build on Newton’s theory continued throughout the late 18th and early 19th centuries. In particular, a group of scholars led by Pierre-Simon Laplace sought to refine the basic principles of Newtonianism and apply them to various fields of physics. They expanded and deepened Newton’s theory of gravity and attempted to explain various natural phenomena, such as electromagnetic phenomena, heat, and optics, through the concepts of particles and forces.
In this process, theoretical tools such as “massless particles” and “action at a distance” continued to be used, and attempts to reduce the complex natural world to simple mathematical models continued unabated. However, in the 19th century, Newtonian worldview faced a decisive challenge. The starting point was a new theory about the nature of light, namely, the “wave theory of light.”
The claim that light is a wave rather than a particle had long been a subject of debate, but in the early 19th century, its validity began to be proven through various experimental results, such as interference and diffraction phenomena. As a result, the scientific community came to accept the new perspective that light is not a tiny particle, but a vibration of a specific medium.
The wave theory of light is based on the assumption that light propagates through a specific medium. This medium was called “ether,” which was believed to be an invisible continuous substance filling the entire space. Ether was considered to be extremely fine but elastic, and it was believed that light vibrations propagated through this medium. This concept required a completely different way of thinking from the existing particle theory worldview.
Subsequently, new theoretical approaches to explain electrical and magnetic phenomena emerged, and particle theory gradually lost its place. At the center of this change was Michael Faraday. He proposed a unique concept called “lines of force” to explain electromagnetic phenomena. Faraday presented a new way of thinking that electric and magnetic forces were not simply instantaneous interactions between particles, but rather continuous flows of force distributed throughout space.
Lines of force were understood to be curved rather than straight, mediating electromagnetic interactions by pushing and pulling in space. From this perspective, Faraday saw that the space through which forces were transmitted was not empty, but filled with a continuous field with fluid-like properties. Although invisible, this field became the spatial background for electromagnetic phenomena and established itself as a new aspect of physical reality.
This way of thinking meant that nature could no longer be understood as a collection of individual particles, and scientists had to establish a new theoretical basis for “continuous entities.”
James Clerk Maxwell was the person who mathematically established Faraday’s ideas. He succeeded in mathematically explaining how electromagnetic forces are transmitted through space, and based on this, he established a system of equations that encompasses almost all aspects of electromagnetic phenomena. Maxwell believed that electromagnetic fields fill space and that changes in these fields cause the interaction of electricity and magnetism.
The series of equations presented by Maxwell came to be known as “Maxwell’s equations,” which were used not only to explain existing phenomena but also to predict new physical facts. In particular, when these equations were combined, the existence of “electromagnetic waves” propagating at the speed of light was theoretically derived, and it was discovered that light is a type of electromagnetic wave. This discovery was a decisive turning point that fundamentally changed the paradigm of physics.
At first, Maxwell proposed mechanical models of a continuum filling space to justify these equations, but he soon realized that such models were unnecessary. This was because the equations themselves were sufficient to explain electromagnetic phenomena completely and enable experimental predictions. He therefore discarded the continuum model and came to regard the equations themselves as expressions of ultimate physical reality.
As a result, Maxwell’s electromagnetic field came to be understood as an independent entity that could no longer be reduced to other physical entities, which was an important turning point in physics, establishing the concept of “field” as an independent reality. This new field theory opened up a new field of physics that transcended Newton’s particle-centered worldview and laid the foundation for modern physics, leading to Albert Einstein’s theory of relativity and the development of quantum mechanics.
