In this blog post, we take a closer look at how Newtonian mechanics, the representative system of classical mechanics, was replaced by field theory.
According to Isaac Newton’s system of physics established in the 17th century, physical reality is explained by empty space, material points moving within that space, and the forces acting between these material points. In this system, physical events were considered to be the process of material points moving in space under the control of certain laws of motion and universal gravitation.
Here, “mass point” refers to an idealized particle that has only pure mass and position, with all other physical properties such as size and volume removed. Within this theoretical framework, Newton introduced the concept of “action at a distance” between particles, or forces acting along straight lines across empty space, to explain physical events. This framework is particle-based in that it interprets the world in terms of particles, and it is mechanical in that it understands physical phenomena as mechanical motion and interaction. However, there were several problems with this system, the most significant of which was related to the concept of light.
Newton argued that light was also composed of particles based on his theory, but at the time, the question of “What happens to particles when light is absorbed by objects?” was already being actively discussed in academic circles. In particular, the fact that material particles with mass and light particles without mass had to be explained in different ways was a major source of dissatisfaction in terms of theoretical consistency.
The problem did not end there. Over time, a new type of particle with different properties from the previous material particles and light particles was added as a third type: electric particles. These particles appeared to have no mass, but unlike light, they exhibited unique interactions, pushing and pulling each other. These characteristics caused cracks in the existing concept of particles, further deepening the confusion in the physics community.
Nevertheless, in the late 18th and early 19th centuries, scientists, mainly from the Laplace school, sought to carry on Newtonianism. They continued to expand Newton’s theory of gravity while actively attempting to utilize the concepts of special massless particles and remote action to explain natural phenomena. Newtonianism remained the mainstream in the scientific community and was considered the most powerful theoretical tool for explaining the world.
However, a full-scale challenge to Newtonianism arose in the early 19th century. At the center of this challenge was the wave theory of light, which directly contradicted Newton’s particle theory of light. The wave theory explained light as a vibration of a medium called “ether” that fills space, rather than as particles. In other words, light is not a flow of particles, but a wave generated by the vibration of a continuous medium.
Since then, ether has been regarded not as a mere abstract concept, but as a continuum with unique mechanical properties. This change was a precursor to the shift in the direction of physics from particles to continuous fields. The next figure to appear was Michael Faraday. In order to interpret his own electromagnetic experiments, he abandoned the existing concept of particles and introduced a new system of force transmission. What he proposed was the concept of “lines of force.”
Faraday’s concept of lines of force assumes that forces do not act directly from one point to another, but are transmitted continuously along curves in space. This is a concept in which forces spread out in space as if they were fluids, and the space in which those forces exist, or “field,” was assumed to be a continuous physical medium. This new concept of physical reality departed from the existing particle theory, but still retained its mechanical properties.
James Clerk Maxwell was the one who mathematically systematized Faraday’s unique concept. He expressed in mathematical language how the medium filling space is transformed and electromagnetic influences are propagated. The result of this process was Maxwell’s equations, which are extremely important in modern physics.
With these equations, Maxwell was able to describe most of the electromagnetic phenomena known at the time in a single unified system and even showed that it was possible to predict new phenomena that had not yet been experimentally verified. In particular, the combined Maxwell equations predicted the existence of electromagnetic waves propagating at the speed of light, leading to the surprising conclusion that light is a type of electromagnetic wave.
Initially, it was thought that a model of a mechanical medium filling space was necessary to justify these equations, but Maxwell soon realized that the equations themselves were sufficient to explain and predict natural phenomena. As a result, the mechanical models that had been introduced to explain physical reality were discarded, and instead, electromagnetic fields gained the status of ultimate reality that could no longer be reduced.
This change was not a simple modification of theory, but a fundamental shift in the worldview of physics. The shift from a particle-centered, mechanical worldview to a continuous, field-centered theoretical system had a decisive influence on the subsequent development of physics, especially relativity theory and quantum mechanics. Maxwell’s electromagnetism no longer relied on mechanical interpretations and presented a new way of describing physical reality through the concept of fields. This laid the foundation for modern physics and became a turning point in the history of science.
In conclusion, physics, which began with Newton’s particle theory in the 17th century, was reestablished as a field-centered theory at the end of the 19th century through numerous experimental observations and theoretical reconstructions. This process has a meaning that goes beyond the mere advancement of science. It means that science’s answer to the philosophical question of “What is reality?” has changed. We have gained a new insight that the world we live in is not just a collection of isolated particles interacting with each other, but a space filled with continuous fields and energy flows.
Understanding this historical trend goes beyond simply knowing the development of physics and greatly helps us understand the evolution of thinking about how science views the world. The transition from particles to fields, and from a material-centered to a structure-centered view, is still ongoing, and in the midst of this trend, we are establishing a new scientific worldview.
