Light: Particle or Wave?
Whether light, which had been examined by the physicist Newton and many of his colleagues, is made up of particles or has a wave-like character constantly led to many intense discussions in scientific circles from the end of the 17th century.
On the basis of his observations Newton was one of the most vehement supporters of a particle theory of light. However, in the formulation of his Law of Reflection Newton assumed that light moves more quickly in water than in air. Refraction of light appears in the transition of a ray of light from one medium into another (light into water). In doing so a deflection takes place and sometimes also to a change in speed of the refracted ray of light, a fact that was unknown to Newton.
The arguments of the wave "surfers"
Advocates of a wave theory of light, and thus opponents of Newton in the argument, were the physicists Christiaan Huygens and Robert Hooke. By means of a conclusive theory on the dispersion of light in wave form Huygens was successful in explaining the phenomena of reflection and diffraction observable with light. He therefore assumed that the speed of the dispersion of light in water or glass was slower in water or glass in comparison to air. Newton also rejected a wave-like explanation for the nature of light because he could not "subscribe to" the linear dispersion of light. What was not known at the time was the diffraction of light beams, that is deviation from straight dispersion, in the proximity of edges. But today diffraction is considered as the decisive factor for the appearance of light in wave form.
Newton's 100-year particle dominance
The great influence of Newton already during his lifetime ultimately led to the acceptance of the particle theory of light in wide circles in physics. Even among the generation of physicists following Newton and even the discovery of light diffraction phenomena did not lead to an immediate end to Newton's particle theory. Diffraction phenomena were still seen as a spreading of light particles at edges. For over 100 years the dominance of the Newtonian interpretation of the nature of light was preserved.
Light: wave AND particle
New impulses towards the wave nature of light came at the beginning of the 19th century from the English doctor and physicist Thomas Young. In 1801 he presented his theory, which was later confirmed, according to which the eye generates all colours by combining only three wavelengths. This "Theory of Trichromatic Vision" is also based on the primary additive colours red, green and blue. Through the observation of interference phenomena, that is the overlapping of lightwaves, Young found confirmation for the wave aspects of light. His results were confirmed and substantiated shortly after his discovery by those of the French physicist Augustin Fresnel on diffraction and interference.
Only with the birth of Quantum Theory and a little later Quantum Mechanics in the 1920s could it be verified that Isaac Newton was not totally wrong after all. Under certain conditions light can be observed both as particles and waves, an explanation that was also known as "wave-particle duality" and in which physicists such as Heisenberg, Schrödinger, Born and Bohrt were decisively involved. This was a partial and late rehabilitation of Newton's particle theory of light.
