The belief that light was made up of particles, known as the corpuscular theory of light, originated from the observations and experiments conducted by scientists in the 17th century. Several factors contributed to this initial belief:
Newton's Experiments: Sir Isaac Newton conducted a series of experiments with light, including passing light through a prism and observing the formation of a spectrum. He also conducted experiments on light and shadow, as well as reflection and refraction. Newton's experiments led him to propose that light was composed of tiny particles, which he called "corpuscles," that traveled in straight lines.
Particle-like Behavior: Light exhibits certain behaviors that can be explained by a particle model. For instance, light can travel in straight lines, cast sharp shadows, and be reflected off surfaces at specific angles, similar to the behavior of particles.
Wave-Particle Duality: The understanding of light's nature evolved further with the concept of wave-particle duality. In the 19th century, scientists such as Thomas Young and Augustin-Jean Fresnel conducted experiments that demonstrated the wave-like behavior of light, particularly in phenomena like interference and diffraction. This led to the acceptance of light as a wave phenomenon.
However, it's important to note that the wave-particle duality of light wasn't fully understood until the development of quantum mechanics in the early 20th century. Through experiments like the double-slit experiment, it became clear that light can exhibit both wave-like and particle-like properties depending on the experimental setup.
In summary, scientists initially believed light was made up of particles due to observations and experiments conducted by Newton and others. However, further experimental evidence, along with the development of quantum mechanics, eventually established the dual nature of light as both a wave and a particle.