History of Light Theories

Study Notes

Introduction

In 1637, Descartes proposed that light was made of particles, which explained reflection and refraction.
Descartes' model predicted a faster light speed in the second medium when it refracts towards the normal.
Isaac Newton, in his book "Opticks", further developed the corpuscular theory, which became widely accepted.
In 1678, Christiaan Huygens presented a wave theory of light.
The wave theory explained reflection and refraction but contradicted the corpuscular theory by predicting a slower light speed in the second medium when it refracts towards the normal.
The wave theory was validated experimentally in 1850 by Foucault, who showed that light travels slower in water than in air.
The wave theory's acceptance was hindered by Newton's authority and the belief that waves required a medium to propagate.
Thomas Young's interference experiment in 1801 demonstrated that light is a wave phenomenon.
The wavelength of visible light was measured to be extremely small, about 0.6mm for yellow light.
The small wavelength of visible light compared to typical mirror and lens sizes allows light to travel in straight lines; this is the basis of geometrical optics.
Geometrical optics describes light propagation as rays in the limit of zero wavelength.
From 1801 to 1840, numerous interference and diffraction experiments solidified the wave theory of light.
The propagation of light through vacuum was a major challenge for the wave theory until James Clerk Maxwell's electromagnetic theory of light.
Maxwell's equations for electricity and magnetism produced a wave equation predicting the existence of electromagnetic waves.
Maxwell calculated the speed of electromagnetic waves in free space and found it to be close to the measured speed of light, suggesting that light is an electromagnetic wave.
Electromagnetic waves are associated with oscillating electric and magnetic fields.
A changing electric field produces a time-varying magnetic field, and vice versa.
The mutual interaction of changing electric and magnetic fields results in the propagation of electromagnetic waves, including light, even in a vacuum.