James Clerk Maxwell did indeed formulate the theory of electromagnetism, which included the concept that the speed of light is constant in a vacuum. This groundbreaking idea, known as Maxwell's equations, laid the foundation for our understanding of electromagnetic waves and the unification of electricity and magnetism.
However, it was Albert Einstein who revolutionized our understanding of space, time, and motion through the development of the theory of relativity. Einstein's work built upon and extended the ideas put forth by Maxwell and others.
Einstein's special theory of relativity, published in 1905, introduced the concept of the constancy of the speed of light in all inertial frames of reference. He showed that the laws of physics, including the behavior of light, are the same for all observers in uniform motion relative to each other. This idea challenged the classical notion of space and time as separate and absolute entities.
Einstein's theory of relativity also introduced the famous equation E=mc², which relates energy (E) and mass (m) and demonstrates the equivalence of matter and energy. This equation played a crucial role in the development of nuclear physics and has far-reaching implications in various scientific disciplines.
While Maxwell's work paved the way for the understanding of light and electromagnetism, it was Einstein who took those ideas and expanded them into a more comprehensive framework that revolutionized our understanding of the fundamental nature of space, time, and motion.