The realization that Newtonian mechanics is not the complete description of the laws of nature came about through several key developments in the history of physics. Here are a few important milestones that led to this understanding:
Michelson-Morley experiment (1887): This experiment was designed to detect the existence of the luminiferous ether, a hypothetical medium through which light was thought to propagate. However, the experiment yielded null results, suggesting that the ether did not exist. This posed a challenge to the prevailing Newtonian mechanics, which assumed an absolute reference frame for the laws of motion.
Maxwell's equations (1865): James Clerk Maxwell formulated a set of equations that described the behavior of electric and magnetic fields. These equations unified the phenomena of electricity and magnetism and successfully predicted the existence of electromagnetic waves traveling at the speed of light. This implied that light was itself an electromagnetic wave, contradicting the idea that it required a material medium like the luminiferous ether.
Planck's quantum hypothesis (1900): Max Planck introduced the concept of quantization, suggesting that energy is not continuous but rather comes in discrete packets called quanta. This was a departure from classical physics, where energy was assumed to be continuous. Planck's quantum hypothesis later formed the basis of quantum mechanics, which would supersede classical mechanics.
Einstein's theory of relativity (1905 and 1915): Albert Einstein developed the theory of special relativity in 1905, which introduced the idea that the laws of physics are invariant under Lorentz transformations and that the speed of light is constant in all inertial reference frames. This contradicted the notion of absolute space and time in Newtonian mechanics. Later, in 1915, Einstein formulated the theory of general relativity, which provided a new understanding of gravity and described the curvature of spacetime.
These and other discoveries and theoretical advancements collectively undermined the classical Newtonian worldview. While Newtonian mechanics remains highly useful for everyday applications, it is now understood to be an approximation valid only under certain conditions, specifically when speeds are much lower than the speed of light and gravitational effects are not extreme. In the realm of subatomic particles, high speeds, or strong gravitational fields, the more comprehensive frameworks of quantum mechanics and general relativity respectively take precedence.