1. Blackbody Radiation: Classical physics predicted that a blackbody should emit an infinite amount of energy at high frequencies, which is not observed. This problem was resolved by Planck's quantum theory, which introduced the concept of energy quantization.
2. Photoelectric Effect: Classical physics couldn't explain why electrons are emitted from a metal surface only when light above a certain frequency is shone on it, regardless of the intensity. Einstein's explanation using the concept of photons, packets of light energy, provided the solution.
3. Atomic Spectra: The discrete spectral lines observed in the light emitted by atoms could not be explained by classical physics. Bohr's model of the atom, incorporating quantum concepts, successfully accounted for these spectral lines.
4. The Stability of Atoms: Classical physics predicted that electrons orbiting the nucleus should spiral inwards and eventually crash into the nucleus, leading to the collapse of atoms. Quantum mechanics resolved this by describing electrons as wave functions, preventing them from collapsing.
5. Wave-Particle Duality: Classical physics viewed light as waves and matter as particles. However, experiments like the double-slit experiment demonstrated that both light and matter exhibit wave-like and particle-like behavior, a concept that is explained by quantum mechanics.
6. Relativity: Classical physics assumes that time and space are absolute and independent of each other. Einstein's theory of relativity, however, revealed that time and space are relative to the observer's motion and that they are intertwined.
7. The Expanding Universe: Classical physics couldn't explain the redshift of light from distant galaxies, which provided evidence for the expansion of the universe. This expansion is explained by general relativity and cosmology.
8. The Existence of Dark Matter and Dark Energy: The observed rotation of galaxies and the accelerating expansion of the universe cannot be fully explained by the matter and energy we can see. The existence of dark matter and dark energy, which are not accounted for in classical physics, is required to explain these phenomena.
In summary, classical physics is a powerful theory, but it has limitations in explaining phenomena involving very small scales (quantum physics), very large scales (relativity), and the nature of the universe as a whole (cosmology). These limitations led to the development of modern physics, which incorporates new concepts like quantization, wave-particle duality, and the curvature of spacetime.
