What is the opposite of modern physics

The opposite of modern physics is typically classical physics or Newtonian physics—the physical theories developed before the revolutionary changes of the early 20th century, particularly before quantum mechanics and relativity. Classical physics includes Newton's laws of motion and gravity, classical mechanics, classical electromagnetism (Maxwell's equations), and classical thermodynamics. These theories work excellently for everyday-scale phenomena—objects moving at non-relativistic speeds and systems much larger than atoms—but break down at extreme scales (very fast, very small, or very massive).

Modern physics emerged when classical theories failed to explain phenomena like blackbody radiation, the photoelectric effect, atomic spectra, and discrepancies in Mercury's orbit. Quantum mechanics replaced classical mechanics for atomic and subatomic scales, introducing probabilistic rather than deterministic predictions and wave-particle duality. Relativity (special and general) replaced classical mechanics and gravity for high speeds and strong gravitational fields, showing that space and time are relative rather than absolute. The classical-modern physics divide represents a fundamental shift in understanding reality's nature, not just incremental progress. Interestingly, classical physics remains useful—engineers still use Newtonian mechanics for most applications because it's simpler and accurate enough for non-extreme conditions. Modern physics hasn't made classical physics obsolete but defined its domain of applicability.