Quantum Foundations – Origins of Modern Physics Explained

Quantum Foundations | Modern Physics

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Transition from classical physics to quantum physics — Quantum physics emerges when classical ideas fail at microscopic scales.

Central idea
Quantum physics arose because classical physics could not explain atomic-scale phenomena.

1. Crisis of Classical Physics

By the end of the 19th century, classical physics seemed complete. However, several experiments produced results that could not be explained using Newtonian mechanics or classical electromagnetism.

2. Blackbody Radiation

Classical theory predicted infinite energy emission at high frequencies, a result known as the ultraviolet catastrophe.

Blackbody radiation curves showing classical failure — Classical predictions diverge at high frequencies, contradicting experiments.

Max Planck resolved this by proposing that energy is exchanged in discrete packets.

3. Photoelectric Effect

When light shines on a metal surface, electrons are emitted only if the light frequency exceeds a threshold value.

Photoelectric effect experiment — Electron emission depends on frequency, not intensity.

This showed that light behaves as particles called photons.

Einstein explained the effect using photons with energy $E = h\nu$ , giving the relation for maximum kinetic energy $K_{\max} = h\nu - \phi$ , where $\phi$ is the work function.

4. Wave–Particle Duality

Light behaves as both a wave and a particle. Surprisingly, matter such as electrons also exhibits wave-like behavior.

Electron interference pattern demonstrating wave-particle duality — Individual particles collectively form wave interference patterns.

5. de Broglie Hypothesis

Louis de Broglie proposed that every particle has an associated wavelength.

$\lambda = \frac{h}{p}$

Matter waves associated with particles — Matter exhibits wave properties at microscopic scales.

6. Heisenberg Uncertainty Principle

It is fundamentally impossible to know both the exact position and momentum of a particle simultaneously; their uncertainties obey $\Delta x\, \Delta p \ge \frac{\hbar}{2}$ .