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Failure of classical physics
Beginner
Blackbody, photoelectric effect and atomic spectra defeated classical theory.
By 1900 classical theory failed on blackbody radiation (the ultraviolet catastrophe), the photoelectric effect, atomic stability and line spectra, and the heat capacity of solids at low temperature. These failures pointed to energy being quantised.
Classical theory predicted infinite energy in the ultraviolet from a hot body.
Classical physics remains valid as a limit of quantum theory.
In more detail
Classical physics could not explain blackbody radiation, the photoelectric effect, atomic spectra or the stability of atoms. These failures led to quantum theory in the early twentieth century.
Real-world uses
- Quantum theory underpins modern electronics, lasers and chemistry.
- Engineers rely on quantum models to design semiconductor devices.
- Physicists designing LEDs and solar cells rely on quantum ideas, because classical physics cannot explain how light and matter exchange energy.
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Frequently asked questions
Did classical physics fail completely?
No. It works very well for everyday objects, and quantum theory reduces to it in the appropriate limit.
When did the crisis happen?
Mostly between 1880 and 1920, as experiments contradicted classical predictions.
Why did classical physics fail?
It predicted infinite energy for blackbody radiation at short wavelengths, and could not explain discrete atomic spectra or the photoelectric effect.
Related topics in Quantum Mechanics
Planck's quantum hypothesis · Planck's constant · Photoelectric effect