An axion is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics. If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.
Within a year Niels Bohr had a model of the hydrogen atom that “explained” the spectral lines. Bohr introduced a new concept, the energy level. The electron in hydrogen had certain allowed energy levels, and the sharp spectral lines were emitted when the electron jumped from one energy level to another.
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An axion is a hypothetical elementary particle postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics. If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.
Answer:
Within a year Niels Bohr had a model of the hydrogen atom that “explained” the spectral lines. Bohr introduced a new concept, the energy level. The electron in hydrogen had certain allowed energy levels, and the sharp spectral lines were emitted when the electron jumped from one energy level to another.