Robert McCausland

@robertmcc

Personal account all comments my own. Mostly science and cyber, like Linux and 🐧 Identity and Access management specialist Robert McC

Northern Ireland

Joined October 2007

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Philosophy Of Physics

@PhilosophyOfPhy

about 1 month ago

What if you cannot see inside an atom, but the light it emits follows an exact mathematical pattern? How much could that pattern tell you about what exists inside? In the hydrogen spectrum experiment, an electric discharge passes through hydrogen gas at low pressure. Collisions excite the hydrogen atoms, and a prism or diffraction grating separates the emitted light by wavelength. Instead of producing a continuous rainbow, hydrogen produces distinct lines: red near 656.3 nanometres, blue-green near 486.1 nanometres, and violet lines near 434.0 and 410.2 nanometres. Using wavelength measurements published by Anders Ångström, Johann Jakob Balmer discovered in 1885 that these visible lines followed a simple numerical rule. Written in its modern form: 1/λ = R_H(1/2² − 1/n²), n = 3, 4, 5, … Each integer generated one of the measured wavelengths. The formula could describe the pattern and predict further lines, but it did not explain why hydrogen emitted only those particular wavelengths. In 1913, Niels Bohr gave the integers a physical meaning. He proposed that the hydrogen atom could occupy only certain stationary energy states. Each visible line appeared when the atom moved from a higher energy state to the state labelled n = 2, emitting the energy difference as a photon. Bohr’s picture of electrons travelling in fixed classical orbits was later replaced by quantum mechanics. But the connection between discrete energy states and spectral lines remained. Bohr later recalled: “As soon as I saw Balmer’s formula, the whole thing was immediately clear to me.” The experiment did not show scientists the inside of an atom. It made the atom’s hidden energy structure measurable through light.

$PhilosophyOfPhy's tweet photo. What if you cannot see inside an atom, but the light it emits follows an exact mathematical pattern? How much could that pattern tell you about what exists inside? In the hydrogen spectrum experiment, an electric discharge passes through hydrogen gas at low pressure. Collisions excite the hydrogen atoms, and a prism or diffraction grating separates the emitted light by wavelength. Instead of producing a continuous rainbow, hydrogen produces distinct lines: red near 656.3 nanometres, blue-green near 486.1 nanometres, and violet lines near 434.0 and 410.2 nanometres. Using wavelength measurements published by Anders Ångström, Johann Jakob Balmer discovered in 1885 that these visible lines followed a simple numerical rule. Written in its modern form: 1/λ = R_H(1/2² − 1/n²), n = 3, 4, 5, … Each integer generated one of the measured wavelengths. The formula could describe the pattern and predict further lines, but it did not explain why hydrogen emitted only those particular wavelengths. In 1913, Niels Bohr gave the integers a physical meaning. He proposed that the hydrogen atom could occupy only certain stationary energy states. Each visible line appeared when the atom moved from a higher energy state to the state labelled n = 2, emitting the energy difference as a photon. Bohr’s picture of electrons travelling in fixed classical orbits was later replaced by quantum mechanics. But the connection between discrete energy states and spectral lines remained. Bohr later recalled: “As soon as I saw Balmer’s formula, the whole thing was immediately clear to me.” The experiment did not show scientists the inside of an atom. It made the atom’s hidden energy structure measurable through light.$

Robert McCausland

@robertmcc

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