The universe's most important number has no units or dimensions

Science · Published 24 October 2026 Swipe more like this →

In short: Unlike the speed of light, which changes depending on your measurement units, the fine-structure constant is a pure, dimensionless number. This unique value characterizes the strength of the electromagnetic force and serves as a fundamental ratio that determines how atoms, molecules, and all biological life are structured in our universe.

While the speed of light is famous, its numerical value depends on the units used. In contrast, alpha is a pure number—approximately 1/137—meaning it remains the same regardless of the measurement system. Because electromagnetism governs chemistry, this tiny number is the reason atoms, molecules, and life can exist. The constant first gained prominence in 1916 when German physicist Arnold Sommerfeld expanded the Bohr model of the atom. He discovered that spectral lines—the specific wavelengths of light emitted by atoms—were split into "fine structure" sub-orbitals. To explain this, Sommerfeld introduced alpha into his equations. Today, it is one of the most precisely measured constants in physics, with a current estimate of 0.0072973525693. It can be measured experimentally by accelerating electrons in magnetic fields at cyclotron accelerators to determine their magnetic moments. The specific value of alpha is critical for the existence of the universe. Because 1/137 is relatively small, electromagnetism is weak enough to allow electrons to orbit at a distance from protons, enabling them to be exchanged to form chemical bonds. However, if the value were different by as little as 4%, stars would be unable to fuse helium into carbon. In 1957, astronomer Fred Hoyle calculated that such a shift would mean carbon and oxygen could not exist. While some speculate its value was set by quantum fluctuations at the Big Bang or by hidden dimensions, many physicists now view its specific value as a "cosmic dice roll. Interestingly, alpha is not strictly constant. According to Quantum Electrodynamics (QED), it changes based on energy levels. During the Big Bang's 10^15 Kelvin era, the value approximated 1/127, eventually hitting 1/137 as cosmic temperatures dropped. However, for almost all practical purposes in our current low-energy world, it remains a stable, defining ratio of our reality.

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