Measurement
The 2010 CODATA recommended value of α is
This has a relative standard uncertainty of 0.32 parts per billion. For reasons of convenience, historically the value of the reciprocal of the fine-structure constant is often specified. The 2010 CODATA recommended value is given by
While the value of α can be estimated from the values of the constants appearing in any of its definitions, the theory of quantum electrodynamics (QED) provides a way to measure α directly using the quantum Hall effect or the anomalous magnetic moment of the electron. The theory of QED predicts a relationship between the dimensionless magnetic moment of the electron and the fine-structure constant α (the magnetic moment of the electron is also referred to as "Landé g-factor" and symbolized as g). The most precise value of α obtained experimentally (as of 2012) is based on a measurement of g using a one-electron so-called "quantum cyclotron" apparatus, together with a calculation via the theory of QED that involved 12,672 tenth-order Feynman diagrams:
This measurement of α has a precision of 0.25 parts per billion. This value and uncertainty are about the same as the latest experimental results.
Read more about this topic: Fine-structure Constant
Famous quotes containing the word measurement:
“That’s the great danger of sectarian opinions, they always accept the formulas of past events as useful for the measurement of future events and they never are, if you have high standards of accuracy.”
—John Dos Passos (1896–1970)