Electron g factor
Atomic & nuclearMeasured
= −2.002 319 304 360 92(36)
- Value
- −2.002 319 304 360 92
- Standard uncertainty
- 3.6 × 10−13
- Relative uncertainty
- 1.8 × 10−13 (0.18 parts per trillion)
- Status
- Measured
- Symbol
- Source
- CODATA 2022 via NIST · NIST entry
Use in a calculation
Plain
LaTeX
Python
# electron g factor, CODATA 2022 (NIST)
electron_g_factor = -2.00231930436092 # standard uncertainty 3.6e-13
# SciPy: scipy.constants.physical_constants['electron g factor']What it is
The ratio of the electron's magnetic moment to the value expected from its spin with the Bohr magneton as the unit. Dirac's theory predicts exactly −2; the small excess, the anomaly, comes from quantum electrodynamics and is measured to about a part in 10¹³, the most precise test of a physical theory.
Equations
- relation to the moment
- anomaly
How the value changed, 1998–2022
Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).
Relative uncertainty
| CODATA | Value (uncertainty) | Relative uncertainty | Change from previous |
|---|---|---|---|
| 2022 | −2.002 319 304 360 92(36) | 1.8 × 10−13 | +4.7 σ of 2018 |
| 2018 | −2.002 319 304 362 56(35) | 1.7 × 10−13 | −1.4 σ of 2014 |
| 2014 | −2.002 319 304 361 82(52) | 2.6 × 10−13 | −0.5 σ of 2010 |
| 2010 | −2.002 319 304 361 53(53) | 2.6 × 10−13 | +0.4 σ of 2006 |
| 2006 | −2.002 319 304 3622(15) | 7.5 × 10−13 | +1.3 σ of 2002 |
| 2002 | −2.002 319 304 3718(75) | 3.7 × 10−12 | +0.2 σ of 1998 |
| 1998 | −2.002 319 304 3737(82) | 4.1 × 10−12 |
“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).