In April 1881, 28-year-old U.S. Navy Master and physicist Albert Abraham Michelson (1852–1931), working in Hermann von Helmholtz’s laboratory in Potsdam and Berlin, published his breakthrough paper in the American Journal of Science (Vol. 22) titled “The Relative Motion of the Earth and the Luminiferous Ether”.

Michelson invented the Michelson Interferometer—an optical instrument using amplitude-splitting beam splitters to measure distances to fractions of an optical light wavelength ($\sim 10\,\text{nanometers}$).

Optical Design & Interference Fringe Mechanics

The Michelson Interferometer splits a coherent light beam into two perpendicular optical arms ($L_1, L_2$) that reflect off flat mirrors and recombine:

1. Optical Path Difference ($\Delta d$)

Light from a source strikes a half-silvered beam splitter at $45^\circ$, dividing into two orthogonal beams:

$$\Delta d = 2 (L_1 - L_2)$$

2. Interference Condition

When the recombined light waves meet at the observer eyepiece:

  • Constructive Interference (Bright Fringe): $2(L_1 - L_2) = m \lambda \quad (m = 0, 1, 2, \dots)$
  • Destructive Interference (Dark Fringe): $2(L_1 - L_2) = \left(m + \frac{1}{2}\right) \lambda$

1881 Potsdam Ether Drift Test

Michelson used his new interferometer to test whether Earth moves through a stationary “luminiferous ether” at orbital velocity $v \approx 30\,\text{km/s}$. He detected no significant fringe shift, concluding that ether drift was far smaller than predicted.

Key Takeaways

  • Year: 1881
  • Key Figure: Albert A. Michelson (American Physicist)
  • Core Discovery: Invented the Michelson Optical Interferometer, achieving nanometer optical precision.
  • Nobel Prize: Awarded the 1907 Nobel Prize in Physics (first American Nobel laureate).
  • Quantum Relevance: Underpins modern laser gravitational wave observatories (LIGO) and quantum optical interference.