In May 1889, 37-year-old Irish physicist George Francis FitzGerald (1851–1901) published a short letter in Science (Vol. 13) titled “The Ether and the Earth’s Atmosphere”.

FitzGerald proposed the world’s first explanation for the 1887 Michelson-Morley null result: the Length Contraction Hypothesis (also known as FitzGerald-Lorentz Contraction).

The Length Contraction Formula

FitzGerald hypothesized that any physical body moving through the ether at velocity $v$ undergoes a physical contraction along its direction of motion:

$$L' = L \sqrt{1 - \frac{v^2}{c^2}} = \frac{L}{\gamma}$$

Where:

  • $L$ is the proper length at rest.
  • $L'$ is the contracted length parallel to motion.
  • $\gamma = 1 / \sqrt{1 - v^2/c^2}$ is the Lorentz factor.

Resolution of Michelson-Morley

Because the longitudinal optical arm of the Michelson interferometer contracts by exactly $\sqrt{1 - v^2/c^2}$, the extra round-trip time required by light traveling parallel to Earth’s motion is perfectly compensated, producing a zero optical fringe shift!

Transition to Einstein’s Special Relativity (1905)

In 1892, Hendrik Lorentz independently derived the same formula from electron theory.

In 1905, Albert Einstein proved that length contraction is not a physical deformation caused by ether pressure, but an inherent geometric property of Relativistic Spacetime.

Key Takeaways

  • Year: 1889
  • Key Figure: George Francis FitzGerald (Irish Physicist)
  • Core Discovery: Proposed Length Contraction ($L' = L / \gamma$), explaining the Michelson-Morley null result.
  • Spacetime Geometry: First introduction of the contraction factor $\sqrt{1 - v^2/c^2}$ into mechanics.
  • Quantum Relevance: Relativistic length contraction governs high-energy particle accelerators and relativistic quantum states.