Empirical Earth · Rotation & How We Measure It

Measuring Earth's spin — from a flipped tube of water to entangled photons

The claim

“Nobody has ever measured the Earth spinning — it’s just an assumption.”

What is true

A rotation you cannot feel is a fair thing to be suspicious of. Standing still, there is nothing in ordinary experience that tells you the ground is moving.

What is measured

Earth’s spin is pinned to nanoseconds by ring-laser gyros and VLBI (very long baseline interferometry). One rotation takes 23h 56m 04s (a sidereal day), not a flat 24.

What would show this is wrong

ring-laser gyroscopes and length-of-day measurements reading zero net rotation.

Sources

  1. Ring-laser / fiber-optic gyros & inertial navigation. Sagnac-effect optical gyros; gyrocompass alignment senses Earth rate (15.04°/hr). Standard avionics/IRS references (e.g., Honeywell/Nort link
  2. Earth's rotation measured with quantum entanglement. R. Silvestri, H. Yu, T. Strömberg, C. Hilweg, R. W. Peterson & P. Walther, "Experimental Observation of Earth's Rotation with Quantum Ent link
  3. Compton generator (1913). A. H. Compton, "A Laboratory Method of Demonstrating the Earth's Rotation," Science 37, no. 960 (1913), 803–806 — a flipped water ring showing Coriolis drift. Compt link
  4. Wettzell "G" ring laser gyroscope. Geodetic Observatory Wettzell (Schreiber et al.); 4 m square ring laser measuring Earth's rotation / length-of-day; Nature Photonics (2023). Nature Photoni link
  5. Hafele-Keating experiment (1971). J. C. Hafele & R. E. Keating, "Around-the-World Atomic Clocks," Science 177 (1972) — flying-clock confirmation of rotation (Sagnac) and relativistic time di link
  6. Ring-laser gyroscopes measure rotation absolutely (Sagnac effect). The Wettzell “G” ring laser senses Earth’s rotation (~15°/h) to ~1 part in 10⁸ with no external reference, and independentl link
  7. Earth’s rotation, in numbers. One sidereal rotation takes 23h 56m 04.0905s (86,164.0905 s) and the mean solar day is 86,400 s, giving an angular velocity Ω = 7.2921×10⁻⁵ rad/s (15.0411°/h). link
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