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 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
The full entry, with the working →