FE Meme
Einstein vs Foucault on Earth's Motion
#207: Foucault's pendulum (1851) cannot square with Einstein's 1922 claim that Earth's motion cannot be detected by optical experiment.
The Meme
Split poster: historical Foucault engraving above Einstein portrait quoting motion undetectable by optical experiment.
Why It Spreads
Pairing Foucault's 1851 pendulum with a mined Einstein quote about optical experiments looks like an internal contradiction in physics. Historical portraits and dates add textbook gravitas, so viewers assume mainstream science disagrees with itself about whether Earth's motion can be detected.
What It Gets Wrong
The split poster juxtaposing Foucault's 1851 pendulum engraving with a clipped Einstein quote about Earth's motion being undetectable by optical experiment merges two unrelated questions. Foucault pendulums and ring-laser gyros measure mechanical rotation at ~15°/h without violating relativity; Einstein discussed optical isotropy in inertial frames and the absence of a preferred ether rest frame, not whether astronomical instruments detect spin. VLBI Earth orientation parameters update daily alongside mechanical gyros, so an optical-frame snippet is not a pendulum cancel button. TestTheGlobe's Foucault Pendulum Strawman and TestTheGlobe's Earth Rotation Speed walk through the observations and predictions this image skips.
The Debunk
The split poster juxtaposes Foucault's 1851 pendulum engraving with a clipped Einstein quote about Earth's motion being undetectable by optical experiment, conflating two different questions. Foucault and ring-laser gyros measure mechanical rotation at ~15°/h; Einstein's 1922 remark concerns optical frame definitions, not a denial that Earth spins.
- Foucault pendulums precess at a rate tied to latitude and Earth's ~15°/h spin; TestTheGlobe's Foucault Pendulum Strawman explains what the 1851 demo actually tests and why the Einstein snippet is misapplied.
- Uniform rotation at ~1670 km/h equatorial speed is not felt as wind because the atmosphere co-rotates; TestTheGlobe's We Do Not Feel Earth Moving separates spin from the optical-frame discussion the meme merges.
- VLBI and ring-laser gyros measure Earth rate directly in degrees per hour; TestTheGlobe's Earth Rotation Speed quantifies the rate the juxtaposition does not refute.
- Equatorial centrifugal effect slightly reduces apparent weight; TestTheGlobe's Effective Gravity includes that ~0.3% signature absent from a strictly non-rotating model.