Empirical Earth · The Boomerangs — Flat-Earth Proofs That Backfire
The claim
“Motion is relative, so you cannot prove the Earth moves. A still, flat Earth is as valid as any other frame.”
What is measured
A reference frame is the platform you measure motion against, and you are free to choose any one. What you cannot choose is what the instruments read. Put the Earth at rest if you like, and its rotation still shows up in every gyro and pendulum. Bend your coordinates however you please, and the Earth stays as round as it was. The relativity of motion is real. The relativity of shape does not exist.
What would show this is wrong
a reference frame in which the Earth’s Coriolis and gyroscope signals fall to zero, or one in which a large triangle on the surface sums to 180 degrees. Neither has been found. Rotation shows in every frame, and curvature is the same in all of them.
Sources
This is one card from Empirical Earth, a free reference that states each flat-Earth claim at its strongest and then answers it with sourced measurements. Nothing is for sale and there are no advertisements.