How to verify that Earth is not flat
2026-05-02 02:06 by Ian
I think the flat-earth crowd are either master trolls, and don't really believe what they claim, or they are disinformation agents, and don't really believe what they claim. In either case, I'm not in on the joke. So here is a good-faith explanation that I'm tired of typing out for the third time. There are any number of ways that you would be forced into concluding the Earth is a globe, but let me give you my favorites.
For a few thousand dollars, and some travel expenses, you can verify for yourself that the Earth is spheroidal. Please allow me to introduce you to a beautiful piece of praxis: laser ring gyroscopes. Or LRG's, going forward.
LRGs are amazing devices because they take advantage of a physical phenomenon so fine in scale, that the daily rotation of the Earth is well above their noise floor. That is to say, you can see the rotation of the Earth unambiguously, even if that rotation is as slow as 360-deg/day. And they come in sturdy 3-axis varieties powered by batteries. Which will be important for your upcoming travel plans.
At the poles, the rotation of the gyro would be entirely about the vertical axis (a constant yaw, in AHRS terms). At the opposing pole, the same rotation will be present, but in the opposite direction. On your way between poles, there will be a point where the daily rotation is orthogonal to the vertical, depending on which direction you are oriented. If you face your instrument N or S, you will see a constant roll of 360-deg/day. If you face E or W, it will be a constant pitch.
Nothing but a globe explains this. You could learn the same thing with a Foucault pendulum, but it would take much more effort.
I have heard some flat-earth people explain the operation of Foucault pendulums by saying: "Well the flat disc is rotating, of course. Once per day."
Yet, there is no radially-acting force tangent to the surface. There is, however, a radial force countering gravity that makes things weigh slightly (but measurably) more at the poles, where there is no centripetal component to their motion to offset gravity. Objects "standing still" at the equator are actually hauling ass, in absolute terms (something like Mach 1.4, if the atmosphlat wasn't also rotating with it). So if you prefer to use a very accurate scale, instead of a very accurate gyroscope, you could do it that way, as well.
I'm too broke to afford a 3-axis LRG
If you don't want to spend the money on instrumentation, you could get by with patient observation, as the ancients did. By choosing guide stars for various purposes, you can over the course of travel N/S, find the horizons of those guide stars. That their visibility on the horizon night-to-night is a function of your latitude should convince you that the horizon (flat as though it may look at your perceptual scale, is spherical.
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