stock here: I have run into several flat earther over the last 10 years, and the reason I would take the time to dispel their assumptions and beliefs, is that they can be useful in other ways of societal pushback, especially if they are not immediately discredited by the flat earth lies.
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Here are five thought experiments, based on real-world observations, that demonstrate the Earth is a sphere, not a flat disk.
1. The Disappearing Ship Hull
The Thought Experiment: Imagine standing by the ocean and watching a ship sail away toward the horizon.
- Flat Earth Prediction: On a flat plane, the ship would simply get smaller and smaller until it became a pinprick and then disappeared due to the limits of human vision/perspective. The entire ship would remain visible, just tiny.
- Spherical Earth Observation: What actually happens is that the ship appears to sink below the horizon, hull first. The sails or mast (the highest parts) are the last things you see before they, too, disappear.
- Conclusion: This phenomenon can only be explained by the ship sailing down and around the curvature of a ball-shaped Earth, which blocks your view of the lowest parts first. If you climb up a watchtower as the ship’s mast is about to disappear, the entire ship would reappear for a moment, proving the surface is curved.
2. The Changing Night Sky and Polaris
The Thought Experiment: Imagine traveling a great distance directly south, from the North Pole to the equator and then into the Southern Hemisphere, while observing the night sky.
- Flat Earth Prediction: In the Flat Earth model (often a disk centered on the North Pole), the North Star, Polaris, should always be visible from everywhere on the flat surface, just lower in the sky the further south you go. All the constellations should also appear in the same orientation, regardless of your location.
- Spherical Earth Observation:
- At the North Pole, Polaris is directly overhead (≈90∘ above the horizon).
- At the Equator, Polaris is barely visible, sitting right on the northern horizon (0∘).
- In the Southern Hemisphere (e.g., Australia), Polaris is completely invisible. Furthermore, entirely new constellations (like the Southern Cross) appear, which are never visible from the north.
- Conclusion: The only geometric shape that can explain Polaris dropping from overhead to the horizon, and then disappearing entirely, while revealing new star patterns, is a sphere. As you travel south, you’re rotating your position around the globe, which changes your view of the celestial sphere.
3. Simultaneous Shadows and Time Zones
The Thought Experiment (Eratosthenes’ Method): Imagine two people placing a vertical stick into the ground at noon on the summer solstice, one in the city of Syene (Aswan, Egypt) and one in Alexandria, which is directly north of Syene.
- Flat Earth Prediction: If the Earth were flat and the sun were millions of miles away, its rays would be effectively parallel. Both sticks would cast shadows of the same length at the same time. Even in the Flat Earth “spotlight” model, all clocks would read the same time, or the difference would be inconsistent with the small, local light source model.
- Spherical Earth Observation:
- In Syene, the sun is directly overhead, and the stick casts no shadow.
- In Alexandria, the sun is slightly off-center, and the stick casts a measurable shadow (about 7.2∘).
- Conclusion: The difference in shadow length is explained because the sun’s parallel rays hit a curved surface at different angles. Eratosthenes used this angle difference and the measured distance between the two cities to calculate the circumference of the spherical Earth with remarkable accuracy over 2,000 years ago. A flat Earth cannot logically support both a localized light source (as some flat-earthers propose) and the observable time differences and shadows across great distances.
4. The Geometry of a Lunar Eclipse
The Thought Experiment: Imagine watching a total lunar eclipse, where the Earth passes directly between the Sun and the Moon, casting a shadow on the Moon’s surface.
- Flat Earth Prediction: For a flat, disc-shaped Earth to cast a shadow on the Moon, the shadow would only be circular if the eclipse happened when the Sun and Moon were exactly lined up perpendicular to the flat face. For any other geometry, the shadow would be an oval or a line. Furthermore, the Flat Earth model often places the Sun and Moon much smaller and closer than they are, which makes Earth’s shadow a different, much more complex problem to model than a simple disc.
- Spherical Earth Observation: Regardless of the time of night, the location of the observer, or which way the Earth is “facing” the Sun, the Earth’s shadow on the Moon’s surface is always a circular arc.
- Conclusion: The only object that always casts a perfectly circular shadow, regardless of its rotation or angle to the light source, is a sphere. This observation, noted by Aristotle around 350 B.C., is a clean and undeniable demonstration of Earth’s spherical shape.
5. The Flight Path Conundrum
The Thought Experiment: Imagine planning a commercial flight from Sydney, Australia, to Santiago, Chile, or any other great-circle route in the Southern Hemisphere.
- Flat Earth Prediction: On a flat Earth map (often a disc with Antarctica as an ice wall ringing the edge), a flight between two points in the Southern Hemisphere would be incredibly long, potentially passing over the North Pole or requiring a path that seems wildly inefficient. For instance, a flight from Santiago to Sydney would have to fly over North America or Asia to cross the vast, exaggerated distances near the “rim” of the flat disk.
- Spherical Earth Observation: The flight from Sydney to Santiago is a relatively direct and short path over the Pacific Ocean. The route is an arc, known as a Great Circle route, which is the shortest distance between two points on the surface of a sphere. Such flights are routine and take around 12–15 hours.
- Conclusion: The flight times, fuel consumption, and navigational tools (like GPS) used by every airline in the world are based on spherical geometry. They would be entirely inoperable and inconsistent if the world were a flat disk, especially for Southern Hemisphere travel.
For a visual explanation of these proofs, watch this video: 3 proofs that debunk flat-Earth theory | NASA’s Michelle Thaller | Big Think.
3 proofs that debunk flat-Earth theory | NASA’s Michelle Thaller | Big Think – YouTube
https://www.youtube.com/embed/CGjFAe018oA?hl=en&rel=0&showinfo=0&enablejsapi=1&origin=https%3A%2F%2Fgemini.google.com&widgetid=3&forigin=https%3A%2F%2Fgemini.google.com%2Fapp%2F9381e6b202008679&aoriginsup=1&vf=1 Sources
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