Updated: Sep 21, 2021
There is not even a single observable, measurable, repeatable and testable scientific experiment that proves the curvature of the earth. Let us start with spherical trigonometry, the formula for measuring rate of drop due to curvature. To find out the drop due to curvature we need to multiply 8 inches to the square of the distance. For example if the height of the observer from ground level is 6 ft and the object is at a distance of 40 miles, then the target hidden height would be 912.94 feet. Here is the link to the curvature calculator based on spherical trigonometry.
Now lets verify this curvature anywhere on earth and try to prove wrong everyone who believe that they are living on a flat/plane/level earth.
Example 1 - It is often possible to see the Chicago skyline from sea-level 60 miles away across Lake Michigan. In 2015 after photographer Joshua Nowicki photographed this phenomenon several news channels quickly claimed his picture to be a “superior mirage,” an atmospheric anomaly caused by temperature inversion. While these certainly do occur, the skyline in question was facing right-side up and clearly seen unlike a hazy illusory mirage, and on a ball-Earth 25,000 miles in circumference should be 2,400 feet below the horizon.
Neither the spherical trigonometry formula nor the authenticity of the picture has been challenged by anyone till date.
Example 2 - From Genoa, Italy at a height of just 70 feet above sea-level, the island of Corsica can often be seen 99 miles away. If Earth were a ball 25,000 miles in circumference, Corsica should fall 5,245 feet, almost an entire mile below the horizon.
Example 3 - From Genoa, Italy 70 feet above sea-level, the island of Capraia 102 miles away can often be seen as well. If Earth were a ball 25,000 miles in circumference, Capraia should always remain hidden behind 5,605 feet, over a mile of supposed curvature
Also from Genoa, on bright clear days, the island of Elba can be seen an incredible 125 miles away! If Earth were a ball 25,000 miles in circumference, Elba should be forever invisible behind 8770 feet of curvature.
Mountains of Canigou from height of 1000 feet and a distance of 175 miles. The hidden height should be 12380 feet. mountain peak is 9000 feet!! mountains are clearly NOT 3000 feet behind the curvature.
Now if you are really interested in doing some calculations, start your research on the visibility of Himalayan mountain range. Figure out till how far can the mountain range be seen. Check the distance and the drop due to curvature the curvature calculator link I shared above. Tell me in the comments whether there is any possibility of a spherical earth. Good Luck!