The “Flat-Earthers” continue to insist that the earth is flat, and that the only way to find out if it is flat or spherical is to go into space and look at it with your own eyes. The claim is that any human that has never been into space simply cannot know if it is true or not. This claim is totally untrue.
Here is how to see for yourself that the earth has curvature:
get on a ship or ferry or boat, and travel away from shore. As you travel, you will notice the features of land that rise up from the coast, being increasingly concealed from the bottom up as you travel further away. You will see less and less of mountains, only seeing their peaks, and eventually you will not be able to see land. That is, gradually the land features disappear below the horizon.
Flat Earthers claim that this effect is due to refraction, or the bending of light. Yet you can see this effect no matter what the weather, or conditions. We also know that red light bends less than blue light – if refraction caused this effect, you would see the distant land features start to separate into blue and red hues. this doesnt happen when i observe it.
Edit: Notably, Flat-Earthers always refer to experiments done over water, where refraction is known to cause light to bend downward, thus allowing objects below the geometric horizon to be visible. But, this effect is dependent on the weather and conditions at the time, and will not always occur.
So, if it is so easy to see the effect of the curvature of the earth, why do some people continue to insist that the earth is flat? What do they gain from doing this? Perhaps they are doing it simply to get attention, to be noticed in a world full of people successfully getting attention for themselves. Perhaps they get satisfaction from deceiving others, and can conclude that they are definitely superior to those they deceive – thus getting a sense of security form this. Perhaps other reasons associated with cults.
You can be certain that anyone making this claim is lying, intentionally or unwittingly. Those lying intentionally derive a creepy sense of glee at deceiving others. Those lying unwittingly suffer from a state of mind that is able to accept something is true without evidence, and dont wish to investigate themselves. Such people are gullible, and this is found in humans that have been punished at a young age for questioning authority. Gullible people may be very intelligent, they just have learned to accept as true whatever they are told by those who they trust.
Edit in response to a comment:
i got a comment from a “flat-earther” claiming that when looked at through a powerful telescope, the parts of objects hidden below the horizon can once again be seen. Because it is a “matter of perspective” It follows that any use of magnification will begin to reduce the effect of things appearing to be hidden below the horizon. However, in my experience with binoculars and telescopes, there is no difference at all, no reduction in obscuring by th horizon. i expect flat-earthers will simply claim that i havent used a telescope powerful enough. yet this implies that at a particular optical magnification, there is a threshold, above which the horizon cannot obscure distant objects.
Also there is the issue of those who travel around the world. Flat-earthers claim that they are simply traveling in a circle – and that Antarctica forms a ring around the flat earth. if this is the case, then the sun and the moon must also be traveling in a circle.
Really, the flat-earthers will create a claim to oppose any claim made by those who believe the earth is a sphere. Their primary strategy is to create claims that make people uncertain about what they have learned, and what they have experienced. It requires just a little logic to analyse these opposing claims. Also, the flat-earthers are not putting in their effort for no gain. They either believe they are speaking the truth, or they are intentionally trying to lead others astray. there are emotional and social motivations for each reason.