I stand up and I look at two parallel railroad tracks. I find that converge away from me. Why? Can someone explain me why parallel lines seem to converge, please?
Answer
Keep in mind that your eyes perceive a fixed field of view. That is, you see a certain angle in front of you. They do not see a fixed distance across your line of sight. This means that the farther away for you you look, the more distance there is from one side of your FOV to the other. When you look at parallel railroad tracks that maintain a certain distance apart, they seem to converge as they go off into the distance. This is because the proportion of your field of view that the tracks take up diminishes.
Let's say the tracks are $x$ meters apart and close to you, your FOV encompasses $6x$ meters across. That means $1/6$ of your field of view is taken up by the tracks' separation. But far away from you, your field of view might encompass $600x$ meters across. This means the tracks would have converged to only take up $1/600$ of your FOV. They're still the same distance apart, but the distance between them takes up less of your field of view. The brain interprets this as converging because if an image did this that was at the same distance in front of you throughout, it would actually be converging.
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