The other train appears to move backward because youโre on a faster train. It creates relative motion that tricks your brain. Think of it like passing a slow car โ it seems to reverse.
When youโre sitting on a train, your train feels like your own little world thatโs standing still. But really, your train is moving forward at a certain speed.
Now, when another train passes going the same direction, itโs also moving forward. But if your train is moving faster, the other train looks like itโs falling behind you. Your brain sees the difference in speeds and interprets this as the other train going backward, compared to you.
Itโs like if youโre jogging past a walker. Even though youโre both moving forward, to you it looks like youโre leaving the walker behind.
Hereโs why the illusion is so convincing:
As the other train goes by, you first see the front cars, then the middle cars, and then finally the back cars. This sequence tricks your brain because itโs exactly how something would look if it was actually moving backward!
So in reality, both trains are still traveling forward at their own speeds. The illusion comes from your perspective on the faster train. An observer on the platform would just see two trains moving forward at different speeds.