# Week 2: 笑わない数学者 - Mathematical Goodbye (S&M Vol.3)

Yes :-)

When I read that passage, I thought about two different examples (they are not exactly the same but somehow related, I think).

The first is a very old attraction (I think it existed in the 80’s already); it is a dome where a video gets projected from the inside. People would just stand inside (on the concrete floor) and watch the video. Usually the video has a shock-effect like e.g. I once watched a helicopter flight over the Grand Canyon or something, filmed from the helicopter down. First you would see the top of the cliff, and then all of a sudden the helicopter would fly across the edge of the cliff and you look down like 1000 meters or so. There are usually a few people that fall down onto the ground (on their own, just from watching) because the brain somehow reacts to the visuals and forces the body to move in order to counter-balance a movement that is not actually there, which leads to them falling. So here you have bodily reactions without actual movement, which is sort of the inverse of our case.

The second one is much more technically sophisticated and newer (I think it came out in the mid-90’s); it is also a dome, and people get to sit in a little cart (maybe 6 rows of 4 people each or a bit larger) inside the dome. This cart is being moved in a super-precise way to match up the scene that is projected onto the dome. In my case it was a dystopian roller-coaster ride through open space, with the roller-coaster cart leaving the (broken) tracks, flying through the air and landing on the tracks on the other side of the gap, etc. It felt so realistic to me that it took me a few minutes to realize that we did not actually move at all, and I only realized because there was no wind from the movement

Today I also remembered this phenomenon when you sit in a train that stands in a train station, and sometimes when the neighbor train would start to leave the train station, it sometimes feels to me as if my own train started moving and we are going in the opposite direction.

In all these three cases visuals are strong enough to “override” bodily sensations (or the lack thereof). Especially the last example makes me think that if we think that the train moved although it did not move, then its real movement must be so subtle that we usually don’t notice it at all. (At least for the first few meters.)

Back to our scene with the rotating main hall: If the visuals are strong enough (e.g. the sky is rotating as well) I guess that might override any real movement we are experiencing, thus leaving us with the impression that it was “just the rotating projection”.

This calls for an interesting experiment: If you close your eyes and plug your ears, will you notice whether a train starts moving? (Given it is a high-speed train with good cushioning and stuff, not a simple tram.) I’m not sure I would…

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