How to Visualize a Sagging Mattress

i love that you help me understand it by calling it a sagging mattress. I can't visualize it. So what makes you think out of seven billion people, you're going to be the one who can? i'm being snarky. No, well, our minds evolve to make use of a certain universe and they're very good at doing that. It's easier to do the math on the paper than to actually visualize it into visualize anything in four dimensions.