I came across this picture/sketch on the internet, however there is no any explanation about it:
What is "UNPREDICTIBLE"? "UNSTABLE"? "TOO SIMPLE"? "elliptic", "ultrahyperbolic"??
Some related questions here:
Is 3+1 spacetime as privileged as is claimed?
What makes four dimensions special?
Why are there 4 Dimensions and 4 Fundamental Forces?
Why doesn't the number of space dimensions equal the number of time dimensions?