Linearity refers to the proportion and linear relationship between quantities, which can be mathematically understood as a function with a constant first derivative; Nonlinear nonlinearity refers to the relationship between proportionality and linearity, and the first derivative is not constant.

For example, how many times is the eyesight of two eyes more than that of one eye? It's easy to think it's twice, but it's actually 6- 10! This is nonlinearity. Laser is also nonlinear! The motion of celestial bodies is chaotic; The oscillation of electricity, light and sound waves will suddenly fall into chaos; The geomagnetic field changed direction 16 times in 4 million years, also because of chaos. Even human beings are inherently nonlinear: contrary to traditional thinking, the EEG and heartbeat of healthy people are not regular, but chaotic, and chaos is the expression of vitality. Chaotic systems respond faster to external stimuli than non-chaotic systems.