But in four-dimensional spacetime, a rotation in the \(y-z\) plane keeps the entire \(t-x\) plane fixed, so the notion of rotation “about an axis” breaks down. (Notice the pattern: in two dimensions w...But in four-dimensional spacetime, a rotation in the \(y-z\) plane keeps the entire \(t-x\) plane fixed, so the notion of rotation “about an axis” breaks down. (Notice the pattern: in two dimensions we rotate about a point, in three dimensions rotation is about a line, and in four dimensions we rotate about a fixed plane.) In section 9.3, we show that \(L^{ab}\) is conserved.
