In 1987, he and two postdoctoral researchers, Chao Tang and Kurt Wiesenfeld, published an article in Physical Review Letters setting a new concept they called self-organized criticality.
I 1987 skrev Bak og to postdoc-studerende, Chao Tang og Kurt Wiesenfeld en artikel til Physical Review Letters, der opsatte et ny koncept kaldet selvorganiseret kritikalitet.