You can integrate happiness over the proper time along those world lines; I suspect that’s equivalent to integrating a happiness density that looks like SUM_i h_i(t) delta(x—x_i(t)) over spacetime.
You can integrate happiness over the proper time along those world lines; I suspect that’s equivalent to integrating a happiness density that looks like SUM_i h_i(t) delta(x—x_i(t)) over spacetime.