The Importance of Mass in the Universe

When we think about gravity also not just like the inertial nature of the thing but also the gravitational nature the thing how much it bends space time it makes the most sense to think about rest mass. Newtonian momentum is not conserved in the universe it's only this Einsteinian momentum mass times velocity times this gamma factor that's actually conserving in the universe. Noether's theorem says that for every symmetry in the universe there is a conserved quantity.