>>11762306He is talking about freshman classical physics as I said. It's not appropriate to the context of wormholes or cosmology. The idea of negative potential energy is when two masses are infinitely far away the potential energy is zero (or you can set it to any arbitrary constant actually) but as the distance between the masses decreases it needs to become more negative because their kinetic energy is going up.
This is ignoring the energy inherent in the masses themselves, and in general relativity we don't even use the concept of gravitational potential energy. The comment you heard about wormholes is talking about the usual definition of energy density in general relativity
