I've been trying to find out what the definition of negative pressure in the context of General Relativity. There are some information on negative pressure and I found this: https://www.physicsforums.com/archive/index.php/t-299495.html The starter of that thread also doesn't know what the physical meaning of negative pressure. According to General Relativity, positive mass, positive energy, and negative pressure leads to repulsive gravity. I read somewhere that repulsive gravity is related to the negative pressure that exists on the cosmological scale or inside spherical objects such as planets. I guess maybe I should explain why I want to know the definition of negative pressure. There's a researcher who's trying to create a device that can spin electrons in a crystal lattice. Since spinning an object that possesses gravitational mass creates a gravito-magnetism (a second gravitational field so to speak), spinning electrons would also create a minuscule gravitational field as well. If you spin these astronomically-large number of electrons in a crystal lattice in the same direction at the same frequency, a coherent gravitational field will emerge. It would seem that the gravitational field is being amplified around the crystal lattice. I think some of you might be already familiar with this technology that is being developed. I was wondering if it's possible to amplify the negative pressure at a given point so to create an amplified coherent gravitational repulsive field. Technology that can produce this effect would have an amazing effect on space exploration development.