What it takes to produce a gravitational repulsion is a negative pressure. According to general relativity, it turns out... both pressures and energy densities can produce gravitational fields, unlike Newtonian physics, where it's only mass densities that produce gravitational fields.
Alan GuthRelated topics
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The way that the background fields generates mass is rather like the way in which when light passes through a transparent medium like glass or water, it gets slowed down. It no longer travels with the fundamental velocity of light c. And that's the way to think of the generation of mass.
Peter Higgs
No man can be a good citizen unless he has a wage more than sufficient to cover the bare cost of living, and hours of labor short enough so after his day's work is done he will have time and energy to bear his share in the management of the community, to help in carrying the general load.
Theodore Roosevelt