Negative Gravity (not dark matter)

[Duzza]

This theory just dawned upon as i feel asleep-

In the same sense matter bends spacetime fabric to create the force of gravity (matter and light are attracted to it), is it possible for spacetime fabric to be inverted, so matter and light flow (repel) away from this 'negative gravity'?

Instead of a ditch, a hill.

[relativityfan]

well I do not know the answer for this question but here is a hint:
the stress energy tensor determines how gravity curves spacetime. if pressure increases, then gravity increases. a decrease of pressure would lead therefore to a relative antigravity.
I am thinking of the electromagnetic stress energy tensor, because it demonstrates negative components.
Could one say whether such stress energy tensor can contribute to a decrease of pressure or of gravity, especially since electromagnetism can be attractive or repulsive?

[Ich]

Yes, pressure gravitates. In geometric units and relatively symmetric circumstances, the effective mass density for gravitation is \rho+3p. If you have p=-\rho, you have double antigravity. A "substance" with this equation of state is called Dark Energy and is believed to make up 73% of the total universe mass.