Maybe the Universe somehow has a natural form of this effect in the intergalactic medium (or in spacetime) that causes negative pressure and is the mechanism of

Maybe the Universe somehow has a natural form of this effect in the intergalactic medium (or in spacetime) that causes negative pressure and is the mechanism of dark energy? "Negative temperatures imply negative pressures and open up new parameter regimes for cold atoms, enabling fundamentally new many-body states."