Quote:
http://blogs.discovermagazine.com/cosmicvariance/2011/10/04/dark-energy-faq/


Interesting link, Orac. I struggled with this, though.

The answer to the question:

“If negative pressure is like tension, why doesn’t it pull things together rather than pushing them apart?”

is as follows:

“Sometimes you will hear something along the lines of “dark energy makes the universe accelerate because it has negative pressure.” This is strictly speaking true, but a bit ass-backwards; it gives the illusion of understanding rather than actual understanding. You are told “the force of gravity depends on the density plus three times the pressure, so if the pressure is equal and opposite to the density, gravity is repulsive.” Seems sensible, except that nobody will explain to you why gravity depends on the density plus three times the pressure. And it’s not really the “force of gravity” that depends on that; it’s the local expansion of space.
The “why doesn’t tension pull things together?” question is a perfectly valid one. The answer is: because dark energy doesn’t actually push or pull on anything. It doesn’t interact directly with ordinary matter, for one thing; for another, it’s equally distributed through space, so any pulling it did from one direction would be exactly balanced by an opposite pull from the other. It’s the indirect effect of dark energy, through gravity rather than through direct interaction, that makes the universe accelerate.
The real reason dark energy causes the universe to accelerate is because it’s persistent.”

Perhaps it’s just me, but this doesn’t seem to answer the question.

There never was nothing.