Dark Energy

The new results narrow the list of possibilities.

Two candidates remain standing, says David Spergel, a theorist in astrophysics
at Princeton University in Princeton, N.J.

One involves an ultralight subatomic particle, dubbed quintessence, that is
associated with the kind of force field that interacts very weakly with matter
and is unstable. Some researchers suggest that this energy drove the rapid
expansion the universe underwent in its inflationary period, calculated to have
happened during the first trillionth of a second after the big bang. Energy from
this quintessence field could be dark energy.

The other candidate is something called vacuum energy ? a form of energy
predicted by quantum physics. This energy would be present even if the universe
had no matter.