For decades, cosmologists have had an awkward number sitting at the center of their equations. The universe is expanding, and that expansion began speeding up in the recent cosmological past. The usual way to describe that behavior is with a positive cosmological constant, often written as Λ. But when physicists try to calculate that value using quantum field theory, the answer comes out wildly wrong, up to 120 orders of magnitude larger than what astronomers actually observe. That mismatch is one of the biggest unresolved problems in modern physics. A new paper in Physical Review D does not claim to solve it outright. But researchers from the University of Thessaly in Greece argue that a strange ingredient from quantum gravity, microscopic wormholes flickering through spacetime foam, could generate an effective cosmological constant of the right kind, and possibly behave like a dark energy sector as well. Wormholes do not act as dark energy in a simple, direct sense. (CREDIT: iStock images) Where the mismatch begins The paper starts from a familiar tension in cosmology. One …