From the September 2007 issue

Does the fact that our universe is accelerating imply that it will expand forever?

Norman Phillips, Branchville, New Jersey
By | Published: September 1, 2007
We don’t know why the universe’s expansion is accelerating. This acceleration may be propelled by some form of “dark energy” that has negative pressure and, therefore, is a repulsive gravitational force. If dark energy is Einstein’s famous “cosmological constant,” then the universe will expand forever.