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 | Last updated on May 18, 2023
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.