But some researchers are coming up with evidence suggesting that something may be missing from GR in any case. Last autumn, teams led by Michael Pierce of Kitt Peak Observatory in Arizona, and Wendy Freedman of the Carnegie Institute of Washington's observatories in Pasadena, California, both announced findings that put the age of the Universe at around 8 billion years. This was embarrassing, because there is sound evidence that some stars in our Galaxy are around twice this age. One way out of this bind would be a vacuum state that did not vanish after inflating the Universe. This would boost the speed at which galaxies race away from each other, and give the impression that the Universe as it is now is nearer to the big bang state and thus younger - than it really is.
Vacuum energy can do more, however.
Though inflation predicts that the density of mass-energy in the Universe is right on the borderline between expansion and collapse, astronomers have only found between 10 and 20 per cent of the required mass. This is another problem that a remnant nonzero vacuum may solve. By Einstein's equation, an energy density is equivalent to a mass density, so vacuum energy could account for some perhaps most of the missing mass. Some cosmologists, notably George Efstathiou at Oxford University, estimate that for vacuum energy to solve these problems it would have to amount to 80 per cent of the mass-energy of the Universe. Chris Kochanek of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, says that observations of gravitational lensing show that it can't.