Once again, the infamous cosmological constant is rearing its head. A constant of integration, this mathematical relic has some serious implications for the end of the universe. We thought we had it nailed down from the last batch of observations, but maybe we were measuring the wrong thing.
First Einstein set the cosmological constant to a fixed value to keep the universe at a steady-state. After Hubble observed the redshift of an expanding universe, it was thrown out for decades. Then a team of experimentalists realized the static in their readings was the cosmic background radiation (and not the original hypothesis, birdshit), radiation from 380,000 years after the Big Bang.
That set off a whole series of observational experiments to detect minute variations in the very cold cosmic background radiation, each with its own fantastic acronym: the Cosmic Background Explorer (COBE) and the Balloon Observations Of Millimetric Extragalactic Radiation ANd Geophysics (BOOMERanG), the Wilkinson Microwave Anisotropy Probe (WMAP), and finally the Planck mission (which makes up for its mundane name by originally going by COBRAS/SAMBA). At the end, we thought we had an answer.
Well, maybe not... Read the embedded post from the main page, then head over here for astronomer Dr. Kate Mack interpreting the original paper, and the io9 write-up.