From Nature News:
Much of what scientists know about the relative contributions of dark matter and dark energy comes from the relic radiation left behind from the Big Bang, called the cosmic microwave background. The most exhaustive study of it — essentially a portrait of the young Universe at about 400,000 years of age — was done in recent years by the European Space Agency’s Planck observatory. Based on Planck’s measurements, cosmologists can predict how that young Universe will evolve, including how fast it expands at any point in its history.
For years, those predictions have disagreed with direct measurements of the current rate of cosmic expansion — also known as the Hubble constant. But until now the error margins in this constant were large enough that the disagreement could be ignored. More.
Expansion is roughly 8% faster than Planck data predictions. One possibility is that the index stars (“standard candles”) aren’t as reliable as hoped. Another is that dark energy is stronger than it used to be. Anyway, something isn’t quite adding up.