Ethan Siegel in Forbes:
In 1998, the two leading independent collaborations working to measure distant supernovae in the Universe reported the same bizarre findings: they seemed to indicate that the Universe was accelerating. The only way to explain how distant these lights appeared was if the fabric of space was expanding at a rate that wasn’t decreasing like we’d expect, and if the most distant galaxies were receding faster and faster, despite the pull of gravity. Over the next 13 years, the evidence grew stronger and stronger for this picture, and in 2011 three pioneers in the field were awarded the Nobel Prize. And then, just last week, a new study came out alleging that the supernova evidence for this picture was marginal at best. The study concludes that perhaps the Universe hasn’t been accelerating, after all.
But is that fair and correct? Certainly the news reports are claiming it is, but what does the science say? Let’s start with what the supernova data is, and what it’s told us so far.