How much to read into the calculation depends on how uncertain it is, and whether systematic errors associated with the telescope and the analysis skewed the result. “It’s generally accepted that telescope calibration, supernova physics and galaxy properties are big sources of uncertainties, so everyone’s trying to figure these out in different ways,” says Daniel Scolnic of Johns Hopkins University, who led an accompanying paper estimating the data’s uncertainties. “I think that Dan did an excellent job characterizing their systematics,” says Alexander Conley of the University of Colorado at Boulder who worked on a different supernova study called the Supernova Legacy Survey that found similar results. “They still have a lot of work to do to improve the characterization for future papers, but they know that and are working on it.” However, another survey researcher, Julien Guy of University Pierre and Marie Curie in Paris, says the team may have underestimated their systematic error by ignoring an extra source of uncertainty from supernova light-curve models. He’s been in touch with the Pan-STARRS researchers, who are looking into that factor. Ultimately, most experts say the new results are tantalizing, but don’t prove the existence of new physics. “The Pan-STARRS paper presents a very thorough, careful analysis and a solid result, but it doesn't qualitatively change our view of the cosmological parameters,” says Joshua Frieman, an astrophysicist at Fermilab in Batavia, Ill., who was not involved in the research.
The fact that multiple cosmology experiments are producing values of w that diverge from –1, however, is causing many to take notice. “This paper is now the third survey of distant supernovae that’s coming to this conclusion,” says STScI astronomer Adam Riess, a member of the Pan-STARRS team who won the 2011 Nobel Prize in Physics for the discovery of dark energy. “We can’t just say this survey or that survey screwed up. It could be something fundamental to one of these measurements. Or it could be that dark energy is more interesting in a way that actually we hope.” Whereas the cosmological constant explains dark energy mathematically, it does not elucidate why such a force exists. An alternative value of w might indicate that dark energy hasn’t been constant over time, but varies—an idea called quintessence. Either way, more data from Pan-STARRS and other surveys are expected soon to either support or refute the latest value of w. “I expect in the next year or two this will probably either become definitive, or go away,” Riess says.