At this point, I think there’s been a paper averaging almost every day for the past 12 years with theorists of physics trying out different ideas for what could be the explanation. If you ask almost any of them, ‘Do you stand behind your theory? Is this the answer?’ I think almost every one would say, ‘No, no no. I’m just trying to expand the range of possibilities.’ We really don’t know what’s going on.
— A Nobel Prize-winning physicist says if you’re puzzled by what dark energy is, you’re in good company.