Re: In what universe is this hard science?
I think that that is a rather simplistic view of the way in which scientific ideas develop. The reality is more nuanced, and indeed the authors of the paper state that:
"The mechanism could therefore be a natural explanation for the observed correlations between past climate variations and cosmic rays, modulated by either solar activity or caused by supernova activity..."
Furthermore, there was a degree of hypothesis testing. The authors, after having used some nifty mathematical modelling, raised the hypothesis that cosmic rays could increase the size of cloud condensation nucleii, and tested this experimentally, and in doing so failed to disprove the hypothesis.
Very few things are absolutely (dis)provable in science: hypothesis are put forward, tested and evidence accumulated. This leads to a "best current view" of the world, although what "best" is is rarely uncontentious, and most scientists would anyway acknowledge that their "best current view" is a best incomplete, and very likely incorrect in some aspects.