For 25 years, Ross Hoffman has had a vision: to use tiny changes in the environment to alter the paths of hurricanes, slow down snow storms and turn dark days bright. For most of those years, Hoffman kept his ideas largely to himself. His adviser at the Massachusetts Institute of Technology told him weather control was too outlandish for his Ph.D. thesis. The chances of a buttoned-down foundation or government agency funding such research were so slim, Hoffman didn’t even bother to ask. But, in 2001, all that changed. Hoffman stumbled upon a tiny, obscure cranny of the American space program — the NASA Institute for Advanced Concepts, or NIAC. In this $4 million-a-year agency, Hoffman found a place where the wildest of ideas were not only tolerated, they were welcome.