There’s an old joke about nuclear fusion: It’s the energy source of the future — and always will be. When headlines blared last month that researchers at Lawrence Livermore National Laboratory had hit on a history-making fusion breakthrough, the future felt one giant step closer. To get a sense of just how much closer, we reached out to Jim Bray, who’s worked for GE Research for 48 years and is now a chief scientist in its electrical power group — and the company’s go-to expert on all things fusion (including that joke).