Lockheed Martin’s announcement last week that it had secretly developed a promising design for a compact nuclear fusion reactor has met with excitement but also skepticism over the basic feasibility of its approach.

Ian Hutchinson, a professor of nuclear science and engineering at MIT, says he was only able to comment on what Lockheed has released—some pictures, diagrams, and commentary, which can be found here. “Based on that, as far as I can tell, they aren’t paying attention to the basic physics of magnetic-confinement fusion energy. And so I’m highly skeptical that they have anything interesting to offer,” he says...