Nuclear fusion has always been the holy grail of energy: it’s endlessly productive and largely clean—and so far, it’s remained elusive. But in October, Lockheed Martin said it had achieved a technological breakthrough that will enable it to make compact fusion reactors small enough to fit on the back of a truck within a decade. The design uses “magnetic mirror confinement” to control the reaction. Absent further details on how it works, some outside scientists are skeptical. But if Lockheed really can produce a workable fusion reactor, the world of energy may never be the same.