Starship conferences attract a hopeful crowd: researchers, inventors, and hobbyists enthused by the idea of building spacecraft that can fly between star systems. The excitement at these gatherings can make it feel as if anything is possible—but also as if nothing is. Many of the schemes put forward are too vague, and they almost always have too many technological gaps to fill.

In 2015, Philip Lubin, a cosmologist from the University of California, Santa Barbara, took the stage at the 100-Year Starship Symposium in Santa Clara. He outlined his plan to build a laser so powerful that it could accelerate tiny spacecraft to 20% of the speed of light, getting them to Alpha Centauri in just 20 years. We could become interstellar explorers within a single generation. It was quite the hook.

Because Lubin is an excellent public speaker, and because the underlying technologies already existed, and because the science was sound, he was mobbed after the talk. He also met Pete Worden, a former research director of NASA’s Ames Research Center, for the first time. Worden had recently taken over as head of the Breakthrough Initiatives, a nonprofit program funded by Russian technology billionaire Yuri Milner. Six months later, Lubin’s project had $100 million in funding from Breakthrough and the endorsement of Stephen Hawking, who called it the “next great leap into the cosmos.”

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