The idea of traveling through interstellar space using spacecraft propelled by ultrathin sails may sound like the stuff of sci-fi novels. But in fact, a program started in 2016 by Stephen Hawking and Yuri Milner, known as the Breakthrough Starshot Initiative, has been exploring the idea. The concept is to use lasers to propel miniature space probes attached to “lightsails” to reach ultrafast speeds and eventually our nearest star system, Alpha Centauri.