Later on, when I asked him how he came to start his company SpaceX, the audacity of his answer startled me. “For a long time,” he answered, “I’ve thought that it’s inevitable that something bad is going to happen on a planetary scale—a plague, a meteor—that will require humanity to start over somewhere else, like Mars. One day I went to the NASA website to see what progress they were making on their Mars program, and I realized that they weren’t even thinking about going there anytime soon. “I had gotten $180 million when my partners and I sold PayPal,” he continued, “and it occurred to me
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