Elon Musk’s plans refer to an idea conceived in the 1960s. What is the Kardashev scale?

By Jacopo Prisco, CNN (CNN) — Elon Musk’s plans for the future of SpaceX, and humanity, are rooted in an idea conceived in the 1960s when astronomers began to pick up mysterious, unknown radio sources in the cosmos. Soviet astronomer Nikolai Kardashev was a pioneer in the search for extraterrestrial intelligence at the time, and