Imagine a computer the size of a solar system. For power, it would use a Dyson sphere—a solar array that completely surrounds the host star to collect almost all of its energy. That energy-collecting sphere would double as an ultra-powerful computer processor. Once the sphere had collected all the energy it needed, it would pass the excess to another larger Dyson-sphere processor that completely surrounded the first, repeating the process until all of the energy was being used. That's why this theoretical computer is called a Matrioshka brain: the nested Dyson spheres would resemble matryoshka dolls, or Russian nesting dolls.

Of course, if you surround your star with Dyson spheres, it would be difficult for life on your planet to continue. That's kind of the point: this Matrioshka brain would be so powerful that a species could upload their entire consciousness into it and live within an alternate universe simulated by the computer. The species itself could die and its planet could be destroyed, but the civilization would live on in a digital world identical to the one it left behind. In fact, many people, including Elon Musk, believe we're living in a simulation like that at this very moment. This provides one answer to the Fermi Paradox—that is, the question of why we haven't encountered aliens despite the likelihood that they're out there. It's possible that any civilization advanced enough to find us has already decided to abandon reality entirely and upload themselves to a Matrioshka brain. Delve deeper into megastructures and theoretical tech with the videos below.