The Dyson Sphere

Although Dyson Spheres in the form of a swarm are theoretically possible, building a stable megastructure around the Sun is currently far beyond humanity's engineering capacity. The number of craft required to obtain, transmit, and maintain a complete Dyson sphere exceeds present-day industrial capabilities.
Dyson Spheres have prompted speculation into the feasibility of a class of proposed stellar engines, hypothetical megastructures whose purpose is to extract useful energy from a star, sometimes for specific purposes.

For example, Matrioshka brains have been proposed to use energy extracted by Dyson Spheres for computation, while Shkadov thrusters would extract energy for propulsion. Some proposed stellar engine designs are based on the Dyson Sphere. Futurist George Dvorsky has advocated the use of self-replicating robots to overcome the limitation of humanity's engineering capacity in the relatively near term.