ELI5 Dyson Sphere - did aliens already build one?

What exactly is a Dyson Sphere? What materials would be required? What is a Dyson Swarm and a Dyson Bubble? Could any other civilizations have built a dyson sphere already? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: apprehensivemedia999, loki-l, kriss3d and joushmark To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]