ELI5 Tesseract - what is it and what does it look like?

What is the tesseract? The geometric shape, not the fictional Marvel space stone! How can we visualize a 4D shape in a 3D world? What did the great Carl Sagan say about why it’s so hard for us to imagine 4 dimensions? Who discovered the tesseract in the first place? ... 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: lifewitheloise, portarossa, geetarmikey, green_meklar, sabertoothedpudding and okami31 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]