How do one way mirrors allow light to pass in only one direction? If light travels through the glass equally from both sides, why does the simple flip of a light switch create a hidden observer? How does a microscopic layer of aluminum or silver on a piece of glass actually bounce light back to create a reflection? Why does our brain instantly prefer our flipped mirror image over the real perspective captured in a photograph? ... 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: avalancheofneed, afropuf, coolminded, tequilaamocking_bird, blade_torlock, imtrollin_theyhatin, antiproton and spilgrim16 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]