The Biggest Ideas in the Universe is a series of videos where I talk informally about some of the fundamental concepts that help us understand our natural world. Exceedingly casual, not overly polished, and meant for absolutely everybody. This is the Q&A video for Idea #10, "Interactions." I talk about the circumstances under which it's okay to use Feynman diagrams and think of fields as being particle-like vs. wave-like, and am a bit more precise about locality and the infinite number of degrees of freedom in a field theory. My web page: http://www.preposterousuniverse.com/ My YouTube channel: https://www.youtube.com/c/seancarroll Mindscape podcast: http://www.preposterousuniverse.com/podcast The Biggest Ideas playlist: https://www.youtube.com/playlist?list=PLrxfgDEc2NxZJcWcrxH3jyjUUrJlnoyzX Blog posts for the series: http://www.preposterousuniverse.com/blog/category/biggest-ideas-in-the-universe/ Background image: https://www.ecopetit.cat/ecvi/JwTib_wallpaper-sphere-mechanism-cabel-neon-cube-cool-wallpapers/ #science #physics #ideas #universe #learning #cosmology #philosophy #quantum #fields #feynman