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 third Q&A video, following the idea "Force, Energy, and Action" discussed here: https://www.youtube.com/watch?v=sZb64bZ07aE&ab_channel=SeanCarroll 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/watch?v=HI09kat_GeI&list=PLrxfgDEc2NxZJcWcrxH3jyjUUrJlnoyzX&ab_channel=SeanCarroll Blog posts for the series: http://www.preposterousuniverse.com/blog/category/biggest-ideas-in-the-universe/ Background image: https://www.freeimages.co.uk/galleries/backdrops/fractal/slides/abstract_orange_fractal_1.htm #science #physics #ideas #universe #learning #cosmology #philosophy #math #force #energy #action #classicalmechanics