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 Idea #6, "Spacetime." Which, naturally, is about the major idea underlying special relativity -- that both space and time are different parts of one unified, four-dimensional spacetime. Learn the real reason why two twins age differently if one stays home and the other zips out near the speed of light. 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.amazon.com/Spacetime-Geometry-Introduction-General-Relativity-ebook/dp/B07T9MCTWF/ #science #physics #ideas #universe #learning #cosmology #philosophy #math #spacetime #relativity