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 #22, " Cosmology." Perhaps more a field of study than an "idea," but it is made possible by an extremely powerful idea: that our universe is uniform and simple enough to be understandable. We go through the expansion of space, the thermal history of what makes up the universe, and a bit about dark matter and the cosmic microwave background. 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.spacetelescope.org/images/heic0611b/ #science #physics #ideas #universe #learning #cosmology #philosophy