One of the most fascinating concepts that I discovered while reading chapters on stellar workings and cosmology (the study of the evolution of the universe) was the idea that not only do stars die (including our own), but the universe too will die. This of course depended on the universe's present properties which had yet to be fully explored on the book's publication.
Today, the answer to the question of how our universe will die is a little more certain if not more mysterious than I thought before. This TEDEd video sums it all up. Enjoy!