The question of how the world will end has always been the subject of speculation and debate among poets and philosophers throughout history. Now, thanks to science, of course, we know the answer: fire. Fire, absolutely. The sun, in about five billion years, will balloon into a red giant, swallowing up the orbit of Mercury and possibly Venus, leaving Earth as a charred, lifeless rock covered in molten lava. Even this sterile, fiery remnant will probably eventually end up in the outer layers of the sun and be scattered atoms into the dying star's fraying atmosphere. So: fire. Settle in. Frost was right the first time. He just wasn't thinking deeply enough. I'm a cosmologist. I study the universe as a whole, on the largest scale. From that perspective, the world is a tiny, dainty speck of dust lost in a vast, diverse cosmos. What interests me, professionally and personally, is a bigger question: How will the world end?