If you pose the question "What is the hottest object in the universe?" to a group of scientists, you are going to get a lesson. One says it depends on what you mean by "hot." The next says it depends on what you mean by "object." And another will say it depends on what you mean by "universe." Then each will pick a definition and give an explanation of what they think. The most common answer among them is that the hottest object ever was the Big Bang, which mean they are defining "universe" as including all time. You can get pretty deep in a question like this! But that wasn't the only answer, and you'll learn something about all those terms in a roundup at Gizmodo.
(Image credit: Benjamin Currie/Gizmo