You’ve probably read about how the Universe is expanding, and has been expanding since the beginning of time. Over the course of 13.8 billion years or so, it’s stretched from the size of a billionth of a proton to the vast, unknowable expanse it is today. In fact, recent research suggests that it’s actually expanding faster than our current laws of physics can explain, and that’s kind of a problem.
But all of that aside, whenever someone mentions our expanding Universe, we get a big, fat (turtle-surfing) elephant in the room. Because if the Universe is expanding, what exactly is it expanding into?