What Is the Universe Expanding Into—and Where Is It Going?
The idea that the universe is expanding sounds simple on the surface—but it leads to some of the most profound and difficult questions in all of cosmology. Among the most common: “If the universe is expanding, what is it expanding into?” and “Where is it going?” Let’s break this down, not with metaphors or mystical prose, but with solid science, hard examples, and visuals that clarify each concept. 🧠 The Basics: What Do We Mean by 'Expansion'? When cosmologists say “the universe is expanding,” they don’t mean that galaxies are flying outward into empty space like shrapnel from an explosion. Instead, space itself is expanding. The metric that defines the distance between two points in the universe—known as the Friedmann–Lemaître–Robertson–Walker (FLRW) metric —is changing over time. That means the very fabric of space-time is stretching. 📌 Key Concept : It’s not galaxies moving through space, but space itself growing between galaxies. 🌀 So, What Is the Universe ...