We’ve all heard it: the universe is expanding. But what does that really mean? And the question that naturally follows is just as puzzling:
If the universe is expanding… what is it expanding into?
The short answer may surprise you: nothing. And everything. At the same time.
Let’s break it down.
What Does «Expanding Universe» Really Mean?
The expansion of the universe doesn’t mean galaxies are flying through space, like debris from an explosion. It means space itself is stretching—the distances between galaxies are increasing, even though the galaxies themselves may be standing still relative to one another.
Imagine dots on a balloon. As you inflate the balloon, the dots move apart, not because they’re moving, but because the surface itself is growing. The balloon isn’t expanding into anything from the dots’ perspective—it’s just getting bigger.
That’s what’s happening with our universe—in three dimensions.
So… Is There an «Outside»?
In current cosmological models, the universe doesn’t expand into space—because there is no external space. Space and time began with the Big Bang. They define the universe itself. There’s no «outside» in the way we think of it, because «outside» implies space, and space doesn’t exist beyond the universe.
Even stranger, the universe might be infinite in size. In that case, it’s not expanding into anything at all—it’s simply becoming more infinite, if such a thing can be imagined.
Then Why Do We See Expansion?
We observe galaxies moving away from us in every direction. The farther they are, the faster they seem to recede. This is due to the expansion of space, not motion through space.
It’s like baking raisin bread: the dough (space) rises, and the raisins (galaxies) move apart—not because the raisins are running away, but because the dough between them is stretching.
So What Is It Expanding Into?
From our current understanding, the universe is not expanding into a physical space. Instead, space itself is expanding, and the very fabric of reality is stretching.
It’s a concept that resists visualization—because our brains evolved to think in three dimensions, within fixed boundaries. But the universe has no edge. No center. No container.
Just expansion.
