How Big is the Universe?

The universe’s size depends on which “universe” people mean: the observable universe (everything we can see) is about 93 billion light-years across today, while the whole universe is likely far larger—possibly infinite. The key reason the observable universe isn’t the simple 27.5 billion light-years you might expect from the universe’s age is that space itself has been expanding. Light that left distant galaxies roughly 13.8 billion years ago has been traveling through an expanding space-time, so those sources are now more than 46 billion light-years away. Double that distance for opposite directions and the observable diameter comes out to about 93 billion light-years.

That scale also clarifies why “edge” and “center” are different questions for the observable universe versus the whole universe. The observable universe has a center because it’s defined by what can be seen from a given location on Earth. From our vantage point, the visible region forms a sphere centered on us—much like the circular view from a tall tower is centered on the tower. In fact, each person effectively occupies the center of their own observable universe, even though that doesn’t mean everyone shares a single physical center of the whole cosmos. The “whole universe” likely has no special center, just as the tower’s center is only the center of the view up to the horizon, not the center of the entire world.

The observable universe also has an “edge,” but it’s not a wall in space; it’s a horizon set by time. We can only see light that has had enough time to reach us since the universe began. Anything farther than about 46 billion light-years lies beyond our cosmic horizon. Yet that boundary isn’t fixed: as the universe ages, light from slightly farther away has time to arrive. Each second, the furthest reachable light source increases by about one light-second, so the observable universe grows continuously.

As for whether the universe is getting bigger, the answer is yes in two linked ways. Space is expanding, which stretches distances and makes both the observable universe and the whole universe larger. At the same time, the observable universe grows because we can see older light from farther away as time passes. Taken together, these effects mean the “view from the tower” keeps expanding.

In short: the observable universe is about 93 billion light-years across, it has a center at the observer and an edge defined by the cosmic horizon, and it expands over time. The whole universe is probably infinite in size, almost certainly lacks a spatial edge, has a temporal beginning, and likely has no overall center—so the statement “you are the center of the universe” is true only in the limited, observational sense.