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93 Billion Light-Years Wide: How the Observable Universe Can Be Larger Than Its Age Implies
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93 Billion Light-Years Wide: How the Observable Universe Can Be Larger Than Its Age Implies

March 28, 2026 · 4 min read

The Fact

The observable universe is estimated to be 93 billion light-years in diameter.

If the universe is 13.8 billion years old and light travels at a finite speed, the intuitive conclusion is that the farthest we could possibly see is 13.8 billion light-years — the distance light could cover in the time since the Big Bang. The observable universe, however, is measured at approximately 46.5 billion light-years in radius, or about 93 billion light-years in diameter. The discrepancy is not a measurement error. It reflects one of the most counterintuitive features of our universe: the fabric of space itself has been expanding, and continues to expand, at speeds that can exceed the speed of light.

This does not violate Einstein's special relativity, which prohibits only the motion of matter or energy through space at superluminal speeds. Space itself can expand at any rate — and during the early universe, and throughout cosmic history, it has been doing exactly that.

The Expanding Universe

In the immediate aftermath of the Big Bang, the universe was an extraordinarily hot and dense state. From the beginning, space has been expanding — galaxies are not flying through space away from each other, but rather the space between them is growing, carrying them apart like raisins in an expanding loaf of bread. This expansion has been documented through the redshift of light from distant galaxies: the farther a galaxy, the more its light is stretched to longer, redder wavelengths as the universe expands during the light's journey.

The light we receive today from the edge of the observable universe was emitted when those regions were much closer to us — approximately 42 million light-years away, early in cosmic history. In the 13.8 billion years since that light was emitted, the region that emitted it has been carried by cosmic expansion to its current distance of 46.5 billion light-years. The light we're receiving now left from a location that is currently far beyond the distance a simple "speed of light times age" calculation would suggest.

The Cosmic Horizon

The observable universe is bounded not by a wall or an edge in space, but by a horizon defined by the speed of light and the age of the universe: the maximum distance from which any light signal could have reached us since the Big Bang. Beyond this horizon, the universe almost certainly continues — possibly infinitely — but we have no way to receive any information from those regions because no light from there has had time to reach us yet.

Interestingly, some regions that are currently within our observable universe will eventually pass beyond our cosmological event horizon as dark energy continues to accelerate the universe's expansion. Galaxies beyond a certain distance are already receding from us faster than light can cross the expanding space between us, meaning that any light they emit now will never reach us. The observable universe is not a fixed region but a shrinking effective neighborhood, as more of the cosmos becomes permanently inaccessible to our observation.

What We Can't Know

The 93-billion-light-year diameter describes only the observable universe — what we can in principle detect with electromagnetic radiation. The total universe may be vastly larger, potentially infinite. Cosmic inflation, the rapid expansion of space thought to have occurred in the universe's first fraction of a second, would have taken regions that were initially in causal contact and separated them by distances far exceeding what any future observation could access.

Some cosmological models suggest the total universe is at least 250 times the diameter of the observable universe, and theoretical arguments based on cosmic inflation allow for much larger or infinite extents. The 93-billion-light-year figure is therefore not a description of the universe but a description of our observational horizon — the edge of what is, in principle, knowable to us, and a boundary that is itself a product of the universe's most fundamental dynamical process.

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FactOTD Editorial Team

Published March 28, 2026 · 4 min read

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