Is The Universe Actually Infinite?

Cosmologists do not know whether the entire universe is actually infinite; current data are compatible with both a very large finite universe and an infinite one.  What can be described with confidence is only the observable universe, which is definitely finite in size. The observable universe is the region from which light has had time to reach us since the Big Bang, given the finite age of the cosmos and the expansion of space.  With current cosmological parameters, its radius is about 46–47 billion light‑years, giving a diameter of roughly 93 billion light‑years.  This region is bounded by a horizon set by spacetime dynamics, not by any physical edge or wall. 
 
The entire universe includes regions beyond our observable horizon that we cannot see because their light has not yet reached us.  Those regions could extend only somewhat beyond our horizon or continue without end; current observations cannot distinguish these possibilities. 
 
Whether the universe is finite or infinite is tightly tied to its spatial curvature in standard cosmology.  Measurements of the cosmic microwave background, especially from the Planck satellite and related probes, show that the present‑day spatial curvature parameter is extremely close to zero, consistent with a flat universe to within about one part in a thousand.  A perfectly flat universe with the usual assumptions about topology would be spatially infinite, but a nearly flat finite universe whose curvature radius is far larger than the observable universe also fits the data.
 
Additional methods, such as cosmic chronometers and other geometric tests, generally agree that any curvature is very small, reinforcing the picture of a universe that is either flat or so gently curved that its size must be much larger than the observable region.  However, these measurements are not precise enough to rule out extremely large but finite models. 
 
Standard models do not include a literal edge in space where the universe ‘stops;’ instead, finite models curve back on themselves, somewhat like the 2‑D surface of a sphere, but in three spatial dimensions.  In such a case, travelling in a straight line long enough could in principle return you to your starting point, yet you would never hit a boundary.  There are also possible flat but finite topologies (like higher‑dimensional analogues of a torus), where space is globally finite but locally looks flat everywhere; these are still consistent with current constraints because any repeating patterns would occur on scales beyond what we can observe. 
 
Observationally, cosmologists search for signatures such as repeated patterns in the cosmic microwave background or specific distortions in large‑scale structure that could reveal a finite, multiply connected topology.  So far, no definitive evidence of such patterns has been found, which leaves both infinite and very‑large‑finite scenarios viable.
 
Putting this together, current evidence indicates:
The observable universe is finite and about 93 billion light‑years across. Space on those scales is extremely close to flat, implying that if the universe is finite, its size must be much larger than the observable volume. Observations place strong limits on curvature and some topologies but cannot yet tell whether space ultimately goes on forever or closes on itself on scales far beyond what we can see. 
 
So the honest answer is that the universe might be infinite, and many simple flat models treat it that way, but this is not experimentally established; it remains an open question constrained by increasingly tight but not decisive measurements.
 
References
Linke, L. (2020, December 3). Measuring the Curvature of the Universe with Cosmic Clocks. Astrobites.
 
Segal, E. (2024, June 14). Ask Ethan: Is the Universe Finite or Infinite? Big Think.
 
(2025, November 21). Shape of the Universe. In Wikipedia, https://en.wikipedia.org/wiki/Shape_of_the_universe#Curvature_of_the_universe
 
(2025, November 7). Observable Universe. In Wikipedia, https://en.wikipedia.org/wiki/Observable_universe