Is the universe infinite?
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tl;dr
Space is flat as far as we can measure, which fits a universe far larger than the 93-billion-light-year bubble we can see — possibly infinite, provably unknowable for now.
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Nobody knows — and nobody may ever know. The universe we can observe is a bubble about 93 billion light-years wide, and space clearly continues beyond it with no edge in sight. Every measurement says space is flat, which fits an infinite universe — but flatness can hint at infinity, never prove it.
The bubble we live in
Our view has a hard limit: light needs time to travel, and the universe has only existed for 13.8 billion years. That should cap our view at 13.8 billion light-years — except space itself kept stretching while the light was in transit. The oldest galaxies we see are now about 46 billion light-years away, putting the full width of the observable universe near 93 billion.
What flatness hints
If space curved like a sphere, parallel light beams would slowly converge and the angles of huge triangles would betray it. Planck and its successors looked, hard. To a precision of roughly one part in 400, space is flat — exactly what an infinite universe would look like, and also what a finite universe hundreds of times larger than our bubble would look like.
Why we may never know
Here is the honest wall: a measurement can find curvature, but it can never find its absence with infinite precision. If tomorrow's instruments detect a gentle curve or a repeating pattern in the sky, the universe is finite and we'll know. Until then, "infinite" stays a live possibility that no telescope can ever fully confirm.
cited
Sources
- [01]Observable universe — Wikipedia
“The observable universe is a spherical region of the universe... approximately 93 billion light-years in diameter.”
- [02]Is the Universe truly infinite in size? — Big Think
“Measurements from WMAP to Planck to ACT to SPT and beyond all indicate that the Universe is spatially flat on the largest scales... to a precision of 0.25%.”
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Keep asking
What is beyond the observable universe?
More universe, by every indication — the sky looks the same in all directions, so space past our horizon should look much like it does here: more galaxies, same physics, no wall.
How is it 93 billion light-years wide after only 13.8 billion years?
Space expanded while the light traveled. A galaxy whose light left 13.8 billion years ago has since been carried to about 46 billion light-years away by the stretching of space itself — no speed limit broken.
Could the universe be finite without an edge?
Yes — like the surface of a sphere or a torus, space could close back on itself. Travel far enough in a straight line and you'd arrive home. Nothing in the data rules this out yet.
Will we ever know for sure?
Only a detected curvature or a repeating pattern in the sky could settle it as finite. Perfect flatness — what we keep measuring — fits both answers, so "infinite" may stay forever unprovable.
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