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SESK: Stuff Everyone Should Know · sesk.info/astro-observable-universe-radius

About how large is the observable universe's present radius?

Its present radius is about 46.5 billion light-years.

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  1. 13.8 billion light-years
  2. 4.65 billion light-years
  3. 46.5 billion light-years ✔

Why: The radius exceeds the light-travel age because space expanded while ancient light was in transit. The observable limit is a horizon, not necessarily the edge of all space.

Huh, didn't know that: The actual universe extends beyond the part we can observe.

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The observable universe has a big radius and an even bigger personal space bubble.
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References

Answer: 46.5 billion light-years. The radius exceeds the light-travel age because space expanded while ancient light was in transit. The observable limit is a horizon, not necessarily the edge of all space.

  1. The James Webb Space Telescope: Unfolding the Universe nepp.nasa.gov/docs/etw/2022/13-JUN-MON/1055-Geithner-v3-20220009134.pdf
    Observable universe is ~46.5 billion light-years in radius; actual universe is larger
    Checked 2026-10-10.

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