# Universal Sizing (DD-546)

> The observable universe is a sphere set by how far light has traveled since the Big Bang, with a radius of about 46.5 billion light-years. The universe as a whole may be infinite, and accelerating expansion means light from beyond a certain distance will never reach Earth.

- Department: Space
- First published: 2025-04-17
- Last updated: 2025-04-17
- Permalink: https://detailenjoyer.com/case/universal-sizing/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-546-F01**: About 93 billion ly. _(Write-up · Exhibit A (Measured as a radius))_
- **DD-546-F02**: 13.8 billion years. _(Write-up · Exhibit A (Measured as a radius))_

## Write-up

The observable universe is defined less by where things are than by what light has had time to reach us, and part of the cosmos will never be seen at all.

1. **Measured as a radius**: Astronomers estimate the observable universe's radius at about 14.26 gigaparsecs, or 46.5 billion light-years.
2. **Maybe infinite**: The size of the whole universe is unknown, and it may be infinite in extent.
3. **A permanent horizon**: If dark energy stays constant, light emitted today by objects beyond about 19 gigaparsecs (62 billion light-years) will never reach Earth.
4. **Galaxies fading out**: In practice, more and more distant galaxies will become so redshifted by expansion that they effectively disappear from view.
5. **Weighing the visible part**: Using the critical density, the ordinary matter in the observable universe is estimated at about 1.5 × 10^53 kg.

## Reel vs. record

- **Note**: The Reel says 'over 2 trillion galaxies'; that 2016 estimate has since been revised downward by some studies to a few hundred billion.

## Video: Universal Sizing: The Observable Universe Is About 93 Billion Light-Years Across

- Duration: 28.6 s · Published: 2025-04-17
- File: https://detailenjoyer.com/assets/videos/DIjCuPIRzM9.mp4

### Transcript

Did you know, the universe is incomprehensibly vast, with the observable portion stretching about 93 billion light years across, meaning light from the farthest regions has taken over 13.8 billion years to reach us, but due to the universe's expansion, those regions are now much farther away. Our galaxy, the Milky Way, is about 100,000 light years wide, and contains an estimated 100 to 400 billion stars, while the observable universe contains over 2 trillion galaxies, each with billions of stars and potentially even more planets. NOW YOU KNOW!

## Questions & answers

**Q: Diameter?**  
A: Expansion. _(Source: Write-up · Exhibit D (Galaxies fading out) · Wikipedia: Observable universe)_

**Q: Milky Way width?**  
A: Disk. _(Source: Write-up · Exhibit A (Measured as a radius) · Wikipedia: Observable universe)_

**Q: Stars in Milky Way?**  
A: Estimate. _(Source: Write-up · Exhibit A (Measured as a radius) · Wikipedia: Observable universe)_

**Q: Age of oldest light?**  
A: Big Bang. _(Source: Write-up · Exhibit A (Measured as a radius) · Wikipedia: Observable universe)_

**Q: Why bigger than 13.8 billion ly?**  
A: Space stretches. _(Source: Write-up · Exhibit A (Measured as a radius) · Wikipedia: Observable universe)_

## Sources

- [Wikipedia: Observable universe](https://en.wikipedia.org/wiki/Observable_universe)

## Cite this case file

Easterling, Marcus. "Universal Sizing." The Detail Department (DetailEnjoyer), case file DD-546, last updated Apr 17, 2025. https://detailenjoyer.com/case/universal-sizing/