How Big Is the Universe? (93 Billion Light-Years, and Still Growing)

The observable universe is 93 billion light-years in diameter — and that's only the part we can see. Light from the most distant galaxies we've detected left them 13.4 billion years ago. The actual universe could be infinite; we'd never know because the light from beyond hasn't had time to reach us.

Here's what those numbers mean in practice.

Light-year, briefly

A light-year = the distance light travels in one year = 9.46 trillion km (5.88 trillion miles). It's a distance unit, not a time unit.

For scale: the nearest star (Proxima Centauri) is 4.24 light-years away. 93 billion is a number your brain cannot picture. Nobody's brain can.

Why is the observable universe bigger than its age?

The universe is 13.8 billion years old. You'd expect the light we see to come from at most 13.8 billion light-years away. Wrong.

Space itself has been expanding the whole time. A galaxy whose light left 13 billion years ago has physically moved farther since. So the 13.8 billion-year-old light is now coming from objects currently ~46 billion light-years away — hence the 93 billion diameter.

The expansion is accelerating

In the late 1990s, observations of distant supernovae showed the universe isn't just expanding — it's expanding faster. The driver (dark energy) makes up about 68% of everything in the universe. We don't know what it is.

Project forward: in ~100 billion years, most galaxies will recede faster than light from our vantage point. Our observable universe shrinks.

How many galaxies are out there?

Hubble deep-field counts: ~100–200 billion observable galaxies. 2020s JWST revisions push the estimate toward 2 trillion. Each galaxy hosts 100 million to 1 trillion stars.

Napkin math: 2 × 10^23 stars in the observable universe. That's more stars than grains of sand on Earth.

Where are we in all this?

The Milky Way is one of ~54 galaxies in the Local Group. The Local Group is one of maybe 100 groups in the Virgo Supercluster. That's one of thousands of superclusters in the Laniakea Supercluster. Laniakea is one node in the cosmic web.

Zoom out far enough and the universe looks like foam — voids and filaments. See Galaxy Map for a navigable version.

Could the universe be infinite?

Possible. Current observations are consistent with an infinite, flat universe. They're also consistent with a finite-but-very-large one. The geometry isn't settled — and may never be.

What about multiverses?

Multiverse theories (eternal inflation, Many Worlds, string landscape) predict other universes. No direct evidence. They're consistent with current physics but probably untestable.

Don't trust anyone who tells you the multiverse is settled science.

How do we measure any of this?

Three methods stack:

• Parallax: nearby stars, using Earth's orbital shift
• Cepheid variables: certain pulsating stars whose brightness reveals distance
• Type Ia supernovae: standard-candle explosions visible across billions of light-years

Each step has error bars, and the Hubble constant — the rate of expansion — is still a source of tension between measurement methods.

For more cosmic context, see how fast does light travel and how do black holes form.