Cosmology
Cosmic Web
Universe's largest structure — galaxies organized along filaments, sheets, and voids
The cosmic web is the largest-scale structure of the universe — galaxies and dark matter organized into a filamentary network. Components: nodes (galaxy clusters), filaments (galaxy chains connecting clusters), walls/sheets (2D structures), voids (~50% of volume — nearly empty). Largest filaments span 100+ million light-years. Visible in galaxy redshift surveys (SDSS), confirmed by N-body simulations. Origin: gravitational collapse of small initial density fluctuations during structure formation. Universe today: cosmic web growing, voids expanding.
- Survey scale~100 million ly filaments
- SurveySloan Digital Sky Survey (SDSS) — 1 million galaxies
- Voids~50% of volume
- FilamentsConnect galaxy clusters
- Walls2D structures (e.g., Sloan Wall ~1 billion ly)
- OriginDensity fluctuations from inflation; gravitational growth
Interactive visualization
Press play, or step through manually. The visualization is yours to drive — try it before reading on.
Watch the 60-second explainer
A condensed visual walkthrough — narrated, captioned, under a minute.
Why cosmic web matters
- Largest structures. Universe organized at vast scales.
- Cosmology. Confirms structure formation theory.
- Dark matter. Cosmic web traces invisible halos.
- Dark energy. Affects void expansion.
- Galaxy environment. Where galaxies live affects evolution.
- Surveys. Major scientific products from SDSS, etc.
- Cosmological constraints. BAO embedded in structure.
Common misconceptions
- Universe is uniform. Highly structured; web-like.
- Galaxies are random. Clustered along filaments.
- Voids are pure vacuum. Some matter; just much less.
- Cosmic web is 2D. 3D filamentary network.
- Web is static. Growing under gravity; modified by DE.
- Local universe is typical. Variations on all scales.
Frequently asked questions
How is the cosmic web mapped?
Galaxy redshift surveys. (1) Determine galaxy positions on sky. (2) Measure redshifts (distance via Hubble's law). (3) Build 3D map. SDSS (Sloan Digital Sky Survey) — most detailed; ~1 million galaxies mapped over 14,000 deg². 2dF, BOSS, eBOSS — additional surveys. JWST extends to higher z.
What are filaments?
Long, thread-like structures of dark matter and galaxies connecting clusters. Formed by gravity preferentially in directions of initial density excess. Span 100-300 million ly. Galaxy density 5-10× higher than mean. Filaments contain most galaxies.
What's a void?
Nearly empty region of space. Diameter 100-300 million ly. Few galaxies inside. Density 5-10× lower than mean. Make up ~50% of volume. Famous: Boötes void, Eridanus supervoid. Galaxies in voids tend to be smaller, less massive, more isolated.
Why does the cosmic web form?
Gravitational instability. Small density variations grow over time — overdense regions attract more matter; underdense regions become voids. 1D collapse first → "pancakes" / sheets. Then 2D collapse → filaments. Then 3D collapse → halos at intersections. Process continues today.
What's the Sloan Wall?
Largest known structure (until recently). 1.37 billion ly long. Discovered 2003 in SDSS data. Wall of galaxies. Even larger structure: Hercules-Corona Borealis Great Wall ~10 billion ly long (debated whether real or artifact).
Are voids really empty?
Mostly. Some galaxies present (void galaxies are special — small, blue, gas-rich). Cosmic dust very low. Hot gas (intergalactic medium) at very low density. Light travels through voids almost unimpeded. Voids expand faster than rest of universe.
How does dark energy affect cosmic web?
Dark energy drives accelerated expansion. Once voids start expanding, they expand faster as space increases. Filaments and walls maintained by gravity locally, but separated. Eventually (in distant future): cosmic web dissolves as expansion overcomes gravity. Recurrent feature today; transient feature on cosmic timescales.