The universe is expanding.
On large scales, the distances between unbound galaxies grow as the universe expands.
Show me why
Astronomers compare galaxy distances with the shifts of recognizable features in their spectra. The overall distance–redshift relation supports cosmic expansion. Nearby objects can have additional motions that differ from the large-scale pattern.
A common misconception
Expansion does not require every galaxy to move away from every other galaxy locally.
Where the limits are
Bound systems such as the solar system do not simply expand with the universe. The exact expansion rate and the nature of dark energy remain active research questions.
How we know
NASA explains cosmological redshift. The linked supernova research uses brightness-based distances and redshifts to study the expansion history. Expansion, the precise rate of expansion and its acceleration are related but distinct claims.
What would change this conclusion?
A competing model would need to explain the distance–redshift relation and other cosmological observations at least as well.
Sources you can inspect
- NASAHubble Cosmological Redshift
Explains the observed distance–redshift relationship.
Publication date not stated · Checked in initial research 2026-10-08 - Riess et al.Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant
Primary supernova observations of expansion history.
1998-05-15 · Checked in initial research 2026-10-08
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