Hubble Constant
The Hubble constant (H0) is the current expansion rate of the universe, linking a galaxy's distance to how fast it moves away. It is measured in km/s per megaparsec and helps cosmologists estimate the universe's age and dark energy values.
The Hubble constant, denoted as H0, is the rate at which the universe is currently expanding, measured in kilometers per second per megaparsec. It relates the distance of a galaxy to its recession velocity, providing a fundamental parameter for cosmological models. Determined through methods like baryon acoustic oscillations (BAO) and the cosmic microwave background (CMB), it helps constrain values for dark energy and the universe's age.
What this means in real life
Imagine dots on an inflating balloon: as the balloon expands, every dot moves away from every other dot at a speed proportional to how far apart they are. The Hubble Constant describes that expansion rate for our universe.
What it isn’t
It is not a measure of how fast individual galaxies move through space on their own. It describes only the recession velocity caused by space itself expanding, not the motion of galaxies relative to a fixed background.
Commonly misused online
Often conflated with the 'Hubble tension'—the discrepancy between different measurement methods. Social media sometimes treats disagreement over its exact value as evidence the universe is 'broken' rather than a normal scientific refinement.
Based on 1 reference source, including Wikipedia. Last verified July 11, 2026.