Simulation · Astrophysics & Cosmology
Hubble's Law Simulation
This simulation lets you place a galaxy at different distances and see, in real time, how its recession velocity and observed redshift change according to Hubble's law, alongside a simple visual of galaxies spreading apart as space expands.
Interactive simulation
Recession velocity: — km/s
As fraction of light speed: —
Approximate redshift (z): —
The physics behind this simulation
Hubble's law states that a galaxy's recession velocity is directly proportional to its distance:
v = H₀d
The farther away a galaxy is, the faster it appears to recede from us — not because it's moving through space in the ordinary sense, but because more expanding space lies between us and it. At low redshift (nearby galaxies, where v is much less than the speed of light), the approximate relationship between velocity and redshift is z ≈ v/c.
Common mistakeThis simulation uses the simple, low-redshift approximation v = H₀d and z ≈ v/c, valid for relatively nearby galaxies. For galaxies at cosmological distances (a significant fraction of the observable universe's size), the relationship between distance, redshift, and recession velocity becomes considerably more complex, requiring full general-relativistic cosmological models rather than this simple linear approximation — the simulation's slider range is kept within the regime where the simple approximation remains reasonably accurate.
Sources
- Hubble, E. (1929). Proceedings of the National Academy of Sciences, 15(3), 168–173.
Last verified: August 2026 · Source: Hubble (1929) · Confidence: high