🌌 Hubble's Law — Expanding Universe
Every galaxy recedes at a speed proportional to its distance: v = H₀ × d. Adjust the Hubble constant, observe redshift, and find the Hubble sphere where recession speed equals c.
Hubble's Law (1929)
Edwin Hubble found that distant galaxies recede faster than nearby ones — with recession speed directly proportional to distance. This is not galaxies moving through space, but space itself stretching. The Hubble constant H₀ sets the expansion rate.
The Hubble sphere (dashed circle) marks the distance at which recession equals c. Galaxies beyond it recede faster than light — they are not causally disconnected, but their light takes increasing time to reach us. The colour of each galaxy encodes its redshift: blue = nearby, red = distant.