Cosmic Expansion Rate Calculator Formula

Understand the math behind the cosmic expansion rate calculator. Each variable explained with a worked example.

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Formulas Used

Recession Velocity

recession_velocity = hubble_constant * distance_mpc

Recession Velocity (m/s)

recession_ms = hubble_constant * distance_mpc * 1000

Variables

VariableDescriptionDefault
hubble_constantHubble Constant (H0)(km/s/Mpc)70
distance_mpcDistance(Mpc)100

How It Works

How the Cosmic Expansion Rate Works

Edwin Hubble discovered that galaxies recede from us at speeds proportional to their distance.

Hubble-Lemaitre Law

v = H0 * d

  • *H0* is the Hubble constant (around 70 km/s/Mpc)
  • *d* is the co-moving distance in megaparsecs

    • This linear relation holds for nearby galaxies; at cosmological distances, corrections from the Friedmann equations are needed.

    Worked Example

    A galaxy sits 100 Mpc away with H0 = 70 km/s/Mpc.

    hubble_constant = 70distance_mpc = 100
    1. 01v = H0 * d
    2. 02v = 70 * 100
    3. 03v = 7 000 km/s

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