Cosmic Expansion Rate Calculator Formula
Understand the math behind the cosmic expansion rate calculator. Each variable explained with a worked example.
Formulas Used
Recession Velocity
recession_velocity = hubble_constant * distance_mpcRecession Velocity (m/s)
recession_ms = hubble_constant * distance_mpc * 1000Variables
| Variable | Description | Default |
|---|---|---|
hubble_constant | Hubble Constant (H0)(km/s/Mpc) | 70 |
distance_mpc | Distance(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
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.
- 01v = H0 * d
- 02v = 70 * 100
- 03v = 7 000 km/s
Frequently Asked Questions
What is the accepted value of H0?
Measurements from the Planck satellite give about 67.4 km/s/Mpc, while the distance-ladder method yields about 73 km/s/Mpc. This discrepancy is called the Hubble tension.
Does the Hubble law mean we are at the centre of the universe?
No. Every observer in an expanding universe sees all other galaxies receding. There is no special centre.
Can recession velocity exceed the speed of light?
Yes, for very distant objects. This does not violate relativity because it is the expansion of space itself, not motion through space.
Ready to run the numbers?
Open Cosmic Expansion Rate Calculator