Equations · equation
Second Friedmann Equation
Cosmology · 1922
- Equation
- ä/a = −4πG(ρ + 3p/c²)/3 + Λc²/3
- Field
- Cosmology
- Named After
- Alexander Friedmann
- Year
- 1922
Symbols
a the scale factor of the universe · ä its second time derivative, the acceleration of the expansion · G gravitational constant · ρ energy density · p pressure — it is the 3p term that makes radiation slow the expansion harder than matter does, and a negative enough p that reverses the sign · Λ the cosmological constant · c speed of light
Significance
Whether the expansion speeds up or slows down. Matter and pressure put on the brakes; the cosmological constant steps on the gas — exactly what the 1998 supernova surveys found the universe doing.
Referenced by
constant
equation
event
instrument
theory
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