MathLiveSecond Friedmann equation
This equation gives the rate of change of the expansion speed of the universe, showing that the expansion accelerates when the density plus three times the pressure term is negative. It is used in cosmology to relate the acceleration of the scale factor to energy density and pressure, for example when dark energy drives accelerating expansion.
\frac{\ddot{a}}{a}=-\frac{4\pi G}{3}\left(\rho+\frac{3P}{c^2}\right)What the symbols mean
| cosmic scale factor, a dimensionless measure of the size of the universe | |
| second time derivative of the scale factor | |
| gravitational constant | |
| energy density of the universe (kg/m^3 or J/m^3) | |
| pressure of the cosmic fluid (Pa) | |
| speed of light in vacuum (m/s) |
About this formula
- FieldPhysics
- TopicCosmology
- LevelUniversity
- Also calledacceleration equation, accelerating expansion of the universe, acceleration of the universe, Friedmann acceleration equation, universe acceleration formula, dark energy acceleration equation
- SourceWikidata Q1049613
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