# Cosmological constant of standard model of cosmology and observational data

I am curious whether the current Lambda-CDM model of cosmology matches well with observational data, especially expansion of the universe.

How well does Lambda-CDM defend its established status from other models, such as quintessence (quintessence can be said to extend Lambda-CDM, but there are some models against the standard model, I guess.)?

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It fits remarkably well. One of the defining features of a cosmological constant is its equation of state. The equation of state, $w$, is given by $p \over \rho$, where $p$ is the pressure it contributes, and $\rho$ is the energy density. A cosmological constant has $w=-1$. The WMAP seven year report recorded the value as $w=-1.1 ± 0.14$. Within the error margins, the cosmological constant fits very well.