Dark energy is introduced as a constant inside Einstein's equations. Its primary purpose, from what I understand, is to make Einstein's equations compatible with the accelerating expansion of the universe. As a consequence, of the "predictions" of dark energy is the expansion of the universe according to Hubble's law.
I know there are numerous experiments that verify this expansion (and its acceleration), and thus indirectly support the dark energy theory. My question is:
Are there other factors that give credit to the existence of dark energy?
Are there any experiments that support this theory, but not only through the verification of Hubble expansion?
Answer
I think the strongest evidence comes from the CMB fluctuations, namely the location of the first acoustic peak. This gives the overall geometry of the Universe ($\Omega_{tot}=1$; the Universe is flat). Then with a multitude of observations of dark matter (e.g., galaxy cluster counts, large-scale structure, and weak lensing) to get $\Omega_{matter}=0.3$, we are left with
$$\Omega_{\Lambda}=\Omega_{tot}-\Omega_{matter}=0.7$$
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