A measurement of the scale of homogeneity in the Early Universe

Understand

We present the first measurement of the homogeneity index, $\mathcal{H}$, a fractal or Hausdorff dimension of the early Universe from the Planck CMB temperature variations $\delta T$ in the sky.

• This characterization of the isotropy scale is model-free and purely geometrical, independent of the amplitude of $\delta T$.
• We find evidence of homogeneity ($\mathcal{H}=0$) for scales larger than $\theta_{\mathcal{H}} = 65.9 \pm 9.2 \deg $ on the CMB sky.
• This finding is at odds with the $\Lambda$CDM prediction, which assumes a scale invariant infinite universe.