Is our definition of 'cosmic voids' misleading the H₀ discussion?

[qql504]

TL;DR

I suspect the Hubble tension has a very simple origin: regions with higher matter density have a higher local H₀, while deep cosmic voids have a significantly lower H₀. The global average just ends up at 67.4 from averaging over the whole universe.

The voids being discussed in local H₀ measurements are actually sub-voids inside superclusters like Laniakea. They are underdense relative to the supercluster, but their absolute density is still above the universal average. That's why the local H₀ comes out high (~73).

True cosmic voids — far from any supercluster, with genuinely below-average density — have never been measured for H₀. If they were, I'd predict H₀ significantly lower than 67.4.

Does this make sense?

 

[Bandersnatch]

While I'd take issue with your characterisation of local H0 measurements - they reach out to roughly z=1, so way farther than the scale of superclusters or the distances between them, i.e. reaching across the voids - and am not sure what line of thought have made you conclude the H0 should be smaller in the voids as you haven't elaborated on the physics, the inhomogeneities in matter distribution as the source of many issues with the concordance model are indeed being explored. Look up 'backreaction' in the context of cosmology.

And, fwiw, if I were a betting man, I'd also peg the tension on deviations from homogeneity that evolved over time.