We point out that the physics at the extreme IR — cosmology — might provide tests of the physics of the extreme UV — the Weak Gravity Conjecture. The current discrepancies in the determination of H0 may hint at a modification of ΛCDM. An extension which may fit better comprises an early contribution to dark energy which “decays” into relativistic matter. On the other hand, the discourse on WGC to date suggests that fields which support cosmic acceleration may produce relativistic matter after they traverse a ～ Planckian distance in field space. We explain how this offers a simple realization of the requisite cosmic phenomenology. Thus, if the resolution of H0 discrepancies is really early dark energy that ends with a shower of relativistic matter and the current ideas on WGC are indicative, this may be a rare opportunity to link the two extreme limits of quantum field theory.
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