Comment on "Evidence of a first-order phase transition to metallic hydrogen"

A recent article by Zaghoo et al. [Phys. Rev. B 93, 155128 (2016)] presented high-pressure high-temperature optical experiments claiming the observation of a first-order transition to atomic liquid metallic hydrogen. Here, we demonstrate that the experimental evidence presented is unsubstantial for such a claim. Furthermore, the claimed results and conclusions contradict previously published works, including those by the same research group.