Mansuripur is sticking to his guns. He argues that hidden momentum, which was identified in the 1960s, is an ill-defined concept that merely papers over the problem. "That's always been the problem with hidden momentum," Mansuripur says. "You know that something is missing, so you just postulate its existence." He says his approach eliminates the need for hidden momentum.There was a question towards the end of this article on whether this should have been published or not. I see no problem in it getting published (although, I don't think it should have been in PRL). Mansuripur clearly found something intriguing that needed to be sorted out. It was not done out of deceit and it was definitely a legitimate question. The rest of the community then responded in kind to correct what they see missing or in error. That's what this whole publication process is supposed to do, and this is how it should work. Publication never guarantees validity.
Others say that hidden momentum is part and parcel of relativity. "If you have a system with internal motion that is subject to an external force, then hidden momentum is a general property," says Daniel Vanzella, a commenter at the University of São Paulo in São Carlos, Brazil. "It's not an ad hoc invention put in to reconcile things." Vanzella also notes that mathematically, the Lorentz force law can be written in a form that guarantees it will jibe with relativity, so it's "simply impossible" for it to contradict the theory.