You misunderstand the Casimir effect. It's a relativistic analogue of the van der Waals interaction, with a very curious alternative derivation from zero point

You misunderstand the Casimir effect. It's a relativistic analogue of the van der Waals interaction, with a very curious alternative derivation from zero point energies. It is not free/negative energy, it is not free momentum, it was never a controversial subject, we only didn't have the practical means to measure it. Exploiting the Casimir effect can't give free momentum, because the derivation of the force is rooted in quantum field theory, which like any other physical theory of the last 400 years contains conservation of momentum at its very core.