The metrics that give rise to closed time like curves, wormholes, or the FTL metric (Alcubierre metric) don't seem really feasible given the constraints imposed

The metrics that give rise to closed time like curves, wormholes, or the FTL metric (Alcubierre metric) don't seem really feasible given the constraints imposed on the stress-energy tensor. The paper seems interesting as it seems to attempt to apply what physics is observable assuming the metric that gives CTC exists, but I think the article is making too strong claims about time travel.