Einstein’s equations certainly permit the existence of pathways into the past; many solutions with that property have been discovered. Until recently, the accepted practice has been systematically to ignore such solutions. But this has not been for any reason arising from within the theory, nor from any argument within physics at all. It has been because physicists were under the impression that time travel would ‘lead to paradoxes’, and that such solutions of Einstein’s equations must therefore be ‘unphysical’.
