I can give an example. If something moves back in time, it interacts as if it has negative mass relative to us, who move forward in time. Of course nothing moves back in time but tachyons which exist only on paper. The worlds of things moving forward in time and backward in time never meet because they are just two different solutions to the same equation and we have absolutely no evidence that the second world exists. Inverted matter from Tenet should have received negative mass but we most likely will never see it because time may be an illusion likewise to rotation.