Suppose there was an area of the universe filled tusk to arsehole with invisible giant pink elephants? What would that prove? The universe–our world–is all and only those areas we can observer or infer by observing consistent phenomenon. Nobody outside of an episode of Dr. Who has ever seen a “time-reversed star” or anything of the sort, and we have no evidence by which to infer that such a thing could even exist.
This is not a sensible question. I don’t know where this notion of “retrograde causality” comes from, but it is not to be found anywhere in scientific literature, and no actual physicist has a “clearest understanding” of it. There are ways within the framework of relativity to formulate closed time-like curves which have endpoints that terminate before the start in the time direction, but that isn’t a violation of (local) causality, as the system following that path is always experiencing time as advancing, and there are physical reasons to believe that such paths, like roller coasters, have to return to their beginning point before one can exit.
There are interpretations of quantum mechanics that are acausal (transactional, consistent histories, Everett-DeWitt many-worlds) and explicitly allow for time symmetric behavior, but there is no credible interpretation that could be called reverse causality (or as you refer to it, “retrograde causality”). The interpretation that comes closest would be the consciousness causes collapse interpretation, but outside of a few attempts at pairing Eastern mysticism with the conundrum that is quantum mechanics, and a few genuine physicists who have ventured far afield from any testable and falsifiable speculations, this isn’t given much credibility, and is largely regarded, like solipsism, to be a topic unsuited for civil discussion among intelligent adults.
There are actual techniques within quantum field theories that assume causal loops with virtual particles and other counterintuitive behavior such as the spontaneous generation or destruction of energy (non-conservation), but nobody accepts this as being “real” as they happen on time scales that are literally too small to measure, and always balance out to zero. They are instead accepted as mathematical formalisms that work and describe some process of which we do not have a complete or intuitive understanding; and indeed, any working physicist or engineer applying quantum mechanics to any real world experiment will “shut up and calculate” rather than noodle about with untestable philosophy.
Stranger