" it's literally like playing a movie in reverse" seems overly authoritative for something we haven't observed. I have seen Tenet, but it's a work of fiction.
Have we observed reflected gravitational waves? In reverse-time, where would they originate from if they presumably rippled out into space and didn't collide with anything in forward-time?
.... they would "originate" from all the locations the gravity waves spread to and converge on the source.
Tenet has nothing to do with this- I'm just explaining it as it was covered in my many physics classes that covered the nature of the arrow of time (https://en.wikipedia.org/wiki/Arrow_of_time) and how I interpret it in terms of what seems most likely/least unlikely.
