They’re not space ghosts, they’re literally the main character interacting with the past from within a black hole, where the whole of spacetime has collapsed into a single point. As the other commenter said, this is the science fiction part.

Physicists have said that physics as we know it break down in the singularity of a black hole. Kip Thorne signed off on their artistic license plot device of having spacetime collapse into the “tesseract.”

Anyway, that isn’t what I was referring to when I said “the physics are accurate.” I was only referring to the parts involving the black hole and planets and tidal forces and time dilation, which were what they worked very hard on to get right.

Well that's the science fiction part lol and it's pretty out-there