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.