Board Thread:Manga/@comment-44086949-20191205133131/@comment-37493549-20191220025540

I think the smoking gun that disproves your 'Eren and Zeke time travelled' thing is the fact that Grisha can only perceive Zeke when he's in both Eren and Grisha's himself field of vision. Unless you think this is a total coincidence, which I highly doubt.

When Eren isn't looking at Zeke, Grisha has no window into the future through which to perceive Zeke. He's seeing a superposition of the moment he's currently living through, along with the future memory of Eren while he's observing Grisha's memory of the same moment. Zeke only exists in the latter.

It's kind of like how both of your eyes are seeing a different perspective to each other, two different images. But your brain makes sense of it by creating a single composite image. For example, your left eye can't see the right side of your nose. In this case Zeke is the right side of your nose, and when Eren isn't looking at him that's the equivalent of having your right eye closed.