and no-one else does

If your personhood definition requires there to be only one of you, I think it already fails.

The full quote was, "and no-one else does until you go so far from here as to start encoding those memories into the spacetime coordinates." . Don't quote out of context.

It is a physical fact of reality that within ridiculously huge volume, I am the only one who remembers what I thought about on a train ride in the year 2000 or so on the way back home from work, err, i mean school. It's only when you get extremely far, where the memory of this and other thoughts can be encoded into the coordinate, that you begin to see instances that hold this memory.

(subject to there being a zillion of mes comparatively 'nearby' if the MWI is true, of course)

edit: and okay, i was thinking about electrical aircraft propulsion, using electric arc to accelerate the air. I can remember in vivid details what I imagined then because I committed it to memory (the train was packed and I had to stand, so I couldn't write it down). I have terabytes of such stuff in the head, and while someone on earth can have approximately similar memories, the edit distance is huge.