There is no "I" in "You"

[I_am_not_mafia]

Can anyone answer why you're you.....and not me?

Why here, why now...why not exist a thousand years from now or a thousand years past?

what determined both our particular experiences and could one have been shunt in place of another (by what alternate means could I have experienced existence through your perspective or vice versa)?

Why here, why now...why not exist a thousand years from now or a thousand years past?

Asking why presupposes meaning. There is no meaning. There is no why. It just is.

By what method of determination do I experience existence separate from your experience;

What does this question mean?

Can this ever be coherently approached or determined materialistically/scientifically? Or, is metaphysics a fundamental necessity?

Metaphysics by definition does not exist. For your questions to be scientifically explored they first need to be falsifiable. They are currently not.