A friendly conversation

[HerenIstarion]

Are these worlds supposed to mix together?

First off, they are already a result of such a mix, and world owes its very existence to such a mix:

S77

Therefore I say: Eä! Let these things Be! And I will send forth into the Void the Flame Imperishable, and it shall be at the heart of the World, and the World shall Be

Besides, in some distant future (ME's future, that is), more concrete intersection (or, rather, descending of the higher into the lower) is guessed at, or expected, or hoped for:

AFaA

'They say,' answered Andreth: 'they say that the One [i.e. - Eru -- HerenIstarion] will himself enter into Arda, and heal Men and all the Marring from the beginning to the end. This they say also, or they feign, is a rumour that has come down through years uncounted, even from the days of our undoing.

cheers