This contains spoilers for TLJ. So in TLJ, we see that Snoke is able to create a mind connection between Rey and Kylo Ren. What if the Emperor did a similar thing in Empire and ROTJ between Luke and Vader? After their fight on Bespin, we see Luke and Vader able to connect with each other in a way that (I interpret at least) to be close to that of Rey and Kylo Ren. Meaning, I believe, that they are able to see each other's forms and hear each other speak, but not able to see each other's surroundings. One can believe this is a natural connection the force forms between them being that they are father and son, or that their fates are intertwined, etc., but what if the Emperor created this connection to bring them together again? What if the Emperor created a connection between them so that Luke would be drawn to Vader again, so that he could seduce him to the Dark Side and replace Vader, rather than just relying on fate to have Luke come to Vader again?