Near the end of The Last Jedi, after

astral projecting himself to the battlefield and allowing the rebels to escape, Luke just disappears, causing his body to disintegrate.

As far as I know, this isn't a side-effect of "too much force usage", so what is the actual cause of

his conversion (presumably) to the Force?

I understand from a purely plot perspective, it could be argued that

he intentionally converts in order to provide more "power" to Ray (for lack of a better word), as the Force keeps balance and would provide either Kylo Ren with enough power to match both Luke and Ray, or would send something over to the Dark side as an equalizer. This explanation however does not seem to show us why he disintegrates unless by choice, which given the timing seems like a bit of an odd choice to make as we don't have hard evidence that Ray has been fully trained in not only fighting with a lightsaber, but also in basics of how the force works.

I just want to know how it worked in the movie, so please only canonic sources.

Note: The linked duplicate asks how he astral projects himself, which I am not questioning in this. I'm asking closer to

what was the cause of his disappearance, seeing as we've never seen a "running out of Force power" as an actual side-effect of using the force.

  • 1
    Luke had little/no interest in teaching Rey how to be a Jedi. – Valorum Dec 18 '17 at 19:03
  • @Valorum That's only true for the times before he started teaching her. He ends up giving her a single lesson, gets scared, then stops for a while; that is until Yoda shows up and gives him a pep-talk about how to effectively help Ray. Regardless, the question is why it happened to him, not necessarily the motivations. – Anoplexian Dec 18 '17 at 19:08
  • @Machavity Please see the edited note. The answered questions make assumptions that he either used too much power or gave himself over, but which is it? Of course, if enough people don't think this is different enough, I can delete it. – Anoplexian Dec 18 '17 at 19:39
  • 1
    This is almost the exact same question. If the answers there are insufficient you should provide a bounty. But note, we likely won't find out until the novelisation comes out on the 6th of March. – Edlothiad Dec 18 '17 at 19:56