Why do some Jedi disappear when they die while others don't?
Some Jedi disappear when they die:
In Star Wars Episode IV: A New Hope
At the end of his duel with Vader on the first Death Star, Obi-Wan Kenobi let down his guard and concentrated for a moment, disappearing entirely just as Vader's lightsaber passed through his empty robe.
In Star Wars Episode VI: Return of the Jedi
When Luke returned to Dagobah in the Return of the Jedi, Yoda also disappears when he peacefully dies.
In Star Wars Episode VIII: The Last Jedi
When Luke is exhausted after “being” on Crait he looks into the Horizon and disappears.
And others don't:
Star Wars Episode I: The Phantom Menace
When Qui-Gon Jinn's dies after his duel with Darth Maul, he doesn't disappear and is cremated.
Star Wars Episode VI: Return of the Jedi
When Vader/Anakin Skywalker dies on the second Death Star, he does not disappear and he is cremated by Luke.
Also, they all became a "ghost" after their death.
In the Expanded Universe novels it is shown that most Jedi do NOT disappear upon death. Those who do have 'become One with the Force'.
It is implied that only those who disappear can re-appear as Force Ghosts, but Vader seems to invalidate this (EDIT: Correction - Vader's organic body DID disappear, what was burned was just his suit - see the section on his death, near the bottom.). A better theory is that learning how to become a Force Ghost - a technique Qui-Gonn is said to have rediscovered enables a Jedi who is prepared for death to disappear upon their physical form dying.
To disappear upon death requires great strength in the Force (equivalent to a Jedi Master), great wisdom and understanding of its ways, and for the person who dies to be at peace.
In the movie you can't see whether Vader's body is in the armor or not when it is cremated, and while the link you have above says the body disappeared there is no reference for that information. Is this detail given in one of the books or comics?
Not that I'm aware of, but the Wookiepedia is linked to from Darth Vader's character profile on starwars.com - that's a pretty strong endorsement.
I think this was the 3rd greatest blasphemy that was inflicted upon us in the e1-3. In the original RoTJ Vader did not fade away after death. The Second being midiclorians and of course the first being JarJar.
There wasn't much of Vader left to disappear, too. His legs were gone, an arm, most of the other arm...he was more machine than man after all his cybernetic replacements were in place.
@Bart Silverstrim - That's true. Then Vader's so called "ghost" should be without his arms & legs.
Extracts are form the Force Ghost wikia article:
Force Ghost is a technique that Qui-Gon Jinn rediscovered with the assistance of a Shaman of the Whills.
The disappearance of the physical body is probably an evolved technique from Obi-Wan and Yoda, under Qui-Gon's guidance.
As for Darth Vader/Anakin Skywalker, it's more complicated:
Darth Vader learned of this ability through Darth Sidious, and upon his death, the spirits of Kenobi and Yoda completed his training by granting him the last step in becoming a spirit. Anakin's spirit appeared as that of his younger self, prior to his fall to the dark side.
It is explicitly stated in Champions of the Force and the databank at the official site that the organic part of Anakin's body disappeared, and that Luke just burned his suit and mechanical parts for ritualistic purposes.
My theory: At the time of the original releases in the late 70s/early 80s the concept was that either all Jedis, or else all powerful Force users that come to realize the peace promoted by the Jedi teachings, would have their mental will preserved within the Force and would become Force ghosts, period. By realizing this peace, you become one with the Force, there was no special knowledge, teaching, or special disappearing-upon-death required, and thus with your will preserved, could apparition to anyone sensitive to the Force.
I think the Force users that disappeared already had acquired this zen and were aware of their imminent deaths (Obi-Wan allowed Vader to cut him down, Yoda was aware due to the heightened sense provided by the Force) and manipulated the Force into allowing their bodies to disintegrate into the Force to either avoid the pain of death, or believed it a more "holy" way to pass (for lack of a better word). Anakin's love for his son made him realize this peace, allowing himself to be turned into a Force ghost after he died, but hadn't known it long enough to allow his body to dissipate. Again, let me state, I believed this was the case for the initial releases only.
Because then Episodes I - III were released, followed by another set of re-releases of IV - VI with additional tweaks and changes from the 1997 re-releases. The concepts and ideas presented in I - III irked many fans, and the additional changes in IV - VI further stabbed fans in the heart because, like most people, they can't handle change and felt their childhood's were being raped. It was in these new episodes and new round of changes that introduced and provided more complex information and understandings of how the Force worked, and people didn't like it.
There's a concept that Lucas talked about that gave me a little more peace when it came to the changes and tweaks that have constantly been made with every re-release of the series (Like Anakin's younger form as the Force ghost being a one of many for instances), which is Lucas believes his true vision of how the films being depicted couldn't fully be completed in the beginning, and every change is a reflection of the complete story he initially wanted to depict. That, like many books and plays, the initial versions were rough drafts or "rough cuts" of the ultimate final version of these films, and each change is closer to the actual, true realization of his story of the tragedy of Anakin Skywalker. That makes a lot of sense to me. While the classic releases will always be the nostalgic pieces of my childhood that they are, I accept that the minor and major tweaks and changes aren't perversions of what I held as true, but more like evolved concepts of the unexplained or vague ideas that I had always wondered about, or had a personal idea of that I can admit I was wrong about considering the explanations George Lucas provides.
(And since someone mentioned Jar Jar as a blasphemy, I would like to say that he may have been an annoying character probably created solely for children, but him being an idiot and becoming a senator greatly reflects on our modern day politicians, ESPECIALLY when you considered he's directly responsible for the legislation that all but ended the Jedi Order. It makes him the second greatest tragic character in the series, if you ask me, and more than justifies his existence).
I know I kind of got off on a tangent there but my point is that the changes between why Jedis ghost, how they died, who disappeared and who didn't, have definitely changed based on how we remember them from the initial releases and that isn't a bad thing.
If the commentaries for TPM and ROTJ are any indication, you could say the retcon was re-retconned, because in the 2004 ROTJ commentary Lucas refers to Luke burning Anakin's body, not some armor. Even though he didn't manifest visually, Qui-Gon ghosted, so Qui-Gon shows that disappearing is not always a prerequisite of ghosting. It is not justifiable to call the original retcon a blasphemy inflicted by the prequels, because the prequels themselves cover a different time period and did not establish it. It apparently came along with the Special Editions.
Or the real reason, which is that George Lucas intended for Obi-Wan to get cut in two but was unable to use model bodies in a way that looked at all believable. Therefore, he came up with the disappearing act and was inconsistent about it. These are some interesting explanations for what was essentially a special effects nightmare.