What "exactly" happens when someone turns to the Dark Side?

Question

When I saw the original Star Wars saga as a kid, the concept of the Dark Side imprinted in me was quite simple. You did a bad thing, so you're a bad person so you go to the Dark Side and keep doing bad things.

Now, obviously this doesn't hold true in reality. In my mind it is perfectly reasonable for Luke to kill the Emperor and Vader and then just flee the Death Star and rejoin the Alliance. After all they are at war, those are enemy officers that have captured him and are taunting him by threatening with death of all loved ones and the whole operation was intended to kill the Emperor anyway.

The same would hold true for Anakin. He could have killed Mace Windu to save the Chancellor and Padme but that doesn't mean he's going to then go mad and kill all Jedis including children. It doesn't add up from a merely psychological point of view. He had a set of objectives and that made him want to keep the Chancellor alive (quite valid by the way, Mace Windu is quite clumsy on that) but just after killing him he goes into "Yes master I'll do whatever you say" which from a normal point of view will NEVER ever make sense.

In both cases it seems like the assumption is once you use the Dark Side you completely turn to the Dark Side and become a different person that you were before. That would be coherent with Anakin "dying" and Vader being born.

Is that the way the Dark Side works? Is there any canon information about what happens when someone turns to the Dark Side? Specifically to whether they become a different person or how he or she actually changes?

Note: Vader is angry after he finds out Padme is dead, even though he's already turned.

Example of what I mean. In Buffy they explain how people that turn into Vampires lose their soul and it's taken over by a demon, and thus they are, in all effects, a different person with their memories.

Answer 1

The Dark Side does affect you both mentally and physically, in many ways it is like an addictive drug in that the more you use it, the more you change be become dependent on it:

The dark side, much like a strong, addictive narcotic, affected not only the mind of the user but the appearance as well. As one immersed oneself deeper within the dark side of the Force, its malevolent power took a toll on the body. Darth Bane explained that the reason for this physical degradation was because flesh and bone lacked the endurance to channel the immense power of the dark side indefinitely. Revan also explained that while the light side and Jedi teachings were devoted to preventing physical change through the Force, the dark side changes had to be accepted by the Sith, or they would fail due to their attempts at moderation.

As for completely hollowing you out and replacing you with a demon of some kind, that doesn't happen. Although after enough time had passed and you fall far enough to the Dark Side, it would probably appear as if the old you was indeed dead and replaced by some evil entity.

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One interesting case is Darth Nihilus, who was totally consumed by the Dark Side and became some sort of Dark Side poltergeist. Something like this is extremely rare and as far as we know, only ever happened to Nihilus:

In time, the corruption could go beyond mere cosmetic details and directly impair physical abilities. King Ommin of Onderon was a proficient Sith sorcerer for most of his life, and the dark side held him under its decaying influence until he eventually became incapable of movement and needed support from a cyborg exoskeleton in order to survive. Another extreme case of dark side corruption was Darth Zash, whose extensive study of the dark side led to immense physical degradation and eventually a fatal terminal condition. The worst case of this transformation would be Darth Nihilus, who was completely consumed by the dark side both mentally and physically. Eventually, he became an aberration of the dark side that existed only to consume life.

Answer 2

I've thought of that myself.

The implication that was made in The Empire Strikes Back and in Revenge of the Sith is that use of the Dark Side affects one's mental state, and at least in part this is because of how it's invoked.

From a Jedi's perspective, Yoda says: "Once you start down the Dark Path, forever will it dominate your destiny. Consume you, it will."

And, "A Jedi uses the Force for defense, never for attack."

Fairly vague, but in Revenge of the Sith, Anakin says, quoting knowledge gained from his Jedi teachings:

"The Sith rely on their passion, they think inwardly, only of themselves.."

Later, Sidious says to Vader: "Do what must be done Lord Vader. Do not hesitate, spare no one. Only then will you be strong enough in the Dark Side to save Padme."

Now it's possible that Sidious was just lying in order to convince Anakin to do what he wanted, but if we take this statement at face value, it says something.

First, the Dark Side responds to aggression: "I can sense your anger, it gives you focus, makes you stronger" or from Dooku "You have hate, you have anger, but you don't use them."

Second, allowing compassion to influence one's decisions weakens one's connection with the Dark Side.

The Dark Side therefore seems like something that will tempt someone to go further and further, like trying to stop eating chocolate cake after having a bite. It leaves open the possibility that one could try to be disciplined and use the Dark Side "responsibly", but that it would be exceedingly difficult.

As you point out, this makes for a rather simplistic view of aggression and morality. Why can't one channel anger, and still make moral decisions? Then again, the Jedi are very controlling of their members.

Perpetuating this way of thinking seems like a way that the Jedi kept people in line with their world view, rightly or wrongly: "You've gotta act our way, and think our way, or you'll turn evil. Oh, and you're not allowed to have a lover either."

Answer 3

Anakin's strength in the force always makes him arrogant (as we see in Attack of the Clones + and even the Phantom Menance) but it's fear that turns him to the dark side. In Episode II and the first part of III he fears losing Obi-Wan as much as Padme, but by the end of Revenge of the Sith his fear of losing Padme leads him to the Darkside.

The murder of the younglings is the event where Vader really is born (more so than Windu's murder which is an instinctive action). I'd argue that their murder is part of a narcism that's an ever present in Anakin's make up. The dark side seems to weaken empathy for anyone else. A bit like using a narcotic, Anakin quickly only cares about his own needs, hence their murder.

Anakin/Vader's temper is exacerbated by Dark Side use. I think he struggles to control his temper more than any other dark side user in all the films (Kylo Ren's temper is mere tantrum when compared to Vader's) In Vader's early stages he can't control his anger. The strangulation of Padme shows how quickly Dark Side use means that the user only focuses on himself.

Obi-Wan does not attempt to reason with Vader at all in their Death Star encounter (I know that Lucas didn't intend Vader to be Anakin at this point but it luckily fits!) as he knows that prolonged Dark Side use has eradicated compassion and empathy (in the way prolonged drug use does the same - all that matters is the next fix).

Vader's treatment of Dr Alpha again demonstrates the lack of compassion, and worse the pleasure of malice with torture. Throughout the films Vader enjoys the fear he generates and views everyone as instruments in him getting what he wants. Palpatine has a similar view, a self-centredness and narcissism that is the net result of hungering for power, just for it's own sake. Many dictators display similar behaviour tendencies.

Vader lacks his master's control. Probably because he's emotionally damaged from his various childhood traumas. Vader struggles to control his anger/hatred in the first fight with Luke in Empire. He does not intend to chop off his son's hand, but such is the power of the dark side he can't control himself. One could argue that it is again fear of losing another possession (i.e. his son) rather than the oft quoted compassion that sees him tackle Palpatine. I'd argue it is selflessness that wins out, Vader is fully aware of the terrible risk of interceding on his son's behalf for his own well-being.

I don't think any of the media really tackle this question though, Vader quitting the Dark Side and releasing his hate, although oft discussed is both physically and emotionally incredibly difficult for him. As a child of the Force he personifies both side.

Answer 4

Simple use of the dark side doesn't necessarily result in a turn, however. Many, many light siders find themselves in extremis and draw on the dark side, yet few of these Jedi subsequently fall.

Obi-Wan uses the dark side to gain the upper hand against Maul. Luke uses the dark side when he classically beats Vader down and cuts his hand off. Anakin uses by my count eight separate dark side powers he has control of, and three more during moments of extreme distress during the Clone Wars, but doesn't turn until he seems to make the conscious decision to yield to it for his own gain.

In Star Wars Rebels, Ezra Bridger uses some of the most extreme of dark side powers he learned from a Sith Holocron with deliberate control for weeks, yet while he was clearly beginning to trod the dark path, he ultimately doesn't fall.

Yoda may say simple use of the dark side can be equated with falling to the dark side, but there's more to it than that.