I want to know what it means to say that someone or something is the "source" of the Dark side. Isn't the Dark side of the Force simply the negative energy of hatred, aggression, and fear that you tap into for strength and power? If there is a "source" for the Dark side, is there a "source" for the Light? It sounds too much like that dumb episode 9 "summary" that used to be on Supershadow's site. Or was this character referring to a source of Dark side energy that Palpatine had detected? I can see Snoke being that. There's a Living Force and a Cosmic Force.
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The Living Force is the energy of all things living. The Cosmic Force is the universe's background Force. Once something dies, that Living Energy goes into the Cosmic Force (Afterlife).
There are beings that, and ways to communicate between the two. Force Ghosts are "people" in the Cosmic Force using the midi-chlorians to talk to people living. The Force Priestesses are also one such being in-between the Living Force and Cosmic Force, that being has split into five "beings" over time.
"According to legend, midi-chlorians originated on a
planet in the heart of the galaxy, from which life was also said to have emerged. The midi-chlorians played a role in
eternal consciousness; as all living beings generated the
Living Force, it fed into the
Cosmic Force and communicated through the midi-chlorians, allowing a being who had the knowledge to manifest themselves after death." --Clone Wars TV show
So if life originated on the "Force Planet," then the Living Force originated there too. The Living Force is both darkside and lightside...so I assume the Force Planet can be considered the "origin (source?) of the darkside."
Or it could also have to do with the destruction of the Mortis "family." Father, Son, Daughter..
There's a ton of lore in the Clone Wars TV show...