(w/ comments)
1. TP happens to be the site of the WL, which happens to be in our world and in our time-plane. The BL also has a physical 'site', though it is in a different temporal and spatial plane. Both worlds are completely independent of one other, but occasionally there are points in time and space at which physical gateways open up between the worlds -- as depicted by the petroglyph in Owl cave.
2. Coop tries to explain the fact that time for each Lodge is independent to Sheriff Truman using the meteor metaphor, essentially describing the ideas of relativity.
3. Just as there are spirits that inhabit the BL, there are spirits in the WL. The WL spirits still exist in the woods, but they have very little power in our present.
4. At some point in the history of TP power over the WL was possessed by the spirits of the BL. In fact, we are told precisely when this occurred, again by Earle. It was when the Dugpas began to experiment with the power that they could gain via the BL. The spirits in the BL conferred some of their power on the Dugpas in return for an entry to the woods of TP. The power of the Dugpas was really an illusion -- the BL spirits were exploiting them to increase their own power. The BL spirits are not able to cross between the two worlds at will - they need a special 'invitation': the spoken words "Fire Walk With Me". When these words are spoken, a spirit may cross from one Lodge to the other. So, in return for certain power, the Dugpas gave the spirits the opportunity to enter the WL through their chants, and they also provided the spirits with the fear that they need to survive outside the BL.
Thanks for the comments, iva. Before I launch in to a reply, let me make clear that I know I'm stretching the linearity of these points quite a bit beyond their intent. But I do want to try and reach a resolution with regard to the way in which good and evil are portrayed in Lynch's RR, BL/WL notation. And, related to that, if there's a sense of balance between good and evil in this story. Thanks for humoring me.
1. I agree with this idea--that the BL exists on a different spiritual/temporal/spatial plane and that living persons (from our perspective) are able to enter this "place". I also agree with Ditte's point--that the RR is a window into Coop's mind and I think that the BL would look quite differently if we were taken there from the POV of another character.
So maybe where my thinking is flawed is here: I always thought that the map lead to the place where the BL and the WL coexisted, so to speak. A different plane, yes, but one in which good and evil were kind of on an equal playing field. 'Ok BL, you've got doppelgangers. We've got X.' A person living in our plane (say, TP) OR a spirit after death might enter this place as a spiritual test of sorts. According to TP mythology, if confronting this place with perfect courage (or an absence of fear??), an enlightened state may follow. If confronting this place with less than perfect courage, BL inhabitants are fed their garmonbozia, grow stronger, and the person who entered may be SOL...at least for a bit. With this as my theory, what troubles me is that the "good" just isn't as easy to see in the spiritual plane. The only way to stay out of the BL appears to me to be actions in our plane/TP/present day. This strikes me more as the whole, "I'll show you my faith by my works" bit rather than what a person can have in their heart, in their spiritual walk, in their meditative, enlightened state--whatever you want to call it--to combat BL inhabitants. Are we perhaps not able to see the goodness in the RR representation of this place because it is colored through Coop's lenses?
2. Yeah, I like this part!
3. This gets at my first point--why are the WL spirits so weak? Well, perhaps that's a bit more obvious from a story-teller's perspective. Perhaps they are weak because that's the picture Lynch/Frost wished to paint of the present world. Perhaps my more burning question is: who are the WL spirits? Everyone who's not a doppelganger?
4. So a symbiotic relationship between WL and BL....hmmm, I like that too. Pure good can't even exist without pure evil.
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tatemae