I'm interested in the concept they're going for,
"Are you sure that the only you is you?
What with the talk of multiple dimensions, there might be the idea of doppelgangers?
The logic I go by in Silent Hill concerning the world is this -
The Real World (Awake) - The Fog World (Dream) The Otherworld (Nightmare)
When you're in the Fog World, you're in a dream world. You've left reality. When the Otherworld starts to seep in, you're in a nightmare.
The entire concept of Silent Hill was created around the dreams and nightmares of Alessa.
I don't believe Silent Hill to be a self aware judge, jury and executioner entity as some believe, as it was implied in Downpour. I think everything directly stems from a person's subconscious and therefore, you have no control over it, except when piece of mind is achieved. The only one who can release you from the town is yourself, in a positive or negative way. The Otherworld is your nightmare. The God uses that in the attempt to form a home, a bridge into our world. Once born through the subconscious of the nightmare, via the Otherworld, it would then break the Fog World, which is the second step, because it is the dimension of a dream world, created by your subconscious and fueled by the creation of Alessa and the ancient power. Once through the Fog World (dream), it would get into our reality and infect it, turning it into the Otherworld (nightmare). I'm not quite sure who created the Fog World? Alessa? Samael? But without the dream world, the nightmare world couldn't exist, and it's powers couldn't possibly flourish...and with its control when around, I'm guessing it was Samael who did it...but only thanks to Alessa's powers as a psychic. Alessa created it, but Samael intended it.
That's why she was chosen, because of her powers. But because Alessa split her soul, Samael couldn't be born into reality, so had to rely on Alessa's powers in order to muster its strength in order to survive...and this caused the side effect of the whole ordeal. Her powers could only flourish through the survival of Alessa and through the link it had from its own dimension, brought about by human nightmares. If Alessa had died, the God would've died and so would its link, via nightmares from the human mind. The Fog world is a side-effect of the Alessa's dream world and the Otherworld is a side-effect of Samael's influence. The dimension remains and is triggered and powered by dark/anguished souls, like Alessa.
Samael does have a level of control over the fog world and that's because her hellish forces from her realm and human followers bring it about. But without human followers to will anything into existence, Samael can't do jack. She relies on her cult.
Separate from that? The dark souls have a subconscious and uncontrollable influence over it, like Alessa. Like in dreams.
As for multiple dimensions and possibly people stemming from this?
