We know that souls are somehow tied to the lunar cycle in the Constant: during the full moon, desecrated tombs can generate ghosts. Not only that: even during the aporkalypse, the ruins of the pigs are populated by the spirits of ancient pigs.
When Wendy crosses the celestial portal (dying in the process?) a moment before going beyond she claims to see Abigail. Abigail herself becomes more powerful with four lunar flowers in the Sisturn, as if the otherworldly flowers made her "closer" to the world of the living.
What if Alter were nothing more than a gigantic hive mind, the result of the union in the skies of the Constant of millions, perhaps billions, of souls? The gestalts would therefore be shadows of ancient consciousnesses, now fused into a whole that shines and pulsates in the sky.
