Current datasets impose strong constraints, and the model can remain viable if:
The interlayer coupling ij\alpha_{ij} remains small enough not to violate time-delay lensing consistency,
Angular variation in redshift drift is below the CODEX detection threshold (~cm/s/decade),
Gravitational wave echoes occur only in specific merger orientations or early-universe bursts, not in all events.
These features make the model highly testable in the coming decade and offer clear pathways to falsification or validation.
E. Theoretical Robustness: Stability of Multi-layer Configuration, Validity under Swampland Conjecture
1. Stability of Multi-layer Cosmological Configuration
The proposed framework postulates a universe with a stratified, multi-layered topology, where each layer represents a quasi-independent Friedmann-like patch with potentially distinct curvature kik_i, density i\rho_i, and phase i\theta_i. While such a configuration introduces additional complexity, it also raises two central theoretical concerns:
Dynamical Stability: Will such layered configurations persist or decay under Einstein evolution?
Gravitational Backreaction: Can interference terms or tunneling remnants induce instabilities?
Stability Analysis Highlights:
The modified Friedmann equation includes interlayer interaction terms of the form
 jiijcos(ij),\epsilon \sum_{j \ne i} \alpha_{ij} \cos(\theta_i - \theta_j),
 which, under suitable bounds on ij\alpha_{ij}, act as stabilizing phase-locking terms, not destabilizing fluctuations.
The model mirrors phase-coupled oscillator lattices, where bounded coupling strength leads to synchronized but non-chaotic evolution.
Numerical solutions with reasonable initial conditions (see Sec. 4A) show converging attractor behavior for most cosmological observables (e.g., averaged H(t)H(t), effective k\Omega_k).
Layer boundaries respect causal structure and do not violate the dominant energy condition, ensuring that geodesic propagation and perturbative growth remain consistent.
In summary, the stratified configuration represents a meta-stable vacuum patchwork rather than a chaotic or fine-tuned architecture. It generalizes conventional bubble-universe scenarios but adds internal holographic consistency and fractal structure.
2. Validity Under Swampland Conjecture Constraints
The Swampland Program in string theory places powerful constraints on the low-energy effective field theories (EFTs) that can emerge from a consistent UV completion in quantum gravity. Any cosmological model purporting to be fundamental must avoid the Swampland and remain in the Landscape of consistent theories. The key relevant criteria include:
(i) de Sitter Swampland Conjecture
This states that EFTs with stable or metastable de Sitter vacua are not consistent with string theory. Formally,
