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# Cosmology and GR — RST foundation
**Cosmology** and **GR** (expansion $\theta = 3H$, FLRW; noise floor $a_0 = cH/(2\pi)$; dark energy as baseline) are the eighth foundational area. They supply the physical noise floor and the three regimes (Newton / MOND / $\Lambda$).
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## I. Classical side
- **FLRW:** Homogeneous, isotropic expansion; $\theta = \nabla_\mu u^\mu = 3\dot{a}/a = 3H$.
- **Dark energy / $\Lambda$:** Constant energy density; $W \to N$ when $I \to 0$.
- **Gravity:** Newton, MOND, and the transition scale $a_0$.
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## II. Mapping to RRT / RST
| Concept | RRT / RST identity | Equation / link |
|:---|:---|:---|
| **Expansion $\theta$** | $3H$ in FLRW; sets the cosmic "noise" scale. | A4, A5; Noise Floor. |
| **Noise floor $a_0$** | $a_0 = c\theta/(6\pi) = cH/(2\pi)$; gravitational threshold. | Noise Floor; RST Core Reduction. |
| **Newton regime** | $\Omega \gg N$; $\mu \to 1$; $\Omega = I$. | High SNR. |
| **MOND regime** | $\Omega \ll N$; $\mu \to \eta$; $\Omega = \sqrt{I \cdot N}$. | Low SNR. |
| **Dark energy** | $I \to 0$; $W \to N$; baseline workload. | RST Part II; $\Lambda$. |
So: **cosmology** gives $\theta$, $H$, $a_0$; **GR** gives the geometric setting; together they fix the noise $N$ and the three regimes of the Resource Allocation Equation.
At macroscopic scale ($N \to \infty$), accumulated lacunarity yields $D_f \approx 1.86$ and the MOND fidelity $n \approx 1.24$. See [[N to Infinity — Cosmology (RST)]].
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## Links
- **Graph Size Hierarchy ($N \to \infty$):** [[N to Infinity — Cosmology (RST)]]
- **Foundation index:** [[../Foundation index]]
- **Noise Floor:** [[expanded theory/Noise Floor]]
- **RST Core Reduction:** [[expanded theory/RST Core Reduction]]
- **Applications Roadmap:** [[../../Applications Roadmap]]