Test 31 — CMB Acoustic Peak Geometry Test
The photon-baryon plasma before recombination rang like a bell: pressure waves driven by gravity and photon pressure froze into a pattern of harmonic peaks in the Cosmic Microwave Background (CMB) temperature power spectrum. If early-universe history really is "increasing recordable distinction," this peak pattern is one of the richest compressed records of that history that exists — a single angular power spectrum encoding the sound horizon, the baryon-to-photon ratio, the matter and radiation content, and the spatial curvature, all at once. Does the peak structure predicted by the model's cosmological parameters match what has actually been measured?
- Observable
- CMB first acoustic-peak position, ℓ₁ ≈ 220 (with ℓ₂ ≈ 537, ℓ₃ ≈ 810)
- Standard cosmology
- Peak sequence from the ΛCDM fit (Planck 2018: sound horizon rₛ = 144.43 ± 0.26 Mpc, 100θ∗ = 1.04092 ± 0.00031), giving ℓ₁ ≈ 220
- Granularity (consistency reading)
- Same peak geometry, ℓ₁ ≈ 220 — the framework uses the identical acoustic calculation and reproduces the whole sequence rather than re-deriving it
- Measured
- ℓ₁ ≈ 220, a firmly detected peak (BOOMERANG → WMAP → Planck 2018; Planck Collaboration V, 2020, A&A 641, A5), pinned to sub-percent precision by 100θ∗
- The epoch
- Recombination, zₛ = 1089.92 ± 0.25 — about 380,000 years after the beginning, T ≈ 0.26 eV
- Verdict
- GREEN — Agrees
The number matches the number. The first acoustic peak sits at ℓ₁ ≈ 220, one of the most cleanly detected features in all of cosmology — first caught by balloon experiments, then nailed down by WMAP and Planck to a fraction of a percent. The framework lands on exactly the same peak, in exactly the same place. There is no daylight between the two.
And it earns that agreement honestly. The framework does not run a rival calculation and hope to sneak into range; it uses the same acoustic physics — the same sound horizon, the same distance to the last-scattering surface — and gets the same answer because it is the same answer. When a quantity is this well measured and this unambiguous, reproducing it is not a hedge. It is a real, checkable match against a real detection.
So this one is not open, and it is not owed to anyone. The peak is measured, the framework meets it, and the two agree. That is the plain reading, and it is green.
1. Verdict
The number, both ways
- Number we’re testing
- Position of the CMB TT acoustic peaks — first peak multipole ℓ₁ ≈ 220 (with ℓ₂ ≈ 537, ℓ₃ ≈ 810), plus peak-height ratios set by Ω_b h²
- Standard cosmology & measured
- Standard cosmology here is the measurement itself — Peak sequence from the ΛCDM fit (Planck 2018: sound horizon r* = 144.43 ± 0.26 Mpc, 100θ* = 1.04092 ± 0.00031), giving ℓ₁ ≈ 220 · ℓ₁ ≈ 220, a firmly detected peak (BOOMERANG → WMAP → Planck 2018; Planck Collaboration V 2020, A&A 641, A5), pinned to sub-percent precision by 100θ*
- This framework (granularity)
- The independent read: Same peak geometry, ℓ₁ ≈ 220 — the framework uses the identical acoustic calculation and reproduces the whole sequence rather than re-deriving it
- Agreement
- The number matches the number — ℓ₁ ≈ 220 both ways, pinned to sub-percent precision by 100θ* = 1.04092 ± 0.00031; 'no daylight between the two' (consistency check — shared inputs)
Check the source → the calculation shown on this page (Data Used · Calculation Summary)
Agrees with existing models. The observed TT, TE, and EE acoustic-peak positions and relative heights are reproduced by the standard cosmological parameter set (baryon density, cold dark matter density, Hubble constant, spatial curvature consistent with zero, standard radiation content including \(N_{\rm eff}=3.044\), and standard recombination physics) using the standard linear Boltzmann transport framework (e.g. CAMB/CLASS), as fit to Planck 2018 data. This framework doesn't run its own independent Boltzmann code — it uses the same cosmological parameters standard cosmology uses, and gets the same answer, because it's the same calculation. What this framework adds is a way of reading the result: the peak pattern is the compressed record of the pre-recombination photon-baryon plasma, frozen in at the moment the universe went transparent. No deviation from the standard multi-peak acoustic structure is predicted or required.
2. Tested Claim
The precise granularity claim under test: the photon-baryon plasma between weak-scale relic decoupling and recombination (\(z\approx1089\), \(t\approx380{,}000\) yr, \(T\approx0.26\) eV) supported acoustic oscillations whose compression/rarefaction phases at the moment of last scattering are "frozen in" as a harmonic series of peaks in the CMB angular power spectrum \(C_\ell^{TT}\), \(C_\ell^{TE}\), \(C_\ell^{EE}\). If the granularity doctrine's picture of this epoch is right — that the plasma's oscillation pattern is a valid, stable, recordable distinction fixed at the recombination window and read out unchanged today — then (a) the peak positions \(\ell_n\) should follow the standard acoustic scale set by the sound horizon at last scattering divided by the angular diameter distance to last scattering, and (b) the peak height ratios (odd peaks suppressed relative to even peaks) should follow the standard baryon-loading signature set by \(\Omega_b h^2\). This is a consistency check against the fully standard ΛCDM calculation, not a test of a distinctive alternative mechanism.
3. Data Used
- Planck 2018 final cosmological parameters (Planck Collaboration VI, 2020, A&A 641, A6, arXiv:1807.06209), TT,TE,EE+lowE+lensing baseline (base-ΛCDM column, Table 2): \(\Omega_b h^2 = 0.02237\pm0.00015\), \(\Omega_c h^2 = 0.1200\pm0.0012\), \(H_0 = 67.36\pm0.54\) km/s/Mpc, \(n_s = 0.9649\pm0.0042\), spatial curvature consistent with zero (\(\Omega_K = 0.0007^{+0.0037}_{-0.0037}\)), angular acoustic scale \(100\,\theta_* = 1.04092\pm0.00031\).
- Planck 2018 measured peak multipoles (Planck Collaboration V, 2020, A&A 641, A5, arXiv:1907.12875; Planck 2018 power-spectra/likelihood release): first acoustic peak at \(\ell_1 \approx 220\), second peak at \(\ell_2 \approx 537\), third peak at \(\ell_3 \approx 810\) (standard literature values consistent with the Planck 2018 TT spectrum, e.g. also tabulated in earlier WMAP/Planck peak-fitting papers such as Hinshaw et al. 2013, ApJS 208:19, arXiv:1212.5226, for the same peak sequence with earlier-mission precision).
- Sound horizon at recombination: Planck 2018 base-ΛCDM value \(r_* = 144.43\pm0.26\) Mpc (comoving sound horizon at last scattering, Planck Collaboration VI 2020, Table 2).
- Angular diameter distance to last scattering: Planck 2018 base-ΛCDM value \(D_A(z_*) \approx 13.87\) Gpc (comoving angular diameter distance, consistent with \(100\,\theta_* = 1.04092\)).
- Baryon-loading / peak-height physics: standard result that odd-peak amplitudes are suppressed relative to even peaks by a factor controlled by \(\Omega_b h^2\) (Hu & Sugiyama 1996, ApJ 471:542; Hu & Dodelson 2002, Annu. Rev. Astron. Astrophys. 40:171, arXiv:astro-ph/0110414) — the Planck 2018 best-fit \(\Omega_b h^2=0.02237\) reproduces the observed second/first and third/first peak height ratios within the quoted Planck likelihood errors (Planck Collaboration VI 2020, §2 and Fig. 1).
- Recombination redshift: \(z_* = 1089.92\pm0.25\) (Planck Collaboration VI 2020, Table 2), consistent with Test 29 (Recombination Visibility Function Test) in this suite.
4. Calculation Summary
Step 1 — Acoustic scale from sound horizon and angular diameter distance. The characteristic angular scale of the peaks is set by \[ \theta_* = \frac{r_*}{D_A(z_*)} . \] Using the Planck 2018 values \(r_*=144.43\) Mpc and \(D_A(z_*)\approx13.87\) Gpc \(=13{,}870\) Mpc: \[ \theta_* \approx \frac{144.43}{13{,}870} \approx 1.0413\times10^{-2}\ {\rm rad} = 0.5966^\circ , \] i.e. \(100\,\theta_* \approx 1.0413\), consistent (to the precision retained here) with the Planck-quoted \(100\,\theta_*=1.04092\pm0.00031\).
Step 2 — First peak location from the acoustic scale. The first peak occurs at \(\ell_1 \approx \pi/\theta_*\) to leading order (a standard approximation; the exact location is shifted slightly by driving effects, see Hu & Sugiyama 1996): \[ \ell_1 \approx \frac{\pi}{1.0413\times10^{-2}} \approx 302 , \] which overshoots the precise, radiation-driving-corrected observed value \(\ell_1\approx220\) by about \(37\%\) — exactly as expected, because the naive \(\pi/\theta_*\) formula omits the well-known phase shift from the early-Integrated-Sachs-Wolfe / radiation-driving effect (a shift of roughly \(\Delta\ell\sim-\)tens, driven by the still-nontrivial radiation density at recombination; see Hu & Sugiyama 1996; Doran & Lilley 2002, MNRAS 330:965, arXiv:astro-ph/0104486, who quantify this phase shift explicitly). This is a standard, well-documented correction in ΛCDM cosmology, not a distinctive discrepancy — full Boltzmann codes (CAMB/CLASS) reproduce \(\ell_1\approx220\) exactly once the phase shift and multipole-vs-angle mapping are treated properly; the simplified formula used here is only a back-of-envelope cross-check, not the precision calculation.
Step 3 — Peak spacing. To leading order, subsequent peaks are approximately evenly spaced in \(\ell\) by the same acoustic scale, \(\Delta\ell\approx\pi/\theta_*\approx302\), though harmonic spacing is also modified by the same driving-phase corrections. The observed spacings, \(\ell_2-\ell_1\approx537-220=317\) and \(\ell_3-\ell_2\approx810-537=273\), bracket this leading-order estimate and match the full Boltzmann-code prediction for the Planck 2018 base-ΛCDM parameters (this bracketing/near-even-spacing pattern is itself a classic, textbook consistency signature of a spatially-flat, standard-radiation-content universe — see Hu & Dodelson 2002, §3).
Step 4 — Peak-height ratio (baryon loading). The standard qualitative and quantitative result (Hu & Sugiyama 1996; Hu & Dodelson 2002) is that increasing \(\Omega_b h^2\) suppresses odd peaks (compressions resisted by baryon inertia are enhanced; rarefactions, i.e. even peaks in some conventions, are relatively enhanced) — the Planck best-fit \(\Omega_b h^2=0.02237\) reproduces the observed second-peak-to-first-peak height ratio (\(C_2/C_1\sim0.4\)–\(0.45\) in the Planck TT spectrum) within Planck's quoted likelihood uncertainties (Planck Collaboration VI 2020, Fig. 1, residuals plot). No separate baryon density is needed for the peak-height fit than the one already fixed independently by BBN-CMB concordance (see Test 21 in this suite) — the same \(\Omega_b h^2\) closes both checks simultaneously, which is itself a nontrivial internal consistency property of the standard model, not something this framework adds.
Cross-epoch consistency (required check per suite method). The parameters used here (\(\Omega_b h^2\), \(N_{\rm eff}=3.044\), \(z_*\approx1090\)) are the same parameters checked in Tests 21 (baryon-to-photon ratio), 22 (neutrino decoupling / \(N_{\rm eff}\)), 28 (matter-radiation equality), and 29 (recombination visibility function) elsewhere in this suite; nothing computed here requires a different value for any of those quantities, so closing this test does not create tension with BBN, neutrino decoupling, or recombination-timing results elsewhere in the suite.
5. Granularity Interpretation
On the framework's reading, the acoustic peaks are the paradigm case of a "compressed record": the photon-baryon plasma's pressure-wave oscillations do not themselves need to be treated as a new granularity event requiring a first-principles derivation from this framework's geometry. Instead, the peak pattern is the observable, frozen-in signature of granularity distinctions that were already established earlier (baryon density fixed at baryogenesis and checked at BBN; radiation content fixed by particle content and checked via \(N_{\rm eff}\); spatial geometry and expansion history fixed by the background cosmology) — recombination simply "reads out" those pre-existing distinctions into a single, extraordinarily information-dense angular power spectrum. This is exactly the kind of record the granularity doctrine expects to find: a physical process (Thomson scattering shutting off as the universe becomes neutral) that converts a transient dynamical pattern into a permanent, recordable, observer-accessible relic. No new "newly distinguishable" object is being claimed here beyond what standard cosmology already asserts.
6. Gate Routing
This test informs the Compressed cosmic record gate in the Physics/GUT/TOE program. The acoustic-peak positions, heights, and the underlying sound horizon and angular diameter distance are all taken directly from the standard Planck 2018 fit — this framework does not derive any of \(\Omega_b h^2\), \(\Omega_c h^2\), \(H_0\), \(r_*\), or the recombination redshift from its own geometry; it only shows that reading the peak structure as a compressed record of the plasma's history is fully consistent with, and requires no deviation from, the standard ΛCDM fit to Planck 2018 data.
7. Failure Mode
Not applicable in the strict sense — the compressed-record reading is consistent with the data as fit by standard cosmological parameters. For completeness, the specific failure modes named in the test-suite document's guardrails, and confirmed absent here:
- No qualitative-match substitution: Section 4 above ties the verdict to explicit numerical checks (acoustic scale, peak spacing, peak-height ratio against \(\Omega_b h^2\)), not a narrative-only claim that "the plasma rang like a bell."
- No measured-value-treated-as-derived error: \(\Omega_b h^2\), \(\Omega_c h^2\), \(H_0\), \(r_*\), and \(z_*\) are explicitly carried as observed/fit inputs from Planck 2018, not claimed as first-principles outputs of this framework's geometry.
- No inherited result dressed up as a derivation: this test does not claim the framework derives the peak structure; it claims only that reading the peaks as a compressed record is consistent with data that standard ΛCDM already fully explains.
- Simplified-formula caveat flagged honestly: the leading-order \(\ell_1\approx\pi/\theta_*\) estimate in Step 2 overshoots the precise observed \(\ell_1\) by \(\sim\)37% because it omits the radiation-driving phase shift; this is disclosed explicitly rather than silently corrected to match data, and the discrepancy is attributed to a known, named physical effect (not a framework failure) with a citation to the literature that quantifies it.
8. Next Action
Data lookup / monitoring, not derivation: (a) if this framework's own GUT/TOE construction ever proposes a mechanism that would shift \(\Omega_b h^2\), \(N_{\rm eff}\), the recombination redshift, or the background expansion history away from the Planck 2018 base-ΛCDM values, re-run this consistency check against the resulting peak spectrum using a full Boltzmann code (CAMB/CLASS) rather than the leading-order estimates used here; (b) monitor ACT DR6 and SPT-3G high-\(\ell\) polarization data and any future CMB-S4 release for refinements to the peak positions/heights and to \(\Omega_b h^2\), \(N_{\rm eff}\); (c) no further routing is needed beyond treating the underlying cosmological parameters as measured inputs, the same way standard cosmology treats them — this test only certifies that reading the acoustic peaks as a recorded history of the plasma does not conflict with that standard fit.
Bottom line
This is a result this framework agrees with existing models on: the acoustic-peak positions and heights belong to standard hot-Big-Bang cosmology and linear perturbation theory, which this framework inherits wholesale rather than independently deriving. What it adds is a way of reading the result — the peaks as a compressed, permanent record of the pre-recombination plasma's history rather than a primitive object requiring its own first-principles derivation. That reading is consistent with, though not independently confirmed or predicted by, the Planck 2018 data checked here.
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