Note: This preprint has been superseded. The phenomenological filter presented here has been replaced by a derived model. Please refer to: \"The Participatory Horizon as an Angular Recording Filter: A Derived CMB Suppression Scale\", doi:10.5281/zenodo.19647157.
\nSeveral persistent anomalies in the Cosmic Microwave Background (CMB) appear concentrated at the largest angular scales, most notably an anomalous suppression of temperature correlations for separations $\\theta \\gtrsim 60^\\circ$. Curiously, the scale at which these correlations vanish corresponds to a comoving distance comparable to the radius of the observable universe. Plausible explanations invoke statistics, while tuned primordial initial conditions have also been considered. Here, we explore an alternative hypothesis motivated by Wheeler's participatory view of quantum measurement. We propose that classical cosmological records are instantiated only to the extent that correlations can be resolved and irreversibly registered within an observer's causal domain. In this stance, the CMB is treated as a relational reference frame rather than a fixed fossil record, with correlations on scales comparable to the 'participatory horizon' remaining under-instantiated as classical records, effectively filtering their contribution to the realised sky.
\nThis concept is explored phenomenologically by applying a smooth horizon-scale infrared suppression to a fiducial $\\Lambda$CDM spectrum while leaving the background cosmology unchanged. Fitting to Planck TT bandpowers over $2 \\leq \\ell \\leq 30$ yields a preferred cutoff scale $k_{\\rm cut} = \\alpha (\\pi / \\eta_0)$ with $\\alpha \\simeq 0.69$ (for a representative sharpness $p=6$), corresponding to $k_{\\rm cut} \\simeq 1.53 \\times 10^{-4} \\, \\text{Mpc}^{-1}$. This result indicates a preference for a suppression scale anchored to the observer's present horizon. Using a diagonal bandpower $\\chi^2$ diagnostic, the fit is improved by $\\Delta \\chi^2 \\simeq -5.7$. A complementary per-multipole inverse-gamma likelihood, which accounts for the non-Gaussian distribution of low-$\\ell$ power spectrum estimators and for cosmic variance via effective degrees of freedom, yields a consistent best-fit $\\alpha$ with $2\\Delta\\ln\\mathcal{L} \\simeq +3.1$ The large-angle statistic $S_{1/2}$ is reduced by ${\\sim}\\,85\\%$ relative to fiducial $\\Lambda$CDM, while the acoustic peak structure at $\\ell \\gtrsim 50$ remains unchanged.
\nThe model offers potenially falsifiable predictions for the low-$\\ell$ $EE$-mode spectrum and temperature--polarisation cross-correlations, with the precise strength of the polarisation suppression depending on whether the filter operates in angular or comoving $k$-space. These exploratory results cautiously suggest that the low power anomaly might be feasibly reframed as a dynamic participatory effect, providing a viable quantitative overlay to the $\\Lambda$CDM model.
", "languages": [ { "id": "eng", "title": { "en": "English" } } ], "publication_date": "2026-04-22", "publisher": "Zenodo", "related_identifiers": [ { "identifier": "https://doi.org/10.5281/zenodo.17956984", "relation_type": { "id": "issupplementedby", "title": { "de": "Wird erg\u00e4nzt durch", "en": "Is supplemented by" } }, "resource_type": { "id": "publication-preprint", "title": { "de": "Preprint", "en": "Preprint" } }, "scheme": "url" }, { "identifier": "https://doi.org/10.5281/zenodo.17946300", "relation_type": { "id": "issupplementedby", "title": { "de": "Wird erg\u00e4nzt durch", "en": "Is supplemented by" } }, "resource_type": { "id": "publication-preprint", "title": { "de": "Preprint", "en": "Preprint" } }, "scheme": "url" }, { "identifier": "https://10.5281/zenodo.19528259", "relation_type": { "id": "issupplementedby", "title": { "de": "Wird erg\u00e4nzt durch", "en": "Is supplemented by" } }, "resource_type": { "id": "publication-preprint", "title": { "de": "Preprint", "en": "Preprint" } }, "scheme": "url" }, { "identifier": "10.5281/zenodo.19647157", "relation_type": { "id": "iscontinuedby", "title": { "de": "Wird fortgesetzt durch", "en": "Is continued by" } }, "resource_type": { "id": "publication-preprint", "title": { "de": "Preprint", "en": "Preprint" } }, "scheme": "doi" } ], "resource_type": { "id": "publication-preprint", "title": { "de": "Preprint", "en": "Preprint" } }, "rights": [ { "description": { "en": "The Creative Commons Attribution license allows re-distribution and re-use of a licensed work on the condition that the creator is appropriately credited." }, "icon": "cc-by-icon", "id": "cc-by-4.0", "props": { "scheme": "spdx", "url": "https://creativecommons.org/licenses/by/4.0/legalcode" }, "title": { "en": "Creative Commons Attribution 4.0 International" } } ], "subjects": [ { "subject": "Cosmic Microwave Background" }, { "subject": "John Archibald Wheeler" }, { "subject": "Quantum Cosmology" }, { "subject": "Causal Diamond" }, { "subject": "Low Power Anomaly" }, { "subject": "Planck" }, { "subject": "CMB anomalies" }, { "subject": "LambaCDM" }, { "subject": "low multpole suppression" }, { "subject": "IR filter" }, { "subject": "measureverse" } ], "title": "The 'Participatory Horizon': Causal Limits and the CMB Low Power Anomaly", "version": "5" }, "parent": { "access": { "owned_by": { "user": "1490775" }, "settings": { "accept_conditions_text": null, "allow_guest_requests": false, "allow_user_requests": false, "secret_link_expiration": 0 } }, "communities": { "default": "3744609d-c330-4e60-9ff1-54a7df845590", "entries": [ { "access": { "member_policy": "open", "members_visibility": "public", "record_submission_policy": "open", "review_policy": "closed", "visibility": "public" }, "children": { "allow": false }, "created": "2025-12-17T03:30:22.104568+00:00", "custom_fields": {}, "deletion_status": { "is_deleted": false, "status": "P" }, "id": "3744609d-c330-4e60-9ff1-54a7df845590", "links": {}, "metadata": { "description": "This programme explores cosmic anomalies and foundational problems through participatory principles. The project is emerging from its conceptual stages, and is now establishing feasibility and falsifiability. Enquiries welcome.", "organizations": [ { "id": "03b94tp07" } ], "page": "This is a highly exploratory programme exploring anomalies through participatory principles.
\nThe project is at its earliest conceptual stages, and is currently attempting to find its first steps in feasibility and falsifiability. The current studies can be considered simply as thought experiments, posed through phenomenological models.
Enquiries welcome.