The epistemology of dark matter and modified gravity

Project Information

ANDROMEDA

Grant agreement ID: 101130750

DOI

10.3030/101130750

Project closed

EC signature date 3 November 2023

Start date 1 September 2024

End date 31 August 2026

Funded under

• Widening participation and spreading excellence

Total cost

No data

EU contribution

€ 153 486,72

Coordinated by

ETHNIKO KAI KAPODISTRIAKO PANEPISTIMIO ATHINON
Greece

Periodic Reporting for period 1 - ANDROMEDA (The epistemology of dark matter and modified gravity)

Reporting period: 2024-09-01 to 2026-08-31

Summary of the context and overall objectives of the project

For over five decades, astrophysical observations have revealed a persistent mass discrepancy in the universe: the dynamics of galaxies, galaxy clusters, and the large-scale structure of the universe cannot be explained by visible baryonic matter alone. To reconcile the standard theory of gravity with these observations, the scientific community has pursued two primary pathways. The dominant paradigm, the Lambda Cold Matter (ΛCDM) model, postulates the existence of undetected, non-baryonic dark matter particles. Conversely, Modified Newtonian Dynamics (MOND) and its relativistic formulations propose that the laws of gravity themselves undergo a structural transition in the ultra-weak-field regime of low accelerations.

While the standard model enjoys immense success at cosmological scales, the laboratory detection of dark matter remains elusive. At the same time, modified gravity frameworks struggle to explain cosmological observations without introducing their own auxiliary fields. Rather than a straightforward empirical dispute, this controversy centers on fundamental questions of scientific methodology, theory evaluation, and the epistemic standards by which competing physical explanations are judged.

The ANDROMEDA project integrates the History and Philosophy of Science (HPS) directly with modern cosmology to address these foundational issues. Utilizing historical epistemology and philosophical analysis, the project evaluates the conceptual underpinnings of both research programs. The overall objectives are: (1) to construct a philosophically informed historical narrative of the parallel development of dark matter and modified gravity since the 1970s; (2) to critically assess the epistemic standards—such as predictive power, falsifiability, and theoretical reduction—used to adjudicate between them; and (3) to investigate their compatibility across different physical scales.

This interdisciplinary approach provides a rigorous framework for theory evaluation and clarifies the rational, multi-scale foundations of modern cosmological research.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project successfully achieved all core research objectives, producing a series of high-impact publications that advance our understanding of theory choice in physics:

Under the historical work package (WP1), the project reconstructed how the galactic "missing mass" problem became integrated with cosmological-scale non-baryonic dark matter in the 1970s and 1980s. The historical analysis demonstrated that early cosmological preferences for flat or closed geometries (where the density parameter is at least equal to 1) were strongly guided by non-empirical, Machian considerations and a rejection of temporal fine-tuning, long before precision observational data became available.

Under the epistemological work package (WP2), the project delivered two major conceptual advancements: (1) It systematically evaluated the prominent scientific analogy comparing modern dark matter to the 19th-century luminiferous ether. By establishing four fundamental disanalogies—specifically the superior multi-scale convergence of independent empirical evidence for dark matter, the absence of contradictory physical properties, the local nature of its sub-galactic anomalies, and the profound asymmetry in the theoretical ambitions of special relativity versus MOND—the research proved that the historical demise of the ether does not serve as a valid precedent against dark matter. This paper was submitted to Studies in History and Philosophy of Science. (2) It analyzed MOND's inter-theoretical relation to Newtonian gravity. The research demonstrated that MOND fails to satisfy "reduction-wise justification" because its transition to the Newtonian regime is mediated by an ad-hoc interpolating function that lacks a fundamental theoretical origin. To resolve this, the project refined the limiting reduction framework by introducing two new criteria: "downward theoretical grounding" (derivation from a parent theory) and "upward theoretical grounding" (natural embedding within a broader mathematical structure).

Under the compatibility work package (WP3), the project evaluated the mutual exclusivity of both frameworks. By analyzing recent relativistic MOND formulations (such as AeST/RMOND), the research proved that matching cosmological-scale observations, such as the cosmic microwave background (CMB) anisotropies, mathematically forces these theories to introduce extra gravitational degrees of freedom that behave exactly like pressureless, collisionless dust. This demonstrates that modified gravity does not eliminate dark matter at these scales, but structurally reintroduces it as an effective dark field.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The project’s results advance the state of the art in both physical cosmology and the philosophy of science. Traditional philosophical models of inter-theoretic reduction are too coarse-grained to distinguish healthy theoretical transitions from ad-hoc mathematical patches. By introducing the criteria of upward and downward theoretical grounding, this project provides a sophisticated tool to objectively evaluate the conceptual maturity and structural integrity of speculative, unconfirmed physical theories prior to direct empirical testing.

Even further, by deconstructing the "ether analogy," the project moves beyond simplistic pessimistic inductions regarding unobservable entities. It establishes a rigorous methodological framework demonstrating how unobservable posits are justified through multi-scale, independent convergent evidence.

Finally, the compatibility research reframes the traditional binary division of the debate, proving that relativistic modifications of gravity are mathematically forced to mimic the behavior of a dark matter field at cosmological scales.

To ensure the further uptake of these results, key needs are identified:

Further Research: Continuing the collaborative dialogue between cosmologists, astrophysicists, and philosophers of physics to apply these refined reduction frameworks to other emerging alternative gravity models.

Methodological Integration: Incorporating qualitative, structural criteria (such as reduction-wise justification) into active scientific peer-review and theory-evaluation processes.

Scientific Networking: Sustaining the interdisciplinary specialist networks established during the project's flagship workshop to foster ongoing communication between the dark matter and modified gravity research communities.