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The failures of the standard model of cosmology require a new paradigm
Pavel Kroupa, Marcel Pawlowski, Mordehai Milgrom
TL;DR
The paper asks whether cold- or warm-dark-matter cosmology can explain observed galaxy-scale regularities and mass discrepancies. It tests the model against observations and examines MOND as an alternative dynamics theory. It argues that the standard model fails these tests and that galaxy data are excellently described by MOND.
Problem
Cold- or warm-dark-matter cosmology does not explain observed dwarf-galaxy regularities, anisotropic satellite distributions, or the correlation between mass discrepancy and acceleration.
Source: §1 · p. 3Method
The paper tests cosmological-model predictions against observations and assesses MOND's account of galaxy dynamics.
Source: §1 · p. 3Results
Takeaways & Limitations
The observed galaxy-scale results suggest that a deeper theory may connect dynamics within local systems to the state of the universe at large.
Source: §9 · p. 11The cited MOND theories introduce a0 and additional degrees of freedom but may not capture the deeper theory; the proposed economy linking a0 to the cosmological constant lacks a compelling mechanism.
Source: §6 · p. 8
Abstract
from arXiv · showhide
Cosmological models that invoke warm or cold dark matter can not explain observed regularities in the properties of dwarf galaxies, their highly anisotropic spatial distributions, nor the correlation between observed mass discrepancies and acceleration. These problems with the standard model of cosmology have deep implications, in particular in combination with the observation that the data are excellently described by Modified Newtonian Dynamics (MOND). MOND is a classical dynamics theory which explains the mass discrepancies in galactic systems, and in the universe at large, without invoking dark entities. MOND introduces a new universal constant of nature with the dimensions of acceleration, a0, such that the pre-MONDian dynamics is valid for accelerations a >> a0, and the deep MONDian regime is obtained for a << a0, where space-time scale invariance is invoked. Remaining challenges for MOND are (i) explaining fully the observed mass discrepancies in galaxy clusters, and (ii) the development of a relativistic theory of MOND that will satisfactorily account for cosmology. The universal constant a0 turns out to have an intriguing connection with cosmology: \bar a0 == 2 pi a0 \approx c H_0 \approx c^2(Lambda/3)^{1/2}. This may point to a deep connection between cosmology and internal dynamics of local systems.
1. Introduction
The standard cosmological model adds several postulates to explain structure and expansion, but faces observational problems. The paper advocates tests insensitive to baryonic physics and argues that galaxy data support MOND over standard dynamics.
1. Introduction
- The standard model combines five postulates, including inflation, cold or warm dark matter, and dark energy, to describe cosmology.Its parameters are determined using observational data.Source: §1 · p. 2
- Although the model yields rigorous predictions for sub-halo distributions and tidal dwarfs, tunable baryonic modelling limits other convincing predictions.It predicts many satellite sub-halos and that tidal dwarfs cannot contain substantial dark matter.Source: §1 · p. 2
- Milky Way and Andromeda should host hundreds of satellite galaxies, but only 24 are currently known around the Milky Way and slightly more around Andromeda.The model attributes the shortfall to complex, tunable baryonic processes that remove baryons from most satellite halos.Source: §1 · pp. 2–3
- The paper calls for tests insensitive to baryonic-physics details and argues that galaxy kinematics support a non-Newtonian theory, with MOND fitting the data excellently.It describes MOND as an apparently correct account of galaxy-scale dynamics.Source: §1 · p. 3
2. The dual dwarf galaxy theorem
The standard model predicts two distinct dwarf-galaxy classes: primordial dwarfs dominated by dark matter and tidal dwarfs without substantial dark matter. Their observed shared scaling relations and structural properties contradict that predicted distinction.
2. The dual dwarf galaxy theorem
- Primordial type A dwarfs form from dark-matter halos, while tidal type B dwarfs form from interacting galaxies and cannot capture significant dark matter.The model predicts many type A substructures and enough type B dwarfs that most observed dwarf ellipticals would statistically need to be type B.Source: §2 · pp. 3–4
- A tidal dwarf's apparent dark matter can be mimicked by disequilibrium under a varying host-galaxy tidal field or by gas accretion before rotational equilibrium.Such apparent dark matter alone does not immediately disprove the model.Source: §2 · p. 4
- The dual-dwarf prediction is falsified: type B dwarfs and type A galaxies lie on the same Baryonic-Tully-Fisher Relation, contrary to the model's distinct-class prediction.The passage concludes that galactic dark-matter halos cannot exist within this argument.Source: §2 · p. 4
- Type B dwarfs are observed to be indistinguishable from dwarf ellipticals, although the model predicts different final structural parameters for these populations.The paper draws the same dark-matter-halo conclusion from this comparison.Source: §2 · p. 4
3. Significant anisotropic phase-space distribution of satellite galaxies
The standard model predicts satellite systems that are nearly spheroidal, with only mild anisotropy from filamentary infall. Instead, the Milky Way and Andromeda have highly anisotropic satellite structures.
3. Significant anisotropic phase-space distribution of satellite galaxies
- The model predicts primordial dark-matter-dominated satellites to be spheroidally distributed, with filamentary infall producing only mild anisotropies..Source: §3 · p. 4
- Nine of ten Milky Way satellites with measured proper motions orbit within the VPOS, a configuration ruled out with very high confidence under the model.The VPOS is a disk-like structure about 40 kpc thick and 400 kpc in diameter.Source: §3 · pp. 4–5
- Andromeda also has an anisotropic satellite system, and other galaxies show correlated satellite phase-space structures, so the Milky Way is not unique..Source: §3 · p. 5
4. Consistency tests
The paper presents multiple consistency tests that the standard model does not pass, including failures in the Local Volume and nearby 50 Mpc region. It argues that these problems collectively undermine the model.
4. Consistency tests
- If each of 22 listed failures reduced confidence by only 50%, the theory-confidence calculation gives an overall validity confidence of 2.3 × 10^-5 percent.The passage contrasts commonly acknowledged problems with failures it calls catastrophic, including the dual dwarf theorem, satellite anisotropy, and Local Volume matter distribution.Source: §4 · p. 5
- The Local Volume within 8 Mpc has a matter distribution in the Local Void and along filament edges that is incompatible with model expectations..Source: §4 · p. 5
- Within 50 Mpc, the region is missing dark matter by a factor of 3–4, while density fluctuations must remain no larger than about 10% under the model..Source: §4 · p. 5
- Disk galaxies of similar mass show too little scatter in their properties, implying laws that do not emerge from the standard model..Source: §4 · p. 5
5. The mass-discrepancy-acceleration correlation: towards galaxy laws
Disk-galaxy mass discrepancy shows a tight correlation with baryonic-Newtonian acceleration, departing from Newtonian behavior below a0; this relation motivates MOND’s acceleration scale.
5. The mass-discrepancy-acceleration correlation: towards galaxy laws
- Plotting mass discrepancy against baryonic-Newtonian acceleration reveals a tight correlation, unlike plotting it against radius.Mass discrepancy at radius r is represented by V²/Vb²; gN = Vb²/r.Source: §5 · pp. 5–6
- a0 ≈ 1.2 × 10−10 m/s², or 3.8 pc/Myr², marks where the correlation departs from Newtonian behavior—about five orders below Neptune’s Solar System acceleration.This correlation is presented as evidence for non-Newtonian gravitational dynamics when a < a0.Source: §5 · p. 6
- MOND introduces a0 to explain the mass-discrepancy–acceleration correlation without dark matter, while some tension remains at globular- and galaxy-cluster scales.MOND’s predictions have passed observational tests from dwarf disk galaxies to massive elliptical galaxies.Source: §5 · p. 6
6. The MOND paradigm
MOND introduces a0 as a demarcation between standard dynamics at high accelerations and a scale-invariant low-acceleration regime. The section sets out general predictions, notes observational successes and possible cosmological connections, and discusses the limits of current theories.
6. The MOND paradigm
- MOND introduces a0 as an acceleration scale: standard dynamics applies for a ≫ a0, while the low-acceleration limit is postulated to be space-time scale invariant.The demarcation role is compared with Planck’s constant and the speed of light as boundaries between older and newer physics.Source: §6 · pp. 6–7
- Several non-relativistic and relativistic MOND theories exist, but a full-fledged modified-inertia theory is not yet available.Examples listed include modified-gravity formulations, TeVeS, Einstein-aether adaptations, BIMOND, and non-local single-metric formulations.Source: §6 · p. 7
- The coincidence 2πa0 ≈ c H0 ≈ c²(Λ/3)1/2 is presented as a possible connection between local dynamics and cosmology.One proposed route relates a0 to a de Sitter acceleration scale; other proposals connect MOND to entropic dynamics.Source: §6 · pp. 7–8
- The mentioned MOND theories may be effective theories that capture the essence of a deeper future theory.The appearance of an interpolating function in these theories is identified as an indication that they may be effective theories.Source: §6 · p. 8
- In several theories, a0 ∼ aΛ follows when one length parameter in the action is used both to define the cosmological constant and a0, but no compelling mechanism forces that choice.The relation is described as depending on economy or naturalness in those theories.Source: §6 · p. 8
- MOND’s ten general laws include V∞(M) = (M G a0)1/4, a transition near V²(r)/r = a0, and effects of the external field on intrinsic dynamics.The laws also address limits on inferred dark acceleration, surface densities, velocity dispersion, disc and spherical components, and stability.Source: §6 · p. 9
- MOND’s general laws are presented as core predictions shared by its theories and as comparatively easy-to-test targets for the competing Newtonian-dynamics-plus-dark-matter paradigm.They use limited information about systems, such as global attributes.Source: §6 · p. 9
- MOND’s full rotation-curve predictions were reported as accurate in an analysis of over a hundred disc galaxies, and it also passed an acute test of elliptical-galaxy dynamics.The rotation-curve predictions follow almost entirely from MOND’s basic premises.Source: §6 · p. 9
7. MOND vs dark matter
The section contrasts MOND’s baryon-based dynamical predictions with the freedom of dark-matter fits and argues that observed tight regularities run counter to the dark-matter paradigm’s expected complex histories. It also notes a failed dark-matter prediction for tidal dwarfs.
7. MOND vs dark matter
- The many tight correlations between baryonic and inferred dark-matter properties confirmed in data are contrary to the dark-matter paradigm’s expectation of a haphazard history affecting them differently.The passage identifies these regularities as a cogent argument against the standard model of cosmology.Source: §7 · p. 9
- Given a self-gravitating system’s baryon distribution, MOND strictly predicts its dynamics, whereas the standard model cannot predict an individual primordial galaxy’s dynamics from its baryons alone.For a disc galaxy, MOND predicts the rotation curve, while dark matter allows an infinite family of halo fits.Source: §7 · pp. 9–10
- For tidal dwarf galaxies, whose formation histories are described as well understood, the standard model makes a prediction but fails it.The passage cites this tidal-dwarf prediction as an exception to the standard model’s inability to predict individual galaxy dynamics.Source: §7 · p. 10
8. MOND and the dwarfs
MOND predicts no systematic dynamical difference between primordial and tidal dwarf galaxies, and the section connects this prediction to the Milky Way’s satellite structure.
8. MOND and the dwarfs
- MOND predicts that primordial and tidal dwarf galaxies show no systematic dynamical differences and fall on the same baryonic-Tully-Fisher relation despite different formation paths.This is stated for rotational types A and B of dwarfs.Source: §8 · p. 10
- MOND is described as consistent with the Milky Way’s VPOS being an ancient tidal structure in which satellites formed as tidal dwarf galaxies and globular clusters.Tidal dwarf galaxies form naturally in MONDian galaxy interactions.Source: §8 · p. 10
- The section says MOND explains the internal constitution of the Galaxy’s dwarf-spheroidal satellites, while their high Newtonian mass-to-light ratios conflict with their being ancient tidal dwarfs in the standard model.The passage identifies the ancient tidal-dwarf interpretation as the only physically plausible explanation it gives for the VPOS with counter-orbiting satellites.Source: §8 · p. 10
9. Conclusions
The standard model of cosmology has grave failures despite successes on large scales, and observations indicate dynamics depart from Newtonian/Einsteinian behavior below a critical acceleration. MOND’s success in accounting for galactic-scale data suggests a connection between local dynamics and the universe at large.
9. Conclusions
- At accelerations below a0 ≈1.2 × 10−10m/s2, data correlations indicate dynamics are not Einsteinian/Newtonian.The standard model is reported to describe large-scale structure and the CMB, but also to have a long history of grave failures.Source: §9 · p. 10
- Dynamically significant cold or warm dark matter particles cannot explain the mass discrepancies, motivating a departure from standard dynamics below a constant critical acceleration.Source: §9 · p. 10
- The standard model’s failures are contrasted with the particle physics model, which is incomplete yet has consistently agreed with data.Source: §9 · p. 10
- Galactic-scale MOND data and properties suggest a deep connection between dynamics in local systems and the state of the universe at large.Understanding MOND’s deeper physical meaning remains a challenge.Source: §9 · p. 11