Observations That Transcend Law and Politics
Theoretical physicist C.N. Yang has died at the age of 103 years.
He is the Yang in Yang-Mills theory, which he and his collaborators devised in 1953, which is a generic quantum field theory that is used by scientists to study amplitudes (i.e. vector probabilities) that are foundational in all Standard Model processes and most quantum gravity theories.
He also won a Nobel prize in 1957 for his work on CP violation.
A new paper provides a possible explanation for observational evidence of a MOND-like external field effect, without definitively ruling it out. I made a post about the paper that is being re-examined exactly five years ago today.
We examine the claimed observations of a gravitational external field effect (EFE) reported in Chae et al.
We show that observations suggestive of the EFE can be interpreted without violating Einstein's equivalence principle, namely from known correlations between morphology, environment and dynamics of galaxies.
While Chae et al's analysis provides a valuable attempt at a clear test of Modified Newtonian Dynamics, an evidently important topic, a re-analysis of the observational data does not permit us to confidently assess the presence of an EFE or to distinguish this interpretation from that proposed in this article.
We derive a relativistic extension of Modified Newtonian Dynamics (MOND) within the framework of entropic gravity by introducing temperature-dependent corrections to the equipartition law on a holographic screen.
Starting from a Debye-like modification of the surface degrees of freedom and employing the Unruh relation between acceleration and temperature, we obtain modified Einstein equations in which the geometric sector acquires explicit thermal corrections. Solving these equations for a static, spherically symmetric spacetime in the weak-field, low-temperature regime yields a corrected metric that smoothly approaches Minkowski space at large radii and naturally contains a characteristic acceleration scale.
In the very-low-acceleration regime, the model reproduces MOND-like deviations from Newtonian dynamics while providing a relativistic underpinning for that phenomenology. We confront the theory with rotation-curve data for NGC~3198 and perform a Bayesian parameter inference, comparing our relativistic MOND (RMOND) model with both a baryons-only Newtonian model and a dark-matter halo model. We find that RMOND and the dark-matter model both fit the data significantly better than the baryons-only Newtonian prediction, and that RMOND provides particularly improved agreement at r≳20kpc. These results suggest that temperature-corrected entropic gravity provides a viable relativistic framework for MOND phenomenology, motivating further observational tests, including gravitational lensing and extended galaxy samples.
Recent analyses combining cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) challenge particle physics constraints on the total neutrino mass, pointing to values smaller than the lower limit from neutrino oscillation experiments. To examine the impact of different CMB likelihoods from Planck, lensing potential measurements from Planck and ACT, and BAO data from DESI, we introduce an effective neutrino mass parameter (∑m̃ ν) which is allowed to take negative values.
We investigate its correlation with two extra parameters capturing the impact of gravitational lensing on the CMB: one controlling the smoothing of the peaks of the temperature and polarization power spectra; one rescaling the lensing potential amplitude. In this configuration, we infer ∑m̃ ν=−0.018+0.085−0.089 eV (68% C.L.), which is fully consistent with the minimal value required by neutrino oscillation experiments.
We attribute the apparent preference for negative neutrino masses to an excess of gravitational lensing detected by late-time cosmological probes compared to that inferred from Planck CMB angular power spectra. We discuss implications in light of the DESI BAO measurements and the CMB lensing anomaly.
In our local-to-global cosmological framework, cosmic acceleration arises from local dynamics in an inhomogeneous Einstein-de Sitter (iEdS) universe without invoking dark energy.
An iEdS universe follows a quasilinear coasting evolution from an Einstein-de Sitter to a Milne state, as an effective negative curvature emerges from growing inhomogeneities without breaking spatial flatness. Acceleration can arise from structure formation amplifying this effect.
We test two realizations, iEdS(1) and iEdS(2), with H(0) = {70.24,74.00} km s^−1 Mpc^−1 and Ω(m,0) = {0.290,0.261}, against CMB, BAO, and SN Ia data.
iEdS(1) fits better than ΛCDM and alleviates the H0 tension, whereas iEdS(2) fully resolves it while remaining broadly consistent with the data. Both models yield t0≃13.64 Gyr, consistent with globular-cluster estimates.