Thursday, October 16, 2025

The Population Genetics Of Egypt Have Been Stable For A Long Time

An ancient DNA sample from ca. 2500 BCE in Egypt reveals a great deal of continuity in the population genetics of Egypt then and the population genetics of Egypt today. 

I didn't have a lot of time to look carefully at this study, but prior studies have shown a modest increase in sub-Saharan African admixture since then, due to the trans-Saharan slave trade in more recent time periods.

Ultralight Dark Matter

While ultra-light bosonic dark matter (ULDM) in a Bose-Einstein condensate (BEC) state could naturally account for the central core in some galaxies and resolve the core-cusp problem, the dark matter density distribution in the outer regions of galaxies remains less explored. We propose a trial wavefunction to model the ULDM distribution beyond the BEC core. We derive the corresponding rotation velocity curve, which shows excellent agreement with those of 12 dwarf spheroidal galaxies. The best-fit ULDM particle mass for each dwarf galaxy falls within a strikingly narrow range of m = (1.8−3.2) × 10^−23 eV.
Tian-yao Fang, Ming-Chung Chu, "Constraining Ultra-Light Dark Matter mass with Dwarf Galaxy Rotation Curves" arXiv:2510.12848 (October 14, 2025).

The best fit particle mass is in line with other studies and very close to the average mass-energy of a graviton, if they exist (and gravitons are, of course, bosons).

In general, ultralight bosonic dark matter proposals are are better fit to the data than any of the other dark matter particle models. 

Even warm dark matter, in the keV mass range, only barely improves upon failed cold dark matter and ultraheavy dark matter models. Self-interacting dark matter models have also not stood up well against the data from galaxy dynamics.

Tuesday, October 14, 2025

A Quantum Gravity Observation From Sabine

This basic idea has been floating around in quantum gravity circles for a while, but Hossenfelder's take is more cogent and careful than many of these attempts. Her model is basically a superdeterministic one.
I present a simple argument for why a fundamental theory that unifies matter and gravity gives rise to what seems to be a collapse of the wavefunction. The resulting model is local, parameter-free and makes testable predictions.
Sabine Hossenfelder, "How Gravity Can Explain the Collapse of the Wavefunction" arXiv:2510.11037 (October 13, 2025).

The conclusion states:
I have shown here how the assumption that matter and geometry have the same fundamental origin requires the time evolution of a quantum state to differ from the Schr¨odinger equation. This has the consequence that the ideal time evolutions which minimise the action are those with end states that are to good approximation classical. We can then identify these end states with the eigenstates of the measurement device. 
This new model therefore explains why quantum states seem to ‘collapse’ into eigenstates of the measurement observable, and how this can happen while preserving locality. Since the collapse process is governed by quantum gravitational contributions whose strength is known, the resulting model is parameter free. 
Collapse happens in this model whenever the accumulated phase difference between dislocated branches, τm|Φ12|, exceeds ∼ 1. The model’s phenomenology—notably the collapse itself—can be tested in roughly the same parameter range as other tests of the weak field limit of quantum gravity.