The Mystery of Alpha and the Isotopes

TL;DR

This study uses high-quality spectroscopic data to investigate potential spatial variations of the fine structure constant alpha, revealing discrepancies that depend on isotopic assumptions and highlighting the need for further high-precision measurements.

Contribution

First unbiased measurements of alpha in two proximate quasar absorption systems using laser-calibrated spectra, exploring isotope effects and potential spatial variations.

Findings

Discrepancy in alpha at 7σ assuming terrestrial isotopic ratios.

A 3σ discrepancy persists under extreme isotopic assumptions.

Reconciliation possible if isotopic abundances differ between systems.

Abstract

We report unbiased AI measurements of the fine structure constant $\alpha$ in two proximate absorption regions in the spectrum of the quasar HE0515$-$4414. The data are high resolution, high signal to noise, and laser frequency comb calibrated, obtained using the ESPRESSO spectrograph on the VLT. The high quality of the data and proximity of the regions motivate a differential comparison, exploring the possibility of spatial variations of fundamental constants, as predicted in some theories. We show that if the magnesium isotopic relative abundances are terrestrial, the fine structure constants in these two systems differ at the 7$\sigma$ level. A 3$\sigma$ discrepancy between the two measurements persists even for the extreme non-terrestrial case of 100\% $^{24}$Mg, if shared by both systems. However, if Mg isotopic abundances take independent values in these two proximate systems, one terrestrial, the other with no heavy isotopes, both can be reconciled with a terrestrial $\alpha$, and the discrepancy between the two measurements falls to 2$\sigma$. We cannot rule out other systematics that are unaccounted for in our study that could masquerade as a varying alpha signal. We discuss varying constant and varying isotope interpretations and resolutions to this conundrum for future high precision measurements.