Quasar absorption lines provide a precise test of whether the fine‐structure constant, α, is the same in different places and through cosmological time. We present a new analysis of a large sample of quasar absorption‐line spectra obtained using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT) in Chile. We apply the many‐multiplet method to derive values of Δα/α≡ (αz−α0)/α0 from 154 absorbers, and combine these values with 141 values from previous observations at the Keck Observatory in Hawaii. In the VLT sample, we find evidence that α increases with increasing cosmological distance from Earth. However, as previously shown, the Keck sample provided evidence for a smaller α in the distant absorption clouds. Upon combining the samples, an apparent variation of α across the sky emerges which is well represented by an angular dipole model pointing in the direction RA = 17.3 ± 1.0 h and Dec. =−61°± 10°, with amplitude . The dipole model is required at the 4.1σ statistical significance level over a simple monopole model where α is the same across the sky (but possibly different from the current laboratory value). The data sets reveal remarkable consistencies: (i) the directions of dipoles fitted to the VLT and Keck samples separately agree; (ii) the directions of dipoles fitted to z < 1.6 and z > 1.6 cuts of the combined VLT+Keck samples agree; and (iii) in the equatorial region of the dipole, where both the Keck and VLT samples contribute a significant number of absorbers, there is no evidence for inconsistency between Keck and VLT. The amplitude of the dipole is clearly larger at higher redshift. Assuming a dipole‐only (i.e. no‐monopole) model whose amplitude grows proportionally with ‘lookback‐time distance’ (r=ct, where t is the lookback time), the amplitude is (1.1 ± 0.2) × 10−6 GLyr−1 and the model is significant at the 4.2σ confidence level over the null model (Δα/α≡ 0). We apply robustness checks and demonstrate that the dipole effect does not originate from a small subset of the absorbers or spectra. We present an analysis of systematic effects, and are unable to identify any single systematic effect which can emulate the observed variation in α. To the best of our knowledge, this result is not in conflict with any other observational or experimental result.

Observations of the redshift z = 7.085 quasar J1120+0641 are used to search for variations of the fine structure constant, a, over the redshift range 5:5 to 7:1. Observations at z = 7:1 probe the physics of the universe at only 0.8 billion years old. These are the most distant direct measurements of a to date and the first measurements using a near-IR spectrograph. A new AI analysis method is employed. Four measurements from the x-shooter spectrograph on the Very Large Telescope (VLT) constrain changes in a relative to the terrestrial value (α0). The weighted mean electromagnetic force in this location in the universe deviates from the terrestrial value by Δα/α = (αz − α0)/α0 = (−2:18 ± 7:27) × 10−5, consistent with no temporal change. Combining these measurements with existing data, we find a spatial variation is preferred over a no-variation model at the 3:9σ level.

We present an analysis of 23 absorption systems along the lines of sight towards 18 quasars in the redshift range of 0.4 z abs 2.3 observed on the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Considering both statistical and systematic error contributions we find a robust estimate of the weighted mean deviation of the fine-structure constant from its current, laboratory value of ∆α/α = (0.22 ± 0.23) × 10 −5 , consistent with the dipole variation reported in Webb et al. (2011) and King et al. (2012). This paper also examines modelling methodologies and systematic effects. In particular we focus on the consequences of fitting quasar absorption systems with too few absorbing components and of selectively fitting only the stronger components in an absorption complex. We show that using insufficient continuum regions around an absorption complex causes a significant increase in the scatter of a sample of ∆α/α measurements, thus unnecessarily reducing the overall precision. We further show that fitting absorption systems with too few velocity components also results in a significant increase in the scatter of ∆α/α measurements, and in addition causes ∆α/α error estimates to be systematically underestimated. These results thus identify some of the potential pitfalls in analysis techniques and provide a guide for future analyses.

Observations of the redshift z = 7.085 quasar J1120+0641 have been used to search for variations of the fine structure constant, α, over the redshift range 5.5 to 7.1. Observations at z = 7.1 probe the physics of the universe when it was only 0.8 billion years old. These are the most distant direct measurements of α to date and the first measurements made with a near-IR spectrograph. A new AI analysis method has been employed. Four measurements from the X-SHOOTER spectrograph on the European Southern Observatory's Very Large Telescope (VLT) directly constrain any changes in α relative to the value measured on Earth (α 0 ). The weighted mean strength of the electromagnetic force over this redshift range in this location in the universe is ∆α/α = (α z − α 0 )/α 0 = (−2.18 ± 7.27) × 10 −5 , i.e. we find no evidence for a temporal change from the 4 new very high redshift measurements. When the 4 new measurements are combined with a large existing sample of lower redshift measurements, a new limit on possible spatial variation of ∆α/α is marginally preferred over a no-variation model at the 3.7σ level. Main textWhat fundamental aspects of the universe give rise to the laws of Nature? Are the laws finelytuned from the outset, immutable in time and space, or do they vary in space or time such that our local patch of the universe is particularly suited to our existence? We characterize the laws of Nature using the numerical values of the fundamental constants, for which increasingly precise and ever-distant measurements are accessible using quasar absorption spectra.The quest to determine whether the bare fine structure constant, α, is indeed a constant in space and time has received impetus from the recognition that the possibility that there are additional dimensions of space, or that our constants are partly or wholly determined by symmetry breaking at ultra-high energies in the very early universe. The first proposals for time variation in α by Stanykovich (1), Teller (2) and Gamow (3) were actually motivated by the large numbers coincidences noted by Dirac (4,5) but were quickly ruled out by observations ( 6). This has led to an extensive literature on varying constants that is reviewed in refs. (7)(8)(9)(10)(11).There are also interesting new problems that have been about extreme fine tuning of quantum corrections in theories with variation of α by O'Donoghue (12) and Marsh (13). Accordingly, self-consistent theories of gravity and electromagnetism which incorporate the fine structure 'constant' as a self-gravitating scalar field with self-consistent dynamics that couple to the geometry of spacetime, have been formulated in refs. (14-20) and extended to the Weinberg-Salam theory in refs. (21,22). They generalise Maxwell's equations and general relativity in the way that Jordan-Brans-Dicke gravity theory (23, 24) extends general relativity to include space or time variations of the Newtonian gravitational constant, G, by upgrading it to become a scalar field. This enables different constraints on a changing α(z) at ...