A Stringent Limit on Variation of the Fine-Structure Constant Using Absorption Line Multiplets in the Early Universe

One of the key questions of modern physics concerns the possibility that physical constants have varied throughout the history of the Universe. The standard model of physics is built on these constants, but it does not provide any explanation for their values, nor does it require their constancy over space and time. Here, we set a new limit on possible spatial and temporal variations of the fine-structure constant α = e ²/4πε₀ ħc by comparing transitions and line multiplets in an ensemble of Fe II λ 1608, λ 2344, λ 2374, λ 2383, λ 2587, and λ 2600 observed in the early Universe with those measured in the laboratory. Based on the optical spectrum observations of QSO HE 0515-4414, we deduce a constraint of Δα/α = (-0.157± 0.300)×10^-6 at redshift z = 1.15. At present, this represents the tightest limit on Δα/α in early cosmological epochs compared to the published results in the literature.