專題演講

2020/01/17(Fri)     11:00 -12:30    七樓研討室7th Floor(P7F)

Title

Four direct measurements of the fine-structure constant 13 billion years ago

Speaker

Dr. Chung-Chi Lee

Department of Applied Mathematics and Theoretical Physics, University of Cambridge

Abstract

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 (α0). The weighted mean strength of the electromagnetic force over this redshift range in this location in the universe deviates from the present-day terrestrial value by an amount dα/α = (αz − α0)/α0 = (−2.18 ± 7.27) × 10−5. We thus find no evidence for a temporal change from these 4 new very high redshift measurements. Combining the 4 new measurements with a large sample of existing lower redshift measurements, we derive a new constraint on possible spatial variation; the data suggest that a spatial variation is marginally preferred over a no-variation model at the 3.9σ level.