Probing the variation of the fine-structure constant using QSO absorption lines

Search for the time variation of the fundamental constants is motivated by various unification theories. Here we present constraints on the variation of the fine-structure constant α(≡ {e²/hbar c}) obtained using UVES/VLT samples of QSO absorption systems. We find {_w={(-0.06±0.06)×10^-5} using 23 Mg II systems and the many-multiplet (mm) method. Well selected 15 Si IV systems provide {_w={(0.15±0.43)×10^-5}. Absence of detectable variation in α is also confirmed by our new very high resolution (r∼ 100,000) observation of z_abs=1.1508 toward He 0515-4414 using harps on the ESO 3.6m telescope.