On June 8, 2018, ISSI-BJ organized an Understanding Science seminar on "Gravitational Lenses: Mirages in the Universe”. The lecture was held by Prof. Georges Meylan, honorary professor of astrophysics and cosmology at the Ecole Polytechnique Fédérale de Lausanne (EPFL). As usual, the seminar took place at the Bridge Café in Wudaokou, Beijing.

Prof. Georges Meylan (EPFL) giving his seminar on Gravitational Waves

Prof. Meylan started his talk by providing different examples of mirages on Earth, to introduce then the concept of the mirages in the Universe. He explained that the total solar eclipse of 1919 unveiled the gravitational lens nature of our Sun and proved the veracity of a prediction of the theory of General Relativity by Albert Einstein. Anotherexample of agravitational lens was discovered only in 1979. Originally considered as a mere curiosity, gravitational lensing has matured, during the last two decades, into a genuine astrophysical tool, used in a large variety of astrophysical problems, from planet search to the quest for the most distant galaxies.

Following the introduction of the phenomenon of gravitational lensing, Prof. Meylan presentedthen, in an easily comprehensible manner, its few recent cosmological applications, obtained at EPFL, such as direct determination of the total mass of the lensing galaxy and cosmological parameters, study of mass distribution of dark matter, as well as natural telescopes for the observations of very distant objects at very high redshifts.

The talk concluded with the short introduction of the ESA satellite Euclid, which is to investigate the nature of dark energy and dark matter through their impacts on gravitational lensing. 

Seminar audience at the Bridge Cafe in Wudaokou, Beijing

The event was well attended, and after the talk many interesting questions were asked. Professor Georges Meylan’s seminar on “Gravitational Lenses” was indeed a successful event which received a highly positive feedback from the attendees.