Cosmology and fundamental physics

We start with the Universe in its largest dimensions. The question of the emergence of space, popularly known as the big bang, is obviously a central one and requires one to study the Universe at its earliest times, i.e. the most distant Universe (because of the finiteness of the speed of light). The Universe has been transparent to light since about 380 000 years after the big bang. This first light is in the present epoch observed in the form of a microwave background, the so-called cosmic microwave background (CMB). Investigating times close to the big bang (the so-called inflation period) requires the identification of very tiny details on maps of fluctuations of the CMB (those for which G. Smoot received the Nobel Prize in 2006) and thus precision measurement methods. Another promising approach is the detection of deformations of spacetime known as gravitational waves. These waves could have formed immediately after the big bang and would provide the only direct test of the content of the Universe emerging from the big bang. Since those early epochs, the expansion of the Universe has been decelerating. It was discovered in 1998 that the expansion has been accelerating again for the past 4 billion years. This is attributed to some new form of energy, called dark energy. Identifying dark energy has been singled out by both the astrophysics and fundamental physics communities as the priority task of the coming decade. It is obviously related to the question of the future of our Universe.