Speaker
Description
In our daily life, gravity is always an attractive force. After Hubble discovered the expansion of the Universe in 1929, it has been usual to think that the expansion of the Universe must be decelerating, although there have also been other ideas. In fact, Einstein first in 1917 inserted the “cosmological constant” in his equations, as a kind of universal repelling force, to allow a static universe, something he later called his greatest blunder. This cosmological constant has come back. In 1998 it was clear from observations of exploding stars, awarded with the Nobel Prize, that the Universe in fact is accelerating and not decelerating, and that the data fits well with Einstein’s cosmological constant. However, the existence of a cosmological constant is perhaps the greatest mystery of current theoretical physics, as theory would predict a cosmological constant more than 60 magnitudes larger than given by the data. Is it really Einstein’s cosmological constant we are seeing, or some kind of dynamic field, dubbed “dark energy”, or is something wrong with general relativity? To get a handle on this, the European Space Agency in 2011 selected Euclid as a future mission. Euclid was launched on the 1st of July 2023 and is now surveying the sky to get a detailed picture of the expansion history of the Universe, to try to give a better explanation of what is causing the expansion of the Universe to accelerate. In this talk, I will describe the Euclid mission and its background.
