Euclid is a visible to near-infrared space telescope currently under development by the European Space Agency (ESA), and the Euclid Consortium. The objective of the Euclid mission is to better understand dark energy (an unknown form of energy which is hypothesised to permeate all of space, tending to accelerate the expansion of the Universe) and dark matter (a form of matter thought to account for approximately eighty-five per cent of the matter in the Universe, and about a quarter of its total energy density), by accurately measuring the acceleration of the Universe. This extraordinary European instrument will produce an unprecedented cartography of the largest structures in the Universe from 2022.
In all space missions, there is a sort of “valley of oblivion” between the moment when they are officially chosen, and when they are launched. For a decade, a media silence, more or less deep, tends to settle. This is not due to any superstition, nor to the observance of a vague cult of secrecy, but rather to the difficulty of creating the event in the process of slow and patient development, inherent in a sector in which each piece is unique, and the right to fail does not exist.
Thales Alenia Space, the European Space Agency (ESA) responsible for the construction of the Euclid space telescope, invited the press late last week to contemplate the “thermo-structural model” of the machine, being finalised in its premises in Cannes. This is a real size model that must validate its design undergoing a battery of extensive tests. But, it will be understood, it is especially the occasion to recall that the “building site” of this extraordinary instrument, selected in 2011 by the ESA, and whose cost could reach more than one billion American dollars, continues its courses. The launch aboard an Ariane 6 is thus still planned for mid-2022 in Kourou, French Guiana.
The Euclid telescope promises to be one of the most powerful instruments of the coming decade
The Euclid telescope promises to be one of the most powerful instruments of the coming decade, with NASA’s much anticipated James Webb Space Telescope (JWST). Its designers believe that it could revolutionise cosmology, that is, our understanding of the Universe and its origins. Nothing less.
In the current state of our knowledge, the Universe was born for an unknown reason from a point of infinite density almost fourteen billion years ago. This strange event, commonly called “Big Bang” gave rise to an accelerating Universe under the effect of a mysterious “dark matter”, which forms according to the models, gigantic filaments on which the galaxies (each of which gathers billions of stars, in the image of our “Milky Way”) come to stick as on fly paper.
“We introduced two ad hoc parameters, which we called dark matter and dark energy, and all of a sudden everything worked. But it’s pretty miraculous. We must not lose sight of the fact that we just put words on things that we did not really understand, and for which everything is still possible”. The Universe might not be as homogeneous in space and time, as we imagine.
Up to ten billion years in the past
Euclid’s objective is precisely to provide data in order to discriminate existing theories, or even to make emerge new ones. The telescope is going to do the survey of the most complete Universe to date, determining the position and the distance of more than two billion galaxies, going up to ten billion years in the past (for memory, the Universe is almost fourteen billion years old). It will also give the infrared “spectrum” of ten million of them, a kind of extremely bright identity card information. This should make it possible to map out this kind of dark matter spider web that structures the Universe, and to study how it has deformed and evolved over time.
To get an idea of the performance needed to achieve this feat, imagine that it would take nine hundred years to the famous Hubble Space Telescope to make such a comprehensive survey, covering one third of the sky. In fact, all areas that are not obstructed by the stars of our own galaxy, or by the light of the planets of our own Solar System. “We are going to produce this huge catalogue in only six years, which is a real challenge for data management on the ground”. And probably an inexhaustible source of discoveries for astronomers, like the catalogue of another European space telescope, Gaia, which already lists a billion stars in our environment.
1905 — A static universe according to Einstein
It was in 1905 that Albert Einstein proposed his theory of gravitation. It would not be a force, but the manifestation of the deformation of the very fabric of the Universe, to which he gives the name of “space-time”, because the two are inextricably linked: gravity deforms both the space and slows down time. The great German scientist thinks that the Universe is static, one of his biggest mistakes.
1922 — A much needed expansion
It is a Russian physicist, Alexander Friedmann, who proposes for the first time in 1922 the idea that the Universe would be expanding. This helps to prevent it from collapsing under the effect of its own weight, which seems inevitable in the Einsteinian framework. This intuition is verified in 1929 by the American astronomer Edwin Hubble, who discovers that galaxies are indeed moving away from each other, and all the faster they are far away. It means in the background that the Universe was once concentrated in a point of infinite density, and that there is a start, what is called the “Big Bang”.
1970 — A mysterious dark matter
In the 1970s, astronomers such as the American Vera Rubin show that the rotation of galaxies is always faster than expected… Everything happens as if large quantities of a mysterious “dark matter”, of unknown nature, were to the work, and as if this dark matter manifested itself only by its gravitational effects, remaining transparent to any other physical reality.
1998 — Acceleration!
In 1998, astronomers discovered to everyone’s surprise that the expansion of the Universe was not uniform in time, but accelerated! This implies the existence of a mysterious repulsive energy, of a nature also unknown, whose calculations show that it should compose almost three quarters of the Universe.