We’re starting strong today. The great pillars of physics work very well in our daily environment, providing our technological societies with applications that have changed the way we live, such as cancer therapies, the internet, cell phones, microprocessors or GPS. However, on a large scale, namely in cosmology, these same pillars have serious problems. That’s why we send telescopes like Euclid into space to understand what’s happening in the universe.
First, let’s look at where the problem lies. It only takes a few numbers to appreciate the extent of our ignorance. Ordinary atoms that make up you and me and the cat next door account for only a small fraction of the energy density of the universe, 4.9%. The rest, 95.1%, is dark and consists of two components, matter and energy, the nature of which we do not know. Both components have contributed to the construction of the cosmos: dark matter gives gravity to galaxies and their clusters, and dark energy at larger scales has accelerated the expansion of the universe.
Since we don’t know what they are, we won’t stop explaining them; Suffice it to say that our existence is closely linked to both, for without them not enough material (of the 5% that we can explain well) would have been collected to form planets, galaxies, frogs and mountains. Understanding these fundamental components of the universe is another step in understanding our origins. For this reason, it is not surprising that more than 2,500 scientists and engineers from 15 countries have agreed that, under the guidance of the European Space Agency and after more than ten years of development, Euclid is finally on the way to the second Lagrangian point (L2) of the sun-earth system.
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The mission has cost 1,400 million euros (does that seem like a lot? It’s less than half the cost of the film “Avatar”) and has an important Spanish contribution: a crucial scientific part led by the Institute for Space Studies of Catalonia The Institut de Astrofísica de Canarias and with scientific operations carried out by the European Center for Space Astronomy (ESAC in Madrid) and the Cebreros antenna in Ávila will receive the data collected by the telescope.
To carry out his cosmological work and help unravel the great mysteries of today’s physics, Euclid will measure weak gravitational lensing and acoustic baryon oscillations (BAOs). Since lenses are relatively easy to explain, let’s turn to BAOs, which are a bit more complex and rarely covered in the media.
Cosmological BAOs (although they share names and, one might say, shape, with Chinese buns, which they obviously have nothing to do with) are frozen relics of the pre-decoupling universe. That was a long, long time ago: at the young age of 380,000 years, when the cosmos formed the first neutral atoms that allowed matter to cool efficiently, bringing it into the realm of gravity.
Before that time, the matter of the universe was in the form of plasma and was evenly distributed until gravity (which brings everything together) began to change this distribution and form galaxies. When you try to bring matter together, it heats up and exerts an opposite effect to gravity, causing these regions to expand, cooling as they expand until gravity can once again be the dominant force. This opposing effect between gravity and pressure created a vibration equivalent to sound waves that propagated outward in the form of bubbles. We could visualize them intuitively, although they are not the same, like the ripples that spread when we throw a stone into a calm lake.
The matter bubbles of the universe
Large structures began to form in the bubbles of matter created by the sound waves. These tracks are visible today: they are 490 million light-years across and Euclid’s task is to discover them across a large part of the universe. To put it more simply, if we pick a galaxy in the universe, we are more likely to find a second galaxy 490 million light-years away than we are to find a second galaxy 400 or 600 million light-years away.
BAOs are the standard rules of choice for 21st-century cosmology because they provide distance estimates that, for the first time, are firmly rooted in well-understood linear physics. We’ll postpone the deeper explanation of this for another day, for now suffice it to say that we can use them to measure the expansion of the universe very well, since they are standard rules.
For now, we know that Euclid is headed to L2, where he will meet the James Webb and Gaia space telescopes. While the James Webb is taller and can see far back in time and zoom in on detail, the Euclid can be fast in a large field of view. In a single observation and with the stroke of a pen, Euclid can record data from an area of the sky more than 100 times larger than that represented by the James Webb NIRCam camera. The sky coverage strategy is based on the need to cover more than 35 percent of the celestial sphere during the six-year mission duration of ESA’s new space telescope. In addition, along the way we not only learn about galaxies, matter and dark energy, but also see the stars of the nearest galaxies (including our own) and many other things that complement the science that the Gaia space observatory conducts. Above all, we will find things that we have not even imagined.
Cosmic Void is a section that qualitatively and quantitatively presents our knowledge of the universe. It is intended to illustrate how important it is to understand the cosmos not only from a scientific point of view, but also from a philosophical, social and economic point of view. The name “cosmic vacuum” refers to the fact that the universe is mostly empty and there is less than one atom per cubic meter, although paradoxically in our environment there are trillions of atoms per meter cubic, which invites us to wonder about our existence and contemplating the presence of life in the universe. The section consists of Pablo G Perez GonzalezResearchers at the Center for Astrobiology, and Eva VillaverResearch Professor at the Instituto de Astrofísica de Canarias.
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