2023-12-29 10:06:55
As recalled in an article on Jean-Pierre Luminetfrom the 1920s to the 1930s Georges Lemaître anticipated with remarkable prescience the essentials of modern cosmology, to the point of outlining the quantum cosmology subsequently explored notably by Stephen Hawking in the company of James Hartle, and more recently by Abhay Ashtekar.
Lemaître took very seriously the ideas of Bohr and Heisenberg questioning the fundamental existence of space-time in the quantum world. In the context of the relativistic cosmology of which he was the pioneer, he deduced that the current beginning of the expansion of observable space must have begun with what he called a primitive atom, a quantum object without real extension in space and time which would have made a sort of quantum jump in real space-time like a nucleus disintegrating by radioactivity into alpha particles, giving birth to the particles of matter that we observe around us.
During the 1940s, Georges Gamow focused on the idea of an initial state analogous to a gas of neutrons forming an atomic nucleus. This gas is hot and accompanies an expanding Universe there too by disintegrating, but by beta radioactivity giving protons and neutrons.
Neither Gamow nor Lemaître are really taken seriously by the majority of the scientific community who prefer the stationary cosmology model of Hoyle, Bondi and Gold which is infinite in space but also in time although expanding (incidentally , contrary to what is often thought, an expanding relativistic Universe therefore does not automatically imply that it must be smaller in the past by finding itself at a moment, as the Big Bang theory requires, in a dense and hot state of matter and the radiation it contains).
The price Frontiers of Knowledge Award in Fundamental Sciences from the BBVA Foundation was awarded in 2015 to physicists Stephen Hawking and Viatcheslav Mukhanov for discovering that galaxies formed from quantum fluctuations in the early days of the Universe. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Automatically translate”. Choose “French”. © BBVA Foundation
From Sakharov quantum fluctuations to Mukhanov quantum fluctuations
Everything will change of course with the discovery of fossil radiation in 1965. Paradoxically, just before this discovery, on the other side of the Iron Curtain, the famous Andrei Sakharov and his colleague co-creator of the Soviet H-bomb, Yakov Zeldovich, consider a Big Bang…cold!
They have reasons for this, until the discovery of fossil radiation. The initial idea is that everything begins with a liquid of nuclear matter (we have known since Bohr and the 1930s that a nucleus is a sort of drop of nuclear liquid, Lemaître’s primitive atom could therefore be seen as a nucleus primitive), therefore ultimately cold and not in the form of a hot gas. Additionally, a cold liquid has a lower entropy than a hot liquid, which causes the cosmos to begin in a state of low entropy which will be increasing, giving an arrow of time.
At the very beginning of the 1980s, while the inflationary cosmology proposed by Alexei Starobinski and especially Alan Guth was taking off, there were two other Russians, Viatcheslav Mukhanov et Gennady Chibisov, who discovered that quantum fluctuations analogous to that of Sakharov, but amplified by the exponentially rapid and transient expansion phase of inflation theory, can become overdensities of matter collapsing gravitationally into future galaxies. Hawking independently arrives at similar, but less developed, results.
Subsequently, numerous experiments measuring the temperature fluctuations of fossil radiation, such as WMap and Planck, have given credence to this hypothesis, although the proof of the occurrence of an inflation phase still eludes us. In 1985, Mukhanov developed a rigorous formalism for describing density disturbances in many inflationary models.
This now leads us to carefully consider an article published in Physical Review D and a version of which exists in open access on arXiv. We owe it to Toshiki Kurita and Masahiro Takada of the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), an international research institute in physics and mathematics located in Kashiwa, Japan, near Tokyo.
The video produced by John Hopkins University details the creation of the map. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Automatically translate”. Choose “French”. © John Hopkins University
Galaxies whose shapes are altered by encounters
The galaxies that were born from density fluctuations will interact with each other at the beginning of the history of the observable cosmos, to the point of sometimes merging. Elliptical galaxies are thus the result of mergers between spiral galaxies.
More generally, we can show that we can expect to have a connection between the history of these interactions, therefore also their forms, and the characteristics of the density fluctuations which gave rise to the first galaxies and their distributions in the ‘space.
Toshiki Kurita and Masahiro Takada therefore had the idea of analyzing the correlations between the distributions and shapes of galaxies by combining spectroscopic data of the spatial distribution of galaxies and imaging data of individual galaxy shapes provided by observations. of about a million galaxies from the Sloan Digital Sky Survey (SDSS), the world’s largest galaxy survey to date.
As a result, they were able to place constraints on the statistical properties of the primordial fluctuations that seeded the formation of the structure of the entire Universe.
The undertaking was significant because there is a huge zoo of inflationary models with new physics making slightly different predictions for these fluctuations. Technically, the researchers notably hunted for so-called non-Gaussian fluctuations and they did not find a trace of them.
This does not necessarily mean that they are not present, but that they are at least weaker than a certain value – the one that we can measure now. The fact remains that it is a new test of the quantum theory of the origin of galaxies, a test which has once again been successfully passed.
1703846393
#shape #galaxies #betray #quantum #birth #Universe