How was the idea of ​​dark energy born?

In cosmology, two problems have emerged and no one can predict the conceptual upheavals they can lead to. Both relate to the material inventory and the energetic content of the universe: it has been discovered that a large part of a completely unknown nature! However, according to the theory of general relativity, it is the content of the universe that determines its evolution, that is, what will happen in the future, but also what it was in the past, including its past. … This is why physicists have been talking for several years about “dark matter” and “dark energy” …

The expansion of the universe has accelerated for several billion years

Today let’s talk about dark energy. Twenty years ago, astrophysicists realized that the expansion of the universe was occurring in the acceleration phase for several billion years. What does it mean? In the process of expansion, gravity, which is always attractive, acts as a brake: it tends to bring massive bodies closer together, so matter can only slow down the expansion. But what the measurements show is that another process counteracts it by acting as an accelerator. It was as if some kind of antigravity had taken over the space, causing space to expand more and more and constantly increasing its expansion speed.

What is driving this acceleration? Several tracks have been mentioned, but nothing is confirmed. Physicists speak cautiously of a mysterious energy that they describe as “dark”, on the one hand because we cannot see it, on the other hand because they are unaware of its true nature. The bravest, however, put forward some hypotheses. Dark energy can be a “cosmological constant”, which has flavour, color and smell, without being able to prove that the first is mixed with the second. This parameter, introduced by Einstein in 1917, corresponds to a kind of repulsion of space towards itself. (…)

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