The universe could have been born only as a result of the Big Bang, since all alternative scenarios for its formation lead to the immediate collapse of the newborn universe and its destruction, according to an article published in the journal Physical Review D.
“All these theories were developed in order to explain the original“smooth”structure of the Universe at the moment of its birth and“grope”the primary conditions of its formation. We have shown that, in fact, they generate the opposite picture - powerful disturbances arise in them, which ultimately lead to the collapse of the entire system, writes Jean-Luc Lehners of the Institute for Gravitational Physics in Potsdam (Germany) and his colleagues.
Most cosmologists believe that the Universe was born from a singularity, which began to expand rapidly in the first moments after the Big Bang. Another group of astrophysicists believes that the birth of our Universe was preceded by the death of its “progenitor”, which probably happened during the so-called “Big Rip”.
The main problem of these theories is that they are incompatible with the theory of relativity - at the moment when the Universe was a dimensionless point, it should have had an infinite energy density and curvature of space, and powerful quantum fluctuations should have appeared inside it, which is impossible from the point vision of the brainchild of Einstein.
To solve this problem, scientists have developed in the last 30 years several alternative theories in which the universe is born in different, less extreme conditions. For example, Stephen Hawking and James Hartle 30 years ago suggested that the Universe was a point not only in space, but also in time, and before its birth, time, in our understanding of the word, simply did not exist. When time appeared, space was already relatively “flat” and homogeneous so that a “normal” Universe with “classical” laws of physics could arise.
In turn, the Soviet-American physicist Alexander Vilenkin believes that our Universe is a kind of "bubble" of false vacuum inside the eternal and constantly expanding giant multi-Universe, where such bubbles constantly arise as a result of quantum fluctuations of the vacuum, literally born out of nothing.
Both of these theories allow us to get around the question of the "beginning of time" and the incompatibility of the Big Bang conditions with Einstein's physics, but at the same time they raise a new question - are such options for the expansion of the Universe capable of generating it in the form in which it now exists?
As calculations by Leners and his colleagues show, in fact, such scenarios for the birth of the Universe cannot work in principle. In most cases, they do not lead to the birth of a "flat" and calm Universe like ours, but to the appearance of powerful disturbances in its structure, which will make such "alternative" Universes unstable. Moreover, the likelihood of the birth of such an unstable universe is much higher than its stable counterparts, which casts doubt on the ideas of Hawking and Vilenkin.
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Accordingly, the Big Bang cannot be avoided - scientists, as Lehners and his colleagues conclude, will have to find a way to reconcile quantum mechanics and the theory of relativity, as well as understand how quantum fluctuations were suppressed at extremely high density of matter and curvature of space-time.
