source: La Presse
author: Mathieu Perreault
translation: Bing Translate/doxa-louise
Demystifying Science The Mystery of the Big Bang
Every week, our journalist answers scientific questions from readers.
"What was there before the Big Bang?"
Richard Deschênes
We don't know, but many astrophysicists are working on models that explain this "singularity".
"In cosmology, we have a model that explains the expansion of the universe after the Big Bang," says Laurence Perreault-Levasseur, an astrophysicist at the Université de Montréal. "When you rewind time, the universe gets smaller and smaller. The physical distances between things are decreasing. We get to a point where the universe is so dense that the expansion equations stop working. We need a theory to tell the story of the Big Bang that we don't have right now. »
The density of the universe at the Big Bang is unphatomable. "It's called a singularity,"says Perreault-Levasseur. The equations we have are no longer valid. It's the same thing inside a black hole, there's an extremely dense zone for which we don't have a theory, which we also call a singularity. »
"For everyday life, Newtonian physics can explain phenomena very well, such as the speed and acceleration of a car or a ball," says the Montreal-based astrophysicist, whose work has a strong mathematical component. "For larger masses and distances, general relativity works better. GPS, for example, works with general relativity, which is also needed to calculate Mercury's orbit because it is so close to the Sun. This does not mean that Newtonian mechanics is wrong, but that it is an approximation of general relativity," the researcher continues.
For very, very small scales, however, we have quantum mechanics, which explains how particles such as electrons sometimes behave like waves. "Things in the world of quantum mechanics can be in two places at the same time. It's a probabilistic world, not a deterministic one. It is because of the theory of quantum mechanics that we have the internet and computers. »
The catch is that at the very small scales of the Big Bang, there are "large quantum effects", but also a very large mass. "Normally, quantum mechanics works with low-mass particles. When there's a lot of mass, it's problematic. »
There are many theories to unify general relativity and quantum mechanics, but none work perfectly. The most promising, accordingto Perreault-Levasseur, is "string theory," a complicated mathematical model where particles are like immensely long, one-dimensional strings. But there are also equations that describe an infinite space with several very different universes where light cannot reach, also called the "bubble universe", or "bounces" with a series of expansions and contractions.
An example of this type of modeling was published in 2017 in the journal General Relativity and Gravitation by Juliano César Silva Neves, an astrophysicist at the Federal University of Alfenas, north of São Paulo, Brazil. In particular, his study postulates that some very old black holes were created during earlier phases of expansion or contraction of the Universe. "I did my PhD on the physics of black holes," says Neves. I tried to apply the bounce patterns to them. »
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