Every week, our journalist answers scientific questions from readers.
“What was there before the Big Bang?” »
Richard Deschenes
We don’t know it, but many astrophysicists are working on models explaining this “singularity”.
“In cosmology, we have a model that explains the expansion of the universe after the Big Bang,” says Laurence Perreault-Levasseur, astrophysicist at the University of Montreal. “As we rewind time, the universe gets smaller and smaller. The physical distances between things are decreasing. We reach a point where the universe is so dense that the expansion equations stop working. We need a theory to explain the Big Bang, which we don’t have at the moment. »
PHOTO TAKEN FROM THE UNIVERSITY OF MONTREAL SITE
Laurence Perreault-Levasseur, astrophysicist at the University of Montreal
The density of the universe during the Big Bang is infinite. “We call it a singularity,” says M.me Perreault-Levasseur. The equations we have are no longer valid. It’s the same thing inside a black hole, there is an extremely dense zone for which we have no theory, which we also call a singularity. »
These efforts to explain singularities, notably the Big Bang, are part of the general challenge of unifying “general relativity” and “quantum mechanics”.
“For everyday life, Newtonian physics can very well explain phenomena, for example the speed and acceleration of a car or a ball,” says the Montreal 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 necessary to calculate Mercury’s orbit because it is very close to the Sun. This does not mean that Newtonian mechanics is false, but that it is an approximation of general relativity,” continues the researcher.
For very, very small scales, however, we have quantum mechanics, which explains how particles like 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 deterministic. It is because of the theory of quantum mechanics that we have the internet and computers. »
The problem is that on the very small scales of the Big Bang, there are “important quantum effects”, but also very large mass. “Normally, quantum mechanics works with low-mass particles. When there is a lot of mass, it is problematic. »
Theories to unify general relativity and quantum mechanics are numerous, but none work perfectly. The most promising according to Mme Perreault-Levasseur’s “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 “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, astrophysicist from the Federal University of Alfenas, north of São Paulo, Brazil. His study postulates in particular that certain very old black holes were created during previous phases of expansion or contraction of the Universe. “I did my doctorate on the physics of black holes,” explains Mr. Neves. I tried to apply the bounce models to them. »
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- 13.8 billion years
- Generally accepted age of the universe
Source: nasa