The new study highlights a troubling problem with concepts of a cyclic universe that experiences endlessly alternating periods of rapid expansion and contraction, known as “jumping universe” models.
These bouncing universe models assume that the cosmos has no beginning, eliminating the need for a disturbing singularity prior to the initial period of rapid inflation, commonly known as the Big Bang, required for “beginning of time” models.
Researchers at the University at Buffalo say a recently proposed recipe for a bouncing universe that attempts to solve the problem of entropy — a measure of the useless energy in the universe that can only increase — suffers from a problem that has plagued previous models of infinite expansion and contraction. Still need a start.
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“People have suggested dropping universes to make the universe infinite in the past, but we show that one of the newest types of these models does not work,” said Will Kinney, a physicist at the University at Buffalo. (will open in a new tab) “In this new type of model that solves problems with entropy, even if the universe has cycles, it still has to have a beginning.”
This means that proposals for cyclical models of the universe may have to go back to the drawing board.
The leading theory of the origin of the universe is the so-called “cosmic inflation”. This suggests that before the beginning of time, all the energy of the cosmos was contained in a singularity – an infinite dimensionless point, not described by the laws of physics.
This ended in a period of rapid inflation – the Big Bang – when the universe expanded and cooled, allowing matter to form – first hydrogen atoms, then heavier elements, and finally stars and galaxies.
The problem is that although this theory describes the universe very well as it ages from fractions of a second to the cosmic structure we see today, about 13.8 billion years later, it cannot describe the conditions of the singularity that existed before. inflation started. Or even how it started.
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This problem is eliminated by the jumping universe, because if the periods of inflation and collapse are endless, then there was no beginning and therefore no need to explain what preceded it. This would cause the universe to experience inflation similar to the cosmic inflation model, but then “bounce” off itself in a kind of “Big Crunch”.
Thus, each new period of inflation will begin with the “wreckage” of the previous period of expansion, and not with a singularity. But Kinney thinks jumping universes have their own unique problems.
“Unfortunately, it has been known for almost 100 years that these cyclic models do not work because disorder, or entropy, accumulates in the universe over time, so each cycle is different from the previous one. It’s not really cyclical,” notes UB. said the researcher. “The recent cyclical model solves this problem of entropy accumulation by assuming that the universe expands with each cycle, diluting the entropy.”
Kinney said this new model of the bouncing universe is trying to stretch everything to get rid of cosmic structures like black holes, thereby returning the universe to its original homogeneous state before a new bounce starts.
“We showed that when you solve the problem of entropy, you create a situation where the universe should have a beginning. Our proof as a whole shows that any cyclic model that eliminates entropy by expansion must have a beginning,” he said, adding one hopping universe. can withstand this assessment. “Our proof does not apply to the cyclic model proposed by Roger Penrose, in which the universe expands infinitely in each cycle. We are working on it”.
Kinney’s collaborator is New York University physics graduate student Nina Stein. She highlighted the problem the bouncing universe duo faced: “The idea that there was a point in time before which there was nothing, there was no time, worries us and we want to know what came before that, scientists included.
“But, as far as we can tell, there must have been a “beginning” in models that refer to entropy. There is a point for which there is no answer to the question: “What happened before this?”
This means that for the moment the mystery of what existed before the universe and time itself remains and will be the subject of heated debate among cosmologists for some time to come.
“There are many reasons to be interested in the early universe, but I think my favorite is the natural human tendency to want to know what happened before,” Stein said. “In all cultures and histories, people have told stories about creation, about the “beginning.” We always want to know where we come from.”
Kinney and Stein’s findings are discussed in a paper published in the June issue of the Journal of Cosmology and Astroparticle Physics. (will open in a new tab)
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