Does the ‘bouncing universe’ begin?


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In trying to understand the nature of the universe, some theorists propose that the universe expands and contracts in endless cycles.

Because this behavior is designed to last forever, Universe There must be no beginning and no end – only eternal cycles of growing and shrinking that stretch forever into the future and forever into the past.

This is an attractive concept partly because it removes the need for a state called a singularity that corresponds to the “beginning of time” in other models.

But a new study by University of Buffalo physicists Will Kinney and Nina Stein sheds light on a way that cyclical or “bouncing” cosmology falls flat.

Research shows that the latest version of this theory—a cyclical model that addresses long-standing concerns entropy– introduces a new problem (or rather, returns to an old one). The cyclic universes described under this model must have a beginning, Kinney and Stein conclude.

“People proposed buoyant universes to make the universe infinite in the past, but what we show is that one of the latest variants of these models doesn’t work,” says Kinney, a professor in the UB College of Physics. Arts and Sciences. “In this new type of model, which addresses the problems with entropy, even if there are cycles in the universe, it must have a beginning.”

“There are many reasons to be curious about early universeBut I think my favorite is the natural human instinct to want to know what happened first,” says Stein, a UB PhD student in physics about the importance of research. “Across cultures and history, humans have told stories about I have told about creation, ‘in the beginning’. We always want to know where we have come from.”

The study, funded by the National Science Foundation, was published in June Journal of Cosmology and Astroparticle Physics, The paper is titled “Cyclic Cosmology and Geodetic Completeness”.

If the universe had a beginning, how did it begin?

Kinney is the author of the 2022 book “An Infinity of Worlds,” which tells the epic story of cosmic inflation, a competing theory about the origins of the universe. Under this model, the early universe was characterized by a period of rapid expansion from a singularity, followed by the superhot Big Bang, which created galaxies and stars and planets, and the fundamental elements that make up the atoms in our bodies and all. other living things.

Cosmic inflation is a major theory. But it focuses on what happens during and after an age of rapid expansion. It does not explain what preceded it, and it does not describe the conditions of the initial singularity.

A truly cyclic universe would overcome these problems: if the universe is engaged in endless cycles of expansion and contraction, it does not need a beginning. But as Kinney noted, these bouncing models raise shaky questions of their own.

“Unfortunately, it has been known for almost 100 years that these cyclic models do not work because disorder, or entropy, builds up in the universe over time, so each cycle Different from the previous one. It’s not really cyclic,” Kinney says. “A recent cyclic model gets around this entropy build-up problem by proposing that the universe expands a whole bunch with each cycle, increasing entropy. Makes it thinner. You spread everything to get rid of cosmic structures like black holeswhich returns the universe to its original homogeneous state before another boom begins.”

“But,” he adds, “long story short, we showed that in solving the entropy problem, you create a condition where the universe must begin. Our proof shows in general that any cyclic model that expands removes entropy by a start.”

“The idea that there was a point in time before which there was nothing, there was no time, baffles us, and we want to know what preceded it—scientists included,” Stein says. “But as far as we can tell, there must have been a ‘beginning’.” There is a point to which there is no answer to the question, “What came before that?” ,

And, of course, there are further research questions, Kinney says: “Our proof does not apply to cyclic pattern Proposed by Roger Penrose, in which the universe expands infinitely in each cycle. We are working on it.”

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more information:
William H. Kinney et al, Cyclic Cosmology and Geodetic Completeness, Journal of Cosmology and Astroparticle Physics (2022). DOI: 10.1088/1475-7516/2022/06/011

CitationDo ‘jumping universes’ have a beginning? (2022, 5 August) Retrieved 6 August 2022 from

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