Do ‘return universes’ have a beginning?


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In an effort to understand the nature of the universe, some theorists suggest that the universe is expanding and contracting in endless cycles.

Since this behavior is supposed to be permanent, Universe It should have neither beginning nor end – only eternal cycles of growth and contraction that extend forever into the future, and forever into the past.

It is an attractive concept because it removes the need for a state called singularity which corresponds to the “beginning of time” in other paradigms.

But a new study by University of Buffalo physicists Will Kenny and Nina Stein highlights one of the ways in which cyclical, or “bounce”, cosmology falls.

The research shows that the latest version of this theory – a cyclic model that solves long-standing concerns about it entropyIntroduces a new problem (or rather returns to an old problem). Kenny and Stein concluded that the cyclical universes described in this model must have had a beginning.

says Kenny, Ph.D., professor of physics at the UB College of Arts and Sciences. “In this new type of model, which addresses entropy problems, even if the universe had cycles, it still must have had a beginning.”

“There are so many reasons to be curious about early universe, but I think my favorite is the natural human tendency to want to know what came before, says Stein, a PhD student at the University of California in Physics, regarding the importance of the research. “Across cultures and history, humans have told stories about creation, about “in the beginning.” We always want to know where we came from.”

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

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

Kenny is the author of the 2022 book Infinity of Realms, which tells the epic story of cosmic inflation, a rival theory about the origins of the universe. Under this model, the early universe was marked by a period of rapid expansion of the singularity, followed by the super-Big Bang, which forged the primordial elements that went on to make galaxies, stars, planets, and atoms in and all of our bodies. other living organisms.

Cosmic inflation is a leading theory. But it focuses on what happens during and after the era of rapid expansion. It does not explain what came before it, nor does it describe the conditions for the initial singularity.

A truly cyclical universe would overcome these problems: if the universe were engaged in endless cycles of expansion and contraction, it would need no beginning at all. But as Kenny notes, these bouncing archetypes raise their own set of untenable questions.

Unfortunately, it has been known for nearly 100 years that these periodic models do not work because chaos, or entropy, builds up in the universe over time, so Course It differs from the previous one. “It’s not really cyclical,” says Kenny. A modern cyclic model overcomes the problem of entropy buildup by proposing that the universe expands an entire set with each cycle, which leads to a weakening of entropy. You extend everything to get rid of cosmic structures like black holeswhich restores the universe to its original homogeneous state before another bounce begins.”

He adds, “But, long story short, we’ve shown that when you solve the entropy problem, you create a situation in which the universe must have a beginning. And our evidence generally shows that any cyclic model that removes entropy by expansion must be the beginning.”

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

And of course, there are more research questions, as Kenny says: “Our proof does not apply to periodic Model Proposed by Roger Penrose, the universe expands infinitely with each cycle. We are working on it.”

Use holograms to illuminate de-setter space

more information:
Kenny et al., Periodic Cosmology and Geodetic Completeness, Journal of Cosmology and Astrophysics (2022). DOI: 10.1088 / 1475-7516 / 06/011 2022

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