Tech UPTechnologyOur universe could bounce around forever (and still had...

Our universe could bounce around forever (and still had to have a beginning)


While, in cosmic terms, time scales are too large for us to conceive of adequately, a new study posits that even if the universe is cyclical, instead collapsing and restarting over and over again in an eternal process, it continues to hold . important limitations.


Theory about the origins of the universe

The Big Bang is not consistent with some aspects of general relativity, Einstein’s famous theory that explains how matter and energy interact. According to the Big Bang theory, the universe initially expanded from a small, static point for reasons not yet understood. According to the Big Bounce theory, the current universe resulted from the collapse of a previous universe.

Thus, the Big Bounce or Great Bounce theory, although not widely accepted, is theorized by some cosmologists in which our universe could be just one in a long series of births, deaths and rebirths without beginning or end, within that bounce. eternal . In the Big Bounce hypothesis, a collapsing universe would recover before reaching such a groundbreaking moment as a singularity. In fact, if the universe had a high entropy at the Big Bang, it could not exist as we know it.

“Scientists have proposed bouncing universes to make the universe infinite in the past, but what we show is that one of the newer types of these models doesn’t work,” said physicist Will Kinney of the University at Buffalo and co-author. of the study published in the Journal of Cosmology and Astroparticle Physics. “In this new type of model, which addresses entropy problems, even if the universe has cycles, it still has to have a beginning.”

This theory introduces a new problem (or rather, returns to an old one) by introducing a cyclic model that solves old entropy problems : cyclic universes must start at some point.

“There are many reasons to be curious about the early universe, but I think my favorite is the natural human tendency to want to know what came before,” the authors comment. “In all cultures and histories, humans have told stories of creation, of the beginning. We always want to know where we come from.”

“Unfortunately, it’s been known for almost 100 years that these cyclical models don’t work because disorder or entropy builds up in the universe over time, so each cycle is different from the last. It’s not really cyclical,” says Kinney. “In a nutshell, we show that solving the entropy problem creates a situation where the universe had to have a beginning. Our proof shows in general that any cyclic model that removes entropy by expansion must have a beginning. “

“Our test does not apply to the cyclical model proposed by Roger Penrose, in which the universe expands infinitely in each cycle. We are working on that,” they conclude. . According to your version of a repeating universe, each cycle expands infinitely with no period of contraction. That is quite a complex thing, and will require more analysis.

“The idea that there was a point in time before which there was nothing, there was no time, bothers us, and we want to know what was before that, including scientists. But as far as we know, in models that address entropy, there must be a ‘beginning’. There is a point to which there is no answer to the question , ‘What came before that?'”

Referencia: William H. Kinney et al, Cyclic cosmology and geodesic completeness, Journal of Cosmology and Astroparticle Physics (2022). DOI: 10.1088/1475-7516/2022/06/011

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