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The universe has been expanding for billions of years and will continue to do so. But scientists expect that one day there will be a turnaround, after which the universe will shrink again and eventually become one. big crunch jumpscares. Will this last forever? And what happened before big Bangwhat was the beginning of the expansion?
In an effort to get to the heart of the genesis and evolution of the cosmos, some theorists have suggested that the universe expands and contracts in an endless cycle. Since this process would be perpetual, there could be no beginning or end, but it is only a continuous cycle of growth and contraction extending into eternity, both past and future.
A head and a tail
It is an attractive concept, because in this theory there is no need for a starting point, a state of singularity, where “time begins” in other models. But physicists Will Kinney and Nina Stein of University at Buffalo (UaB) described in a new study why the model of a cyclical or “reflexive” cosmos is problematic.
The latest version of this theory, a cyclical model that appears to solve persistent problems of entropy, or disorder, is debunked by the UaB team. There is a problem that keeps cropping up: the cyclic universes described by this model must have a beginning, say Kinney and Stein.
“Several people have come up with the idea of bouncing universes to explain the infinite past, but our findings show that one of the newer types of this type of model is wrong,” says physics professor Kinney. “In this new model, which examines the problems with entropy, even though the universe has a cyclical nature, there must be a point where everything begins.”
The primitive universe
“There are so many reasons to be curious about the early universe, but my favorite is the basic human question of what came before it,” Stein says of the importance of research. “In many cultures and at different times, people have told each other stories about the origin of man, the world and the universe. “The beginning of the world” is often at the heart of this. “We always wanted to know where we come from.”
Kinney has the book this year An infinity of worlds writing. In it he describes the epic story of cosmic inflation (expansion), another theory that describes the origin of the universe. It describes an early phase of the universe, in which a period of rapid expansion follows a singularity and a super hot Big Bang. This Big Bang forged the primordial elements, from which later galaxies, stars, planets and atoms of our body were born.
The Carina Nebula. Photo: James Webb (NASA)
cosmic inflation
Cosmic inflation is a well-known pattern, but it focuses on what happens during and after the period of rapid expansion. It doesn’t burn your fingers at what happened before the expansion, nor does it explain the starting point or the original singularity.
A purely cyclical model with no beginning or end negates these problems, but Kinney explains that these “bouncing universe” models raise all sorts of issues and questions of their own. “Unfortunately, it has been known for almost a hundred years that these cyclical patterns cannot work because of the disorder, or entropy, that builds up in the universe over time. Each subsequent cycle is therefore different from the previous one. It can’t be a copy of the previous cycle, so it’s not really cyclic.
The entropy problem
“A recent cyclical model contradicts this entropy argument by proposing that the universe expands enormously with each cycle, causing entropy to decrease further. Everything is falling apart enormously, so that cosmic structures such as black holes disappear. That way the universe returns to its original homogeneous state before another reversal begins,” Kinney said.
“We have shown in our research that the entropy problem can only be solved if we assume a situation where the universe had a beginning. We have proven that any cyclic pattern that dissolves entropy by expansion must have a beginning.
For the first start
“We find the idea that there was a time in the past when it all started, and there was nothing before, not even time, that’s a difficult concept. We really want to know what happened before that. Scientists have also wrestled with these questions since time immemorial,” says Stein. “But as far as I know, there must have been a ‘beginning’ at some point.’ So there is a time somewhere in the past for which there is no answer to the question “what preceded this?”
Of course, there are still plenty of scientific questions to answer after that, according to Kinney: “Our evidence does not apply to the cyclic models devised by Roger Penrose. He had the idea that the universe expands infinitely with each cycle. We are still working on that.
