The new research highlights a disturbing problem with the concept of a periodic universe that goes through infinitely alternating cycles of rapid expansion and contraction, known as the “bouncing universe” model.
These bouncing universe models show that the universe didn’t begin, eliminating the need for a disturbing singularity before the early days of rapid expansion (often called the Big Bang) required by the “start of time” model.
A newly proposed bouncing universe recipe attempts to solve the problem of entropy — a measure of the unusable energy in the universe that can only increase — that has plagued previous endless expansion and expansion, University at Buffalo researchers say. Shrink the model. It still needs a start.
related: The Big Bang: What really happened when the universe was born?
“People have proposed bouncing the universe to make cosmic infinity a thing of the past, but what we’re showing is that one of the latest types of these models doesn’t work,” says physicist at the University at Buffalo Wilkinney said in a statement. (opens in new tab) “In this new model for solving the entropy problem, even if the universe has cycles, it still has to have a beginning.”
That means proponents of the cosmic cycle model 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 time began, all the energy in the universe was contained in a singularity—an infinite dimensionless point not described by the laws of physics.
This ended with a period of rapid expansion — the Big Bang — where the universe expanded and cooled, allowing matter to form — first hydrogen atoms, then heavier elements, and finally stars and galaxies.
The problem is that, while the theory is very good at describing the structure of the universe from a fraction of a second to the one we see today, about 13.8 billion years later, it fails to describe the conditional singularity that existed before inflation kicked in. What even started it.
This problem is eliminated by a bouncing universe, because if the cycles of expansion and collapse are infinite, then there is no beginning, so there is no need to explain what it was before. This would see the universe experience a similar inflation to what the inflationary model of the universe would suggest, but then “bounce back” on itself in some sort of “big crunch”.
Therefore, each new inflationary period will start from the “wreckage” of the previous expansion period, not from a singularity. However, Kinney believes that the bouncing universe has its own unique problems.
“Unfortunately, it has been known for nearly 100 years that these cyclic models don’t work because each cycle is different from the last because disorder or entropy builds up in the universe over time. It’s not really a cycle, ” said the UB researcher. “A recent model of cycles addresses this entropy buildup problem by proposing that the universe expands by a large amount each cycle, diluting the entropy.”
This new bouncing universe model tries to stretch everything out to get rid of cosmic structures like black holes, bringing the universe back to its original homogenous state before another bouncing begins, Kinney said.
“We show that in solving the entropy problem, you create a situation where the universe must have a beginning. Our proof shows in general that any cyclic model that removes entropy through inflation must have a beginning,” he said, adding Added a bouncing universe that might survive this evaluation. “Our proof doesn’t apply to the cycle model proposed by Roger Penrose, where the universe expands infinitely with each cycle. We’re working on that.”
Kinney’s collaborator is a Ph.D. in physics at UB. student, Nina Stein. She highlighted the duo’s problems with the bouncing universe: “The idea of nothing before a certain point, no time, haunts us, and we want to know what’s before that—including scientists.
“But as far as we know, in models that deal with entropy, there must be a ‘beginning.’ There’s one point that doesn’t answer the question, ‘What happened before that?'”
This means that, for now, the mysteries that existed before the universe and time itself remain and will be hotly debated by cosmologists for some time to come.
“There are many reasons to be curious about the early universe, but I think my favorite is that humans have a natural tendency to wonder what happened before,” Stein said. “Across cultures and history, humans tell creative stories about ‘the beginning.’ We always wonder where we came from.”
Kinney and Stein’s findings are discussed in a paper published in the June edition. Journal of Cosmology and Astroparticle Physics. (opens in new tab)
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