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Science And Nature

‘Bouncing’ universe theory still can’t explain what came first

An illustration showing the bouncing universe model. Two cone-shaped grids full of stars and galaxies are arranged closed end to closed end.

A bouncing style of the universe could get rid of a short singularity, but include its problems. (Image credit: NASA/WMAP Science Team/Robert Lea)

New research highlights a troubling problem with concepts of a cyclical universe that experiences infinitely alternating periods of rapid expansion and contraction, referred to as ‘bouncing universe’ models.

These bouncing universe models suggest the cosmos does not have any beginning, eliminating the necessity for a troubling singularity before the initial amount of rapid inflation often called the Big Bang needed by ‘beginning of time’ models.

University at Buffalo researchers say a newly suggested bouncing universe recipe that attempts to cope with the issue of entropy the way of measuring unusable energy in the universe, that may only increase is suffering from a problem which has plagued previous types of endless inflation and contraction. It still requires a beginning.

Related: The Big Bang: What really happened at our universe’s birth?

“People proposed bouncing universes to help make the universe infinite in to the past, but what we show is that among the newest forms of these models fails,” University of Buffalo physicist Will Kinney said in a statement. (opens in new tab) “In this new kind of model, which addresses issues with entropy, even though the universe has cycles, it still has to get a beginning.”

Which means that proponents of cyclical types of the universe may need to get back to the drawing board.

The best theory of the universe’s origins is so-called ‘cosmic inflation.’ This shows that before time began all of the energy in the cosmos was within a singularity an infinite dimensionless point not described by the laws of physics.

This ended with an interval of rapid inflation the Big Bang that saw the universe expand and cool, thus allowing the forming of matter first atoms of hydrogen, then heavier elements, and finally stars and galaxies.

The thing is, while this theory is great at describing the universe since it ages from fractions of another before cosmic structure we see today, around 13.8 billion years later, it can’t describe the conditions of the singularity that existed before this inflation was kick-started. As well as what kick-started it.

A model of the big bang showing a large explosion that produces the rest of the universe

An illustration of the expansion of the universe. (Image credit: Getty images)

This problem is eliminated by way of a bouncing universe because if periods of inflation and collapse are infinite, then there is no beginning and therefore you don’t need to explain what preceded it. This might start to see the universe undergo similar inflation as suggested by the cosmic inflation model, but ‘springing back’ on itself in a ‘Big Crunch’ of sorts.

Each new inflation period would, therefore, begin from the ‘wreckage’ of a previous amount of expansion rather than singularity. But, Kinney thinks that bouncing universes include their own problems.

“Unfortunately, it has been known for nearly 100 years these cyclic models don’t work because disorder, or entropy, accumulates in the universe as time passes, so each cycle differs from the final one. It isn’t truly cyclic,” the UB researcher said. “A recently available cyclic model gets for this entropy build-up problem by proposing that the universe expands a big pile with each cycle, diluting the entropy.”

Kinney said that new bouncing universe model tries to stretch everything out to eliminate cosmic structures such as for example black holes thus returning the universe to its original homogenous state before another bounce begins.

“We showed that in solving the entropy problem, you develop a situation where in fact the universe needed a newbie. Our proof shows generally that any cyclic model which removes entropy by expansion will need to have a newbie,” he said, adding one bouncing universe can survive this assessment. “Our proof will not connect with a cyclic model proposed by Roger Penrose, where the universe expands infinitely in each cycle. We’re focusing on that certain.”

Kinney’s collaborator is UB physics Ph.D. student, Nina Stein. She highlighted the issue the duo had with a bouncing universe: “The theory that there is a point with time before which there is nothing, virtually no time, bothers us, and we need to know what there is before that scientists included.

“But so far as we are able to tell, in models that address entropy, there will need to have been a ‘beginning.’ There exists a point that there is absolutely no response to the question, ‘What came before that?'”

This implies, for the present time, the mystery of what existed prior to the universe and time itself remains and you will be hotly debated by cosmologists for quite a while ahead.

“There are a great number of reasons to be interested in the first universe, but I believe my favorite may be the natural human tendency to wish to know what came before,” Stein said. “Across cultures and histories, humans have told stories about creation, about ‘in the start.’ We always wish to know where we originated from.”

Kinney and Stein’s findings are discussed in a paper published in the June edition of the Journal of Cosmology and Astroparticle Physics. (opens in new tab)

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Robert Lea

RobertLeais a science journalist in the U.K. whose articles have already been published in Physics World, New Scientist, Astronomy Magazine, ABOUT Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.s Open University. Follow him on Twitter @sciencef1rst.

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