admin New research pokes holes in the idea that the cosmos expanded and then contracted before beginning again.
How was the universe born? Did we start with a big bang or was there a rebound? Can the universe evolve in a cycle of boom and bust, repeating forever? Now, in two papers, researchers have poked holes in different models of the so-called bouncing universe, suggesting that the universe we see around us may be a proposition. unique.
Proponents of cosmology argue that our universe did not emerge from nothing. Instead, proponents claim, a universe that previously shrank itself and then reassembled the universe in which we live. It may have happened once or, according to some theories, countless times.
So which scenario is correct? The most widely accepted explanation for the history of the universe is that it began with a big bang, followed by a period of rapid expansion known as cosmic inflation. According to this model, the light left behind at a time when the universe was hot and young, known as the cosmic microwave background (CMB), would be roughly the same no matter which way you looked. But data from the Planck space observatory, which mapped the CMB between 2009 and 2013, shows unexpected variations in microwave radiation. They could be statistically insignificant fluctuations in the temperature of the universe, or they could be signs of something interesting going on.
One possibility is that the CMB anomalies imply that the universe did not form from thin air. Instead, it happened after an earlier universe collapsed and recovered to create the space and time we live in today.
Cosmic reverberation models could explain these CMB models as well as answer lingering questions about the standard description of the origin and evolution of the universe. In particular, the big bang model of the universe begins with a singularity – a point that appears out of thin air and contains the precursors of everything in the universe in an area so small that it has almost no size. at all. The idea is that the universe evolved from a singularity and, after inflation, stabilized into the gradually expanding universe we see today. But singularities matter because physics and math by themselves make no sense when everything is lumped into an infinitely small point. Many physicists prefer to avoid singularities.
A model that bounces to avoid singularities and make the CMB anomaly slightly less anomalous is called the ring quantum universe (LQC). It builds on a bridge between classical physics and quantum mechanics known as ring quantum gravity, which assumes that gravity declines at very small distances instead of increasing to infinity. “Cosmic models inspired by ring quantum gravity can solve a number of problems,” explains University of Geneva cosmologist Ruth Durrer, “especially the singularity problem.” . Durrer is a co-author of one of two new studies on the bouncing universe. In it, she and her colleagues looked for astronomical signatures of such patterns.
In an LQC model, a progenitor of our universe might have contracted under the influence of gravity until it became extremely dense. Eventually, quantum mechanics will take over. Instead of collapsing into a singularity, the universe would begin to expand again and may even have gone through a period of inflation, as many cosmologists believe our universe did.
If that happens, Louisiana State University physicist Ivan Agullo says, it will leave a mark in the universe. Agullo, who is not affiliated with any of the recent analyses, has suggested that the sign will appear in a feature of the CMB data known as the “dual spectrum,” a measure of how different parts of the universe are. will interact in a spiral. script. Bispectrum will not be apparent in CMB images, but it will show up in old CMB microwave frequency analyses.
“If observed,” Agullo said, the dipole “would be convincing evidence for the existence of a bounce instead of a bang.” Agullo’s group had previously calculated the bispectral because it would appear 400,000 years after a cosmic collision. Durrer and his colleagues took the calculation further, but when they compared it with current Planck CMB data, there was no significant sign of a bipolar fingerprint.
Although many other bouncing cosmological models may still be possible, the failure to find a significant dipole means that models that rely on LQC to handle CMB anomalies can be ruled out. It was a sad end for Agullo, who had always hoped to find concrete evidence of a bouncing universe. But Paola Delgado, who has a PhD in cosmology. candidate at Jagiellonian University in Poland, who studied new analysis co-authored by Durrer, says there is upside potential. “I have long heard that [the attempt to merge quantum physics and cosmology] cannot be tested,” says Delgado. “I think it’s great to see that for certain types of models, you still have some contact with the observations.”
The exclusion of signs of an LQC-induced cosmic bounce in the Planck data means that the CMB anomalies remain unexplained. But an even bigger cosmological problem persists:
Did the universe have a beginning? For supporters of the big bang, it was. But that leaves us with the puzzling singularity that started it all.
In addition, according to the theories of the so-called cyclic cosmology, the universe is immortal and undergoes an endless process of restoration. Although a bouncing universe can go through one or more cycles, a truly cyclical universe has no beginning or end. It consists of a series of bounces over an infinite number of cycles and will continue for an infinite number of more. And because such a universe has no beginning, there is no big bang or singularity.
The study co-authored by Durrer and Delgado does not rule out immortal cyclic universes. Many theories describe such a bouncing universe in ways that are difficult, if not impossible, to distinguish from the “big bang plus inflation” model by looking at Planck’s CMB data.
But a serious flaw lies in the idea of a universe with eternal cycles, according to University of Buffalo physicist William Kinney, who co-authored a recent second analysis. That hole is entropy, which builds up as the universe orbits. Often thought of as the degree of disorder in a system, entropy is related to the amount of useful energy the system has:
The higher the entropy, the less energy. If the universe increases entropy and loses order with each bounce, the amount of usable energy decreases each time. In this case, the universe would have had a greater amount of useful energy than in the previous time. If you extrapolate far enough back, this implies a big bang-like start with an extremely small amount of entropy, even for a universe that subsequently undergoes periodic bounces. (If you’re wondering how this scenario doesn’t violate the law of conservation of energy, we’re talking about available energy. Although the total amount of energy in the universe remains constant, the amount can be now useful work is decreasing. with increasing entropy.)
Kinney and one of his colleagues discovered that new cyclic models overcome the problem by requiring that the universe expand greatly with each cycle. The expansion allowed the universe to become flatter, dissipating entropy before collapsing again. Although this explanation solves the entropy problem, the researchers calculated in their recent paper that the solution itself ensures that the universe is not immortal. “I feel like we’ve proven something fundamental about the universe,” Kinney said, “that it could have had a beginning.” This implies that a big bang happened at some point, even though the event happened many universes ago, which suggests that a singularity is needed to make all happened from the very beginning.
Kinney’s paper is the latest in the cyclic universe debate, but proponents of a universe without a beginning and an end have yet to respond in the scientific literature. Two leading proponents of the periodic universe, astrophysicists Paul Steinhardt of Princeton University and Anna Ijjas of New York University, declined to comment for this article. However, if the history of the debate is any indication, we could soon hear of a workaround to counter Kinney’s analysis.
Cosmologist Nelson Pinto-Neto of the Brazilian Center for Physical Research, who has studied reverberation and other cyclic models, agrees that the Planck data can rule out cosmic bounces. loop quantum, but he is more optimistic about the cosmic cycle question. “Existence is a fact. We are all here and now. Non-existence is an abstraction of the human mind,” says Nelson. “That’s why I think a [cyclic universe] that always exists is simpler than a created universe. However, as a scientist, I have to be open to both possibilities.
