Because this behavior is hypothesized to be perpetual, the universe should have no beginning and no end — only eternal cycles of growing and shrinking that extend forever into the future, and forever into the past.

It’s an appealing concept in part because it removes the need for a state called a singularity that corresponds to the “beginning of time” in other models.

But a new study by University at Buffalo physicists Will Kinney and Nina Stein highlights one way that cyclic or “bouncing” cosmologies fall flat.

The research shows that the latest version of this theory — a cyclic model that resolves long-standing concerns about entropy — introduces a new problem (or rather, returns to an old one). Cyclic universes described under this model must have a beginning, Kinney and Stein conclude.

“People proposed bouncing universes to make the universe infinite into the past, but what we show is that one of the newest types of these models doesn’t work,” says Kinney, PhD, professor of physics in the UB College of Arts and Sciences. “In this new type of model, which addresses problems with entropy, even if the universe has cycles, it still has to have a beginning.”

“There are a lot of 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,” says Stein, a UB PhD student in physics, regarding the importance of such research. “Across cultures and histories, humans have told stories about creation, about ‘in the beginning.’ We always want to know where we came from.”

The study, funded by the National Science Foundation, was published in June in the Journal of Cosmology and Astroparticle Physics. The paper is titled, “Cyclic cosmology and geodesic completeness.”

If the universe had a beginning, how did it begin?

Kinney is author of a 2022 book titled, “An Infinity of Worlds,” which tells the epic story of cosmic inflation, a competing theory about the origins of the universe. Under this model, the early universe was characterized by a period of rapid expansion from a singularity, followed by the superhot Big Bang, which forged the primordial elements that went on to make galaxies and stars and planets, and the atoms in our bodies and all other living things.

Cosmic inflation is a leading theory. But it focuses on what happens during and after the age of rapid expansion. It doesn’t explain what came before that, and it doesn’t describe the conditions of the initial singularity.

A truly cyclic universe would circumvent these problems: If the universe is engaged in endless cycles of expansion and contraction, it need not have a beginning at all. But as Kinney notes, these bouncing models raise their own array of untenable questions.

“Unfortunately, it’s been known for almost 100 years that these cyclic models don’t work because disorder, or entropy, builds up in the universe over time, so each cycle is different from the last one. It’s not truly cyclic,” Kinney says. “A recent cyclic model gets around this entropy build-up problem by proposing that the universe expands a whole bunch with each cycle, diluting the entropy. You stretch everything out to get rid of cosmic structures such as black holes, which returns the universe to its original homogenous state before another bounce begins.”

“But,” he adds, “long story short, we showed that in solving the entropy problem, you create a situation where the universe had to have a beginning. Our proof shows in general that any cyclic model which removes entropy by expansion must have a beginning.”

“The idea that there was a point in time before which there was nothing, no time, bothers us, and we want to know what there was before that — scientists included,” Stein says. “But as far as we can tell, in models that address entropy, there must have been a ‘beginning.’ There is a point for which there is no answer to the question, ‘What came before that?’ “

And, of course, there are further research questions, Kinney says: “Our proof does not apply to a cyclic model proposed by Roger Penrose, in which the universe expands infinitely in each cycle. We’re working on that one.”

“Working with precious fossils is a challenge since it is important not to destroy or harm the specimen,” said the article’s senior author, Tilo Niemann, M.D., head of CT, and cardiac and thoracic radiology in the Department of Radiology at Kantonsspital Baden in Baden, Switzerland. “Even if there exist various imaging techniques to evaluate the internal structure, it was not possible to scan a whole tusk in toto without the need for fragmentation or at least having to do multiple scans that then had to be painstakingly assembled.”

The extinct woolly mammoth (Mammuthus primigenius) was the size of a modern-day African elephant and lived throughout Eurasia and North America. Most of the woolly mammoths went extinct with the conclusion of the last Ice Age, and the last specimens lived approximately 6,000 years ago. They belong to the order Proboscidea, which includes today’s elephants as well as other extinct mammoths, mastodons and gomphotheres.

Mammoths were covered in fur and had small ears and a small tail to abate frostbite. They also had tusks that they used for scraping bark off trees, digging on the ground for food and fighting. The tusks of proboscideans have allowed researchers to determine the age and identification of specific life-altering occurrences based on annual growth increment analysis.

Newer CT scanners have larger gantries, which is the ring or cylinder into which a patient, or in this case the tusk, is placed. The introduction of larger gantries now allows the opportunity for scanning larger objects that was not possible before, Dr. Niemann noted.

The tusk that the researchers examined was found in central Switzerland and excavated by the heritage and archaeology office of Canton Zug. The tusk is a total of 206 centimeters (cm) in length — nearly 7 feet. It has a basal (measurement at the base) diameter of 16 cm — just over 6 inches. The total object diameter — taking into account its helical, or spiral, curvature — is 80 cm, or just over 2.5 feet.

Tusks mostly consist of two types of material: cementum, a bonelike substance, and dentin, which lies beneath the cementum and accounts for the majority of the tusk’s mass. Mammoth tusks are internally structured by annual increments of dentin apposition which, when viewed in longitudinal section (as opposed to cross-section), resemble cone-shaped cups stacked on top of one another. The first “cone” a mammoth creates forms the tip of the tusk, while the cone at the tusk base is the most recent, generated just prior to the animal’s death. The cones in between are formed throughout the mammoth’s lifetime.

Using the larger-gantry CT scanner, researchers, in collaboration with the Institute of Evolutionary Medicine, University of Zurich, were able to capture a clear image of the entire tusk’s interior.

“It was fascinating to see the internal structure of the mammoth tusk,” Dr. Niemann said.

The researchers found a total of 32 cones, resulting in a minimum age of 32 years at the time of death. Even though the mammoth tusk is well-preserved, it is missing the tip, so the estimate obtained is slightly below the actual age of the animal at the time of death.

“Our mammoth had died at the age of around 32 years, approximately 17,000 years ago,” Dr. Niemann said.

In Applied Physics Reviews, by AIP Publishing, scientists at UCLA describe their development of a type of HMI that is stretchable, inexpensive, and waterproof. The device is based on a soft magnetoelastic sensor array that converts mechanical pressure from the press of a finger into an electrical signal.

The device involves two main components. The first component is a layer that translates mechanical movement to a magnetic response. It consists of a set of micromagnets in a porous silicone matrix that can convert the gentle fingertip pressure into a magnetic field variation.

The second component is a magnetic induction layer consisting of patterned liquid metal coils. These coils respond to the magnetic field changes and generate electricity through the phenomenon of electromagnetic induction.

“Owing to the material’s flexibility and durability, the magnetoelastic sensor array can generate stable power under deformations, such as rolling, folding, and stretching,” said author Jun Chen, from UCLA. “Due to these compelling features, the device can be adopted for human-body powered HMI by transforming human biomechanical activities into electrical signals.”

The power required to run the HMI comes from the wearer’s movements. This means no batteries or other external power components are required, rendering the HMI more environmentally friendly and sustainable.

The device was tested in a variety of real-world situations, including in the presence of a water spray, such as might exist in the shower, a rainstorm, or during vigorous athletic activity. The device worked well when wet, since the magnetic field was not greatly affected by the presence of water.

The investigators studied a range of fabrication and assembly techniques to optimize the biomechanical-to-electrical energy conversion of the device. They found they could achieve a balance between performance and flexibility by controlling the thickness of the flexible film and the concentration of the magnetic particles.

To test their system, the investigators carried out a series of experiments in which a subject applied finger taps to turn a lamp off and on and control a music player.

“Our magnetoelastic sensor array not only wirelessly functions as the on and off buttons of a lamp but also controls a music player’s command features, representing the actions of play, pause, next, and previous,” Chen said.

These tests promise new applications for versatile water-resistant HMIs that can be used to control many types of smart devices.

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