Putting the 'bang' in the Big Bang

Big Bang illustration

As the Big Bang theory goes, somewhere around 13.8 billion years ago the universe exploded into being, as an infinitely small, compact fireball of matter that cooled as it expanded, triggering reactions that cooked up the first stars and galaxies, and all the forms of matter that we see (and are) today.

Just before the Big Bang launched the universe onto its ever-expanding course, physicists believe, there was another, more explosive phase of the early universe at play: cosmic inflation, which lasted less than a trillionth of a second. During this period, matter -- a cold, homogeneous goop -- inflated exponentially quickly before processes of the Big Bang took over to more slowly expand and diversify the infant universe.

Recent observations have independently supported theories for both the Big Bang and cosmic inflation. But the two processes are so radically different from each other that scientists have struggled to conceive of how one followed the other.

Now physicists at MIT, Kenyon College, and elsewhere have simulated in detail an intermediary phase of the early universe that may have bridged cosmic inflation with the Big Bang. This phase, known as "reheating," occurred at the end of cosmic inflation and involved processes that wrestled inflation's cold, uniform matter into the ultrahot, complex soup that was in place at the start of the Big Bang.

"The postinflation reheating period sets up the conditions for the Big Bang, and in some sense puts the 'bang' in the Big Bang," says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. "It's this bridge period where all hell breaks loose and matter behaves in anything but a simple way."

Kaiser and his colleagues simulated in detail how multiple forms of matter would have interacted during this chaotic period at the end of inflation. Their simulations show that the extreme energy that drove inflation could have been redistributed just as quickly, within an even smaller fraction of a second, and in a way that produced conditions that would have been required for the start of the Big Bang.

The team found this extreme transformation would have been even faster and more efficient if quantum effects modified the way that matter responded to gravity at very high energies, deviating from the way Einstein's theory of general relativity predicts matter and gravity should interact.

"This enables us to tell an unbroken story, from inflation to the postinflation period, to the Big Bang and beyond," Kaiser says. "We can trace a continuous set of processes, all with known physics, to say this is one plausible way in which the universe came to look the way we see it today."

The team's results appear today in Physical Review Letters. Kaiser's co-authors are lead author Rachel Nguyen, and John T. Giblin, both of Kenyon College, and former MIT graduate student Evangelos Sfakianakis and Jorinde van de Vis, both of Leiden University in the Netherlands.

"In sync with itself"

The theory of cosmic inflation, first proposed in the 1980s by MIT's Alan Guth, the V.F. Weisskopf Professor of Physics, predicts that the universe began as an extremely small speck of matter, possibly about a hundred-billionth the size of a proton. This speck was filled with ultra-high-energy matter, so energetic that the pressures within generated a repulsive gravitational force -- the driving force behind inflation. Like a spark to a fuse, this gravitational force exploded the infant universe outward, at an ever-faster rate, inflating it to nearly an octillion times its original size (that's the number 1 followed by 26 zeroes), in less than a trillionth of a second.

Kaiser and his colleagues attempted to work out what the earliest phases of reheating -- that bridge interval at the end of cosmic inflation and just before the Big Bang -- might have looked like.

"The earliest phases of reheating should be marked by resonances. One form of high-energy matter dominates, and it's shaking back and forth in sync with itself across large expanses of space, leading to explosive production of new particles," Kaiser says. "That behavior won't last forever, and once it starts transferring energy to a second form of matter, its own swings will get more choppy and uneven across space. We wanted to measure how long it would take for that resonant effect to break up, and for the produced particles to scatter off each other and come to some sort of thermal equilibrium, reminiscent of Big Bang conditions."

The team's computer simulations represent a large lattice onto which they mapped multiple forms of matter and tracked how their energy and distribution changed in space and over time as the scientists varied certain conditions. The simulation's initial conditions were based on a particular inflationary model -- a set of predictions for how the early universe's distribution of matter may have behaved during cosmic inflation.

The scientists chose this particular model of inflation over others because its predictions closely match high-precision measurements of the cosmic microwave background -- a remnant glow of radiation emitted just 380,000 years after the Big Bang, which is thought to contain traces of the inflationary period.

A universal tweak

The simulation tracked the behavior of two types of matter that may have been dominant during inflation, very similar to a type of particle, the Higgs boson, that was recently observed in other experiments.

Before running their simulations, the team added a slight "tweak" to the model's description of gravity. While ordinary matter that we see today responds to gravity just as Einstein predicted in his theory of general relativity, matter at much higher energies, such as what's thought to have existed during cosmic inflation, should behave slightly differently, interacting with gravity in ways that are modified by quantum mechanics, or interactions at the atomic scale.

In Einstein's theory of general relativity, the strength of gravity is represented as a constant, with what physicists refer to as a minimal coupling, meaning that, no matter the energy of a particular particle, it will respond to gravitational effects with a strength set by a universal constant.

However, at the very high energies that are predicted in cosmic inflation, matter interacts with gravity in a slightly more complicated way. Quantum-mechanical effects predict that the strength of gravity can vary in space and time when interacting with ultra-high-energy matter -- a phenomenon known as nonminimal coupling.

Kaiser and his colleagues incorporated a nonminimal coupling term to their inflationary model and observed how the distribution of matter and energy changed as they turned this quantum effect up or down.

In the end they found that the stronger the quantum-modified gravitational effect was in affecting matter, the faster the universe transitioned from the cold, homogeneous matter in inflation to the much hotter, diverse forms of matter that are characteristic of the Big Bang.

By tuning this quantum effect, they could make this crucial transition take place over 2 to 3 "e-folds," referring to the amount of time it takes for the universe to (roughly) triple in size. In this case, they managed to simulate the reheating phase within the time it takes for the universe to triple in size two to three times. By comparison, inflation itself took place over about 60 e-folds.

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Study casts doubt on carbon capture

One proposed method for reducing carbon dioxide (CO2) levels in the atmosphere -- and reducing the risk of climate change -- is to capture carbon from the air or prevent it from getting there in the first place. However, research from Mark Z. Jacobson at Stanford University, published in Energy and Environmental Science, suggests that carbon capture technologies can cause more harm than good.

"All sorts of scenarios have been developed under the assumption that carbon capture actually reduces substantial amounts of carbon. However, this research finds that it reduces only a small fraction of carbon emissions, and it usually increases air pollution," said Jacobson, who is a professor of civil and environmental engineering. "Even if you have 100 percent capture from the capture equipment, it is still worse, from a social cost perspective, than replacing a coal or gas plant with a wind farm because carbon capture never reduces air pollution and always has a capture equipment cost. Wind replacing fossil fuels always reduces air pollution and never has a capture equipment cost."

Jacobson, who is also a senior fellow at the Stanford Woods Institute for the Environment, examined public data from a coal with carbon capture electric power plant and a plant that removes carbon from the air directly. In both cases, electricity to run the carbon capture came from natural gas. He calculated the net CO2 reduction and total cost of the carbon capture process in each case, accounting for the electricity needed to run the carbon capture equipment, the combustion and upstream emissions resulting from that electricity, and, in the case of the coal plant, its upstream emissions. (Upstream emissions are emissions, including from leaks and combustion, from mining and transporting a fuel such as coal or natural gas.)

Common estimates of carbon capture technologies -- which only look at the carbon captured from energy production at a fossil fuel plant itself and not upstream emissions -- say carbon capture can remediate 85-90 percent of carbon emissions. Once Jacobson calculated all the emissions associated with these plants that could contribute to global warming, he converted them to the equivalent amount of carbon dioxide in order to compare his data with the standard estimate. He found that in both cases the equipment captured the equivalent of only 10-11 percent of the emissions they produced, averaged over 20 years.

This research also looked at the social cost of carbon capture -- including air pollution, potential health problems, economic costs and overall contributions to climate change -- and concluded that those are always similar to or higher than operating a fossil fuel plant without carbon capture and higher than not capturing carbon from the air at all. Even when the capture equipment is powered by renewable electricity, Jacobson concluded that it is always better to use the renewable electricity instead to replace coal or natural gas electricity or to do nothing, from a social cost perspective.

Given this analysis, Jacobson argued that the best solution is to instead focus on renewable options, such as wind or solar, replacing fossil fuels.

Efficiency and upstream emissions

This research is based on data from two real carbon capture plants, which both run on natural gas. The first is a coal plant with carbon capture equipment. The second plant is not attached to any energy-producing counterpart. Instead, it pulls existing carbon dioxide from the air using a chemical process.

Jacobson examined several scenarios to determine the actual and possible efficiencies of these two kinds of plants, including what would happen if the carbon capture technologies were run with renewable electricity rather than natural gas, and if the same amount of renewable electricity required to run the equipment were instead used to replace coal plant electricity.

While the standard estimate for the efficiency of carbon capture technologies is 85-90 percent, neither of these plants met that expectation. Even without accounting for upstream emissions, the equipment associated with the coal plant was only 55.4 percent efficient over 6 months, on average. With the upstream emissions included, Jacobson found that, on average over 20 years, the equipment captured only 10-11 percent of the total carbon dioxide equivalent emissions that it and the coal plant contributed. The air capture plant was also only 10-11 percent efficient, on average over 20 years, once Jacobson took into consideration its upstream emissions and the uncaptured and upstream emissions that came from operating the plant on natural gas.

Due to the high energy needs of carbon capture equipment, Jacobson concluded that the social cost of coal with carbon capture powered by natural gas was about 24 percent higher, over 20 years, than the coal without carbon capture. If the natural gas at that same plant were replaced with wind power, the social cost would still exceed that of doing nothing. Only when wind replaced coal itself did social costs decrease.

For both types of plants this suggests that, even if carbon capture equipment is able to capture 100 percent of the carbon it is designed to offset, the cost of manufacturing and running the equipment plus the cost of the air pollution it continues to allow or increases makes it less efficient than using those same resources to create renewable energy plants replacing coal or gas directly.

"Not only does carbon capture hardly work at existing plants, but there's no way it can actually improve to be better than replacing coal or gas with wind or solar directly," said Jacobson. "The latter will always be better, no matter what, in terms of the social cost. You can't just ignore health costs or climate costs."

This study did not consider what happens to carbon dioxide after it is captured but Jacobson suggests that most applications today, which are for industrial use, result in additional leakage of carbon dioxide back into the air.

Focusing on renewables

People propose that carbon capture could be useful in the future, even after we have stopped burning fossil fuels, to lower atmospheric carbon levels. Even assuming these technologies run on renewables, Jacobson maintains that the smarter investment is in options that are currently disconnected from the fossil fuel industry, such as reforestation -- a natural version of air capture -- and other forms of climate change solutions focused on eliminating other sources of emissions and pollution. These include reducing biomass burning, and reducing halogen, nitrous oxide and methane emissions.

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Skiing, snowboarding injuries more serious -- skull and face fractures -- in younger children

Winter sports like skiing and snowboarding are a great way to keep kids active in the winter, but they are also linked to injuries and for younger children those injuries are more likely to involve fractures to the head or face, according to new research being presented at the American Academy of Pediatrics (AAP) 2019 National Conference & Exhibition.

The research abstract, "Pediatric Snow Sport Injuries Differ By Age," will be presented during the AAP 2019 National Conference & Exhibition.

Researchers looked at a cross-sectional analysis of the 2009 and 2012 Kids' Inpatient Database, examining 845 hospital admissions for snow sport injuries in kids. They found that over half of hospitalized children required major surgical intervention, and elementary school-age children were at significantly greater odds than those older than high school to suffer a skull or facial fracture. Middle school, high school and those older were more likely to experience intra-abdominal injury.

"We were interested to find that the type of injuries children had varied according to their age, and we believe these findings can better inform educational and legislative efforts aimed at reducing injuries in children who participate in winter sports," said Robert J. McLoughlin, MD, MSCI. "These injuries can be very severe and should be a concern to any parent with a child involved in these sports. Almost a quarter -- 23% of children -- suffered intercranial injuries, which we found were more common among young children."

Of the young skiers who were admitted into hospitals in this research, 75.8% were male and 87.4% white. The injuries included: lower extremity fractures (28.7%), intracranial injury (22.7%), splenic injury (15.6%), upper extremity fracture (15.5%), and skull fracture (9.1%).

From Science Daily

Science reveals improvements in Roman building techniques

The Romans were some of the most sophisticated builders of the ancient world. Over the centuries, they adopted an increasingly advanced set of materials and technologies to create their famous structures. To distinguish the time periods over which these improvements took place, historians and archaeologists typically measure the colours, shapes and consistencies of the bricks and mortar used by the Romans, along with historical sources. In new research published in EPJ Plus, Francesca Rosi and colleagues at the Italian National Research Council improved on these techniques through scientific analysis of the materials used to build the Roman Forum's Atrium Vestae. They found that successive phases of modification to the building saw improvements including higher quality raw materials, higher brick firing temperatures, and better ratios between carbonate and silicate building materials.

The team's analysis could offer important supplements to the techniques currently used by historians and archaeologists. It could also help these academics to end long-standing disputes regarding the time periods of certain building techniques. Since the Atrium Vestae was modified in five distinctive building phases spanning several centuries, the study highlighted technological improvements throughout the Roman age in unprecedented levels of detail.

The techniques employed by Rosi and colleagues included optical and electron microscopy, and measurements of how x-rays were diffracted as they passed through the materials. They also determined the molecular fingerprints, or spectra, of the materials. These are based on the characteristic ways in which their molecules vibrate when illuminated by electromagnetic radiation of specific energies. Using these methods, the team revealed the colours, textures and chemical compositions of Roman building materials on microscopic scales for the first time; clearly revealing technological improvements over the centuries. The findings of Rosi's team are a clear demonstration of the advantages of scientific methods in archaeological analysis. Their techniques could soon be used in future studies to unlock further mysteries concerning the technologies employed by ancient civilisations.

From Science Daily

Memory training builds upon strategy use

Researchers from Åbo Akademi University, Finland, and Umeå University, Sweden, have for the first time obtained clear evidence of the important role strategies have in memory training. Training makes participants adopt various strategies to manage the task, which then affects the outcome of the training.

Strategy acquisition can also explain why the effects of memory training are so limited. Typically, improvements are limited only to tasks that are very similar to the training task -- training has provided ways to handle a given type of task, but not much else.

A newly published study sheds light on the underlying mechanisms of working memory training that have remained unclear. It rejects the original idea that repetitive computerized training can increase working memory capacity. Working memory training should rather be seen as a form of skill learning in which the adoption of task-specific strategies plays an important role. Hundreds of commercial training programs that promise memory improvements are available for the public. However, the effects of the programs do not extend beyond tasks similar to the ones one has been trained on.

The study included 258 adult individuals which were randomized into three groups. Two of the groups completed a four-week working memory training period during which participants completed 3 x 30-minute training sessions per week with a working memory updating task. One group trained with an externally provided strategy instruction, while the other group trained without the strategy instruction. The third group served as controls and only participated in a pretest, intermediate test and posttest. Self-generated strategies were probed with questionnaires at each training session and assessment point. This study was conducted within the BrainTrain project, one of the Research Centers of Excellence 2015-2018 at Åbo Akademi University.

From Science Daily

What 26,000 books reveal when it comes to learning language

What can reading 26,000 books tell researchers about how language environment affects language behavior? Brendan T. Johns, an assistant professor of communicative disorders and sciences in the University at Buffalo's College of Arts and Sciences, has some answers that are helping to inform questions ranging from how we use and process language to better understanding the development of Alzheimer's disease.

But let's be clear: Johns didn't read all of those books. He's an expert in computational cognitive science who has published a computational modeling study that suggests our experience and interaction with specific learning environments, like the characteristics of what we read, leads to differences in language behavior that were once attributed to differences in cognition.

"Previously in linguistics it was assumed a lot of our ability to use language was instinctual and that our environmental experience lacked the depth necessary to fully acquire the necessary skills," says Johns. "The models that we're developing today have us questioning those earlier conclusions. Environment does appear to be shaping behavior."

Johns' findings, with his co-author, Randall K. Jamieson, a professor in the University of Manitoba's Department of Psychology, appear in the journal Behavior Research Methods.

Advances in natural language processing and computational resources allow researchers like Johns and Jamieson to examine once intractable questions.

The models, called distributional models, serve as analogies to the human language learning process. The 26,000 books that support the analysis of this research come from 3,000 different authors (about 2,000 from the U.S. and roughly 500 from the U.K.) who used over 1.3 billion total words.

George Bernard Shaw is often credited with saying Britain and America are two countries separated by a common language. But the languages are not identical, and in order to establish and represent potential cultural differences, the researchers considered where each of the 26,000 books was located in both time (when the author was born) and place (where the book was published).

With that information established, the researchers analyzed data from 10 different studies involving more than 1,000 participants, using multiple psycholinguistic tasks.

"The question this paper tries to answer is, 'If we train a model with similar materials that someone in the U.K. might have read versus what someone in the U.S. might have read, will they become more like these people?'" says Johns. "We found that the environment people are embedded in seems to shape their behavior."

The culture-specific books in this study explain much of the variance in the data, according to Johns.

"It's a huge benefit to have a culture-specific corpus, and an even greater benefit to have a time-specific corpus," says Johns. "The differences we find in language environment and behavior as a function of time and place is what we call the 'selective reading hypothesis.'"

Using these machine-learning approaches demonstrates the richly informative nature of these environments, and Johns has been working toward building machine-learning frameworks to optimize education. This latest paper shows how you can take a person's language behavior and estimate the types of materials they've read.

"We want to take someone's past experience with language and develop a model of what that person knows," says Johns. "That lets us identify which information can maximize that person's learning potential."

But Johns also studies clinical populations, and his work with Alzheimer's patients has him thinking about how to apply his models to potentially help people at risk of developing the disease.

He says some people show slight memory loss without other indications of cognitive decline. These patients with mild cognitive impairment have a 10-15% chance of being diagnosed with Alzheimer's in any given year, compared to 2% of the general population over age 65.

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Did an extraterrestrial impact trigger the extinction of ice-age animals?

A controversial theory that suggests an extraterrestrial body crashing to Earth almost 13,000 years ago caused the extinction of many large animals and a probable population decline in early humans is gaining traction from research sites around the world.

The Younger Dryas Impact Hypothesis, controversial from the time it was presented in 2007, proposes that an asteroid or comet hit the Earth about 12,800 years ago causing a period of extreme cooling that contributed to extinctions of more than 35 species of megafauna including giant sloths, sabre-tooth cats, mastodons and mammoths. It also coincides with a serious decline in early human populations such as the Clovis culture and is believed to have caused massive wildfires that could have blocked sunlight, causing an "impact winter" near the end of the Pleistocene Epoch.

In a new study published this week in Scientific Reports, a publication of Nature, UofSC archaeologist Christopher Moore and 16 colleagues present further evidence of a cosmic impact based on research done at White Pond near Elgin, South Carolina. The study builds on similar findings of platinum spikes -- an element associated with cosmic objects like asteroids or comets -- in North America, Europe, western Asia and recently in Chile and South Africa.

"We continue to find evidence and expand geographically. There have been numerous papers that have come out in the past couple of years with similar data from other sites that almost universally support the notion that there was an extraterrestrial impact or comet airburst that caused the Younger Dryas climate event," Moore says.

Moore also was lead author on a previous paper documenting sites in North America where platinum spikes have been found and a co-author on several other papers that document elevated levels of platinum in archaeological sites, including Pilauco, Chile -- the first discovery of evidence in the Southern Hemisphere.

"First, we thought it was a North American event, and then there was evidence in Europe and elsewhere that it was a Northern Hemisphere event. And now with the research in Chile and South Africa, it looks like it was probably a global event," he says.

In addition, a team of researchers found unusually high concentrations of platinum and iridium in outwash sediments from a recently discovered crater in Greenland that could have been the impact point. Although the crater hasn't been precisely dated yet, Moore says the possibility is good that it could be the "smoking gun" that scientists have been looking for to confirm a cosmic event. Additionally, data from South America and elsewhere suggests the event may have actually included multiple impacts and airbursts over the entire globe.

While the brief return to ice-age conditions during the Younger Dryas period has been well-documented, the reasons for it and the decline of human populations and animals have remained unclear. The impact hypothesis was proposed as a possible trigger for these abrupt climate changes that lasted about 1,400 years.

The Younger Dryas event gets its name from a wildflower, Dryas octopetala, which can tolerate cold conditions and suddenly became common in parts of Europe 12,800 years ago. The Younger Dryas Impact Hypothesis became controversial, Moore says, because the all-encompassing theory that a cosmic impact triggered cascading events leading to extinctions was viewed as improbable by some scientists.

"It was bold in the sense that it was trying to answer a lot of really tough questions that people have been grappling with for a long time in a single blow," he says, adding that some researchers continue to be critical.

The conventional view has been that the failure of glacial ice dams allowed a massive release of freshwater into the north Atlantic, affecting oceanic circulation and causing the Earth to plunge into a cold climate. The Younger Dryas hypothesis simply claims that the cosmic impact was the trigger for the meltwater pulse into the oceans.

In research at White Pond in South Carolina, Moore and his colleagues used a core barrel to extract sediment samples from underneath the pond. The samples, dated to the beginning of the Younger Dryas with radiocarbon, contain a large platinum anomaly, consistent with findings from other sites, Moore says. A large soot anomaly also was found in cores from the site, indicating regional large-scale wildfires in the same time interval.

In addition, fungal spores associated with the dung of large herbivores were found to decrease at the beginning of the Younger Dryas period, suggesting a decline in ice-age megafauna beginning at the time of the impact.

"We speculate that the impact contributed to the extinction, but it wasn't the only cause. Over hunting by humans almost certainly contributed, too, as did climate change," Moore says. "Some of these animals survived after the event, in some cases for centuries. But from the spore data at White Pond and elsewhere, it looks like some of them went extinct at the beginning of the Younger Dryas, probably as a result of the environmental disruption caused by impact-related wildfires and climate change."

Additional evidence found at other sites in support of an extraterrestrial impact includes the discovery of meltglass, microscopic spherical particles and nanodiamonds, indicating enough heat and pressure was present to fuse materials on the Earth's surface. Another indicator is the presence of iridium, an element associated with cosmic objects, that scientists also found in the rock layers dated 65 million years ago from an impact that caused dinosaur extinction.

While no one knows for certain why the Clovis people and iconic ice-age beasts disappeared, research by Moore and others is providing important clues as evidence builds in support of the Younger Dryas Impact Hypothesis.

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New data on the evolution of plants and origin of species

The history and evolution of plants can be traced back by about one billion years.

There are over 500,000 plant species in the world today. They all evolved from a common ancestor. How this leap in biodiversity happened is still unclear. In the upcoming issue of Nature, an international team of researchers, including scientists from Martin Luther University Halle-Wittenberg, presents the results of a unique project on the evolution of plants. Using genetic data from 1,147 species the team created the most comprehensive evolutionary tree for green plants to date.

The history and evolution of plants can be traced back by about one billion years. Algae were the first organisms to harness solar energy with the help of chloroplasts. In other words, they were the first plant organisms to perform photosynthesis. Today, there are over 500,000 plant species, including both aquatic and terrestrial plants. The aim of the new study in Nature was to unravel the genetic foundations for this development. "Some species began to emerge and evolve several hundreds of millions of years ago. However, today we have the tools to look back and see what happened at that time," explains plant physiologist Professor Marcel Quint from the Institute of Agricultural and Nutritional Sciences at MLU.

Quint is leading a sub-project with bioinformatician Professor Ivo Grosse, also from MLU, as part of the "One Thousand Plant Transcriptomes Initiative," a global network of about 200 researchers. The team collected samples of 1,147 land plant and algae species to analyse each organism's genome-wide gene expression patterns (transcriptome). Using these data, the researchers reconstructed the evolutionary development of plants and the emergence of individual species. Their focus was on plant species that, as of yet, have not been studied on this level, including numerous algae, moss and also flowering plants.

"This was a very special project because we did not just analyse individual components, but complete transcriptomes, of over one thousand plants, providing a much broader foundation for our findings," explains Ivo Grosse. The sub-project led by MLU scientists looked at the development and expansion of large gene families in plants. "Some of these gene families have duplicated over the course of millions of years. This process might have been a catalyst for the evolution of plants: Having significantly more genetic material might unleash new capacities and completely new characteristics," says Marcel Quint. One of the main objectives of the project was to identify a potential connection between genetic duplications and key innovations in the plant kingdom, such as the development of flowers and seeds. Quint and Grosse carried out their research in collaboration with scientists from the universities in Marburg, Jena, and Cologne, and the Max Planck Institute for Evolutionary Biology in Plön. The majority of the analyses was conducted by Martin Porsch, a PhD student in the lab of Ivo Grosse.

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How to spot a wormhole (if they exist)

A new study outlines a method for detecting a speculative phenomenon that has long captured the imagination of sci-fi fans: wormholes, which form a passage between two separate regions of spacetime.

Such pathways could connect one area of our universe to a different time and/or place within our universe, or to a different universe altogether.

Whether wormholes exist is up for debate. But in a paper published on Oct. 10 in Physical Review D, physicists describe a technique for detecting these bridges.

The method focuses on spotting a wormhole around Sagittarius A*, an object that's thought to be a supermassive black hole at the heart of the Milky Way galaxy. While there's no evidence of a wormhole there, it's a good place to look for one because wormholes are expected to require extreme gravitational conditions, such as those present at supermassive black holes.

In the new paper, scientists write that if a wormhole does exist at Sagittarius A*, nearby stars would be influenced by the gravity of stars at the other end of the passage. As a result, it would be possible to detect the presence of a wormhole by searching for small deviations in the expected orbit of stars near Sagittarius A*.

"If you have two stars, one on each side of the wormhole, the star on our side should feel the gravitational influence of the star that's on the other side. The gravitational flux will go through the wormhole," says Dejan Stojkovic, PhD, cosmologist and professor of physics in the University at Buffalo College of Arts and Sciences. "So if you map the expected orbit of a star around Sagittarius A*, you should see deviations from that orbit if there is a wormhole there with a star on the other side."

Stojkovic conducted the study with first author De-Chang Dai, PhD, of Yangzhou University in China and Case Western Reserve University.

A close look at S2, a star orbiting Sagittarius A*

Stojkovic notes that if wormholes are ever discovered, they're not going to be the kind that science fiction often envisions.

"Even if a wormhole is traversable, people and spaceships most likely aren't going to be passing through," he says. "Realistically, you would need a source of negative energy to keep the wormhole open, and we don't know how to do that. To create a huge wormhole that's stable, you need some magic."

Nevertheless, wormholes -- traversable or not -- are an interesting theoretical phenomenon to study. While there is no experimental evidence that these passageways exist, they are possible -- according to theory. As Stojkovic explains, wormholes are "a legitimate solution to Einstein's equations."

The research in Physical Review D focuses on how scientists could hunt for a wormhole by looking for perturbations in the path of S2, a star that astronomers have observed orbiting Sagittarius A*.

While current surveillance techniques are not yet precise enough to reveal the presence of a wormhole, Stojkovic says that collecting data on S2 over a longer period of time or developing techniques to track its movement more precisely would make such a determination possible. These advancements aren't too far off, he says, and could happen within one or two decades.

Stojkovic cautions, however, that while the new method could be used to detect a wormhole if one is there, it will not strictly prove that a wormhole is present.

"When we reach the precision needed in our observations, we may be able to say that a wormhole is the most likely explanation if we detect perturbations in the orbit of S2," he says. "But we cannot say that, 'Yes, this is definitely a wormhole.' There could be some other explanation, something else on our side perturbing the motion of this star."

Though the paper focuses on traversable wormholes, the technique it outlines could indicate the presence of either a traversable or non-traversable wormhole, Stojkovic says. He explains that because gravity is the curvature of spacetime, the effects of gravity are felt on both sides of a wormhole, whether objects can pass through or not.

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New measurement of Hubble constant adds to cosmic mystery

New measurements of the rate of expansion of the universe, led by astronomers at the University of California, Davis, add to a growing mystery: Estimates of a fundamental constant made with different methods keep giving different results.

"There's a lot of excitement, a lot of mystification and from my point of view it's a lot of fun," said Chris Fassnacht, professor of physics at UC Davis and a member of the international SHARP/H0LICOW collaboration, which made the measurement using the W.M. Keck telescopes in Hawaii.

A paper about the work is published by the Monthly Notices of the Royal Astronomical Society.

The Hubble constant describes the expansion of the universe, expressed in kilometers per second per megaparsec. It allows astronomers to figure out the size and age of the universe and the distances between objects.

Graduate student Geoff Chen, Fassnacht and colleagues looked at light from extremely distant galaxies that is distorted and split into multiple images by the lensing effect of galaxies (and their associated dark matter) between the source and Earth. By measuring the time delay for light to make its way by different routes through the foreground lens, the team could estimate the Hubble constant.

Using adaptive optics technology on the W.M. Keck telescopes in Hawaii, they arrived at an estimate of 76.8 kilometers per second per megaparsec. As a parsec is a bit over 30 trillion kilometers and a megaparsec is a million parsecs, that is an excruciatingly precise measurement. In 2017, the H0LICOW team published an estimate of 71.9, using the same method and data from the Hubble Space Telescope.

Hints of new physics

The new SHARP/H0LICOW estimates are comparable to that by a team led by Adam Reiss of Johns Hopkins University, 74.03, using measurements of a set of variable stars called the Cepheids. But it's quite a lot different from estimates of the Hubble constant from an entirely different technique based on the cosmic microwave background. That method, based on the afterglow of the Big Bang, gives a Hubble constant of 67.4, assuming the standard cosmological model of the universe is correct.

An estimate by Wendy Freedman and colleagues at the University of Chicago comes close to bridging the gap, with a Hubble constant of 69.8 based on the luminosity of distant red giant stars and supernovae.

A difference of 5 or 6 kilometers per second over a distance of over 30 million trillion kilometers might not seem like a lot, but it's posing a challenge to astronomers. It might provide a hint to a possible new physics beyond the current understanding of our universe.

On the other hand, the discrepancy could be due to some unknown bias in the methods. Some scientists had expected that the differences would disappear as estimates got better, but the difference between the Hubble constant measured from distant objects and that derived from the cosmic microwave background seems to be getting more and more robust.

Read more at Science Daily