Physician, heal thyself?

Research shows doctors and their families are less likely to follow guidelines about medicine. Why do the medically well-informed comply less often?

Peer-Reviewed Publication

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

Following established guidelines about prescription drugs would seem to be an obvious course of action, especially for the professionals that do the prescribing. Yet doctors and their family members are less likely than other people to comply with those guidelines, according to a large-scale study co-authored by an MIT economist.

Depending on your perspective, that result might seem surprising or it might produce a knowing nod. Either way, the result is contrary to past scholarly hypotheses. Many experts have surmised that knowing more, and having easier communication with medical providers, leads patients to follow instructions more closely.

The new study is based on over a decade of population-wide data from Sweden and includes suggestive evidence about why doctors and their families may ignore medical advice. Overall, the research shows that the rest of the population adheres to general medication guidelines 54.4 percent of the time, while doctors and their families lag 3.8 percentage points behind that.

“There’s a lot of concern that people don’t understand guidelines, that they’re too complex to follow, that people don’t trust their doctors,” says Amy Finkelstein, a professor in MIT’s Department of Economics. “If that’s the case, you should see the most adherence when you look at patients who are physicians or their close relatives. We were struck to find that the opposite holds, that physicians and their close relatives are less likely to adhere to their own medication guidelines.”

The paper, “A Taste of Their Own Medicine: Guideline Adherence and Access to Expertise,” is published this month in the American Economic Review: Insights. The authors are Finkelstein, the John and Jennie S. MacDonald Professor of Economics at MIT; Petra Persson, an assistant professor of economics at Stanford University; Maria Polyakova PhD ’14, an assistant professor of health policy at the Stanford University School of Medicine; and Jesse M. Shapiro, the George Gund Professor of Economics and Business Administration at Harvard University.

Millions of data points

To conduct the study, the scholars examined Swedish administrative data from 2005 through 2016, as applied to 63 prescription drug guidelines. The data enabled the researchers to determine who is a doctor; the study largely defined close relatives as partners, parents, and children. All told, the research involved 5,887,471 people to whom at least one of the medication guidelines applied. Of these people, 149,399 were doctors or their close family members.

Using information on prescription drug purchases, hospital visits, and diagnoses, the researchers could see if people were adhering to medication guidelines by examining whether prescription drug decisions matched these patients’ medical circumstances. In the study, six guidelines pertained to antibiotics; 20 involved medication use by the elderly; 20 focused on medication attached to particular diagnoses; and 17 were about prescription drug use during pregnancy.

Some guidelines recommended use of a particular prescription drug, like a preference of narrow-spectrum antibiotics for an infection; other guidelines were about not taking certain medications, such as the recommendation that pregnant women avoid antidepressants.

Out of the 63 guidelines used in the study, doctors and their families followed the standards less often in 41 cases, with the difference being statistically significant 20 times. Doctors and their families followed the guidelines more often in 22 cases, with the difference being statistically significant only three times.

“What we found, which is quite surprising, is that they [physicians] are on average less adherent to guidelines,” says Polyakova, who received her PhD from MIT’s Department of Economics. “So, in this paper we are also trying to figure out what experts do differently.”

Ruling out other answers

Since doctors and their close relatives adhere to medical guidelines less often than the rest of the population, what exactly explains this phenomenon? While homing in on an answer, the research team examined and rejected several hypotheses.

First, the lower compliance by those with greater access to expertise is unrelated to socioeconomic status. In society overall, there is a link between income and adherence levels, but physicians and their families are an exception to this pattern. As the scholars write in the paper, special “access to doctors is associated with lower adherence despite, rather than because of, the high socioeconomic status” of those families.

Additionally, the researchers did not find any link between existing health status and adherence. They also studied whether a greater comfort with prescription medication — due to being a doctor or related to one — makes people more likely to take prescription drugs than guidelines recommend. This does not appear to be the case. The lower adherence rates for doctors and their relatives were similar in magnitude whether the guidelines pertained to taking medication or, alternately, not taking medication.

“There are a number of first-order alternative explanations that we could rule out,” Polyakova says.

Resolving a medical mystery

Instead, the researchers believe the answer is that doctors possess “superior information about guidelines” for prescription drugs — and then deploy that information for themselves. In the study, the difference in adherence to guidelines between experts and nonexperts is largest in the case of antibiotics: Doctors and their families are 5.2 percentage points less in compliance than everyone else.

Most guidelines in this area recommend starting patients off with “narrow-spectrum” antibiotics, which are more targeted, rather than “broader-spectrum” antibiotics. The latter might be more likely to eradicate an infection, but greater use of them also increases the chances that bacteria will develop resistance to these valuable medications, which can reduce efficacy for other patients. Thus for things like a respiratory tract infection, guidelines call for a more targeted antibiotic first.

The issue, however, is that what is good for the public in the long run — trying more targeted drugs first — may not work well for an individual patient. For this reason, doctors could be more likely to prescribe broader-spectrum antibiotics for themselves and their families.

“From a public-health perspective, what you want to do is kill it [the infection] off with the narrow-spectrum antibiotic,” Finkelstein observes. “But obviously any given patient would want to knock that infection out as quickly as possible.” Therefore, she adds, “You can imagine the reason doctors are less likely to follow the guidelines than other patients is because they … know there’s this wedge between what’s good for them as a patients and what’s good for society.”

Another suggestive piece of data comes from different types of prescription drugs that are typically avoided during pregnancies. For so-called C-Class drugs, where empirical evidence about the dangers of the drugs is slightly weaker, doctors and their families have an adherence rate 2.3 percentage points below other people (meaning, in this case, that they are more likely to take these medications during pregnancy). For so-called D-Class drugs with slightly stronger evidence of side effects, that dropoff is only 1.2 percentage points. Here too, doctors’ expert knowledge may be influencing their actions.

“The results imply that probably what’s going on is that experts have a more nuanced understanding of what is the right course of action for themselves, and how that might be different than what the guidelines suggest,” Polyakova says.

Still, the findings suggest some unresolved tensions in action. It could be, as Polyakova suggests, that guidelines about antibiotics should be more explicit about the public and private tradeoffs involved, providing more transparency for patients. “Maybe it’s better for the guidelines to be transparent and say they recommend this not because it is [always] the best course of action for you, but because it is the best for society,” she says.

Additional research could also aim to identify areas where lower expert adherence with guidelines may be associated with better health outcomes — to see how often doctors have a point, as it were. Or, as the researchers write in the paper, “An important avenue for further research is to identify whether and when nonadherence is in the patient’s best interest.”

The research was supported, in part, by the Population Studies and Training Center and the Eastman Professorship at Brown University, and the National Institute on Aging.

Written by Peter Dizikes, MIT News Office

Additional background

Paper: “A Taste of Their Own Medicine: Guideline Adherence and Access to Expertise”

https://www.aeaweb.org/articles?id=10.1257/aeri.20210591

 

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JOURNAL

American Economic Review

DOI

10.1257/aeri.20210591 

ARTICLE TITLE

“A Taste of Their Own Medicine: Guideline Adherence and Access to Expertise”

The AVID college prep program leads to lower substance use, better health behaviors among high school students, UCLA-led research suggests

The findings suggest that “academic tracking,” the practice of separating high and low performing students into different classes, reinforces risky social networks and behaviors

Peer-Reviewed Publication

UNIVERSITY OF CALIFORNIA - LOS ANGELES HEALTH SCIENCES

New UCLA-led research finds that a college preparatory program for youth experiencing educational inequities that operates in about 13% of U.S public high schools has a positive effect on students’ social networks, psycho-social outcomes, and health behaviors. 

The findings, published Dec. 16 in the peer-reviewed journal Pediatrics, suggests that the Advancement via Individual Determination (AVID) program, aimed at increasing educational opportunities for under-represented and economically disadvantaged students, also significantly reduces substance use.

“Academic tracking” is a common practice in high schools through which lower-performing students are clustered with others of similar academic achievement. Although intended to tailor academic rigor to students’ level of preparation, the study findings suggest that this practice may be counterproductive by reinforcing risky behaviors that students pick up from their peers.

“Untracking” these students by mixing them in with higher-performing peers may lead to better physical and psychological health, said lead author Dr. Rebecca Dudovitz, associate professor of pediatrics and director of pediatric health services research at the David Geffen School of Medicine at UCLA.

“This is the first randomized controlled trial of AVID in the United States, so it’s really exciting to see that this program that was designed to help open up educational opportunities for kids, also improved their health,” Dudovitz said.

AVID works with high school students earning B or C grade averages who might not otherwise be placed in more rigorous college preparatory tracks. It operates in 5,400 secondary schools, including both middle and high school, in 46 states and exposes academically middling students to tougher courses than they would have been assigned to under normal circumstances. AVID helps students develop agency, relational capacity, and opportunity knowledge.

“We believe that surrounding students with a supportive community and providing them with the skills and resources they need to reach their goals within existing educational structures is how we make college and career readiness possible for every student,” said Thuan Nguyen, AVID’s CEO. “The findings of the UCLA study are not surprising because AVID educators invest so much in their students’ lives.”

The researchers randomized 270 students in five large public schools who were placed in either an AVID group or in usual school programs. Students completed surveys at the end of 8th grade or beginning of 9th grade, and again at the end of 9th grade.

They found that students in the AVID group had lower odds of using substances--a 33% reduced risk compared to the control group--in addition to a 26% lower risk of associating with substance-using peers and about 1.7 times the odds of socializing with peers who were more involved with academics.

In addition, AVID males experienced lower stress and higher self-efficacy, determination and engagement with school than their peers who were assigned to the usual tracked academic program. These effects, however, were not seen among females, possibly because supportive academic environment have a greater effect on boys of color, the researchers write.

“AVID positively impacts social networks, health behaviors, and psycho-social outcomes suggesting academic untracking may have substantial beneficial spillover effects on adolescent health,” the researchers write.

The study has some limitations. The schools were all from a single school district and primarily serve low-income Latino students, and the findings were all from one school year, the researchers note. They did not directly observe how AVID was implemented or examine if the program actually increased college enrollment. In addition, it was not possible to blind the participants, meaning that students knew who was assigned to each group, which could have led them to respond to survey questions in ways that they thought the researchers would view favorably.

While more research is needed, the findings still provide important evidence that “ensuring schools have the resources and structures necessary to expand access to educational opportunities and facilitate healthy social connections, particularly in marginalized communities, may be key to achieving education and health equity more broadly,” the researchers write.

The Robert Wood Johnson Foundation Evidence for Action Program (Grant 74086) and National Institutes of Health (1K23DA040733-01A1) funded this research.

Study co-authors are Dr. Paul Chung, Kulwant Dosanjh, Meredith Phillips, Christopher Biely, Chi-Hong Tseng, and Dr. Mitchell Wong of UCLA; Joan Tucker of RAND Corporation; Mary Ann Pentz of USC; and Arzie Galvez and Guadalupe Arellano of Los Angeles Unified School District. Chung is also affiliated with Kaiser Permanente.

 

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JOURNAL

PEDIATRICS

DOI

10.1542/peds.2022-057183) 

METHOD OF RESEARCH

Randomized controlled/clinical trial

SUBJECT OF RESEARCH

People

ARTICLE TITLE

Outcome of the AVID College Preparatory Program on Adolescent Health: A Randomized Trial

ARTICLE PUBLICATION DATE

16-Dec-2022

FOR PROFIT HEALTHCARE U$A

Cost concerns keep older adults from seeking emergency care

People in their pre-Medicare years, especially those who are uninsured or have low incomes, are most likely to skip a trip to the ER because of what they might have to pay

Peer-Reviewed Publication

MICHIGAN MEDICINE - UNIVERSITY OF MICHIGAN

Worries about what emergency care might cost them have kept some older adults from seeking medical attention even when they felt they might need it, a new study shows.

In all, 22% of older adults who may have needed care from the emergency department didn’t go because of concerns about what they might have to pay, according to the new findings published in the American Journal of Managed Care.

People in their 50s and early 60s, women, those who lack health insurance, people with household incomes under $30,000, and those who say their mental health is fair or poor were most likely to say they’d avoided getting emergency care because of cost concerns.

The study, based on a survey conducted in June 2020, asked older adults to think back on the previous two years, including the first months of the COVID-19 pandemic.

Even among those who hadn’t had a medical emergency in this time, worries about what an emergency visit might cost them were high. Four out of five older adults said they were concerned about the cost of emergency care (35% somewhat concerned and 45% very concerned, and 18% were not confident they could afford a visit.

The data from the study come from the National Poll on Healthy Aging, based at the University of Michigan Institute for Healthcare Policy and Innovation and supported by AARP and Michigan Medicine, U-M’s academic medical center. The findings build on the poll report published earlier and are based on responses from a nationally representative sample of 2,074 people age 50 to 80.

The findings confirm the experience of lead author Rachel Solnick, M.D., M.Sc., who trained in IHPI’s National Clinician Scholars Program before joining the faculty at the Icahn School of Medicine at Mount Sinai Health System in New York.

“As an emergency physician, I have seen patients come to the emergency room having postponed their care. They often come in sicker than they would have been had they received care sooner,” she said. “That scenario is what I find most alarming in this survey’s findings. Some groups that are medically vulnerable or have suffered worse outcomes from COVID-19 were more likely to report cost-related avoidance of the ER than their counterparts. These findings highlight the importance of reducing the number of uninsured individuals and the need for insurers to clearly communicate coverage for emergency services.”

Keith Kocher, M.D., the study’s senior author and an associate professor of emergency medicine at U-M, notes that the federal No Surprises Act was enacted after the study was done. That act seeks to reduce “surprise billing” for emergency care when a privately insured person receives it from hospitals or providers outside their health insurance plan’s network. At the time of the study, Medicare and Medicaid already prohibited emergency care providers from doing this kind of “balance billing.”

Even so, a person with private insurance might owe hundreds of dollars in co-pays or deductibles for an emergency visit, the authors note. That’s especially true for people with high-deductible health plans, which are growing in enrollment.

Even though the percentage of older adults who lack any health insurance is small (4% of the study sample), they were 35% more likely to say they were not confident they could afford emergency care. Solnick notes that both the pandemic’s economic impacts, and the decision by more than a dozen states including Texas and Florida to not expand Medicaid to all low-income adults, mean that millions of people may face paying out of pocket for emergency visits.

American Journal of Managed Care, 2023;29(4): In Press, https://www.ajmc.com/view/older-adults-perspectives-on-emergency-department-costs-during-covid-19

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JOURNAL

The American Journal of Managed Care

METHOD OF RESEARCH

Survey

SUBJECT OF RESEARCH

People

ARTICLE TITLE

Older Adults’ Perspectives on Emergency Department Costs During COVID-19

ARTICLE PUBLICATION DATE

16-Dec-2022

Scientists discover what was on the menu of the first dinosaurs

Peer-Reviewed Publication

UNIVERSITY OF BRISTOL

 

IMAGE: THE THREE MAIN DINOSAUR LINEAGES AND THEIR TYPICAL TOOTH SHAPES view more 

CREDIT: ANTONIO BALLELL

The earliest dinosaurs included carnivorous, omnivorous and herbivorous species, according to a team of University of Bristol palaeobiologists.

By looking at the tooth shapes of the earliest dinosaurs and simulating their tooth function with computational modelling, experts were able to compare them to living reptiles and their diets. Their findings, published today in Science Advances, show that many groups of plant-eating dinosaurs were ancestrally omnivorous and that the ancestors of our famous long-necked herbivores, such as Diplodocus, ate meat. This ability to diversify their diets early in their evolution likely explains their evolutionary and ecological success.

The earliest dinosaurs are enigmatic: they were much smaller than their later relatives and for most of the Triassic they were in the shadow of the crocodile-like reptiles. It is unknown how diverse they were in terms of diets and ecology, but scientists know something must have happened in the Triassic that allowed dinosaurs to endure the Triassic–Jurassic mass extinction and adapt in its aftermath, becoming the dominant group for the rest of the Mesozoic.

Lead author Dr. Antonio Ballell from the University of Bristol said “Soon after their origin, dinosaurs start to show an interesting diversity of skull and tooth shapes. For decades, this has made palaeontologists suspect that different species were already experimenting with different kinds of diets. They have compared them to modern lizard species and tried to infer what they ate based on the similarities in their teeth.

“We investigated this by applying a set of computational methods to quantify the shape and function of the teeth of early dinosaurs and compare them to living reptiles that have different diets. This included mathematically modelling their tooth shapes and simulating their mechanical responses to biting forces with engineering software.”

Professor Mike Benton, co-author of the study, said: “With this battery of methods, we were able to numerically quantify how similar early dinosaurs were to modern animals, providing solid evidence for our inferences of diets. Theropod dinosaurs have pointy, curved and blade-like teeth with tiny serrations, which behaved like those of modern monitor lizards. In contrast, the denticulated teeth of ornithischians and sauropodomorphs are more similar to modern omnivores and herbivores, like iguanas.”

The study is also innovative in using machine learning models to classify the earliest dinosaurs in different diet categories based on their tooth shape and mechanics. For instance, Thecodontosaurus, the Bristol dinosaur, had teeth well adapted for a diet of plants.

Professor Emily Rayfield, senior co-author, said: “Our analyses reveal that ornithischians – the group that includes many plant-eating species like the horned dinosaurs, the armoured ankylosaurs and the duck-billed dinosaurs – started off as omnivores. And another interesting finding is that the earliest sauropodomorphs, ancestors of the veggie long-necked sauropods like Diplodocus, were carnivores. This shows that herbivory was not ancestral for any of these two lineages, countering traditional hypotheses, and that the diets of early dinosaurs were quite diverse.”

Dr. Ballell concluded: “It seems that one of the things that made the first dinosaurs special is that they evolved different diets throughout the Triassic, and we think this might have been key for their evolutionary and ecological success.”

Dinosaurs dominated the land during the Mesozoic era until their extinction 66 million years ago. They included giant veggie groups like the long-necked sauropods and meat-eating species like Tyrannosaurus rex and its relatives. However, their origins were much humbler and date back to the Triassic period, with the first definitive dinosaurs appearing approximately 235 million years ago.

Paper:

‘Dental form and function in the early feeding diversification of dinosaurs’ by Antonio Ballell, Michael J. Benton and Emily J. Rayfield in Science Advances.

DOI: 10.1126/sciadv.abq5201

Early dinosaurs and their diets. Lesothosaurus is an omnivore, Buriolestes is a carnivore and Thecodontosaurus is an herbivore.

CREDIT

Gabriel Ugueto

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JOURNAL

Science Advances

METHOD OF RESEARCH

Computational simulation/modeling

SUBJECT OF RESEARCH

Animals

ARTICLE TITLE

Dental form and function in the early feeding diversification of dinosaurs’

ARTICLE PUBLICATION DATE

16-Dec-2022

Linking fossil climate proxies to living bacteria helps climate predictions

Missing link in climate reconstuctions, also helps understand early evolution of life

Peer-Reviewed Publication

ROYAL NETHERLANDS INSTITUTE FOR SEA RESEARCH

 

IMAGE: FLUORESCENT MICROSCOPY IMAGE OF A BACTERIUM FORMING MEMBRANE-SPANNING LIPIDS UTILIZED AS A MODEL ORGANISM IN THIS STUDY. THERMOTOGA MARITIMA CELLS STAINED WITH A DNA DYE (DAPI) (LEFT PANEL) AND WITH A MEMBRANE DYE (FM4-64) (RIGHT PANEL) SIMULTANEOUSLY. IMAGE: DIANA SAHONERO, NIOZ view more 

CREDIT: DIANA SAHONERO, NIOZ

Microbial skins are made out of lipids – fatty molecules – which can be preserved as fossils telling us stories about how these microbes lived in the past. “Some microbial lipids are widely used to reconstruct past climates. They have always been surrounded by mystery, as we did not know which microbes were making them and under which conditions. This lack of information limits the predictive power of these molecules to reconstruct past environmental conditions,” says Sahonero, Now, her study shows which bacteria make these lipids and also how they have evolved their lipid skin to adapt to environmental changes – another step towards reconstructing and predicting climate change in more detail.

Climate reconstructions

Lipids, the molecular building blocks of the cell membrane, are unique for each microbial species. “It works just like fingerprints, they can be used to identify microbial remains,” says Laura Villanueva, associate professor in the Faculty of Geosciences in Utrecht University and senior scientist at NIOZ. The lipids of ancient microbes can be found in old sediments. Once these molecules from the past are separated, identified and related to currently living groups of bacteria, the lipids can work like ‘biomarkers’. These markers can tell us about the atmospheric and oceanic conditions of the ancient earth, because we know from the living relatives of the microbes how they interact with their environment.

Who made these molecules and how?

For long, it was unclear precisely which bacteria were making these specific lipids, called branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs). This type of lipids are often used in climate reconstructions. Diana and her colleagues have finally discovered the bacteria forming these lipids. And also how these bacteria actually make the lipids. “It was like looking for a needle in a haystack”, says Sahoreno. “From the start, we knew we had to answer this question with a massive approach. We needed to investigate more than 1850 proteins to identify microbes making these lipid molecules.”

Once researchers know which currently living bacteria make these lipid molecules, they can be used to make more accurate climate reconstructions. Researchers can measure the interactions of these living bacteria with their surrounding seawater or atmosphere. This information leads to ‘proxies’ – keys to correlate details of the lipid molecules (abundance for instance) to values of the environment. This is an important step in reconstructing past environmental and climate conditions, based on old sediment samples.

Early evolution of life

“Our study indicates that there are many species of currently living bacteria that can make these type of membrane lipids. Also, we found that those bacteria are all limited to environments where oxygen is absent,” says Sahonero. “This study into archaeal-like lipids of bacteria shows how this group of microbes that produces them evolved their lipid membrane billions of years ago. It is fantastic to get a glimpse of this part of life’s history. It was mostly a mystery until now.”

What next?

The work of Sahonero and her colleagues is still ongoing. “Now we know which bacteria form these molecular building blocks and we understand how they do that. Next, we need to find out how the production of these molecules depends on environmental factors like water temperature or pH,” says Villanueva. “Then, the proxy based on these bacterial lipids can be used more confidently by (paleo)climatologists. This gives them new possibilities to reconstruct and predict climate change in more detail.”

Publication in Science Advances

Disentangling the lipid divide: Identification of key enzymes for the biosynthesis of membrane-spanning and ether lipids in Bacteria
Diana X. Sahonero-Canavesi, Melvin F. Siliakus, Alejandro Abdala Asbun, Michel Koenen, F. A. Bastiaan von Meijenfeldt, Sjef Boeren, Nicole J. Bale, Julia C. Engelman, Kerstin Fiege, Lora Strack van Schijndel, Jaap S. Sinninghe Damsté and Laura Villanueva.
16 December 2022, 2pm EST

Lipids form the membrane of a microbe. 

Set-up of the growth experiments in serum bottles without oxygen for obtaining samples for omics analysis (lipidomic, transcriptomic and proteomics). Photo: Diana Sahonero, NIOZ

CREDIT

Photo: Diana Sahonero, NIOZ

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JOURNAL

Science Advances

DOI

10.1101/2022.04.21.487849v1 

SUBJECT OF RESEARCH

Cells

ARTICLE TITLE

Disentangling the lipid divide: Identification of key enzymes for the biosynthesis of membrane-spanning and ether lipids in Bacteria

ARTICLE PUBLICATION DATE

16-Dec-2022

Underground Italian lab searches for signals of quantum gravity

FQXi-funded project in the Gran Sasso mountains hunts for evidence of violations of the ‘Pauli Exclusion Principle’

Peer-Reviewed Publication

FOUNDATIONAL QUESTIONS INSTITUTE, FQXI

 

IMAGE: CATALINA OANA CURCEANU IS SEARCHING FOR SIGNS OF RADIATION EMANATING FROM A LEAD TARGET. view more 

CREDIT: CATALINA CURCEANU

For decades physicists have been hunting for a quantum-gravity model that would unify quantum physics, the laws that govern the very small, and gravity. One major obstacle has been the difficulty in testing the predictions of candidate models experimentally. But some of the models predict an effect that can be probed in the lab: a very small violation of a fundamental quantum tenet called the Pauli exclusion principle, which determines, for instance, how electrons are arranged in atoms. An FQXi-funded project carried out at the INFN underground laboratories under the Gran Sasso mountains in Italy, has been searching for signs of radiation produced by such a violation, in the form of atomic transitions forbidden by the Pauli exclusion principle. In two papers appearing  in the journals Physical Review Letters (published on 19th September 2022) and Physical Review D (accepted for publication on 7th December 2022) the team reports that no evidence of violation has been found, thus far, ruling out some quantum-gravity models.

"You, me, we are Pauli-exclusion-principle-based. The fact we cannot cross walls is another consequence," says Curceanu.

“The Pauli exclusion principle is the main pillar of our comprehension of the structure of matter and of its stability,” says Catalina Curceanu, a member of the physics think-tank, the Foundational Questions Institute, FQXi, and the lead physicist on the experiments at INFN, Italy. In school chemistry lessons we are taught that electrons can only arrange themselves in certain specific ways in atoms, which turns out to be due to the Pauli exclusion principle. At the center of the atom there is the atomic nucleus, surrounded by orbitals, with electrons. The first orbital, for instance, can only house two electrons. The Pauli exclusion principle, formulated by Austrian physicist Wolfang Pauli in 1925, says that no two electrons can have the same quantum state; so, in the first orbital of an atom the two electrons have oppositely pointing 'spins' (a quantum internal property usually depicted as an axis of rotation, pointing up or down, although no literal axis exists in the electron). The happy result of this for humans is that it means matter cannot pass through other matter. “It is ubiquitous—you, me, we are Pauli-exclusion-principle-based,” says Curceanu. “The fact we cannot cross walls is another practical consequence.”

The principle extends to all elementary particles belonging to the same family as electrons, called fermions, and has been derived mathematically from a fundamental theorem known as the spin-statistics theorem. It has also been confirmed experimentally–thus far–appearing to hold for all fermions in tests. The Pauli exclusion principle forms one of the core tenets of the Standard Model of Particle Physics.

Violating the principle

But some speculative models of physics, beyond the Standard Model, suggest that the principle may be violated. For decades now, physicists have been searching for a fundamental theory of reality. The Standard Model is terrific at explaining the behavior of particles, interactions and quantum processes on the microscale. However, it does not encompass gravity. So, physicists have been trying to develop a unifying theory of quantum gravity, some versions of which predict that various properties that underpin the Standard Model, such as the Pauli exclusion principle, may be violated in extreme circumstances. “Many of these violations are naturally occurring in so-called 'noncommutative' quantum-gravity theories and models, such as the ones we explored in our papers,” says Curceanu. One of the most popular candidate quantum-gravity frameworks is string theory, which describes fundamental particles as tiny vibrating threads of energy in multidimensional spaces. Some string theory models also predict such a violation.

"The analysis we reported disfavors some concrete realizations of quantum gravity," says Curceanu.

It is traditionally thought to be hard to test such predictions because quantum gravity will usually only become relevant in arenas where there is a huge amount of gravity concentrated into a tiny space—think of the center of a black hole or the beginning of the universe. However, Curceanu and her colleagues realized that there may be a subtle effect—a signature that the exclusion principle and the spin-statistics theorem have been violated—that could be picked up in lab experiments on Earth.

Deep under the Gran Sasso mountains, near the town of L’Aquila, in Italy, Curceanu’s team is working on the VIP-2 (Violation of the Pauli Principle) lead experiment. At the heart of the apparatus is a thick block made of Roman lead, with a nearby germanium detector that can pick up small signs of radiation emanating from the lead. The idea is that if the Pauli exclusion principle is violated, a forbidden atomic transition will occur within the Roman lead, generating an X-ray with a distinct energy signal. This X-ray can be picked up by the germanium detector.

Cosmic silence

The lab must be housed underground because the radiation signature from such a process will be so faint, it would otherwise be drowned out by the general background radiation on Earth from cosmic rays. “Our laboratory ensures what is called ‘cosmic silence,’ in the sense that the Gran Sasso mountain reduces the flux of cosmic rays by a million times,” says Curceanu. That alone is not enough, however. “Our signal has a possible rate of just one or two events per day, or less,” says Curceanu. That means that materials used in the experiment must themselves be “radio-pure”—that is, they must not emit any radiation themselves—and the apparatus must be shielded from radiation from the mountain rocks and radiation coming from underground.

“What is extremely exciting is that we can probe some quantum-gravity models with such a high precision, which is impossible to do at present-day accelerators,” says Curceanu.

In their recent Physical Review Letters paper, published in September, and in a follow up paper in Physical Review D (accepted in December), the team reports having found no evidence for violation of the Pauli principle. “FQXi-funding was fundamental for developing the data analysis techniques,” says Curceanu. This allowed the team to set limits on the size of any possible violation and helped them constrain some proposed quantum-gravity models. In particular, the team analyzed the predictions of the so-called “theta-Poincaré” model and were able to rule out some versions of the model to the Planck scale (the scale at which the known classical laws of gravity break down). In addition, “the analysis we reported disfavors some concrete realizations of quantum gravity,” says Curceanu.

The team now plans to extend its research to other quantum-gravity models, with their theoretician colleagues Antonino Marcianò from Fudan University and Andrea Addazi from Sichuan University, both in China. “On the experimental side, we will use new target materials and new analysis methods, to search for faint signals to unveil the fabric of spacetime,” says Curceanu.

“What is extremely exciting is that we can probe some quantum-gravity models with such a high precision, which is impossible to do at present-day accelerators,” Curceanu adds. “This is a big leap, both from theoretical and experimental points of view.”

This work was partially supported through FQXi's Consciousness in the Physical World program. You can read more about the team’s grant in the FQXi article: “Can We Feel What It's Like to Be Quantum?” by Brendan Foster.

Journal reference, PRL: Strongest Atomic Physics Bounds on Noncommutative Quantum Gravity Models

Journal reference, PRD: Experimental test of noncommutative quantum gravity by VIP-2 Lead; preprint available.

The Gran Sasso low radioactivity underground lab.

CREDIT

Massimiliano De Deo, LNGS-INFN

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The Foundational Questions Institute, FQXi, catalyzes, supports, and disseminates research on questions at the foundations of science, particularly new frontiers in physics and innovative ideas integral to a deep understanding of reality but unlikely to be supported by conventional funding sources. Visit fqxi.org for more information.

Dr. Curceanu acknowledges the Gran Sasso underground laboratory of INFN, INFN-LNGS, and its Director, Ezio Previtali, the LNGS staff, and the Low Radioactivity laboratory for the experimental activities dedicated to the search for PEP violating signals.

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JOURNAL

Physical Review Letters

DOI

10.1103/PhysRevLett.129.131301 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Strongest Atomic Physics Bounds on Noncommutative Quantum Gravity Models