The idea was simple. Recruit hundreds of people in their 80s and 90s, equip them with fitness trackers, and monitor their physical activity. Then, when the participants died, collect their brains and examine the tissue. Is there evidence, lurking in the tissue, that exercise benefits the brain?
The results, from a 2022 collaboration between the University of California in San Francisco and the University of British Columbia, were striking. Physical exercise, late in life, seemed to protect the ageing connections between brain cells – the synapses where memories are made. The work, if backed up by further studies, could see exercise, and potentially drugs that mimic biochemical aspects of activity – prescribed to help slow the onset of dementia.
We know there is a 30%-80% reduced risk of dementia in people who exercise
“We know there is a 30%-80% reduced risk of dementia in people who exercise,” says Kaitlin Casaletto, the lead author on the study and an assistant professor in neurology at UCSF. “My question was, wouldn’t it be cool if we could figure out exactly how this is happening? If we could identify some of the mechanisms of exercise for brain health? These are potential therapeutic targets we can bottle.”
A small mountain of work has linked physical exercise to better brain health and lower risk of dementia in older age. One recent study of nearly 80,000 people in the UK found that the risk of dementia was halved in people who reached the goal of 10,000 steps a day. But much is still unclear. Part of the observed benefit could be down to people with healthier brains simply exercising more.
While there are definite benefits to be had from exercise – greater blood flow to the brain, better cardiovascular health, lower blood pressure, less obesity and diabetes – there is still plenty to nail down.
Dementia is the number one killer in the UK, with the disorder affecting about 900,000 people. Most cases, about two-thirds, are driven by Alzheimer’s disease, but it is far from the only cause. Other forms, namely vascular dementia, dementia with Lewy bodies, and frontotemporal dementia, arise from other processes.
Whatever the cause, the steady destruction of brain cells erodes memory, thinking, movement and personality. In old age, dementia can be several of these conditions at once.
Some of the highest rates of dementia are found in developed countries with older populations. In Germany, Italy and Japan, more than 20 in every 1,000 people have dementia compared with fewer than nine per 1,000 in proportionally younger countries including Mexico, Turkey and South Africa.
The UK sits in the middle. Indigenous groups in the Amazon have some of the lowest rates. In one recent study, researchers confirmed only six cases among 604 Bolivian Tsimane and Moseten people aged 60 and over, suggesting that lifelong physical activity and healthier preindustrial diets substantially reduce the risk.
Over the next three decades, global dementia is due to rise substantially, particularly in north Africa, the Middle East and eastern sub-Saharan Africa, where population growth and ageing will be among the driving forces.
But dementia is not inevitable, nor is it the reward for dodging other fatal conditions. Take all of the risk factors that we as individuals, or nations through their policies, might improve, and potentially 40% of cases could be prevented or delayed. We would not eradicate dementia, and many people who did everything to keep their brains healthy would still succumb to the disease…
Loneliness doesn’t just make people feel isolated. It alters their brain in ways that can hinder their ability to trust and connect to others. In The Neumayer III polar station sits near the edge of Antarctica’s unforgiving Ekström Ice Shelf during the winter, when temperatures can plunge below minus 50 degrees Celsius and the winds can climb to more than 100 kilometers per hour, no one can come or go from the station.
Its isolation is essential to the meteorological, atmospheric and geophysical science experiments conducted there by the mere handful of scientists who staff the station during the winter months and endure its frigid loneliness.
But a few years ago, the station also became the site for a study of loneliness itself. A team of scientists in Germany wanted to see whether the social isolation and environmental monotony marked the brains of people making long Antarctic stays.
Eight expeditioners working at the Neumayer III station for 14 months agreed to have their brains scanned before and after their mission and to have their brain chemistry and cognitive performance monitored during their stay. (A ninth crew member also participated but could not have their brain scanned for medical reasons.)
As the researchers described in 2019, in comparison to a control group, the socially isolated team lost volume in their prefrontal cortex — the region at the front of the brain, just behind the forehead, that is chiefly responsible for decision-making and problem-solving.
They also had lower levels of brain-derived neurotrophic factor, a protein that nurtures the development and survival of nerve cells in the brain. The reduction persisted for at least a month and a half after the team’s return from Antarctica.
It’s uncertain how much of this was due purely to the social isolation of the experience. But the results are consistent with evidence from more recent studies that chronic loneliness significantly alters the brain in ways that only worsen the problem.
Neuroscience suggests that loneliness doesn’t necessarily result from a lack of opportunity to meet others or a fear of social interactions. Instead, circuits in our brain and changes in our behavior can trap us in a catch-22 situation: While we desire connection with others, we view them as unreliable, judgmental and unfriendly.
Consequently, we keep our distance, consciously or unconsciously spurning potential opportunities for connections. Loneliness can be difficult to study empirically because it is entirely subjective. Social isolation, a related condition, is different — it’s an objective measure of how few relationships a person has.
The experience of loneliness has to be self-reported, although researchers have developed tools such as the UCLA Loneliness Scale to help with assessing the depths of an individual’s feelings. From such work, it’s clear that the physical and psychological toll of loneliness across the globe is profound.
In one survey, 22% of Americans and 23% of British people said they felt lonely always or often. And that was before the pandemic. As of October 2020, 36% of Americans reported “serious loneliness.”
Organizations and governments often attempt to help with loneliness by encouraging people to go out more and by setting up hobby clubs, community gardens and craft groups. Yet as the neuroscience shows, getting rid of loneliness isn’t always that simple.
A Bias Toward Rejection
When neuroscientists from Germany and Israel set out to investigate loneliness a few years ago, they expected to find that its neural underpinnings were like those of social anxiety and involved the amygdala. Often called the fear center of the brain, the amygdala tends to activate when we face things we dread, from snakes to other humans.
“We thought, ‘Social anxiety is associated with increased amygdala activity, so this should also be the case for lonely individuals,’” said Jana Lieberz, a doctoral student at the University of Bonn in Germany who was part of the research team.
I wanted to report this story last month, but I was too sick with COVID. My kid gave it to me. My colleagues on the health reporting team would have tackled the story, but they’ve been sick, too, thanks to their children. (Just last week, one colleague dropped off her daughter for her first day back at preschool after recovering from a bug, only to pick her up that same afternoon, sniffling from a new illness. Yikes.)
And we’re far from alone in our woes. “Like so many parents out there, you know, my husband and I have been sick all winter. We’ve been sneezing, coughing, had fevers. It’s gross,” says Dr. Rachel Pearson, a pediatrician at The University of Texas Health Science Center at San Antonio and University Hospital. She’s also the mother of 2-year-old Sam.
“I feel like half the time he has a virus, has a runny nose, is coughing – to the point where my dad was like, ‘Is there something wrong with Sam?’ ” she says. With flu, RSV, colds and COVID all coming at once, it can feel like things may be worse than ever for parents of little kids. But as Pearson tells her dad – and the parents of her own young patients – this seemingly never-ending cycle of sniffles is normal, if miserable.
“When I counsel parents, I say you can have a viral infection every month. Some kids are going to cough for four weeks to six weeks after a virus. And so they’re going to catch their next virus before they even stop coughing from the last one.” In fact, if you’ve ever described your child as an adorable little germ vector, you’re not wrong, says Dr. Carrie Byington, a pediatric infectious disease specialist and executive vice president for the University of California Health System. And she’s got hard data to back that up.
“We all think it, but it was really incredible to have the definitive proof of it,” says Byington. The “proof” she’s referring to comes from a study she and her colleagues began back in 2009, when she was at the University of Utah. They wanted to understand the role kids play in the transmission of respiratory viruses in their homes. So they recruited 26 households to take nasal samples of everyone living in the home, every week, for an entire year. What they found was eye-opening.
“We saw as soon as a child entered the house, the proportion of weeks that an adult had an infection increased significantly,” Byington says. And more kids meant more infections. For families with two, three or four kids, someone at home had an infection a little more than half the year. Families with six kids had a viral detection a whopping 87% of the year. Childless households, on the other hand, only had a viral detection 7% of the year.
The findings also suggest that the youngest kids are the ones bringing germs home most often: Children under age 5 were infected with some kind of respiratory virus a full 50% of the year – twice as often as older kids and adults. And while a viral detection didn’t always translate into illness, when they were infected, the littlest kids were 1.5 times more likely to have symptoms, like fever or wheezing.
And that’s just respiratory viruses. As Byington notes, the study wasn’t even looking at other kinds of infections, such as strep throat, which is caused by bacteria. “So obviously, there could be other things that happened throughout the year to even make it seem worse,” she says.
Byington says all of this means that, in the grand scheme of things, it’s normal for kids to be getting all these viruses. But it’s all more intense right now because of the disruptions of the pandemic. Children were kept at home instead of going to daycare or school, where they would typically be exposed to viruses and bacteria one after another, she says.
As children returned to regular routines, “there were lots of kids ages 1, 2 and 3 who had never really seen a lot of viruses or bacteria,” Byinton says. “And so what might have been spread out in the past over 12 months, a year, they were now seeing it all at once in this very concentrated time.”
Byington says the pandemic also disrupted the seasonality of viruses. Flu season hit earlier than usual this year, as RSV and COVID were also circulating. Young children without prior exposure to these viruses were hit especially hard.
Pearson notes that’s because kids are likely to have a more severe course of illness the first time they encounter a virus like RSV, before they have some level of immunity. She says there’s a larger cohort of kids this year that didn’t have that prior exposure.
And there is evidence that younger kids who get multiple infections – say, COVID and RSV– at the same time can end up with more severe illness than if they’d gotten just one virus at a time. The end result is that many pediatric hospitals and care units have seen a surge in sick kids over the fall and winter. That includes University Hospital in San Antonio, where Pearson sees hospitalized kids in the acute care unit.
Nationwide, “pediatric care right now is at this point of strain,” Pearson says, not just because of the current surge but because of an underinvestment that predates the pandemic. And “the kids who get admitted to the hospital are the tip of the iceberg,” Pearson says. For every kid sick enough to be hospitalized, there are likely many more with the same virus recuperating at home, she says.
The good news is that the viral stew seems to be easing up. Recent data from the CDC show the number of emergency department visits for flu, COVID and RSV dropped to the lowest they’ve been since September for all age groups. But of course, the respiratory virus season isn’t over yet.
As for families who are currently living in what one headline memorably dubbed “virus hell,” Byington hopes the findings of the BIG-LoVE study should offer some comfort that eventually this, too, shall pass. “It’s nice to have done the study and to offer some real-world data to families that what they’re living through is normal and will pass and their children will be well,” she says.
By: Maria Godoy
Maria Godoy is a senior science and health editor and correspondent with NPR News. Her reporting can be heard across NPR’s news shows and podcasts. She is also one of the hosts of NPR’s Life Kit.
But is time travel in fact possible? Given the popularity of the concept, this is a legitimate question. As a theoretical physicist, I find that there are several possible answers to this question, not all of which are contradictory.
The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity. There are also technical challenges: it might be possible but would involve vast amounts of energy.
There is also the matter of time-travel paradoxes; we can — hypothetically — resolve these if free will is an illusion, if many worlds exist or if the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must flow in a linear manner and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.
Laws of Physics
Since Albert Einstein’s theory of relativity — which describes the nature of time, space and gravity — is our most profound theory of time, we would like to think that time travel is forbidden by relativity. Unfortunately, one of his colleagues from the Institute for Advanced Study, Kurt Gödel, invented a universe in which time travel was not just possible, but the past and future were inextricably tangled.
We can actually design time machines, but most of these (in principle) successful proposals require negative energy, or negative mass, which does not seem to exist in our universe. If you drop a tennis ball of negative mass, it will fall upwards. This argument is rather unsatisfactory, since it explains why we cannot time travel in practice only by involving another idea — that of negative energy or mass — that we do not really understand.
Time travel also violates the second law of thermodynamics, which states that entropy or randomness must always increase. Time can only move in one direction — in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.
This argument originated with the English cosmologist Arthur Eddington, and is at best incomplete. Perhaps it stops you travelling into the past, but it says nothing about time travel into the future. In practice, it is just as hard for me to travel to next Thursday as it is to travel to last Thursday.
Resolving Paradoxes
There is no doubt that if we could time travel freely, we run into the paradoxes. The best known is the “grandfather paradox”: one could hypothetically use a time machine to travel to the past and murder their grandfather before their father’s conception, thereby eliminating the possibility of their own birth. Logically, you cannot both exist and not exist.
Kurt Vonnegut’s anti-war novel Slaughterhouse-Five, published in 1969, describes how to evade the grandfather paradox. If free will simply does not exist, it is not possible to kill one’s grandfather in the past, since he was not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points on his world line (the timeline he exists in), but not to any other point in space-time, so he could not even contemplate killing his grandfather.
The universe in Slaughterhouse-Five is consistent with everything we know. The second law of thermodynamics works perfectly well within it and there is no conflict with relativity. But it is inconsistent with some things we believe in, like free will — you can observe the past, like watching a movie, but you cannot interfere with the actions of people in it.
Could we allow for actual modifications of the past, so that we could go back and murder our grandfather — or Hitler? There are several multiverse theories that suppose that there are many timelines for different universes. This is also an old idea: in Charles Dickens’ A Christmas Carol, Ebeneezer Scrooge experiences two alternative timelines, one of which leads to a shameful death and the other to happiness.
We can imagine that time does flow past every point in the universe, like a river around a rock. But it is difficult to make the idea precise. A flow is a rate of change — the flow of a river is the amount of water that passes a specific length in a given time. Hence if time is a flow, it is at the rate of one second per second, which is not a very useful insight.
Theoretical physicist Stephen Hawking suggested that a “chronology protection conjecture” must exist, an as-yet-unknown physical principle that forbids time travel. Hawking’s concept originates from the idea that we cannot know what goes on inside a black hole, because we cannot get information out of it. But this argument is redundant: we cannot time travel because we cannot time travel!
Researchers are investigating a more fundamental theory, where time and space “emerge” from something else. This is referred to as quantum gravity, but unfortunately it does not exist yet. So is time travel possible? Probably not, but we don’t know for sure!
By: Peter Watson, The Conversation
Peter Watson is an emeritus professor of physics at Carleton University.
The Clock That Went Backward”(PDF). Archived from the original(PDF) on October 15, 2011. Retrieved December 4, 2011.Uribe, Augusto (June 1999). “The First Time Machine: Enrique Gaspar’s Anacronópete”.
NASA Goes FTL Part 1: Wormhole Physics”. Analog Science Fiction & Fact Magazine. Archived from the original on June 27, 2006. Retrieved December 2, 2006.Visser, Matt; Sayan Kar; Naresh Dadhich (2003). “Traversable wormholes with arbitrarily small energy condition violations”.
A new study in Nature Sustainability incorporates the damages that climate change does to healthy ecosystems into standard climate-economics models. The key finding in the study by Bernardo Bastien-Olvera and Frances Moore from the University of California at Davis:
The models have been underestimating the cost of climate damages to society by a factor of more than five. Their study concludes that the most cost-effective emissions pathway results in just 1.5 degrees Celsius (2.7 degrees Fahrenheit) additional global warming by 2100, consistent with the “aspirational” objective of the 2015 Paris Climate Agreement.
Models that combine climate science and economics, called “integrated assessment models” (IAMs), are critical tools in developing and implementing climate policies and regulations.
In 2010, an Obama administration governmental interagency working group used IAMs to establish the social cost of carbon – the first federal estimates of climate damage costs caused by carbon pollution. That number guides federal agencies required to consider the costs and benefits of proposed regulations.
Economic models of climate have long been criticized by those convinced they underestimate the costs of climate damages, in some cases to a degree that climate scientists consider absurd. Given the importance of the social cost of carbon to federal rulemaking, some critics have complained that the Trump EPA used what they see as creative accounting to slash the government’s estimate of the number. In one of his inauguration day Executive Orders, President Biden established a new Interagency Working Group to re-evaluate the social cost of all greenhouse gases.
IAMs often have long been criticized by those convinced they underestimate the costs of climate damages, in some cases to a degree that climate scientists consider absurd. Perhaps the most prominent IAM is the Dynamic Integrated Climate-Economy (DICE) model, for which its creator, William Nordhaus, was awarded the 2018 Nobel Prize in Economic Sciences.
Judging by DICE, the economically optimal carbon emissions pathway – that is, the pathway considered most cost-effective – would lead to a warming increase of more than 3°C (5.4°F) from pre-industrial temperatures by 2100 (under a 3% discount rate). IPCC has reported that reaching this level of further warming could likely result in severe consequences, including substantial species extinctions and very high risks of food supply instabilities.
In their Nature Sustainability study, the UC Davis researchers find that when natural capital is incorporated into the models, the emissions pathway that yields the best outcome for the global economy is more consistent with the dangerous risks posed by continued global warming described in the published climate science literature.
Accounting for climate change degrading of natural capital
Natural capital includes elements of nature that produce value to people either directly or indirectly. “DICE models economic production as a function of generic capital and labor,” Moore explained via email. “If instead you think natural capital plays some distinct role in economic production, and that climate change will disproportionately affect natural capital, then the economic implications are much larger than if you just roll everything together and allow damage to affect output.”
Bastien-Olvera offered an analogy to explain the incorporation of natural capital into the models: “The standard approach looks at how climate change is damaging ‘the fruit of the tree’ (market goods); we are looking at how climate change is damaging the ‘tree’ itself (natural capital).” In an adaptation of DICE they call “GreenDICE,” the authors incorporated climate impacts on natural capital via three pathways:
The first pathway accounts for the direct influence of natural capital on market goods. Some industries like timber, agriculture, and fisheries are heavily dependent on natural capital, but all goods produced in the economy rely on these natural resources to some degree.
According to GreenDICE, this pathway alone more than doubles the model’s central estimate of the social cost of carbon in 2020 from $28 per ton in the standard DICE model to $72 per ton, and the new economically optimal pathway would have society limit global warming to 2.2°C (4°F) above pre-industrial temperatures by 2100.
The second pathway incorporates ecosystem services that don’t directly feed into market goods. Examples are the flood protection provided by a healthy mangrove forest, or the recreational benefits provided by natural places.
In the study, this second pathway nearly doubles the social cost of carbon once again, to $133 per ton in 2020, and it lowers the most cost-effective pathway to 1.8°C (3.2°F) by 2100. Finally, the third pathway includes non-use values, which incorporate the value people place on species or natural places, regardless of any good they produce. The most difficult to quantify, this pathway could be measured, for instance, by asking people how much they would be willing to pay to save one of these species from extinction.
In GreenDICE, non-use values increase the social cost of carbon to $160 per ton of carbon dioxide in 2020 (rising to about $300 in 2050 and $670 per ton in 2100) and limit global warming to about 1.5°C (2.8°F) by 2100 in the new economically optimal emissions pathway. (Note for economics wonks – the model runs used a 1.5% pure rate of time preference.)
Climate economics findings increasingly reinforce Paris targets
It may come as no surprise that destabilizing Earth’s climate would be a costly proposition, but key IAMs have suggested otherwise. Based on the new Nature Sustainability study, the models have been missing the substantial value of natural capital associated with healthy ecosystems that are being degraded by climate change.
Columbia University economist Noah Kaufman, not involved in the study, noted via email that as long as federal agencies use the social cost of carbon in IAMs for rulemaking cost-benefit analyses, efforts like GreenDICE are important to improving those estimates. According to Kaufman, many papers (including one he authored a decade ago) have tried to improve IAMs by following a similar recipe: “start with DICE => find an important problem => improve the methodology => produce a (usually much higher) social cost of carbon.”
For example, several other papers published in recent years, including one authored by Moore, have suggested that, because they neglect ways that climate change will slow economic growth, IAMs may also be significantly underestimating climate damage costs. Poorer countries – often located in already-hot climates near the equator, with economies relying most heavily on natural capital, and lacking resources to adapt to climate change – are the most vulnerable to its damages, despite their being the least responsible for the carbon pollution causing the climate crisis.
Another recent study in Nature Climate Change updated the climate science and economics assumptions in DICE and similarly concluded that the most cost-effective emissions pathway would limit global warming to less than 2°C (3.6°F) by 2100, without even including the value of natural capital. Asked about that paper, Bastien-Olvera noted, “In my view, the fact that these two studies get to similar policy conclusions using two very different approaches definitely indicates the urgency of cutting emissions.”
Recent economics and climate science research findings consistently support more aggressive carbon emissions efforts consistent with the Paris climate targets.
Wesleyan University economist Gary Yohe, also not involved in the study, agreed that the new Nature Sustainability study “supports growing calls for aggressive near-term mitigation.” Yohe said the paper “provides added support to the notion that climate risks to natural capital are important considerations, especially in calibrating the climate risk impacts of all sorts of regulations like CAFE standards.”
But Yohe said he believes that considering the risks to unique and threatened systems at higher temperatures makes a more persuasive case for climate policy than just attempting to assess their economic impacts. In a recent Nature Climate Change paper, Kaufman and colleagues similarly suggested that policymakers should select a net-zero emissions target informed by the best available science and economics, and then use models to set a carbon price that would achieve those goals.
Their study estimated that to reach net-zero carbon pollution by 2050, the U.S. should set a carbon price of about $50 per ton in 2025, rising to $100 per ton by 2030. However climate damages are evaluated, whether through a more complete economic accounting of adverse impacts or via risk-based assessments of physical threats to ecological and human systems, recent economics and climate science research findings consistently support more aggressive carbon emissions efforts consistent with the Paris climate targets.
Illustration: Fran Pulido/The Guardian
