The original version ofthis storyappeared in Quanta Magazine.
Whenever you’re actively performing a task—say, lifting weights at the gym or taking a hard exam—the parts of your brain required to carry it out become “active” when neurons step up their electrical activity. But is your brain active even when you’re zoning out on the couch?
The answer, researchers have found, is yes. Over the past two decades they’ve defined what’s known as the default mode network, a collection of seemingly unrelated areas of the brain that activate when you’re not doing much at all. Its discovery has offered insights into how the brain functions outside of well-defined tasks and has also prompted research into the role of brain networks—not just brain regions—in managing our internal experience.
In the late 20th century, neuroscientists began using new techniques to take images of people’s brains as they performed tasks in scanning machines. As expected, activity in certain brain areas increased during tasks—and to the researchers’ surprise, activity in other brain areas declined simultaneously. The neuroscientists were intrigued that during a wide variety of tasks, the very same brain areas consistently dialed back their activity.
It was as if these areas had been active when the person wasn’t doing anything, and then turned off when the mind had to concentrate on something external.
Researchers called these areas “task negative.” When they were first identified, Marcus Raichle, a neurologist at the Washington University School of Medicine in St. Louis, suspected that these task-negative areas play an important role in the resting mind. “This raised the question of ‘What’s baseline brain activity?’” Raichle recalled. In an experiment, he asked people in scanners to close their eyes and simply let their minds wander while he measured their brain activity.
He found that during rest, when we turn mentally inward, task-negative areas use more energy than the rest of the brain. In a 2001 paper, he dubbed this activity “a default mode of brain function.” Two years later, after generating higher-resolution data, a team from the Stanford University School of Medicine discovered that this task-negative activity defines a coherent network of interacting brain regions, which they called the default mode network.
The discovery of the default mode network ignited curiosity among neuroscientists about what the brain is doing in the absence of an outward-focused task. Although some researchers believed that the network’s main function was to generate our experience of mind wandering or daydreaming, there were plenty of other conjectures. Maybe it controlled streams of consciousness or activated memories of past experiences. And dysfunction in the default mode network was floated as a potential feature of nearly every psychiatric and neurological disorder, including depression, schizophrenia, and Alzheimer’s disease.
Since then, a flurry of research into the default mode has complicated that initial understanding. “It’s been very interesting to see the types of different tasks and paradigms that engage the default mode network in the past 20 years,” said Lucina Uddin, a neuroscientist at the University of California, Los Angeles.
This story originally appeared on Grist and is part of the Climate Desk collaboration.
Ariana Tibon was in college at the University of Hawaii in 2017 when she saw the photo online: a black-and-white picture of a man holding a baby. The caption said: “Nelson Anjain getting his baby monitored on March 2, 1954, by an AEC RadSafe team member on Rongelap two days after ʻBravo.’”
Tibon had never seen the man before. But she recognized the name as her great-grandfather’s. At the time, he was living on Rongelap in the Marshall Islands when the US conducted Castle Bravo, the largest of 67 nuclear weapon tests there during the Cold War. The tests displaced and sickened Indigenous people, poisoned fish, upended traditional food practices, and caused cancers and other negative health repercussions that continue to reverberate today.
A federal report by the Government Accountability Office published last month examines what’s left of that nuclear contamination, not only in the Pacific but also in Greenland and Spain. The authors conclude that climate change could disturb nuclear waste left in Greenland and the Marshall Islands. “Rising sea levels could spread contamination in RMI, and conflicting risk assessments cause residents to distrust radiological information from the US Department of Energy,” the report says.
In Greenland, chemical pollution and radioactive liquid are frozen in ice sheets, left over from a nuclear power plant on a US military research base where scientists studied the potential to install nuclear missiles. The report didn’t specify how or where nuclear contamination could migrate in the Pacific or Greenland, or what if any health risks that might pose to people living nearby. However, the authors did note that in Greenland, frozen waste could be exposed by 2100.
“The possibility to influence the environment is there, which could further affect the food chain and further affect the people living in the area as well,” said Hjalmar Dahl, president of Inuit Circumpolar Council Greenland. The country is about 90 percent Inuit. “I think it is important that the Greenland and US governments have to communicate on this worrying issue and prepare what to do about it.”
The authors of the GAO study wrote that Greenland and Denmark haven’t proposed any cleanup plans, but also cited studies that say much of the nuclear waste has already decayed and will be diluted by melting ice. However, those studies do note that chemical waste such as polychlorinated biphenyls, man-made chemicals better known as PCBs that are carcinogenic, “may be the most consequential waste at Camp Century.”
The report summarizes disagreements between Marshall Islands officials and the US Department of Energy regarding the risks posed by US nuclear waste. The GAO recommends that the agency adopt a communications strategy for conveying information about the potential for pollution to the Marshallese people.
Nathan Anderson, a director at the Government Accountability Office, said that the United States’ responsibilities in the Marshall Islands “are defined by specific federal statutes and international agreements.” He noted that the government of the Marshall Islands previously agreed to settle claims related to damages from US nuclear testing.
“It is the long-standing position of the US government that, pursuant to that agreement, the Republic of the Marshall Islands bears full responsibility for its lands, including those used for the nuclear testing program.”
To Tibon, who is back home in the Marshall Islands and is currently chair of the National Nuclear Commission, the fact that the report’s only recommendation is a new communications strategy is mystifying. She’s not sure how that would help the Marshallese people.
“What we need now is action and implementation on environmental remediation. We don’t need a communication strategy,” she said. “If they know that it’s contaminated, why wasn’t the recommendation for next steps on environmental remediation, or what’s possible to return these lands to safe and habitable conditions for these communities?”
The Biden administration recently agreed to fund a new museum to commemorate those affected by nuclear testing as well as climate change initiatives in the Marshall Islands, but the initiatives have repeatedly failed to garner support from Congress, even though they’re part of an ongoing treaty with the Marshall Islands and a broader national security effort to shore up goodwill in the Pacific to counter China.
But there may be opportunities to indirectly spot the signatures of those gravitons.
One strategy Vafa and his collaborators are pursuing draws on large-scale cosmological surveys that chart the distribution of galaxies and matter. In those distributions, there might be “small differences in clustering behavior,” Obied said, that would signal the presence of dark gravitons.
When heavier dark gravitons decay, they produce a pair of lighter dark gravitons with a combined mass that is slightly less than that of their parent particle. The missing mass is converted to kinetic energy (in keeping with Einstein’s formula, E = mc2), which gives the newly created gravitons a bit of a boost—a “kick velocity” that’s estimated to be about one-ten-thousandth of the speed of light.
These kick velocities, in turn, could affect how galaxies form. According to the standard cosmological model, galaxies start with a clump of matter whose gravitational pull attracts more matter. But gravitons with a sufficient kick velocity can escape this gravitational grip. If they do, the resulting galaxy will be slightly less massive than the standard cosmological model predicts. Astronomers can look for this difference.
Recent observations of cosmic structure from the Kilo-Degree Survey are so far consistent with the dark dimension: An analysis of data from that survey placed an upper bound on the kick velocity that was very close to the value predicted by Obied and his coauthors. A more stringent test will come from the Euclid space telescope, which launched last July.
Meanwhile, physicists are also planning to test the dark dimension idea in the laboratory. If gravity is leaking into a dark dimension that measures 1 micron across, one could, in principle, look for any deviations from the expected gravitational force between two objects separated by that same distance. It’s not an easy experiment to carry out, said Armin Shayeghi, a physicist at the Austrian Academy of Sciences who is conducting the test. But “there’s a simple reason for why we have to do this experiment,” he added: We won’t know how gravity behaves at such close distances until we look.
The closest measurement to date—carried out in 2020 at the University of Washington—involved a 52-micron separation between two test bodies. The Austrian group is hoping to eventually attain the 1-micron range predicted for the dark dimension.
While physicists find the dark dimension proposal intriguing, some are skeptical that it will work out. “Searching for extra dimensions through more precise experiments is a very interesting thing to do,” said Juan Maldacena, a physicist at the Institute for Advanced Study, “though I think that the probability of finding them is low.”
Joseph Conlon, a physicist at Oxford, shares that skepticism: “There are many ideas that would be important if true, but are probably not. This is one of them. The conjectures it is based on are somewhat ambitious, and I think the current evidence for them is rather weak.”
Of course, the weight of evidence can change, which is why we do experiments in the first place. The dark dimension proposal, if supported by upcoming tests, has the potential to bring us closer to understanding what dark matter is, how it is linked to both dark energy and gravity, and why gravity appears feeble compared to the other known forces. “Theorists are always trying to do this ‘tying together.’ The dark dimension is one of the most promising ideas I have heard in this direction,” Gopakumar said.
But in an ironic twist, the one thing the dark dimension hypothesis cannot explain is why the cosmological constant is so staggeringly small—a puzzling fact that essentially initiated this whole line of inquiry. “It’s true that this program does not explain that fact,” Vafa admitted. “But what we can say, drawing from this scenario, is that if lambda is small—and you spell out the consequences of that—a whole set of amazing things could fall into place.”
Original storyreprinted with permission from Quanta Magazine, an editorially independent publication of theSimons Foundationwhose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.
This story originally appeared on Inside Climate News and is part of the Climate Desk collaboration.
Picture the minute hand at about 8 past the hour. That’s the slope of Viet’s backyard in southern Los Angeles County. It’s a bit too aggressive for a slip-and-slide. In fact, Viet doesn’t even let his 7-year-old daughter play on the family’s small back patio.
“I don’t need her falling down that hill,” he said.
When Viet and his wife bought their house-on-a-hill five years ago, it was a win, their piece of “the Hollywood Riviera,” as real estate agents like to call the area. (A self-employed marketer in his forties, Viet asked that his last name not be used to protect his family’s privacy.)
Viet’s street runs horizontally across a huge incline that begins the Palos Verdes Peninsula, a marvel of steep cliffs and Mediterranean-style homes at the south hook of Santa Monica Bay. If you squint, it could be the terraced hills of Tuscany or, indeed, a stretch of the Côte d’Azur. The address was a solid investment and housing insurance not a problem, even though parts of the peninsula have been known to shape-shift, cracking roads and knocking houses off foundations. But not every day. The family enjoyed some easy SoCal years on their perch with its great views and gentle, dry climate.
“Whenever it rained, we’d be happy: ‘We’re not in a severe drought anymore, yay!’” Viet said. “But after this, every time it rains, I get scared.”
“This” was the atmospheric river storms that hit LA with a one-two punch (the first, a jab, the second, a wallop) in the first week of February. The usual winter rainy season in California has been amped up this year by a parade of such storms. This week again, Santa Barbara, Ventura, and LA counties are in the midst of high-volume, road-cracking, flash-flooding, climate-amplified downpours juiced by warmer Pacific Ocean temperatures. The storms are causing an unusual amount of high-profile damage, setting everyone on edge, especially Viet.
After the initial rain burst on February 1, he noticed that the top of his backyard slope, swathed in a hand-high succulent called “ice plant,” looked odd. A patch of mushy soil seemed to be shrugging off its ground cover. He asked a gardener to try and fix it. That was a Friday. Then the monster rain cells moved in on Sunday, February 3.
“All night, all I could hear was pounding on the roof, the wind blowing sideways,” he said. “It was unsettling, so when I woke up at 7:30, the first thing I did was try to go look at the rain drains and make sure everything was doing fine.”
Viet circled his home in sneakers because he’d never had cause to buy rain boots.
“I walked around to the backyard, looked down, and I was like, ‘Ohhhhh myyyyyy goooood.’”
A 40-foot-wide river of mud, rock, and roots was in full flow down his hill, already jamming up a city road 70 feet below where Viet stood, somehow safe, on the precipice.
“The answer ended up being, yes, in all US states, on average heat pumps will reduce greenhouse gas emissions,” says Eric Wilson, a senior research engineer at the National Renewable Energy Laboratory and the lead author of the new paper. “Even if it’s a relatively low-efficiency heat pump that relies on electric resistance heating during the coldest times, and even if it’s the most pessimistic grid scenario that has prices for wind and solar being higher than their current trajectory has been.”
Because a heat pump can be reversed to provide cooling, getting more of the devices into homes could also improve public health during the summer, the study notes. That is, with a heat pump, a home that has never had AC now has a way to ensure comfortable indoor temperatures. That’ll be all the more critical as outdoor temperatures march relentlessly upward, especially in cities, where the built environment absorbs and slowly releases the sun’s energy. The tricky bit is that even though a heat pump can be more efficient at cooling than a traditional AC unit, its operating cost during the summer may surprise a household that has never had AC before.
It’s important to note that a household will get the most out of a heat pump if it also opts for better insulation. If you have double-paned windows, for instance, less of that indoor heating or cooling will escape in the winter or summer. That sort of insulation comes with its own upfront cost, sure, but reduces the upfront cost of the heat pump by thousands of dollars, the new study finds: If your home is sealed nice and tight, you’ll require a smaller, less expensive device to provide proper warming. “I worry a little bit about people putting in heat pumps in very poorly insulated homes, and just not being comfortable,” says Wilson. (To that end, the Inflation Reduction Act provides 30 percent off the cost of insulation. The legislation also offers thousands of bucks to upgrade your home’s electrical system, which may be required to accommodate a new heat pump.)
The study further notes that if deploying lowest-efficiency heat pumps, energy bills could increase in 39 percent of households, but that drops to 19 percent if they also reinsulate. (This is based on state-average energy prices from the winter of 2021-2022.) When using higher-efficiency heat pumps, only 5 percent of households could see an increase in their energy bills. The upfront cost of this insulation or higher-efficiency heat pumps could be offset by financial incentives, the study says, like those provided by the IRA.
This modeling isn’t predicting the future, but calculating scenarios for how the adoption of heat pumps could unfold in the US. In the coming years, the heat pump industry could well generate surprises—the good kind—especially as the US invests hundreds of millions of dollars into domestic production. “What are the efficiency improvements, the surprising innovations, the leaps here that one can only get when you in fact start deploying these at scale?” asks climate economist Gernot Wagner of the Columbia Business School, who wasn’t involved in the paper.
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