Scientists have lost their latest round of hide-and-seek with dark matter, but they’re not out of the game.

Despite overwhelming evidence that an exotic form of matter lurks unseen in the cosmos, decades of searches have failed to definitively detect a single particle of dark matter. While some scientists continue down the road of increasingly larger detectors designed to catch the particles, others are beginning to consider a broader landscape of possibilities for what dark matter might be.

“We’ve been looking where our best guess told us to look for all these years, and we’re starting to wonder if we maybe guessed wrong,” says theoretical astrophysicist Dan Hooper of Fermilab in Batavia, Ill. “People are just opening their minds to a wider range of options.”

Dark matter permeates the cosmos: The material keeps galaxies from flying apart and has left its imprints in the oldest light in the universe, the cosmic microwave background, which dates back to just 380,000 years after the Big Bang. Indirect evidence from dark matter’s gravitational influences shows that it makes up the bulk of the mass in the universe. But scientists can’t pin down what dark matter is without detecting it directly.
In new results published in August and September, three teams of scientists have come up empty-handed, finding no hints of dark matter. The trio of experiments searched for one particular variety of dark matter — hypothetical particles known as WIMPs, or weakly interacting massive particles, with a range of possible masses that starts at several times that of a proton. WIMPs, despite their name, are dark matter bigwigs — they have long been the favorite explanation for the universe’s missing mass. WIMPs are thought to interact with normal matter only via the weak nuclear force and gravity.

Part of WIMPs’ appeal comes from a prominent but unverified theory, supersymmetry, which independently predicts such particles. Supersymmetry posits that each known elementary particle has a heavier partner; the lightest partner particle could be a dark matter WIMP. But evidence for supersymmetry hasn’t materialized in particle collisions at the Large Hadron Collider in Geneva, so supersymmetry’s favored status is eroding (SN: 10/1/16, p. 12). Supersymmetry arguments for WIMPs are thus becoming shakier — especially since WIMPs aren’t showing up in detectors.

Scientists typically search for WIMPs by looking for interactions with normal matter inside a detector. Several current experiments use tanks of liquefied xenon, an element found in trace amounts in Earth’s atmosphere, in hopes of detecting the tiny amounts of light and electric charge that would be released when a WIMP strikes a xenon nucleus and causes it to recoil.

The three xenon experiments are the Large Underground Xenon, or LUX, experiment, located in the Sanford Underground Research Facility in Lead, S.D.; the PandaX-II experiment, located in China’s JinPing underground laboratory in Sichuan; and the XENON100 experiment, located in the Gran Sasso National Laboratory in Italy. Teams of scientists at the three locations each reported no signs of dark matter particles. The experiments are most sensitive to particles with masses around 40 or 50 times that of a proton. Scientists can’t completely rule out WIMPs of these masses, but the interactions would have to be exceedingly rare.
In initial searches, proponents of WIMPs expected that the particles would be easy to find. “It was thought to be like, ‘OK, we’ll run the detector for five minutes, discover dark matter, and we’re all done,’” says physicist Matthew Szydagis of the University at Albany in New York, a member of LUX. That has turned into decades of hard work. As WIMPs keep failing to turn up, some scientists are beginning to become less enamored with the particles and are considering other possibilities more closely.

One alternative dark matter contender now attracting more attention is the axion. This particle was originally proposed decades ago as part of the solution to a particle physics quandary known as the strong CP problem — the question of why the strong nuclear force, which holds particles together inside the nucleus, treats matter and antimatter equally. If dark matter consists of axions, the particle could therefore solve two problems at once.

Axions are small fry as dark matter goes — they can be as tiny as a millionth of a billionth the mass of a WIMP. The particles interact so feebly that they are extremely difficult to detect. If axions are dark matter, “you’re sitting in an enormous, dense sea of axions and you don’t even notice them,” says physicist Leslie Rosenberg of the University of Washington in Seattle, the leader of the Axion Dark Matter eXperiment. After a recent upgrade to the experiment, ADMX scientists are searching for dark matter axions using a magnetic field and special equipment to coax the particles to convert into photons, which can then be detected.
Although WIMPs and axions remain the front-runners, scientists are beginning to move beyond these two possibilities. In between the featherweight axions and hulking WIMPs lies a broad range of masses that hasn’t been well explored. Scientists’ favorite theories don’t predict dark matter particles with such intermediate masses, says theoretical physicist Kathryn Zurek of Lawrence Berkeley National Laboratory in California, but that doesn’t mean that dark matter couldn’t be found there. Zurek advocates a diverse search over a broad range of masses, instead of focusing on one particular theory. “Dark matter direct detection is not one-size-fits-all,” she says.
In two papers published in Physical Review Letters on January 7 and September 14, Zurek and colleagues proposed using superconductors — materials that allow electricity to flow without resistance — and superfluids, which allow fluids to flow without friction, to detect light dark matter particles. “We are trying to broaden as much as possible the tools to search for dark matter,” says Zurek. Likewise, scientists with the upcoming Super Cryogenic Dark Matter Search SNOLAB experiment, to be located in an underground lab in Sudbury, Canada, will use detectors made of germanium and silicon to search for dark matter with smaller masses than the xenon experiments can.

Scientists have not given up on xenon WIMP experiments. Soon some of those experiments will be scaling up — going from hundreds of kilograms of liquid xenon to tons — to improve their chances of catching a dark matter particle on the fly. The next version of XENON100, the XENON1T experiment (pronounced “XENON one ton”) is nearly ready to begin taking data. LUX’s next generation experiment, known as LUX-ZEPLIN or LZ, is scheduled to begin in 2020. PandaX-II scientists are also planning a sequel. Physicists are still optimistic that these detectors will finally find the elusive particles. “Maybe we will have some opportunity to see something nobody has seen,” says Xiangdong Ji of Shanghai Jiao Tong University, the leader of PandaX-II. “That’s what’s so exciting.”

In the sea of nondetections of dark matter, there is one glaring exception. For years, scientists with the DAMA/LIBRA experiment at Gran Sasso have claimed to see signs of dark matter, using crystals of sodium iodide. But other experiments have found no signs of DAMA’s dark matter. Many scientists believe that DAMA has been debunked. “I don’t know what generates the weird signal that DAMA sees,” says Hooper. “That being said, I don’t think it’s likely that it’s dark matter.”

But other experiments have not used the same technology as DAMA, says theoretical astrophysicist Katherine Freese of the University of Michigan in Ann Arbor. “There is no alternative explanation that anybody can think of, so that is why it is actually still very interesting.” Three upcoming experiments should soon close the door on the mystery, by searching for dark matter using sodium iodide, as DAMA does: the ANAIS experiment in the Canfranc Underground Laboratory in Spain, the COSINE-100 experiment at YangYang Underground Laboratory in South Korea, and the SABRE experiment, planned for the Stawell Underground Physics Laboratory in Australia.

Scientists’ efforts could still end up being for naught; dark matter may not be directly detectable at all. “It’s possible that gravity is the only lens with which we can view dark matter,” says Szydagis. Dark matter could interact only via gravity, not via the weak force or any other force. Or it could live in its own “hidden sector” of particles that interact among themselves, but mostly shun normal matter.

Even if no particles are detected anytime soon, most scientists remain convinced that an unseen form of matter exists. No alternative theory can explain all of scientists’ cosmological observations. “The human being is not going to give up for a long, long time to try to search for dark matter, because it’s such a big problem for us,” says Ji.

In empty space, quantum particles flit in and out of existence, electromagnetic fields permeate the vacuum, and space itself trembles with gravitational waves. What may seem like nothingness paradoxically teems with activity.

In Void: The Strange Physics of Nothing, physicist and philosopher James Owen Weatherall explores how physicists’ beliefs about nothingness have changed over several revolutionary periods. The void, Weatherall argues, is physics distilled to its bare essence. If physicists can’t agree on the properties of empty space, they won’t be able to explain the physics of planets or particles either.
Scientists have argued over nothingness since the early days of physics. Vacant space was unthinkable to Aristotle, and Descartes so abhorred the idea of a vacuum that he posited that an invisible “plenum” suffused the gaps between objects. But Isaac Newton upended this view, arguing that space was just a barren container into which matter is placed.

Since then, physicists have continued to flip-flop on this issue. The discovery in the mid-1800s that light is an electromagnetic wave led scientists to conclude that a vibrating medium, an “ether,” filled space. Just as sound waves vibrate the air, physicists thought there must be some medium for light waves to ripple. Albert Einstein tore down that idea with his special theory of relativity. Since the speed of light was the same for all observers, no matter their relative speeds, he reasoned, light could not be traveling through some absolute, stationary medium. But he later predicted, as part of his general theory of relativity, that space itself can ripple with gravitational waves (SN: 3/5/16, p. 6) — suggesting that the void is not quite empty.

Under the modern view of quantum physics, various fields pervade all of space, and particles are simply excitations, or waves, in these fields. Even in a vacuum, experiments show, fluctuating fields produce a background of transient particles and antiparticles. Does a space pulsating with gravitational waves and bubbling with particles really qualify as empty? It depends on the scientific definition of “nothing,” Weatherall argues, which may not conform to intuition.

Weatherall serves readers a fairly typical buffet of physics theories, dishing up Newtonian mechanics, relativity, quantum mechanics and a small helping of string theory. But he does this through a lens that highlights connections between those theories in a novel way. Weatherall contends, for instance, that differing notions of nothingness between theories of general relativity and quantum mechanics could help explain why scientists are still struggling to unite the two ideas into one theory of quantum gravity.

Exploring the physics of nothing demands quite a bit of wading through the physics of something, and it’s not always clear how the threads Weatherall is following will lead back to the void. When he finally makes these connections, though, they often reveal insights that are missed in the typical focus on things of substance.

The new record-holder for fastest flying animal isn’t a bat out of hell. It’s a bat from Brazil, a new study claims. Brazilian free-tailed bats (Tadarida brasiliensis) can reach ground speeds of 160 kilometers per hour.

It’s unclear why they need that kind of speed to zoom through the night sky, but Brazilian bats appear to flap their wings in a similar fashion to ultrafast birds, an international group of researchers report November 9 in Royal Society Open Science. A sleek body, narrow wings and a wingspan longer than most other bats’ doesn’t hurt either.

Radio transmitters attached to the backs of seven bats allowed the team, led by evolutionary biologist Gary McCracken of the University of Tennessee, Knoxville, to track the flight path and speed of the bats after they emerged from a cave in southwestern Texas. All seven reached almost 100 km/hr when flying horizontally; one bat hit about 160 km/hr.

Until now, common swifts held the record of fastest fliers, soaring at up to 112 km/hr, often with help from wind and gravity. The Brazilian bats, however, reached their higher speeds with no assist. Since bat flight is rarely studied, there may be even faster bats out there, the researchers speculate.

An oddball superconductor is the first of its kind — and if scientists are lucky, its discovery may lead to others.

At a frigid temperature 5 ten-thousandths of a degree above absolute zero, bismuth becomes a superconductor — a material that conducts electricity without resistance — physicists from the Tata Institute of Fundamental Research in Mumbai, India, report online December 1 in Science.

Bismuth, a semimetallic element, conducts electricity less efficiently than an ordinary metal. It is unlike most other known superconductors in that it has very few mobile electrons. Consequently, the prevailing theory of superconductivity doesn’t apply.
The result is “quite important,” says theoretical physicist Marvin Cohen of the University of California, Berkeley. New ideas — either a different theory or a tweak to the standard one — are needed to explain bismuth’s superconductivity. “It might lead us to a better theory of superconductivity with more details,” Cohen says.

An improved theoretical understanding might lead scientists to other superconductors, potentially ones that work at more practical temperatures, says Srinivasan Ramakrishnan, a coauthor of the paper. “It opens a new path for discovering new superconducting materials.”

Physicists’ ultimate goal is to find a superconductor that operates at room temperature. Such a material could be used to replace standard metals in wires and electronics, providing massive energy savings and technological leaps, from advanced supercomputers to magnetically levitating trains.

To confirm that bismuth was superconducting, Ramakrishnan and collaborators chilled ultrapure crystals of bismuth, while shielding the crystals from magnetic fields. Below 0.00053 kelvins (about –273° Celsius), the researchers observed a hallmark of superconductivity known as the Meissner effect, in which the superconductor expunges magnetic fields from within itself.

In the standard theory of superconductivity, electrons partner up in a fashion that removes resistance to their flow, thanks to the electrons’ interactions with ions in the material. But the theory, known as the Bardeen-Cooper-Schrieffer, or BCS, theory, works only for materials with many free-floating electrons. A typical superconductor has about one mobile electron for each atom in the material, while in bismuth each electron is shared by 100,000 atoms.
Bismuth has previously been made to superconduct when subjected to high pressure or when formed into nanoparticles, or when its atoms are disordered, rather than neatly arranged in a crystal. But under those conditions, bismuth behaves differently, so the BCS theory still applies. The new result is the first sign of superconducting bismuth in its normal form.

Another class of superconductors, known as high-temperature superconductors, likewise remains enigmatic (SN: 8/8/15, p. 12). Scientists have yet to reach a consensus on how they work. Though these superconductors must be cooled, they operate at relatively high temperatures, above the boiling point of liquid nitrogen (77 kelvins, or –196° Celsius).

Bismuth’s unusual behavior provides another handle with which to investigate the still-mysterious phenomenon of superconductivity. In addition to its low electron density and unexpected superconductivity, bismuth has several anomalous properties, including unusual optical and magnetic behavior. “A good global picture is missing” for explaining the abnormal element, says theoretical physicist Ganapathy Baskaran of the Institute of Mathematical Sciences in Chennai, India. “I think it’s only a tip of an iceberg.”

In a better world, it would be the big news of the year just to report that Arctic sea ice shrank to 4.14 million square kilometers this summer, well below the 1981–2010 average of 6.22 million square kilometers (SN Online: 9/19/16). But in this world of changing climate, extreme summer ice loss has become almost expected. More novel in 2016 were glimpses of the complex biological consequences of melting at the poles and the opening of Arctic passageways, talked about for at least a decade and now well under way.

With top-of-the-world trade and tourist shortcuts opening, less ice means more travel. Europe-to-Asia shipping routes will typically shorten by about 10 days by midcentury, a report in Geophysical Research Letters predicted. Hopes for Northwest Passage routes obsessed (and killed) explorers in previous centuries, but in 2016, the thousand-passenger cruise ship Crystal Serenity offered the first megascale tourist trip from Alaska to New York with fine dining, casino gambling and an escort icebreaker vessel.
Biologists are delving into consequences for organisms other than human tourists — or the much-discussed polar bear. “There’s been a marked shift in the research community,” says climate change ecologist Eric Post of the University of California, Davis. There’s new interest in considering more than just species that dwell on sea ice, with researchers looking for the less direct effects of declining ice.
In the February Global Change Biology, eight scientists issued a call for observations of what could be early signs of faunal exchange: the mingling of Atlantic and Pacific species. One possible indicator is the sighting of gray whales off the coast of Namibia and also off Israel, even though that species went extinct in the Atlantic two centuries ago. These whales feed by snouting around in soft ocean bottoms, adding another predator to the system but also creating new habitat opportunities for some creatures (SN: 1/23/16, p. 14).

Since the call was published, biodiversity scientist Seabird McKeon of Colby College in Waterville, Maine, has heard new reports, such as a sighting of an ancient murrelet off the coast of Maine. It’s not the first wrong-coast report for the bird, which typically resides in the northern Pacific, but repeat sightings could be important, too. “What I think we’re seeing is not just new species coming across, but also perhaps an increased chance of survival and reproduction if more come over,” McKeon says. He is hoping to get new data from the online Encyclopedia of Life’s upcoming Fresh Data system, which connects scientists to people reporting nature observations.
For terrestrial northerners, melting ice often means loss of mobility. Peary caribou on the 36,000 or more islands of Canada’s northern archipelago occasionally use ice bridges to travel to new territories and mix genes with other populations. Yet ice losses since 1979 have

made it some 15 percent harder

to find traveling paths, researchers reported in September inBiology Letters

(

SN: 10/29/16, p. 8

).

Even some plants such as dwarf birch probably travel by ice, scientists also reported in September in Biology Letters. Reconstructing long-ago sea ice extent and plant colonization dates suggests that seeds hitchhiked on slowly creeping frozen conveyors around northern Europe to colonize new territory at the end of the Ice Age. Losing ice roads could lead to tattered, disconnected populations as recolonization becomes less likely. Yet, there are pluses and minuses, says Post, who is helping to develop a package of scientific articles for Biology Letters on the biological effects of sea ice loss. Reseeding populations after a wipeout could be more difficult with tattered ice, but for the highly specialized and vulnerable plants very far north, the loss of sea ice could slow the arrival of invasive species that threaten the natives.

The minimum summer sea ice extent since 1979 has declined by about 87,000 square kilometers per year, equivalent to an area more than three times the size of New Jersey disappearing annually, as Post has put it. The September 2016 sea ice minimum didn’t break a record, as some had expected it might. It tied for second worst, behind the 2012 minimum, and roughly equaled the 2007 minimum. 2016 did set a new record low for winter Arctic ice extent (SN Online: 3/28/16).
Sea ice changes reverberate through the ecosystem. Ice melting cues the springtime phytoplankton blooms that feed copepods and other tiny marine grazers. The grazers feed their predators and, in turn, the predators of those predators. In years when spring warming brings an early ice retreat, the phyto-plankton bloom is not a huge, rich burst. It favors smaller grazing zooplankton that don’t fuel as much of a boom in their predators, marine ecologist Martin Renner of Homer, Alaska, and colleagues reported in a paper for the Biology Letters special collection.

Tracing the effects of shrinking ice through these grazers to fish to seabirds revealed a tangled web of ups and downs and shifting foraging grounds. In the end, Renner and colleagues predict “a very different eastern Bering Sea ecosystem and fishery than we know today.” And that may be far from the only sea change in the far north.

Future moon colonies could be totally tubular.

Slight variations in the moon’s gravitational tug have hinted that kilometers-wide caverns lurk beneath the lunar surface. Like the lava tubes of Hawaii and Iceland, these structures probably formed when underground rivers of molten rock ran dry, leaving behind a cylindrical channel. On Earth, such structures max out at around 30 meters across, but the gravitational data suggest that the moon’s tubes are vastly wider.

Assessing the sturdiness of lava tubes under lunar gravity, planetary geophysicist Dave Blair of Purdue University in West Lafayette, Ind., and colleagues estimate that the caves could remain structurally sound up to 5 kilometers across. That’s wide enough to fit the Golden Gate Bridge, Brooklyn Bridge and London Bridge end to end.

Such colossal caves will be prime real estate for lunar pioneers, the researchers report in the Jan. 15 Icarus. Lava tubes could offer protection from the extreme temperatures, harsh radiation and meteorite impacts on the surface.

New research is stirring the pot about an ancient Egyptian burial practice.

Many ancient peoples, including Egyptians, buried some of their dead in ceramic pots or urns. Researchers have long thought these pot burials, which often recycled containers used for domestic purposes, were a common, make-do burial for poor children.

But at least in ancient Egypt, the practice was not limited to children or to impoverished families, according to a new analysis. Bioarchaeologist Ronika Power and Egyptologist Yann Tristant, both of Macquarie University in Sydney, reviewed published accounts of pot burials at 46 sites, most near the Nile River and dating from about 3300 B.C. to 1650 B.C. Their results appear in the December Antiquity.
A little over half of the sites contained the remains of adults. For children, pot burials were less common than expected: Of 746 children, infants and fetuses interred in some type of burial container, 338 were buried in wooden coffins despite wood’s relative scarcity and cost. Another 329 were buried in pots. Most of the rest were placed in baskets or, in a few cases, containers fashioned from materials such as reeds or limestone.

In the tomb of a wealthy governor, an infant was found in a pot containing beads covered in gold foil. Other pot burials held myriad goods — gold, ivory, ostrich eggshell beads, clothing or ceramics. Bodies were either placed directly into urns, or sometimes pots were broken or cut to fit the deceased.

People deliberately chose the containers, in part for symbolic reasons, the researchers now propose. The hollow vessels, which echo the womb, may have been used to represent a rebirth into the afterlife, the scientists say.

Gold’s glimmer is not the only reason the element is so captivating. For decades, scientists have puzzled over why theoretical predictions of gold’s properties don’t match up with experiments. Now, highly detailed calculations have erased the discrepancy, according to a paper published in the Jan. 13 Physical Review Letters.

At issue was the energy required to remove an electron from a gold atom, or ionize it. Theoretical calculations of this ionization energy differed from scientists’ measurements. Likewise, the energy released when adding an electron — a quantity known as the electron affinity — was also off the mark. How easily an atom gives up or accepts electrons is important for understanding how elements react with other substances.
“It was well known that gold is a difficult system,” says chemist Sourav Pal of the Indian Institute of Technology Bombay, who was not involved with the study. Even gold’s most obvious feature can’t be explained without calling Einstein’s special theory of relativity into play: The theory accounts for gold’s yellowish color. (Special relativity shifts around the energy levels of electrons in gold atoms, causing the metal to absorb blue light, and thereby making reflected light appear more yellow.)

With this new study, scientists have finally resolved the lingering questions about the energy involved in removing or adding an electron to the atom. “That is the main significance of this paper,” Pal says.

Early calculations, performed in the 1990s, differed from the predicted energies by more than a percent, and improved calculations since then still didn’t match the measured value. “Every time I went to a conference, people discussed that and asked, ‘What the hell is going on?’” says study coauthor Peter Schwerdtfeger, a chemist at Massey University Auckland in New Zealand.

The solution required a more complete consideration of the complex interplay among gold’s 79 electrons. Using advanced supercomputers to calculate the interactions of up to five of gold’s electrons at a time, the scientists resolved the discrepancy. Previous calculations had considered up to three electrons at a time. Also essential to include in the calculation were the effects of special relativity and the theory of quantum electrodynamics, which describes the quantum physics of particles like electrons.

The result indicates that gold indeed adheres to expectations — when calculations are detailed enough. “Quantum theory works perfectly well, and that makes me extremely happy,” says Schwerdtfeger.

WASHINGTON — Researchers have devised a test to see if pairs of black holes — famous for creating gravitational waves when they merge — themselves formed from multiple mergers of smaller black holes.

The Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, has detected spacetime ripples from two sets of merging black holes (SN: 7/9/16, p. 8). Scientists typically assume that such black holes formed in the collapse of a massive star. But in especially crowded patches of the universe, black holes could have formed over generations of unions, astrophysicist Maya Fishbach of the University of Chicago explained January 28 at a meeting of the American Physical Society. Or the merging cycle could have occurred in the very early universe, starting with primordial black holes — objects that may have formed when extremely dense pockets of matter directly collapsed.
Fishbach and colleagues studied how quickly black holes whirl around. In simulations, black holes that repeatedly merged reached a high rate of spin, the scientists found. That result didn’t depend on certain properties of the initial black holes, like whether they were spinning to begin with or not. “It’s cool,” says Fishbach. “The predictions from this in terms of spin are very robust,” making the idea easy to test.

So far, the spins of LIGO’s black holes are lower than the predictions. If the multiple merging process occurs, it could be very rare, so to conclusively test the idea would require tens to hundreds of black hole detections, Fishbach says.

Abnormal is the new normal in mental health.

A small, poorly understood segment of the population stays mentally healthy from age 11 to 38, a new study of New Zealanders finds. Everyone else encounters either temporary or long-lasting mental disorders.

Only 171 of 988 participants, or 17 percent, experienced no anxiety disorders, depression or other mental ailments from late childhood to middle age, researchers report in the February Journal of Abnormal Psychology. Of the rest, half experienced a transient mental disorder, typically just a single bout of depression, anxiety or substance abuse by middle age.
“For many, an episode of mental disorder is like influenza, bronchitis, kidney stones, a broken bone or other highly prevalent conditions,” says study coauthor Jonathan Schaefer, a psychologist at Duke University. “Sufferers experience impaired functioning, many seek medical care, but most recover.”

The remaining 408 individuals (41 percent) experienced one or more mental disorders that lasted several years or more. Their diagnoses included more severe conditions such as bipolar and psychotic disorders.

Researchers analyzed data for individuals born between April 1972 and March 1973 in Dunedin, New Zealand. Each participant’s general health and behavior were assessed 13 times from birth to age 38. Eight mental health assessments occurred from age 11 to 38.
Surprisingly, those who experienced lasting mental health did not display several characteristics previously linked to a lower likelihood of developing mental disorders. Those attributes consist of growing up in unusually affluent families, enjoying especially sound physical health and scoring exceptionally high on intelligence tests.
Instead, mentally healthy participants tended to possess advantageous personality traits starting in childhood, Schaefer and colleagues found. These participants rarely expressed strongly negative emotions, had lots of friends and displayed superior self-control. Kiwis with rock-solid mental health also had fewer first- and second-degree relatives with mental disorders compared with their peers.

As adults, participants with enduring mental health reported, on average, more education, better jobs, higher-quality relationships and more satisfaction with their lives than their peers did. But lasting mental health doesn’t guarantee an exceptional sense of well-being, Schaefer says. Nearly one-quarter of never-diagnosed individuals scored below the entire sample’s average score for life satisfaction.

Less surprising was the 83 percent overall prevalence rate for mental disorders. That coincides with recent estimates from four other long-term projects. In those investigations — two in the United States, one in Switzerland and another in New Zealand — between 61 percent and 85 percent of participants developed mental disorders over 12- to 30-year spans.

Comparably high rates of emotional disorders were reported in 1962 for randomly selected Manhattan residents. Many researchers doubted those findings, which relied on a diagnostic system that was less strict than the three versions of psychiatry’s diagnostic manual that were introduced and used to evaluate New Zealand participants as they got older, says psychiatric epidemiologist William Eaton of Johns Hopkins Bloomberg School of Public Health. But the Manhattan study appears to have been on the right track, Eaton says.

Increased awareness that most people will eventually develop a mental disorder (SN: 10/10/09, p. 5), at least briefly, can reduce stigma attached to these conditions (SN Online: 10/13/16), he suspects.

Psychiatric epidemiologist Ronald Kessler suspects the numbers of people experiencing a mental disorder may be even higher than reported. Many participants deemed to have enduring mental health likely developed brief mental disorders that got overlooked, such as a couple of weeks of serious depression after a romantic breakup, says Kessler of Harvard Medical School, who directs U.S. surveys of mental disorders. Rather than focusing on rare cases of lasting mental health, “the more interesting thing is to compare people with persistent mental illness to those with temporary disorders,” he says.