If you have a hankering for a hamburger, math may have some timesaving cooking tips for you.
Increasing the number of times a burger is flipped from one side to the other reduces its cook time by up to nearly a third , theoretical calculations suggest. But cooks at home probably won’t see much benefit out of more than three to four flips, mathematician Jean-Luc Thiffeault reports June 17 in Physica D .
Thiffeault used math to model how heat moves through an “infinite” slab of meat, which cooks continuously on only the bottom side and cools on the top until the meat is flipped. Flipping heated the meat evenly, speeding up cooking, the analysis showed. And more flips led to a faster cook. For example, flipping this theoretical 1-centimeter-thick patty just once gave it a cook time of 80 seconds, while flipping it 10 times at intervals ranging from six to 11 seconds resulted in a cook time of 69 seconds. Continuing to flip the burger led to a maximum decrease of 29 percent in cooking time.
But the timesaving benefit seemed to diminish as the number of flips increased beyond a certain threshold, says Thiffeault, of the University of Wisconsin–Madison. “After three or four flips, the gain in time is negligible.”
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Thiffeault’s findings align with what chef and food writer J. Kenji López-Alt has observed in the kitchen. In a 2019 article for the food and drink website Serious Eats, Kenji López-Alt compared how long it took for a burger’s internal temperature to reach about 52° Celsius, or 125° Fahrenheit, based on cooking method. Flipping a burger every 15 seconds — as opposed to flipping the patty just once — shortened cooking time by nearly a third.
But there isn’t a one-size-fits-all way to cook a burger, Kenji López-Alt notes. “The idea of the perfect anything is just nonsense, right?” he says. “It’s all based on what you want.”
Thiffeault’s friends probably wouldn’t want his theoretical hamburger, the mathematician jokes. The infinite slab of meat is considered cooked when it reaches 70° Celsius, or 158° Fahrenheit. “That’s no burger that they would want to eat because it’s quite a well-done burger,” he says.
Anil Oza is the summer 2022 science writing intern at Science News . He graduated from Cornell University with a degree in neurobiology and science communication.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
An array of 169 reflectors focus sunlight on a solar reactor at the top of this tower. The light reacts with carbon dioxide and water vapor, forming a mixture that can be turned into kerosene and diesel fuel.
Or at least that’s the case in Móstoles, Spain, where researchers demonstrated that an outdoor system could produce kerosene , used as jet fuel, with three simple ingredients: sunlight, carbon dioxide and water vapor. Solar kerosene could replace petroleum-derived jet fuel in aviation and help stabilize greenhouse gas emissions, the researchers report in the July 20 Joule .
Burning solar-derived kerosene releases carbon dioxide, but only as much as is used to make it, says Aldo Steinfeld, an engineer at ETH Zurich. “That makes the fuel carbon neutral, especially if we use carbon dioxide captured directly from the air.”
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Kerosene is the fuel of choice for aviation, a sector responsible for around 5 percent of human-caused greenhouse gas emissions. Finding sustainable alternatives has proven difficult, especially for long-distance aviation, because kerosene is packed with so much energy, says chemical physicist Ellen Stechel of Arizona State University in Tempe who was not involved in the study.
In 2015, Steinfeld and his colleagues synthesized solar kerosene in the laboratory , but no one had produced the fuel entirely in a single system in the field. So Steinfeld and his team positioned 169 sun-tracking mirrors to reflect and focus radiation equivalent to about 2,500 suns into a solar reactor atop a 15-meter-tall tower. The reactor has a window to let the light in, ports that supply carbon dioxide and water vapor as well as a material used to catalyze chemical reactions called porous ceria.
When heated with solar radiation, the ceria reacts with carbon dioxide and water vapor in the reactor to produce syngas — a mixture of hydrogen gas and carbon monoxide. The syngas is then piped to the tower’s base where a machine converts it into kerosene and other hydrocarbons.
Over nine days of operation, the researchers found that the tower converted about 4 percent of the used solar energy into roughly 5,191 liters of syngas, which was used to synthesize both kerosene and diesel. This proof-of-principle setup produced about a liter of kerosene a day, Steinfeld says.
“It’s a major milestone,” Stechel says, though the efficiency needs to be improved for the technology to be useful to industry. For context, a Boeing 747 passenger jet burns around 19,000 liters of fuel during takeoff and the ascent to cruising altitude. Recovering heat unused by the system and improving the ceria’s heat absorption could boost the tower’s efficiency to more than 20 percent, making it economically practical, the researchers say.
Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News . He has a master’s degree in geology from McGill University, and a master’s degree in science communication from the University of California, Santa Cruz.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
Many moths are nocturnal pollinators of plants. But the insects, like this Mythimna farrago , weren’t known to be regular visitors of red clover flowers until now.
Bees aren’t the only insects pollinating red clover. Moths do about a third of the flower visits after dark, new research suggests.
The findings, detailed in the July Biology Letters , come as a surprise, since almost all the credit for pollination of red clover has gone to bees. The discovery highlights what researchers may be missing during the night shift of plant pollination , including a previously unknown benefit the moth pollination bestows on the clover — a boost in seed production.
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This work may help deepen scientists’ understanding of the pollination services provided by nocturnal moths, says Daichi Funamoto, a pollination biologist at the University of Tokyo who was not involved with the new study.
For about a century, the general understanding of clover pollination has been that bees — and bees alone — are the key insect players. Clover is a “valuable agricultural plant and has received a lot of study,” says Jamie Alison, a pollinator ecologist at Aarhus University in Denmark. “Yet none of those studies have said anything about the possibility of moth pollination.”
Alison and his colleagues discovered moths’ pollination role while studying how plants and their insect pollinators respond to climate change by potentially moving uphill. To track pollinator visitation to grassland plants, the team set up 15 time-lapse cameras in the Swiss Alps.
From June to August 2021, the cameras monitored 36 flowers of red clover ( Trifolium pratense ), an important crop used as forage for livestock. Such cameras are very useful for monitoring sites that are difficult to reach daily, Alison says.
Nine of the cameras took images in a slice of the afternoon and again at night, while six of them continuously captured photos every five minutes. The technology provides substantial practical benefits.
“You can’t feasibly have someone stand there for 24 hours and record consistently what is visiting a flower,” Alison says. “Fortunately, you can do that with cameras.”
The method also allowed Alison and his colleagues to investigate nighttime visitors. In all, the team collected more than 164,000 photos of red clover flowers, with 44 of these images capturing visits by insect pollinators. Most of these nectar-seekers — some 61 percent — were bumblebees ( Bombus ). But a substantial proportion — 34 percent — were moths, mostly large yellow underwings ( Noctua pronuba ), visiting in the early morning hours. Butterflies and either a wasp or another bee species rounded out the other 5 percent of visits.
Moths are well-known as habitual pollinators of many other plants, but their role in clover pollination seems to have been overlooked, Alison says ( SN: 6/27/17 ). He and his colleagues also investigated how many seeds the clover blossoms produced, finding that nighttime visits from moths added to seed yield.
It’s clear “the role of nocturnal moths as pollinators of crops has largely been neglected,” Funamoto says. “I think future studies will reveal many plant species that are thought to be dependent on pollination by diurnal insects are indeed pollinated by nocturnal moths, to some extent.”
Alison and his team are now looking to replicate their observations at different latitudes in Europe to confirm that N. pronuba moths pollinate red clover in other places. The researchers also would like to equip cameras with artificial intelligence–driven programs that are trained to identify and swiftly categorize the type of pollinator making a visit.
“The future isn’t just cameras,” Alison says, “but cameras should be a big part of it.”
Jake Buehler is a freelance science writer, covering natural history, wildlife conservation and Earth’s splendid biodiversity, from salamanders to sequoias. He has a master’s degree in zoology from the University of Hawaii at Manoa.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
More than 2,000 people dead from extreme heat and wildfires raging in Portugal and Spain. High temperature records shattered from England to Japan. Overnights that fail to cool.
Brutal heat waves are quickly becoming the hallmark of the summer of 2022.
And even as climate change continues to crank up the temperature, scientists are working fast to understand the limits of humans’ resilience to heat extremes. Recent research suggests that heat stress tolerance in people may be lower than previously thought. If true, millions more people could be at risk of succumbing to dangerous temperatures sooner than expected.
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“Bodies are capable of acclimating over a period of time” to temperature changes, says Vivek Shandas, an environmental planning and climate adaptation researcher at Portland State University in Oregon. Over geologic time, there have been many climate shifts that humans have weathered, Shandas says. “[But] we’re in a time when these shifts are happening much more quickly.”
Just halfway through 2022, heat waves have already ravaged many countries. The heat arrived early in southern Asia: In March, Wardha, India, saw a high of 45° Celsius (113° Fahrenheit); in Nawabshah, Pakistan, recorded temperatures rose to 49.5° C (121.1° F).
Extreme heat alerts blared across Europe beginning in June and continuing through July, the rising temperatures exacerbating drought and sparking wildfires. The United Kingdom shattered its hottest-ever record July 19 when temperatures reached 40.3° C in the English village of Coningsby. The heat fueled fires in France, forcing thousands to evacuate from their homes.
And the litany goes on: June brought Japan its worst heat wave since record-keeping began in 1875, leading to the country’s highest-ever recorded temperature of 40.2° C. China’s coastal megacities, from Shanghai to Chengdu, were hammered by heat waves in July as temperatures in the region also rose above 40° C. And in the United States, a series of heat waves gripped the Midwest, the South and the West in June and July. Temperatures soared to 42° C in North Platte, Neb., and to 45.6° C in Phoenix.
The heat already is taking an increasing toll on human health. It can cause heat cramps, heat exhaustion and heat stroke, which is often fatal. Dehydration can lead to kidney and heart disease. Extreme heat can even change how we behave , increasing aggression and decreasing our ability to focus ( SN: 8/18/21 ).
On July 13, multiple heat waves seared much of Europe, Asia and North Africa, smashing temperature records. China’s Shanghai Xujiahui Observatory recorded its highest-ever temperature of 40.9° C in almost 150 years of record-keeping. Tunis, Tunisia, reached a 40-year record of 48° C. And the scorching heat fueled fires in Portugal, Spain and France.
The human body has various ways to shed excess heat and keep the core of the body at an optimal temperature of about 37° C (98.6° F). The heart pumps faster, speeding up blood flow that carries heat to the skin ( SN: 4/3/18 ). Air passing over the skin can wick away some of that heat. Evaporative cooling — sweating — also helps.
But there’s a limit to how much heat humans can endure. In 2010, scientists estimated that theoretical heat stress limit to be at a “wet bulb” temperature of 35° C . Wet bulb temperatures depend on a combination of humidity and “dry bulb” air temperature measured by a thermometer. Those variables mean a place could hit a wet bulb temperature of 35° C in different ways — for instance, if the air is that temperature and there’s 100 percent humidity, or if the air temperature is 46° C and there’s 50 percent humidity. The difference is due to evaporative cooling.
When water evaporates from the skin or another surface, it steals away energy in the form of heat, briefly cooling that surface. That means that in drier regions, the wet bulb temperature — where that ephemeral cooling effect happens readily — will be lower than the actual air temperature. In humid regions, however, wet and dry bulb temperatures are similar, because the air is so moist it’s difficult for sweat to evaporate quickly.
So when thinking about heat stress on the body, scientists use wet bulb temperatures because they are a measure of how much cooling through evaporation is possible in a given climate, says Daniel Vecellio, a climate scientist at Penn State.
“Both hot/dry and warm/humid environments can be equally dangerous,” Vecellio says — and this is where the body’s different cooling strategies come into play. In hot, dry areas, where the outside temperature may be much hotter than skin temperature, human bodies rely entirely on sweating to cool down, he says. In warm, humid areas, where the air temperature may actually be cooler than skin temperatures (but the humidity makes it seem warmer than it is), the body can’t sweat as efficiently. Instead, the cooler air passing over the skin can draw away the heat.
Given the complexity of the body’s cooling system, and the diversity of human bodies, there isn’t really a one-size-fits-all threshold temperature for heat stress for everybody. “No one’s body runs at 100 percent efficiency,” Vecellio says. Different body sizes, the ability to sweat, age and acclimation to a regional climate all have a role.
Still, for the last decade, that theoretical wet bulb 35° C number has been considered to be the point beyond which humans can no longer regulate their bodies’ temperatures. But recent laboratory-based research by Vecellio and his colleagues suggests that a general, real-world threshold for human heat stress is much lower, even for young and healthy adults.
The researchers tracked heat stress in two dozen subjects ranging in age from 18 to 34, under a variety of controlled climates. In the series of experiments, the team varied humidity and temperature conditions within an environmental chamber, sometimes holding temperature constant while varying the humidity, and sometimes vice versa.
The subjects exerted themselves within the chamber just enough to simulate minimal outdoor activity, walking on a treadmill or pedaling slowly on a bike with no resistance. During these experiments, which lasted for 1.5 to two hours, the researchers measured the subjects’ skin temperatures using wireless probes and assessed their core temperatures using a small telemetry pill that the subjects swallowed.
In warm and humid conditions, the subjects in the study were unable to tolerate heat stress at wet bulb temperatures closer to 30° or 31° C, the team estimates. In hot and dry conditions, that wet bulb temperature was even lower , ranging from 25° to 28° C, the researchers reported in the February Journal of Applied Physiology . For context, in a very dry environment at about 10 percent humidity, a wet bulb temperature of 25° C would correspond to an air temperature of about 50° C (122° F).
These results suggest that there is much more work to be done to understand what humans can endure under real-world heat and humidity conditions, but that the threshold may be much lower than thought, Vecellio says. The 2010 study’s theoretical finding of 35° C may still be “the upper limit,” he adds. “We’re showing the floor.”
And that’s for young, healthy adults doing minimal activity. Thresholds for heat stress are expected to be lower for outdoor workers required to exert themselves, or for the elderly or children. Assessing laboratory limits for more at-risk people is the subject of ongoing work for Vecellio and his colleagues.
If the human body’s tolerance for heat stress is generally lower than scientists have realized, that could mean millions more people will be at risk from the deadliest heat sooner than scientists have realized. As of 2020, there were few reports of wet bulb temperatures around the world reaching 35° C , but climate simulations project that limit could be regularly exceeded in parts of South Asia and the Middle East by the middle of the century.
Some of the deadliest heat waves in the last two decades were at lower wet bulb temperatures: Neither the 2003 European heat wave, which caused an estimated 30,000 deaths, nor the 2010 Russian heat wave, which killed over 55,000 people, exceeded wet bulb temperatures of 28° C.
How best to inform the public about heat risk is “the part that I find to be tricky,” says Shandas, who wasn’t involved in Vecellio’s research. Shandas developed the scientific protocol for the National Integrated Heat Health Information System’s Urban Heat Island mapping campaign in the United States.
It’s very useful to have this physiological data from a controlled, precise study, Shandas says, because it allows us to better understand the science behind humans’ heat stress tolerance. But physiological and environmental variability still make it difficult to know how best to apply these findings to public health messaging, such as extreme heat warnings, he says. “There are so many microconsiderations that show up when we’re talking about a body’s ability to manage [its] internal temperature.”
One of those considerations is the ability of the body to quickly acclimate to a temperature extreme. Regions that aren’t used to extreme heat may experience greater mortality, even at lower temperatures, simply because people there aren’t used to the heat. The 2021 heat wave in the Pacific Northwest wasn’t just extremely hot — it was extremely hot for that part of the world at that time of year, which makes it more difficult for the body to adapt, Shandas says ( SN: 6/29/21 ).
Heat that arrives unusually early and right on the heels of a cool period can also be more deadly, says Larry Kalkstein, a climatologist at the University of Miami and the chief heat science advisor for the Washington, D.C.–based nonprofit Adrienne Arsht-Rockefeller Foundation Resilience Center. “Often early season heat waves in May and June are more dangerous than those in August and September.”
In the 1960s, the average time between the earliest and latest heat waves that might occur in a year was just about 22 days. By the 2010s, the average heat wave season had lengthened to almost 70 days.
One way to improve communities’ resilience to the heat may be to treat heat waves like other natural disasters — including give them names and severity rankings ( SN: 8/14/20 ). As developed by an international coalition known as the Extreme Heat Resilience Alliance , those rankings form the basis for a new type of heat wave warning that explicitly considers the factors that impact heat stress, such as wet bulb temperature and acclimation, rather than just temperature extremes.
The rankings also consider factors such as cloud cover, wind and how hot the temperatures are overnight. “If it’s relatively cool overnight, there’s not as much negative health outcome,” says Kalkstein, who created the system. But overnight temperatures aren’t getting as low as they used to in many places. In the United States, for example, the average minimum temperatures at nighttime are now about 0.8° C warmer than they were during the first half of the 20th century, according to the country’s Fourth National Climate Assessment , released in 2018 ( SN: 11/28/18 ).
By naming heat waves like hurricanes, officials hope to increase citizens’ awareness of the dangers of extreme heat. Heat wave rankings could also help cities tailor their interventions to the severity of the event. Six cities are currently testing the system’s effectiveness: four in the United States and in Athens, Greece, and Seville, Spain. On July 24, with temperatures heading toward 42° C, Seville became the first city in the world to officially name a heat wave, sounding the alarm for Heat Wave Zoe.
As 2022 continues to smash temperature records around the globe, such warnings may come not a moment too soon.
Carolyn Gramling is the earth & climate writer. She has bachelor’s degrees in geology and European history and a Ph.D. in marine geochemistry from MIT and the Woods Hole Oceanographic Institution.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
Some people like drinking milk more than others, but it helps to be lactose tolerant. This genetic trait spread among ancient Europeans not because they drank a lot of milk but as a result of recurring famines and disease outbreaks, a new study suggests.
Ancient Europeans may have evolved an ability to digest milk thanks to periodic famines and disease outbreaks.
Europeans avidly tapped into milk drinking starting around 9,000 years ago , when dairying groups first reached the continent’s southeastern corner, researchers report July 27 in Nature . Yet it took several thousand years before large numbers of Europeans evolved a gene for digesting lactose, the sugar in milk, the investigators say.
These discoveries — based on animal fat residue samples from hundreds of archaeological sites and a trove of DNA data — undermine an influential idea that milk use dramatically increased as the product’s nutritional and health benefits drove the evolution of lactose tolerance, say biogeochemist Richard Evershed of the University of Bristol in England and colleagues.
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Milk drinkers who can’t digest lactose experience diarrhea, gas, bloating and intestinal cramps. Those uncomfortable reactions were too mild to move the evolutionary needle toward lactose tolerance on their own, Evershed’s group says. But during periodic famines and infectious disease outbreaks, lactose-induced diarrhea became fatal for severely malnourished individuals in farming communities, the scientists suggest. Those recurring threats hotwired the evolution of lactose tolerance, they contend.
Evershed’s report “comprehensively rules out” widespread milk consumption as the evolutionary force behind lactose tolerance, says bioarchaeologist Oliver Craig of the University of York in England. Further research needs to clarify the scale and extent of famines or infectious disease episodes that may have influenced how ancient Europeans digested milk, adds Craig, who did not participate in the new study. Investigators must also keep in mind that cheese and other low-lactose dairy products date to as early as around 7,400 years ago in Europe ( SN: 12/12/12 ). If these foods were widely available, it’s unclear why lactose intolerant Europeans would not have survived times of famine or disease, Craig says.
Evershed’s team mapped estimated frequencies of milk use across Europe from around 9,000 to 500 years ago by analyzing previously published data from animal fat residues extracted from more than 13,000 pottery fragments at about 550 archaeological sites.
At the beginning of that time span, migrating farmers introduced dairying to southeastern Europe’s Balkan Peninsula, where residents embraced regular milk drinking, the investigators say. Milk use then fluctuated over time in different parts of the continent. After about 7,500 years ago, relatively heavy milk use characterized western France, northern Europe and the British Isles. Dairying occurred less often in central Europe.
Evershed’s team also tracked the emergence and spread of the main gene responsible for lactose tolerance using published ancient DNA data from nearly 1,800 Europeans and Asians. The earliest European evidence of a gene variant in adults responsible for boosting the activity of lactase, an enzyme that confers tolerance by chemically breaking down lactose, dates to about 6,650 years ago, the researchers say. But this trait, known as lactase persistence, did not become common in Europe until around 3,000 years ago, they find.
Before that time, increasing levels of lactase persistence tended to align with population busts linked to famines in particular regions, the researchers report. Between 8,000 and 4,000 years ago, excavated farming sites across Europe display signs of periodic population declines that were influenced by severe food shortages, the researchers say ( SN: 10/1/13 ).
Estimates of settlement density, a measure of how closely together people lived, also tended to decline at times of increasing lactase persistence. The spread of animal-borne infections such as salmonella lowered settlement densities as residents unable to digest lactose suffered an excess of deaths, the scientists suspect. In those periods of malnourishment and illness, lactase persistence boosted access to badly needed nutrients in milk, Evershed’s group speculates.
But archaeologist Ron Pinhasi of the University of Vienna is not convinced the famine and disease theory holds up. Diarrhea causes death more often in malnourished children, he says, so he questions whether it would have led to enough adult fatalities to trigger the evolution of milk tolerance. No current proposal explains how lactase persistence spread, he says.
In other parts of the world, and for equally mysterious reasons, regular milk consumption doesn’t necessarily stimulate the spread of lactose tolerance. For instance, lactose tolerance rarely occurs among milk-drinking Central Asian herders but biological signs of lactose tolerance often appear in East African Hadza hunter-gatherers, who don’t drink milk.
Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
Quantum entanglement, a type of ethereal link between particles, improves the security of quantum communication, as demonstrated in three experiments (the one pictured, by researchers in France, Switzerland and England, used strontium ions in its test).
Stealthy communication just got more secure, thanks to quantum entanglement.
Quantum physics provides a way to share secret information that’s mathematically proven to be safe from the prying eyes of spies. But until now, demonstrations of the technique, called quantum key distribution, rested on an assumption: The devices used to create and measure quantum particles have to be known to be flawless. Hidden defects could allow a stealthy snoop to penetrate the security unnoticed.
Now, three teams of researchers have demonstrated the ability to perform secure quantum communication without prior confirmation that the devices are foolproof. Called device-independent quantum key distribution, the method is based on quantum entanglement, a mysterious relationship between particles that links their properties even when separated over long distances.
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In everyday communication, such as the transmission of credit card numbers over the internet, a secret code, or key, is used to garble the information, so that it can be read only by someone else with the key. But there’s a quandary: How can a distant sender and receiver share that key with one another while ensuring that no one else has intercepted it along the way?
Quantum physics provides a way to share keys by transmitting a series of quantum particles, such as particles of light called photons, and performing measurements on them. By comparing notes, the users can be sure that no one else has intercepted the key. Those secret keys , once established, can then be used to encrypt the sensitive intel ( SN: 12/13/17 ). By comparison, standard internet security rests on a relatively shaky foundation of math problems that are difficult for today’s computers to solve, which could be vulnerable to new technology, namely quantum computers ( SN: 6/29/17 ).
But quantum communication typically has a catch. “There cannot be any glitch that is unforeseen,” says quantum physicist Valerio Scarani of the National University of Singapore. For example, he says, imagine that your device is supposed to emit one photon but unknown to you, it emits two photons. Any such flaws would mean that the mathematical proof of security no longer holds up. A hacker could sniff out your secret key, even though the transmission seems secure.
Device-independent quantum key distribution can rule out such flaws. The method builds off of a quantum technique known as a Bell test, which involves measurements of entangled particles. Such tests can prove that quantum mechanics really does have “spooky” properties, namely nonlocality, the idea that measurements of one particle can be correlated with those of a distant particle. In 2015, researchers performed the first “loophole-free” Bell tests, which certified beyond a doubt that quantum physics’ counterintuitive nature is real ( SN: 12/15/15 ).
“The Bell test basically acts as a guarantee,” says Jean-Daniel Bancal of CEA Saclay in France. A faulty device would fail the test, so “we can infer that the device is working properly.”
In their study, Bancal and colleagues used entangled, electrically charged strontium atoms separated by about two meters. Measurements of those ions certified that their devices were behaving properly, and the researchers generated a secret key , the team reports in the July 28 Nature .
Typically, quantum communication is meant for long-distance dispatches. (To share a secret with someone two meters away, it would be easier to simply walk across the room.) So Scarani and colleagues studied entangled rubidium atoms 400 meters apart. The setup had what it took to produce a secret key, the researchers report in the same issue of Nature . But the team didn’t follow the process all the way through: The extra distance meant that producing a key would have taken months.
In the third study, published in the July 29 Physical Review Letters , researchers wrangled entangled photons rather than atoms or ions. Physicist Wen-Zhao Liu of the University of Science and Technology of China in Hefei and colleagues also demonstrated the capability to generate keys, at distances up to 220 meters. This is particularly challenging to do with photons, Liu says, because photons are often lost in the process of transmission and detection.
Loophole-free Bell tests are already no easy feat, and these techniques are even more challenging, says physicist Krister Shalm of the National Institute of Standards and Technology in Boulder, Colo. “The requirements for this experiment are so absurdly high that it’s just an impressive achievement to be able to demonstrate some of these capabilities,” says Shalm, who wrote a perspective in the same issue of Nature .
That means that the technique won’t see practical use anytime soon, says physicist Nicolas Gisin of the University of Geneva, who was not involved with the research.
Still, device-independent quantum key distribution is “a totally fascinating idea,” Gisin says. Bell tests were designed to answer a philosophical question about the nature of reality — whether quantum physics really is as weird as it seems. “To see that this now becomes a tool that enables something else,” he says, “this is the beauty.”
Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.
Science News was founded in 1921 as an independent, nonprofit source of accurate information on the latest news of science, medicine and technology. Today, our mission remains the same: to empower people to evaluate the news and the world around them. It is published by the Society for Science, a nonprofit 501(c)(3) membership organization dedicated to public engagement in scientific research and education.
