Supercooled water is two of a kind, a new study shows.

Scientists have long suspected that water at subfreezing temperatures comes in two distinct varieties: a high-density liquid that appears at very high pressures and a low-density liquid at lower pressures. Now, ultrafast measurements have caught water morphing from one type of liquid to the other, confirming that hunch. The discovery, reported in the Nov. 20 Science, could help explain some of water’s quirks.

The experiment “adds more and more evidence to the idea that water really is two components … and that that is the reason that underlies why water is so weird,” says physicist Greg Kimmel of Pacific Northwest National Laboratory in Richland, Wash., who was not involved in the study.

When free from impurities, water can remain liquid below its typical freezing point of zero degrees Celsius, forming what’s called a supercooled liquid. But the dual nature of supercooled water was expected to appear in a temperature realm so difficult to study that it’s been dubbed “no-man’s-land.” Below around –40° C, water remains liquid for mere instants before it crystallizes into ice. Making the task even more daunting, the high-density phase appears only at very high pressures. Still, “people have dreamt about how to do an experiment,” says Anders Nilsson of Stockholm University.
Thanks to speedy experimental maneuvers, Nilsson and colleagues have infiltrated that no-man’s-land by monitoring water’s properties on a scale of nanoseconds. “This is one of the major accomplishments of this paper,” says computational chemist Gül Zerze of Princeton University. “I’m impressed with their work.”

The scientists started by creating a type of high-density ice. Then, a pulse from an infrared laser heated the ice, forming liquid water under high pressure. That water then expanded, and the pressure rapidly dropped. Meanwhile, the researchers used an X-ray laser to investigate how the structure of the water changed, based on how the X-rays scattered. As the pressure decreased, the water transitioned from a high-density to low-density fluid before crystallizing into ice.

Previous studies have used ultrafast techniques to find hints of water’s two-faced demeanor, but those have been done mainly at atmospheric pressure (SN: 9/28/20). In the new work, the water was observed at about 3,000 times atmospheric pressure and –68° C. “It’s the first time we have real experimental data at these pressures and temperatures,” says physicist Loni Kringle of Pacific Northwest National Laboratory, who was not involved with the experiment.

The result could indicate that supercooled water has a “critical point” — a certain pressure and temperature at which two distinct phases merge into one. In the future, Nilsson hopes to pinpoint that spot.

Such a critical point could explain why water is an oddball liquid. For most liquids, cooling makes them become denser and more difficult to compress. Water gets denser as it is cooled to 4° C, but becomes less dense as it is cooled further. Likewise, its compressibility increases as it’s cooled.

If supercooled water has a critical point, that could indicate that the water experienced in daily life is strange because, under typical pressures and temperatures, it is a supercritical liquid — a weird state that occurs beyond a critical point. Such a liquid would not be the high-density or low-density form, but would consist of some regions with a high-density arrangement of water molecules and other pockets of low density. The relative amounts of those two structures, which result from different arrangements of hydrogen bonds between the molecules, would change as the temperature changes, explaining why water behaves strangely as it is cooled.

So despite the fact that the experiment involved extreme pressures and temperatures, Nilsson says, “it influences water in our ordinary life.”

2022 was the year many people decided the coronavirus pandemic had ended.

President Joe Biden said as much in an interview with 60 Minutes in September. “The pandemic is over,” he said while strolling around the Detroit Auto Show. “We still have a problem with COVID. We’re still doing a lot of work on it. But the pandemic is over.”

His evidence? “No one’s wearing masks. Everybody seems to be in pretty good shape.”

But the week Biden’s remarks aired, about 360 people were still dying each day from COVID-19 in the United States. Globally, about 10,000 deaths were recorded every week. That’s “10,000 too many, when most of these deaths could be prevented,” the World Health Organization Director-General Tedros Adhanom Ghebreyesus said in a news briefing at the time. Then, of course, there are the millions who are still dealing with lingering symptoms long after an infection.
Those staggering numbers have stopped alarming people, maybe because those stats came on the heels of two years of mind-boggling death counts (SN Online: 5/18/22). Indifference to the mounting death toll may reflect pandemic fatigue that settled deep within the public psyche, leaving many feeling over and done with safety precautions.

“We didn’t warn people about fatigue,” says Theresa Chapple-McGruder, an epidemiologist in the Chicago area. “We didn’t warn people about the fact that pandemics can last long and that we still need people to be willing to care about yourselves, your neighbors, your community.”

Public health agencies around the world, including in Singapore and the United Kingdom, reinforced the idea that we could “return to normal” by learning to “live with COVID.” The U.S. Centers for Disease Control and Prevention’s guidelines raised the threshold for case counts that would trigger masking (SN Online: 3/3/22). The agency also shortened suggested isolation times for infected people to five days, even though most people still test positive for the virus and are potentially infectious to others for several days longer (SN Online: 8/19/22).

The shifting guidelines bred confusion and put the onus for deciding when to mask, test and stay home on individuals. In essence, the strategy shifted from public health — protecting your community — to individual health — protecting yourself.
Doing your part can be exhausting, says Eric Kennedy, a sociologist specializing in disaster management at York University in Toronto. “Public health is saying, ‘Hey, you have to make the right choices every single moment of your life.’ Of course, people are going to get tired with that.”

Doing the right thing — from getting vaccinated to wearing masks indoors — didn’t always feel like it paid off on a personal level. As good as the vaccines are at keeping people from becoming severely ill or dying of COVID-19, they were not as effective at protecting against infection. This year, many people who tried hard to make safe choices and had avoided COVID-19 got infected by wily omicron variants (SN Online: 4/22/22). People sometimes got reinfected — some more than once (SN: 7/16/22 & 7/30/22, p. 8).
Those infections may have contributed to a sense of futility. “Like, ‘I did my best. And even with all of that work, I still got it. So why should I try?’ ” says Kennedy, head of a Canadian project monitoring the sociological effects of the COVID-19 pandemic.

Getting vaccinated, masking and getting drugs or antibody treatments can reduce the severity of infection and may cut the chances of infecting others. “We should have been talking about this as a community health issue and not a personal health issue,” Chapple-McGruder says. “We also don’t talk about the fact that our uptake [of these tools] is nowhere near what we need” to avoid the hundreds of daily deaths.

A lack of data about how widely the coronavirus is still circulating makes it difficult to say whether the pandemic is ending. In the United States, the influx of home tests was “a blessing and a curse,” says Beth Blauer, data lead for the Johns Hopkins University Coronavirus Resource Center. The tests gave an instant readout that told people whether they were infected and should isolate. But because those results were rarely reported to public health officials, true numbers of cases became difficult to gauge, creating a big data gap (SN Online: 5/27/22).
The flow of COVID-19 data from many state and local agencies also slowed to a trickle. In October, even the CDC began reporting cases and deaths weekly instead of daily. Altogether, undercounting of the coronavirus’s reach became worse than ever.

“We’re being told, ‘it’s up to you now to decide what to do,’ ” Blauer says, “but the data is not in place to be able to inform real-time decision making.”

With COVID-19 fatigue so widespread, businesses, governments and other institutions have to find ways to step up and do their part, Kennedy says. For instance, requiring better ventilation and filtration in public buildings could clean up indoor air and reduce the chance of spreading many respiratory infections, along with COVID-19. That’s a behind-the-scenes intervention that individuals don’t have to waste mental energy worrying about, he says.

The bottom line: People may have stopped worrying about COVID-19, but the virus isn’t done with us yet. “We have spent two-and-a-half years in a long, dark tunnel, and we are just beginning to glimpse the light at the end of that tunnel. But it is still a long way off,” WHO’s Tedros said. “The tunnel is still dark, with many obstacles that could trip us up if we don’t take care.” If the virus makes a resurgence, will we see it coming and will we have the energy to combat it again?

A group at the National Bureau of Standards at B­oulder, Colo., now reports an extremely accurate [speed of light] measurement using the wavelength and frequency of a helium-neon laser.… The result gives the speed of light as 299,792.4562 kilometers per second.

Update
That 1972 experiment measured the two-way speed of light, or the average speed of photons that traveled from their source to a reflective surface and back. The result, which still holds up, helped scientists redefine the standard length of the meter (SN: 10/22/83, p. 263). But they weren’t done putting light through its paces. In the late 1990s and early 2000s, photons set a record for slowest measured speed of light at 17 meters per second and froze in their tracks for one-thousandth of a second (SN: 1/27/01, p. 52). For all that success, one major hurdle remains: directly testing the one-way speed of light. The measurement, which many scientists say is impossible to make, could resolve the long-standing question of whether the speed of light is uniform in all directions.