Three months ago, no one knew that SARS-CoV-2 existed. Now the virus has spread to almost every country, infecting at least 446,000 people whom we know about, and many more whom we do not. It has crashed economies and broken health-care systems, filled hospitals and emptied public spaces. It has separated people from their workplaces and their friends. It has disrupted modern society on a scale that most living people have never witnessed. Soon, most everyone in the United States will know someone who has been infected. Like World War II or the 9/11 attacks, this pandemic has already imprinted itself upon the nation’s psyche.

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A global pandemic of this scale was inevitable. In recent years, hundreds of health experts have written books, white papers, and op-eds warning of the possibility. Bill Gates has been telling anyone who would listen, including the 18 million viewers of his TED Talk. In 2018, I wrote a story for The Atlantic arguing that America was not ready for the pandemic that would eventually come. In October, the Johns Hopkins Center for Health Security war-gamed what might happen if a new coronavirus swept the globe. And then one did. Hypotheticals became reality. “What if?” became “Now what?”

In a matter of weeks, the coronavirus has gone from a novel, distant threat to an enemy besieging cities and towns across the world. The burden of COVID-19 and the economic upheaval wrought by the measures to contain it feel epochal. Humanity now has a common foe, and we will grow increasingly familiar with its face.

Yet plenty of this virus’s aspects remain unknown. The developing wisdom—earned the hard way in Wuhan, Washington, and Italy—has been that older people and sicker people are substantially more likely to suffer severe illness or die from COVID-19 than their younger, healthier counterparts. Older people are much more likely than young people to have lung disease, kidney disease, hypertension, or heart disease, and those conditions are more likely to transform a coronavirus infection into something nastier. But what happens when these assumptions don’t hold up, and the young people battling the pandemic share the same risks?

Updated at 10:06 a.m. ET on April 3, 2020.

As the coronavirus pandemic continues, many people are now overthinking things they never used to think about at all. Can you go outside? What if you’re walking downwind of another person? What if you’re stuck waiting at a crosswalk and someone is there? What if you’re going for a run, and another runner is heading toward you, and the sidewalk is narrow? Suddenly, daily mundanities seem to demand strategy.

Much of this confusion stems from the shifting conversation around the pandemic. Thus far, the official line has been that the new coronavirus, SARS-CoV-2, could be transmitted only through close contact with infected people or contaminated surfaces. But recently, news reports have suggested that the coronavirus can spread through the air. After 60 choir members in Washington State rehearsed together, 45 fell sick, even though no one seemed symptomatic at the time. Now people who were already feeling cooped up are worrying about going outside. Many state guidelines are ambiguous, and medical advice can muddy matters further. When the writer Deborah Copaken came down with COVID-19 symptoms, her doctor chided her for riding her bike through New York City a week earlier. Going outside in the city wasn’t safe, the physician implied, with “viral load everywhere.”

At this stage in the COVID-19 pandemic, uncertainty prevails. The greatest error that geopolitical analysts can make may be believing that the crisis will be over in three to four months, as the world’s leaders have been implying. As documented in The Atlantic and elsewhere, public-health experts make a compelling case that COVID-19 could be with us in one way or another until a vaccine comes on the market or herd immunity is achieved—either of which could take 12 to 18 months, unless we get lucky with a cure or an effective treatment before then. A long crisis, which is more likely than not, could stretch the international order to its breaking point. Even after a vaccine is available, life will not go back to normal. COVID-19 was not a black swan and will not be the last pandemic. A nervous world will be permanently changed.

Donald Trump’s exchanges with Democratic politicians usually go something like this: He picks a petty fight, almost always lobbing a tweet with a low-grade schoolyard taunt. The politician he targeted makes some bland statement about not engaging, but slips in a few passive-aggressive comments to needle him back. Political reporters lap it up.

That’s what’s been playing out between Trump and Michigan Governor Gretchen Whitmer over the past week.

Except this time is different, Whitmer says. This time, Trump’s routine is going to lead to Americans dying.

While Trump is taking shots at her from the White House, Whitmer told me, “more people are going to get sick and more lives are going to be lost because we don’t have enough testing, because we don’t have enough [personal protective equipment], because there aren’t enough ventilators, because the national stockpile, I understand, is getting close to being depleted. And we’re not even close to meeting the needs of people that are already sick, and more and more are going to get sick.” This isn’t a normal political fight, she said. “There’s going to be a horrible cost.”

From inside her living room in London, Paula Koelemeijer can feel the world around her growing quieter.

Koelemeijer, a seismologist, has a miniature seismometer sitting on a concrete slab at the base of her first-floor fireplace. The apparatus, though smaller than a box of tissues, can sense all kinds of movement, from the rattle of trains on the tracks near Koelemeijer’s home to the waves of earthquakes rolling in from afar. Since the United Kingdom announced stricter social-distancing rules last month, telling residents not to leave their home except for essential reasons, the seismometer has registered a sharp decrease in the vibrations produced by human activity.

With fewer trains, buses, and people pounding the pavement, the usual hum of public life has vanished, and so has its dependable rhythms: Before the spread of COVID-19 shut down the city, Koelemeijer could plot the seismometer’s data and see the train schedule reflected in the spikes, down to the minute. Now, with fewer trains running, the spikes seem to come at random.

In the emergency-department waiting room, 150 people worry about a fever. Some just want a test, others badly need medical treatment. Those not at the brink of death have to wait six, eight, 10 hours before they can see a doctor. Those admitted to the hospital might wait a full day for a bed.

I am an emergency-medicine doctor who practices in both Manhattan and Queens; at the moment, I’m in Queens. Normally, I love coming to work here, even though in the best of times, my co-residents and I take care of one of New York City’s most vulnerable, underinsured patient populations. Many have underlying illnesses and a language barrier, and lack primary care.

For his entire adult life, and for his entire presidency, Donald Trump has created his own alternate reality, complete with his own alternate set of facts. He has shown himself to be erratic, impulsive, narcissistic, vindictive, cruel, mendacious, and devoid of empathy. None of that is new.

But we’re now entering the most dangerous phase of the Trump presidency. The pain and hardship that the United States is only beginning to experience stem from a crisis that the president is utterly unsuited to deal with, either intellectually or temperamentally. When things were going relatively well, the nation could more easily absorb the costs of Trump’s psychological and moral distortions and disfigurements. But those days are behind us. The coronavirus pandemic has created the conditions that can catalyze a destructive set of responses from an individual with Trump’s characterological defects and disordered personality.

Get your battle rhythm, I keep telling myself, as I put on my oversize sweatpants for the third day in a row. Staying inside, away from our offices, routines, and community, feels jarring even for those who, on a rational level, understand the need for extreme social distancing. The good side is having more family time. But everything seems upended, even to homeland-security professionals who argued for upending everything to slow the spread of COVID-19.

Just as seasickness abates once you can see the shore, the disruptions that the country is now experiencing would be easier to manage if we knew they would end soon. The community-isolation effort happened remarkably fast—within days, whole communities all but closed down, and earlier this week the federal government finally recommended the same. On Thursday, Governor Gavin Newsom ordered the entire state of California to stay home “until further notice.” But the way the crisis ends will be far more muddled. There isn’t going to be one all-clear signal—and certainly not one anytime soon.

The Trump administration has just released the model for the trajectory of the COVID-19 pandemic in America. We can expect a lot of back-and-forth about whether its mortality estimates are too high or low. And its wide range of possible outcomes is certainly confusing: What’s the right number? The answer is both difficult and simple. Here’s the difficult part: There is no right answer. But here’s the simple part: Right answers are not what epidemiological models are for.

Epidemiologists routinely turn to models to predict the progression of an infectious disease. Fighting public suspicion of these models is as old as modern epidemiology, which traces its origins back to John Snow’s famous cholera maps in 1854. Those maps proved, for the first time, that London’s terrible affliction was spreading through crystal-clear fresh water that came out of pumps, not the city’s foul-smelling air. Many people didn’t believe Snow, because they lived in a world without a clear understanding of germ theory and only the most rudimentary microscopes.