American cities are becoming more and more unfriendly to families, and new parents are fleeing for the exurbs, where housing is more affordable and public schools are better.

Axios' Erica Pandey writes: In a trend that is building its own momentum, cities are increasingly dominated by wealthy, childless residents. In the future, shifting local priorities could write kids out of urban life for good.

As the chart above shows, the share of young people under 20 years old in nearly every big city in the country has fallen over the last 4 decades. Zooming in, losing a few percentage points here and there seems minor. But taken together, it signals a major demographic shift in urban America.

"You're seeing [declining birth rates] in the most extreme form in cities. It's a window into a larger demographic trend where kids are few and far between."

Experts chalk up the exodus of families to a number of concurrent trends:

• "There's no doubt that a cluster of extraordinarily successful companies and the massive wealth that they've created has impacted housing prices," says Karen Harris, managing director of macro trends at Bain & Company. This is especially apparent in tech and finance hubs like San Francisco, New York and Boston.
• "The high cost of living makes it hard for young parents to pay for the housing and living expenses of young children of school age so they move elsewhere," Terry Clark, a sociologist at the University of Chicago, tells Axios.

The result: Cities are barbells, with young, affluent and single people on one end and wealthy empty-nesters on the other, says Richard Florida, a University of Toronto urban theorist. Urban populations are constantly rotating as families move out and make way for newly minted graduates who have disposable income to spend in bars and shops — and drive gentrification.

• Even immigrants, who used to populate cities, are moving straight to suburbs where homes are cheaper and schools are better, Florida says.

The big picture: "Historically, cities have a hard time surviving, and much less thriving, if they must constantly replenish their populations from outside," Mihm says.

• Big, vibrant hubs like San Francisco, Chicago or New York might not have difficulty luring scores of young people every year.
• But smaller cities like Hartford, Cleveland, Detroit and Rochester, which are too expensive for families and have a hard time attracting young talent, suffer.
• These four cities have seen the sharpest declines in kid population in recent years.

And if the most visible, most successful residents of cities are rich, single, young people, "schools, playgrounds and other amenities may not be funded with quite the same enthusiasm," says Mihm.

The other side: The kids haven't disappeared completely, but the families that do stay in cities are typically those that have the money to buy large homes and pay for private schools. "It's not that there aren't children in cities, it's that they're rich," says Harris. "In fact, we've seen real renewals of cities with parks and museums and green spaces, but for the rich."

According to the story out there, gig workers adore being their own bosses — setting their own hours, whom they work for and what exactly they do. But the data show something slightly different.

• It's true that gig workers love feeling they are in charge of their own life. But they also appear to want to work at least 30 hours a week, and often 40.
• And once they are settled on a place of employment, they want to work there for awhile.
• In other words, gig workers crave stability.

The big picture: "They want the stability of saying, 'I'll be at this place for a couple of weeks to several months.' But they also want the stability of choosing where they will be working," says Gino Rooney, co-founder of BlueCrew, a platform that connects gig workers and employers.

• Rooney's company signs up gig clients as formal employees of BlueCrew, which handles their pay and guarantees them health benefits, overtime and workman's comp.
• 75% of BlueCrew's clients are looking for more than 30 hours a week of work, and half want 40 hours.
• Consumer pressure will drive gig-centered companies like Uber and staffing platforms and websites to increasingly provide these services for workers, Rooney tells Axios.

The bottom line: "Businesses will have to be more adaptable to how consumers want things," he said. "And they are creating immense pressure to get things immediately. You need to have on-demand labor for business peaks."

After a post last week on the potential for a new quantum internet, we received a note from Jacob Epstein, a quantum information experimentalist at The Johns Hopkins University Applied Physics Laboratory.

Epstein was responding to this section of our story:

• Data won't travel across the 30-mile distance.
• Instead, quantum mechanics will teleport it instantaneously, with two particles linked despite being located in different places — a property known as quantum entanglement.
• When they are entangled, whatever happens to one particle happens to the other, even when they are separated by many miles.

Epstein wrote:

This is incorrect. Data will still travel across a quantum network (This is the point of a network!). Instead of classical data being sent across the network, however, it will be quantum data. I.E., instead of 1's and 0's, we are sending points on a sphere. (This is for the 1 qubit case. Geometric analogies fall apart as we get to more qubits/higher dimensions.). 

Additionally, there is no instantaneous transport of information! This would violate the "speed limit" of the speed of light imposed by Einstein's theory of relativity, one of the foundational statements of modern physics.

Though quantum entanglement produces perfectly correlated results between entangled qubits across large distances, we have no way of controlling what those results are. It is only after the fact that we can observe the effect.

If we are clever, we can use that observation to determine if we are using a comprised communication channel.

Note that we have corrected the post.

A bond surprise for Puerto Rico (Felix Salmon — Axios)

Digitally preserved actors (Erin Winick — MIT Tech Review)

The shipwreck from the time of the Odyssey (Stephanie Pappas — WP)

The map transforms before our eyes (Nicola Jones — Yale Environment 360)

Apple stores are struggling in China (Wayne Ma — The Information)

Fast-food joints and coffee shops have long served as sanctuaries for homeless people to escape winter winds and wash up, with some managers kicking them out and others looking the other way for a while. Now, some libraries are making it a policy to help.

Erica reports: As a service, more than 30 libraries in big U.S. cities and suburbs are employing full-time staffers who can help those in need find housing, jobs and health care, reports the Chicago Tribune.

The first city to introduce a full-time social worker in its library was San Francisco. Since 2009, Leah Esguerra has helped more than 120 people find permanent housing, per the Tribune. The San Francisco Public Library has also hired a number of its homeless patrons.

• There are approximately 554,000 homeless people in the U.S., according to government estimates.
• Justine Janis, who works with Chicago's public libraries, told the Tribune that among the people she has helped are a homeless immigrant who needed medical attention for an infection and an elderly woman who fled her rat-infested home for a new apartment.