The walls of the Central Intelligence Agency’s original headquarters, in Langley, Virginia, contain more than thirty miles of four-inch steel tubing. The tubes were installed in the early nineteen-sixties, as part of an elaborate, vacuum-powered intra-office mail system. Messages, sealed in fibreglass containers, rocketed at thirty feet a second among approximately a hundred and fifty stations spread over eight floors. Senders specified each capsule’s destination by manipulating brass rings at its base; electro-mechanical widgets in the tubes read those settings and routed each capsule toward its destination. At its peak, the system delivered seventy-five hundred messages each day.

According to oral histories maintained by the C.I.A., employees were saddened when, in the late nineteen-eighties, during an expansion of the headquarters, this steampunk mail system was shut down. Some of them reminisced about the comforting thunk, thunk of the capsules arriving at a station; others worried that internal office communication would become unacceptably slow, or that runners would wear themselves out delivering messages on foot. The agency’s archives contain a photograph of a pin that reads “Save the Tubes.”

The C.I.A.’s tube system is a defining example of one of the major technological movements of the twentieth century: the push to create what communication specialists call “asynchronous messaging” in the workplace. An interaction is said to be synchronous when all parties participate at the same time, while standing in the same room, perhaps, or by telephone. Asynchronous communication, by contrast, doesn’t require the receiver to be present when a message is sent. I can send a message to you whenever I want; you answer it at your leisure.

For much of workplace history, collaboration among colleagues was synchronous by default. From Renaissance workshops to the nineteenth-century rooms occupied by Charles Dickens’s Bob Cratchit and Herman Melville’s Bartleby, an office was usually a single space where a few people toiled. Though letter-writing—an asynchronous style of communication—had been a part of commerce for centuries, it was too slow for day-to-day collaboration. For most office work, synchrony ruled.

This status quo was upended by the rise of a new work setting: the large office. In the book “Cubed: A Secret History of the Workplace,” the critic and New Yorker contributor Nikil Saval writes that this shift took place between 1860, when the U.S. Census counted around seven hundred and fifty thousand people who worked in “professional service,” and 1920, by which time that number had increased to more than four million—a period, Saval writes, in which “business became big business.” The small counting house gave way to edifices such as the Larkin Building, designed in 1903, by Frank Lloyd Wright, which housed eighteen hundred employees, spread over five floors and a basement, and was anchored by a cavernous, light-bathed central atrium. The introduction of office telephone exchanges, in the early twentieth century, helped make such spaces more functional. But coördinating telephone conversations required drawn-out games of secretarial phone tag.

As message slips piled up on office desks, what seemed to be missing was a system of practical asynchronous messaging: a way for me to send you a message when it was convenient for me, and for you to read that message when it was convenient for you, all at speeds less sluggish than that of intra-office mail. If such a system could be built, managers thought, then efficient non-real-time collaboration would become possible: no more missed-call slips, no more waiting for the mail cart. In the emerging age of large offices, practical asynchrony seemed like a productivity silver bullet. This belief motivated investment in projects such as the C.I.A.’s pneumatic-tube network.

Other large office buildings also experimented with pneumatic solutions. But the expense and complexity of these systems rendered them essentially impractical. Then, in the nineteen-eighties, a far more convenient technology arrived, in the form of desktop computers connected through digital networks. As these networks spread, e-mail emerged as the killer app for bringing asynchronous communication to the office. To better understand this shift, I talked to Gloria Mark, a professor at the University of California, Irvine, who studies the impact that computer technology has had on the workplace. “I can show it to you,” she told me, when I asked about the spread of e-mail. She showed me a data table she had constructed, which summarized the results of office-time-use studies from 1965 to 2006. The studies can be divided into two groups: before e-mail and after. In the studies conducted before e-mail, workers spent around forty per cent of their time in “scheduled meetings,” and twenty per cent engaged in “desk work.” In those conducted after e-mail, the percentages are swapped.

With the arrival of practical asynchronous communication, people replaced a significant portion of the interaction that used to unfold in person with on-demand digital messaging, and they haven’t looked back. The Radicati Group, a technology-research firm, now estimates that more than a hundred and twenty-eight billion business e-mails will be sent and received daily in 2019, with the average business user dealing with a hundred and twenty-six messages a day. The domination of asynchronous communication over synchronous collaboration has been so complete that some developers of digital-collaboration tools mock the fact that we ever relied on anything so primitive as in-person meetings. In a blog post called “Asynchronous Communication Is the Future of Work,” the technology marketer Blake Thorne compares synchronous communication to the fax machine: it’s a relic, he writes, that will “puzzle your grandkids” when they look back on how people once worked.

As e-mail was taking over the modern office, researchers in the theory of distributed systems—the subfield in which, as a computer scientist, I specialize—were also studying the trade-offs between synchrony and asynchrony. As it happens, the conclusion they reached was exactly the opposite of the prevailing consensus. They became convinced that synchrony was superior and that spreading communication out over time hindered work rather than enabling it.

The synchrony-versus-asynchrony issue is fundamental to the history of computer science. For the first couple of decades of the digital revolution, programs were designed to run on individual machines. Later, with the development of computer networks, programs were written to be deployed on multiple machines that operated together over a network. Many of these early distributed systems, as they came to be known, were asynchronous by default. In such a system, Machine A could send a message to Machine B, hoping that it would eventually be delivered and processed, but Machine A couldn’t know for sure how long that would take. (If the network was slow, or if Machine B’s processor was busy with other tasks, or if Machine B crashed, it might take a while—or it might not happen at all.) An obvious solution was to engineer synchronous distributed systems. In such a system, communication would be closer to real time, with messages being passed back and forth within tight and predictable time frames. Machines could work together in rounds, with all the loose ends tied up before each round ended.

A few synchronous distributed systems were built in the nineteen-seventies and -eighties. NASA, for example, developed a computerized aircraft-control system, which relied on multiple computer processors to operate the aircraft’s control surfaces. The system was designed so that, if one processor failed in the extreme conditions of high-altitude flight, the system as a whole could keep functioning—preventing a crash from causing a crash. To simplify the task of writing software that safely implemented this sort of fault tolerance, the processors were connected on a custom timing circuit that kept their operations synchronized to within around fifty microseconds. But these synchronous systems were often costly to build. They required either custom hardware or special software that could precisely organize the processors’ activity. As in the world of workplace communication, synchrony was a more convenient way to communicate, once it was arranged, but arranging it required effort.

It was in the nineteen-eighties that business thinkers and computer scientists began to diverge in their thinking. People in office settings fixated on the organizational overhead required to organize synchronous collaboration. They believed that eliminating this overhead through asynchronous systems would make collaboration more efficient. Computer scientists, meanwhile, came to the opposite conclusion. Investigating asynchronous communication using a mathematical approach known as algorithm theory, they discovered that spreading out communication with unpredictable delays introduced new complexities that were difficult to reduce. While the business world came to see synchrony as an obstacle to overcome, theorists began to realize that it was fundamental for effective collaboration.