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Gigantic trenches known as gullies are opening up in cities in Africa, swallowing up homes and businesses, sometimes in an instant, a study has found.

About 118,600 people, on average, in the Democratic Republic of the Congo (DRC) alone were displaced between 2004 and 2023, according to researchers reporting their findings in Nature.

Without urgent action, researchers estimate that hundreds of thousands of people across Africa are likely to be displaced within the next 10 years, including more than one-quarter of the 770,000 or so people in the DRC living in the expected expansion zone of these gullies.

“It’s an underestimated and severely under-researched hazard,” says study co-author Matthias Vanmaercke, a geographer at the Catholic University of Leuven (KU Leuven) in Belgium. It is caused by “a combination of natural and human factors,” he says, but this is “not at all unavoidable.”

Expanding gullies

Gullies are expanding across cities that are built on sandy soils and lack adequate drainage. When there are heavy rains, water accumulates on roads and rooftops. When the drainage systems are inadequate, the water finds its way into unprotected ground, carving deep holes that can stretch for hundreds of metres. Over time, the gullies swallow houses and other infrastructure, and sometimes even result in deaths.

Vanmaercke and his colleagues used satellite images taken between 2021 and 2023 to identify 2,922 urban gullies in 26 of 47 cities, covering a cumulative distance of nearly 740 kilometres. The team cross-checked these images with historical aerial photographs stored at the Royal Museum for Central Africa in Belgium and found that only 46 of the gullies were present in the 1950s. This “gave the first clear indication that this is indeed attributable to the ongoing urbanization,” Vanmaercke says.

In 99% of cases, the gullies had expanded by at least 10 square metres between 2004 and 2023. The average gully was 253 metres long and 31 metres across at its widest point, and nearly all of them were linked to the road network. “The water cannot infiltrate, and it concentrates along these roads, which basically become big canals that turn into rivers,” says Vanmaercke.

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Aaron Lauda has been exploring an area of mathematics that most physicists have seen little use for, wondering if it might have practical applications. In a twist even he didn’t expect, it turns out that this kind of math could be the key to overcoming a long-standing obstacle in quantum computing—and maybe even for understanding the quantum world in a whole new way.

Quantum computers, which harness the peculiarities of quantum physics for gains in speed and computing ability over classical machines, may one day revolutionize technology. For now, though, that dream is out of reach. One reason is that qubits, the building blocks of quantum computers, are unstable and can easily be disturbed by environmental noise. In theory, a sturdier option exists: topological qubits spread information out over a wider area than regular qubits. Yet in practice, they’ve been difficult to realize. So far, the machines that do manage to use them aren’t universal, meaning they cannot do everything full-scale quantum computers can do. “It’s like trying to type a message on a keyboard with only half the keys,” Lauda says. “Our work fills in the missing keys.” He and his group at the University of Southern California published their findings in a new paper in the journal Nature Communications.

Lauda and his colleagues solve some of the problems with topological qubits by using a class of theoretical particles they call neglectons, named for how they were derived from overlooked theoretical math. These particles could open a new pathway toward experimentally realizing universal topological quantum computers.

Unlike ordinary qubits, which store information in the state of a single particle, topological qubits store it in the arrangement of several particles—which is a global property, not a local one, making them far more robust.

Take, for example, braided hair. The type and number of braids that a person has are global properties that remain the same regardless of how they shake their head. In contrast, the position of an individual hair strand is a local property that can shift with the slightest movement.

In our three-dimensional world, swapping two particles is like weaving one string over or under the other. You can always unweave them back to their original structure. When you swap particles in two dimensions, however, you cannot go over or under; you have to make the strings go through each other, which permanently changes the structure of the strings.

Because of this property, swapping two anyons can completely transform the state of a system. These swaps can be repeated among multiple anyons—a process called anyon braiding. The final state depends on the order in which the swaps, or braids, are formed, much like the way the pattern of a braid depends on the sequence of its strands.

Because braiding anyons changes the quantum state of the qubit, the procedure can be used as a quantum gate. Just as a logical gate in a regular computer changes bits from 0 to 1 to allow computation, quantum gates manipulate qubits. This braid-based logic is the foundation of how topological quantum computers compute.

Theoretically, many types of anyons exist. One variety, called Ising anyons, “are our best chance for quantum computing in real systems,” Lauda says. “However, by themselves, they are not universal for quantum computation.”

Picture a qubit as a number on a calculator display and the quantum gates as the buttons on the calculator. A nonuniversal computer is like a calculator that only has buttons for doubling or halving. You can reach plenty of numbers—but not all of them, which limits your computing power. A universal quantum computer would be able to reach all numbers.

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The Trump administration is aggressively stoking tensions with Venezuela and its president, Nicolás Maduro, and appears to be creating conditions that could lead to a military confrontation.

A major buildup of U.S. naval forces is underway outside Venezuela’s waters as the administration has stepped up belligerent rhetoric about fighting drug cartels and labeled Mr. Maduro a terrorist-cartel leader. All that raises the question of whether the end goal is just to counter drug-smuggling boats, or a potential regime-change war.

President Trump signed a still-secret directive last month instructing the Pentagon to use military force against some Latin American drug cartels that his administration has labeled “terrorist” organizations. Around the same time, the administration declared that a Venezuelan criminal group was a terrorist organization and that Mr. Maduro was its leader, while calling his government illegitimate.

Since then, the Pentagon has been moving U.S. Navy assets, including warships, into the southern Caribbean Sea. In response, Mr. Maduro announced on Monday that he was deploying 4.5 million militiamen around his country and vowed to “defend our seas, our skies and our lands” from any incursions.
The administration has said little about its intentions. On Tuesday, the White House press secretary, Karoline Leavitt, was asked about the movements and whether the administration was considering putting forces on the ground in Venezuela. She responded by calling Mr. Maduro illegitimate and invoking his indictment, late in the first Trump administration, on U.S. drug trafficking charges.

Mr. Trump, she said, is “prepared to use every element of American power to stop drugs from flooding into our country and to bring those responsible to justice. The Maduro regime is not the legitimate government of Venezuela. It is a narco-terror cartel.”

The Pentagon declined to comment publicly about the specifics of the deployment. But Sean Parnell, the chief Pentagon spokesman, said that cartels “have engaged in historic violence and terror throughout our hemisphere — and around the globe — that has destabilized economies and internal security of countries but also flooded the United States with deadly drugs, violent criminals, and vicious gangs.”

He added that the Defense Department would “undoubtedly play an important role towards meeting the president’s objective to eliminate the ability of these cartels to threaten the territory, safety, and security of the United States and its people.”

U.S. officials said that up to three guided-missile destroyers would soon arrive in the region. The naval warships will target boats operated by drug cartels transporting fentanyl to the United States, the officials said, but have not said how they will do so.

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President Nicolás Maduro of Venezuela at a military event in January. The Trump administration has labeled him a terrorist-cartel leader. Credit…The New York Times

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