The original version of this story appeared in Quanta Magazine.

If you want to solve a tricky problem, it often helps to get organized. You might, for example, break the problem into pieces and tackle the easiest pieces first. But this kind of sorting has a cost. You may end up spending too much time putting the pieces in order.

This dilemma is especially relevant to one of the most iconic problems in computer science: finding the shortest path from a specific starting point in a network to every other point. It’s like a souped-up version of a problem you need to solve each time you move: learning the best route from your new home to work, the gym, and the supermarket.

“Shortest paths is a beautiful problem that anyone in the world can relate to,” said Mikkel Thorup, a computer scientist at the University of Copenhagen.

Intuitively, it should be easiest to find the shortest path to nearby destinations. So if you want to design the fastest possible algorithm for the shortest-paths problem, it seems reasonable to start by finding the closest point, then the next-closest, and so on. But to do that, you need to repeatedly figure out which point is closest. You’ll sort the points by distance as you go. There’s a fundamental speed limit for any algorithm that follows this approach: You can’t go any faster than the time it takes to sort.

Forty years ago, researchers designing shortest-paths algorithms ran up against this “sorting barrier.” Now, a team of researchers has devised a new algorithm that breaks it. It doesn’t sort, and it runs faster than any algorithm that does.

“The authors were audacious in thinking they could break this barrier,” said Robert Tarjan, a computer scientist at Princeton University. “It’s an amazing result.”

The Frontier of Knowledge

To analyze the shortest-paths problem mathematically, researchers use the language of graphs—networks of points, or nodes, connected by lines. Each link between nodes is labeled with a number called its weight, which can represent the length of that segment or the time needed to traverse it. There are usually many routes between any two nodes, and the shortest is the one whose weights add up to the smallest number. Given a graph and a specific “source” node, an algorithm’s goal is to find the shortest path to every other node.

The most famous shortest-paths algorithm, devised by the pioneering computer scientist Edsger Dijkstra in 1956, starts at the source and works outward step by step. It’s an effective approach, because knowing the shortest path to nearby nodes can help you find the shortest paths to more distant ones. But because the end result is a sorted list of shortest paths, the sorting barrier sets a fundamental limit on how fast the algorithm can run.

Australian airline Qantas said Sunday that data from 5.7 million customers stolen in a major cyberattack this year had been shared online, part of a leak affecting dozens of firms.

Disney, Google, IKEA, Toyota, McDonald’s and fellow airlines Air France and KLM are also reported to have had data stolen in a cyberattack targeting software firm Salesforce, with the information now being held to ransom.

Salesforce said this month it was “aware of recent extortion attempts by threat actors.”

Qantas confirmed in July that hackers had targeted one of its customer contact centers, breaching a computer system used by a third party now known to have been Salesforce.

They secured access to sensitive information such as customer names, email addresses, phone numbers and birthdays, the blue-chip Australian company said.

No further breaches have taken place since and the company is cooperating with Australian security services.

“Qantas is one of a number of companies globally that has had data released by cyber criminals following the airline’s cyber incident in early July, where customer data was stolen via a third party platform,” the company said in a statement.

Most of the data leaked was names, email addresses and frequent flyer details, the firm said.

But some of the data included customers’ “business or home address, date of birth, phone number, gender and meal preferences.”

“No credit card details, personal financial information or passport details were impacted,” Qantas said.

It also said it had obtained a legal injunction with the Supreme Court of New South Wales, where the firm is headquartered, to prevent the stolen data being “accessed, viewed, released, used, transmitted or published.”

Cybersecurity expert Troy Hunt told AFP that would do little to prevent the spread of the data.

“It’s frankly ridiculous,” he said.

“It obviously doesn’t stop criminals at all anywhere, and it also really doesn’t have any effect on people outside of Australia.”

Hackers ‘laying siege’

In response to questions about the leak, tech giant Google pointed AFP to an August statement in which it said one of its corporate Salesforce servers had been targeted. It did not confirm if the data had been leaked.

“Google responded to the activity, performed an impact analysis and has completed email notifications to the potentially affected businesses,” Melanie Lombardi, head of Google Cloud Security Communications, said.

Cybersecurity analysts have linked the hack to individuals with ties to an alliance of cybercriminals called Scattered Lapsus$ Hunters.

Research group Unit 42 said in a note the group had “asserted responsibility for laying siege to customer Salesforce tenants as part of a coordinated effort to steal data and hold it for ransom.”

The hackers had reportedly set an October 10 deadline for ransom payment.

‘Oldest tricks in the book’

The hackers stole the sensitive data using a social engineering technique, referring to a tactic of manipulating victims by pretending to be a company representative or other trusted person, experts said.

The FBI last month issued a warning about such attacks targeting Salesforce.

The agency said hackers posing as IT workers had tricked customer support employees into granting them access to sensitive data.

“They have been very effective,” expert Hunt said.

“And it hasn’t been using any sophisticated technical exploits… they have exploited really the oldest tricks in the books.”

The hack of data from Australia’s biggest airline comes as a string of major cyberattacks in the country has raised concerns about the protection of personal data.

Qantas apologized last year after a glitch with its mobile app exposed some passengers’ names and travel details.

And major ports handling 40% of Australia’s freight trade ground to a halt in 2023 after hackers infiltrated computers belonging to operator DP World.

© 2025 AFP

A proposed constellation of satellites has astronomers very worried. Unlike satellites that reflect sunlight and produce light pollution as an unfortunate byproduct, the ones by US startup Reflect Orbital would produce light pollution by design.

The company promises to produce “sunlight on demand” with mirrors that beam sunlight down to Earth so solar farms can operate after sunset.

It plans to start with an 18-meter test satellite named Earendil-1 which the company has applied to launch in 2026. It would eventually be followed by about 4,000 satellites in orbit by 2030, according to the latest reports.

So how bad would the light pollution be? And perhaps more importantly, can Reflect Orbital’s satellites even work as advertised?

Bouncing sunlight

In the same way you can bounce sunlight off a watch face to produce a spot of light, Reflect Orbital’s satellites would use mirrors to beam light onto a patch of Earth.

But the scale involved is vastly different. Reflect Orbital’s satellites would orbit about 625km above the ground, and would eventually have mirrors 54 meters across.

When you bounce light off your watch onto a nearby wall, the spot of light can be very bright. But if you bounce it onto a distant wall, the spot becomes larger—and dimmer.

This is because the sun is not a point of light, but spans half a degree in angle in the sky. This means that at large distances, a beam of sunlight reflected off a flat mirror spreads out with an angle of half a degree.

What does that mean in practice? Let’s take a satellite reflecting sunlight over a distance of roughly 800km—because a 625km-high satellite won’t always be directly overhead, but beaming the sunlight at an angle. The illuminated patch of ground would be at least 7km across.

Even a curved mirror or a lens can’t focus the sunlight into a tighter spot due to the distance and the half-degree angle of the sun in the sky.

Would this reflected sunlight be bright or dim? Well, for a single 54 meter satellite it will be 15,000 times fainter than the midday sun, but this is still far brighter than the full moon.

The balloon test

Last year, Reflect Orbital’s founder Ben Nowack posted a short video which summarized a test with the “last thing to build before moving into space”. It was a reflector carried on a hot air balloon.

In the test, a flat, square mirror roughly 2.5 meters across directs a beam of light down to solar panels and sensors. In one instance the team measures 516 watts of light per square meter while the balloon is at a distance of 242 meters.

For comparison, the midday sun produces roughly 1,000 watts per square meter. So 516 watts per square meter is about half of that, which is enough to be useful.

However, let’s scale the balloon test to space. As we noted earlier, if the satellites were 800km from the area of interest, the reflector would need to be 6.5km by 6.5km—42 square kilometers. It’s not practical to build such a giant reflector, so the balloon test has some limitations.

So what is Reflect Orbital planning to do?

Reflect Orbital’s plan is “simple satellites in the right constellation shining on existing solar farms”. And their goal is only 200 watts per square meter—20% of the midday sun.

Can smaller satellites deliver? If a single 54 meter satellite is 15,000 times fainter than the midday sun, you would need 3,000 of them to achieve 20% of the midday sun. That’s a lot of satellites to illuminate one region.

Another issue: satellites at a 625km altitude move at 7.5 kilometers per second. So a satellite will be within 1,000km of a given location for no more than 3.5 minutes.

This means 3,000 satellites would give you a few minutes of illumination. To provide even an hour, you’d need thousands more.

Reflect Orbital isn’t lacking ambition. In one interview, Nowack suggested 250,000 satellites in 600km high orbits. That’s more than all the currently catalogued satellites and large pieces of space junk put together.

And yet, that vast constellation would deliver only 20% of the midday sun to no more than 80 locations at once, based on our calculations above. In practice, even fewer locations would be illuminated due to cloudy weather.

Additionally, given their altitude, the satellites could only deliver illumination to most locations near dusk and dawn, when the mirrors in low Earth orbit would be bathed in sunlight. Aware of this, Reflect Orbital plan for their constellation to encircle Earth above the day-night line in sun-synchronous orbits to keep them continuously in sunlight.

Bright lights

So, are mirrored satellites a practical means to produce affordable solar power at night? Probably not. Could they produce devastating light pollution? Absolutely.

In the early evening it doesn’t take long to spot satellites and space junk—and they’re not deliberately designed to be bright. With Reflect Orbital’s plan, even if just the test satellite works as planned, it will sometimes appear far brighter than the full moon.

A constellation of such mirrors would be devastating to astronomy and dangerous to astronomers. To anyone looking through a telescope the surface of each mirror could be almost as bright as the surface of the sun, risking permanent eye damage.

The light pollution will hinder everyone’s ability to see the cosmos and light pollution is known to impact the daily rhythms of animals as well.

Although Reflect Orbital aims to illuminate specific locations, the satellites’ beams would also sweep across Earth when moving from one location to the next. The night sky could be lit up with flashes of light brighter than the moon.

The company did not reply to The Conversation about these concerns within deadline. However, it told Bloomberg this week it plans to redirect sunlight in ways that are “brief, predictable and targeted”, avoiding observatories and sharing the locations of the satellites so scientists can plan their work.

The consequences would be dire

It remains to be seen whether Reflect Orbital’s project will get off the ground. The company may launch a test satellite, but it’s a long way from that to getting 250,000 enormous mirrors constantly circling Earth to keep some solar farms ticking over for a few extra hours a day.

Still, it’s a project to watch. The consequences of success for astronomers—and anyone else who likes the night sky dark—would be dire.

This article is republished from The Conversation under a Creative Commons license. Read the original article.