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A solid electrolyte gives lithium-sulfur batteries ludicrous endurance

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Sulfur can store a lot more lithium but is problematically reactive in batteries.

If you weren’t aware, sulfur is pretty abundant. Credit: P_Wei

Lithium may be the key component in most modern batteries, but it doesn’t make up the bulk of the material used in them. Instead, much of the material is in the electrodes, where the lithium gets stored when the battery isn’t charging or discharging. So one way to make lighter and more compact lithium-ion batteries is to find electrode materials that can store more lithium. That’s one of the reasons that recent generations of batteries are starting to incorporate silicon into the electrode materials.

There are materials that can store even more lithium than silicon; a notable example is sulfur. But sulfur has a tendency to react with itself, producing ions that can float off into the electrolyte. Plus, like any electrode material, it tends to expand in proportion to the amount of lithium that gets stored, which can create physical strains on the battery’s structure. So while it has been easy to make lithium-sulfur batteries, their performance has tended to degrade rapidly.

But this week, researchers described a lithium-sulfur battery that still has over 80 percent of its original capacity after 25,000 charge/discharge cycles. All it took was a solid electrolyte that was more reactive than the sulfur itself.

When lithium meets sulfur…

Sulfur is an attractive battery material. It’s abundant and cheap, and sulfur atoms are relatively lightweight compared to many of the other materials used in battery electrodes. Sodium-sulfur batteries, which rely on two very cheap raw materials, have already been developed, although they only work at temperatures high enough to melt both of these components. Lithium-sulfur batteries, by contrast, could operate more or less the same way that current lithium-ion batteries do.

With a few major exceptions, that is. One is that the elemental sulfur used as an electrode is a very poor conductor of electricity, so it has to be dispersed within a mesh of conductive material. (You can contrast that with graphite, which both stores lithium and conducts electricity relatively well, thanks to being composed of countless sheets of graphene.) Lithium is stored there as Li2S, which occupies substantially more space than the elemental sulfur it’s replacing.

Both of these issues, however, can be solved with careful engineering of the battery’s structure. A more severe problem comes from the properties of the lithium-sulfur reactions that occur at the electrode. Elemental sulfur exists as an eight-atom ring, and the reactions with lithium are slow enough that semi-stable intermediates with smaller chains of sulfur end up forming. Unfortunately, these tend to be soluble in most electrolytes, allowing them to travel to the opposite electrode and participate in chemical reactions there.

This process essentially discharges the battery without allowing the electrons to be put to use. And it gradually leaves the electrode’s sulfur unavailable for participating in future charge/discharge cycles. The net result is that early generations of the technology would discharge themselves while sitting unused and would only survive a few hundred cycles before performance decayed dramatically.

But there has been progress on all these fronts, and some lithium-sulfur batteries with performance similar to lithium-ion have been demonstrated. Late last year, a company announced that it had lined up the money needed to build the first large-scale lithium-sulfur battery factory. Still, work on improvements has continued, and the new work seems to suggest ways to boost performance well beyond lithium-ion.

The need for speed

The paper describing the new developments, done by a collaboration between Chinese and German researchers, focuses on one aspect of the challenges posed by lithium-sulfur batteries: the relatively slow chemical reaction between lithium ions and elemental sulfur. It presents that aspect as a roadblock to fast charging, something that will be an issue for automotive applications. But at the same time, finding a way to limit the formation of inactive intermediate products during this reaction goes to the root of the relatively short usable life span of lithium-sulfur batteries.

As it turns out, the researchers found two.

One of the problems with the lithium-sulfur reaction intermediates is that they dissolve in most electrolytes. But that’s not a problem if the electrolyte isn’t a liquid. Solid electrolytes are materials that have a porous structure at the atomic level, with the environment inside the pores being favorable for ions. This allows ions to diffuse through the solid. If there’s a way to trap ions on one side of the electrolyte, such as a chemical reaction that traps or de-ionizes them, then it can enable one-way travel.

Critically, pores that favor the transit of lithium ions, which are quite compact, aren’t likely to allow the transit of the large ionized chains of sulfur. So a solid electrolyte should help cut down on the problems faced by lithium-sulfur batteries. But it won’t necessarily help with fast charging.

The researchers began by testing a glass formed from a mixture of boron, sulfur, and lithium (B2S3 and Li2S). But this glass had terrible conductivity, so they started experimenting with related glasses and settled on a combination that substituted in some phosphorus and iodine.

The iodine turned out to be a critical component. While the exchange of electrons with sulfur is relatively slow, iodine undergoes electron exchange (technically termed a redox reaction) extremely quickly. So it can act as an intermediate in the transfer of electrons to sulfur, speeding up the reactions that occur at the electrode. In addition, iodine has relatively low melting and boiling points, and the researchers suggest there’s some evidence that it moves around within the electrolyte, allowing it to act as an electron shuttle.

Successes and caveats

The result is a far superior electrolyte—and one that enables fast charging. It’s typical that fast charging cuts into the total capacity that can be stored in a battery. But when charged at an extraordinarily fast rate (50C, meaning a full charge in just over a minute), a battery based on this system still had half the capacity of a battery charged 25 times more slowly (2C, or a half-hour to full charge).

But the striking thing was how durable the resulting battery was. Even at an intermediate charging rate (5C), it still had over 80 percent of its initial capacity after over 25,000 charge/discharge cycles. By contrast, lithium-ion batteries tend to hit that level of decay after about 1,000 cycles. If that sort of performance is possible in a mass-produced battery, it’s only a slight exaggeration to say it can radically alter our relationships with many battery-powered devices.

What’s not at all clear, however, is whether this takes full advantage of one of the original promises of lithium-sulfur batteries: more charge in a given weight and volume. The researchers specify the battery being used for testing; one electrode is an indium/lithium metal foil, and the other is a mix of carbon, sulfur, and the glass electrolyte. A layer of the electrolyte sits between them. But when giving numbers for the storage capacity per weight, only the weight of the sulfur is mentioned.

Still, even if weight issues would preclude this from being stuffed into a car or cell phone, there are plenty of storage applications that would benefit from something that doesn’t wear out even with 65 years of daily cycling.

Nature, 2025. DOI: 10.1038/s41586-024-08298-9  (About DOIs).

Photo of John Timmer

John is Ars Technica’s science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.

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Here’s what NASA would like to see SpaceX accomplish with Starship this year

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Iterate, iterate, and iterate some more

The seventh test flight of Starship is scheduled for launch Thursday afternoon.

SpaceX’s upgraded Starship rocket stands on its launch pad at Starbase, Texas. Credit: SpaceX

SpaceX plans to launch the seventh full-scale test flight of its massive Super Heavy booster and Starship rocket Thursday afternoon. It’s the first of what might be a dozen or more demonstration flights this year as SpaceX tries new things with the most powerful rocket ever built.

There are many things on SpaceX’s Starship to-do list in 2025. They include debuting an upgraded, larger Starship, known as Version 2 or Block 2, on the test flight preparing to launch Thursday. The one-hour launch window opens at 5 pm EST (4 pm CST; 22: 00 UTC) at SpaceX’s launch base in South Texas. You can watch SpaceX’s live webcast of the flight here.

SpaceX will again attempt to catch the rocket’s Super Heavy booster—more than 20 stories tall and wider than a jumbo jet—back at the launch pad using mechanical arms, or “chopsticks,” mounted to the launch tower. Read more about the Starship Block 2 upgrades in our story from last week.

You might think of next week’s Starship test flight as an apéritif before the entrées to come. Ars recently spoke with Lisa Watson-Morgan, the NASA engineer overseeing the agency’s contract with SpaceX to develop a modified version of Starship to land astronauts on the Moon. NASA has contracts with SpaceX worth more than $4 billion to develop and fly two Starship human landing missions under the umbrella of the agency’s Artemis program to return humans to the Moon.

We are publishing the entire interview with Watson-Morgan below, but first, let’s assess what SpaceX might accomplish with Starship this year.

There are many things to watch for on this test flight, including the deployment of 10 satellite simulators to test the ship’s payload accommodations and the performance of a beefed-up heat shield as the vehicle blazes through the atmosphere for reentry and splashdown in the Indian Ocean.

If this all works, SpaceX may try to launch a ship into low-Earth orbit on the eighth flight, expected to launch in the next couple of months. All of the Starship test flights to date have intentionally flown on suborbital trajectories, bringing the ship back toward reentry over the sea northwest of Australia after traveling halfway around the world.

Then, there’s an even bigger version of Starship called Block 3 that could begin flying before the end of the year. This version of the ship is the one that SpaceX will use to start experimenting with in-orbit refueling, according to Watson-Morgan.

In order to test refueling, two Starships will dock together in orbit, allowing one vehicle to transfer super-cold methane and liquid oxygen into the other. Nothing like this on this scale has ever been attempted before. Future Starship missions to the Moon and Mars may require 10 or more tanker missions to gas up in low-Earth orbit. All of these missions will use different versions of the same basic Starship design: a human-rated lunar lander, a propellant depot, and a refueling tanker.

Artist’s illustration of Starship on the surface of the Moon. Credit: SpaceX

Questions for 2025

Catching Starship back at its launch tower and demonstrating orbital propellant transfer are the two most significant milestones on SpaceX’s roadmap for 2025.

SpaceX officials have said they aim to fly as many as 25 Starship missions this year, allowing engineers to more rapidly iterate on the vehicle’s design. SpaceX is constructing a second launch pad at its Starbase facility near Brownsville, Texas, to help speed up the launch cadence.

Can SpaceX achieve this flight rate in 2025? Will faster Starship manufacturing and reusability help the company fly more often? Will SpaceX fly its first ship-to-ship propellant transfer demonstration this year? When will Starship begin launching large batches of new-generation Starlink Internet satellites?

Licensing delays at the Federal Aviation Administration have been a thorn in SpaceX’s side for the last couple of years. Will those go away under the incoming administration of President-elect Donald Trump, who counts SpaceX founder Elon Musk as a key adviser?

And will SpaceX gain a larger role in NASA’s Artemis lunar program? The Artemis program’s architecture is sure to be reviewed by the Trump administration and the nominee for the agency’s next administrator, billionaire businessman and astronaut Jared Isaacman.

The very expensive Space Launch System rocket, developed by NASA with Boeing and other traditional aerospace contractors, might be canceled. NASA currently envisions the SLS rocket and Orion spacecraft as the transportation system to ferry astronauts between Earth and the vicinity of the Moon, where crews would meet up with a landing vehicle provided by commercial partners SpaceX and Blue Origin.

Watson-Morgan didn’t have answers to all of these questions. Many of them are well outside of her purview as Human Landing System program manager, so Ars didn’t ask. Instead, Ars discussed technical and schedule concerns with her during the half-hour interview. Here is one part of the discussion, lightly edited for clarity.

Ars: What do you hope to see from Flight 7 of Starship?

Lisa Watson-Morgan: One of the exciting parts of working with SpaceX are these test flights. They have a really fast turnaround, where they put in different lessons learned. I think you saw many of the flight objectives that they discussed from Flight 6, which was a great success. I think they mentioned different thermal testing experiments that they put on the ship in order to understand the different heating, the different loads on certain areas of the system. All that was really good with each one of those, in addition to how they configure the tiles. Then, from that, there’ll be additional tests that they will put on Flight 7, so you kind of get this iterative improvement and learning that we’ll get to see in Flight 7. So Flight 7 is the first Version 2 of their ship set. When I say that, I mean the ship, the booster, all the systems associated with it. So, from that, it’s really more just understanding how the system, how the flaps, how all of that interacts and works as they’re coming back in. Hopefully we’ll get to see some catches, that’s always exciting.

Ars: How did the in-space Raptor engine relight go on Flight 6 (on November 19)?

Lisa Watson-Morgan: Beautifully. And that’s something that’s really important to us because when we’re sitting on the Moon… well, actually, the whole path to the Moon as we are getting ready to land on the Moon, we’ll perform a series of maneuvers, and the Raptors will have an environment that is very, very cold. To that, it’s going to be important that they’re able to relight for landing purposes. So that was a great first step towards that. In addition, after we land, clearly the Raptors will be off, and it will get very cold, and they will have to relight in a cold environment (to get off the Moon). So that’s why that step was critical for the Human Landing System and NASA’s return to the Moon.

A recent artist’s illustration of two Starships docked together in low-Earth orbit. Credit: SpaceX

Ars: Which version of the ship is required for the propellant transfer demonstration, and what new features are on that version to enable this test?

Lisa Watson-Morgan: We’re looking forward to the Version 3, which is what’s coming up later on, sometime in ’25, in the near term, because that’s what we need for propellant transfer and the cryo fluid work that is also important to us… There are different systems in the V3 set that will help us with cryo fluid management. Obviously, with those, we have to have the couplers and the quick-disconnects in order for the two systems to have the right guidance, navigation, trajectory, all the control systems needed to hold their station-keeping in order to dock with each other, and then perform the fluid transfer. So all the fluid lines and all that’s associated with that, those systems, which we have seen in tests and held pieces of when we’ve been working with them at their site, we’ll get to see those actually in action on orbit.

Ars: Have there been any ground tests of these systems, whether it’s fluid couplers or docking systems? Can you talk about some of the ground tests that have gone into this development?

Lisa Watson-Morgan: Oh, absolutely. We’ve been working with them on ground tests for this past year. We’ve seen the ground testing and reviewed the data. Our team works with them on what we deem necessary for the various milestones. While the milestone contains proprietary (information), we work closely with them to ensure that it’s going to meet the intent, safety-wise as well as technically, of what we’re going to need to see. So they’ve done that.

Even more exciting, they have recently shipped some of their docking systems to the Johnson Space Center for testing with the Orion Lockheed Martin docking system, and that’s for Artemis III. Clearly, that’s how we’re going to receive the crew. So those are some exciting tests that we’ve been doing this past year as well that’s not just focused on, say, the booster and the ship. There are a lot of crew systems that are being developed now. We’re in work with them on how we’re going to effectuate the crew manual control requirements that we have, so it’s been a great balance to see what the crew needs, given the size of the ship. That’s been a great set of work. We have crew office hours where the crew travels to Hawthorne [SpaceX headquarters in California] and works one-on-one with the different responsible engineers in the different technical disciplines to make sure that they understand not just little words on the paper from a requirement, but actually what this means, and then how systems can be operated.

Ars: For the docking system, Orion uses the NASA Docking System, and SpaceX brings its own design to bear on Starship?

Lisa Watson-Morgan: This is something that I think the Human Landing System has done exceptionally well. When we wrote our high-level set of requirements, we also wrote it with a bigger picture in mind—looked into the overall standards of how things are typically done, and we just said it has to be compliant with it. So it’s a docking standard compliance, and SpaceX clearly meets that. They certainly do have the Dragon heritage, of course, with the International Space Station. So, because of that, we have high confidence that they’re all going to work very well. Still, it’s important to go ahead and perform the ground testing and get as much of that out of the way as we can.

Lisa Watson-Morgan, NASA’s HLS program manager, is based at Marshall Space Flight Center in Huntsville, Alabama. Credit: ASA/Aubrey Gemignani

Ars: How far along is the development and design of the layout of the crew compartment at the top of Starship? Is it far along, or is it still in the conceptual phase? What can you say about that?

Lisa Watson-Morgan: It’s much further along there. We’ve had our environmental control and life support systems, whether it’s carbon dioxide monitoring fans to make sure the air is circulating properly. We’ve been in a lot of work with SpaceX on the temperature. It’s… a large area (for the crew). The seats, making sure that the crew seats and the loads on that are appropriate. For all of that work, as the analysis work has been performed, the NASA team is reviewing it. They had a mock-up, actually, of some of their life support systems even as far back as eight-plus months ago. So there’s been a lot of progress on that.

Ars: Is SpaceX planning to use a touchscreen design for crew displays and controls, like they do with the Dragon spacecraft?

Lisa Watson-Morgan: We’re in talks about that, about what would be the best approach for the crew for the dynamic environment of landing.

Ars: I can imagine it is a pretty dynamic environment with those Raptor engines firing. It’s almost like a launch in reverse.

Lisa Watson-Morgan: Right. Those are some of the topics that get discussed in the crew office hours. That’s why it’s good to have the crew interacting directly, in addition to the different discipline leads, whether it’s structural, mechanical, propulsion, to have all those folks talking guidance and having control to say, “OK, well, when the system does this, here’s the mode we expect to see. Here’s the impact on the crew. And is this condition, or is the option space that we have on the table, appropriate for the next step, with respect to the displays.”

Ars: One of the big things SpaceX needs to prove out before going to the Moon with Starship is in-orbit propellant transfer. When do you see the ship-to-ship demonstration occurring?

Lisa Watson-Morgan: I see it occurring in ’25.

Ars: Anything more specific about the schedule for that?

Lisa Watson-Morgan: That’d be a question for SpaceX because they do have a number of flights that they’re performing commercially, for their maturity. We get the benefit of that. It’s actually a great partnership. I’ll tell you, it’s really good working with them on this, but they’d have to answer that question. I do foresee it happening in ’25.

Ars: What things do you need to see SpaceX accomplish before they’re ready for the refueling demo? I’m thinking of things like the second launch tower, potentially. Do they need to demonstrate a ship catch or anything like that before going for orbital refueling?

Lisa Watson-Morgan: I would say none of that’s required. You just kind of get down to, what are the basics? What are the basics that you need? So you need to be able to launch rapidly off the same pad, even. They’ve shown they can launch and catch within a matter of minutes. So that is good confidence there. The catching is part of their reuse strategy, which is more of their commercial approach, and not a NASA requirement. NASA reaps the benefit of it by good pricing as a result of their commercial model, but it is not a requirement that we have. So they could theoretically use the same pad to perform the propellant transfer and the long-duration flight, because all it requires is two launches, really, within a specified time period to where the two systems can meet in a planned trajectory or orbit to do the propellant transfer. So they could launch the first one, and then within a week or two or three, depending on what the concept of operations was that we thought we could achieve at that time, and then have the propellant transfer demo occur that way. So you don’t necessarily need two pads, but you do need more thermal characterization of the ship. I would say that is one of the areas (we need to see data on), and that is one of the reasons, I think, why they’re working so diligently on that.

Ars: You mentioned the long-duration flight demonstration. What does that entail?

Lisa Watson-Morgan: The simple objectives are to launch two different tankers or Starships. The Starship will eventually be a crewed system. Clearly, the ones that we’re talking about for the propellant transfer are not. It’s just to have the booster and Starship system launch, and within a few weeks, have another one launch, and have them rendezvous. They need to be able to find each other with their sensors. They need to be able to come close, very, very close, and they need to be able to dock together, connect, do the quick connect, and make sure they are able, then, to flow propellant and LOX (liquid oxygen) to another system. Then, we need to be able to measure the quantity of how much has gone over. And from that, then they need to safely undock and dispose.

Ars: So the long-duration flight demonstration is just part of what SpaceX needs to do in order to be ready for the propellant transfer demonstration?

Lisa Watson-Morgan: We call it long duration just because it’s not a 45-minute or an hour flight. Long duration, obviously, that’s a relative statement, but it’s a system that can stay up long enough to be able to find another Starship and perform those maneuvers and flow of fuel and LOX.

Ars: How much propellant will you transfer with this demonstration, and do you think you’ll get all the data you need in one demonstration, or will SpaceX need to try this several times?

Lisa Watson-Morgan: That’s something you can ask SpaceX (about how much propellant will be transferred). Clearly, I know, but there’s some sensitivity there. You’ve seen our requirements in our initial solicitation. We have thresholds and goals, meaning we want you to at least do this, but more is better, and that’s typically how we work almost everything. Working with commercial industry in these fixed-price contracts has worked exceptionally well, because when you have providers that are also wanting to explore commercially or trying to make a commercial system, they are interested in pushing more than what we would typically ask for, and so often we get that for an incredibly fair price.

Photo of Stephen Clark

Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.

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Heroes, villains, and childhood trauma in the MCEU and DCU

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They also limited their study to Marvel and DC characters depicted in major films, rather than including storylines from spinoff TV series. So Wanda Maximoff/The Scarlet Witch was not included since much of her traumatic backstory appeared in the series WandaVision. Furthermore, “We omitted gathering more characters from comic books in both Marvel and DC universes, due to their inconsistency in character development,” the authors wrote. “Comic book storylines often feature alternative plot lines, character arcs, and multiverse outcomes. The storytelling makes comic book characters highly inconsistent and challenging to score.”

With great power…

They ended up watching 33 films, with a total runtime of 77 hours and 5 minutes. They chose 19 male characters, eight female characters, and one gender-fluid character (Loki) as “subjects” for their study, applying the ACE questionnaire to their childhoods as portrayed in the films.

The results: “We found no statistically significant differences between heroes and villains, Marvel and DC characters, or men and women and ACE scores,” said Jackson. “This means that characters who were portrayed as having difficult childhoods were not more likely to be villains. This study somewhat refutes the idea that villains are a product of their experiences. Based on the films we watched, people chose to be heroes and that was what made the difference—not their experiences.”

Notably, Black Widow had the highest ACE score (eight) and yet still became an Avenger, though the authors acknowledge that the character did some bad things before then and famously wanted to wipe out the “red” in her ledger. She “represents resilience of characters who have experienced trauma,” the authors wrote, as well as demonstrating that “socio-ecological resilience, including access to social relationships and supportive communities, can play a mitigating role in the effect of ACEs.” The Joker, by contrast, scored a six and “wreaked havoc across Gotham City.”

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Two lunar landers are on the way to the Moon after SpaceX’s double moonshot

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Julianna Scheiman, director of NASA science missions for SpaceX, said it made sense to pair the Firefly and ispace missions on the same Falcon 9 rocket.

“When we have two missions that can each go to the Moon on the same launch, that is something that we obviously want to take advantage of,” Scheiman said. “So when we found a solution for the Firefly and ispace missions to fly together on the same Falcon 9, it was a no-brainer to put them together.”

SpaceX stacked the two landers, one on top of the other, inside the Falcon 9’s payload fairing. Firefly’s lander, the larger of the two spacecraft, rode on top of the stack and deployed from the rocket first. The Resilience lander from ispace launched in the lower position, cocooned inside a specially designed canister. Once Firefly’s lander separated from the Falcon 9, the rocket jettisoned the canister, performed a brief engine firing to maneuver into a slightly different orbit, then released ispace’s lander.

This dual launch arrangement resulted in a lower launch price for Firefly and ispace, according to Scheiman.

“At SpaceX, we are really interested in and invested in lowering the cost of launch for everybody,” she said. “So that’s something we’re really proud of.”

The Resilience lunar lander is pictured at ispace’s facility in Japan last year. The company’s small Tenacious rover is visible on the upper left part of the spacecraft. credit: ispace Credit: ispace

The Blue Ghost and Resilience landers will take different paths toward the Moon.

Firefly’s Blue Ghost will spend about 25 days in Earth orbit, then four days in transit to the Moon. After Blue Ghost enters lunar orbit, Firefly’s ground team will verify the readiness of the lander’s propulsion and navigation systems and execute several thruster burns to set up for landing.

Blue Ghost’s final descent to the Moon is tentatively scheduled for March 2. The target landing site is in Mare Crisium, an ancient 350-mile-wide (560-kilometer) impact basin in the northeast part of the near side of the Moon.

After touchdown, Blue Ghost will operate for about 14 days (one entire lunar day). The instruments aboard Firefly’s lander include a subsurface drill, an X-ray imager, and an experimental electrodynamic dust shield to test methods of repelling troublesome lunar dust from accumulating on sensitive spacecraft components.

The Resilience lander from ispace will take four to five months to reach the Moon. It carries several intriguing tech demo experiments, including a water electrolyzer provided by a Japanese company named Takasago Thermal Engineering. This demonstration will test equipment that future lunar missions could use to convert the Moon’s water ice resources into electricity and rocket fuel.

The lander will also deploy a “micro-rover” named Tenacious, developed by an ispace subsidiary in Luxembourg. The Tenacious rover will attempt to scoop up lunar soil and capture high-definition imagery of the Moon.

Ron Garan, CEO of ispace’s US-based subsidiary, told Ars that this mission is “pivotal” for the company.

“We were not fully successful on our first mission,” Garan said in an interview. “It was an amazing accomplishment, even though we didn’t have a soft landing… Although the hardware worked flawlessly, exactly as it was supposed to, we did have some lessons learned in the software department. The fixes to prevent what happened on the first mission from happening on the second mission were fairly straightforward, so that boosts our confidence.”

The ispace subsidiary led by Garan, a former NASA astronaut, is based in Colorado. While the Resilience lander launched Wednesday is not part of the CLPS program, the company will build an upgraded lander for a future CLPS mission for NASA, led by Draper Laboratory.

“I think the fact that we have two lunar landers on the same rocket for the first time in history is pretty substantial,” Garan said. I think we all are rooting for each other.”

Investors need to see more successes with commercial lunar landers to fully realize the market’s potential, Garan said.

“That market, right now, is very nascent. It’s very, very immature. And one of the reasons for that is that it’s very difficult for companies that are contemplating making investments on equipment, experiments, etc., to put on the lunar surface and lunar orbit,” Garan said. “It’s very difficult to make those investments, especially if they’re long-term investments, because there really hasn’t been a proof of concept yet.”

“So every time we have a success, that makes it more likely that these companies that will serve as the foundation of a commercial lunar market movement will be able to make those investments,” Garan said. “Conversely, every time we have a failure, the opposite happens.”

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Researchers use AI to design proteins that block snake venom toxins

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Since these two toxicities work through entirely different mechanisms, the researchers tackled them separately.

Blocking a neurotoxin

The neurotoxic three-fingered proteins are a subgroup of the larger protein family that specializes in binding to and blocking the receptors for acetylcholine, a major neurotransmitter. Their three-dimensional structure, which is key to their ability to bind these receptors, is based on three strings of amino acids within the protein that nestle against each other (for those that have taken a sufficiently advanced biology class, these are anti-parallel beta sheets). So to interfere with these toxins, the researchers targeted these strings.

They relied on an AI package called RFdiffusion (the RF denotes its relation to the Rosetta Fold protein-folding software). RFdiffusion can be directed to design protein structures that are complements to specific chemicals; in this case, it identified new strands that could line up along the edge of the ones in the three-fingered toxins. Once those were identified, a separate AI package, called ProteinMPNN, was used to identify the amino acid sequence of a full-length protein that would form the newly identified strands.

But we’re not done with the AI tools yet. The combination of three-fingered toxins and a set of the newly designed proteins were then fed into DeepMind’s AlfaFold2 and the Rosetta protein structure software, and the strength of the interactions between them were estimated.

It’s only at this point that the researchers started making actual proteins, focusing on the candidates that the software suggested would interact the best with the three-fingered toxins. Forty-four of the computer-designed proteins were tested for their ability to interact with the three-fingered toxin, and the single protein that had the strongest interaction was used for further studies.

At this point, it was back to the AI, where RFDiffusion was used to suggest variants of this protein that might bind more effectively. About 15 percent of its suggestions did, in fact, interact more strongly with the toxin. The researchers then made both the toxin and the strongest inhibitor in bacteria and obtained the structure of their interactions. This confirmed that the software’s predictions were highly accurate.

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Meta takes us a step closer to Star Trek’s universal translator

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The computer science behind translating speech from 100 source languages.

In 2023, AI researchers at Meta interviewed 34 native Spanish and Mandarin speakers who lived in the US but didn’t speak English. The goal was to find out what people who constantly rely on translation in their day-to-day activities expect from an AI translation tool. What those participants wanted was basically a Star Trek universal translator or the Babel Fish from the Hitchhiker’s Guide to the Galaxy: an AI that could not only translate speech to speech in real time across multiple languages, but also preserve their voice, tone, mannerisms, and emotions. So, Meta assembled a team of over 50 people and got busy building it.

What this team came up with was a next-gen translation system called Seamless. The first building block of this system is described in Wednesday’s issue of Nature; it can translate speech among 36 different languages.

Language data problems

AI translation systems today are mostly focused on text, because huge amounts of text are available in a wide range of languages thanks to digitization and the Internet. Institutions like the United Nations or European Parliament routinely translate all their proceedings into the languages of all their member states, which means there are enormous databases comprising aligned documents prepared by professional human translators. You just needed to feed those huge, aligned text corpora into neural nets (or hidden Markov models before neural nets became all the rage) and you ended up with a reasonably good machine translation system. But there were two problems with that.

The first issue was those databases comprised formal documents, which made the AI translators default to the same boring legalese in the target language even if you tried to translate comedy. The second problem was speech—none of this included audio data.

The problem of language formality was mostly solved by including less formal sources like books, Wikipedia, and similar material in AI training databases. The scarcity of aligned audio data, however, remained. Both issues were at least theoretically manageable in high-resource languages like English or Spanish, but they got dramatically worse in low-resource languages like Icelandic or Zulu.

As a result, the AI translators we have today support an impressive number of languages in text, but things are complicated when it comes to translating speech. There are cascading systems that simply do this trick in stages. An utterance is first converted to text just as it would be in any dictation service. Then comes text-to-text translation, and finally the resulting text in the target language is synthesized into speech. Because errors accumulate at each of those stages, the performance you get this way is usually poor, and it doesn’t work in real time.

A few systems that can translate speech-to-speech directly do exist, but in most cases they only translate into English and not in the opposite way. Your foreign language interlocutor can say something to you in one of the languages supported by tools like Google’s AudioPaLM, and they will translate that to English speech, but you can’t have a conversation going both ways.

So, to pull off the Star Trek universal translator thing Meta’s interviewees dreamt about, the Seamless team started with sorting out the data scarcity problem. And they did it in a quite creative way.

Building a universal language

Warren Weaver, a mathematician and pioneer of machine translation, argued in 1949 that there might be a yet undiscovered universal language working as a common base of human communication. This common base of all our communication was exactly what the Seamless team went for in its search for data more than 70 years later. Weaver’s universal language turned out to be math—more precisely, multidimensional vectors.

Machines do not understand words as humans do. To make sense of them, they need to first turn them into sequences of numbers that represent their meaning. Those sequences of numbers are numerical vectors that are termed word embeddings. When you vectorize tens of millions of documents this way, you’ll end up with a huge multidimensional space where words with similar meaning that often go together, like “tea” and “coffee,” are placed close to each other. When you vectorize aligned text in two languages like those European Parliament proceedings, you end up with two separate vector spaces, and then you can run a neural net to learn how those two spaces map onto each other.

But the Meta team didn’t have those nicely aligned texts for all the languages they wanted to cover. So, they vectorized all texts in all languages as if they were just a single language and dumped them into one embedding space called SONAR (Sentence-level Multimodal and Language-Agnostic Representations). Once the text part was done, they went to speech data, which was vectorized using a popular W2v (word to vector) tool and added it to the same massive multilingual, multimodal space. Of course, each embedding carried metadata identifying its source language and whether it was text or speech before vectorization.

The team just used huge amounts of raw data—no fancy human labeling, no human-aligned translations. And then, the data mining magic happened.

SONAR embeddings represented entire sentences instead of single words. Part of the reason behind that was to control for differences between morphologically rich languages, where a single word may correspond to multiple words in morphologically simple languages. But the most important thing was that it ensured that sentences with similar meaning in multiple languages ended up close to each other in the vector space.

It was the same story with speech, too—a spoken sentence in one language was close to spoken sentences in other languages with similar meaning. It even worked between text and speech. So, the team simply assumed that embeddings in two different languages or two different modalities (speech or text) that are at a sufficiently close distance to each other are equivalent to the manually aligned texts of translated documents.

This produced huge amounts of automatically aligned data. The Seamless team suddenly got access to millions of aligned texts, even in low-resource languages, along with thousands of hours of transcribed audio. And they used all this data to train their next-gen translator.

Seamless translation

The automatically generated data set was augmented with human-curated texts and speech samples where possible and used to train multiple AI translation models. The largest one was called SEAMLESSM4T v2. It could translate speech to speech from 101 source languages into any of 36 output languages, and translate text to text. It would also work as an automatic speech recognition system in 96 languages, translate speech to text from 101 into 96 languages, and translate text to speech from 96 into 36 languages—all from a single unified model. It also outperformed state-of-the-art cascading systems by 8 percent in a speech-to-text and by 23 percent in a speech-to-speech translations based on the scores in Bilingual Evaluation Understudy (an algorithm commonly used to evaluate the quality of machine translation).

But it can now do even more than that. The Nature paper published by Meta’s Seamless ends at the SEAMLESSM4T models, but Nature has a long editorial process to ensure scientific accuracy. The paper published on January 15, 2025, was submitted in late November 2023. But in a quick search of the arXiv.org, a repository of not-yet-peer-reviewed papers, you can find the details of two other models that the Seamless team has already integrated on top of the SEAMLESSM4T: SeamlessStreaming and SeamlessExpressive, which take this AI even closer to making a Star Trek universal translator a reality.

SeamlessStreaming is meant to solve the translation latency problem. The baseline SEAMLESSM4T, despite all the bells and whistles, worked as a standard AI translation tool. You had to say what you wanted to say, push “translate,” and it spat out the translation. SeamlessStreaming was designed to take this experience a bit closer to what human simultaneous translator do—it translates what you’re saying as you speak in a streaming fashion. SeamlessExpressive, on the other hand, is aimed at preserving the way you express yourself in translations. When you whisper or say something in a cheerful manner or shout out with anger, SeamlessExpressive will encode the features of your voice, like tone, prosody, volume, tempo, and so on, and transfer those into the output speech in the target language.

Sadly, it still can’t do both at the same time; you can only choose to go for either streaming or expressivity, at least at the moment. Also, the expressivity variant is very limited in supported languages—it only works in English, Spanish, French, and German. But at least it’s online so you can go ahead and give it a spin.

Nature, 2025.  DOI: 10.1038/s41586-024-08359-z

Photo of Jacek Krywko

Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.

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Is humanity alone in the Universe? What scientists really think.

Science, syndication / /

News stories about the likely existence of extraterrestrial life, and our chances of detecting it, tend to be positive. We are often told that we might discover it any time now. Finding life beyond Earth is “only a matter of time,” we were told in September 2023. “We are close” was a headline from September 2024.

It’s easy to see why. Headlines such as “We’re probably not close” or “Nobody knows” aren’t very clickable. But what does the relevant community of experts actually think when considered as a whole? Are optimistic predictions common or rare? Is there even a consensus? In our new paper, published in Nature Astronomy, we’ve found out.

During February to June 2024, we carried out four surveys regarding the likely existence of basic, complex, and intelligent extraterrestrial life. We sent emails to astrobiologists (scientists who study extraterrestrial life), as well as to scientists in other areas, including biologists and physicists.

In total, 521 astrobiologists responded, and we received 534 non-astrobiologist responses. The results reveal that 86.6 percent of the surveyed astrobiologists responded either “agree” or “strongly agree” that it’s likely that extraterrestrial life (of at least a basic kind) exists somewhere in the universe.

Less than 2 percent disagreed, with 12 percent staying neutral. So, based on this, we might say that there’s a solid consensus that extraterrestrial life, of some form, exists somewhere out there.

Scientists who weren’t astrobiologists essentially concurred, with an overall agreement score of 88.4 percent. In other words, one cannot say that astrobiologists are biased toward believing in extraterrestrial life, compared with other scientists.

When we turn to “complex” extraterrestrial life or “intelligent” aliens, our results were 67.4 percent agreement, and 58.2 percent agreement, respectively for astrobiologists and other scientists. So, scientists tend to think that alien life exists, even in more advanced forms.

These results are made even more significant by the fact that disagreement for all categories was low. For example, only 10.2 percent of astrobiologists disagreed with the claim that intelligent aliens likely exist.

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There was a straight shot from Earth to the Moon and Mars last night

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The most recent lunar occultation of Mars that was visible from the United States occurred on December 7, 2022. A handful of these events occur every few years around each Martian opposition, but they are usually only visible from a small portion of Earth, often over the ocean or in polar regions. The next lunar occultation of Mars visible across most of the United States will happen on the night of February 4–5, 2042. There are similar occultations of Mars in 2035, 2038, and 2039 visible in narrow swaths of South Florida and the Pacific Northwest.

This photo was taken with a handheld Canon 80D and a 600 mm lens. Settings were 1/2000 sec, f/8, ISO 400. The image was cropped and lightly edited in Adobe Lightroom.

The Moon also periodically covers Venus, Jupiter, Saturn, and the Solar System’s more distant planets. A good resource on lunar occultations is In-The-Sky.org, which lists events where the Moon will block out a planet or a bright star. Be sure you choose your location on the upper right corner of the page and toggle year by year to plan out future viewing opportunities.

Viewing these kinds of events can be breathtaking and humbling. In 2012, I was lucky enough to observe the transit of Venus in front of the Sun, something that only happens twice every 121 years.

Seeing Mars, twice the size of the Moon, rising above the lunar horizon like a rusty BB pellet next to a dusty volleyball provided a perfect illustration of the scale and grandeur of the Solar System. Similarly, viewing Venus dwarfed by the Sun was a revealing moment. The worlds accompanying Earth around the Sun are varied in size, shape, color, and composition.

In one glance, an observer can see the barren, airless lunar surface and a cold, desert planet that once harbored rivers, lakes, and potentially life, all while standing on our own planet, an oasis in the cosmos. One thing that connects them all is humanity’s quest for exploration. Today, robots are operating on or around the Moon and Mars. Governments and private companies are preparing to return astronauts to the lunar surface within a few years, then moving on to dispatch human expeditions to the red planet.

Plans to land astronauts on the Moon are already in motion, but significant financial and technological hurdles remain for a crew mission to put humans on Mars. But for a short time Monday night, it looked like there was a direct path.

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Maker of weight-loss drugs to ask Trump to pause price negotiations: Report

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Popular prescriptions

For now, Medicare does not cover drugs prescribed specifically for weight loss, but it will cover GLP-1 class drugs if they’re prescribed for other conditions, such as Type 2 diabetes. Wegovy, for example, is covered if it is prescribed to reduce the risk of heart attack and stroke in adults with either obesity or overweight. But, in November, the Biden administration proposed reinterpreting Medicare prescription-coverage rules to allow for coverage of “anti-obesity medications.”

Such a move is reportedly part of the argument Lilly’s CEO plans to bring to the Trump administration. Rather than using drug price negotiations to reduce health care costs, Ricks aims to play up the potential to reduce long-term health care costs by improving people’s overall health with coverage of GLP-1 drugs now. This argument would presumably be targeted at Mehmet Oz, the TV presenter and heart surgeon Trump has tapped to run the Centers for Medicare and Medicaid Services.

“My argument to Mehmet Oz is that if you want to protect Medicare costs in 10 years, have [the Affordable Care Act] and Medicare plans list these drugs now,” Ricks said to Bloomberg. “We know so much about how much cost savings there will be downstream in heart disease and other conditions.”

An October report from the Congressional Budget Office strongly disputed that claim, however. The CBO estimated that the direct cost of Medicare coverage for anti-obesity drugs between 2026 and 2034 would be nearly $39 billion, while the savings from improved health would total just a little over $3 billion, for a net cost to US taxpayers of about $35.5 billion.

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Up close and personal with the stag beetle in A Real Bug’s Life S2

A Real Bug's Life, Disney Plus, entomology, National Geographic, Science / /

It’s just one of the many fascinating insect species featured in the second season of this NatGeo docuseries.

A female giant stag beetle Credit: National Geographic/Darlyne A. Murawski

A plucky male American stag beetle thinks he’s found a mate on a rotting old tree stump—and then realizes there’s another male eager to make the same conquest. The two beetles face off in battle, until the first manages to get enough leverage to toss his romantic rival off the stump in a deft display of insect jujitsu. It’s the first time this mating behavior has been captured on film, and the stag beetle is just one of the many fascinating insects featured in the second season of A Real Bug’s Life, a National Geographic docuseries narrated by Awkwafina.

The genesis for the docuseries lies in a past rumored sequel to Pixar’s 1998 animated film A Bug’s Life, which celebrated its 25th anniversary two years ago. That inspired producer Bill Markham, among others, to pitch a documentary series on a real bug’s life to National Geographic. “It was the quickest commission ever,” Markham told Ars last year. “It was such a good idea, to film bugs in an entertaining family way with Pixar sensibilities.” And thanks to the advent of new technologies—photogrammetry, probe and microscope lenses, racing drones, ultra-high-speed camera—plus a handful of skilled “bug wranglers,” the team was able to capture the bug’s-eye view of the world beautifully.

As with the Pixar film, the bugs (and adjacent creatures) are the main characters here, from cockroaches, monarch butterflies, and praying mantises to bees, spiders, and even hermit crabs. The 10 episodes, across two seasons, tell their stories as they struggle to survive in their respective habitats, capturing entire ecosystems in the process: city streets, a farm, the rainforest, a Texas backyard, and the African savannah, for example. Highlights from S1 included the first footage of cockroach egg casings hatching; wrangling army ants on location in a Costa Rica rainforest; and the harrowing adventures of a tiny jumping spider navigating the mean streets of New York City.

Looking for love

A luna moth perched on a twig. National Geographic/Nathan Small

S2 takes viewers to Malaysia’s tropical beaches, the wetlands of Derbyshire in England, and the forests of Tennessee’s Smoky Mountains. Among the footage highlights: Malaysian tiger beetles, who can run so fast they temporarily are unable to see; a young female hermit crab’s hunt for a bigger shell; and tiny peacock spiders hatching Down Under. There is also a special behind-the-scenes look for those viewers keen to learn more about how the episodes were filmed, involving 130 different species across six continents. Per the official synopsis:

A Real Bug’s Life is back for a thrilling second season that’s bolder than ever. Now, thanks to new cutting-edge filming technology, we are able to follow the incredible stories of the tiny heroes living in this hidden world, from the fast-legged tiger beetle escaping the heat of Borneo’s beaches to the magical metamorphosis of a damselfly on a British pond to the Smoky Mountain luna moth whose quest is to grow wings, find love and pass on his genes all in one short night. Join our witty guide, Awkwafina, on new bug journeys full of more mind-blowing behaviors and larger-than-life characters.

Entomologist Michael Carr, an environmental compliance officer for Santa Fe County in New Mexico, served as a field consultant for the “Love in the Forest” episode, which focuses on the hunt for mates by a luna moth, a firefly, and an American stag beetle. The latter species is Carr’s specialty, ever since he worked at the Smithsonian’s Museum of Natural History and realized the beetles flourished near where he grew up in Virginia. Since stag beetles are something of a niche species, NatGeo naturally tapped Carr as its field expert to help them find and film the insects in the Smoky Mountains. To do so, Carr set up a mercury vapor lamp on a tripod—”old style warehouse lights that take a little time to charge up,” which just happen to emit frequencies of light that attract different insect species.

Behind the scenes

Beetle expert Michael Carr and shooting researcher Katherine Hannaford film a stag beetle at night. National Geographic/Tom Oldridge

Stag beetles are saprocylic insects, according to Carr, so they seek out decaying wood and fungal communities. Males can fly as high as 30 feet to reach tree canopies, while the females can dig down to between 1 and 3 meters to lay their eggs in wood. Much of the stag beetle’s lifecycle is spent underground as a white grub molting into larger and larger forms before hatching in two to three years during the summer. Once their exoskeletons harden, they fly off to find mates and reproduce as quickly as possible. And if another male happens to get in their way, they’re quite prepared to do battle to win at love.

Stag beetles might be his specialty, but Carr found the fireflies also featured in that episode to be a particular highlight. “I grew up in rural Virginia,” Carr told Ars. “There was always fireflies, but I’d never seen anything like that until I was there on site. I did not realize, even though I’d grown up in the woods surrounded by fireflies, that, ‘Oh, the ones that are twinkling at the top, that’s one species. The ones in the middle that are doing a soft glow, that’s a different species.'”

And Carr was as surprised and fascinated as any newbie to learn about the “femme fatale” firefly: a species in which the female mimics the blinking patterns of other species of firefly, luring unsuspecting males to their deaths. The footage captured by the NatGeo crew includes a hair-raising segment where this femme fatale opts not to wait for her prey to come to her. A tasty male firefly has been caught in a spider’s web, and our daring, hungry lady flies right into the web to steal the prey:

A femme fatale firefly steals prey from a rival spider’s web.

Many people have a natural aversion to insects; Carr hopes that inventive docuseries like A Real Bug’s Life can help counter those negative perceptions by featuring some lesser-loved insects in anthropomorphized narratives—like the cockroaches and fire ants featured in S1. “[The series] did an amazing job of showing how something at that scale lives its life, and how that’s almost got a parallel to how we can live our life,” he said. “When you can get your mindset down to such a small scale and not just see them as moving dots on the ground and you see their eyes and you see how they move and how they behave and how they interact with each other, you get a little bit more appreciation for ants as a living organism.”

“By showcasing some of the bigger interesting insects like the femme fatale firefly or the big chivalrous stag beetle fighting over each other, or the dung beetle getting stomped by an elephant—those are some pretty amazing just examples of the biodiversity and breadth of insect life,” said Carr. “People don’t need to love insects. If they can, just, have some new modicum of respect, that’s good enough to change perspectives.”

The second season of A Real Bug’s Life premieres on January 15, 2025, on Disney+.

Photo of Jennifer Ouellette

Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban.

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Skull long thought to be Cleopatra’s sister’s was actually a young boy

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Scientists have demonstrated that an ancient human skull excavated from a tomb at Ephesos was not that of Arsinoë IV, half-sister to Cleopatra VII. Rather, it’s the skull of a young male between the ages of 11 and 14 from Italy or Sardinia, who may have suffered from one or more developmental disorders, according to a new paper published in the journal Scientific Reports. Arsinoë IV’s remains are thus still missing.

Arsinoë IV led quite an adventurous short life. She was either the third or fourth daughter of Ptolemy XII, who left the throne to Cleopatra and his son, Ptolemy XIII, to rule together. Ptolemy XIII didn’t care for this decision and dethroned Cleopatra in a civil war—until Julius Caesar intervened to enforce their father’s original plan of co-rulership. As for Arsinoë, Caesar returned Cyprus to Egyptian rule and named her and her youngest brother (Ptolemy XIV) co-rulers. This time, it was Arsinoë who rebelled, taking command of the Egyptian army and declaring herself queen.

She was fairly successful at first in battling the Romans, conducting a siege against Alexandria and Cleopatra, until her disillusioned officers decided they’d had enough and secretly negotiated with Caesar to turn her over to him. Caesar agreed, and after a bit of public humiliation, he granted Arsinoë sanctuary in the temple of Artemis in Ephesus. She lived in relative peace for a few years, until Cleopatra and Mark Antony ordered her execution on the steps of the temple—a scandalous violation of the temple as a place of sanctuary. Historians disagree about Arsinoë’s age when she died: Estimates range from 22 to 27.

Archaeologists have been excavating the ancient city of Ephesus for more than a century. The Octagon was uncovered in 1904, and the burial chamber was opened in 1929. That’s where Joseph Keil found a skeleton in a sarcophagus filled with water, but for some reason, Keil only removed the cranium from the tomb before sealing it back up. He took the skull with him to Germany and declared it belonged to a likely female around 20 years old, although he provided no hard data to support that conclusion.

It was Hilke Thur of the Austrian Academy of Sciences who first speculated that the skull may have belonged to Arsinoë IV, despite the lack of an inscription (or even any grave goods) on the tomb where it was found. Old notes and photographs, as well as craniometry, served as the only evidence. The skull accompanied Keil to his new position at the University of Vienna, and there was one 1953 paper reporting on craniometric measurements, but after that, the skull languished in relative obscurity. Archaeologists at the University of Graz rediscovered the skull in Vienna in 2022. The rest of the skeleton remained buried until the chamber was reopened and explored further in the 1980s and 1990s, but it was no longer in the sarcophagus.

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Getting an all-optical AI to handle non-linear math

AI, Computer science, optical processing, optics, Science / /

The problem is that this cascading requires massive parallel computations that, when done on standard computers, take tons of energy and time. Bandyopadhyay’s team feels this problem can be solved by performing the equivalent operations using photons rather than electrons. In photonic chips, information can be encoded in optical properties like polarization, phase, magnitude, frequency, and wavevector. While this would be extremely fast and energy-efficient, building such chips isn’t easy.

Siphoning light

“Conveniently, photonics turned out to be particularly good at linear matrix operations,” Bandyopadhyay claims. A group at MIT led by Dirk Englund, a professor who is a co-author of Bandyopadhyay’s study, demonstrated a photonic chip doing matrix multiplication entirely with light in 2017. What the field struggled with, though, was implementing non-linear functions in photonics.

The usual solution, so far, relied on bypassing the problem by doing linear algebra on photonic chips and offloading non-linear operations to external electronics. This, however, increased latency, since the information had to be converted from light to electrical signals, processed on an external processor, and converted back to light. “And bringing the latency down is the primary reason why we want to build neural networks in photonics,” Bandyopadhyay says.

To solve this problem, Bandyopadhyay and his colleagues designed and built what is likely to be the world’s first chip that can compute the entire deep neural net, including both linear and non-linear operations, using photons. “The process starts with an external laser with a modulator that feeds light into the chip through an optical fiber. This way we convert electrical inputs to light,” Bandyopadhyay explains.

The light is then fanned out to six channels and fed into a layer of six neurons that perform linear matrix multiplication using an array of devices called Mach-Zehnder interferometers. “They are essentially programmable beam splitters, taking two optical fields and mixing them coherently to produce two output optical fields. By applying the voltage, you can control how much those the two inputs mix,” Bandyopadhyay says.

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