May 21, 202510 min readWhy Some Experts Call Trump’s ‘Golden Dome’ Missile Shield a Dangerous FantasyThe White House’s $175-billion plan to protect the U.S. from nuclear annihilation will probably cost much more—and deliver far less—than has been claimed, says nuclear arms expert Jeffrey LewisBy Lee Billings U.S. President Donald Trump speaks in the Oval Office of the White House on May 20, 2025, during a briefing announcing his administration’s plan for the “Golden Dome” missile defense shield. Jim Watson/AFP via Getty ImagesDuring a briefing from the Oval Office this week, President Donald Trump revealed his administration’s plan for “Golden Dome”—an ambitious high-tech system meant to shield the U.S. from ballistic, cruise and hypersonic missile attacks launched by foreign adversaries. Flanked by senior officials, including Secretary of Defense Pete Hegseth and the project’s newly selected leader, Gen. Michael Guetlein of the U.S. Space Force, Trump announced that Golden Dome will be completed within three years at a cost of $175 billion.The program, which was among Trump’s campaign promises, derives its name from the Iron Dome missile defense system of Israel—a nation that’s geographically 400 times smaller than the U.S. Protecting the vastness of the U.S. demands very different capabilities than those of Iron Dome, which has successfully shot down rockets and missiles using ground-based interceptors. Most notably, Trump’s Golden Dome would need to expand into space—making it a successor to the Strategic Defense Initiative (SDI) pursued by the Reagan administration in the 1980s. Better known by the mocking nickname “Star Wars,” SDI sought to neutralize the threat from the Soviet Union’s nuclear-warhead-tipped intercontinental ballistic missiles by using space-based interceptors that could shoot them down midflight. But fearsome technical challenges kept SDI from getting anywhere close to that goal, despite tens of billions of dollars of federal expenditures.“We will truly be completing the job that President Reagan started 40 years ago, forever ending the missile threat to the American homeland,” Trump said during the briefing. Although the announcement was short on technical details, Trump also said Golden Dome “will deploy next-generation technologies across the land, sea and space, including space-based sensors and interceptors.” The program, which Guetlein has compared to the scale of the Manhattan Project in past remarks, has been allotted $25 billion in a Republican spending bill that has yet to pass in Congress. But Golden Dome may ultimately cost much more than Trump’s staggering $175-billion sum. An independent assessment by the Congressional Budget Office estimates its price tag could be as high as $542 billion, and the program has drawn domestic and international outcries that it risks sparking a new, globe-destabilizing arms race and weaponizing Earth’s fragile orbital environment.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.To get a better sense of what’s at stake—and whether Golden Dome has a better chance of success than its failed forebears—Scientific American spoke with Jeffrey Lewis, an expert on the geopolitics of nuclear weaponry at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies.[An edited transcript of the interview follows.]It’s been a while, but when last I checked, most experts considered this sort of plan a nonstarter because the U.S. is simply too big of a target. Has something changed?Well, yes and no. The killer argument against space-based interceptors in the 1980s was that it would take thousands of them, and there was just no way to put up that many satellites. Today that’s no longer true. SpaceX alone has put up more than 7,000 Starlink satellites. Launch costs are much cheaper now, and there are more launch vehicles available. So, for the first time, you can say, “Oh, well, I could have a 7,000-satellite constellation. Do I want to do that?” Whereas, when the Reagan administration was talking about this, it was just la-la land.But let’s be clear: this does not solve all the other problems with the general idea—or the Golden Dome version in particular.What are some of those other problems?Just talking about space-based interceptors, there are a couple [of issues that] my colleagues and I have pointed out. We ran some numbers using the old SDI-era calculation from [SDI physicists] Ed Teller and Greg Canavan—so we couldn’t be accused of using some hippie version of the calculation, right? And what this and other independent assessments show is that the number of interceptors you need is super-duper sensitive to lots of things. For instance, it’s not like this is a “one satellite to one missile” situation—because the physics demands that these satellites ... have to be in low-Earth orbit, and that means they’re going to be constantly moving over different parts of the planet.So if you want to defend against just one missile, you still need a whole constellation. And if you want to defend against two missiles, then you basically need twice as many interceptors, and so on.You probably have to shoot down missiles during the boost phase, when the warheads are still attached. For SDI, the U.S. was dealing with Soviet liquid-fueled missiles that would boost, or burn, for about four minutes. Well, modern ones burn for less than three—that’s a whole minute that you no longer have. This is actually much worse than it sounds because you’re probably unable to shoot for the first minute or so. Even with modern detectors [that are] much better than [those] we had in the 1980s, you may not see the missile until it rises above the clouds. And once it does, your sensors, your computers, still have to say, “Aha! That is a missile!” And then you have to ensure that you’re not shooting down some ordinary space launch—so the system says, “I see a missile. May I shoot at it, please?” And someone or something has to give the go-ahead. So let’s just say you’ll have a good minute to shoot it down; this means your space-based interceptor has to be right there, ready to go, right? But by the time you’re getting permission to shoot, the satellite that was overhead to do that is now too far away, and so the next satellite has to be coming there. This scales up really, really fast.Presumably artificial intelligence and other technologies could be leveraged to make that sort of command and control more agile and responsive. But clearly there are still limits here—AI can’t be some sort of panacea.Sure, that’s right. But technological progress overall hasn’t made the threat environment better. Instead it’s gotten much worse.Let’s get back to the sheer physics-induced numbers for a moment, which AI can’t really do much about. That daunting scaling I mentioned also depends on the quality of your interceptors, your kill vehicles—which, by the way, are still going to be grotesquely expensive even if launch costs are low. If your interceptors can rapidly accelerate to eight or 10 kilometers per second (km/s), your constellation can be smaller. If they only reach 4 km/s, your constellation has to be huge.The point is: any claim that you can do this with relatively low numbers—let’s say 2,000 interceptors—assumes a series of improbable miracles occurring in quick succession to deliver the very best outcome that could possibly happen. So it’s not going to happen that way, even if, in principle, it could.So you’re telling me there’s a chance! No, seriously, I see what you mean. The arguments in favor of this working seem rather contrived. No system is perfect, and just one missile getting through can still have catastrophic results. And we haven’t even talked about adversarial countermeasures yet.There’s a joke that’s sometimes made about this: “We play chess, and they don’t move their pieces.” That seems to be the operative assumption here: that other nations will sit idly by as we build a complex, vulnerable system to nullify any strategic nuclear capability they have. And of course, it’s not valid at all. Why do you think the Chinese are building massive fields of missile silos? It’s to counteract or overwhelm this sort of thing. Why do you think the Russians are making moves to put a nuclear weapon in orbit? It’s to mass kill any satellite constellation that would shoot down their missiles.Golden Dome proponents may say, “Oh, we’ll shoot that down, too, before it goes off.” Well, good luck. You put a high-yield nuclear weapon on a booster, and the split second it gets above the clouds, sure, you might see it—but now it sees you, too, before you can shoot. All it has to do at that point is detonate to blow a giant hole in your defenses, and that’s game over. And by the way, this rosy scenario assumes your adversaries don’t interfere with all your satellites passing over their territory in peacetime. We know that won’t be the case—they’ll light them up with sensor-dazzling lasers, at minimum!You’ve compared any feasible space-based system to Starlink and noted that, similar to Starlink, these interceptors will need to be in low-Earth orbit. That means their orbits will rapidly decay from atmospheric drag, so just like Starlink’s satellites, they’d need to be constantly replaced, too, right?Ha, yes, that’s right. With Starlink, you’re looking at a three-to-five-year life cycle, which means annually replacing one third to one fifth of a constellation.So let’s say Golden Dome is 10,000 satellites; this would mean the best-case scenario is that you’re replacing 2,000 per year. Now, let’s just go along with what the Trump administration is saying, that they can get these things really cheap. I’m going to guess a “really cheap” mass-produced kill vehicle would still run you $20 million a pop, easily. Just multiply $20 million by 2,000, and your answer is $40 billion. So under these assumptions, we’d be spending $40 billion per year just to maintain the constellation. That’s not even factoring in operations.And that’s not to mention associated indirect costs from potentially nasty effects on the upper atmosphere and the orbital environment from all the launches and reentries.That, yes—among many other costly things.I have to ask: If fundamental physics makes this extremely expensive idea blatantly incapable of delivering on its promises, what’s really going on when the U.S. president and the secretary of defense announce their intention to pump $175 billion into it for a three-year crash program? Some critics claim this kind of thing is really about transferring taxpayer dollars to a few big aerospace companies and other defense contractors.Well, I wouldn’t say it’s quite that simple.Ballistic missile defense is incredibly appealing to some people for reasons besides money. In technical terms, it’s an elegant solution to the problem of nuclear annihilation—even though it’s not really feasible. For some people, it’s just cool, right? And at a deeper level, many people just don’t like the concept of deterrence—mutual assured destruction and all that—because, remember, the status quo is this: If Russia launches 1,000 nuclear weapons at us—or 100 or 10 or even just one—then we are going to murder every single person in Russia with an immediate nuclear counterattack. That’s how deterrence works. We’re not going to wait for those missiles to land so we can count up our dead to calibrate a more nuanced response. That’s official U.S. policy, and I don’t think anyone wants it to be this way forever. But it’s arguably what’s prevented any nuclear exchange from occurring to date.But not everyone believes in the power of deterrence, and so they’re looking for some kind of technological escape. I don’t think this fantasy is that different from Elon Musk thinking he’s going to go live on Mars when climate change ruins Earth: In both cases, instead of doing the really hard things that seem necessary to actually make this planet better, we’re talking about people who think they can just buy their way out of the problem. A lot of people—a lot of men, especially—really hate vulnerability, and this idea that you can just tech your way out of it is very appealing to them. You know, “Oh, what vulnerability? Yeah, there’s an app for that.”You’re saying this isn’t about money?Well, I imagine this is going to be good for at least a couple of SpaceX Falcon Heavy or Starship launches per year for Elon Musk. And you don’t have to do too many of those launches for the value proposition to work out: You build and run Starlink, you put up another constellation of space-based missile defense interceptors, and suddenly you’ve got a viable business model for these fancy huge rockets that can also take you to Mars, right?Given your knowledge of science history—of how dispassionate physics keeps showing space-based ballistic missile defense is essentially unworkable, yet the idea just keeps coming back—how does this latest resurgence make you feel?When I was younger, I would have been frustrated, but now I just accept human beings don’t learn. We make the same mistakes over and over again. You have to laugh at human folly because I do think most of these people are sincere, you know. They’re trying to get rich, sure, but they’re also trying to protect the country, and they’re doing it through ways they think about the world—which admittedly are stupid. But, hey, they’re trying. It’s very disappointing, but if you just laugh at them, they’re quite amusing.I think most people would have trouble laughing about something as devastating as nuclear war—or about an ultraexpensive plan to protect against it that’s doomed to failure and could spark a new arms race.I guess if you’re looking for a hopeful thought, it’s that we’ve tried this before, and it didn’t really work, and that’s likely to happen again.So how do you think it will actually play out this time around?I think this will be a gigantic waste of money that collapses under its own weight.They’ll put up a couple of interceptors, and they’ll test those against a boosting ballistic missile, and they’ll eventually get a hit. And they’ll use that to justify putting up more, and they’ll probably even manage to make a thin constellation—with the downside, of course, being that the Russians and the Chinese and the North Koreans and everybody else will make corresponding investments in ways to kill this system.And then it will start to really feel expensive, in part because it will be complicating and compromising things like Starlink and other commercial satellite constellations—which, I’d like to point out, are almost certainly uninsured in orbit because you can’t insure against acts of war. So think about that: if the Russians or anyone else detonate a nuclear weapon in orbit because of something like Golden Dome, Elon Musk’s entire constellation is dead, and he’s probably just out the cash.The fact is: these days we rely on space-based assets much more than most people realize, yet Earth orbit is such a fragile environment that we could muck it up in many different ways that carry really nasty long-term consequences. I worry about that a lot. Space used to be a benign environment, even throughout the entire cold war, but having an arms race there will make it malign. So Golden Dome is probably going to make everyone’s life a little bit more dangerous—at least until we, hopefully, come to our senses and decide to try something different.

May 22, 20255 min readHow One Astronomer Helped to Discover Nearly 200 Moons of SaturnScientific American spoke with the astronomer who has contributed to the discovery of two thirds of Saturn’s known moonsBy Meghan Bartels edited by Lee Billings NASA, ESA, John T. Clarke (Boston University), Zolt G. Levay (STScI)A mere decade ago, astronomers knew of just 62 moons around Saturn. Today the ringed planet boasts a staggering 274 official satellites. That’s more than any other world in the solar system—and far too many for most people to keep track of. Astronomer Edward Ashton is no exception, even though he has helped to discover 192 of them—he thinks that’s the total, anyway, after pausing to do some mental math.Ashton is now a postdoctoral fellow at the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan. He fell into hunting for Saturn’s moons in 2018, when his then academic adviser suggested the project for his Ph.D. at the University of British Columbia. It has been a fruitful search. Most recently, in March, Ashton and his colleagues announced a batch of 128 newfound Saturnian satellites.Scientific American spoke with Ashton about the science of discovering so many relatively tiny moons—most of them just a few kilometers wide—using vast amounts of data gathered by the Canada-France-Hawaii Telescope (CFHT), located in Hawaii.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.[An edited transcript of the interview follows.]How have you found these moons?To detect the moons, we use a technique known as shifting and stacking. We take 44 sequential images of the same patch of sky over a three-hour period because, in that time frame, the moons move relative to the stars at a rate similar to Saturn. If we just stack the images normally, then the moon appears as a streak across the images, and that dilutes the signal of the moon.So what we do is: we shift the images relative to one another at multiple different rates near that of Saturn, and then we basically blink between the different shift rates. If the shift rate is not quite at the rate of the moon, then it’s going to be slightly elongated. As you get closer to the rate of the moon, then it slowly combines into a dot. And then, as you get faster than the moon’s rate, it expands again. So basically, we look at the images and then quickly blink through the different rates, and you can see the moon coalescing.That’s for a single night. But just seeing an object moving at a Saturn-like rate near Saturn doesn’t guarantee that it is a moon. It’s highly likely that the object is a moon, but that hasn’t been confirmed. So what we need to do is track the objects to show that they are in orbit around the planet. To do that, we repeat the [shift and stack] process multiple times over many months and years.Why did this happen now? Did you need new techniques and observatories to do this work?The technique and the technology have been there for a while—the same technique has been used to find moons of Neptune and Uranus. But the sky area around those planets where moons can exist is a lot smaller, so it takes less time to search through the data. One of the reasons why this hadn’t been done for Saturn is because it’s very time-consuming.Why do those other planets have less space where moons could be than Saturn does?Those planets are less massive, so the stable orbits that moons can have are smaller.I had been wondering if this technique works for other planets, and clearly the answer is yes. But do you think there are other moons that have yet to be found around Saturn or other planets with the method?We did find moon candidates around Saturn that we weren’t able to track long enough to be able to confirm them. So if you redo this technique again, you will be able to find more moons around Saturn, but this is a case of diminishing returns. If you use a larger telescope [than the CFHT], then you’d be able to see fainter moons, so you’d be able to find more.At the moment, if you use the same technique for Jupiter, you will be able to find fainter moons. The problem is: the amount of sky that moons of Jupiter can occupy is significantly larger than [the amount of sky that can be occupied by moons of] Saturn, so the method is even more time-consuming for Jupiter. And Jupiter is much brighter than Saturn and the other planets, so there’s a lot of scattered light that makes it harder to see the moons.So it’s even harder to find satellites around Jupiter, and as you mentioned, other groups have already done this work for Uranus and Neptune. Does that mean we’re sort of “maxed out” on moons until we have better observations?Yeah, you probably have to wait until better technology comes along.Is there something being built or planned right now that could be that “better technology”?There currently are telescopes that can see deeper [than the CFHT], such as the James Webb Space Telescope (JWST). The problem is: JWST’s field of view is very small, so you have to do quite a few observations to be able to cover the required area. But there is a telescope that’s set to launch pretty soon, the Nancy Grace Roman Space Telescope, that has quite a large field of view. So that’ll be a good telescope to use for hunting more moons.What do we know about these new moons?You basically can only get the moons’ orbits and approximate sizes. But if you look at the distribution of the orbits, you can understand a bit more about the history of the system. Moons that are sort of clumped together in orbital space are most likely the result of a collision, so you can see what moons come from the same parent object.Is seeing so many moons around Saturn unusual?What’s unusual is how many there are. It appears that the planets have more or less equal numbers of the larger moons. But when you get down to the smaller ones that we’re discovering, Saturn seems to shoot up in terms of the numbers. So that’s quite interesting. This could just be because there was a recent collision within the Saturnian system that produced a large number of fragments.Do you get to name them all? Do you have to name them all?I guess I don’t have to. Some of these new moons, they’ve been linked back to observations by a different group from more than 10 years ago. That’s maybe 20 to 30 of them. For the rest, we get full discovery credit, which, I think, means we get the right to name them. But they can’t be named just yet; first, they’re just given a number when they have a high-precision orbit, and I’m not sure how long that’s going to take.Do you have more moon-hunting observations to analyze?No, I’m taking a little break from moons! I’ve got other projects to work on, relating to trans-Neptunian objects. They’re quite far away. They’re hard to see. There are some mysteries about them at the moment. It’s interesting to understand their structure and how it relates to planet formation.

Total construction starts fell 9% in April to a seasonally adjusted annual rate of $1.03 trillion, according to Dodge Construction Network.  Nonresidential building starts declined by 3%, residential starts dropped 4%, and nonbuilding starts decreased by 22%. On a year-to-date basis through April, total construction starts were down 3% from last year. Nonresidential starts were down 10%, residential starts were down 5%, while nonbuilding starts were up 8%. For the 12 months ending in April 2025, total construction starts were up 2% from the year ending in April 2024. Nonresidential starts were up 1%, nonbuilding starts rose by 5%, and there was no change in residential starts. Related on Archinect: Architecture industry saw 'accelerated decrease in billing activity' in April, says AIA/Deltek Architecture Billings Index“Broad-based monthly declines in construction starts represent a troubling signal for the sector,” said Dodge Construction Network chief economist Eric Gaus. “While no...

In its April Architecture Billings Index (ABI), the AIA shared that billings have dropped “in 28 out of the past 31 months.” This last month was no exception: April reported a score of 43.2, a decrease from March’s 44.1—any number below 50 indicates a decrease in billings from the previous month. Uncertain economic conditions have undoubtedly contributed to these latest declines, something that AIA Chief Economist Kermit Baker remarked on a statement, included in this month’s report. “Uncertainty as to the economic outlook continues to hold back progress on new construction projects,” Baker said. Baker remained optimistic, however, sharing that firms seem to be retaining staff and continuing to have steady work on their plates. “Despite the slowdown in billing activity, architecture firms continue to navigate this business cycle quite effectively, as staffing at firms remains relatively stable and project backlogs are holding up better than expected,” he added. The AIA included “resources to help architects successfully navigate an uncertain economy” in its April report. It shared past ABI data, the AIA Consensus Construction Forecast, the AIA Business of Architecture Firm Survey Report, and other relevant industry data. In addition to the national ABI, the index for new project inquiries and the value of design contracts also continues to dip with each passing month. Regionally, all parts of the country are reporting drops in billings, with the Northeast still the lowest at 40.2. The South remains the region with the lowest rate of decline, and highest score, reporting 46.2 for April, a drop from March’s 48.3. Firms specializing in more than one typology seem to be faring the best in terms of declined billings, with a score of 47.6 for April. It remains a waiting game to see how the economy will go on. At its meeting last month, the Federal Reserve opted again to leave interest rates be, presumably to see what happens as the tariffs take hold, and unemployment remains relatively low.

Disappointing economic data for the architecture industry this morning: The latest AIA/Deltek Architecture Billings Index reports another noticeable drop to 43.2 in April, down from 44.1 in March. Any score below 50.0 signals a decline. Likewise, billings continued to slip, decreasing now in 28 out of the past 31 months. Scores for new project inquiries and the value of new design contracts reported ongoing declines as well.  Related explainer on Archinect: How to Understand Architecture Business Conditions Using the AIA's Architecture Billings Index"Uncertainty as to the economic outlook continues to hold back progress on new construction projects," AIA Chief Economist Kermit Baker commented on today's numbers. "Despite the slowdown in billing activity, architecture firms continue to navigate this business cycle quite effectively, as staffing at firms remains relatively stable and project backlogs are holding up better than expected." April ABI Highlights Regional averages: South ...

May 13, 20255 min readVenus Isn’t (Geologically) DeadA reappraisal of decades-old data suggests that strange circular formations on Venus could be volcanic “rings of fire” created by ongoing geological activityBy Elise Cutts edited by Lee BillingsThe northern hemisphere of Venus, as captured in radar data from NASA’s Magellan spacecraft. Some of the circular features seen in this image are coronae, mysterious formations that recent studies suggest could be sites of ongoing geological activity. NASA/JPL-CaltechEarth’s geology is downright vital. Here, giant “plates” of the crust rift apart and smash together like pieces of an ever changing planetary jigsaw puzzle. Mountains rise, volcanoes spew, and Earth itself quakes as the crust constantly remakes itself in the ceaseless cycle of plate tectonics. This is a process that controls the flow of carbon through our planet and stabilizes its climate; were it not for plate tectonics, Earth might not be habitable at all.No other rocky world in our solar system has anything approaching Earth’s degree of geological activity. At least, that’s what scientists used to think. Mercury, Mars and the moon appear essentially inert. But Venus, our closest neighbor and the only other large rocky world around the sun, is now starting to look far livelier than once thought. A fresh look at decades-old data from NASA’s Magellan probe has found evidence of active tectonics—around dozens of circular volcanic features called coronae—on Venus today. The finding, published on Wednesday in Science Advances, provides some of the best evidence to date that Venus isn’t dead—at least, not when it comes to tectonics.“Venus works differently than the Earth but not as different as what was originally assumed,” says the study’s co-lead author Anna Gülcher of the University of Bern in Switzerland. “We should think of tectonics as not just a black-and-white picture.”On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.“Questions as fundamental as ‘Is Venus alive today?’ are extremely hard to answer,” says planetary scientist Paul Byrne of the University of Washington in St. Louis, who wasn’t involved in the study. This new evidence of geological activity around the coronae suggests “the heart of Venus still beats today. I think that’s extremely invaluable for us to understand the big, rocky world next door.”Venus is called “Earth’s evil twin” for good reason: the planet is almost exactly as large as the Earth and is made of roughly the same stuff. But while Earth is a verdant water world, Venus is a scorched hellscape with temperatures hot enough to melt lead, a dreary, permanently overcast sky and air so thick that it crushes spacecraft as if they were tin cans.For a while, Venus was widely assumed to be just as dead on the inside as it is on the outside. Lacking any obvious plate tectonics—which can help release a world’s internal heat—Venus’s interior was thought to instead just simmer like the contents of a tight-lidded pot on a stove. According to one popular hypothesis, the pot had eventually boiled over: after eons of frustrated heating, some 800 million years ago, the planet’s outer shell buckled, and Venus’s entire surface was paved over with immense outpourings of fresh lava. And, the thinking went, with all that heat dissipated, the planet’s geology basically shut down.But evidence is mounting that Venus is, geologically at least, still kicking. Most notably, in 2023 two researchers scrutinizing 30-year-old Magellan data realized that the probe had caught a volcanic eruption in the act: radar images of the volcano Maat Mons that were taken months apart showed what looked like a caldera collapse and subsequent lava flow. Venus, it seems, still has active volcanoes. Some researchers now think it could have active tectonics, too. And in 2020 Gülcher and her colleagues showed via simulations of Venusian tectonics that the planet’s mysterious, ring-shaped coronae could be a good place to look for such activity.Tectonics refers to the processes that deform a rocky planet’s brittle outer shell. On Earth, this outer shell—the lithosphere, which includes the crust and part of the upper mantle—is broken into tectonic plates that drift over the hot, plastic mantle. When two plates collide, one of them can slide below the other and dive down into the mantle in a process called subduction. On Earth, subducting plates start melting as they sink, feeding volcanoes along plate boundaries. Such volcanoes include Japan’s Mount Fuji and western North America’s Cascade Range.Unlike Earth, Venus doesn’t have global plate tectonics. The new study suggests, however, that around coronae, something quite similar to subduction could be happening.Gülcher and her colleagues simulated several tectonic processes that might be occurring around coronae and compared their predictions to real observations collected by the Magellan probe 30 years ago. The comparisons were more than skin-deep: the researchers used gravity data to take a peek underground. Hot rock is generally less dense than cold rock, and these density variations from place to place can correspondingly alter the strength of a planet’s gravitational field. So Magellan’s spatial mapping of Venus’s gravity can “see” if there’s hot, light material under a corona—a sign that rock is actively rising up from the mantle below.Of the 75 coronae that the team could resolve in Magellan’s gravitational maps, 52 seem to be geologically active. The predicted and real data lined up so well for some coronae that “we could hardly believe our eyes,” says the study’s other co-lead author Gael Cascioli of NASA’s Goddard Space Flight Center and the University of Maryland, Baltimore County. Most of the active coronae were encircled by trenches, a hint that old crust dives into Venus’s mantle around these rocky rings, where it is driven downward as buoyant rock rises from below in the middle of each corona’s ring structure. “Basically, if something goes down, something goes up,” Gülcher says. Where the lithosphere is softer and more pliable, bits of it could break off and “drip” down into the mantle in globs. In places where the lithosphere is stiffer, entire slabs of crust could subduct in a small-scale, circular mirror of Earth’s subduction zones, like those that form the Pacific Ocean’s famed volcanic Ring of Fire.Working with 30-year-old data comes with an obvious limitation: the data quality often isn’t very good compared with newer observations. The new study’s researchers did well with what they had, Byrne says. But NASA’s upcoming VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) mission could do much better—and the team predicted exactly how much better in the paper. “The improvement would be extraordinary,” Cascioli says. Instead of being limited to analyzing 75 coronae, VERITAS’s gravity dataset should allow scientists to examine hundreds of the strange ring-shaped features.For the foreseeable future, Venus is the only other large, rocky world that we or our robotic emissaries will ever reach. Understanding why Earth and Venus ended up so different despite having so much in common helps us understand our own planet—and whether the rocky worlds we’re beginning to glimpse around other stars are more like Earth or instead resemble its evil twin.“Venus is the world that we probably understand least,” Byrne says. “Yet it’s the one, arguably, I think, that’s the most important.”

May 13, 20256 min readDeep Math from String Theory Appears in Clashing Black HolesResearchers have shown that abstract mathematical functions from the frontiers of theoretical physics have a real-world use in modeling gravitational wavesBy Ramin Skibba edited by Lee BillingsAn illustration of two black holes about to merge and emitting copious gravitational waves. Chris Henze/NASA/SPL/Getty ImagesA decade ago astrophysicists at the Laser Interferometer Gravitational-Wave Observatory (LIGO), operated by the California Institute of Technology and the Massachusetts Institute of Technology, managed to detect subtle ripples in spacetime called gravitational waves, released by a pair of black holes spiraling into each other, for the first time. That impressive discovery—which earned the 2017 Nobel Prize in Physics—has since become commonplace, with researchers regularly detecting gravitational waves from myriad far-distant celestial sources.And as the numbers of gravitational-wave observations have increased, physicists’ careful modeling is revealing new details about their mysterious origins. Some of the most intriguing gravitational-wave events, it turns out, could arise not from catastrophic collisions but rather from near misses. Furthermore, these cosmic close calls might be best understood using concepts derived from string theory—a notional theory of everything that posits that all of nature is fundamentally composed of countless, wriggling subatomic strings. This arguably marks the first linkage to date between a core mathematical aspect of the arcane theory and real-world astrophysics.At least, that’s the conclusion of an international team of researchers that applied geometric structures inspired by particle physics and string theory to the behavior of black holes when the colossal objects closely pass and deflect each other. Such interactions between black holes or neutron stars (compact remnants of exploded massive stars) can be studied through the deflection angle, the energy released through the near miss and the momentum of the objects’ recoil—all of which may be discerned in gravitational waves. The team’s results were published in the journal Nature on Wednesday.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Black Holes as ParticlesIn their study, the researchers used an obscure class of abstract mathematical functions to solve the formidable equations involved in determining the radiated energy from a near miss. “You need these new functions, which, in math and mathematical physics, have been studied intensively but, to date, have not appeared in any real physical observable. That’s what makes it quite interesting,” says Jan Plefka, a theoretical physicist at the Humboldt University of Berlin and a co-author of the new study. Those obscure functions, known as six-dimensional Calabi-Yau manifolds, had never been shown as directly relevant to descriptions of real astrophysical phenomena before.In the years since LIGO’s initial detection, two additional major gravitational-wave observatories, Europe’s Virgo and Japan’s Kamioka Gravitational-Wave Detector (KAGRA), have come online. Together, they form the international LIGO-Virgo-KAGRA collaboration and have amassed detections of nearly 300 gravitational-wave events over the past decade, mostly from colliding pairs of black holes. Also called black hole “mergers,” such events are the cacophonous moment when these dense gravitational behemoths smash together to form a single, larger beast. Plefka and his colleagues are studying different interactions known as “scattering” events, which occur when paired black holes slip by each other, usually in prelude to their eventual coalescence. During these close encounters, the clashing gravity of the black holes causes each to accelerate past the other, generating a significant gravitational-wave signal, but the objects are sufficiently separated to avoid merging.It’s no coincidence that this resembles elementary particles deflecting each other. “You can use the techniques developed for the scattering of microscopic objects to describe this scattering of macroscopic ones,” Plefka says. Considered from far enough away, well beyond the event horizon—that pivotal region within which neither matter nor light can escape—a black hole can be modeled as a particlelike point with mass and spin, albeit one that generates gravitational rather than electromagnetic waves.On that basis, Plefka and his colleagues applied techniques from quantum field theory that are more typically used to analyze the behavior of elementary particles. “We’re building on decades of work that has been done to make predictions for collider experiments,” says Gustav Mogull, a particle physicist at Queen Mary University of London and one of Plefka’s co-authors.Closer to Complex RealitiesThe team’s goal was to bring its numerical approximations as close as possible to mirroring reality—which, of course, tends to be more messy. To do that, Mogull, Plefka and their team toiled to crank up the complexity of their calculations. In this work, the researchers incorporated five levels of that complexity—to what is known as the fifth post-Minkowskian order of precision—for describing the scattering angles of black hole pairs, their radiated energies and their recoils.This is where the Calabi-Yau geometric structures, normally associated with string theory, come in. In string theory, Calabi-Yau geometries involve the compactification of higher dimensions. Here, they are not merely abstractions but instead emerge from the researchers’ calculations of black hole scattering. It’s perhaps ironic that string theory, notoriously derided as untestable, has given rise to mathematical structures of relevance to measurable physics far from the rarefied realm of strings.A visualization of two black holes scattering off each other and emitting gravitational waves, which are rendered in shades of blue (darker shades correspond to higher energies). This visualization was computed with the aid of advanced mathematical functions known as Calabi-Yau manifolds.Mathias Driesse/Humboldt Universtität zu BerlinAny mathematical function is associated with some kind of geometry, Mogull explains—and as the function increases in complexity, so, too, does its geometry. In the case of something basic, such as the sine or cosine functions used in trigonometry, that geometry is a simple circle. Elliptic functions, on the other hand, imply a doughnut-shaped geometry called a torus, which is also a Calabi-Yau onefold. It turns out that the functions Mogull, Plefka and their team developed for black hole scattering are associated with Calabi-Yau threefold structures, which involve six-dimensional surfaces. “I don’t think the appearance of Calabi-Yaus was that unexpected within our community. I would say this represents confirmation of something that people had suspected but was yet to be verified,” Mogull says.To demonstrate the utility of their approach in their study, Plefka, Mogull and their colleagues compare their approximations of black hole scattering angles to other, presumably more precise ones that were derived from numerical simulations. Such simulations can be time-consuming to run, even on state-of-the-art supercomputers—hence the search for accurate approximations. The team’s highest-order approximation closely matches the results of supercomputer number crunching for cases of black holes that gently deflect each other across great distances. But when the black holes come closer to a head-on collision, the team’s calculations begin diverging from the numerical simulations.Such work may seem to be a purely academic exercise, but in fact, the research could prove vital for making new discoveries. Signals from scattering black holes and neutron stars should be within reach of the next generation of gravitational-wave detectors that are set to come online in the late 2030s. These detectors, which will also need a new generation of models called waveform templates to discern true gravitational-wave signals from a sea of cosmic and terrestrial noise, include the proposed Einstein Telescope in Europe and Cosmic Explorer in the U.S. The latter, like LIGO, is supported by the National Science Foundation, and so far these kinds of gravitational-wave projects have avoided being directly targeted by the Trump administration’s aggressive proposed cuts to federally funded science.The work’s prospect for enhancing our understanding of gravitational-wave sources excites scientists who are gearing up for this new wave of detectors. They include Jocelyn Read, a physicist at California State University, Fullerton, who works with the Cosmic Explorer project. “Next-generation facilities can measure nearby signals with exquisite fidelity,” she says. (Here “nearby” means “within a few billion light-years.”) “So having very accurate and precise predictions from our current theories is definitely needed to test them against those kinds of future observations,” Read adds.Yet she also urges caution when assessing the significance of Plefka, Mogull and their colleagues’ work. “If they’re talking about implications for gravitational-wave astronomy, there are a few more steps that are needed,” she says. And their team has competitors, too, including some who have been deploying numerical simulations of their own.These kinds of approximate methods could eventually inform the waveform templates that are so crucial for filtering out noise in upcoming gravitational-wave detectors, Plefka says. Geraint Pratten, a LIGO physicist at the University of Birmingham in England, agrees. “I think it’s a heroic calculation by the group. It will provide a lot of insight into how we can structure next-generation waveform models,” he says. Pratten adds that more work will need to be done to move past the new study’s limitations. For example, the paper focuses on black holes without spin and those that undergo “unbound” scattering, which means that they deflect each other and never meet again. In reality, most, if not all, black holes are thought to spin, and usually scattering events precede an eventual merger.But in any case, he believes some gravitational waves from black hole and neutron star deflections will eventually be detectable, such as through observations of globular clusters, where these dense objects are packed together in a small space, cosmically speaking.For Plefka, Mogull and their peers, this macroscopic version of quantum field theory is still a young field, and there are many new types of astrophysically relevant calculations that they and others can do. These esoteric Calabi-Yau structures, formerly on the frontier of theoretical physics, could be just the beginning. “You’ve had this whole new class of mathematical functions—these theoretical things that had appeared in string theory,” Mogull says. “And we’re saying, ‘Look, this is tangible. This [radiated energy from scattering] is something you can try to detect, try to measure. This is real physics now.’”

May 12, 20257 min readPhysicists Build a ‘Black Hole Bomb’ in the LaboratoryAstronomical amounts of energy could be extracted from black holes—to build a gigantic bomb, for example. Experts have now implemented this principle in the laboratoryBy Manon Bischoff edited by Lee BillingsAn artist’s rendition of a black hole surrounded by a glowing accretion disc of material, the light from which is warped by the strong gravity. In principle, energy could be harvested from a spinning black hole—and lab-based demonstrations are beginning to show physicists how this could occur. Mark Garlick/Science Photo Library/Getty ImagesA bomb from a black hole would probably be the most destructive weapon in the universe. Hypothetically, it could be created by wrapping one of these cosmic monsters in mirrors and waiting for it to go “boom.” Now Hendrik Ulbricht of the University of Southampton in England and his colleagues have demonstrated this principle, called superradiance, in the lab using a rotating metal cylinder instead of a black hole. They submitted their results, which have not yet been peer-reviewed, to the preprint server arXiv.org in late March.“This work shows that a ‘black hole bomb’ can actually be built in the laboratory,” says physicist Vitor Cardoso of the Niels Bohr Institute in Denmark, who was not involved in the study. “It thus provides a solid basis for studying the entire physics of black holes.”Among the strangest objects in the universe, black holes pack so much mass into such a small space that they can radically warp spacetime. A black hole’s gravitational pull is so strong that within a certain distance, nothing can escape it—not even light. Theorist Roger Penrose is one of the pioneers who first studied black holes mathematically in detail—work for which he shared the Nobel Prize in Physics in 2020. And amid that early work, he realized something surprising.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.As Penrose knew, nothing stands still in our cosmos, not even black holes. These massive monsters can spin, distorting spacetime in the process to form a kind of vortex. An approaching object can be caught up in this vortex and spiral around the spinning black hole. Even before the object passes the event horizon, beyond which not even light can escape gravity’s clutches, it reaches an area that physicists call the “ergosphere.” There the object would have to move faster than light to escape the rotation around the black hole.This ergosphere is a strange place, as Penrose noted, because objects there can possess negative energy. A particle, for example, could split into two equal-but-opposite parts: one with negative energy and another with positive energy. The former would then crash into the black hole (thus reducing the black hole’s energy), allowing the latter to escape the cosmic behemoth’s mighty grip. An external observer would see a particle with a certain energy falling toward the black hole, only to apparently rebound outward with higher energy. The black hole loses part of its rotational energy in the process.Black Hole Mining and SuperradianceIn principle, this would allow black holes to serve as gigantic sources of energy. The process could not only imbue massive objects with more energy but also amplify electromagnetic waves in a phenomenon called superradiance. This realization spurred some physicists to even imagine how advanced alien civilizations might use superradiance to generate energy. But despite how relatively simple it is to describe on paper, no one knew how the signal of superradiance could be observed in real black holes. Thus, the concept initially remained mere speculation.In 1971, however, two years after Penrose first described this phenomenon, physicist Yakov Zel’dovich published research that suggested that black holes aren’t the only objects that can be tapped as superradiant energy sources. Any rotating, axially symmetrical body that absorbs electromagnetic radiation—such as a metal cylinder—can also exhibit superradiance under certain circumstances. “Roughly speaking, the rotating absorber must rotate faster than the phase rotation of the incident radiation,” explains physicist Maria Chiara Braidotti of the University of Glasgow in Scotland, who was involved in the latest work. “If this condition is met, the absorption coefficient of the cylinder changes sign, thus amplifying the radiation.”Zel’dovich even went one step further by showing that superradiance could also take place in a vacuum and wouldn’t require an incoming electromagnetic wave. That’s because on quantum scales the vacuum is anything but empty. At any time, pairs of virtual particles and antiparticles can pop into existence, although they typically immediately annihilate each other again. The phenomenon is known as vacuum fluctuation. And these fluctuations could also be amplified in the vicinity of black holes —or a rotating metal cylinder. “Stephen Hawking didn’t believe this idea and tried to refute it,” explains Marion Cromb, a researcher in Ulbricht’s group at the University of Southampton and a contributor to the new work. “Not only did [Hawking] admit that Zel’dovich was right but he was also able to prove that even nonrotating black holes—without an ergosphere—spontaneously emit radiation.” This realization led to the discovery of Hawking radiation.According to the theoretical calculations, however, vacuum-based superradiance would be so faint that it could not be detected—unless, that is, it was somehow amplified. As Zel’dovich described, the rotating body (black hole or metal cylinder) could be encased in mirrors to reflect the amplified radiation back to the rotating body, intensifying it over and over again. As physicists William Press and Saul Teukolsky realized, so much energy could accumulate inside the mirrors that a gigantic explosion would occur. Press and Teukolsky, therefore, referred to the setup as a black hole bomb.Depending on how much rotational energy the black hole or the metal cylinder has, a result other than a gigantic explosion is conceivable, though. Cardoso and his colleagues described this possibility in a paper published in 2004 that showed how superradiance can cease if the black hole or metal cylinder loses too much angular momentum, thus defusing the explosion.Explosions in the LaboratoryUlbricht, Braidotti and their colleagues now wanted to test all these theoretical predictions in the laboratory. “Originally, we thought it would be too difficult to observe the actual effect,” Braidotti says, nothing that a cylinder would have to rotate so fast that it would be destroyed in the process. For this reason, she initially turned her attention to simpler systems in which superradiance can occur, including a setup with sound waves. “The breakthrough was our noticing how to reduce the frequencies of electromagnetic fields in a very simple way so that they are smaller than the rotation frequencies of the metal cylinders,” Ulbricht explains. The researchers only needed alternating current circuits for this. “This finding opened up the possibility of conducting the experiment with electromagnetic waves,” Braidotti says.The team then turned its attention to electromagnetic superradiance. “The experimental setup itself is quite simple: it consists of a rotating cylinder and the stator coils of a commercially available induction motor, combined with some capacitors and resistors,” Cromb says. These devices were placed around the metal cylinder to generate a magnetic field inside it, which produced electromagnetic radiation. At the same time, these devices also served as mirrors because they reflected the electromagnetic waves back toward the cylinder.“The biggest difficulty was that things were constantly exploding,” Cromb says. “It was a balancing act between measuring a reasonable signal and overloading the system. When the current through the coils became too high, the resistors in the circuit exceeded their rated voltage and burned out. This interrupted the electrical circuit, thus destroying the ‘mirror.’”The researchers initially feared that these overloads would prevent any observation of superradiance. But they were lucky. “The reinforcement was large enough to overcome the loss and enter the area of instability,” Cromb says. In fact, the team was able to show that the voltage in their structure increased exponentially, as predicted by Zel’dovich. This underpins the researchers’ claim of the first-ever lab-based demonstration of an electromagnetic version of a black hole bomb.Note, however, that despite the martial connotations of the name, the “bomb” Ulbricht and his team built in their lab isn’t anything like a military-grade munition—or even a firecracker. It would be quite useless as a weapon because its yield is only on the order of a millijoule of energy—that is, about the same amount involved in pressing a single key on a mechanical keyboard.Radiation-Free Superradiance?Next, Cromb and the team used their setup to study whether superradiance can also take place in a vacuum: Would an electromagnetic signal arise in their apparatus even without a magnetic field? Because the experiment took place at room temperature, thermal fluctuations overshadowed any vacuum fluctuations—meaning that the team could not directly detect the latter. But that very same thermal background noise, the researchers realized, would spontaneously generate electromagnetic waves that could theoretically be amplified.And that is what they did manage to demonstrate: by choosing the appropriate rotation speed of the cylinder, they generated electromagnetic waves out of nowhere, so to speak. Their work also confirmed the “defusing” scenario predicted by Cardoso: the metal cylinder was able to lose enough rotational energy to halt superradiance and stave off any explosion.According to Ulbricht, the most special thing about the work is its sheer simplicity. “Many physicists think that all the simple experiments have already been done and that new insights into the fundamentals of physics can only come from very complex and very expensive projects,” he says. “We proved the opposite.”“I didn’t expect that someone would be able to carry out such an experiment now,” Cardoso says. On the day the new work was posted to arXiv.org, he recalls, he was giving a series of lectures at Bangalore University in India. “I talked about superradiance and told the audience that no one had ever proven the electromagnetic superradiance or the bomb effect in the laboratory. So you can imagine my surprise when I saw the paper shortly afterwards!”The new work could lead to deeper insights about black holes, Cardoso says. “Superradiance is a little-known classical effect that plays an important role in the physics of black holes,” he explains. For example, extremely light particles, such as axions or special types of photons considered candidates for dark matter, could absorb the rotational energy of black holes, amplifying their signals. “This means that black holes can be used as gigantic particle detectors,” Cardoso explains. With a lab-based black hole bomb, physicists could test such hypotheses more precisely than ever before.In the future, Ulbricht would like to carry out the quantum version of the experiment, which would entail observing the spontaneous generation of electromagnetic waves and their amplification from the vacuum. Such direct experiments with vacuum fluctuations could open up completely new possibilities for the scientific community and the world, he says, potentially representing “a major breakthrough for physics.” Perhaps, Ulbricht muses, that work could allow researchers “in a few decades to understand whether it is possible in principle to generate energy from the vacuum—which would be an inexhaustible new source of energy.”