Decades later, physicists found that Bethe's method also works for larger particles moving along a line, such as atoms. If those particles attract each other, the math predicts they will bind into clusters called Bethe strings.

Now, physicists have found evidence of these clusters in a line of ultracold atoms. The findings were published Aug. 29 in the journal Nature Communications.

The discovery may not create new gadgets, but it addresses a fundamental mystery in physics. Everything around us, from magnets to phone chips, consists of countless interacting particles. This makes their behavior difficult to predict. Ultracold atoms serve as a clear and adjustable way to study these complex systems.

A "necklace" of atoms

Researchers have spotted small Bethe strings before, in magnetic crystals and superconducting quantum circuits ‪— but those experiments captured strings one at a time.

Theory predicts that crowds of strings, in many sizes, can change how an entire system behaves, and studying that idea requires making many strings at once. That has been hard to do with atoms. Atoms that attract each other usually collapse into a clump. But this time, the team appears to have made many strings of different sizes at once, including some with more than six atoms.

It's tricky to get atoms to attract each other. In three dimensions, a gas made of attracting atoms tends to collapse as the atoms clump together and form molecules. That process releases energy that kicks atoms out of the experiment, so the gas quickly collapses and disappears. But when they're in a single line, the atoms behave differently.

"They are really a bit like pearls on a string, right? Like on a necklace, they cannot go past," study co-author Hanns-Christoph Nägerl, an experimental physicist at the University of Innsbruck, told Live Science. "In 3D, everything would collapse. But in 1D, it does not collapse."

To build their "necklaces," the team started with tens of thousands of cesium atoms cooled into a Bose-Einstein condensate ‪— a state of matter in which atoms chilled to near absolute zero share a single quantum state. Laser beams then divided the condensate into thousands of thin tubes, each of which held up to a few dozen atoms in a line.

At first, the atoms repelled each other. The researchers used a magnetic field to gradually turn that repulsion down to zero, and then turned it into attraction.

The team couldn't see the strings directly. Instead, they let the atoms go and measured how fast the cloud spread. When the atoms could expand only along their tubes, any strings stayed intact. When the atoms were freed in all three dimensions, the strings broke apart and released their binding energy as motion. The researchers found that the 3D clouds spread with about three times as much energy as the one-dimensional ones did.

From that difference, the team estimated how tightly the atoms had been bound. The answer pointed to strings of at least six atoms. The measurements also closely matched predictions from a theory called generalized hydrodynamics, which describes a gas like this one as a fluid made of many kinds of particles, including strings of different sizes. It also tracks how each kind flows over time rather than following every atom.

Nägerl was careful not to call this proof. "That some theory fits to your data is not a proof that something exists," he said; it's just more evidence to support it.

A short-lived state

The strings likely don't survive long. Up close, the atoms still feel the three-dimensional world, and the strings eventually decay into ordinary cesium molecules. In the coldest runs, the team lost about 40% of the atoms.

"Transiently you create these Bethe string states," Nägerl said. "But I don't think they are long-lived."

He has an idea for future experiments. Physicists recently learned to shield ultracold molecules with microwaves, which keeps the molecules from colliding at close range. Strings made from shielded molecules might last long enough to be studied directly. But Nägerl stressed that the idea is untested. "I've had nobody do a theory check on my claims now, but I think intuitively this should work," he said.

Another option is quantum gas microscopy, which images atoms one at a time and could offer more direct evidence of individual strings.

For Nägerl, Bethe strings are one step in understanding how quantum systems with many particles behave and settle down over time. His long-term goal is an experiment in which physicists control both how every particle moves and how its spin flips, letting them assemble model materials piece by piece, "like a LEGO type," he said. His team has begun the next step: using lasers to control the spins of the atoms in its one-dimensional gas. He described Bethe strings as "a little diversion." But because the strings form whenever the atoms attract, they can't be ignored.

'> Physicists froze a 'necklace' of atoms — and witnessed a quantum phenomenon predicted 100 years ago

The dinosaur lived on what is now the Isle of Wight in southern England about 120 million years ago. It belonged to a group of two-legged carnivores called megaraptors, which are related to tyrannosaurs. But unlike tyrannousars, megaraptors are thought to have relied on their powerful arms and large curved claws to attack prey and defend themselves.

The newly identified species was described in an Oct. 14 study in the journal Royal Society Open Science. It is the first megaraptor identified in Europe, filling an important gap in the fossil record of a group whose evolutionary history remains poorly understood.

"It is a real mystery that this fossil was overlooked for so long, sitting in a drawer for nearly 100 years," study first author Cassius Morrison, a researcher in the Department of Earth Sciences at University College London (UCL) said in a statement. "Lots of bones are found on the Isle of Wight — who knows what else is waiting to be discovered."

Unconquered female warrior dinosaur

The discovery of the megaraptor began in 1924, when an amateur fossil collector discovered a dinosaur skull fragment on the Isle of Wight. The specimen eventually entered the collections of London's Natural History Museum, but it was largely forgotten.

Recently, researchers revisited the fossil as part of a study on dinosaur braincases. To identify the animal, the researchers used micro-CT scanning to examine the fossil's internal structure and build detailed 3D digital models of the space that once held the dinosaur's brain.

The researchers then compared the animal's anatomy with that of other meat-eating dinosaurs, including tyrannosaurs, spinosaurs and other theropods (the group of two-legged, mostly meat-eating dinosaurs). Several features differentiated the unknown specimen, including an almost oval opening where the spinal cord entered the skull and an unusual, hourglass-shaped ridge at the back of the braincase.

Computer-based evolutionary analyses placed the fossils within the Megaraptora family tree, supporting the idea that the skull represented a never-before-seen species. The researchers named the dinosaur Invictibellatrix amberina, combining the Latin words "unconquered" and "female warrior" for the genus name, while amberina refers to amber found in the rocks associated with the fossil.

Megaraptors lived between roughly 125 million and 66 million years ago and varied considerably in size. While early members were relatively small, some later species became enormous predators. Maip macrothorax, discovered in Argentina, may have reached up to 33 feet (10 meters) long and weighed as much as an elephant. Based on comparisons with related dinosaurs, I. amberina was much smaller, likely around 10 to 13 feet (3 to 4 m) long and standing roughly 5 feet (1.5 m) tall. The researchers estimated it weighed around 440 to 660 pounds (200 to 300 kilograms), making it one of the smallest known megaraptors.

"It was not the apex predator of its time, but for humans this dinosaur would have been more dangerous than a T. rex," Morrison said. "We would have been perfectly sized prey, about a third of their body weight. They definitely would have chased us."

Although the newly described fossil doesn't preserve the animal's arms or claws, its closest relative suggests that its claws may have measured around 4 to 8 inches (10 to 20 centimeters) long. The researchers also suggested I. amberina may have been feathered, though that feature can't be determined directly from the specimen.

A missing link in the dinosaurs' globetrotting

Scientists have long suspected that megaraptors originated in Asia before spreading to other parts of the world, eventually becoming the dominant predators across the southern supercontinent Gondwana, which included present-day Africa, South America and Antarctica. But a lack of European fossils left an important gap in verifying this migration route.

The new study's evolutionary models suggest that I. amberina descended from Asian megaraptors that dispersed into Europe around 130 million years ago. From there, members of the group may have moved through what is now Africa and further into Gondwana via temporary landbridges and temporary land connections across the shallow Tethys Ocean.

"This new species is the first proof we have that megaraptorans were also present in Europe and that they reached Gondwana this way rather than island-hopping further south," study co-author Charlie Scherer, a doctoral student at UCL Earth Sciences, said in the statement.

However, the specific route these animals took over millions of years is still unknown. The researchers also cannot yet explain why megaraptors disappeared from northern areas, but changes in climate or competition with other predatory dinosaurs may have contributed. More research on other megaraptor fossils like I. amberina could help uncover more clues.

"Work like this shows the exceptional value of working with historical museum collections where there are still many discoveries to be made," study co-author Paul Barrett, a researcher of dinosaur evolution at the Natural History Museum in London, said in the statement.

'> Fossil of 'unconquered female warrior' dinosaur with long claws found in UK museum drawer after 100 years Mark Hollands, an astronomer at the University of Warwick in the U.K. and first author of the study, said in a statement. "It turns out these incredibly dense stars can produce colours nobody expected, and some of them genuinely surprised me."

The variety of colors is possible due to white dwarfs' densities compared with main-sequence stars, the study suggests. Cooler white dwarfs have a density of about 1 gram per cubic centimeter, much like flowing water on Earth. The density of these white dwarfs is also millions of times denser than the sun's visible surface, or photosphere, leading to unusual conditions.

"Any trace elements that may be present, such as carbon, calcium and sodium, interact with the surrounding dense helium plasma and absorb light across a wider range of colours than they would at lower densities," the researchers said in a statement. "This shifts a star's colour away from the orange, white and blue [typical] of a perfect radiator."

White dwarfs are far away and small, making it difficult to verify their color. So, in the new study, astronomers inferred the colors using spectra, the distinctive chemical fingerprints produced by stars' light. The team analyzed the spectra within a model of color vision that the human eye can see, making the color pop out.

Scientists found that carbon-rich white dwarfs tend to be purple or pink, while those that contain debris from asteroids or comets are usually yellower. Cyan or pale-blue white dwarfs occur when hydrogen and helium molecules strike each other in very dense atmospheres.

The team also discovered WD J1330+6435 — a green star that contains rocky material. The green comes from the additional elements of calcium, lithium and sodium in the star's atmosphere, creating a unique "chartreuse green appearance" that would be visible to the human eye, if we could see it up close.

"The traces of sodium in the atmosphere of this white dwarf absorb the orange part of the spectrum, leaving behind a ghostly green glow," Hollands explained, adding that the one-of-a-kind green star "feels like something out of science fiction." The team also discovered what is likely the reddest star ever found. This white dwarf, called WD J1011+2845, is located roughly 48 light-years from our planet. It has carbon closer to its surface — because the element is being lifted from the interior, due to strong convection currents — that is bending the star's light. This process is making a "deep salmon-pink glow" because the carbon molecules are obstructing the star's other wavelengths.

Overall, in the sample of stars studied — 151 white dwarfs within 65 light-years of Earth — about 1 in 30 white dwarfs glowed in a color other than white. This could mean there are far more colorful stellar remnants littering the universe than anyone anticipated.

'> Astronomers discover the first-ever green star, plus the reddest 'white dwarf' ever seen numerous Ramesses II statues have been found throughout Egypt.

Archaeologists had previously found architectural fragments bearing the name of Ramesses II at Behbeit El Hagar, which is known for its temple dedicated to Isis, a goddess associated with healing and magic, said Mahmoud Emam, an Egyptologist at Cairo University who has worked on remains from the site but was not involved with the recent excavation. He noted that the newly found statues were unearthed on the western side of the temple complex.

"Strong Bull"

Both of the newfound statues were once larger than life, with the bigger one likely standing nearly 28 feet (8.5 meters) tall when it was originally built. However, most of what remains is its head, which is 5.2 feet (1.6 m) tall and depicts the pharaoh wearing the double crown of Upper and Lower Egypt.

Part of this large statue's back pillar has a hieroglyphic inscription that gives the pharaoh's "Horus" name: Hor-Ka-Nakht-Mery-Maat. This name means "Strong Bull, Beloved of Right, Truth," Joyce Tyldesley, a professor emeritus of Egyptology at the University of Manchester in the U.K., wrote in her book "Ramesses: Egypt's Greatest Pharaoh" (Penguin Books, 2001). In Egypt, it was common for pharaohs to have several alternate names with a Horus name, given in honor of the sky god Horus.

The second statue, which stands about 7.9 feet (2.4 m), also likely depicts Ramesses II, the statement said. The king is shown wearing the "Nemes" headdress, a type of striped headcloth that pharaohs wore, the Egypt Exploration Society notes on its website.

Near this statue is a block of pink granite with two hieroglyphic inscriptions that name Ramesses II and describe him as "King of Upper and Lower Egypt" and the "Son of Ra," an ancient Egyptian sun god, the statement said.

Previous Ramesses II finds

The new finds add more evidence that Ramesses II was heavily invested in the site.

Previous discoveries include two architectural fragments bearing the name of Ramesses II near the Isis temple at Behbeit El Hagar, Emam and his colleagues reported in a 2017 paper. One is believed to be from the upper part of a statue, and another seems to originate from the upper part of a wall.

"We concluded that Ramesses II had undertaken major building works at the temple and recommended further archaeological investigations to shed more light on the early history of the site," Emam said. He noted that the site is threatened by urban growth and that excavation work should be carried out at the temple.

Live Science reached out to the team but did not hear back by the time of publication.

Are you a fan of mummies and hieroglyphs? Find out with our ancient Egypt quiz!

'> 2 giant Ramesses II statues, one wearing a double crown, discovered by man in Egypt

If it reads like science fiction, that's because it started that way. Called space-based solar power (SBSP), the concept featured prominently in the techno-utopian imaginations of 20th-century visionaries and writers. But for decades, it was dismissed — a pie in the sky proposal.

Now, as a new space race heats up, governments and private companies in China, the U.S., the U.K. and Japan are developing several projects to reassess the idea's feasibility. These include China's ZhuRi ("Chase the Sun") program, Japan's OHISAMA project, the U.K.'s Space Solar, and power-beaming experiments by Caltech and the Air Force Research Laboratory in the U.S., all of which are targeting test launches in the next five years.

Proponents say the technology has the potential to meet Earth's energy needs many times over while causing minimal harm to the environment. But first it needs to get off the ground: In the eyes of critics, space-based solar power is exorbitantly expensive, riddled with untested assumptions, and far too complex to be deployed in time for an urgent green-energy transition.

The challenges include getting the massive solar-panel-covered satellites into space; assembling them; getting those solar panels to constantly face our star; and then finding ways to convert, concentrate and transmit their collected power back to Earth.

Despite these hurdles, researchers keep returning to the idea. Perhaps because the most crucial step — generating energy in the first place — is already being done by the sun. Every second, our star fuses hydrogen atoms to expel the same energy as nine trillion atomic bombs. All that's left to do is catch it.

"We're not a competitor to fusion. We are fusion," Peter Garretson, the U.S. Air Force's former chief of future technology and an SBSP expert, told Live Science.

From science fiction to NASA proposal

The first glimmers of SBSP as a concept came from the Russian rocket scientist and astronautics pioneer Konstantin Tsiolkovsky, who, in 1923, suggested deploying space-based mirrors that could concentrate sunlight to Earth with enough intensity to boil 10 cups of coffee.

Tsiolkovsky's fanciful proposal soon entered science fiction, appearing in the British writer Olaf Stapledon's 1937 novel "Star Maker" as a "gauze of light traps" that an advanced alien civilization used to focus "the escaping solar energy for intelligent use" — an idea later formalized by theoretical physicist Freeman Dyson as a Dyson sphere.

Then, in 1941, Isaac Asimov made the clearest, most famous early sketch of SBSP in his short story "Reason," in which a robot colony toils aboard a power station that collects solar energy and fires it back to Earth in the form of microwaves. Asimov provided few details on the fictional station's engineering, instead focusing on the robots' religious worship of the vessel.

But the transformation from science fiction to a concrete proposal didn't take long. In 1968, aerospace engineer Peter Glaser, a consultant and project manager for the Apollo 11 mission's distance-measuring laser reflectors, drew up an engineering design for a "solar power satellite" consisting of three key elements: a ray-collecting device, a converter and a transmitter.

Glaser's collector was a disk of photovoltaic panels that would be lifted some 22,400 miles (36,000 kilometers) off the ground. Locked in a geostationary orbit above Earth and bathed in near-constant sunlight, the satellite would harvest solar rays before converting them into microwaves to be beamed, largely unimpeded through the atmosphere, to receiving antennae on the ground. Once there, the microwaves would be converted into electricity and distributed across the grid.

NASA awarded Glaser a contract to study the concept further, with both domestic and international energy crises (such as the 1973 oil crisis and the 1979 Three-Mile Island nuclear accident) adding wind to his solar sails.

But Glaser's design hit technical and financial roadblocks, the most forbidding being the project's sheer size. By 1981, when the U.S. Department of Energy's four-year study of space-based solar power was released, it estimated that a "meaningful" contribution of 300 gigawatts (sufficient to power hundreds of millions of homes) would require 60 satellites, each spanning 21 square miles (55 square kilometers) and weighing 50,000 tons (45,000 metric tons). The plan was deemed unaffordable.

Later reassessments, such as a 1997 report by NASA physicist John Mankins, pointed to advances such as improved solar cells that made the concept more realistic. Yet the overall consensus remained hostile. A 2015 report released by the Strategic Studies Institute (SSI) of the U.S. Army War College stated that while SBSP systems are "technically feasible," there was "no compelling evidence that such systems will be economically competitive" with terrestrial power systems. It concluded that "the reality is that such systems always seem to be seen as just 10 years away by their advocates."

Aiming high

But a lot can change in a decade, including the cost of firing rockets. Since the SSI report, SpaceX's reusable Falcon 9 rocket has sent launch costs plummeting to around 30 times less than those of NASA's Space Shuttle, with satellites also getting cheaper due to mass production and advances to the clean rooms where they're made. And SpaceX's even bigger Starship rocket promises to more than quintuple Falcon's payload capacity, lowering prices further.

"What you have is a cadre of people in the space community that have grown up before Starlink and SpaceX," Garretson said. "They literally could not believe that, as your launch rate goes up and you amortize your costs, [the launch cost] approaches the cost of fuel." Some took notice. A 2021 assessment commissioned by the U.K. government estimated that a 2-gigawatt, mile-wide space-based solar power array would cost 17.3 billion British pounds ($23.4 billion) and generate energy at 50 British pounds ($68) per megawatt hour over its century lifetime.

That's the equivalent output of a large power station in the U.K., with the initial costs being 39% to 49% cheaper than biomass, nuclear or the most efficient gas energy sources, according to the assessment. And while it's still 14% to 52% more expensive than current terrestrial wind and solar energy, the technology could be beamed anywhere, even to remote locations.

Based on these findings, in 2023, the U.K. government awarded 4.3 million British pounds ($5.8 million) in seed funding to a handful of companies and universities to develop SBSP further.

The U.K. report chose one satellite design as its reference architecture: CASSIOPeiA. Belonging to the U.K. SBSP company Space Solar, the satellite's design is an attempt to crack a significant challenge faced by early solar satellite blueprints: how to keep solar panels constantly aligned with the sun to maximize radiation collection.

Unlike other satellite designs, such as China's Multi-Rotary Joint Solar Power Satellite or Mankins' SPS-ALPHA, which rotate the panels or use a system of mirrors to constantly redirect sunlight onto them, CASSIOPeiA is shaped like a gigantic DNA strand.

This design, alongside a sun-synchronous orbit and a slow spin, enables CASSIOPeiA to constantly receive and transmit solar energy without any heavy or failure-prone moving parts. Space Solar claims that a single CASSIOPeiA satellite, which would be about 1 mile (1.6 km) in diameter, could microwave-beam as much as 2 gigawatts of constant power to a fixed point on the ground — enough to supply a city of 2 million people.

Space Solar says that once the satellite is in space, it will be far more efficient and economical than gathering sunlight on the ground could ever be. That's because the light hitting the space-based power station isn't deflected or attenuated by the atmosphere.

"You use a lot less materials compared with terrestrial solar, and you utilize them more," Sam Adlen, co-founder and co-CEO of Space Solar, one of the funding recipients, told Live Science. "So it's 100% utilized in space rather than 10% if you're on the ground — and you've got 13 times more instant energy, so you're getting much more out of the materials."

Beaming down

However, the next step — beaming gigawatts of energy down and across tens of miles of atmosphere and through potential cloud cover — remains a major technical hurdle.

Proposed power-beaming methods are currently split between two types: lasers and microwaves. California-based startup Aetherflux, which has plans to beam power from satellites in low Earth orbit, has developed an infrared laser transmission system that it will test using a demonstration satellite launched on October 1. The microwave energy will be transmitted at around one kilowatt (enough to supply the basic electrical demands of a household).

Meanwhile, Caltech and Overview Energy, another U.S. startup, have both demonstrated respective microwave and laser-power beaming from orbit and from a plane, respectively, albeit in negligible amounts ( less than a kilowatt).

Despite their efficiency and proven ability to travel vast distances, optical beams in the infrared and near-infrared ranges are easily scattered by water droplets in the atmosphere, preventing power from being transferred on cloudy days. Persisting efficiency issues with optical power transmission also worsen at gigawatt power levels, meaning lasers are less feasible for use at the utility scale.

Microwaves, on the other hand, can be beamed at frequencies with much higher power and suffer relatively little atmospheric attenuation. That's why Space Solar, Japan's OHISAMA project and China's ZhuRi program all plan to use microwave-beaming systems. Nonetheless, microwaves have comparatively longer wavelengths, so their beams diffract more widely across longer distances. This means that even if beams are sent by transmitters hundreds of meters wide, they would need Earth-based receivers spanning dozens of square miles.

These limitations mean that "it's going to take many years" before gigawatt-scale power beaming is achieved, Remo Proietti Zaccaria, head of the DELTA Lab at the Italian Institute of Technology, told Live Science.

Improvements in power-beaming efficiency will bring their own challenges. Even battery-powered laser pointers can blind or burn, so prototypes by laser-beaming SBSP companies like Aetherflux must be designed with that possibility in mind. They promise safety mechanisms that switch off their lasers if anything flies between the transmitter and the receiver.

"Definitely for the weapon side, this technology now can be used efficiently," Proietti Zaccaria said.

If you're imagining an orbital weapon devised by a Bond villain, you may be disappointed — even fully developed power-beaming lasers and microwaves would take a while to cook an egg, or boil Tsiolkovsky's coffees. But beaming technology could still have potent military use: Scrambling communications systems on Earth to create havoc with relatively little effort.

"If you throw even that amount of intensity of power to our antennas, you're going to freeze the electronics; that's for sure," Proietti Zaccaria said. "It's not necessary to destroy them. As long as you freeze the electronics, you've done the job."

The challenges associated with power beaming have pushed some engineers to simpler concepts. One (going full circle back to Tsiolkovsky's original proposal) envisions the deployment of space-based mirrors that reflect sunlight back to Earth after sunset, with a single reflector extending the daylight delivered onto solar panels by around 20 minutes.

This may not seem like much on its own, "but then you can increase this with multiple reflectors," Onur Celik, a researcher in space technology at the University of Glasgow, told Live Science. "If you have 10 or more of them, you can arrange them in space in such a way that you can extend this to up to two hours or so at that altitude."

"The sunlight that you deliver, if it all turns into electricity, could power thousands of homes," he concluded.

The light of day

The trillion-dollar question is whether that power will be cheaper and more efficient than that generated on the ground. The median cost of the electricity generated by SBSP as estimated by the U.K. government is 50 British pounds per megawatt hour ($68), putting it roughly in line with the costs of offshore wind and terrestrial solar power.

However, this estimate is orders of magnitude too sunny for the 2024 NASA cost report, with its projections suggesting SBSP's baseline electricity costs fall between $610 and $1,590 per megawatt hour, depending on the array design. NASA concluded that the U.K.'s median estimate was achievable only after drastic future reductions in launch and manufacturing costs.

Independent studies are also divided over feasibility. One assessment suggests that SBSP could reduce Europe's need for land-based renewable energy by up to 80%, while another counters that the costs could be 12 to 80 times more expensive than those for terrestrial alternatives. This variability exists within the studies themselves, with research published in the journal Acta Astronautica estimating that SBSP could contribute to meeting anywhere from 3% to 31% of global electricity demand, depending on possible constraints in how many satellites can safely fit into an orbit, the receiver size, and where power is beamed to.

"For the numbers we found, I don't believe that this technology could actually be employed to generate energy for Earth," said Proietti Zaccaria, a co-author of the Acta Astronautica study. If humanity had used up all available space for solar panels on Earth, "then I will tell you it would make sense, because at that point, 3%, 5%, 10% could make a difference."

Proietti Zaccaria does see use cases for SBSP schemes for future moon or Mars missions, but otherwise, "the cost for building technology of this kind is really very, very high," he said. "Vice versa, the cost nowadays of buying and installing a solar panel on the roof of any building has become extremely cheap."

Among the challenges would be ferrying the raw materials for the systems into space and then assembling them. Such a feat would make the construction of the International Space Station — currently the most complex structure built in orbit — seem like child's play. Maintaining arrays and preventing them from crashing into other satellites in Earth's increasingly crowded orbits would also take significant international coordination.

Then there are the unweighed environmental costs. All modern rockets use methane, a potent greenhouse gas, to propel them into space, and they release much of it into Earth's upper atmosphere, where its effects are the strongest.

"And so clearly, there is a question there on how launching 100,000 of these superheavy vehicles into the atmosphere will actually impact the atmosphere itself, as opposed to the benefit that we get in the next 20 years or so from having solar power from space," Matteo Ceriotti, a senior lecturer in space systems engineering at the University of Glasgow, told Live Science. "It's not entirely clear."

Ceriotti said the likeliest route for overcoming all of these difficulties come from smaller companies running, and then streamlining, proof-of-concept tests in space.

"Obviously, it's not something that we have ever done," he said. "So clearly, we need to start somewhere, and we need to start small."

The hopes of SBSP proponents remain unclouded by gloomy estimates. They cite several technologies, from personal computers to reusable rockets, that were once thought to be impossibly expensive, even fictitious, that are now ubiquitous and cheap. Their eyes remain fixed on demonstration missions to be launched over the next four years by the likes of Space Solar, Reflect Orbital, Aetherflux and Virtus Solis. If these missions succeed, another once-impossible idea could appear much brighter.

"The private sector is good at this, because it has to be," Sanjay Vijendran, an SBSP consultant who led the European Space Agency's now-shuttered SOLARIS project to test the feasibility of SBSP, told Live Science. "It can break the problem down to quite a small level and start to do things with today's technology and today's way of doing things, and start to show that this can be valuable."

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'> 'We're not a competitor to fusion. We are fusion': Inside the race to harness unlimited solar power in space