The International Space Station has been a hub for human space exploration and research for over two decades, but its operational life is nearing its end, projected around 2030. As […]
NASA administrator nominee Jared Isaacman says he would, if necessary, prioritize Artemis over human missions to Mars and calls a potential halving of NASA science funding not “optimal.”
Nonlocal correlations that define quantum entanglement could be reconciled with Einstein’s theory of relativity if space–time had two temporal dimensions. That is the implication of new theoretical work that extends nonlocal hidden variable theories of quantum entanglement and proposes a potential experimental test.
Marco Pettini, a theoretical physicist at Aix Marseille University in France, says the idea arose from conversations with the mathematical physicist Roger Penrose – who shared the 2020 Nobel Prize for Physics for showing that the general theory of relativity predicted black holes. “He told me that, from his point of view, quantum entanglement is the greatest mystery that we have in physics,” says Pettini. The puzzle is encapsulated by Bell’s inequality, which was derived in the mid-1960s by the Northern Irish physicist John Bell.
Bell’s breakthrough was inspired by the 1935 Einstein–Podolsky–Rosen paradox, a thought experiment in which entangled particles in quantum superpositions (using the language of modern quantum mechanics) travel to spatially separated observers Alice and Bob. They make measurements of the same observable property of their particles. As they are superposition states, the outcome of neither measurement is certain before it is made. However, as soon as Alice measures the state, the superposition collapses and Bob’s measurement is now fixed.
Quantum scepticism
A sceptic of quantum indeterminacy could hypothetically suggest that the entangled particles carried hidden variables all along, so that when Alice made her measurement, she simply found out the state that Bob would measure rather than actually altering it. If the observers are separated by a distance so great that information about the hidden variable’s state would have to travel faster than light between them, then hidden variable theory violates relativity. Bell derived an inequality showing the maximum degree of correlation between the measurements possible if each particle carried such a “local” hidden variable, and showed it was indeed violated by quantum mechanics.
A more sophisticated alternative investigated by the theoretical physicists David Bohm and his student Jeffrey Bub, as well as by Bell himself, is a nonlocal hidden variable. This postulates that the particle – including the hidden variable – is indeed in a superposition and defined by an evolving wavefunction. When Alice makes her measurement, this superposition collapses. Bob’s value then correlates with Alice’s. For decades, researchers believed the wavefunction collapse could travel faster than light without allowing superliminal exchange of information – therefore without violating the special theory of relativity. However, in 2012 researchers showed that any finite-speed collapse propagation would enable superluminal information transmission.
“I met Roger Penrose several times, and while talking with him I asked ‘Well, why couldn’t we exploit an extra time dimension?’,” recalls Pettini. Particles could have five-dimensional wavefunctions (three spatial, two temporal), and the collapse could propagate through the extra time dimension – allowing it to appear instantaneous. Pettini says that the problem Penrose foresaw was that this would enable time travel, and the consequent possibility that one could travel back through the “extra time” to kill one’s ancestors or otherwise violate causality. However, Pettini says he “recently found in the literature a paper which has inspired some relatively standard modifications of the metric of an enlarged space–time in which massive particles are confined with respect to the extra time dimension…Since we are made of massive particles, we don’t see it.”
Toy model
Pettini believes it might be possible to test this idea experimentally. In a new paper, he proposes a hypothetical experiment (which he describes as a toy model), in which two sources emit pairs of entangled, polarized photons simultaneously. The photons from one source are collected by recipients Alice and Bob, while the photons from the other source are collected by Eve and Tom using identical detectors. Alice and Eve compare the polarizations of the photons they detect. Alice’s photon must, by fundamental quantum mechanics, be entangled with Bob’s photon, and Eve’s with Tom’s, but otherwise simple quantum mechanics gives no reason to expect any entanglement in the system.
Pettini proposes, however, that Alice and Eve should be placed much closer together, and closer to the photon sources, than to the other observers. In this case, he suggests, the communication of entanglement through the extra time dimension when the wavefunction of Alice’s particle collapses, transmitting this to Bob, or when Eve’s particle is transmitted to Tom would also transmit information between the much closer identical particles received by the other woman. This could affect the interference between Alice’s and Eve’s photons and cause a violation of Bell’s inequality. “[Alice and Eve] would influence each other as if they were entangled,” says Pettini. “This would be the smoking gun.”
Bub, now a distinguished professor emeritus at the University of Maryland, College Park, is not holding his breath. “I’m intrigued by [Pettini] exploiting my old hidden variable paper with Bohm to develop his two-time model of entanglement, but to be frank I can’t see this going anywhere,” he says. “I don’t feel the pull to provide a causal explanation of entanglement, and I don’t any more think of the ‘collapse’ of the wave function as a dynamical process.” He says the central premise of Pettini’s – that adding an extra time dimension could allow the transmission of entanglement between otherwise unrelated photons, is “a big leap”. “Personally, I wouldn’t put any money on it,” he says.
China has chosen payloads from a range of international partners to fly on the country’s Chang’e-8 lunar south pole mission, expanding its space diplomacy.
A burst of solar wind triggered a planet-wide heatwave in Jupiter’s upper atmosphere, say astronomers at the University in Reading, UK. The hot region, which had a temperature of over 750 K, propagated at thousands of kilometres per hour and stretched halfway around the planet.
“This is the first time we have seen something like a travelling ionospheric disturbance, the likes of which are found on Earth, at a giant planet,” says James O’Donoghue, a Reading planetary scientist and lead author of a study in Geophysical Research Letters on the phenomenon. “Our finding shows that Jupiter’s atmosphere is not as self-contained as we thought, and that the Sun can drive dramatic, global changes, even this far out in the solar system.”
Jupiter’s upper atmosphere begins hundreds of kilometres above its surface and has two components. One is a neutral thermosphere composed mainly of molecular hydrogen. The other is a charged ionosphere comprising electrons and ions. Jupiter also has a protective magnetic shield, or magnetosphere.
When emissions from Jupiter’s volcanic moon, Io, become ionized by extreme ultraviolet radiation from the Sun, the resulting plasma becomes trapped in the magnetosphere. This trapped plasma then generates magnetosphere-ionosphere currents that heat the planet’s polar regions and produce aurorae. Thanks to this heating, the hottest places on Jupiter, at around 900 K, are its poles. From there, temperatures gradually decrease, reaching 600 K at the equator.
Quite a different temperature-gradient pattern
In 2021, however, O’Donoghue and colleagues observed quite a different temperature-gradient pattern in near-infrared spectral data recorded by the 10-metre Keck II telescope in Hawaii, US, during an event in 2017. When they analysed these data, they found an enormous hot region far from Jupiter’s aurorae and stretching across 180° in longitude – half the planet’s circumference.
“At the time, we could not definitively explain this hot feature, which is roughly 150 K hotter than the typical ambient temperature of Jupiter,” says O’Donoghue, “so we re-analysed the Keck data using updated solar wind propagation models.”
Two instruments on NASA’s Juno spacecraft were pivotal in the re-analysis, he explains. The first, called Waves, can measure electron densities locally. Its data showed that these electron densities ramped up as the spacecraft approached Jupiter’s magnetosheath, which is the region between the planet’s magnetic field and the solar wind. The second instrument was Juno’s magnetometer, which recorded measurements that backed up the Waves-based analyses, O’Donoghue says.
A new interpretation
In their latest study, the Reading scientists analysed a burst of fast solar wind that emanated from the Sun in January 2017 and propagated towards Jupiter. They found that a high-speed stream of this wind arrived several hours before the Keck telescope recorded the data that led them to identify the hot region.
“Our analysis of Juno’s magnetometer measurements also showed that this spacecraft exited the magnetosphere of Jupiter early,” says O’Donoghue. “This is a strong sign that strong solar winds probably compressed Jupiter’s magnetic field several hours before the hot region appeared.
“We therefore see the hot region emerging as a response to solar wind compression: the aurorae flared up and heat spilled equatorward.”
The result shows that the Sun can significantly reshape the global energy balance in Jupiter’s upper atmosphere, he tells Physics World. “That changes how we think about energy balance at all giant planets, not just Jupiter, but potentially Saturn, Uranus, Neptune and exoplanets too,” he says. “It also shows that solar wind can trigger complex atmospheric responses far from Earth and it could help us understand space weather in general.”
The Reading researchers say they would now like to hunt for more of these events, especially in the southern hemisphere of Jupiter where they expect a mirrored response. “We are also working on measuring wind speeds and temperatures across more of the planet and at different times to better understand how often this happens and how energy moves around,” O’Donoghue reveals. “Ultimately, we want to build a more complete picture of how space weather shapes Jupiter’s upper atmosphere and drives (or interferes) with global circulation there.”
German satellite operator OroraTech opened its U.S. headquarters in Denver, Colorado, April 24 to push its growing wildfire-monitoring constellation into a country that regularly experiences some of the world’s most costly fires.
Three Chinese astronauts arrived at the Tiangong space station Thursday aboard the Shenzhou-20 spacecraft, hours after launching from the Jiuquan Satellite Launch Center
China’s megaconstellation launches spark debris concerns; commercial space expands; Lightyear Explorer raises funds; key updates expected during China’s Space Day and Shenzhou-20 launch.
A new study forecasts more than 850,000 measles cases over the next 25 years if US vaccination rates stay the same. Millions of infections are possible if rates drop.
The world’s smallest pacemaker to date is smaller than a single grain of rice, optically controlled and dissolves after it’s no longer needed. According to researchers involved in the work, the pacemaker could work in human hearts of all sizes that need temporary pacing, including those of newborn babies with congenital heart defects.
“Our major motivation was children,” says Igor Efimov, a professor of medicine and biomedical engineering, in a press release from Northwestern University. Efimov co-led the research with Northwestern bioelectronics pioneer John Rogers.
“About 1% of children are born with congenital heart defects – regardless of whether they live in a low-resource or high-resource country,” Efimov explains. “Now, we can place this tiny pacemaker on a child’s heart and stimulate it with a soft, gentle, wearable device. And no additional surgery is necessary to remove it.”
The current clinical standard-of-care involves sewing pacemaker electrodes directly onto a patient’s heart muscle during surgery. Wires from the electrodes protrude from the patient’s chest and connect to an external pacing box. Placing the pacemakers – and removing them later – does not come without risk. Complications include infection, dislodgment, torn or damaged tissues, bleeding and blood clots.
To minimize these risks, the researchers sought to develop a dissolvable pacemaker, which they introduced in Nature Biotechnology in 2021. By varying the composition and thickness of materials in the devices, Rogers’ lab can control how long the pacemaker functions before dissolving. The dissolvable device also eliminates the need for bulky batteries and wires.
“The heart requires a tiny amount of electrical stimulation,” says Rogers in the Northwestern release. “By minimizing the size, we dramatically simplify the implantation procedures, we reduce trauma and risk to the patient, and, with the dissolvable nature of the device, we eliminate any need for secondary surgical extraction procedures.”
Light-controlled pacing When the wearable device (left) detects an irregular heartbeat, it emits light to activate the pacemaker. (Courtesy: John A Rogers/Northwestern University)
The latest iteration of the device – reported in Nature – advances the technology further. The pacemaker is paired with a small, soft, flexible, wireless device that is mounted onto the patient’s chest. The skin-interfaced device continuously captures electrocardiogram (ECG) data. When it detects an irregular heartbeat, it automatically shines a pulse of infrared light to activate the pacemaker and control the pacing.
“The new device is self-powered and optically controlled – totally different than our previous devices in those two essential aspects of engineering design,” says Rogers. “We moved away from wireless power transfer to enable operation, and we replaced RF wireless control strategies – both to eliminate the need for an antenna (the size-limiting component of the system) and to avoid the need for external RF power supply.”
Measurements demonstrated that the pacemaker – which is 1.8 mm wide, 3.5 mm long and 1 mm thick – delivers as much stimulation as a full-sized pacemaker. Initial studies in animals and in the human hearts of organ donors suggest that the device could work in human infants and adults. The devices are also versatile, the researchers say, and could be used across different regions of the heart or the body. They could also be integrated with other implantable devices for applications in nerve and bone healing, treating wounds and blocking pain.
The next steps for the research (supported by the Querrey Simpson Institute for Bioelectronics, the Leducq Foundation and the National Institutes of Health) include further engineering improvements to the device. “From the translational standpoint, we have put together a very early-stage startup company to work individually and/or in partnerships with larger companies to begin the process of designing the device for regulatory approval,” Rogers says.
In this week's episode of Space Minds, Lori Garver, former NASA Deputy Administrator sits down with host David Ariosto. Garver describes what drives spaceflight-and what that means for the agency's shifting priorities.
Winning the new space race with China is contingent on the competitiveness of the United States commercial space industry. While the Chinese space program enjoys the full financial and regulatory […]
Connexion
