From the Global Physics Summit in Anaheim, California
The greatest pleasure of being at a huge physics conference is learning about the science of something that’s familiar, but also a little bit quirky. That’s why I always try to go to sessions given by undergraduate students, because for some reason they seem to do research projects that are the most fun.
I was not disappointed by the talk given this morning by Atharva Lele, who is at the Georgia Institute of Technology here in the US. He spoke about the physics of manu jumping, a competitive sport that originates from the Māori and Pasifika peoples of New Zealand.
The general idea will be familiar to anyone who messed around at swimming pools as a child: who can make the highest splash when they jump into the water.
Cavity creation
According to Lele, the best manu jumpers enter the water back first, creating a V-shape with their legs and upper body. The highest splashes are made when a jumper creates a deep and wide air cavity that quickly closes, driving water upwards in a jet – often to astonishing heights.
Lele and colleagues discovered that a 45° angle between the legs and torso afforded the highest splashes. This is probably because this angle results in a cavity that is both deep and wide. An analysis of videos of manu jumpers revealed that the best ones entered the water at an angle of about 46°, corroborating the teams findings. This is good news for jumpers, because there is risk of injury at higher angles (think belly flop).
Another important aspect of the study looked at what jumpers did when they entered the water – which is to roll and kick. To study the effect of this motion, the team created a “manu bot”, which unfolded as it entered the water. They found that there was an optimal opening time for making the highest splashes – it is a mere 0.26 s.
I was immediately taken back to my childhood in Canada and realized that we were doing our own version of manu from the high diving board at the local pool. The most successful technique that we discovered was to keep our bodies straight, but entering the water at an angle. This would consistently produce a narrow jet of water. I realize now that by entering the water at an angle, we must have been creating a relatively deep and wide cavity – although probably not as efficiently and manu jumpers. Maybe Lele and colleagues could do a follow-up study looking at alternative versions of manu around the world.
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A new study probing quantum phenomena in neurons as they transmit messages in the brain could provide fresh insight into how our brains function.
In this project, described in the Computational and Structural Biotechnology Journal, theoretical physicist Partha Ghose from the Tagore Centre for Natural Sciences and Philosophy in India, together with theoretical neuroscientist Dimitris Pinotsis from City St George’s, University of London and the MillerLab of MIT, proved that established equations describing the classical physics of brain responses are mathematically equivalent to equations describing quantum mechanics. Ghose and Pinotsis then derived a Schrödinger-like equation specifically for neurons.
Our brains process information via a vast network containing many millions of neurons, which can each send and receive chemical and electrical signals. Information is transmitted by nerve impulses that pass from one neuron to the next, thanks to a flow of ions across the neuron’s cell membrane. This results in an experimentally detectable change in electrical potential difference across the membrane known as the “action potential” or “spike”.
When this potential passes a threshold value, the impulse is passed on. But below the threshold for a spike, a neuron’s action potential randomly fluctuates in a similar way to classical Brownian motion – the continuous random motion of tiny particles suspended in a fluid – due to interactions with its surroundings. This creates the so-called “neuronal noise” that the researchers investigated in this study.
Previously, “both physicists and neuroscientists have largely dismissed the relevance of standard quantum mechanics to neuronal processes, as quantum effects are thought to disappear at the large scale of neurons,” says Pinotsis. But some researchers studying quantum cognition hold an alternative to this prevailing view, explains Ghose.
“They have argued that quantum probability theory better explains certain cognitive effects observed in the social sciences than classical probability theory,” Ghose tells Physics World. “[But] most researchers in this field treat quantum formalism [the mathematical framework describing quantum behaviour] as a purely mathematical tool, without assuming any physical basis in quantum mechanics. I found this perspective rather perplexing and unsatisfactory, prompting me to explore a more rigorous foundation for quantum cognition – one that might be physically grounded.”
As such, Ghose and Pinotsis began their work by taking ideas from American mathematician Edward Nelson, who in 1966 derived the Schrödinger equation – which predicts the position and motion of particles in terms of a probability wave known as a wavefunction – using classical Brownian motion.
Firstly they proved that the variables in the classical equations for Brownian motion that describe the random neuronal noise seen in brain activity also obey quantum mechanical equations, deriving a Schrödinger-like equation for a single neuron. This equation describes neuronal noise by revealing the probability of a neuron having a particular value of membrane potential at a specific instant. Next, the researchers showed how the FitzHugh-Nagumo equations, which are widely used for modelling neuronal dynamics, could be re-written as a Schrödinger equation. Finally, they introduced a neuronal constant in these Schrödinger-like equations that is analogous to Planck’s constant (which defines the amount of energy in a quantum).
“I got excited when the mathematical proof showed that the FitzHugh-Nagumo equations are connected to quantum mechanics and the Schrödinger equation,” enthuses Pinotsis. “This suggested that quantum phenomena, including quantum entanglement, might survive at larger scales.”
“Penrose and Hameroff have suggested that quantum entanglement might be related to lack of consciousness, so this study could shed light on how anaesthetics work,” he explains, adding that their work might also connect oscillations seen in recordings of brain activity to quantum phenomena. “This is important because oscillations are considered to be markers of diseases: the brain oscillates differently in patients and controls and by measuring these oscillations we can tell whether a person is sick or not.”
Going forward, Ghose hopes that “neuroscientists will get interested in our work and help us design critical neuroscience experiments to test our theory”. Measuring the energy levels for neurons predicted in this study, and ultimately confirming the existence of a neuronal constant along with quantum effects including entanglement would, he says, “represent a big step forward in our understanding of brain function”.
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From the Global Physics Summit in Anaheim, California
I spent most of Saturday travelling between the UK and Anaheim in Southern California, so I was up very early on Sunday with jetlag. So just as the sun was rising over the Santa Ana Mountains on a crisp morning, I went for a run in the suburban neighbourhood just south of the Anaheim Convention Center. As I made my way back to my hotel, the sidewalks were already thronging with physicists on their way to register for the Global Physics Summit (GPS) – which is being held in Anaheim by the American Physical Society (APS).
The GPS combines the APS’s traditional March and April meetings, which focus on condensed-matter and particle and nuclear physics, respectively – and much more. This year, about 14,000 physicists are expected to attend. I popped out at lunchtime and spotted a “physics family” walking along Harbor Boulevard, with parents and kids all wearing vintage APS T-shirts with clever slogans. They certainly stood out from most families, many of which were wearing Mickey Mouse ears (Disneyland is just across the road from the convention centre).
Uniting physicists
The GPS starts in earnest bright and early Monday morning, and I am looking forward to spending a week surrounded by thousands of fellow physicists. While many physicists in the US are facing some pretty dire political and funding issues, I am hoping that the global community can unite in the face of the anti-science forces that have emerged in some countries.
This year is the International Year of Quantum Science and Technology, so it’s not surprising that quantum mechanics will be front and centre here in Anaheim. I am looking forward to the “Quantum Playground”, which will be on much of this week. It promises, “themed areas; hands-on interactive experiences; demonstrations and games; art and science installations; mini-performances; and ask the experts”. I’ll report back once I have paid a visit.
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Researchers in France have devised a new technique in quantum sensing that uses trapped ultracold atoms to detect acceleration and rotation. They then combined their quantum sensor with a conventional, classical inertial sensor to create a hybrid system that was used to measure acceleration due to Earth’s gravity and the rotational frequency of the Earth. With further development, the hybrid sensor could be deployed in the field for applications such as inertial navigation and geophysical mapping.
Measuring inertial quantities such as acceleration and rotation is at the heart of inertial navigation systems, which operate without information from satellites or other external sources. This relies on the precise knowledge of the position and orientation of the navigation device. Inertial sensors based on classical physics have been available for some time, but quantum devices are showing great promise. On one hand, classical sensors using quartz in micro-electro-mechanical (MEM) devices have gained widespread use due to their robustness and speed. However, they suffer from drifts – a gradual loss of accuracy over time, due to several factors such as temperature sensitivity and material aging. On the other hand, quantum sensors using ultracold atoms achieve better stability over long operation times. While such sensors are already commercially available, the technology is still being developed to achieve the robustness and speed of classical sensors.
Now, the Cold Atom Group of the French Aerospace Lab (ONERA) has devised a new method in atom interferometry that uses ultracold atoms to measure inertial quantities. By launching the atoms using a magnetic field gradient, the researchers demonstrated stabilities below 1 µm/s2 and 1 µrad/s for acceleration and rotation measurements over 24 hours respectively. This was done by continuously performing a 4 s interferometer sequence on the atoms for around 20 min to extract the inertial quantities. That is equivalent to driving a car for 20 min straight and knowing the acceleration and rotation to the µm/s2 and µrad/s level.
Cold-atom accelerometer–gyroscope
They built their cold-atom accelerometer–gyroscope using rubidium-87 atoms. By holding the atoms in a magneto-optical trap, the researchers cool them down to 2 µK, enabling good control over the atoms for further manipulation. By releasing the atoms from the trap, the atoms freely fall along the gravity direction. This allows the researchers to measure their free falling acceleration using atom interferometry. In their protocol, a series of three light pulses that coherently splits an atomic cloud into two paths, redirects and then recombines it allowing the cloud to interfere with itself. From the phase shift of the interference pattern, the inertial quantities can be deduced.
Measuring their rotation rates however, requires that the atoms have an initial velocity in the horizontal direction. This is done by applying a horizontal magnetic field gradient, which results in a horizontal force on atoms with magnetic moments. The rubidium atoms are prepared in one of the magnetic states known as the Zeeman sublevels. The researchers then use a pair of coils that they called the “launching coils” in the horizontal plane to create the necessary magnetic field gradient to give the atoms a horizontal velocity. The atoms are then transferred back to the ground non-magnetic state using a microwave pulse before performing atom interferometry. This avoids any additional magnetic forces that can affect interferometer’s outcome.
Analysing the launch velocity using laser pulses with tuned frequencies, the researchers are able to discriminate the velocity of the atoms whether it being from the magnetic launching scheme or other effects. The researchers observe two dominant and symmetric peaks associated to the velocity of the atoms due to the magnetic launching. However, they also observe a third smaller peak in between. This peak is due to an unwanted effect from the laser beams that transfers additional velocity to the atoms. Further improvement in the stability of the laser beams’ polarization – the orientation of its oscillating electric field with respect to its propagation axis, as well the current noise in the launching coils will allow for more atoms to be launched.
Using their new launch technique, the researchers operated their cold-atom dual accelerometer–gyroscope for two days straight, averaging down their results to obtain an acceleration measurement of 7×10−7 m/s2 and a rotation rate of 4×10−7 rad/s, limited by residual ground vibration noise.
Best of both worlds
While classical sensors suffer from long term drifts, they operate continuously in comparison to a quantum sensor that requires preparation of the atomic sample and the interferometry process which takes around half a second. For this reason, a classical–quantum hybrid sensor benefits from the long-term stability of the quantum sensor and the fast repetition rate of the classical one. By attaching a commercial classical accelerometer and a commercial classical gyroscope to the atom interferometer, they implemented a feedback loop on the classical sensor’s outputs. The researchers demonstrated a respective 100-fold and three-fold improvement on the acceleration and rotation rates stabilities, respectively, of the classical sensors compared to when they are operated alone.
Operating this hybrid sensor continuously and utilizing their magnetic launch technique, the researchers report a measure of the local acceleration due gravity in their laboratory of 980,881.397 mGal (the milligal is a standard unit of gravimetry). They measured Earth’s rotation rate to be 4.82 × 10−5 rad/s. Cross checking with another atomic gravimeter, they find their acceleration value deviating by 2.3 mGal, which they regard to be due to misalignment of the vertical interferometer beams. Their rotation measurement has a significant error of about 25%, which the team attributes to wave-front distortions for the Raman beams used in their interferometer.
Yannick Bidel, a researcher working on this project, explains how such an inertial quantum sensor has room for improvement. Large-momentum-transfer, a technique to increase the arm separation of the interferometer, is one way to go. He further adds that once they reach bias stabilities of 10−9 to 10−10 rad/s within a compact size atom interferometer, such a sensor could become transportable and ready for in-field measurement campaigns.
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(Courtesy: EHT Collaboration; Los Alamos National Laboratory)
1 When the Event Horizon Telescope imaged a black hole in 2019, what was the total mass of all the hard drives needed to store the data? A 1 kg B 50 kg C 500 kg D 2000 kg
2 In 1956 MANIAC I became the first computer to defeat a human being in chess, but because of its limited memory and power, the pawns and which other pieces had to be removed from the game? A Bishops B Knights C Queens D Rooks
(Courtesy: IOP Publishing; CERN)
3 The logic behind the Monty Hall problem, which involves a car and two goats behind different doors, is one of the cornerstones of machine learning. On which TV game show is it based? A Deal or No Deal BFamily Fortunes CLet’s Make a Deal DWheel of Fortune
4 In 2023 CERN broke which barrier for the amount of data stored on devices at the lab? A 10 petabytes (1016 bytes) B 100 petabytes (1017 bytes) C 1 exabyte (1018 bytes) D 10 exabytes (1019 bytes)
5 What was the world’s first electronic computer? A Atanasoff–Berry Computer (ABC) B Electronic Discrete Variable Automatic Computer (EDVAC) C Electronic Numerical Integrator and Computer (ENIAC) D Small-Scale Experimental Machine (SSEM)
6 What was the outcome of the chess match between astronaut Frank Poole and the HAL 9000 computer in the movie 2001: A Space Odyssey? A Draw B HAL wins C Poole wins D Match abandoned
7 Which of the following physics breakthroughs used traditional machine learning methods? A Discovery of the Higgs boson (2012) B Discovery of gravitational waves (2016) C Multimessenger observation of a neutron-star collision (2017) D Imaging of a black hole (2019)
8 The physicist John Hopfield shared the 2024 Nobel Prize for Physics with Geoffrey Hinton for their work underpinning machine learning and artificial neural networks – but what did Hinton originally study? A Biology B Chemistry C Mathematics D Psychology
9 Put the following data-driven discoveries in chronological order. A Johann Balmer’s discovery of a formula computing wavelength from Anders Ångström’s measurements of the hydrogen lines B Johannes Kepler’s laws of planetary motion based on Tycho Brahe’s astronomical observations C Henrietta Swan Leavitt’s discovery of the period-luminosity relationship for Cepheid variables D Ole Rømer’s estimation of the speed of light from observations of the eclipses of Jupiter’s moon Io
10 Inspired by Alan Turing’s “Imitation Game” – in which an interrogator tries to distinguish between a human and machine – when did Joseph Weizenbaum develop ELIZA, the world’s first “chatbot”? A 1964 B 1984 C 2004 D 2024
11 What does the CERN particle-physics lab use to store data from the Large Hadron Collider? A Compact discs B Hard-disk drives C Magnetic tape D Solid-state drives
12 In preparation for the High Luminosity Large Hadron Collider, CERN tested a data link to the Nikhef lab in Amsterdam in 2024 that ran at what speed? A 80 Mbps B 8 Gbps C 80 Gbps D 800 Gbps
13 When complete, the Square Kilometre Array telescope will be the world’s largest radio telescope. How many petabytes of data is it expected to archive per year? A 15 B 50 C 350 D 700
This quiz is for fun and there are no prizes. Answers will be published in April.
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How would the climate and the environment on our planet change if an asteroid struck? Researchers at the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea have now tried to answer this question by running several impact simulations with a state-of-the-art Earth system model on their in-house supercomputer. The results show that the climate, atmospheric chemistry and even global photosynthesis would be dramatically disrupted in the three to four years following the event, due to the huge amounts of dust produced by the impact.
Beyond immediate effects such as scorching heat, earthquakes and tsunamis, an asteroid impact would have long-lasting effects on the climate because of the large quantities of aerosols and gases ejected into the atmosphere. Indeed, previous studies on the Chicxulub 10-km asteroid impact, which happened around 66 million years ago, revealed that dust, soot and sulphur led to a global “impact winter” and was very likely responsible for the dinosaurs going extinct during the Cretaceous/Paleogene period.
“This winter is characterized by reduced sunlight, because of the dust filtering it out, cold temperatures and decreased precipitation at the surface,” says Axel Timmermann, director of the ICCP and leader of this new study. “Severe ozone depletion would occur in the stratosphere too because of strong warming caused by the dust particles absorbing solar radiation there.”
These unfavourable climate conditions would inhibit plant growth via a decline in photosynthesis both on land and in the sea and would thus affect food productivity, Timmermann adds.
Something surprising and potentially positive would also happen though, he says: plankton in the ocean would recover within just six months and its abundance could even increase afterwards. Indeed, diatoms (silicate-rich algae) would be more plentiful than before the collision. This might be because the dust created by the asteroid is rich in iron, which would trigger plankton growth as it sinks into the ocean. These phytoplankton “blooms” could help alleviate emerging food crises triggered by the reduction in terrestrial productivity, at least for several years after the impact, explains Timmermann.
The effect of a “Bennu”-sized asteroid impact
In this latest study, published in Science Advances, the researchers simulated the effect of a “Bennu”-sized asteroid impact. Bennu is a so-called medium-sized asteroid with a diameter of around 500 m. This type of asteroid is more likely to impact Earth than the “planet killer” larger asteroids, but has been studied far less.
There is an estimated 0.037% chance of such an asteroid colliding with Earth in September 2182. While this probability is small, such an impact would be very serious, says Timmermann, and would lead to climate conditions similar to those observed after some of the largest volcanic eruptions in the last 100 000 years. “It is therefore important to assess the risk, which is the product of the probability and the damage that would be caused, rather than just the probability by itself,” he tells Physics World. “Our results can serve as useful benchmarks to estimate the range of environmental effects from future medium-sized asteroid collisions.”
The team ran the simulations on the IBS’ supercomputer Aleph using the Community Earth System Model Version 2 (CESM2) and the Whole Atmosphere Community Climate Model Version 6 (WACCM6). The simulations injected up to 400 million tonnes of dust into the stratosphere.
The climate effects of impact-dust aerosols mainly depend on their abundance in the atmosphere and how they evolve there. The simulations revealed that global mean temperatures would drop by 4° C, a value that’s comparable with the cooling estimated as a result of the Toba volcano erupting around 74 000 years ago (which emitted 2000 Tg (2×1015 g) of sulphur dioxide). Precipitation also decreased 15% worldwide and ozone dropped by a dramatic 32% in the first year following the asteroid impact.
Asteroid impacts may have shaped early human evolution
“On average, medium-sized asteroids collide with Earth about every 100 000 to 200 000 years,” says Timmermann. “This means that our early human ancestors may have experienced some of these medium-sized events. These may have impacted human evolution and even affected our species’ genetic makeup.”
The researchers admit that their model has some inherent limitations. For one, CESM2/WACCM6, like other modern climate models, is not designed and optimized to simulate the effects of massive amounts of aerosol injected into the atmosphere. Second, the researchers only focused on the asteroid colliding with the Earth’s land surface. This is obviously less likely than an impact on the ocean, because roughly 70% of Earth’s surface is covered by water, they say. “An impact in the ocean would inject large amounts of water vapour rather than climate-active aerosols such as dust, soot and sulphur into the atmosphere and this vapour needs to be better modelled – for example, for the effect it has on ozone loss,” they say.
The effect of the impact on specific regions on the planet also needs to be better simulated, the researchers add. Whether the asteroid impacts during winter or summer also needs to be accounted for since this can affect the extent of the climate changes that would occur.
Finally, as well as the dust nanoparticles investigated in this study, future work should also look at soot emissions from wildfires ignited by “impact “spherules”, and sulphur and CO2 released from target evaporites, say Timmermann and colleagues. “The ‘impact winter’ would be intensified and prolonged if other aerosols such as soot and sulphur were taken into account.”
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This episode of the Physics World Weekly podcast features Ileana Silvestre Patallo, a medical physicist at the UK’s National Physical Laboratory, and Ruth McLauchlan, consultant radiotherapy physicist at Imperial College Healthcare NHS Trust.
In a wide-ranging conversation with Physics World’s Tami Freeman, Patallo and McLauchlan explain how ionizing radiation such as X-rays and proton beams interact with our bodies and how radiation is being used to treat diseases including cancer.
This episode was created in collaboration with IPEM, the Institute of Physics and Engineering in Medicine. IPEM owns the journal Physics in Medicine & Biology.
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Helium deep with the Earth could bond with iron to form stable compounds – according to experiments done by scientists in Japan and Taiwan. The work was done by Haruki Takezawa and Kei Hirose at the University of Tokyo and colleagues, who suggest that Earth’s core could host a vast reservoir of primordial helium-3 – reshaping our understanding of the planet’s interior.
Noble gases including helium are normally chemically inert. But under extreme pressures, heavier members of the group (including xenon and krypton) can form a variety of compounds with other elements. To date, however, less is known about compounds containing helium – the lightest noble gas.
Beyond the synthesis of disodium helide (Na2He) in 2016, and a handful of molecules in which helium forms weak van der Waals bonds with other atoms, the existence of other helium compounds has remained purely theoretical.
As a result, the conventional view is that any primordial helium-3 present when our planet first formed would have quickly diffused through Earth’s interior, before escaping into the atmosphere and then into space.
Tantalizing clues
However, there are tantalizing clues that helium compounds could exist in some volcanic rocks on Earth’s surface. These rocks contain unusually high isotopic ratios of helium-3 to helium-4. “Unlike helium-4, which is produced through radioactivity, helium-3 is primordial and not produced in planetary interiors,” explains Hirose. “Based on volcanic rock measurements, helium-3 is known to be enriched in hot magma, which originally derives from hot plumes coming from deep within Earth’s mantle.” The mantle is the region between Earth’s core and crust.
The fact that the isotope can still be found in rock and magma suggests that it must have somehow become trapped in the Earth. “This argument suggests that helium-3 was incorporated into the iron-rich core during Earth’s formation, some of which leaked from the core to the mantle,” Hirose explains.
It could be that the extreme pressures present in Earth’s iron-rich core enabled primordial helium-3 to bond with iron to form stable molecular lattices. To date, however, this possibility has never been explored experimentally.
Now, Takezawa, Hirose and colleagues have triggered reactions between iron and helium within a laser-heated diamond-anvil cell. Such cells crush small samples to extreme pressures – in this case as high as 54 GPa. While this is less than the pressure in the core (about 350 GPa), the reactions created molecular lattices of iron and helium. These structures remained stable even when the diamond-anvil’s extreme pressure was released.
To determine the molecular structures of the compounds, the researchers did X-ray diffraction experiments at Japan’s SPring-8 synchrotron. The team also used secondary ion mass spectrometry to determine the concentration of helium within their samples.
Synchrotron and mass spectrometer
“We also performed first-principles calculations to support experimental findings,” Hirose adds. “Our calculations also revealed a dynamically stable crystal structure, supporting our experimental findings.” Altogether, this combination of experiments and calculations showed that the reaction could form two distinct lattices (face-centred cubic and distorted hexagonal close packed), each with differing ratios of iron to helium atoms.
These results suggest that similar reactions between helium and iron may have occurred within Earth’s core shortly after its formation, trapping much of the primordial helium-3 in the material that coalesced to form Earth. This would have created a vast reservoir of helium in the core, which is gradually making its way to the surface.
However, further experiments are needed to confirm this thesis. “For the next step, we need to see the partitioning of helium between iron in the core and silicate in the mantle under high temperatures and pressures,” Hirose explains.
Observing this partitioning would help rule out the lingering possibility that unbonded helium-3 could be more abundant than expected within the mantle – where it could be trapped by some other mechanism. Either way, further studies would improve our understanding of Earth’s interior composition – and could even tell us more about the gases present when the solar system formed.
While Starlink’s broadband contract wins often grab the spotlight, a panel of multi-orbit operators at the Satellite Conference here highlighted how they are also gaining significant traction with enterprise and government customers.
Connexion
