Space & Physics
The physics of the mysterious Hall effect
In the first article of Ed Publica’s series on the Hall effect, condensed matter physicist Dr. Saraubh Basu, explains the physics of the Hall effect, which has reaped fruits for condensed matter physics research over the past century.

It was in 1879, when the Hall effect was observed in the laboratory for the first time. Then 23-year-old Edwin Hall’s work then led to various avatars of his eponymous effect being discovered. Previously unknown properties inherent in semiconductors among other materials, were now unraveled to the physicist’s eyes.
Unfortunately for Hall, who died in 1938, he never won the Nobel Prize for his work, despite three Noble prizes and a ‘Science Breakthrough Prize’ were awarded over the past century.
But to physicists, the Hall effect has fundamentally advanced our understanding about the properties of electronic systems.
For one, the Hall effect has enabled calculations of the fine structure constant, α ∼ 1/137. This quantity is of paramount importance in quantum mechanics and electromagnetism, for measuring the strength in the interactions that electrically charged particles such as electrons and muons, have with light particles (or photons).
For another, there are various other related discoveries, for example, the role of topology and geometry, fractional statistics, non-abelian anyons among others that have constantly enriched our knowledge in the field of condensed matter physics.
In the rest of this article, I shall set the stage with Edwin Hall’s anecdote into his seminal discovery which marked the period high of his career, to probe the various ‘avatars’ of the Hall effect.
What is the Hall effect?
Hall first came across the concept of a current carrying wire experiencing a mechanical force in presence of a magnetic field, while attending his supervisor Henry Rowland’s lectures.

Edwin Hall. Credit: Wikimedia
But he stumbled upon a fact that the direction of the electric current (beyond certain transient phenomena) remained insensitive to the presence of the magnetic field.
Hall disagreed with this, assured that the force experienced by the charges is proportional to the magnetic field, with the geometry of the conductor does not play any role. Rowland offered him the problem of investigating the effect of a magnet on the current flowing in a fixed conductor for his doctoral dissertation.
Hall found the appearance of a voltage perpendicular to the flow of electric current, while under the presence of a perpendicularly positioned and intense magnetic field. This is now called the Hall voltage. Also, the longitudinal resistivity of the wire, now dubbed Hall resistivity, turned out to be insensitive to the magnitude field.

A schematic diagram depicting the Hall effect. Credit: Karthik / EdPublica (modified from Wikimedia diagram)
But what Hall observed is attributed the classical Hall effect. Again, this is just one of the various avatars of the Hall effect that have been discovered during this period.
In 1980, the ‘integer’ quantum Hall effect was observed, with the ‘fractional’ avatar observed just later in 1982. Thereafter, the anomalous Hall effect, the spin Hall effect along with its quantum counterpart – the quantum spin Hall effect that were discovered by different groups of researchers.
All of these novel findings have significantly influenced our understanding of the material properties, particularly those of the semiconductors.
In the next series of articles, I shall shed light onto the intriguing physics of these various avatars …
Space & Physics
This Sodium-Fuelled Clean Energy Breakthrough Could Electrify Aviation and Shipping
The innovation offers more than triple the energy density of today’s lithium-ion batteries — potentially clearing a major hurdle for electric-powered aviation, rail, and maritime travel

A new type of fuel cell developed by MIT researchers could represent a pivotal breakthrough in the race to decarbonize heavy transportation. Designed around liquid sodium metal, the innovation offers more than triple the energy density of today’s lithium-ion batteries — potentially clearing a major hurdle for electric-powered aviation, rail, and maritime travel.
Unlike traditional batteries that require time-consuming recharging, this system operates like a fuel cell that can be refueled quickly using liquid sodium — a cheap, abundant substance derived from salt. The technology, which uses air as a reactant and a solid ceramic electrolyte to facilitate the reaction, was tested in lab prototypes and demonstrated energy densities exceeding 1,500 watt-hours per kilogram — a level that could enable regional electric flight and clean shipping.
“We expect people to think that this is a totally crazy idea,” said Professor Yet-Ming Chiang, lead author and Kyocera Professor of Ceramics, in a media statement. “If they didn’t, I’d be a bit disappointed because if people don’t think something is totally crazy at first, it probably isn’t going to be that revolutionary.”
Chiang explained that current lithium-ion batteries top out at around 300 watt-hours per kilogram — far short of the 1,000 watt-hours needed for electric aircraft to become viable at scale. The new sodium-based cell meets that benchmark, which could enable 80% of domestic flights and drastically reduce aviation’s carbon footprint.
Moreover, the sodium-fueled system offers environmental benefits beyond zero emissions. Its chemical byproduct, sodium oxide, reacts spontaneously in the atmosphere to capture carbon dioxide and convert it into sodium bicarbonate — better known as baking soda — which may help counteract ocean acidification if it ends up in marine environments.
“There’s this natural cascade of reactions that happens when you start with sodium metal,” Chiang said. “It’s all spontaneous. We don’t have to do anything to make it happen, we just have to fly the airplane.”
The team has already created two functioning lab-scale prototypes: one vertical and one horizontal model. In both, sodium gradually reacts with oxygen from air to generate electricity, and a moist air stream improves the process by allowing liquid byproducts to be expelled more easily.
Karen Sugano, one of the MIT doctoral students on the project, noted, “The key was that we can form this liquid discharge product and remove it easily, as opposed to the solid discharge that would form in dry conditions,” she said in a media statement.
The researchers have founded a startup, Propel Aero, housed in MIT’s startup incubator The Engine, to scale the technology. Their first commercial goal: a brick-sized fuel cell capable of powering a large agricultural drone — expected to be ready within a year.
Chiang emphasized the economic and safety benefits of using sodium, which melts just below 100°C and was once mass-produced in the U.S. for leaded gasoline production. “It reminds us that sodium metal was once produced at large scale and safely handled and distributed around the U.S.,” he said.
Critically, the fuel cell design also avoids many safety concerns of high-energy batteries by physically separating the fuel and oxidizer. “If you’re pushing for really, really high energy density, you’d rather have a fuel cell than a battery for safety reasons,” Chiang said.
By reviving and reimagining sodium-metal chemistry in a practical, scalable form, the MIT team may have lit the path toward clean, electrified transportation systems — from the skies above to the oceans below.
Space & Physics
Is Time Travel Possible? Exploring the Science Behind the Concept
Subtle forms of time travel — such as time dilation — do occur and have practical implications in science and technology.

Everyone is, in a way, a time traveller. Whether we like it or not, we are constantly moving through time — one second per second. From one birthday to the next, we travel through time at a steady pace, just like walking one foot per footstep. However, when we talk about “time travel,” we often imagine something much more dramatic — traveling faster (or even backward) through time, as seen in science fiction movies and novels. But is such a thing truly possible?
From Fiction to Science
The concept of time travel first gained widespread attention through literature, particularly with H.G. Wells’ 1895 novel The Time Machine. In it, time is described as the fourth dimension, akin to space, and the protagonist travels forward and backward in time using a specially built machine. Interestingly, this idea predates Albert Einstein’s theory of relativity, which would later reshape how we understand space and time.

Einstein’s Contribution: Relativity and Time Dilation
In the early 20th century, Albert Einstein introduced a revolutionary idea through his theory of relativity. He proposed that space and time are interconnected, forming a four-dimensional continuum called space-time. According to his theory, the speed of light (186,000 miles per second) is the ultimate speed limit in the universe. But how does this relate to time travel?
Einstein’s theory states that as you move faster — especially at speeds approaching the speed of light — time slows down relative to someone who is stationary. This phenomenon, known as time dilation, has been proven through various experiments. One famous example involved two synchronized atomic clocks — one placed on Earth and the other onboard a high-speed jet. When the plane returned, the onboard clock showed slightly less time had passed compared to the one on the ground. This demonstrates that, at very high speeds, time passes more slowly.
Astronaut Twins and Time
A notable example of time dilation involved twin astronauts Scott and Mark Kelly. Scott spent 520 days aboard the International Space Station, while Mark spent only 54 days in space. Due to the effects of time dilation, Scott aged slightly less than Mark — by about 5 milliseconds. Though this difference is minuscule, it is real and measurable, showing that time can indeed “bend” under certain conditions.
The GPS Example
Surprisingly, even GPS satellites experience time differently than we do on Earth. These satellites orbit at altitudes of about 20,200 kilometers and travel at speeds of roughly 14,000 km/h. Due to both their speed (special relativity) and weaker gravitational pull at high altitudes (general relativity), time ticks slightly faster for the satellites than for devices on Earth. This discrepancy is corrected using Einstein’s equations to ensure precise positioning. Without these adjustments, GPS systems could be off by several miles each day.
Science Fiction vs. Scientific Reality
Science fiction has long explored imaginative time travel — characters jumping into machines and traveling decades into the future or past. Stories often depict them altering historical events or witnessing the far future. However, there is no scientific evidence that anyone has travelled backward or forward in time in such a dramatic way.
Renowned physicist Stephen Hawking addressed this idea humorously in 2009. He hosted a party for time travellers — but only announced it afterward, reasoning that if time travel were possible, people from the future would show up. No one came. Hawking took this as a tongue-in-cheek sign that backward time travel may not be feasible.
Could Wormholes Be the Key?
Theoretical physics does suggest possibilities like wormholes — shortcuts through space-time. According to Einstein’s equations, these could, in theory, connect distant places and times. A wormhole might allow someone to enter at one point in space and exit at another, potentially in a different time. However, this remains purely speculative. The extreme gravitational forces within black holes or wormholes could destroy anything attempting to pass through.
Moreover, the idea of backward time travel introduces major paradoxes — such as the classic “grandfather paradox,” where someone goes back in time and prevents their own existence. Such contradictions challenge our understanding of causality and logic.
The Limitations of Current Science
At present, building a time machine capable of transporting people backward or forward in time by centuries remains outside the realm of scientific possibility. It’s a concept best enjoyed in novels and films for now. However, subtle forms of time travel — such as time dilation — do occur and have practical implications in science and technology.
While we may not have DeLoreans or TARDISes at our disposal, time travel — at least in small, measurable ways — is a part of our reality. The interplay of speed, gravity, and time demonstrates that our universe is far more flexible than it appears. And who knows? In some distant corner of the cosmos, nature might already be bending time in ways we are only beginning to imagine.
Until then, we’ll keep moving forward — one second per second.
Space & Physics
MIT Physicists Capture First-Ever Images of Freely Interacting Atoms in Space
The new technique allows scientists to visualize real-time quantum behavior by momentarily freezing atoms in motion and illuminating them with precisely tuned lasers

In an intriguing advancement for quantum physics, MIT researchers have captured the first images of individual atoms freely interacting in space — a feat that until now was only predicted theoretically.
The new imaging technique, developed by a team led by Professor Martin Zwierlein, allows scientists to visualize real-time quantum behavior by momentarily freezing atoms in motion and illuminating them with precisely tuned lasers. Their results, published in Physical Review Letters, reveal how bosons bunch together and fermions pair up in free space — phenomena crucial to understanding superconductivity and other quantum states of matter.
“We are able to see single atoms in these interesting clouds of atoms and what they are doing in relation to each other, which is beautiful,” said Zwierlein in a press statement.
Using their method — called “atom-resolved microscopy” — the team was able to trap atom clouds with a loose laser, briefly immobilize them with a lattice of light, and then image their positions via fluorescence. This approach allowed the researchers to observe quantum behaviors at the level of individual atoms for the first time.
The MIT group directly visualized sodium atoms (bosons) bunching together in a shared quantum wave — a vivid confirmation of the de Broglie wave theory — and lithium atoms (fermions) pairing up despite their natural repulsion, a key mechanism underlying superconductivity.
“This kind of pairing is the basis of a mathematical construction people came up with to explain experiments. But when you see pictures like these, it’s showing in a photograph, an object that was discovered in the mathematical world,” said co-author Richard Fletcher in a press statement.
Two other research teams — one led by Nobel laureate Wolfgang Ketterle at MIT, and another by Tarik Yefsah at École Normale Supérieure — also reported similar quantum imaging breakthroughs in the same journal issue, marking a significant moment in the experimental visualization of quantum mechanics.
The MIT team plans to expand the technique to probe more exotic quantum behaviors, including quantum Hall states. “Now we can verify whether these cartoons of quantum Hall states are actually real,” Zwierlein added. “Because they are pretty bizarre states.”
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