IN THE Antarctic, things happen at a glacial pace. Just ask Peter Gorham. For a month at a time, he and his colleagues would watch a giant balloon carrying a collection of antennas float high above the ice, scanning over a million square kilometres of the frozen landscape for evidence of high-energy particles arriving from space.

When the experiment returned to the ground after its first flight, it had nothing to show for itself, bar the odd flash of background noise. It was the same story after the second flight more than a year later.

While the balloon was in the sky for the third time, the researchers decided to go over the past data again, particularly those signals dismissed as noise. It was lucky they did. Examined more carefully, one signal seemed to be the signature of a high-energy particle. But it wasn’t what they were looking for. Moreover, it seemed impossible. Rather than bearing down from above, this particle was exploding out of the ground.

That strange finding was made in 2016. Since then, all sorts of suggestions rooted in known physics have been put forward to account for the perplexing signal, and all have been ruled out. What’s left is shocking in its implications. Explaining this signal requires the existence of a topsy-turvy universe created in the same big bang as our own and existing in parallel with it. In this mirror world, positive is negative, left is right and time runs backwards. It is perhaps the most mind-melting idea ever to have emerged from the Antarctic ice ­­– but it might just be true.

The ambitions…

A potential new theory of gravity that ruffles the fabric of the universe, allowing space and time to vary erratically, could solve some of the largest mysteries in physics and do away with the need for dark matter, say its proponents. However, experts say much more evidence is needed before this “post-quantum gravity” can be taken seriously.

Most cosmologists believe…

Time crystals can be used to stabilise fragile states within quantum computers, which could one day give them an edge over traditional computers.

When Nobel laureate Frank Wilczek first theorised that time crystals exist in 2012, the idea was controversial because their defining characteristic is that they flip between two configurations forever without any energy input – a seeming violation of the laws of physics. Since then, however, several research groups have created time crystals in the lab, including inside a quantum…

From Back to the Future to Tenet and Interstellar, cinema has portrayed time travel in many imaginative ways.  Kristie Miller is the joint director of the interdisciplinary Centre for Time at the University of Sydney, and her research focuses on the nature of time and our relationship with it. For her, movies such as these can explore complex ideas around the metaphysics of time.  These are five of her favourites.  But be warned, discussing them properly means there are some spoilers!

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A quantum state of matter has been made for the first time using “dipolar” molecules – molecules that have a positively charged end and a negatively charged end. It could help enhance our understanding of the quantum properties of exotic materials.

Historically, to understand the inner workings of a material, researchers might probe its atomic structure. But the complexity of those structures can make it difficult to figure out how the atoms interact and how the material behaves as a whole.…

AI chatbots that answer medical queries could save doctors’ time, but also run the risk of making recommendations that harm the people seeking advice.

Shan Chen at Harvard University and his colleagues conducted an experiment in which six oncologists addressed a variety of questions from 100 fictional people with cancer, who the doctors knew were not real. The questions were presented via a hospital electronic messaging system.

Each oncologist was …

The 2023 Nobel prize in physics has been awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier for their work on generating ultra-short pulses of light to study how electrons move through matter.

Anne L’Huillier at Lund University in Sweden, who is only the fifth woman to have won the physics Nobel, heard the news when she was midway through teaching her students. “The last half hour of my lecture was a bit difficult to do,” L’Huillier told a press conference on …

Physicists have peered through the proverbial looking glass, and the atoms on the other side belong to a world of opposites. For the first time, researchers have made an exotic quantum object called an Alice ring, which changes the properties of other quantum objects when they pass through it – or when they are simply viewed through it.

Quantum systems – such as collections of very cold atoms, or even our whole universe – should theoretically contain odd objects called topological defects. Some are like long strings, and others are stranger still: Zero-dimensional dots, at the centre of which things like magnetic fields become mathematically impossible to describe.

Such defects are difficult to create and observe. But Mikko Möttönen at Aalto University in Finland and his colleagues have worked out how to create a topological defect that quickly transforms into another.

To do it, they first placed 250,000 rubidium atoms into a small chamber devoid of air, then hit them with lasers to slow their natural motion and push them to a temperature close to absolute zero. Under these conditions, all the atoms behaved as one large quantum object. Because of a quantum property called spin, that object was sensitive to magnetic fields.

Möttönen says the team used computer simulations and mathematical models to determine how to pattern the direction and strength of magnetic fields in order to twist the atoms until a topological defect appeared. This approach had previously been used to create defects called monopoles, particles analogous to a magnet with a single pole.

Now, the researchers also observed a monopole’s fate: After a few milliseconds, each monopole they created expanded into an Alice ring with one very strange property.

“There is a peculiarity to this Alice ring. Depending on whether you look at some nearby monopole through the ring, or from the side of the ring, its charge looks different. So, the ring is inverting the charge of the objects that you look at,” says Möttönen. Computer simulations further showed that a monopole’s charge would fully flip – from positive to negative, say – if it moved through the Alice ring.

Möttönen and his colleagues have previously used this method to create topological defects in ultracold atoms, including knot-like structures and special swirls called skyrmions. The next challenge they are setting their sights on is to not only create a monopole and an Alice ring, but to make one pass through the other to directly test its looking-glass-like function, he says.

Janne Ruostekoski at Lancaster University in the UK says the method the researchers developed is unique, and could even make it possible to visualise abstract mathematical theorems. For example, it could give scientists a way to investigate the so-called “hairy ball theorem”, which dictates the texture of fields around topological defects.

This opens up “unprecedented opportunities” for probing theories in cosmology or high-energy physics “where there has been no experimental evidence before”, he says.

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Moments after supercooled water freezes, a strange kind of spring-like ice is born. The process involved, which researchers have only now seen for the first time, could help explain how clouds, which contain millions of supercooled water droplets, make rain and affect Earth’s climate.

Clouds are made up of many tiny drops of water at temperatures below freezing. These can exist as liquid until they are penetrated by an ice particle, which kick-starts a complex and poorly understood succession of freezing states. The length and frequency of these different states are crucial for models that simulate how certain clouds make rain and reflect light in the atmosphere, but they happen so fast that they are difficult to study.

Now, Claudiu Stan at Rutgers University–Newark in New Jersey and his colleagues have discovered a kind of ice that forms inside supercooled water droplets which is both compressed and stretched at different points, like a spring in motion, microseconds after it first freezes. “It’s something that was definitely unexpected for us,” says Stan. “It took us a while to understand.”

To capture this ice and the overall freezing process, Stan and his team dropped a stream of water droplets through a vacuum which cooled them to around -39°C (-38°F). They then used both a microscope and X-rays to image tens of thousands of these droplets. Although they only had one image for each droplet at a particular stage of freezing, they could map out the entire process by looking at many, a bit like watching a flipbook animation.

The researchers found that each droplet turns into a slush ball, with a network of ice permeating the liquid water, before freezing fully from the outside inward. This ratchets up the internal pressure, until the droplet either shatters or squirts out water, both of which result in ice particles that can freeze other droplets. This, combined with the kind of ice formed, might better explain how and when these droplets form ice in clouds that turns to rain, although the lab environment is too different for the results to be directly applied, says Stan.

Finding this strained ice doesn’t fit with our current molecular-level understanding, says Stephen Cox at the University of Cambridge. “Trying to understand the molecular mechanisms of ice formation is important across many fields, from climate science to food technologies. This study demonstrates that we still have a long way to go, and I expect it to stimulate lots of new research in this area.”

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WHEN scientists reported they had created a space-time wormhole in November last year, the world’s media were all over the story, even though they struggled to make sense of it. A journalist for the website UNILAD put it neatly when they wrote: “So, you might have to bear with us here a bit, because it’s all very complicated and new.”

As far as many observers could see, physicist Maria Spiropulu at the California Institute of Technology and her colleagues had in fact merely used a quantum computer to simulate a wormhole. Good luck flying a spaceship through that. What confused matters was that the team insisted the work amounted to more than just a simulation. The quantum computation, the researchers said, was fully equivalent to the creation of a wormhole.

If you find that hard to swallow, you aren’t alone. Ask other physicists about Spiropulu’s claims and you tend to get a lot of long pauses, chin-stroking and disagreement. It seems there is genuine confusion about if and when a quantum computation can create real entities or just simulate them.

The putative wormhole isn’t the only thing said to have been conjured up by quantum computers recently – there is also the alluringly named time crystal, as well as strange particles called nonabelions, touted as the ideal ingredient for next-generation quantum computers. But whether these amount to instances of true creation or not is a question that takes us into deep waters. It is a new twist on the riddle that has haunted physics since quantum mechanics was devised in the early 20th century: what is truly real?

Regular computers use …