Time crystals could also exist in nature



When the existence of time crystals was first proposed in 2012 by the physicist Frank Wilczek, the scientific community thought that it was a simple theoretical artifice, an exotic consequence of quantum mechanics that could occur in systems formed by many particles. Wilczek argued that these strange “crystals” had the ability to break temporal symmetry, changing to periodically return to the same state. Something very similar to what ordinary crystals do in space.

However, several experiments later proved that time crystals they were not just theorists, but they could, to some extent, actually be created in a laboratory, keeping them in imbalance through some external force.

And now, a team of physicists led by Norman Yao, from the University of California at Berkeley, suggests in an article just published in Nature Physics that time crystals can arise without the need for quantum physics. In their article, the researchers argue that purely classical oscillator systems, such as pendulums, could have the same behavior as their quantum “alter ego.” And what’s more, the Time crystals could exist, also, in Nature.

Classic vs. quantum systems

A discrete time crystal responds to a periodic driving force. And it does so by showing some kind of temporal oscillation with a different period, usually an integer multiple of the impeller. Already in the 1830s, Michael Farday He showed that, in theory, a type of periodically controlled oscillators that are now known as “parametric resonators” can suffer a “doubling of periods”, which means that they oscillate at half the driving frequency. And that is precisely the type of “subharmonic” response that characterizes time crystals.

There has been much discussion about whether classical systems (that is, not quantum) can show the same type of behavior as a time crystal. Last year, for example, a team from the Swiss Federal Institute of Technology in Zurich (ETH) demonstrated that two docked oscillating chains showed a doubling of the period. The researchers also noted that there is a close analogy between that behavior and that observed in quantum time crystals.

But a real time crystal needs something else, Yao and his team point out in their study. Discrete time crystals (DTC) are open systems that remain out of balance because of an energy supply from their environment. But in the classical world, that constant contribution would cause the entire system to slowly warm up. With enough time, the temperature could rise without limit, and eventually “Melt” the time crystal, so that the periodic order would disappear forever. Which does not happen in quantum time crystals, where the “location of many bodies” inhibits the exchange of energy and prevents the spread of heat.

However, in a classical system there is no analogue of the “location of many bodies”, so it is not clear whether the classic time crystals could remain stable against heating. That is precisely the problem with Faraday’s parametric resonators and also with the oscillating chains of the Zurich scientists. In their study, Yao and his colleagues point out that in this way noise is added to the system, and it is not clear whether the oscillations of the time crystals could withstand it.

A first approach

However, researchers have managed to identify a simple classic system that could show the behavior of a time crystal even in the presence of noise. It is a series of pendulums or oscillators, arranged in a row and connected to each other by springs. «And that – affirms Michael Zaletel, co-author of the study – is something that had not been seen until now ».

In Yao’s experiment, the behavior of the time crystal does not last indefinitely, but gradually declines to end up “melting.” In Yao’s words: «We don’t have a real classic time crystal. Although ours dies in very long times ». It isn’t, but it looks a lot like one. It’s what researchers call «activated time crystal».

Yao believes that a time crystal that persists indefinitely could be achieved if the oscillators or pendulums were joined in more complex ways. He is even convinced that systems like his, in which the oscillations of time crystals are maintained for a long time, could be found in nature, specifically in living systems such as colonies of cells that interact with each other. Such periodicity «could be very useful in Biology – adds Zaletel-. And usually it would be enough to have it for finite, but long periods.


Ala Eddine Slim: “In Tunisia, the army remains this hidden monster”

Born in Sousse thirty-seven years ago, a consumer mainly of ninja or Jean-Claude Van Damme films on VHS when he was a teenager, Ala Eddine Slim came to the cinema discovering, being electrified, The Sunchaser of Michael Cimino on TV, “One Thursday evening after Correspondent“. For ten years, he has formed with a nucleus of friends a kind of collective around his company Exit Productions, which allows him “To learn to do by doing” and of “Tinkering, accompanying, more than producing, in the sense that most producers are managers, more imaginative in marketing than in creation. The main thing for me is to have my freedom to change and adapt in each production. ” A few years ago, he reviewed Cimino’s film. “It didn’t have the same effect on me, but I don’t care.”

“Lots of joints”

“I work on my fantasies, in total freedom, so that all sorts of things mix outside of any logic of writing, at least that which presides over most of the films that we see today. I wanted to work in a territory rich in possibilities that I could follow all of them, whether they lead me to contemporary facts or to mythological elements. This film therefore comes from islets of ideas and desires that I try to collect.

Read also“Sortilège”, the call to sleeping wood

“Besides, I smoke a lot of joints when I write and when I shoot … Some things connect the film to my previous one [et premier] feature film, The Last of Us. I went back to the same place: I like the idea that any story can be seen from several angles. There is also this soldier figure which comes from one of my first courts. At the end, the character left the city in a bus where there was a clown, a police officer and a soldier, that is to say the three pillars of Tunisia: the clown who presides, the police force which is the hand of the President, and the soldier which is the body that carries it all. I wanted to return to the latter to discuss the place of the soldier in society. I travel the country a lot by car and I often take soldiers on hitchhiking, with whom I speak on the road. In the Tunisian imagination, the army holds a place of protective figure, very close to the people, because it has never intervened in any political scheme. But it seemed to me that the soldiers were the first to be sacrificed, because they are the ones who confront terrorism, and at the same time they find it difficult to return home. ”

“Neither religious nor mystical”

“In Tunisia, there are two very sensitive subjects, not taboo but risky, likely to provoke very violent reactions: the army and religion. It’s not like Algeria or Egypt, where the army is in command. In Tunisia, after independence, the first presidents made the country more of a police than a military state, and under Ben Ali the army was weakened to the benefit of the police. But it remains this hidden monster that can come from afar and pull the whole country down. For example, I have some reservations about the famous war on terror. I do not deny that there is a threat, but I think that it is inflated, disproportionate, so that in the name of this war we sweep all human rights: we kill people, we card them, there are sudden deaths during interrogation… It is like the disproportionate reaction of the police against the demonstrators and the yellow vests in France.

“But the film, like its protagonist, starts from this to move away from it, sweep everything away from the military postulate and lead the other character into an absolute desertion. And the film, which confronts religious elements in the second part (Adam, Eve, the serpent …), is not an attack on these two monsters that are the army and religion. It is a reading, a vision. Me, I am neither religious nor mystical, and I did not specially think of that consciously, even if I knew the range of the signs: for me, it was very natural presences in territories such as that crossed by the characters in the second part of the film. A territory which one can say is supernatural, but for me this forest is a natural place, complementary to the sceneries of the first part, a place which brings its own laws of functioning of relationships and existence. “

“Society full of unnecessary noise”

“With each film, I try to find a non-verbal means of communication. I had written dialogues but I knew they would not be spoken by the actors. Right before the shooting, I had this idea of ​​field-backlit exchanges with the eyes. As a filmmaker, I try to blur the vision and I said to myself: why not go to the physical source of the gaze? Since information had to be conveyed all the same, I tried to write directly on the image. Until then, I preferred not to work with dialogues, I had a little by chance difficulties on my first short film and since I said to myself: why not try to advance without that?

“Besides, I’m not someone who talks a lot, I don’t love that. I try in each film to experiment with methods, processes, cinema, that’s it, DIY, research like in a lab. And that suits the trajectory of my characters, who are fleeing from codes, a society which speaks to them, full of unnecessary noise. They go elsewhere and meet by look, the first foundation of any contact between two people. It joins the movement of the film which is that of a return to the primary elements, to the primitive. We are going back to the beginning of everything, but it is not about making the same trip. It’s not at all nostalgic. It’s more like shaving everything down and trying to go somewhere else. ”

Julien Gester


Hollywood, not a boulevard for women

When it comes to equality between men and women, we may well think what we want from the taste of Hollywood and its democratic gotha ​​for preach-preach activism. At its best, the documentary produced by Geena Davis (forever the gunsling tough Thelma and Louise, but also the founder of a statistical institute on gender disparities in the media) reminds us that it would be difficult to find a more frontal voluntarism in the matter. Were it likely to hurt beliefs in force in the country of cultural exception.

We learn in particular that in the 80s (!), A group of six female directors, exhausted victims of unemployment, prided themselves on suing the majors for discrimination at work, and made gender equality in the cinema a stake in the fight for civil liberties. (It smells like a biopic project, or we don’t know anything about it.) Nor will we take away from the Americans their know-how in terms of documentary didacticism and display of hypercommunicative conviction: panel of eloquent heroines (from Meryl Streep to Cate Blanchett, via the activist Tarana Burke at the origin of #MeToo, among other more anonymous figures), speeches chopped to keep only the punchlines, sense of the cheerful demonstration which makes the enthusiasm get carried away, music in every corner. Starting from the downstream – the representation of women in films -, Everything can change begins by examining the gendered myths of American cinema, before going backwards on the upstream side of manufacturing. Who embraces too badly embraces, we say unfortunately when discursive side roads end up amalgamating all the symptoms of discrimination in a same mixture of indignation, where the exactions of Harvey Weinstein rub shoulders with the question of the quotas of scriptwriters and the gravelly exits from Donald Trump.

Nevertheless, the objectification of inequalities by the figures gives an unstoppable force to the film, moreover marked by two biases: the fight is on the level of legal action, and the cinema, defrocked with the aura of work dear to our countries, is only apprehended as an object of mass communication, a vector of messages capable of lastingly informing psyches – the striking force of the dream factory thus implies great responsibilities. What to wish for more complexity than what the film presents of the debate in a limpid and unequivocal light, but also to make one strangle a little more the counter-revolutionaries who quickly made see in the movement of redistribution of the powers started l advent of a feminist dictatorship. Too bad for them.

Sandra Onana

Everything can change: what if women counted in Hollywood? of Tom donahue 1 h 35.


Nesyamun’s mummy recovers her voice after 3,000 years of silence

After more than 3,000 years of forced silence, forced by his own death, the Egyptian priest Nesyamun He has recovered his voice. For the first time, an international team of scientists has managed to rebuild a exact copy of the vocal apparatus of a mummy in order to recover at least one sound sample which the religious issued in his rituals in the Karnak temple. Now, fulfilling the last wish that is included in the hieroglyphs that adorn his sarcophagus, this new investigation makes the religious “speak again after his death” to at least pronounce a phoneme (halfway between one ‘to‘ and one ‘and‘) and, from there, imagine how their songs could sound.

The snarl de Nesyamun, presented this Thursday in a new investigation of the journal ‘Science Advances’, is the first voice which has been rescued from ancient Egypt. To achieve this, the remains of the mummy had to be scanned using a CT scan, create a three-dimensional copy of the vocal tract and design an electronic larynx that could finally emit the sound. The multidisciplinary team that designed this study, which includes the perspective of electronic engineers, archaeologists and doctors, frames this technical achievement in the ancient egyptian belief that “to pronounce the name of the dead is to make them live again” and in the last will that the priest left written in his grave.

Deathly silence

This work is the last of many to focus on the mummy of Nesyamun, stored and studied since 1824 in the facilities of the Leeds Museum in the United Kingdom. Already put, many will wonder why once the sound is obtained it has not been tried rebuild speech from Nesyamun or even simulate a speech or a complete song. The answer is simple. “Doing so would require knowledge about the relevant articulations of the vocal tract, phonetics and time patterns of their language,” the researchers stress in the newly published study. Those responsible for this work, who anticipate the possible criticism of the listeners, also apologize remembering that neither the tongue nor the palate of Nesyamun are in their best conditions and, finally, it has been three millennia in sepulchral silence.

The technical achievement that has now made it possible for us to hear Nesyamun’s voice could in the future open the door to rebuild other lost voices From the past. Of course, the researchers warn that to restore a sound it is necessary that the soft tissues are perfectly preserved. The voices of the skeletons, therefore, would remain impossible to recover. But, as the authors of this new study subtly suggest, it would also not be so far fetched to rescue the voices of castrati of the seventeenth century that could not be registered. If their bodies were well preserved, of course.

Beyond speculation, experts argue that rebuilding the voices of the past will allow people to “interact with the past in completely new and innovative ways. “Someday, without going any further, museums could incorporate these real sounds into exhibitions on the time of the pharaohs of ancient Egypt to offer a new perspective on protagonists of the past. Even if it is through some voices from beyond the grave.


The ancient genome expands the mosaic of our species with four lineages

The archaeological site of Shum Laka, in Cameroon, has protected the thousands of years of oldest genome from West Africa This is revealed by a new study in which, for the first time, a complete DNA analysis of four young people who died 3,000 and 8,000 years ago and were buried there. The investigation throws new clues about the populations that at that time converged in the territory and, according to experts argue, illuminate past of our kind.

Research would show that at least 200,000 and 300,000 years ago there were at least four important lineages in the history of mankind. This data, in turn, would support the theory that the origins of our species in Africa could have involved deeply divergent populations and geographically separated. Hence, to reconstruct this genealogy it is necessary to go to the continent considered as the cradle of our species and that today continues to house the greater genetic diversity of the planet.

Bantu Origin

In analysis, published this Wednesday in the journal Nature, also provides a new look at one of the oldest archeological sites that are known in the place where the Bantu, the language that today is still the most widespread and diverse in the entire continent. The genetic profile obtained at the site, in fact, suggests that the DNA of those buried there is more similar to that of hunter-gatherers in Central Africa than to the current populations that inhabit Cameroon. “This suggests that current Bantu speakers do not descend from the population to which the children of Shum Laka belonged, “says Mark Lipson, one of the researchers responsible for this new study.” This underlines the old genetic diversity of the region, “adds the scientist.

The old genome, in addition, has also allowed to identify a set of ‘ghost populations’Previously unknown that contributed small portions of DNA to current African groups. “Genomic analysis of ancient and current African populations denies the conclusions of previous work based solely on mitochondrial DNA analysis and demonstrates that the origin of our species it was a much more complex phenomenon than we thought, “says Carles Lalueza-Fox, a researcher at the Institute of Evolutionary Biology (IBE) and one of the experts responsible for the recently published study.


Why stress generates gray hair

Legend has it that the day of its execution Marie Antoinette He woke up with completely white hair. In just one night, the mane of the last queen of France had lost all her color in the face of the anguish of a imminent decapitation. This anecdote serves as a preamble to a new investigation which shows why the periods of acute stress generate the sudden appearance of gray hair, a phenomenon visible on faces as well known as that of Barack Obama, whose hair looks silver after passing through the anguish of the White House.

The explanation of this secret is the following. Stress triggers premature exhaustion of the mother cells responsible for the formation of the pigment in the hair follicles. That is, it depletes the color reserves which are located at the birth of the hair leaving the characteristic whitish color of gray hair. If we look at this process at the molecular level, the answer is even more interesting. The newly published study, presented in the prestigious journal Nature, determines that in a stress situation the nervous system activates a ‘fight or flight’ mechanism and begins to secrete a neurotransmitter known as norepinephrine. This, in turn, encourages the stem cells present in the follicles to specialize in pigment production, thus depleting the structures they exert from ‘color deposits of the hair.

Experiment in mice

This approach, tested in laboratory mice, I would rule out other theories proposed to explain the range of causes that can cause the gray. The experiments in rodents performed in this work would show that neither the immune system nor hormones such as cortisol are responsible for the whiteness of the hair, since in the tests in which these factors were eliminated from the equation the animals continued to show gray hair. Once these hypotheses were discarded, the researchers focused their attention on the study of the nervous system and there they found an answer to a phenomenon that, although very present in the collective imagination, until now lacked a convincing scientific explanation.

White hair is not only a symbol that is related to the progress of the years, but it can also be a sign of certain food deficiencies or disorders such as alopecia or vitiligo. Experts also emphasize that the gray hair study It goes beyond aesthetic concerns or the merely anecdotal. “Understanding how stress affects the cells that regenerate the pigment we are one step closer to understanding how stress affects other tissues and organs of the body& rdquor ;, says Ya-Chieh Hsu, one of the scientists responsible for the study affiliated with Harvard University. In the future, research on this phenomenon could shed light on how mitigate damage caused by stress. And, from there, there are many fronts to investigate.

Evolutionary function?

“It is fascinating to consider the possible evolutionary advantages that can grant a canosity forced by stress& rdquor ;, comment neuroscientists Shayla A. Clark and Chistopher D. Deppmann of the University of Virginia, in an article complementary to the recently published study. In the animal world, the white fur of gorillas, for example, denotes their ability to lead your group. “Perhaps an animal that has endured enough stress to” win “a gray hair also demonstrates that it can reach a higher status in the social order than it would be for its age & rdquor ;, they argue.