Le 1er juillet 2023, le satellite européen Euclid a quitté la Terre pour cartographier tune partie de l’Univers visible. La mission vise à comprendre comment l’univers se structure et pourquoi son expansion s’accélère depuis ces 10 derniers milliards d’années. Ces phénomènes qui mettent en jeu l’énergie noire et la matière noire.
Euclid est la 2ème mission M2 (dite moyenne) du programme scientifique obligatoire Cosmic Vision de l’ESA, une mission d’astronomie et d’astrophysique sélectionnée au SPC du 04 octobre 2011, puis adoptée au SPC du 20 juin 2012. C’est une mission principalement dédiée à la cosmologie, c’est-à-dire à l’étude de l’origine, de la nature, de la structure et de l’évolution de l’Univers qui va essayer d’accroître nos connaissances sur deux composantes encore mystérieuses de notre univers, l’énergie noire et la matière noire.
La mission a principalement deux buts. Le premier est de comprendre pourquoi l’expansion de l’Univers s’accélère sous l’effet de cette encore mystérieuse « énergie noire », (ou « sombre »). Le second est de cartographier la non moins mystérieuse « matière noire » (ou « sombre »), puisque bien qu’invisible directement à nos yeux et aux instruments, elle participe, avec la matière visible (étoiles, nébuleuses, …etc) aux effets de gravitation qui lient entre elles les étoiles au sein des galaxies et les galaxies au sein des amas.
En observant toujours plus loin, donc en remontant plus loin dans le temps, Euclid tentera de reconstruire l’évolution de notre univers au cours des 10 derniers milliards d’années sous les effets antagonistes de la matière noire et de l’énergie noire.
Au cours de sa mission nominale de 6 ans, Euclid doit observer à peu près un tiers de la voûte céleste, soit un peu moins de 15 000 degrés², le reste étant occulté par le plan galactique (disque dans lequel tournent les galaxies de la Voie Lactée) et par le plan de l’écliptique (disque dans lequel tournent les planètes de notre système solaire).
À ce relevé s’ajouteront des observations environ 10 fois plus profondes visant trois champs situés près des pôles écliptiques, un au nord couvrant 20 degrés et 2 au sud couvrant chacun 10 degrés. Ils seront visités régulièrement pendant toute la durée de la mission, et serviront de données d’étalonnage et de contrôle de stabilité des performances du télescope et des instruments, ainsi que de données scientifiques pour l’observation des galaxies et des quasars les plus lointains de l’Univers.
Euclid observera donc des milliards de galaxies et l’évolution des grandes structures de l’univers à travers les âges jusqu’à 10 milliards d’années dans le passé, dans le domaine visible et proche infrarouge (longueur d’onde de 550 à 2000 nm). Pour ce faire, il est prévu de déterminer les décalages spectraux vers le rouge (appelé redshift et noté z) des sources observées par des méthodes spectrométriques et photométriques issues de mesures instrumentales et complémentées, pour les mesures photométriques, par l’assistance de télescopes terrestres pour des mesures dans le domaine visible.
Avec son immense couverture céleste et ses catalogues de milliards d’étoiles et de galaxies, l’intérêt scientifique de la mission dépasse le cadre de la cosmologie. Cette base de données alimentera en sources l’ensemble de la communauté astronomique mondiale pour des décennies et constituera un réservoir d’objets astronomiques nouveaux pour des observations impliquant les télescopes le JWST, l’E-ELT, le TMT, ALMA, SKA ou le Vera C. Rubin Observatory.
Pour réaliser ce travail de cartographie, Euclid aura à son bord 2 instruments, un spectrophotomètre proche infrarouge appelé NISP (Near Infrared Spectro Photometer) et un imageur travaillant dans le domaine visible, l’Instrument VIS (VISible Instrument), développés par un consortium international dirigé par l’Institut d’Astrophysique de Paris (IAP/CNRS). Celui-cid regroupe plus de 2 200 personnes (dont 425 en France) réparties dans environ 250 laboratoires (dont 40 en France) de 16 pays.
Note
Nul n’a compris encore compris la raison de l’expansion de l’univers. On évoque une mystérieuse énergie noire. Selon les hypothéses actualles, rien ne devrait se produire. Cependant aujourd’hui certains physiciens proposent une solution à cette interrogation. Pour eux, notre univers ne serait qu’un point dans un ensemble beaucoup plus vaste dont une expansion accélérée serait la règle naturelle, entre un hyper-espace de grande dimension et un vide absolu, selon la description qu’en donne Antonio Padilla, de l’Université de Nottingham (UK). Comme l’observe le Newscientist, les lois de la physique semblent appliquer une règle mathématique mysterieuse
Le satellite militaire français d’observation CSO-3 (Composante Spatiale Optique). CSO-3 a été mis en orbite le 6 mars 2025 depuis le Centre spatial guyanais, au moyen du lanceur Ariane 6, à 17h24, heure de Paris.
Le lancement marque la fin d’un cycle de renouvellement des capacités spatiales d’observation de la défense française. Le système CSO, composé de trois satellites dont les deux premiers ont été mis en orbite en 2018 et 2020, constitue la nouvelle génération de satellites d’observation militaire.
Les satellites CSO permettent aux armées d’accéder à des images d’une qualité sans précédent en Europe, d’avoir accès à des détails plus fins et d’identifier des cibles plus petites de jour dans le visible, comme de nuit dans l’infrarouge. Ces satellites représentent ainsi une plus-value significative pour les activités d’appui aux opérations, de renseignement et de ciblage. CSO est également un système agile offrant aux utilisateurs, en un seul survol, plus d’images sur une même zone géographique. Enfin, ses capacités de réactivité permettent une meilleure adaptation au rythme des opérations.
Il constitue un outil indispensable de la politique de défense de la France en garantissant une autonomie d’appréciation et une souveraineté décisionnelle dans l’espace.
Le système CSO, développé dans un cadre national au sein du programme MUSIS mené par la DGA, au profit du CDE, est résolument ouvert aux partenariats européens au travers d’accords bilatéraux avec huit partenaires. En effet, actuellement, l’Allemagne (2015), la Suède (2015), la Belgique (2017), l’Italie (2019), l’Espagne (2021), la Suisse (2023), la Pologne (2024) et la Grèce (2024) ont déjà rejoint la communauté CSO via des accords de coopération.
La DGA assure la maîtrise d’ouvrage du programme MUSIS, en équipe intégrée avec le CDE, grand commandement de l’armée de l’Air et de l’Espace. Elle assure en propre la maîtrise d’ouvrage du segment sol utilisateurs (SSU), ainsi que l’ensemble des aspects ayant trait à la mise en place des partenariats de coopération.
La DGA a délégué au CNES la maîtrise d’ouvrage pour la réalisation et le lancement des satellites CSO, ainsi que pour la réalisation du segment sol mission (SSM). La maîtrise d’œuvre industrielle des satellites CSO est assurée par le groupement d’entreprises Thales Alenia Space et Airbus Defence and Space. Arianespace fournit les services de lancement.
For 100 years, quantum theory has painted the subatomic world as strange beyond words. But bold new interpretations and experiments may help us to finally grasp its true meaning
For 100 years, quantum theory has painted the subatomic world as strange beyond words. But bold new interpretations and experiments may help us to finally grasp its true meaning
Le problème de la théorie quantique (TQ) est qu’elle n’explique pas les relations qu’elle entretient avec la physique ordinaire, dite parfois macroscopique. En résultat, nous ne percevons pas ce que ce chef d’oeuvre signifie pour la compréhension de la réalité.
Les idées ne manquent pas, d’autant plus qu’elles ne proposent pas d’être soumises à des vérifications expérimentales. Selon le physicien David Mermin, « de nouvelles interprétations apparaissent chaque année. Aucune ne disparait ».
Depuis 10 ans, les choses ont commencé à changer. La TQ a fait des prédictions explicites, vérifiables par l’observation, même si elles reposent sur l’hypothèse qu’il n’y a pas de réalité objective. De plus les physiciens trouvent chaque jour de nouvelles méthodes pour juger de la validité de ces jugements.
Selon Eric Cavalcanti, physicien quantique à la Griffith University de Queensland, Australie, les possibilité augmentent régulièrement
La Théorie quantique
Depuis Isaac Newton qui avait formulé ses lois sur le mouvement et la gravitation au 17e siècle (cf Carlo Rovelli, On what we get wrong about the origins of quantum theory” ) les physiciens construisaient leurs théories sur la base que les systèmes physiques étaient définis par des équations précisant comment ils évolueraient avec le temps. Mais les particules subatomiques telles que l’électron et le photon pouvaient se comporter comme des « vagues » ou exister en état de « superposition » de plusieurs états simultanément, sauf à être « mesurées ». Que se passait-il avant la mesure ? La TQ ne le disait pas.
L’équation de Schrödinger a introduit un concept mathématique, la « fonction d’ondes » pour résumer tous les états possible et calculer la probabililé de trouver la particule en un certain état après mesure, mesure où la fonstion d’onde était dite s’effondrer, « collapse » .Mais une seule mesure ne suffisait pas. Il en fallait plusieurs, d’où un retour aux probabilités.
Que se passe-t-il avant mesure, et que signifie précisément une mesure ? Là encore il fallait faire appel aux probabilités.car la TQ ne le précise pas. L’interprétation dite de Copenhague oblige à « calculer » pour répondre à ces question. Comme Mermin l’avait dit, « ferme ta g. et calcule ». Mais Copenhague a été discuté dès le début, depuis qu’Albert Einstein avait déclaré « God does not play dice with the universe ».
De nombreux physiciens considèrent aujourd’hui, tels Roderich Tumulka, de l’University de Tübingen en Allemagne, « nous voulons des jugemnts sur la vraie nature de la réalité. Il n’est pas accceptable de penser que de simples humains puissent faire s’effondrer la fonction d’onde ».
Tumulka est de ceux qui considèrent la fonction d’onde comme physiquement réelle, représentant le monde tel qu’il existe, que nous le voulions ou non. Il faut seulement l’étendre si nécessaire. La plus célèbre de ces extensions est la many-worlds interpretation, qui considère que la fonction d’ondes se concrétise après mesure dans une infinité d’univers séparés connectés au nôtre. Suite de l’article. Version originale non traduite
But there is also objective collapse, a suite of models proposing that quantum mechanics is incomplete and that something else has to be tacked onto the Schrödinger equation to explain wave function collapse. “The [key] difference with the standard interpretation is that the collapse of the wave function is not something that occurs by magic at the end of the measurement process,” says Angelo Bassi, a theorist at the University of Trieste in Italy. “It’s just part of the dynamics.”
Collapse models have garnered more attention than most in recent years, partly because they offer a plausible explanation of how classical reality emerges without reference to human observers. We don’t see large objects like picture frames and paint brushes in a superposition, it says, because the collapse process works in such a way that the more interacting particles there are, the more readily collapse occurs.
One new interpretation can solve several quantum mysteries in one fell swoop
What triggers this continuous collapsing isn’t entirely clear. Some models don’t say, others posit that it is just gravity. But Bassi says there may ultimately be no good answer – it may just be a property of nature. “That’s why I like collapse models, because they try to open the door to a new world which we don’t understand at the moment – something beyond quantum mechanics that we are not grasping.”
What really sets collapse models apart, however, is that they can be put to the test. Uniquely, they make explicit observational predictions that differ from what standard quantum mechanics predicts. The idea is that this constant process of spontaneous collapse should cause quantum objects such as particles to constantly jiggle around, which, in turn, means they emit excess energy that should be detectable, even if the signal is extremely faint.
Testing quantum interpretations
For the past decade, Bassi has been working with colleagues around the world on an ambitious experimental programme in search of such a signal. They have mostly been repurposing detectors designed to sense hints of dark matter or elusive particles called neutrinos, such as the ultra-sensitive instruments located deep underground beneath the Gran Sasso massif in Italy. And the results are trickling in. In 2020, for instance, a team including Bassi and Cătălina Curceanu, an experimentalist at Italy’s National Institute of Nuclear Physics, was able to rule out the simplest form of one model in which gravity does the collapsing.
Similar experiments are ongoing, and with each new analysis we get fresh constraints on which, if any, of these models might work. But while the fact that we finally have a shot at ruling out objective collapse with experimentation is itself progress, actually doing so is a slow process. “So far, we saw no signal, but this is just the beginning,” says Bassi.
If we were to detect a signal that everyone can agree supports objective collapse, it would surely be worthy of a Nobel prize. Whether that would immediately tell us anything about the meaning of quantum theory is another matter, according to Magdalena Zych at Stockholm University in Sweden, because we would still have to figure out what it is in the environment that is doing the collapsing.
“It would solve the measurement problem in the sense of, if you believe that quantum theory is missing something, this is it,” says Zych. “But it doesn’t really reveal what quantum mechanics is telling us about reality, because you still have to impose some meaning yourself to some extent: you have to say what is the ‘noise’ in the environment [that collapses the wave function].”
More importantly, Zych says we would also be none the wiser about why the observable properties of quantum objects emerge in a probabilistic way, from the act of measurement itself. “That’s really the deep mystery of all this, the fact that we have to speak about probabilities at all,” she says. There is no self-evident reason why the behaviour of subatomic particles cannot be governed by deterministic laws. The fact that they aren’t demands an explanation.
Quantum Bayesianism
For Zych, the take on quantum mechanics that tackles that challenge head on falls into a whole different category of interpretations. While the likes of Bassi and Tumulka insist that quantum states are real, some physicists take a starkly different view: that they don’t represent independent reality at all.
Arguably the most striking example of this approach is QBism, originally known as Quantum Bayesianism because it is founded on a framework for interpreting probabilities first developed by 18th-century minister Thomas Bayes.
Conventionally, probabilities are viewed in “frequentist” terms: we count up the outcomes of many coin tosses to conclude that the odds of getting heads or tails are 50/50. Similarly, many measurements of a particle give you the relative probability of it having one state or another when measured. The Bayesian approach, by contrast, recasts probability as a subjective value that updates as you gain more information.
Running with this idea, the central argument of QBism is that quantum mechanics is similarly subjective. It supplies recommendations about what an observer should believe about what they will see on making a measurement, allowing them to update those beliefs as they take into account fresh experiences. “It’s a theory for agents to navigate the world,” says Ruediger Schack at Royal Holloway, University of London, who developed QBism with Chris Fuchs at the University of Massachusetts Boston.
The appeal of this interpretation is that it seems to address several quantum conundrums at once. It deals with the measurement problem by providing and even requiring a central role for subjective experience. The mysterious collapse of the wave function is simply the observer updating their beliefs on making a measurement, says Schack.
QBism’s answer to the question of how classical reality emerges from the quantum fog, meanwhile, is that it is a result of our actions on the world, of our constant updating of our beliefs about it. The idea even makes light work of a notorious conundrum known as the Wigner’s friend paradox, a thought experiment proposed in the 1950s by physicist Eugene Wigner. Essentially, it demonstrates that two observers – Wigner and a friend observing him making measurements on a quantum system – can have two contradictory experiences of reality. For a QBist, there is no paradox because a measurement outcome is always personal to the person experiencing it. All of which means that QBism stands starkly athwart the idea that it is possible to achieve an objective view on the universe. But that is exactly the point, says Schack, and this is the great lesson of quantum mechanics: that reality is more than any third-person perspective can capture. “It’s a radically different way of looking at the world.”
What really set collapse models apart is that they can be put to the test Others find QBism hard to swallow. Bassi, for instance, insists that objective reality is too high a price to pay. “What physics is about is describing nature in an objective way,” he says. Another problem is that QBism doesn’t appear to offer any observable predictions differing from standard quantum mechanics, and no realistic prospect of submitting to experimental tests. “Convincing people might be a case of pointing out the inadequacies of the alternatives,” says Schack.
That arguably leaves us back where we started. If our best hope of an empirical solution to the measurement problem would leave open questions even if it were proved correct, and an alternative that can address those questions can’t be tested, where do we go from here?
There might still be cause for optimism. In the past few years, some physicists have begun to demonstrate that the assumptions underpinning how we think about the meaning of quantum theory – typically considered more in the realm of metaphysics than science – might themselves submit to testing.
Experimental metaphysics
They call it experimental metaphysics. “It’s an approach that tries to be clear about the landscape of metaphysical assumptions made by different interpretations,” says Cavalcanti, who is one of its key proponents. Among those assumptions are the absoluteness of observed events, which is to say that the outcomes of a measurement are the same for all observers; freedom of choice, the notion that the outcome of any measurement isn’t due to factors involved in the measurement; and locality, or the idea that a free choice cannot influence the observed outcome of an experiment at a distance or in the past. “Individually, these may not be testable, but when you group them together, they can be,” says Cavalcanti. In this way, you can potentially at least disprove classes of quantum interpretation, he says.
Cavalcanti was part of the team behind the most powerful demonstration of this approach to date. In 2020, he and his colleagues used photons to perform an extended version of the Wigner’s friend thought experiment that also involved entanglement, another quantum phenomenon that links particles across vast distances. In short, they found that if standard quantum mechanics is right – if we find no signals for objective collapse, for example – we must abandon one of these assumptions: locality, freedom of choice or the absoluteness of observed events.
That placed the most stringent constraints yet on physical reality, says Cavalcanti. “If you want to keep the notion of freedom of choice, together with locality, then you need to reject the assumption of absoluteness of observed events,” says Cavalcanti – just as QBism insists we must. So, although we aren’t at a stage where we can say QBism or any other interpretation is the right way to think about the meaning of quantum mechanics, “we can now narrow down the possibilities,” says Cavalcanti.
He now wants to go further. In their 2020 experiment, Cavalcanti and his colleagues used photon detectors in place of Wigner and photons themselves as a proxy for his friend. Yet photons are obviously a far cry from the human observers imagined by Wigner in the 50s, and most people would presumably say photons don’t count as observers. It is extremely difficult to keep a molecule comprising a couple of thousand atoms in a superposition, owing to the fragility of quantum states, never mind anything approaching the complexity of a human. But Cavalcanti and his colleagues have suggested that we might one day do the same experiment with an advanced artificial intelligence algorithm running on a large quantum computer, performing a simulated experiment in a simulated lab (see “What exactly would a full-scale quantum computer be useful for?”). That, he says, could show us whether we really do have to relinquish our cherished notion of objectivity – even if we are a long way from being able to do such an experiment.
Quantum gravity
What, then, after all that, are the prospects for some sort of resolution on what quantum mechanics is really telling us about reality? In some ways, we are no further along than we were when the pioneers of quantum mechanics fell out over its meaning. “What we do know for sure is that a certain classical way of looking at the world fails, and we can demonstrate that with mathematical and experimental certainty as much as we can know anything in science,” says Cavalcanti. For now, we have to each decide for ourselves which of the various interpretations of what quantum mechanics means is more appealing based on theoretical considerations – whether you are prepared to give up one assumption or another, and what price you are happy to pay in turn for keeping the assumptions you prize above all else.
Cavalcanti says we would ideally get some guidance from our attempts to figure out if quantum mechanics fits with Einstein’s general theory of relativity, which describes gravity as the result of mass warping space-time. If a particular interpretation helps us make progress on that front, he says, it would be a strong clue. “I think these foundational experiments are relevant here,” he says. “Because the question of whether or not events are absolute is important for the construction of a viable theory of quantum gravity.”
In the meantime, we have at least begun to clarify things by putting the problems quantum mechanics throws up in terms we can understand and devising experiments that can narrow down the plausible solutions. And all we can do is to strive for ever more sophisticated ways to do that, says Cavalcanti. “I think you can’t understand the world less by understanding more than one way to see it.”
For 100 years, quantum theory has painted the subatomic world as strange beyond words. But bold new interpretations and experiments may help us to finally grasp its true meaning
Le problème de la théorie quantique (TQ) est qu’elle n’explique pas les relations qu’elle entretient avec la physique ordinaire, dite parfois macroscopique. En résultat, nous ne percevons pas ce que ce chef d’oeuvre signifie pour la compréhension de la réalité.
Les idées ne manquent pas, d’autant plus qu’elles ne proposent pas d’être soumises à des vérifications expérimentales. Selon le physicien David Mermin, « de nouvelles interprétations apparaissent chaque année. Aucune ne disparait ».
Deuis 10 ans, les choses ont commencé à changer. La TQ a fait des prédictions explicites, vérifiables par l’observation, même si elles reposent sur l’hypothèse qu’il n’y a pas de réalité objective. De plus les physiciens trouvent chaque jour de nouvelles méthodes pour juger de la validité de ces jugements.
Selon Eric Cavalcanti, physicien quantique à la Griffith University de Queensland, Australie, les possibilité augmentent régulièrement
La Theorie quantique
Depuis Isaac Newton qui avait formulé ses lois sur le mouvement et la gravitation au 17e siècle (cf Carlo Rovelli, On what we get wrong about the origins of quantum theory” ) les physiciens construisaient leurs théories sur la base que les sysèmes physiques étaient définis par des équations précisant comment ils évolueraient avec le temps. Mais les particules subatomiques telles que l’électron et le photon pouvaient se comporter comme des « vagues » ou exister en état de « superposition » de plusieurs états simultanément, sauf à être « mesurées ». Que se passait-il avant la mesure ? La TQ ne le disait pas.
L’équation de Schrödinger a introduit un concept mathématique, la « fonction d’ondes » pour résumer tous les états possible et calculer la probabitilé de trouver la particule en un certain état après mesure, mesure où la fonstion d’onde était dite s’effondrer, « collapse » ; Mais une seule mesure ne suffisait pas. Il en fallait plusieurs, d’où un retour aux probabilités.
Que se passe-t-il avant mesure, et que signifie précisément une mesure ? Là encore il fallait faire appel aux probabilités.car la TQ ne le précise pas. L’interprétation dite de Copenhague oblige à calculer pour répondre à ces question. Comme Mermin l’avait dit, « ferme ta g. et calcule ». Mais Copenhague a été discuté dès le début, depuis qu’Albert Einstein avait déclaré « God does not play dice with the universe ».
De nombreux physicines considèrent aujourd’hui, tels Roderich Tumulka, de l’University de Tübingen en Allemagne, « nous voulons des jugemnts sur la vraie nature de la réalité. Il n’est pas accceptable de penser que de simples humains puissent faire s’effondrer la fonction d’onde ».
Tumulka est de ceux qui considèrent la fonction d’onde comme physiquement réelle, représentant le monde tel qu’il existe, que nous le voulions ou non. Il faut seulement l’étendre si nécessaire. La plis célèbre de ces extensions est la many-worlds interpretation, qui considère que la fonction d’ondes se concrétise après mesure dans une infinité d’univers séparés connectés au nôtre.
Suite de l’article. Version originale non traduite
But there is also objective collapse, a suite of models proposing that quantum mechanics is incomplete and that something else has to be tacked onto the Schrödinger equation to explain wave function collapse. “The [key] difference with the standard interpretation is that the collapse of the wave function is not something that occurs by magic at the end of the measurement process,” says Angelo Bassi, a theorist at the University of Trieste in Italy. “It’s just part of the dynamics.”
Collapse models have garnered more attention than most in recent years, partly because they offer a plausible explanation of how classical reality emerges without reference to human observers. We don’t see large objects like picture frames and paint brushes in a superposition, it says, because the collapse process works in such a way that the more interacting particles there are, the more readily collapse occurs.
One new interpretation can solve several quantum mysteries in one fell swoop
What triggers this continuous collapsing isn’t entirely clear. Some models don’t say, others posit that it is just gravity. But Bassi says there may ultimately be no good answer – it may just be a property of nature. “That’s why I like collapse models, because they try to open the door to a new world which we don’t understand at the moment – something beyond quantum mechanics that we are not grasping.”
What really sets collapse models apart, however, is that they can be put to the test. Uniquely, they make explicit observational predictions that differ from what standard quantum mechanics predicts. The idea is that this constant process of spontaneous collapse should cause quantum objects such as particles to constantly jiggle around, which, in turn, means they emit excess energy that should be detectable, even if the signal is extremely faint.
Testing quantum interpretations
For the past decade, Bassi has been working with colleagues around the world on an ambitious experimental programme in search of such a signal. They have mostly been repurposing detectors designed to sense hints of dark matter or elusive particles called neutrinos, such as the ultra-sensitive instruments located deep underground beneath the Gran Sasso massif in Italy. And the results are trickling in. In 2020, for instance, a team including Bassi and Cătălina Curceanu, an experimentalist at Italy’s National Institute of Nuclear Physics, was able to rule out the simplest form of one model in which gravity does the collapsing.
Similar experiments are ongoing, and with each new analysis we get fresh constraints on which, if any, of these models might work. But while the fact that we finally have a shot at ruling out objective collapse with experimentation is itself progress, actually doing so is a slow process. “So far, we saw no signal, but this is just the beginning,” says Bassi.
If we were to detect a signal that everyone can agree supports objective collapse, it would surely be worthy of a Nobel prize. Whether that would immediately tell us anything about the meaning of quantum theory is another matter, according to Magdalena Zych at Stockholm University in Sweden, because we would still have to figure out what it is in the environment that is doing the collapsing.
“It would solve the measurement problem in the sense of, if you believe that quantum theory is missing something, this is it,” says Zych. “But it doesn’t really reveal what quantum mechanics is telling us about reality, because you still have to impose some meaning yourself to some extent: you have to say what is the ‘noise’ in the environment [that collapses the wave function].”
More importantly, Zych says we would also be none the wiser about why the observable properties of quantum objects emerge in a probabilistic way, from the act of measurement itself. “That’s really the deep mystery of all this, the fact that we have to speak about probabilities at all,” she says. There is no self-evident reason why the behaviour of subatomic particles cannot be governed by deterministic laws. The fact that they aren’t demands an explanation.
Quantum Bayesianism
For Zych, the take on quantum mechanics that tackles that challenge head on falls into a whole different category of interpretations. While the likes of Bassi and Tumulka insist that quantum states are real, some physicists take a starkly different view: that they don’t represent independent reality at all.
Arguably the most striking example of this approach is QBism, originally known as Quantum Bayesianism because it is founded on a framework for interpreting probabilities first developed by 18th-century minister Thomas Bayes.
Conventionally, probabilities are viewed in “frequentist” terms: we count up the outcomes of many coin tosses to conclude that the odds of getting heads or tails are 50/50. Similarly, many measurements of a particle give you the relative probability of it having one state or another when measured. The Bayesian approach, by contrast, recasts probability as a subjective value that updates as you gain more information.
Running with this idea, the central argument of QBism is that quantum mechanics is similarly subjective. It supplies recommendations about what an observer should believe about what they will see on making a measurement, allowing them to update those beliefs as they take into account fresh experiences. “It’s a theory for agents to navigate the world,” says Ruediger Schack at Royal Holloway, University of London, who developed QBism with Chris Fuchs at the University of Massachusetts Boston.
The appeal of this interpretation is that it seems to address several quantum conundrums at once. It deals with the measurement problem by providing and even requiring a central role for subjective experience. The mysterious collapse of the wave function is simply the observer updating their beliefs on making a measurement, says Schack.
QBism’s answer to the question of how classical reality emerges from the quantum fog, meanwhile, is that it is a result of our actions on the world, of our constant updating of our beliefs about it. The idea even makes light work of a notorious conundrum known as the Wigner’s friend paradox, a thought experiment proposed in the 1950s by physicist Eugene Wigner. Essentially, it demonstrates that two observers – Wigner and a friend observing him making measurements on a quantum system – can have two contradictory experiences of reality.
For a QBist, there is no paradox because a measurement outcome is always personal to the person experiencing it. All of which means that QBism stands starkly athwart the idea that it is possible to achieve an objective view on the universe. But that is exactly the point, says Schack, and this is the great lesson of quantum mechanics: that reality is more than any third-person perspective can capture. “It’s a radically different way of looking at the world.”
What really set collapse models apart is that they can be put to the test
Others find QBism hard to swallow. Bassi, for instance, insists that objective reality is too high a price to pay. “What physics is about is describing nature in an objective way,” he says. Another problem is that QBism doesn’t appear to offer any observable predictions differing from standard quantum mechanics, and no realistic prospect of submitting to experimental tests. “Convincing people might be a case of pointing out the inadequacies of the alternatives,” says Schack.
That arguably leaves us back where we started. If our best hope of an empirical solution to the measurement problem would leave open questions even if it were proved correct, and an alternative that can address those questions can’t be tested, where do we go from here?
There might still be cause for optimism. In the past few years, some physicists have begun to demonstrate that the assumptions underpinning how we think about the meaning of quantum theory – typically considered more in the realm of metaphysics than science – might themselves submit to testing.
Experimental metaphysics
They call it experimental metaphysics. “It’s an approach that tries to be clear about the landscape of metaphysical assumptions made by different interpretations,” says Cavalcanti, who is one of its key proponents. Among those assumptions are the absoluteness of observed events, which is to say that the outcomes of a measurement are the same for all observers; freedom of choice, the notion that the outcome of any measurement isn’t due to factors involved in the measurement; and locality, or the idea that a free choice cannot influence the observed outcome of an experiment at a distance or in the past. “Individually, these may not be testable, but when you group them together, they can be,” says Cavalcanti. In this way, you can potentially at least disprove classes of quantum interpretation, he says.
Cavalcanti was part of the team behind the most powerful demonstration of this approach to date. In 2020, he and his colleagues used photons to perform an extended version of the Wigner’s friend thought experiment that also involved entanglement, another quantum phenomenon that links particles across vast distances. In short, they found that if standard quantum mechanics is right – if we find no signals for objective collapse, for example – we must abandon one of these assumptions: locality, freedom of choice or the absoluteness of observed events.
That placed the most stringent constraints yet on physical reality, says Cavalcanti. “If you want to keep the notion of freedom of choice, together with locality, then you need to reject the assumption of absoluteness of observed events,” says Cavalcanti – just as QBism insists we must. So, although we aren’t at a stage where we can say QBism or any other interpretation is the right way to think about the meaning of quantum mechanics, “we can now narrow down the possibilities,” says Cavalcanti.
He now wants to go further. In their 2020 experiment, Cavalcanti and his colleagues used photon detectors in place of Wigner and photons themselves as a proxy for his friend. Yet photons are obviously a far cry from the human observers imagined by Wigner in the 50s, and most people would presumably say photons don’t count as observers. It is extremely difficult to keep a molecule comprising a couple of thousand atoms in a superposition, owing to the fragility of quantum states, never mind anything approaching the complexity of a human. But Cavalcanti and his colleagues have suggested that we might one day do the same experiment with an advanced artificial intelligence algorithm running on a large quantum computer, performing a simulated experiment in a simulated lab (see “What exactly would a full-scale quantum computer be useful for?”). That, he says, could show us whether we really do have to relinquish our cherished notion of objectivity – even if we are a long way from being able to do such an experiment.
Quantum gravity
What, then, after all that, are the prospects for some sort of resolution on what quantum mechanics is really telling us about reality? In some ways, we are no further along than we were when the pioneers of quantum mechanics fell out over its meaning. “What we do know for sure is that a certain classical way of looking at the world fails, and we can demonstrate that with mathematical and experimental certainty as much as we can know anything in science,” says Cavalcanti.
For now, we have to each decide for ourselves which of the various interpretations of what quantum mechanics means is more appealing based on theoretical considerations – whether you are prepared to give up one assumption or another, and what price you are happy to pay in turn for keeping the assumptions you prize above all else.
Cavalcanti says we would ideally get some guidance from our attempts to figure out if quantum mechanics fits with Einstein’s general theory of relativity, which describes gravity as the result of mass warping space-time. If a particular interpretation helps us make progress on that front, he says, it would be a strong clue. “I think these foundational experiments are relevant here,” he says. “Because the question of whether or not events are absolute is important for the construction of a viable theory of quantum gravity.”
In the meantime, we have at least begun to clarify things by putting the problems quantum mechanics throws up in terms we can understand and devising experiments that can narrow down the plausible solutions. And all we can do is to strive for ever more sophisticated ways to do that, says Cavalcanti. “I think you can’t understand the world less by understanding more than one way to see it.”
This article is part of a special series celebrating the 100th anniversary of the birth of quantum theory.
For 100 years, quantum theory has painted the subatomic world as strange beyond words. But bold new interpretations and experiments may help us to finally grasp its true meaning
Le problème de la théorie quantique (TQ) est qu’elle n’explique pas les relations qu’elle entretient avec la physique ordinaire, dite parfois macroscopique. En résultat, nous ne percevons pas ce que ce chef d’oeuvre signifie pour la compréhension de la réalité.
Les idées ne manquent pas, d’autant plus qu’elles ne proposent pas d’être soumises à des vérifications expérimentales. Selon le physicien David Mermin, « de nouvelles interprétations apparaissent chaque année. Aucune ne disparait ».
Deuis 10 ans, les choses ont commencé à changer. La TQ a fait des prédictions explicites, vérifiables par l’observation, même si elles reposent sur l’hypothèse qu’il n’y a pas de réalité objective. De plus les physiciens trouvent chaque jour de nouvelles méthodes pour juger de la validité de ces jugements.
Selon Eric Cavalcanti, physicien quantique à la Griffith University de Queensland, Australie, les possibilité augmentent régulièrement
La Theorie quantique
Depuis Isaac Newton qui avait formulé ses lois sur le mouvement et la gravitation au 17e siècle (cf Carlo Rovelli, On what we get wrong about the origins of quantum theory” ) les physiciens construisaient leurs théories sur la base que les sysèmes physiques étaient définis par des équations précisant comment ils évolueraient avec le temps. Mais les particules subatomiques telles que l’électron et le photon pouvaient se comporter comme des « vagues » ou exister en état de « superposition » de plusieurs états simultanément, sauf à être « mesurées ». Que se passait-il avant la mesure ? La TQ ne le disait pas.
L’équation de Schrödinger a introduit un concept mathématique, la « fonction d’ondes » pour résumer tous les états possible et calculer la probabitilé de trouver la particule en un certain état après mesure, mesure où la fonstion d’onde était dite s’effondrer, « collapse » ; Mais une seule mesure ne suffisait pas. Il en fallait plusieurs, d’où un retour aux probabilités.
Que se passe-t-il avant mesure, et que signifie précisément une mesure ? Là encore il fallait faire appel aux probabilités.car la TQ ne le précise pas. L’interprétation dite de Copenhague oblige à calculer pour répondre à ces question. Comme Mermin l’avait dit, « ferme ta g. et calcule ». Mais Copenhague a été discuté dès le début, depuis qu’Albert Einstein avait déclaré « God does not play dice with the universe ».
De nombreux physicines considèrent aujourd’hui, tels Roderich Tumulka, de l’University de Tübingen en Allemagne, « nous voulons des jugemnts sur la vraie nature de la réalité. Il n’est pas accceptable de penser que de simples humains puissent faire s’effondrer la fonction d’onde ».
Tumulka est de ceux qui considèrent la fonction d’onde comme physiquement réelle, représentant le monde tel qu’il existe, que nous le voulions ou non. Il faut seulement l’étendre si nécessaire. La plis célèbre de ces extensions est la many-worlds interpretation, qui considère que la fonction d’ondes se concrétise après mesure dans une infinité d’univers séparés connectés au nôtre.
Suite de l’article. Version originale non traduite
But there is also objective collapse, a suite of models proposing that quantum mechanics is incomplete and that something else has to be tacked onto the Schrödinger equation to explain wave function collapse. “The [key] difference with the standard interpretation is that the collapse of the wave function is not something that occurs by magic at the end of the measurement process,” says Angelo Bassi, a theorist at the University of Trieste in Italy. “It’s just part of the dynamics.”
Collapse models have garnered more attention than most in recent years, partly because they offer a plausible explanation of how classical reality emerges without reference to human observers. We don’t see large objects like picture frames and paint brushes in a superposition, it says, because the collapse process works in such a way that the more interacting particles there are, the more readily collapse occurs.
One new interpretation can solve several quantum mysteries in one fell swoop
What triggers this continuous collapsing isn’t entirely clear. Some models don’t say, others posit that it is just gravity. But Bassi says there may ultimately be no good answer – it may just be a property of nature. “That’s why I like collapse models, because they try to open the door to a new world which we don’t understand at the moment – something beyond quantum mechanics that we are not grasping.”
What really sets collapse models apart, however, is that they can be put to the test. Uniquely, they make explicit observational predictions that differ from what standard quantum mechanics predicts. The idea is that this constant process of spontaneous collapse should cause quantum objects such as particles to constantly jiggle around, which, in turn, means they emit excess energy that should be detectable, even if the signal is extremely faint.
Testing quantum interpretations
For the past decade, Bassi has been working with colleagues around the world on an ambitious experimental programme in search of such a signal. They have mostly been repurposing detectors designed to sense hints of dark matter or elusive particles called neutrinos, such as the ultra-sensitive instruments located deep underground beneath the Gran Sasso massif in Italy. And the results are trickling in. In 2020, for instance, a team including Bassi and Cătălina Curceanu, an experimentalist at Italy’s National Institute of Nuclear Physics, was able to rule out the simplest form of one model in which gravity does the collapsing.
Similar experiments are ongoing, and with each new analysis we get fresh constraints on which, if any, of these models might work. But while the fact that we finally have a shot at ruling out objective collapse with experimentation is itself progress, actually doing so is a slow process. “So far, we saw no signal, but this is just the beginning,” says Bassi.
If we were to detect a signal that everyone can agree supports objective collapse, it would surely be worthy of a Nobel prize. Whether that would immediately tell us anything about the meaning of quantum theory is another matter, according to Magdalena Zych at Stockholm University in Sweden, because we would still have to figure out what it is in the environment that is doing the collapsing.
“It would solve the measurement problem in the sense of, if you believe that quantum theory is missing something, this is it,” says Zych. “But it doesn’t really reveal what quantum mechanics is telling us about reality, because you still have to impose some meaning yourself to some extent: you have to say what is the ‘noise’ in the environment [that collapses the wave function].”
More importantly, Zych says we would also be none the wiser about why the observable properties of quantum objects emerge in a probabilistic way, from the act of measurement itself. “That’s really the deep mystery of all this, the fact that we have to speak about probabilities at all,” she says. There is no self-evident reason why the behaviour of subatomic particles cannot be governed by deterministic laws. The fact that they aren’t demands an explanation.
Quantum Bayesianism
For Zych, the take on quantum mechanics that tackles that challenge head on falls into a whole different category of interpretations. While the likes of Bassi and Tumulka insist that quantum states are real, some physicists take a starkly different view: that they don’t represent independent reality at all.
Arguably the most striking example of this approach is QBism, originally known as Quantum Bayesianism because it is founded on a framework for interpreting probabilities first developed by 18th-century minister Thomas Bayes.
Conventionally, probabilities are viewed in “frequentist” terms: we count up the outcomes of many coin tosses to conclude that the odds of getting heads or tails are 50/50. Similarly, many measurements of a particle give you the relative probability of it having one state or another when measured. The Bayesian approach, by contrast, recasts probability as a subjective value that updates as you gain more information.
Running with this idea, the central argument of QBism is that quantum mechanics is similarly subjective. It supplies recommendations about what an observer should believe about what they will see on making a measurement, allowing them to update those beliefs as they take into account fresh experiences. “It’s a theory for agents to navigate the world,” says Ruediger Schack at Royal Holloway, University of London, who developed QBism with Chris Fuchs at the University of Massachusetts Boston.
The appeal of this interpretation is that it seems to address several quantum conundrums at once. It deals with the measurement problem by providing and even requiring a central role for subjective experience. The mysterious collapse of the wave function is simply th observer updating their beliefs on making a measurement, says Schack.
QBism’s answer to the question of how classical reality emerges from the quantum fog, meanwhile, is that it is a result of our actions on the world, of our constant updating of our beliefs about it. The idea even makes light work of a notorious conundrum known as the Wigner’s friend paradox, a thought experiment proposed in the 1950s by physicist Eugene Wigner. Essentially, it demonstrates that two observers – Wigner and a friend observing him making measurements on a quantum system – can have two contradictory experiences of reality.
For a QBist, there is no paradox because a measurement outcome is always personal to the person experiencing it. All of which means that QBism stands starkly athwart the idea that it is possible to achieve an objective view on the universe. But that is exactly the point, says Schack, and this is the great lesson of quantum mechanics: that reality is more than any third-person perspective can capture. “It’s a radically different way of looking at the world.”
What really set collapse models apart is that they can be put to the test
Others find QBism hard to swallow. Bassi, for instance, insists that objective reality is too high a price to pay. “What physics is about is describing nature in an objective way,” he says. Another problem is that QBism doesn’t appear to offer any observable predictions differing from standard quantum mechanics, and no realistic prospect of submitting to experimental tests. “Convincing people might be a case of pointing out the inadequacies of the alternatives,” says Schack.
That arguably leaves us back where we started. If our best hope of an empirical solution to the measurement problem would leave open questions even if it were proved correct, and an alternative that can address those questions can’t be tested, where do we go from here?
There might still be cause for optimism. In the past few years, some physicists have begun to demonstrate that the assumptions underpinning how we think about the meaning of quantum theory – typically considered more in the realm of metaphysics than science – might themselves submit to testing.
Experimental metaphysics
They call it experimental metaphysics. “It’s an approach that tries to be clear about the landscape of metaphysical assumptions made by different interpretations,” says Cavalcanti, who is one of its key proponents. Among those assumptions are the absoluteness of observed events, which is to say that the outcomes of a measurement are the same for all observers; freedom of choice, the notion that the outcome of any measurement isn’t due to factors involved in the measurement; and locality, or the idea that a free choice cannot influence the observed outcome of an experiment at a distance or in the past. “Individually, these may not be testable, but when you group them together, they can be,” says Cavalcanti. In this way, you can potentially at least disprove classes of quantum interpretation, he says.
Cavalcanti was part of the team behind the most powerful demonstration of this approach to date. In 2020, he and his colleagues used photons to perform an extended version of the Wigner’s friend thought experiment that also involved entanglement, another quantum phenomenon that links particles across vast distances. In short, they found that if standard quantum mechanics is right – if we find no signals for objective collapse, for example – we must abandon one of these assumptions: locality, freedom of choice or the absoluteness of observed events.
That placed the most stringent constraints yet on physical reality, says Cavalcanti. “If you want to keep the notion of freedom of choice, together with locality, then you need to reject the assumption of absoluteness of observed events,” says Cavalcanti – just as QBism insists we must. So, although we aren’t at a stage where we can say QBism or any other interpretation is the right way to think about the meaning of quantum mechanics, “we can now narrow down the possibilities,” says Cavalcanti.
He now wants to go further. In their 2020 experiment, Cavalcanti and his colleagues used photon detectors in place of Wigner and photons themselves as a proxy for his friend. Yet photons are obviously a far cry from the human observers imagined by Wigner in the 50s, and most people would presumably say photons don’t count as observers. It is extremely difficult to keep a molecule comprising a couple of thousand atoms in a superposition, owing to the fragility of quantum states, never mind anything approaching the complexity of a human. But Cavalcanti and his colleagues have suggested that we might one day do the same experiment with an advanced artificial intelligence algorithm running on a large quantum computer, performing a simulated experiment in a simulated lab (see “What exactly would a full-scale quantum computer be useful for?”). That, he says, could show us whether we really do have to relinquish our cherished notion of objectivity – even if we are a long way from being able to do such an experiment.
Quantum gravity
What, then, after all that, are the prospects for some sort of resolution on what quantum mechanics is really telling us about reality? In some ways, we are no further along than we were when the pioneers of quantum mechanics fell out over its meaning. “What we do know for sure is that a certain classical way of looking at the world fails, and we can demonstrate that with mathematical and experimental certainty as much as we can know anything in science,” says Cavalcanti.
For now, we have to each decide for ourselves which of the various interpretations of what quantum mechanics means is more appealing based on theoretical considerations – whether you are prepared to give up one assumption or another, and what price you are happy to pay in turn for keeping the assumptions you prize above all else.
Cavalcanti says we would ideally get some guidance from our attempts to figure out if quantum mechanics fits with Einstein’s general theory of relativity, which describes gravity as the result of mass warping space-time. If a particular interpretation helps us make progress on that front, he says, it would be a strong clue. “I think these foundational experiments are relevant here,” he says. “Because the question of whether or not events are absolute is important for the construction of a viable theory of quantum gravity.”
In the meantime, we have at least begun to clarify things by putting the problems quantum mechanics throws up in terms we can understand and devising experiments that can narrow down the plausible solutions. And all we can do is to strive for ever more sophisticated ways to do that, says Cavalcanti. “I think you can’t understand the world less by understanding more than one way to see it.”
Le propre du langage humain est la syntaxe, par laquelle des éléments significatifs se combinent en séquences plus longues, comme des mots formant une phrase. On nomme ce caractère la compositionnalité.
En linguistique, le principe de compositionnalité est le principe selon lequel la signification d’une expression complexe est définie par les significations des expressions la composant, et par les règles employées pour les combiner en phrases.
Or il est apparu que les bonobos communiquent entre eux par un langage dont la structure est identique à celle du langage humain. On y trouve par exemple l’équivalent d’un sujet, d’un verbe et d’un complément. Ainsi ils disent « moi-vouloir-banane » et non, comme tous les autres animaux « moi-banane ».
Pour comprendre la raison de cette propriété, des chercheurs de l »Université de Zurich, en liaison avec des confrères travaillant an Congo, ont étudié des bonobos adultes de la réserve de Kokoloport en République Démocratique du Congo.
lIs ont enregistré plus de 1000 appels correspondant à des échanges entre bonobos adultes confrontés à des situations complexes telles que des demandes d’assistance et les réponses reçues. En étudiant ensuite ces messages, ils ont constaté que les échanges avaient des ressemblances avec le langage humain, sans évidemment pouvoir lui être complètement comparables.
La présence d’une syntaxe n’y est pas discutable.
Ceci tient peut-être au fait qu’il y a au moins 7 millions d’années, les deux espèces avaient eu des ancêtres communs.
Extensive compositionality in the vocal system of bonobos
Apr 2025 Vol 388, Issue 6742 p. 104-108
Editor’s summary
One hallmark of human language is the combination of elements into larger meaningful structures, a pattern referred to as compositionality. Compositionality can be trivial, in which the two parts are added together to give meaning, or nontrivial, in which the meaning in one part modifies the meaning in the other. Recent research has found the presence of trivial compositionality across a number of species, but it has been argued that nontrivial compositionality is unique to humans. Berthet et al. used a large dataset of bonobo vocalizations in conjunction with a distributional semantics approach and found that not only did they display compositionality, but three of the four types were nontrivial. —Sacha Vignieri
Abstract
Compositionality, the capacity to combine meaningful elements into larger meaningful structures, is a hallmark of human language. Compositionality can be trivial (the combination’s meaning is the sum of the meaning of its parts) or nontrivial (one element modifies the meaning of the other element). Recent studies have suggested that animals lack nontrivial compositionality, representing a key discontinuity with language. In this work, using methods borrowed from distributional semantics, we investigated compositionality in wild bonobos and found that not only does each call type of their repertoire occur in at least one compositional combination, but three of these compositional combinations also exhibit nontrivial compositionality. These findings suggest that compositionality is a prominent feature of the bonobo vocal system, revealing stronger parallels with human language than previously thought.
La dernière période glaciaire est une période de refroidissement global, ou glaciation, qui caractérise la fin du Pléistocène sur l’ensemble de la planète. Elle commence il y a 115 000 ans et se termine il y a 11 700 ans, quand commence l’Holocène.
Les humains (Homo sapiens) n’auraient pas eu besoin de migrer comme la plupart des autres espèces durant cette période glaciaire.
En utilisant des données génétiques, des scientifiques ont démontré que certains humains étaient restés en Europe centrale durant la dernière grande période de glaciation. Jusqu’ici, une grande majorité de la communauté archéologique considérait que l’homme moderne s’était retiré dans le sud de l’Europe.
Une équipe de chercheurs de l’université de Bournemouth (Royaume-Uni), a examiné l’histoire génétique de vingt-trois mammifères communs en Europe, dont l’Homo sapiens. L’étude montre que les hommes, au même titre que les ours bruns et les loups « étaient déjà largement répartis à travers l’Europe au plus fort de la dernière glaciation, soit sans refuge discernable, soit avec des refuges au nord et au sud », selon John Stewart et Jeremy Searle, tous deux membres de l’équipe.
Des outils en pierre (racloirs, silex, lissoirs…) ont permis aux préhistoriques de préparer les peaux d’animaux pour les utiliser comme isolant thermique. Par la suite Il y a environ 40 000 ans, l’invention des poinçons en os et des aiguilles à chas ont rendu possible la création des vêtements de peau ajustés et ornés.
Les plus anciennes aiguilles à chas connues datent d’il y a environ 40 000 ans en Sibérie (grotte de Denisova). Les aiguilles à chas sont beaucoup plus difficiles à façonner que les poinçons en os ; pourtant avec l’archéologie expérimentale il apparait que ces derniers étaient suffisants pour créer des vêtements ajustés. Les poinçons en os sont des outils fabriqués à partir d’os d’animaux aiguisés en pointe. Les aiguilles à chas sont extraites des os longs, avec une perforation (un chas) pour passer un fil (en matière animale ou végétale) pour maintenir les deux parties ensemble, sans laisser passer l’air.
L’innovation des aiguilles à chas peut refléter la production de vêtements plus complexes et superposés, ainsi que la décoration des vêtements en attachant des perles et d’autres petits objets décoratifs sur les vêtements : de nombreux artefacts sont pourvus d’un orifice ou d’une rainure permettant de maintenir l’objet, cousu sur le vêlement.
Les auteurs de l’étude soutiennent que les vêtements sont devenus un élément de parure parce que les méthodes traditionnelles de décoration corporelle, comme la peinture corporelle à l’ocre ou la scarification n’étaient pas possible à la fin de la dernière période glaciaire dans les régions les plus froides de l’Eurasie. Les scarifications ou les tracés corporels ne pouvaient être visibles car les individus avaient besoin de porter des vêtements en permanence pour survivre.
C’est pourquoi l’apparition d’aiguilles à chas est particulièrement importante, car elle signale l’utilisation des vêtements comme décoration » ,selon le Dr Gilligan. « Les aiguilles à chas étaient particulièrement utiles pour la couture très fine nécessaire à la décoration des vêtements. »
« Beaucoup des aiguilles que nous avons découvertes ne servaient pas seulement à la confection de vêtements, mais aussi à la broderie et à la décoration. Elles avaient un rôle esthétique »
Les vêtements ont donc évolué pour répondre aux différents besoins des paléolithiques : une nécessité pratique de protection et de confort contre les éléments extérieurs mais aussi une fonction sociale et esthétique pour l’identité individuelle et culturelle.
Ice Age Apparel—Changing Prey Patterns Towards the Last Glacial Maximum and the Role of Reindeer Fur for Clothing at Kammern-Grubgraben
Published: 10 April 2025
Abstract
The site of Kammern-Grubgraben in Lower Austria preserved one of the largest assemblages of stone constructions, lithic and organic artefacts, personal ornaments, and faunal remains of the Last Glacial Maximum (ca. 24–20 ka cal BP) in Europe. Conspicuously, the faunal remains attest to an occupation only during winter and are strongly dominated by reindeer (Rangifer tarandus), indicating a rather selective and narrow hunting focus despite the curated, long-term character of the site. This narrow focus contrasts with findings from older sites in the region, such as the Gravettian sites Krems-Hundssteig, Krems-Wachtberg, and Langenlois A, dated to between 33 and 29 ka cal BP, which show a main focus on mammoth. In this paper, we present new results on the age and sex distribution of reindeer at Kammern-Grubgraben. We argue that winter-hunting of reindeer, in addition to its role in providing energy-rich nutrition and raw material for organic tools, is also indicative of a focus on obtaining high-quality raw material for clothing. The fur of reindeer in winter is particularly valuable and convenient for the production of clothing for cold environments. Together with the recovered large number of eyed needles, a tool for tight and regular seams, our findings suggest that the production of clothing and other goods made of fur and skin was an important activity at Kammern-Grubgraben.
La physique des particules rencontre aujourd’hui deux difficultés. Une approche connue sous le nom de supersymétrie, par exemple, prévoit de nouvelles particules permettant d’annuler les fluctuations quantiques résultant du modèle standard des particules
La supersymétrie (abrégée en SuSy) est une symétrie supposée de la physique des particules qui postule une relation profonde entre les particules de spin demi-entier (les fermions) qui constituent la matière et les particules de spin entier (les bosons) véhiculant les interactions. Dans le cadre de la SuSy, chaque fermion est associé à un « superpartenaire » de spin entier, alors que chaque boson est associé à un « superpartenaire » de spin demi-entier. (Wikipedia).
Une solution alternative a été proposée par Nima Arkani-Hamed, aujourd’hui à l’ Institute for Advanced Study à Princeton, New Jersey.
Celle-ci considère que la gravité peut fuir à travers ces extra-dimensions, la rendant progressivement plus faible qu’elle ne l »est aujourd’hui. Des modèles basés sur cette hypothèse prévoient une échelle de Planck inférieure à l’actuelle, la faisant paraître plus faible qu’elle ne l’est actuellement. Les extradimensions sont actuellement invisibles parce qu’elle sont trop faibles
La longueur de Planck ou échelle de Planck est une unité de longueur qui fait partie du système d’unités naturelles dites unités de Planck et vaut 1,616 25 En physique des particules et en cosmologie physique, l’échelle de Planck est une échelle d’énergie autour de 1,22 × 10 28 eV (l’énergie de Planck, correspondant à l’équivalent énergétique de la masse de Planck, 2,17645 × 10 −8 kg) à laquelle les effets quantiques de la gravité deviennent significatifs. (Wikipedia)
Jusqu’à présent cependant ces hypothèses se sont révélées trop timides pour rendre compte des nouvelles observations du LHC, d’autant plus que celui-ci ne cesse pas d’en produire.
Pour résumer, la physique des particules est en crise. C’est pourquoi un petit groupe de théoriciens ont commencé à explorer une alternative au réductionnisme tel qu’il est connu aujourd’hui.
Au lieu d’étudier les différents niveaux d’énergie de l’univers comme des entités indépendantes, il les traite comme si elles se conditionnaient respectivement.
De la même façon, dans un arc en ciel l’ultraviolet et l’infrarouge, que nous ne pouvons pas voir, enferment les autres couleurs du spectre que nous pouvons voir, le rouge, l’orange, le jaune, le vert, le bleu, l’indigo et le violet. C’est dans l’équivalent de celles-ci qu’opère le modèle standard des particules.
Dans la fin des années 1970, les physiciens Andrew Cohen , David Kaplan et Ann Nelson , en étudiant les trous noirs calculèrent qu’il y avait un minimum d’énergie à partir duquel le modèle standard cessait d’être viable.
La physique des particules rencontre aujourd’hui deux difficultés. Une approche connue sous i le nom de supersymétrie, par exemple, prévoit de nouvelles particules permettant d’annuler les fluctuations quantiques résultant du modèle standard des particule
La théorie des champs effectifs est l’un des principes directeurs les plus approfondis et les plus utiles de la physique. Ses outils et méthodes permettent d’étudier les aspects universels de classes entières de modèles microscopiques inconnus, dont les principales fonctions dépendent de symétries et de degrés de liberté effectifs.
En raison de son universalité, cette théorie permet des applications à toutes les échelles de la physique: Elle a été appliquée avec succès à la cosmologie pour décrire l’inflation cosmique primaire, l’accélération cosmique actuelle, la dynamique de la structure à grande échelle et la matière noire.
Ce champ de recherches a été récemment utilisé dans l’étude des ondes gravitationnelles et les récentes recherches en astrophysique : de nouvelles et convaincantes méthodes de calcul et des prédictions sont élaborées en s’appuyant sur les théories de diffusion d’amplitudes étudiées par les physiciens des particules.
Malgré ses avantages l’EFT peut rendre impossible une compréhension en profondeur de l’univers. Ceci parce qu’elle introduit des problèmes. Ainsi pendant des années les théoriciens des particules ont recherché le boson de Higgs, la particule qui donne leurs masses aux quarks et aux électrons. Dans le modèle standard des particules, celles ci peuvent temporairement se transformer en particules à vie courte dite particules virtuelles pour revenir rapidement à leur état original. Dans une bizarrerie de la mécanique quantique ces fluctuations qui gouvernent le monde des particules contribuent à leur masse. L’importance de cette contribution est fonction du plus haut niveau d’énergie atteint par la particule virtuelle.
Le seuil de ce niveau est défini par l’échelle de Planck, la plus basse échelle existant et le point où les effets gravitationnels deviennent si importants que le modèle standard doit être remplacé par des formules faisant une synthèse entre la gravité et la physique quantique. Mais la prédiction théorique est 27 plus élevé que celle obtenue par l’observation quand la particule fut découverte au LHC.
Un puzzle semblable est observé dans le domaine de l’énergie noire. Mais dans ce cas la valeur de l’énergie du vide mesurée est de trente fois inférieure à celle prédite par la théorie.
L’holisme méthodologique est un principe de méthode selon lequel l’analyse doit partir de la totalité, de l’ensemble, du collectif, qui est plus que la somme des parties. La notion de holisme a été introduite dans les années 1920 par Jan Smuts, qui a été premier ministre de l’Afrique du sud.
Par cette notion, il défend la conception selon laquelle la totalité peut être plus grande que la somme des parties. Cette notion de holisme a notamment été reprise par Louis Dumont qui compare les sociétés holistes aux sociétés individualistes. On en retrouve aussi des applications dans les sciences de la nature à travers les travaux de Pierre Duhem et la notion de holisme épistémologique.
En cosmologie, le réductionnisme consiste à rechercher les composants des corps. Une planète est constituée d’atomes, les atomes sont constitués de protons, de neutrons et d’électrons, les protons et les neutrons de quarks et sans doute d’autres composants encore inconnus, car trop petits pour être observables avec les moyens actuels.
A l’inverse, l’holisme considérera que les particules élémentaires s’assemblent en atomes, les atomes s’assemblent en planètes et les planètes conjointement avec les étoiles, constituent l’univers, ou tout au moins l’univers observable.
En allant plus loin, on pourra considérer qu’il existe un nombre indéfini d’univers, constituant un multivers.
Avec l’importance que prend tous les jours la mécanique quantique, une étude holiste du multivers verra en lui un tout quantique constitué d’objets liés par l’intrication (entanglement)..Parmi ces objets, il y a l’espace et le temps tels que nous les connaissons sur la Terre.
L’hypothèse est radicale et commence seulement à être testée expérimentalement. Certains la trouveront empreinte de mysticisme
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