Tag Archives: Percepção da realidade

Como ciência tenta prever os eventos ‘cisnes negros’ (BBC News Brasil)

bbc.com


Analía Llorente

BBC News Mundo

4 outubro 2021

Cena do filme 'Cisne Negro'

O que o surgimento da internet, os ataques de 11 de setembro de 2001 e a crise econômica de 2008 têm em comum?

Foram eventos extremamente raros e surpreendentes que tiveram um forte impacto na história.

Acontecimentos deste tipo costumam ser chamados de “cisnes negros”.

Alguns argumentam que a recente pandemia de covid-19 também pode ser considerada um deles, mas nem todo mundo concorda.

A “teoria do cisne negro” foi desenvolvida pelo professor, escritor e ex-operador da bolsa libanês-americano Nassim Taleb em 2007.

E possui três componentes, como o próprio Taleb explicou em um artigo no jornal americano The New York Times no mesmo ano:

– Em primeiro lugar, é algo atípico, já que está fora do âmbito das expectativas habituais, porque nada no passado pode apontar de forma convincente para sua possibilidade.

– Em segundo lugar, tem um impacto extremo.

– Em terceiro lugar, apesar de seu status atípico, a natureza humana nos faz inventar explicações para sua ocorrência após o fato em si, tornando-o explicável e previsível.

A tese de Taleb está geralmente associada à economia, mas se aplica a qualquer área.

E uma vez que as consequências costumam ser catastróficas, é importante aceitar que a ocorrência de um evento”cisne negro” é possível — e por isso é necessário ter um plano para lidar com o mesmo.

Em suma, o “cisne negro” representa uma metáfora para algo imprevisível e muito estranho, mas não impossível.

Por que são chamados assim?

No fim do século 17, navios europeus embarcaram na aventura de explorar a Austrália.

Em 1697, enquanto navegava nas águas de um rio desconhecido no sudoeste da Austrália Ocidental, o capitão holandês Willem de Vlamingh avistou vários cisnes negros, sendo possivelmente o primeiro europeu a observá-los.

Como consequência, Vlamingh deu ao rio o nome de Zwaanenrivier (Rio dos Cisnes, em holandês) por causa do grande número de cisnes negros que havia ali.

Tratava-se de um acontecimento inesperado e novo. Até aquele momento, a ciência só havia registrado cisnes brancos.

A primeira referência conhecida ao termo “cisne negro” associado ao significado de raridade vem de uma frase do poeta romano Décimo Júnio Juvenal (60-128).

Desesperado para encontrar uma esposa com todas as “qualidades certas” da época, ele escreveu em latim que esta mulher era rara avis in terris, nigroque simillima cygno (“uma ave rara nestas terras, como um cisne negro”), detalha o dicionário de Oxford.

Porque naquela época e até cerca de 1,6 mil anos depois, para os europeus, não existiam cisnes negros.

Prevendo os ‘cisnes negros’

Um grupo de cientistas da Universidade de Stanford, nos Estados Unidos, está trabalhando para prever o imprevisível.

Ou seja, para se antecipar aos “cisnes negros” — não às aves, mas aos estranhos eventos que acontecem na história.

Embora sua análise primária tenha sido baseada em três ambientes diferentes na natureza, o método computacional que eles criaram pode ser aplicado a qualquer área, incluindo economia e política.

“Ao analisar dados de longo prazo de três ecossistemas, pudemos demonstrar que as flutuações que ocorrem em diferentes espécies biológicas são estatisticamente iguais em diferentes ecossistemas”, afirmou Samuel Bray, assistente de pesquisa no laboratório de Bo Wang, professor de bioengenharia na Universidade de Stanford.

“Isso sugere que existem certos processos universais que podemos utilizar para prever esse tipo de comportamento extremo”, acrescentou Bray, conforme publicado no site da universidade.

Para desenvolver o método de previsão, os pesquisadores procuraram sistemas biológicos que vivenciaram eventos “cisne negro” e como foram os contextos em que ocorreram.

Eles se basearam então em ecossistemas monitorados de perto por muitos anos.

Os exemplos incluíram: um estudo de oito anos do plâncton do Mar Báltico com níveis de espécies medidos duas vezes por semana; medições de carbono de um bosque da Universidade de Harvard, nos EUA, que foram coletadas a cada 30 minutos desde 1991; e medições de cracas (mariscos), algas e mexilhões na costa da Nova Zelândia, feitas mensalmente por mais de 20 anos, detalha o estudo publicado na revista científica Plos Computational Biology.

Os pesquisadores aplicaram a estas bases de dados a teoria física por trás de avalanches e terremotos que, assim como os “cisnes negros”, mostram um comportamento extremo, repentino e de curto prazo.

A partir desta análise, os especialistas desenvolveram um método para prever eventos “cisne negro” que fosse flexível entre espécies e períodos de tempo e também capaz de trabalhar com dados muito menos detalhados e mais complexos.

Posteriormente, conseguiram prever com precisão eventos extremos que ocorreram nesses sistemas.

Até agora, “os métodos se baseavam no que vimos para prever o que pode acontecer no futuro, e é por isso que não costumam identificar os eventos ‘cisne negro'”, diz Wang.

Mas este novo mecanismo é diferente, segundo o professor de Stanford, “porque parte do pressuposto de que estamos vendo apenas parte do mundo”.

“Extrapola um pouco do que falta e ajuda enormemente em termos de previsão”, acrescenta.

Então, os “cisnes negros” poderiam ser detectados em outras áreas, como finanças ou economia?

“Aplicamos nosso método às flutuações do mercado de ações e funcionou muito bem”, disse Wang à BBC News Mundo, serviço de notícias em espanhol da BBC, por e-mail.

Os pesquisadores analisaram os índices Nasdaq, Dow Jones Industrial Average e S&P 500.

“Embora a principal tendência do mercado seja o crescimento exponencial de longo prazo, as flutuações em torno dessa tendência seguem as mesmas trajetórias e escalas médias que vimos nos sistemas ecológicos”, explica.

Mas “embora as semelhanças entre as variações na bolsa e ecológicas sejam interessantes, nosso método de previsão é mais útil nos casos em que os dados são escassos e as flutuações geralmente vão além dos registros históricos (o que não é o caso do mercado de ações)”, adverte Wang.

Por isso, temos que continuar atentos para saber se o próximo “cisne negro” vai nos pegar de surpresa… ou talvez não.

Our brains exist in a state of “controlled hallucination” (MIT Technology Review)

technologyreview.com

Matthew Hutson – August 25, 2021

Three new books lay bare the weirdness of how our brains process the world around us.

Eventually, vision scientists figured out what was happening. It wasn’t our computer screens or our eyes. It was the mental calculations that brains make when we see. Some people unconsciously inferred that the dress was in direct light and mentally subtracted yellow from the image, so they saw blue and black stripes. Others saw it as being in shadow, where bluish light dominates. Their brains mentally subtracted blue from the image, and came up with a white and gold dress. 

Not only does thinking filter reality; it constructs it, inferring an outside world from ambiguous input. In Being You, Anil Seth, a neuroscientist at the University of Sussex, relates his explanation for how the “inner universe of subjective experience relates to, and can be explained in terms of, biological and physical processes unfolding in brains and bodies.” He contends that “experiences of being you, or of being me, emerge from the way the brain predicts and controls the internal state of the body.” 

Prediction has come into vogue in academic circles in recent years. Seth and the philosopher Andy Clark, a colleague at Sussex, refer to predictions made by the brain as “controlled hallucinations.” The idea is that the brain is always constructing models of the world to explain and predict incoming information; it updates these models when prediction and the experience we get from our sensory inputs diverge. 

“Chairs aren’t red,” Seth writes, “just as they aren’t ugly or old-fashioned or avant-garde … When I look at a red chair, the redness I experience depends both on properties of the chair and on properties of my brain. It corresponds to the content of a set of perceptual predictions about the ways in which a specific kind of surface reflects light.” 

Seth is not particularly interested in redness, or even in color more generally. Rather his larger claim is that this same process applies to all of perception: “The entirety of perceptual experience is a neuronal fantasy that remains yoked to the world through a continuous making and remaking of perceptual best guesses, of controlled hallucinations. You could even say that we’re all hallucinating all the time. It’s just that when we agree about our hallucinations, that’s what we call reality.”

Cognitive scientists often rely on atypical examples to gain understanding of what’s really happening. Seth takes the reader through a fun litany of optical illusions and demonstrations, some quite familiar and others less so. Squares that are in fact the same shade appear to be different; spirals printed on paper appear to spontaneously rotate; an obscure image turns out to be a woman kissing a horse; a face shows up in a bathroom sink. Re-creating the mind’s psychedelic powers in silicon, an artificial-intelligence-powered virtual-reality setup that he and his colleagues created produces a Hunter Thompson–esque menagerie of animal parts emerging piecemeal from other objects in a square on the Sussex University campus. This series of examples, in Seth’s telling, “chips away at the beguiling but unhelpful intuition that consciousness is one thing—one big scary mystery in search of one big scary solution.” Seth’s perspective might be unsettling to those who prefer to believe that things are as they seem to be: “Experiences of free will are perceptions. The flow of time is a perception.” 

Seth is on comparatively solid ground when he describes how the brain shapes experience, what philosophers call the “easy” problems of consciousness. They’re easy only in comparison to the “hard” problem: why subjective experience exists at all as a feature of the universe. Here he treads awkwardly, introducing the “real” problem, which is to “explain, predict, and control the phenomenological properties of conscious experience.” It’s not clear how the real problem differs from the easy problems, but somehow, he says, tackling it will get us some way toward resolving the hard problem. Now that would be a neat trick.

Where Seth relates, for the most part, the experiences of people with typical brains wrestling with atypical stimuli, in Coming to Our Senses, Susan Barry, an emeritus professor of neurobiology at Mount Holyoke college, tells the stories of two people who acquired new senses later in life than is usual. Liam McCoy, who had been nearly blind since he was an infant, was able to see almost clearly after a series of operations when he was 15 years old. Zohra Damji was profoundly deaf until she was given a cochlear implant at the unusually late age of 12. As Barry explains, Damji’s surgeon “told her aunt that, had he known the length and degree of Zohra’s deafness, he would not have performed the operation.” Barry’s compassionate, nuanced, and observant exposition is informed by her own experience:

At age forty-eight, I experienced a dramatic improvement in my vision, a change that repeatedly brought me moments of childlike glee. Cross-eyed from early infancy, I had seen the world primarily through one eye. Then, in mid-life, I learned, through a program of vision therapy, to use my eyes together. With each glance, everything I saw took on a new look. I could see the volume and 3D shape of the empty space between things. Tree branches reached out toward me; light fixtures floated. A visit to the produce section of the supermarket, with all its colors and 3D shapes, could send me into a sort of ecstasy. 

Barry was overwhelmed with joy at her new capacities, which she describes as “seeing in a new way.” She takes pains to point out how different this is from “seeing for the first time.” A person who has grown up with eyesight can grasp a scene in a single glance. “But where we perceive a three-dimensional landscape full of objects and people, a newly sighted adult sees a hodgepodge of lines and patches of colors appearing on one flat plane.” As McCoy described his experience of walking up and down stairs to Barry: 

The upstairs are large alternating bars of light and dark and the downstairs are a series of small lines. My main focus is to balance and step IN BETWEEN lines, never on one … Of course going downstairs you step in between every line but upstairs you skip every other bar. All the while, when I move, the stairs are skewing and changing.

Even a sidewalk was tricky, at first, to navigate. He had to judge whether a line “indicated the junction between flat sidewalk blocks, a crack in the cement, the outline of a stick, a shadow cast by an upright pole, or the presence of a sidewalk step,” Barry explains. “Should he step up, down, or over the line, or should he ignore it entirely?” As McCoy says, the complexity of his perceptual confusion probably cannot be fully explained in terms that sighted people are used to.

The same, of course, is true of hearing. Raw audio can be hard to untangle. Barry describes her own ability to listen to the radio while working, effortlessly distinguishing the background sounds in the room from her own typing and from the flute and violin music coming over the radio. “Like object recognition, sound recognition depends upon communication between lower and higher sensory areas in the brain … This neural attention to frequency helps with sound source recognition. Drop a spoon on a tiled kitchen floor, and you know immediately whether the spoon is metal or wood by the high- or low-frequency sound waves it produces upon impact.” Most people acquire such capacities in infancy. Damji didn’t. She would often ask others what she was hearing, but had an easier time learning to distinguish sounds that she made herself. She was surprised by how noisy eating potato chips was, telling Barry: “To me, potato chips were always such a delicate thing, the way they were so lightweight, and so fragile that you could break them easily, and I expected them to be soft-sounding. But the amount of noise they make when you crunch them was something out of place. So loud.” 

As Barry recounts, at first Damji was frightened by all sounds, “because they were meaningless.” But as she grew accustomed to her new capabilities, Damji found that “a sound is not a noise anymore but more like a story or an event.” The sound of laughter came to her as a complete surprise, and she told Barry it was her favorite. As Barry writes, “Although we may be hardly conscious of background sounds, we are also dependent upon them for our emotional well-being.” One strength of the book is in the depth of her connection with both McCoy and Damji. She spent years speaking with them and corresponding as they progressed through their careers: McCoy is now an ophthalmology researcher at Washington University in St. Louis, while Damji is a doctor. From the details of how they learned to see and hear, Barry concludes, convincingly, that “since the world and everything in it is constantly changing, it’s surprising that we can recognize anything at all.”

In What Makes Us Smart, Samuel Gershman, a psychology professor at Harvard, says that there are “two fundamental principles governing the organization of human intelligence.” Gershman’s book is not particularly accessible; it lacks connective tissue and is peppered with equations that are incompletely explained. He writes that intelligence is governed by “inductive bias,” meaning we prefer certain hypotheses before making observations, and “approximation bias,” which means we take mental shortcuts when faced with limited resources. Gershman uses these ideas to explain everything from visual illusions to conspiracy theories to the development of language, asserting that what looks dumb is often “smart.”

“The brain is evolution’s solution to the twin problems of limited data and limited computation,” he writes. 

He portrays the mind as a raucous committee of modules that somehow helps us fumble our way through the day. “Our mind consists of multiple systems for learning and decision making that only exchange limited amounts of information with one another,” he writes. If he’s correct, it’s impossible for even the most introspective and insightful among us to fully grasp what’s going  on inside our own head. As Damji wrote in a letter to Barry: 

When I had no choice but to learn Swahili in medical school in order to be able to talk to the patients—that is when I realized how much potential we have—especially when we are pushed out of our comfort zone. The brain learns it somehow.

Matthew Hutson is a contributing writer at The New Yorker and a freelance science and tech writer.

The Mind issue

This story was part of our September 2021 issue

Photons Run out of Loopholes: Quantum World Really Is in Conflict With Our Everyday Experience (Science Daily)

Apr. 15, 2013 — A team led by the Austrian physicist Anton Zeilinger has now carried out an experiment with photons in which they have closed an important loophole. The researchers have thus provided the most complete experimental proof that the quantum world is in conflict with our everyday experience.

Lab IQOQI, Vienna 2012. (Credit: Copyright: Jacqueline Godany)

The results of this study appear this week in the journal Nature (Advance Online Publication/AOP).

When we observe an object, we make a number of intuitive assumptions, among them that the unique properties of the object have been determined prior to the observation and that these properties are independent of the state of other, distant objects. In everyday life, these assumptions are fully justified, but things are different at the quantum level. In the past 30 years, a number of experiments have shown that the behaviour of quantum particles — such as atoms, electrons or photons — can be in conflict with our basic intuition. However, these experiments have never delivered definite answers. Each previous experiment has left open the possibility, at least in principle, that the observed particles ‘exploited’ a weakness of the experimental setup.

Quantum physics is an exquisitely precise tool for understanding the world around us at a very fundamental level. At the same time, it is a basis for modern technology: semiconductors (and therefore computers), lasers, MRI scanners, and numerous other devices are based on quantum-physical effects. However, even after more than a century of intensive research, fundamental aspects of quantum theory are not yet fully understood. On a regular basis, laboratories worldwide report results that seem at odds with our everyday intuition but that can be explained within the framework of quantum theory.

On the trail of the quantum entanglement mystery

The physicists in Vienna report not a new effect, but a deep investigation into one of the most fundamental phenomena of quantum physics, known as ‘entanglement.’ The effect of quantum entanglement is amazing: when measuring a quantum object that has an entangled partner, the state of the one particle depends on measurements performed on the partner. Quantum theory describes entanglement as independent of any physical separation between the particles. That is, entanglement should also be observed when the two particles are sufficiently far apart from each other that, even in principle, no information can be exchanged between them (the speed of communication is fundamentally limited by the speed of light). Testing such predictions regarding the correlations between entangled quantum particles is, however, a major experimental challenge.

Towards a definitive answer

The young academics in Anton Zeilinger’s group including Marissa Giustina, Alexandra Mech, Rupert Ursin, Sven Ramelow and Bernhard Wittmann, in an international collaboration with the National Institute of Standards and Technology/NIST (USA), the Physikalisch-Technische Bundesanstalt (Germany), and the Max-Planck-Institute of Quantum Optics (Germany), have now achieved an important step towards delivering definitive experimental evidence that quantum particles can indeed do things that classical physics does not allow them to do. For their experiment, the team built one of the best sources for entangled photon pairs worldwide and employed highly efficient photon detectors designed by experts at NIST. These technological advances together with a suitable measurement protocol enabled the researchers to detect entangled photons with unprecedented efficiency. In a nutshell: “Our photons can no longer duck out of being measured,” says Zeilinger.

This kind of tight monitoring is important as it closes an important loophole. In previous experiments on photons, there has always been the possibility that although the measured photons do violate the laws of classical physics, such non-classical behaviour would not have been observed if all photons involved in the experiment could have been measured. In the new experiment, this loophole is now closed. “Perhaps the greatest weakness of photons as a platform for quantum experiments is their vulnerability to loss — but we have just demonstrated that this weakness need not be prohibitive,” explains Marissa Giustina, lead author of the paper.

Now one last step

Although the new experiment makes photons the first quantum particles for which, in several separate experiments, every possible loophole has been closed, the grand finale is yet to come, namely, a single experiment in which the photons are deprived of all possibilities of displaying their counterintuitive behaviour through means of classical physics. Such an experiment would also be of fundamental significance for an important practical application: ‘quantum cryptography,’ which relies on quantum mechanical principles and is considered to be absolutely secure against eavesdropping. Eavesdropping is still theoretically possible, however, as long as there are loopholes. Only when all of these are closed is a completely secure exchange of messages possible.

An experiment without any loopholes, says Zeilinger, “is a big challenge, which attracts groups worldwide.” These experiments are not limited to photons, but also involve atoms, electrons, and other systems that display quantum mechanical behaviour. The experiment of the Austrian physicists highlights the photons’ potential. Thanks to these latest advances, the photon is running out of places to hide, and quantum physicists are closer than ever to conclusive experimental proof that quantum physics defies our intuition and everyday experience to the degree suggested by research of the past decades.

This work was completed in a collaboration including the following institutions: Institute for Quantum Optics and Quantum Information — Vienna / IQOQI Vienna (Austrian Academy of Sciences), Quantum Optics, Quantum Nanophysics and Quantum Information, Department of Physics (University of Vienna), Max-Planck-Institute of Quantum Optics, National Institute of Standards and Technology / NIST, Physikalisch-Technische Bundesanstalt, Berlin.

This work was supported by: ERC (Advanced Grant), Austrian Science Fund (FWF), grant Q-ESSENCE, Marie Curie Research Training Network EMALI, and John Templeton Foundation. This work was also supported by NIST Quantum Information Science Initiative (QISI).

Journal Reference:

  1. Marissa Giustina, Alexandra Mech, Sven Ramelow, Bernhard Wittmann, Johannes Kofler, Jörn Beyer, Adriana Lita, Brice Calkins, Thomas Gerrits, Sae Woo Nam, Rupert Ursin, Anton Zeilinger. Bell violation using entangled photons without the fair-sampling assumptionNature, 2013; DOI: 10.1038/nature12012