Arquivo da tag: Fenomenologia

2021 vai passar voando: movimento da Terra deixará ano mais curto (UOL)

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Marcella Duarte Colaboração para Tilt – 05/01/2021 17h02 4-5 minutos


Parecia que 2020 nunca ia acabar, mas, tecnicamente, ele passou mais depressa que o normal. E este ano será ainda mais ligeiro. O motivo? A Terra tem “girado” estranhamente depressa ultimamente. Por isso, pode ser que a gente precise adiantar nossos relógios, mas você nem vai perceber.

No ano passado, foi registrado o dia mais curto da história, desde que foram iniciadas as medições, há 50 anos. Em 19 de julho de 2020, o planeta completou sua rotação 1,4602 milésimo de segundo mais rápido que os costumeiros 86.400 segundos (24 horas).

O dia mais curto que até então se tinha registro aconteceu em 2005, e foi superado 28 vezes em 2020. E este ano deve ser o mais rápido da história, porque os dias de 2021 deverão ser, em média, 0,5 milissegundo mais curtos que o normal.

Essas pequenas mudanças na duração dos dias só foram descobertas após o desenvolvimento de relógios atômicos superprecisos, na década de 1960. Inicialmente, percebeu-se que a velocidade de rotação da Terra, quando gira em torno de seu próprio eixo resultando nos dias e noites, estava diminuindo ano após ano.

Desde a década de 1970, foi necessário “adicionar” 27 segundos no tempo atômico internacional, para manter nossa contagem de tempo sincronizada com o planeta mais lento. É o chamado “leap second” ou “inserção de segundo intercalado”.

Essas correções acontecem sempre ao final de um semestre, em 31 de dezembro ou 30 de junho. Assim, garante-se que o Sol sempre esteja exatamente no meio do céu ao meio-dia.

A última vez que ocorreu foi no Ano Novo de 2016, quando relógios no mundo todo pausaram por um segundo para “esperar” a Terra.

Mas recentemente, está acontecendo o oposto: a rotação está acelerando. E pode ser que a gente precise “saltar” o tempo para “alcançar” o movimento do planeta. Seria a primeira vez na história que um segundo seria deletado dos relógios internacionais.

Há um debate internacional sobre a necessidade deste ajuste e o futuro do cálculo do tempo. Cientistas acreditam que, ao longo de 2021, os relógios atômicos acumularão um atraso de 19 milésimos de segundos.

Se os ajustes não forem feitos, levaria centenas de anos para uma pessoa comum notar a diferença. Mas sistemas de navegação e de comunicação por satélite —que usam a posição da Terra, do Sol e das estrelas para funcionar— podem ser impactados mais brevemente.

Nossos “guardiões do tempo” são os oficiais do Serviço Internacional de Sistemas de Referência e Rotação da Terra (Iers), em Paris, França. São eles que monitoram a rotação da Terra e os 260 relógios atômicos espalhados pelo mundo e avisam quando é necessário adicionar —ou eventualmente deletar— algum segundo.

Manipular o tempo pode ter consequências. Quando foi adicionado um “leap second” em 2012, gigantes tecnológicos da época, como Linux, Mozilla, Java, Reddit, Foursquare, Yelp e LinkedIn reportaram falhas.

A velocidade de rotação da Terra varia constantemente, dependendo de diversos fatores, como o complexo movimento de seu núcleo derretido, dos oceanos e da atmosfera, além das interações gravitacionais com outros corpos celestes, como a Lua. O aquecimento global, e consequente derretimento das calotas polares e gelo das montanhas também tem acelerado a movimentação.

Por isso, os dias nunca têm duração exatamente igual. O último domingo (3) teve “apenas” 23 horas, 59 minutos e 59,9998927 segundos. Já a segunda-feira (4) foi mais preguiçosa, com pouco mais de 24 horas.

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