scholarly journals Experimental test of local observer independence

2019 ◽  
Vol 5 (9) ◽  
pp. eaaw9832 ◽  
Author(s):  
Massimiliano Proietti ◽  
Alexander Pickston ◽  
Francesco Graffitti ◽  
Peter Barrow ◽  
Dmytro Kundys ◽  
...  
Keyword(s):  
Quantum Mechanics ◽  
Scientific Method ◽  
Free Choice ◽  
Empirical Investigation ◽  
State Of The Art ◽  
Thought Experiment ◽  
Type Inequality ◽  
Repeated Measurements ◽  
Wigner’S Friend ◽  
Local Observer

The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the objectivity of observations is not so clear, most markedly exposed in Wigner’s eponymous thought experiment where two observers can experience seemingly different realities. The question whether the observers’ narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. In a state-of-the-art six-photon experiment, we realize this extended Wigner’s friend scenario, experimentally violating the associated Bell-type inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

scholarly journals Consistent Descriptions of Quantum Measurement

2019 ◽  
Vol 49 (11) ◽  
pp. 1306-1324 ◽  
Author(s):  
Jianhao M. Yang
Keyword(s):  
Quantum Mechanics ◽  
Quantum System ◽  
Quantum Measurement ◽  
Composite System ◽  
Thought Experiment ◽  
Thought Experiments ◽  
Extended Version ◽  
Reasoning Process ◽  
Measurement Result ◽  
Wigner’S Friend

Abstract The Wigner’s friend type of thought experiments manifest the conceptual challenge on how different observers can have consistent descriptions of a quantum measurement event. In this paper, we analyze the extended version of Wigner’s friend thought experiment (Frauchiger and Renner in Nat Commun 3711:9, 2018) in detail and show that the reasoning process from each agent that leads to the no-go theorem is inconsistent. The inconsistency is with respect to the requirement that an agent should make use of updated information instead of outdated information. We then apply the relational formulation of quantum measurement to resolve the inconsistent descriptions from different agents. In relational formulation of quantum mechanics, a measurement is described relative to an observer. Synchronization of measurement result is a necessary requirement to achieve consistent descriptions of a quantum system from different observers. Thought experiments, including EPR, Wigner’s Friend and it extended version, confirm the necessity of relational formulation of quantum measurement when applying quantum mechanics to composite system with entangled but space-like separated subsystems.

scholarly journals A no-go theorem for the persistent reality of Wigner’s friend’s perception

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Philippe Allard Guérin ◽  
Veronika Baumann ◽  
Flavio Del Santo ◽  
Časlav Brukner
Keyword(s):  
Quantum Mechanics ◽  
Quantum Theory ◽  
Thought Experiment ◽  
Joint Probability ◽  
Joint Probability Distribution ◽  
Initial State ◽  
Interpretations Of Quantum Mechanics ◽  
Present Information ◽  
Wigner’S Friend ◽  
Measured System

AbstractThe notorious Wigner’s friend thought experiment (and modifications thereof) has received renewed interest especially due to new arguments that force us to question some of the fundamental assumptions of quantum theory. In this paper, we formulate a no-go theorem for the persistent reality of Wigner’s friend’s perception, which allows us to conclude that the perceptions that the friend has of her own measurement outcomes at different times cannot “share the same reality”, if seemingly natural quantum mechanical assumptions are met. More formally, this means that, in a Wigner’s friend scenario, there is no joint probability distribution for the friend’s perceived measurement outcomes at two different times, that depends linearly on the initial state of the measured system and whose marginals reproduce the predictions of unitary quantum theory. This theorem entails that one must either (1) propose a nonlinear modification of the Born rule for two-time predictions, (2) sometimes prohibit the use of present information to predict the future—thereby reducing the predictive power of quantum theory—or (3) deny that unitary quantum mechanics makes valid single-time predictions for all observers. We briefly discuss which of the theorem’s assumptions are more likely to be dropped within various popular interpretations of quantum mechanics.

Philosophy of Physics: A Very Short Introduction

2021 ◽  
Author(s):  
David Wallace
Keyword(s):  
Quantum Mechanics ◽  
Scientific Method ◽  
Philosophy Of Physics ◽  
Short Introduction ◽  
Fundamental Physics ◽  
The Core ◽  
The World ◽  
Modern Physics ◽  
Parallel Universes ◽  
Large Systems

Philosophy of Physics: A Very Short Introduction explores the core topics of philosophy of physics through three key themes: the nature of space and time; the origin of irreversibility and probability in the physics of large systems; how we can make sense of quantum mechanics. Central issues discussed include: the scientific method as it applies in modern physics; the distinction between absolute and relative motion; the way that distinction changes between Newton’s physics and special relativity; what spacetime is and how it relates to the laws of physics; how fundamental physics can make no distinction between past and future and yet a clear distinction exists in the world we see around us; why it is so difficult to understand quantum mechanics, and why doing so might push us to change our fundamental physics, to rethink the nature of science, or even to accept the existence of parallel universes.

3D Structural Bioinformatics of Proteins and Antibodies: State of the Art Perspectives and Challenges

2013 ◽  
Vol 2 (3) ◽  
pp. 67-74
Author(s):  
Arianna Filntisi ◽  
Dimitrios Vlachakis ◽  
George Matsopoulos ◽  
Sophia Kossida
Keyword(s):  
Quantum Mechanics ◽  
Quantum Chemical ◽  
State Of The Art ◽  
Three Dimensional ◽  
Research Field ◽  
Important Class ◽  
Structural Components ◽  
Molecular Systems ◽  
Mechanical Methods ◽  
Harmful Substances

Proteins are an important class of biochemical molecules, as the structural components of animal and human tissue are based on them. Antibodies are proteins that play a crucial role in the preservation of life since they are produced by the body's immune system as a response to harmful substances. The modelling of proteins and antibodies in particular is a vibrant research field which facilitates the design of drugs, a process otherwise demanding in terms of time and resources. A variety of computational methods and tools are being developed towards that goal, among which are hybrid quantum chemical/molecular mechanical methods and three-dimensional antibody modelling. In this review the authors discuss the knowledge concerning proteins and antibodies, as well as the use of quantum mechanics in the simulation of molecular systems and the three-dimensional antibody modelling.

scholarly journals POPPER'S THOUGHT EXPERIMENT REINVESTIGATED

2012 ◽  
Vol 10 (03) ◽  
pp. 1250033 ◽  
Author(s):  
CHRIS D. RICHARDSON ◽  
JONATHAN P. DOWLING
Keyword(s):  
Quantum Mechanics ◽  
Quantum Theory ◽  
Thought Experiment

Popper's original thought experiment probed some fundamental and subtle rules of quantum mechanics. He claimed that quantum mechanics was incomplete and devised an experiment to prove it. Two experiments have directly and indirectly tested Popper's hypothesis, and they provide some evidence that Popper's prediction may have been correct. The equations governing these two experiments and Popper's thought experiment will be derived from basic quantum principles. The experimental constants will be inputted and it will show that the two experiments reinforce each other and agree completely with quantum theory.

scholarly journals Entropy Balance in the Expanding Universe: A Novel Perspective

Entropy ◽  
2019 ◽  
Vol 21 (4) ◽  
pp. 406
Author(s):  
Arturo Tozzi ◽  
James F. Peters
Keyword(s):  
Quantum Mechanics ◽  
Second Law Of Thermodynamics ◽  
Quantum Systems ◽  
Second Law ◽  
Quantum Vacuum ◽  
Expanding Universe ◽  
Cosmic Expansion ◽  
Thermodynamic Entropy ◽  
Local Observer ◽  
Relational Mechanism

We describe cosmic expansion as correlated with the standpoints of local observers’ co-moving horizons. In keeping with relational quantum mechanics, which claims that quantum systems are only meaningful in the context of measurements, we suggest that information gets ergodically “diluted” in our isotropic and homogeneous expanding Universe, so that an observer detects just a limited amount of the total cosmic bits. The reduced bit perception is due the decreased density of information inside the expanding cosmic volume in which the observer resides. Further, we show that the second law of thermodynamics can be correlated with cosmic expansion through a relational mechanism, because the decrease in information detected by a local observer in an expanding Universe is concomitant with an increase in perceived cosmic thermodynamic entropy, via the Bekenstein bound and the Laudauer principle. Reversing the classical scheme from thermodynamic entropy to information, we suggest that the cosmological constant of the quantum vacuum, which is believed to provoke the current cosmic expansion, could be one of the sources of the perceived increases in thermodynamic entropy. We conclude that entropies, including the entangled entropy of the recently developed framework of quantum computational spacetime, might not describe independent properties, but rather relations among systems and observers.

scholarly journals Empirical Investigation of Optimization Algorithms in Neural Machine Translation

2017 ◽  
Vol 108 (1) ◽  
pp. 13-25 ◽  
Author(s):  
Parnia Bahar ◽  
Tamer Alkhouli ◽  
Jan-Thorsten Peter ◽  
Christopher Jan-Steffen Brix ◽  
Hermann Ney
Keyword(s):  
Neural Networks ◽  
Machine Translation ◽  
Optimization Problem ◽  
Empirical Investigation ◽  
State Of The Art ◽  
Optimization Techniques ◽  
Neural Machine Translation ◽  
Translation Quality ◽  
And Training ◽  
Dimensional Optimization

AbstractTraining neural networks is a non-convex and a high-dimensional optimization problem. In this paper, we provide a comparative study of the most popular stochastic optimization techniques used to train neural networks. We evaluate the methods in terms of convergence speed, translation quality, and training stability. In addition, we investigate combinations that seek to improve optimization in terms of these aspects. We train state-of-the-art attention-based models and apply them to perform neural machine translation. We demonstrate our results on two tasks: WMT 2016 En→Ro and WMT 2015 De→En.

RELATIVITY AND THE SPEED OF LIGHT – A 100 YEAR OLD MISUNDERSTANDING

2006 ◽  
Vol 15 (02) ◽  
pp. 275-283 ◽  
Author(s):  
W. J. ŚWIATECKI
Keyword(s):  
Quantum Mechanics ◽  
Special Relativity ◽  
Thought Experiment ◽  
Minkowski Spacetime ◽  
Speed Of Light ◽  
The Past ◽  
Mistaken Belief

I point out a conceptual misunderstanding in the exposition of relativity, namely the mistaken belief that light has something to do with the essence of relativity. This misunderstanding can be clarified by stressing that the content of Special Relativity is simply that "we live in a Minkowski spacetime", together with a thought experiment that illustrates how one could discover this fact without ever mentioning even the existence of light. I also note a recently uncovered implication of living in Minkowski spacetime, namely the Copenhagen reinterpretation of Quantum Mechanics, developed in the past decade.

scholarly journals POPPER'S EXPERIMENT, COPENHAGEN INTERPRETATION AND NONLOCALITY

2004 ◽  
Vol 02 (03) ◽  
pp. 407-418 ◽  
Author(s):  
TABISH QURESHI
Keyword(s):  
Quantum Mechanics ◽  
Thought Experiment ◽  
Copenhagen Interpretation ◽  
Karl Popper ◽  
Interpretation Of Quantum Mechanics ◽  
Discrete Variables ◽  
Popper's Experiment ◽  
Basic Flaw

A thought experiment, proposed by Karl Popper, which has been experimentally realized recently, is critically examined. A basic flaw in Popper's argument which has also been prevailing in subsequent debates, is pointed out. It is shown that Popper's experiment can be understood easily within the Copenhagen interpretation of quantum mechanics. An alternate experiment, based on discrete variables, is proposed, which constitutes Popper's test in a clearer way. It refutes the argument of absence of nonlocality in quantum mechanics.

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