Hemeroteca de la sección ‘Leyes’

Equivalence-principle Analog of the Gravitational Redshift

Por • 24 jun, 2017 • Category: Leyes

What happens when two synchronized clocks on a rigid beam are both given the exact same acceleration profile? Will they remain synchronized? What if we use a rigid-rod Rindler acceleration profile? The special relativity prediction surprises many people. This experimental setup is the special-relativity analog of the gravitational redshift. Just like two clocks higher and lower in a gravitational field lose synchronization, one sees a loss of synchronization in these clocks with `identical’ acceleration profiles. To the best of our knowledge this equivalence principle analog has never been directly measured, and current experimental techniques are sensitive enough to measure it. We discuss the origin of the essential physics behind this synchronization loss, and some special conditions which simplify its experimental observation.

Making Metric Temporal Logic Rational

Por • 13 jun, 2017 • Category: Leyes

We study an extension of MTL in pointwise time with rational expression guarded modality RatI (re) where re is a rational expression over subformulae. We study the decidability and expressiveness of this extension called RatMTL, as well as its fragment SfrMTL where only star-free rational expressions are allowed. Using the technique of temporal projections, we show that RatMTL has decidable satisfiability by giving an equisatisfiable reduction to MTL. We also identify a subclass of RatMTL for which our equi-satisfiable reduction gives rise to formulae of MITL, yielding elementary decidability. As our second main result, we show a tight automaton-logic connection between SfrMTL and partially ordered (or very weak) 1-clock alternating timed autómata

Introduction to Lambda Calculus

Por • 30 may, 2017 • Category: Leyes

Introduction Some history Leibniz had as ideal the following. (1) Create a ‘universal language’ in which all possible problems can be stated. (2) Find a decision method to solve all the problems stated in the universal language. If one restricts oneself to mathematical problems, point (1) of Leibniz’ ideal is fulfilled by taking some form of set theory formulated in the language of first order predicate logic. This was the situation after Frege and Russell (or Zermelo). Point (2) of Leibniz’ ideal became an important philosophical question. ‘Can one solve all problems formulated in the universal language?’ It seems not, but it is not clear how to prove that. This question became known as the Entscheidungsproblem. In 1936 the Entscheidungsproblem was solved in the negative independently by Alonzo Church and Alan Turing. In order to do so, they needed a formalisation of the intuitive notion of ‘decidable’, or what is equivalent ‘computable’. Church and Turing did this in two different ways by introducing two models of computation.

Whitehead’s mereotopology and the project of formal ontology

Por • 19 may, 2017 • Category: Leyes

Mereology is the theory of wholes and parts. The first formal mereology was developed by Husserl in his third Logical Investigation at the beginning of the twentieth century. In 1916 Stanisław Lesniewski gave the first axiomatization of a classical extensional formal mereology. That same year, Alfred North Whitehead also gave a sketch of a mereology in “La théorie relationniste de l’espace”. It was developed in the perspective of a theory of space in which the concept of point is no longer considered as primitive, but is built in terms of the relations between objects. This project was then taken up and amplified in the wider perspective of the method of extensive abstraction presented in An Enquiry Concerning the Principles of Natural Knowledge and The Concept of Nature.

Demostración y silogismo en los Analíticos segundos: Reconstrucción y discusión.

Por • 22 abr, 2017 • Category: Leyes

En este artículo se discute la relación entre silogismo y demostración con respecto al concepto aristotélico del conocimiento científico formulado en los Analíticos segundos. La argumentación sigue tres líneas principales: (i) se ofrecen razones para rechazar la relegación de la sistematización silogística a la instancia postrera de justificación y exposición didáctica del conocimiento previamente adquirido. Como respuesta alternativa, (ii) se muestra que una explicación aristotélica necesita la silogística en virtud del papel que desempeña la causa como término medio silogístico. En consecuencia, debería estar en condiciones de (iii) sostener que no resulta factible establecer firmemente los principios propios como premisas explicativas sin construir silogismos.

The Time Dimension of Science: Connecting the Past to the Future

Por • 19 abr, 2017 • Category: Leyes

A central question in science of science concerns how time affects citations. Despite the long-standing interests and its broad impact, we lack systematic answers to this simple yet fundamental question. By reviewing and classifying prior studies for the past 50 years, we find a significant lack of consensus in the literature, primarily due to the coexistence of retrospective and prospective approaches to measuring citation age distributions. These two approaches have been pursued in parallel, lacking any known connections between the two. Here we developed a new theoretical framework that not only allows us to connect the two approaches through precise mathematical relationships, it also helps us reconcile the interplay between temporal decay of citations and the growth of science, helping us uncover new functional forms characterizing citation age distributions.

On the Incompatibility of Special Relativity and Quantum Mechanics

Por • 15 abr, 2017 • Category: Leyes

Some of the strategies which have been put forward in order to deal with the inconsistency between quantum mechanics and special relativity are examined. The EPR correlations are discussed as a simple example of quantum mechanical macroscopic effects with spacelike separation from their causes. It is shown that they can be used to convey information, whose reliability can be estimated by means of Bayes’ theorem. Some of the current reasons advanced to deny that quantum mechanics contradicts special relativity are refuted, and an historical perspective is provided on the issue.

Chrysippus’ Indemonstrables and the SemanticMental Models*

Por • 8 abr, 2017 • Category: Leyes

Atendiendo a la lógica estándar, solo uno de los cinco indemostrables propuestos por Crisipo de Solos es realmente indemostrable. Sus otros cuatro esquemas son demos­trables en tal lógica. La pregunta, por tanto, es: si cuatro de ellos no son verdaderamente indemostrables, por qué Crisipo consideró que sí lo eran. López-Astorga mostró que si ignoramos el cálculo proposicional estándar y asumimos que una teoría cognitiva contemporánea, la teoría de la lógica mental, describe correctamente el razonamiento humano, se puede entender por qué Crisipo pensó que todos sus indemostrables eran tan básicos. No obstante, en este trabajo trato de argumentar que la teoría de la lógi­ca mental no es el único marco que puede explicar esto. En concreto, sostengo que otra importante teoría sobre el razonamiento en el presente, la teoría de los modelos mentales, también puede ofrecer una explicación al respecto.

Planck’s radiation law, the light quantum, and the prehistory of indistinguishability in the teaching of quantum mechanics

Por • 23 mar, 2017 • Category: Leyes

Planck’s law for black-body radiation marks the origin of quantum theory and is discussed in all introductory (or advanced) courses on this subject. However, the question whether Planck really implied quantisation is debated among historians of physics. We present a simplified account of this debate which also sheds light on the issue of indistinguishability and Einstein’s light quantum hypothesis. We suggest that the teaching of quantum mechanics could benefit from including this material beyond the question of historical accuracy.

Fifty years of cosmological particle creation

Por • 14 mar, 2017 • Category: Leyes

In the early sixties Leonard Parker discovered that the expansion of the universe can create particles out of the vacuum, opening a new and fruitfull field in physics. We give a historical review in the form of an interview that took place during the Conference ERE2014 (Valencia 1-5, September, 2014).