Artículos con la etiqueta ‘Classical Physics (physics.class-ph)’

Methodological principles of modern thermodynamics

Por • 7 ene, 2014 • Category: Ciencia y tecnología

The article describes basic principles of the theory which unites thermodynamics of reversible and irreversible processes also extends them methods on processes of transfer and transformation of any forms of energy



Justifying Typicality Measures of Boltzmannian Statistical Mechanics and Dynamical Systems

Por • 14 oct, 2013 • Category: Leyes

A popular view in contemporary Boltzmannian statistical mechanics is to interpret the measures as typicality measures. In measure-theoretic dynamical systems theory measures can similarly be interpreted as typicality measures. However, a justification why these measures are a good choice of typicality measures is missing, and the paper attempts to fill this gap. The paper first argues that Pitowsky’s (2012) justification of typicality measures does not fit the bill. Then a first proposal of how to justify typicality measures is presented. The main premises are that typicality measures are invariant and are related to the initial probability distribution of interest (which are translation-continuous or translation-close). The conclusion are two theorems which show that the standard measures of statistical mechanics and dynamical systems are typicality measures. There may be other typicality measures, but they agree about judgements of typicality. Finally, it is proven that if systems are ergodic or epsilon-ergodic, there are uniqueness results about typicality measures.



Are Deterministic Descriptions And Indeterministic Descriptions Observationally Equivalent?

Por • 14 oct, 2013 • Category: Ciencia y tecnología

The central question of this paper is: are deterministic and indeterministic descriptions observationally equivalent in the sense that they give the same predictions? I tackle this question for measure-theoretic deterministic systems and stochastic processes, both of which are ubiquitous in science. I first show that for many measure-theoretic deterministic systems there is a stochastic process which is observationally equivalent to the deterministic system. Conversely, I show that for all stochastic processes there is a measure-theoretic deterministic system which is observationally equivalent to the stochastic process. Still, one might guess that the measure-theoretic deterministic systems which are observationally equivalent to stochastic processes used in science do not include any deterministic systems used in science. I argue that this is not so because deterministic systems used in science even give rise to Bernoulli processes. Despite this, one might guess that measure-theoretic deterministic systems used in science cannot give the same predictions at every observation level as stochastic processes used in science. By proving results in ergodic theory, I show that also this guess is misguided: there are several deterministic systems used in science which give the same predictions at every observation level as Markov processes. All these results show that measure-theoretic deterministic systems and stochastic processes are observationally equivalent more often than one might perhaps expect. Furthermore, I criticise the claims of the previous philosophy papers Suppes (1993, 1999), Suppes and de Barros (1996) and Winnie (1998) on observational equivalence.



On the Observational Equivalence of Continuous-Time Deterministic and Indeterministic Descriptions

Por • 10 oct, 2013 • Category: Filosofía

This paper presents and philosophically assesses three types of results on the observational equivalence of continuous-time measure-theoretic deterministic and indeterministic descriptions. The first results establish observational equivalence to abstract mathematical descriptions. The second results are stronger because they show observational equivalence between deterministic and indeterministic descriptions found in science. Here I also discuss Kolmogorov’s contribution. For the third results I introduce two new meanings of `observational equivalence at every observation level’. Then I show the even stronger result of observational equivalence at every (and not just some) observation level between deterministic and indeterministic descriptions found in science. These results imply the following. Suppose one wants to find out whether a phenomenon is best modeled as deterministic or indeterministic. Then one cannot appeal to differences in the probability distributions of deterministic and indeterministic descriptions found in science to argue that one of the descriptions is preferable because there is no such difference. Finally, I criticise the extant claims of philosophers and mathematicians on observational equivalence.



What Are the New Implications of Chaos for Unpredictability?

Por • 9 oct, 2013 • Category: Ciencia y tecnología

From the beginning of chaos research until today, the unpredictability of chaos has been a central theme. It is widely believed and claimed by philosophers, mathematicians and physicists alike that chaos has a new implication for unpredictability, meaning that chaotic systems are unpredictable in a way that other deterministic systems are not. Hence one might expect that the question ‘What are the new implications of chaos for unpredictability?’ has already been answered in a satisfactory way. However, this is not the case. I will critically evaluate the existing answers and argue that they do not fit the bill. Then I will approach this question by showing that chaos can be defined via mixing, which has not been explicitly argued for. Based on this insight, I will propose that the sought-after new implication of chaos for unpredictability is the following: for predicting any event all sufficiently past events are approximately probabilistically irrelevant.



What is a Singularity in Geometrized Newtonian Gravitation?

Por • 14 ago, 2013 • Category: Ciencia y tecnología

I discuss singular spacetimes in the context of the geometrized formulation of Newtonian gravitation. I argue first that geodesic incompleteness is a natural criterion for when a model of geometrized Newtonian gravitation is singular, and then I show that singularities in this sense arise naturally in classical physics by stating and proving a classical version of the Raychaudhuri-Komar singularity theorem.



Institute for Molecular Physics at the University of Maryland

Por • 8 ago, 2013 • Category: Ambiente

The Institute for Physical Science and Technology at the University of Maryland was founded in 1976 from a merger of the Institute for Fluid Dynamics and Applied Mathematics (IFDAM) and the Institute for Molecular Physics (IMP), which were established at the College Park Campus after World War II to enhance the expertise of the University of Maryland in some areas of science and technology of interest to the US Department of Defense. Here I try to reconstruct the history of the Institute for Molecular Physics at the University of Maryland.



Does the first part of the second law also imply its second part?

Por • 17 jun, 2013 • Category: Educacion

Sommerfeld called the first part of the second law to be the entropy axiom, which is about the existence of the state function entropy. It was usually thought that the second part of the second law, which is about the non-decreasing nature of entropy of thermally isolated systems, did not follow from the first part. In this note, we point out the surprise that the first part in fact implies the second part.



Ways to resolve Selleri’s paradox

Por • 3 mar, 2013 • Category: Opinion

Selleri’s paradox, based on an analysis of rotating frames, appears to show that the speed of light in an inertial system is not normally isotropic. This in turn seems at odds with the second postulate of special relativity requiring a universal light speed in inertial systems. First, it is demonstrated how to circumvent Selleri’s argument using Einstein synchronization in rotating frames. Then the nature of Selleri’s result is exposed: it simply corresponds to the adoption of a synchronization procedure different from Einstein’s. In this scheme, anisotropic one-way speeds of light by no means contradict special relativity.



From aether theory to Special Relativity

Por • 3 mar, 2013 • Category: Leyes

This way of thinking the spacetime emanates from our daily experience and lies at the heart of Newton’s Classical Mechanics. Nevertheless, in 1905 Einstein defied Galileo addition of velocities by postulating that light travels at the same speed c in any inertial frame. In doing so, Einstein extended the principle of relativity to the electromagnetic phenomena described by Maxwell’s laws. In Einstein’s Special Relativity the ether does not exist and the absolute motion is devoid of meaning. The invariance of the speed of light forced the replacement of Galileo transformations with Lorentz transformations. Thus, relativistic length contractions and time dilations entered our understanding of the spacetime. Newtonian mechanics had to be reformulated, which led to the discovery of the mass-energy equivalence.