Artículos con la etiqueta ‘History and Philosophy of Physics (physics.hist-ph)’

Fermi and the Theory of Weak Interactions

Por • 15 mar, 2014 • Category: Educacion

The history of weak interactions starting with Fermi’s creation of the beta decay theory and culminating in its modern avatar in the form of the electroweak gauge theory is described. Discoveries of parity violation, matter-antimatter asymmetry, W and Z bosons and neutrino mass are highlighted.

Reflections on Gibbs: From Statistical Physics to the Amistad

Por • 12 mar, 2014 • Category: Educacion

J. Willard Gibbs, the younger, was the first American physical sciences theorist. He was one of the inventors of statistical physics. He introduced and developed the concepts of phase space, phase transitions, and thermodynamic surfaces in a remarkably correct and elegant manner. These three concepts form the basis of different areas of physics. The connection among these areas has been a subject of deep reflection from Gibbs’ time to our own. This talk therefore tries to celebrate Gibbs by talking about modern ideas about how different parts of physics fit together.

Ya. B. Zeldovich (1914-1987): Chemist, Nuclear Physicist, Cosmologist

Por • 8 mar, 2014 • Category: Ambiente

Ya.B. Zeldovich was a pre-eminent Soviet physicist whose seminal contributions spanned many fields ranging from physical chemistry to nuclear and particle physics, and finally astrophysics and cosmology. March 8, 2014 marks Zeldovich’s birth centenary, and this article attempts to convey the zest with which Zeldovich did science, and the important role he played in fostering and mentoring a whole generation of talented Scientists.

Pathways of History of Elementary Particle Physics

Por • 1 mar, 2014 • Category: Ciencia y tecnología

In this first paper, we briefly retrace some historical pathways of modern physics of 20th Century. In particular, we have considered some moments of cosmic ray physics and, above all, the early theoretical and experimental bases which will lead to the first exact measurements of the anomalous magnetic moment of the muon, one of the main high precision tests of QED.

Thermodynamical Phase transitions, the mean-field theories, and the renormalization (semi)group: A pedagogical introduction

Por • 1 mar, 2014 • Category: Leyes

Mean field theories are good qualitative descriptors of the phase transition behavior. But all mean-field theories (including Landau’s theory) fail at the critical point (the problem of large correlation length). The problems with large correlation length in quantum many-body systems are the hardest problems known in theoretical physics (both in condensed matter and in particle physics). It was Ken Wilson’s physical insights and his powerful mathematical skills that opened a way to the solution of such hard problems. This manuscript is a perspective on these issues. Starting with simple examples of phase transitions (like ice/water; diamond/graphite etc.) we address the following important questions: Why does non-analyticity (sharp phase transitions) arise when thermodynamical functions (i.e., free energies etc) are good analytic functions? How does Landau’s program unify all the previous mean-field theories? Why do all the mean-field theories fail near the critical point? How does Wilson’s program go beyond all the mean-field theories? What is the origin emergence and universality?

Einstein’s cosmological considerations

Por • 24 feb, 2014 • Category: Ciencia y tecnología

The objective of this paper is not simply to present an historical overview of Einstein’s cosmological considerations, but to discuss the central role they played in shaping the paradigm of relativistic cosmology. This, we’ll show, was a result of both his actions and, perhaps more importantly, his inactions. Accordingly, discussion won’t simply be restricted to Einstein’s considerations, as we’ll analyse relevant contributions to the relativistic expansion paradigm during the approximately twenty years following Slipher’s first redshift measurements in 1912.

Schwinger’s Quantum Action Principle. I. From Dirac’s Formulation through Feynman’s Path Integrals to the Schwinger-Keldysh Method

Por • 23 feb, 2014 • Category: Leyes

Starting from the earlier notions of stationary action principles, we show how Schwinger’s Quantum Action Principle descended from Dirac’s formulation, which independently led Feynman to his path-integral formulation of quantum mechanics. The connection between the two is brought out, and applications are discussed. The Keldysh-Schwinger time-cycle method of extracting matrix elements is described. Part II will discuss the variational formulation of quantum electrodynamics and the development of source theory.

Particles, waves and trajectories: 210 years after Young’s experiment

Por • 20 feb, 2014 • Category: Leyes

Mermin’s «shut up and calculate!» somehow summarizes the most widely accepted view on quantum mechanics. This conception has led to a rather constraining way to think and understand the quantum world. Nonetheless, a closer look at the principles and formal body of this theory shows that, beyond longstanding prejudices, there is still room enough for alternative tools. This is the case, for example, of Bohmian mechanics. As it is discussed here, there is nothing contradictory or wrong with this hydrodynamical representation, which enhances the dynamical role of the quantum phase to the detriment (to some extent) of the probability density. The possibility to describe the evolution of quantum systems in terms of trajectories or streamlines is just a direct consequence of the fact that Bohmian mechanics (quantum hydrodynamics) is just a way to recast quantum mechanics in the more general language of the theory of characteristics.

Wilson’s renormalization group: a paradigmatic shift

Por • 17 feb, 2014 • Category: Leyes

A personal and subjective recollection, concerning mainly Wilson’s lectures delivered over the spring of 1972 at Princeton University (summary of a talk at Cornell University on November 16, 2013 at the occasion of the memorial Kenneth G. Wilson conference).

Fermi-Dirac Statistics

Por • 17 feb, 2014 • Category: Opinion

Here we have discussed on Fermi-Dirac statistics, in particular, on its brief historical progress, derivation, consequences, applications, etc. Importance of Fermi-Dirac statistics has been discussed even in connection with the current progress in science. This article is mainly aimed to the undergraduate and graduate students.