Hemeroteca del mes agosto, 2012

Early Atomic Models – From Mechanical to Quantum (1904-1913)

Por • 31 ago, 2012 • Category: sociologia

A complete history of early atomic models would fill volumes, but a reasonably coherent tale of the path from mechanical atoms to the quantum can be told by focusing on the relevant work of three great contributors to atomic physics, in the critically important years between 1904 and 1913: J. J. Thomson, Ernest Rutherford and Niels Bohr. We first examine the origins of Thomson’s mechanical atomic models, from his ethereal vortex atoms in the early 1880’s, to the myriad “corpuscular” atoms he proposed following the discovery of the electron in 1897. Beyond predictions for the periodicity of the elements, the application of Thomson’s atoms to problems in scattering and absorption led to quantitative predictions that were confirmed by experiments with high-velocity electrons traversing thin sheets of metal. Still, the much more massive and energetic {\alpha}-particles being studied by Rutherford were better suited for exploring the interior of the atom, and careful measurements on the angular dependence of their scattering eventually allowed him to infer the existence of an atomic nucleus. Niels Bohr was particularly troubled by the radiative instability inherent to any mechanical atom, and succeeded in 1913 where others had failed in the prediction of emission spectra, by making two bold hypotheses that were in contradiction to the laws of classical physics, but necessary in order to account for experimental facts.



Time and the Higgs (with apologies to J. B. Priestley)

Por • 31 ago, 2012 • Category: Ambiente

A model of discrete space-time is presented which is, in a sense, both Lorentz invariant and has no restriction on the relative velocity between particles (except v < c). The space-time has an inbuilt indeterminacy. Published originally as ‘A quantisation of time’, J. Phys. A: Math. Gen., 10, 2115, 1977; identical to the original, apart from one or two minor corrections, and some simplification towards the end of Section 6. The paper presents a discrete model of time, in which the latter comprises a succession of instants which are identified as collisions with particles called chronons. Proper-time intervals are discrete; the structure of space-time is given by a radar map and has an inbuilt indeterminacy, which leads naturally to Heisenberg’s uncertainty principle. If I were writing this paper today I would identify the chronon with the virtual Higgs boson. Without the latter all particles would be massless and would follow null paths; there would be no such thing as proper time. Time is an emergent phenomenon, and the Higgs boson is the agent of that emergence.



Las republiquitas inventadas

Por • 29 ago, 2012 • Category: Nacionales

La existencia de todo un continente, extendido desde el Río Bravo hasta la Patagonia, con una diversidad geográfica envidiable, con recursos naturales de todo tipo, con los mayores caudales de agua dulce limpia del mundo, con reservas estratégica notables y con una población que se entiende en el mismo idioma, de religión y costumbres idénticas y con un mismo origen e historia, no deja de ser inquietante y atractivo para quienes se consideran dueños del mundo y quisieran gozar ilimitadamente de sus maravillosos recursos.



Sube a 48 cifra de muertos por explosión en Amuay

Por • 27 ago, 2012 • Category: Nacionales

Al menos 48 personas han perdido la vida a causa de la explosión en la refinería Amuay, registrada la madrugada del sábado, así lo confirmó la gobernadora del estado Falcón, Stella Lugo, en declaraciones a Unión Radio.



El ecologismo a ultranza

Por • 27 ago, 2012 • Category: Nacionales

Como este tema puede afectar muchas sensibilidades en grupos muy beligerantes al respecto, y la gente subjetivamente afectada no lee o le y no entiende, inicio diciendo que sin ser experto en el área la abordo con el mejor sentido crítico, precisamente para que aflore una discusión que está un tanto oculta, en un tema en que no existe la unanimidad que debería haber entre los distintos grupos comprometidos existentes, ni con nuestros gobiernos.



Los dos debates chinos

Por • 26 ago, 2012 • Category: Política

¿Derecha-izquierda o soberanía-sumisión? Todo el proceso que China ha vivido tras la muerte de Mao (1976) se ha articulado en torno al objetivo de encontrar una senda que conduzca al renacimiento del país, ideal asociado a dos variables: modernización y soberanía. Sun Yat-sen (1911) y Mao (1949) lo intentaron a su manera. La gaige y la kaifang (1978) ofrecieron una tercera oportunidad para desarrollar el país y alcanzar un nivel de poderío suficiente para eclipsar los dos últimos siglos de decadencia, ruina y capitulación. Ese empeño “nacional” se acabó por imponer a cualquier otra consideración de tipo ideológico basada en nuestros axiomas, siempre tendentes a avizorar contradicciones donde los chinos acostumbran a identificar sinergias y complementariedades. Hay, por tanto, un debate principal y otro secundario, aunque entre ambos no existen fronteras infranqueables.



Constraints on Chronologies

Por • 25 ago, 2012 • Category: Filosofía

The time ordering of two spacelike separated events is arbitrary, when all inertial frames are taken into account, but for three or more events it is not generally so. We determine the structure of possible time orderings, or chronologies, for multiple events in any number of dimensions, analytically and exhaustively for three events in four space-time dimensions, algorithmically in other cases. We also formulate an alternative criterion, based on convexity, for determining the allowed chronologies of a set of events. We show how the metric of a Lorentz invariant spacetime can be partially reconstructed from a knowledge of the chronologies it supports. Finally, we propose a different but related criterion for allowed chronologies in curved spacetimes



Ascienden a 26 los fallecidos por explosión en Amuay

Por • 25 ago, 2012 • Category: Nacionales

“Debemos informar que lamentablemente que el nùmero de fallecidos ha aumentado a 26 compatriotas; 17 efectivos de la Guardia Nacional y continuamos en la bùsqueda de màs afectados por esta situación”, dijo Jaua.



Accelerating Scientific Discovery by Formulating Grand Scientific Challenges

Por • 24 ago, 2012 • Category: sociologia

One important question for science and society is how to best promote scientific progress. Inspired by the great success of Hilbert’s famous set of problems, the FuturICT project tries to stimulate and focus the efforts of many scientists by formulating Grand Challenges, i.e. a set of fundamental, relevant and hardly solvable scientific questions.



Randomness, Information, and Complexity

Por • 23 ago, 2012 • Category: Ciencia y tecnología

We review possible measures of complexity which might in particular be applicable to situations where the complexity seems to arise spontaneously. We point out that not all of them correspond to the intuitive (or “naive”) notion, and that one should not expect a unique observable of complexity. One of the main problems is to distinguish complex from disordered systems. This and the fact that complexity is closely related to information requires that we also give a review of information measures. We finally concentrate on quantities which measure in some way or other the difficulty of classifying and forecasting sequences of discrete symbols, and study them in simple examples.