Artículos con la etiqueta ‘Cosmología’

Benford’s Law and the Universe

Por • 27 ene, 2014 • Category: Ciencia y tecnología

Benford’s law predicts the occurrence of the n th digit of numbers in datasets originating from various sources of the world, ranging from financial data to atomic spectra. It is intriguing that although many features of Benford’s law have been proven and analysed, it is still not fully mathematically understood. In this paper we investigate the distances of galaxies and stars by comparing the first, second and third significant digit probabilities with Benford’s predictions. It is found that the distances of galaxies follow reasonably well the first digit law and the star distances agree very well with the first, second and third significant digit.



De la Física a la Metafísica: cuestiones sobre Teología Natural, Mecánica Cuántica y Cosmología

Por • 22 oct, 2013 • Category: Opinion

En el presente ensayo, usando como «guía de trituración dialéctica» las ideas y tesis defendidas por Francisco José Soler Gil, que en su artículo «La física privada de Javier Pérez Jara» (El Catoblepas, nº 70, diciembre 2007, pág. 11) vierte contra mis posiciones filosóficas, se analizan una serie de tesis metafísico-ideológicas que, pese a su carácter completamente sustancialista y gratuito, se encuentran extendidas profusamente en nuestros días, y que, la mayoría de veces, por el hecho de «disfrazarse» de científicas («operación» realimentada por el uso de confusas y oscuras teorías de filosofía de la ciencia que no suelen, a su vez, ser sometidas a crítica), tienden a pasar como intocables. Estas tesis metafísicas, «disfrazas» de ciencia estricta, alcanzan su culmen metafísico, por no decir mitológico, cuando pretenden conducir, como una Preambula Fidei «reactualizada» en nuestros días, a la posibilidad y existencia del Dios de la Ontoteología cristiana, en cuanto Creador ex nihilo del Universo y de sus leyes ontológicas fundamentales. En estos casos, el fundamentalismo científico, unido al fundamentalismo religioso, forma un fundamentalismo diárquico{1} cuya patentización de su carácter metafísico, gratuito y contradictorio es una de las tareas fundamentales del presente que se ha de llevar a cabo desde el materialismo filosófico, entendido como sistema filosófico necesariamente dialéctico que sólo alcanza su verdadera significación «crítica» cuando se entiende el carácter de las tesis a las que se enfrenta y niega de modo apagógico (es decir, no dogmático).



Cyclic models of the relativistic universe: the early history

Por • 8 ago, 2013 • Category: Leyes

Within the framework of relativistic cosmology oscillating or cyclic models of the universe were introduced by A. Friedmann in his seminal paper of 1922. With the recognition of evolutionary cosmology in the 1930s this class of closed models attracted considerable interest and was investigated by several physicists and astronomers. Whereas the Friedmann-Einstein model exhibited only a single maximum value, R. Tolman argued for an endless series of cycles. After World War II, cyclic or pulsating models were suggested by W. Bonnor and H. Zanstra, among others, but they remained peripheral to mainstream cosmology. The paper reviews the development from 1922 to the 1960s, paying particular attention to the works of Friedmann, Einstein, Tolman and Zanstra. It also points out the role played by bouncing models in the emergence of modern big-bang cosmology.



Is the CMB telling us that dark matter is weaker than weakly interacting?

Por • 9 jul, 2013 • Category: Leyes

If moduli, or other long-lived heavy states, decay in the early universe in part into light and feebly interacting particles (such as axions), these decay products could account for the additional energy density in radiation that is suggested by recent measurements of the CMB. These moduli decays will also, however, alter the expansion history of the early universe, potentially diluting the thermal relic abundance of dark matter. If this is the case, then dark matter particles must annihilate with an even lower cross section than required in the standard thermal scenario (sigma v < 3×10^-26 cm^3/s) if they are to make up the observed density of dark matter. This possibility has significant implications for direct and indirect searches for dark matter.



Generalized gravitational entropy

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

We consider classical Euclidean gravity solutions with a boundary. The boundary contains a non-contractible circle. These solutions can be interpreted as computing the trace of a density matrix in the full quantum gravity theory, in the classical approximation. When the circle is contractible in the bulk, we argue that the entropy of this density matrix is given by the area of a minimal surface. This is a generalization of the usual black hole entropy formula to euclidean solutions without a Killing vector.
A particular example of this set up appears in the computation of the entanglement entropy of a subregion of a field theory with a gravity dual. In this context, the minimal area prescription was proposed by Ryu and Takayanagi. Our arguments explain their conjecture.



The Large N Limit of Superconformal Field Theories and Supergravity

Por • 7 jul, 2013 • Category: Ciencia y tecnología

We show that the large $N$ limit of certain conformal field theories in various dimensions include in their Hilbert space a sector describing supergravity on the product of Anti-deSitter spacetimes, spheres and other compact manifolds. This is shown by taking some branes in the full M/string theory and then taking a low energy limit where the field theory on the brane decouples from the bulk. We observe that, in this limit, we can still trust the near horizon geometry for large $N$. The enhanced supersymmetries of the near horizon geometry correspond to the extra supersymmetry generators present in the superconformal group (as opposed to just the super-Poincare group). The ‘t Hooft limit of 4-d ${\cal N} =4$ super-Yang-Mills at the conformal point is shown to contain strings: they are IIB strings. We conjecture that compactifications of M/string theory on various Anti-deSitter spacetimes are dual to various conformal field theories. This leads to a new proposal for a definition of M-theory which could be extended to include five non-compact



A Critical Look at the Standard Cosmological Picture

Por • 20 mar, 2013 • Category: Crítica

The discovery that the Universe is accelerating in its expansion has brought the basic concept of cosmic expansion into question. An analysis of the evolution of this concept suggests that the paradigm that was finally settled into prior to that discovery was not the best option, as the observed acceleration lends empirical support to an alternative which could incidentally explain expansion in general. I suggest, then, that incomplete reasoning regarding the nature of cosmic time in the derivation of the standard model is the reason why the theory cannot coincide with this alternative concept. Therefore, through an investigation of the theoretical and empirical facts surrounding the nature of cosmic time, I argue that an enduring three-dimensional cosmic present must necessarily be assumed in relativistic cosmology—and in a stricter sense than it has been. Finally, I point to a related result which could offer a better explanation of the empirically constrained expansion rate.



Numerical Simulations of the Dark Universe: State of the Art and the Next Decade

Por • 1 oct, 2012 • Category: Leyes

We present a review of the current state of the art of cosmological dark matter simulations, with particular emphasis on the implications for dark matter detection efforts and studies of dark energy. This review is intended both for particle physicists, who may find the cosmological simulation literature opaque or confusing, and for astro-physicists, who may not be familiar with the role of simulations for observational and experimental probes of dark matter and dark energy. Truly massive dark matter-only simulations are being conducted on national supercomputing centers, employing from several billion to over half a trillion particles to simulate the formation and evolution of cosmologically representative volumes (cosmic scale) or to zoom in on individual halos (cluster and galactic scale). These simulations cost millions of core-hours, require tens to hundreds of terabytes of memory, and use up to petabytes of disk storage. The field is quite internationally diverse, with top simulations having been run in China, France, Germany, Korea, Spain, and the USA. Predictions from such simulations touch on almost every aspect of dark matter and dark energy studies, and we give a comprehensive overview of this connection.



De la Física a la Metafísica:cuestiones sobre Teología Natural, Mecánica Cuántica y Cosmología

Por • 7 jun, 2012 • Category: Filosofía

La cuestión de la finitud o infinitud espacial y/o temporal del Universo, es una cuestión cosmológica que entronca, explícitamente, con la Ontología; es en la Cosmología de nuestros días, donde la «frontera» entre la Física y la Ontología, o la Metafísica, parece más débil y quebradiza. Dicho desde las coordenadas de la Teoría del Cierre Categorial: en la Cosmología como disciplina perteneciente al «cuerpo» de la Física, la presencia de contenidos pertenecientes a la capa conjuntiva o metodológica es «apabullante». No es ahora el tiempo de hablar de cuestiones de Teoría de la Ciencia, sino simplemente quiero patentizar que la cuestión de la finitud o infinitud del espacio, o del tiempo, o del Mundo en general, es una cuestión explícitamente ontológica, o filosófica si se quiere, aunque ésta tenga que nutrirse de los datos aportados por las ciencias positivas, en concreto la Astrofísica.



De la Física a la Metafísica: cuestiones sobre Teología Natural, Mecánica Cuántica y Cosmología

Por • 1 jun, 2012 • Category: Filosofía

En el presente ensayo, usando como «guía de trituración dialéctica» las ideas y tesis defendidas por Francisco José Soler Gil, que en su artículo «La física privada de Javier Pérez Jara» (El Catoblepas, nº 70, diciembre 2007, pág. 11) vierte contra mis posiciones filosóficas, se analizan una serie de tesis metafísico-ideológicas que, pese a su carácter completamente sustancialista y gratuito, se encuentran extendidas profusamente en nuestros días, y que, la mayoría de veces, por el hecho de «disfrazarse» de científicas («operación» realimentada por el uso de confusas y oscuras teorías de filosofía de la ciencia que no suelen, a su vez, ser sometidas a crítica), tienden a pasar como intocables. Estas tesis metafísicas, «disfrazas» de ciencia estricta, alcanzan su culmen metafísico, por no decir mitológico, cuando pretenden conducir, como una Preambula Fidei «reactualizada» en nuestros días, a la posibilidad y existencia del Dios de la Ontoteología cristiana, en cuanto Creador ex nihilo del Universo y de sus leyes ontológicas fundamentales. En estos casos, el fundamentalismo científico, unido al fundamentalismo religioso, forma un fundamentalismo diárquico{1} cuya patentización de su carácter metafísico, gratuito y contradictorio es una de las tareas fundamentales del presente que se ha de llevar a cabo desde el materialismo filosófico, entendido como sistema filosófico necesariamente dialéctico que sólo alcanza su verdadera significación «crítica» cuando se entiende el carácter de las tesis a las que se enfrenta y niega de modo apagógico (es decir, no dogmático).