Artículos con la etiqueta ‘relatividad general’

Un universo “de juguete” revela que el tiempo es una ilusión

Por • 9 ene, 2014 • Category: Leyes

Por primera vez, un equipo de científicos ha conseguido poner a prueba las teorías matemáticas sobre la medida del tiempo de Page y Wootters en un sistema físico “de juguete”, es decir, compuesto sólo por dos fotones (que son las partículas elementales de la luz), informa Newscientist. Se hizo de la siguiente forma. Por un lado, los científicos, del Instituto Nacional de Investigación Meteorológica (INRiM) de Turín, en Italia, midieron el sistema de ambos fotones entrelazados desde “fuera” del universo de éstos, como haría un observador externo . Por otro, usaron uno de los dos fotones entrelazados a modo de “observador” del otro fotón o como “reloj”. Con éste midieron el estado (la polarización u orientación vertical u horizontal) del segundo fotón, mientras ambas partículas atravesaban dos vías independientes y de grosores variables, con los que se afectó a la polarización de los fotones y, por tanto, a su evolución. La medición fue posible porque el estado del primer fotón reflejaba el del segundo, merced al entrelazamiento cuántico.



Emergence of time in quantum gravity: is time necessarily flowing ?

Por • 4 may, 2012 • Category: Ambiente

We discuss the emergence of time in quantum gravity, and ask whether time is always «something that flows»‘. We first recall that this is indeed the case in both relativity and quantum mechanics, although in very different manners: time flows geometrically in relativity (i.e. as a flow of proper time in the four dimensional space-time), time flows abstractly in quantum mechanics (i.e. as a flow in the space of observables of the system). We then ask the same question in quantum gravity, in the light of the thermal time hypothesis of Connes and Rovelli. The latter proposes to answer the question of time in quantum gravity (or at least one of its many aspects), by postulating that time is a state dependent notion. This means that one is able to make a notion of time-as-an-abstract-flow – that we call the thermal time – emerge from the knowledge of both: 1) the algebra of observables of the physical system under investigation, 2) a state of thermal equilibrium of this system. Formally, this thermal time is similar to the abstract flow of time in quantum mechanics, but we show in various examples that it may have a concrete implementation either as a geometrical flow, or as a geometrical flow combined with a non-geometric action. This indicates that in quantum gravity, time may well still be «something that flows» at some abstract algebraic level, but this does not necessarily imply that time is always and only «something that flows» at the geometric level.



The Riddle of Gravitation

Por • 9 dic, 2011 • Category: Opinion

There is no doubt that both the special and general theories of relativity capture the imagination. The anti-intuitive properties of the special theory of relativity and its deep philosophical implications, the bizzare and dazzling predictions of the general theory of relativity: the curvature of spacetime, the exotic characteristics of black holes, the bewildering prospects of gravitational waves, the discovery of astronomical objects as quasers and pulsers, the expansion and the (possible) recontraction of the universe…, are all breathtaking phenomena. In this paper, we give a philosophical non-technical treatment of both the special and the general theory of relativity together with an exposition of some of the latest physical theories. We then give an outline of an axiomatic approach to relativity theories due to Andreka and Nemeti that throws light on the logical structure of both theories. This is followed by an exposition of some of the bewildering results established by Andreka and Nemeti concerning the foundations of mathematics using the notion of relativistic computers. We next give a survey on the meaning and philosophical implications of the the quantum theory and end the paper by an imaginary debate between Einstein and Neils Bohr reflecting both Einstein’s and Bohr’s philosophical views on the quantum world.



de Broglie waves as the «Bridge of Becoming» between quantum theory and relativity

Por • 17 jul, 2011 • Category: Ambiente

It is hypothesized that de Broglie’s ‘matter waves’ provide a dynamical basis for Minkowski spacetime in an antisubstantivalist or relational account. The relativity of simultaneity is seen as an effect of the de Broglie oscillation together with a basic relativity postulate, while the dispersion relation from finite rest mass gives rise to the differentiation of spatial and temporal axes. Thus spacetime is seen as not fundamental, but rather as emergent from the quantum level. A result by Solov’ev which demonstrates that time is not an applicable concept at the quantum level is adduced in support of this claim. Finally, it is noted that de Broglie waves can be seen as the «bridge of becoming» discussed by Elitzur and Dolev (2005).