Artículos con la etiqueta ‘espacio-tiempo’

Present time

Por • 21 mar, 2014 • Category: Educacion

The idea of a moving present or `now’ seems to form part of our most basic beliefs about reality. Such a present, however, is not reflected in any of our theories of the physical world. I show in this article that presentism, the doctrine that only what is present exists, is in conflict with modern relativistic cosmology and recent advances in neurosciences. I argue for a tenseless view of time, where what we call `the present’ is just an emergent secondary quality arising from the interaction of perceiving self-conscious individuals with their environment. I maintain that there is no flow of time, but just an ordered system of events.



Transformation devices: carpets in space and space-time

Por • 25 nov, 2013 • Category: Opinion

Here we extend the theory of space-time or event cloaking into that based on the carpet or ground-plane reflective surface. Further, by recasting and generalizing a scalar acoustic wave model into a new mathematically covariant form, we also show how transformation theories for optics and acoustics can be combined into a single prescription. The single prescription, however, still respects the fundamental differences between electromagnetic and acoustic waves, which then provide us with an existence test for any desired transformation device — are the required material properties (the required constitutive parameters) physically permitted by the wave theory being designed for? Whilst electromagnetism is a flexible theory permitting almost any T-device design, we show that the acoustic model used here is more restricted.



How to Build a Time Cloak with Mirrors

Por • 17 ago, 2013 • Category: Ciencia y tecnología

Miguel Lerma at Northwestern University in Evanston, Illinois, goes even further. Lerma has worked out how to build time cloaks that can operate for arbitrarily long periods of time using little more than a few cleverly placed mirrors. The new approach creates temporal holes that are equal to the time it takes the light to travel the extra distance. So by making this distance arbitrarily long, by bouncing the light back and forth off the Moon or for example, it ought to be possible to make holes in time of almost any length. That’s an impressively simple trick but it is not the first time that physicists have shown that invisibility cloaks are actually much easier to make than had been thought. A couple of months ago, physicists unveiled an invisibility cloak that used mirrors rather than metamaterials to hide objects of almost any size.



Instants in physics – point mechanics and general relativity

Por • 9 jun, 2013 • Category: Filosofía

Theories in physics usually do not address ”the present” or ”the now”. However, they usually have a precise notion of an ”instant” (or state). I review how this notion appears in relational point mechanics and how it suffices to determine durations – a fact that is often ignored in modern presentations of analytical dynamics. An analogous discussion is attempted for General Relativity. Finally I critically remark on the difference between relationalism in point mechanics and field theory and the problematic foundational dependencies between fields and spacetime.



God and Physics: From Hawking to Avicenna

Por • 3 jun, 2013 • Category: Ambiente

The twin pillars of every civilization are religion and science. Contemporary cosmological theories, especially discourse about the origins of the universe, reveal the continuing encounter between physics and theology. It is a discourse which interests thinkers of our own age as much as it did those in the Middle Ages. I should like to sketch some of the current discussion in order to suggest how the contemporary world can learn a great deal from mediaeval analyses of the relationship among physics, metaphysics, and theology. In fact, to go from Stephen Hawking to Avicenna is, in an important sense, to go from confusion to clarity. Recent studies in particle physics and astronomy have produced dazzling speculations about the early history of the universe. Cosmologists now routinely entertain elaborate scenarios which propose to describe what the universe was like when it was the size of a softball, a mere 10-35 second after the Big Bang. The description of the emergence of four fundamental forces and twelve discrete subatomic particles is almost a common-place in modern physics. There is little doubt among scientists that we live in the aftermath of a giant explosion which occurred around 15 billion years ago — give or take a few billion.



Cosmology and Time

Por • 17 abr, 2013 • Category: Filosofía

Time has always played a crucial role in cosmology. I review some of the aspects of the present cosmological model which are more directly related to time, such as: the definition of a cosmic time; the existence of typical timescales and epochs in an expanding universe; the problem of the initial singularity and the origin of time; the cosmological arrow of time.



The Universe is Only Spacetime by John A. Macken

Por • 3 abr, 2013 • Category: Leyes

The approach taken in this book is to build a new conceptual model of the universe that is compatible with the equations of quantum mechanics and general relativity but is based on the simplest possible starting assumption: The universe is only spacetime. The model of the universe described here not only is compatible with existing equations but goes further. For example, this model gives new insights into the forces of nature. Gravity is shown to be closely related to the other forces of nature. Simple equations show this close relationship and explain why gravity is such a weak force compared to the other forces. Inertia is derived and connected to the energy of fundamental particles. An electrical field is shown to be an unsymmetrical distortion of spacetime. Equations are derived that convert charge to a distortion of spacetime. Photons are shown to experience the same impedance as gravitational waves. A new cosmological model of the universe explains how the Big Bang and the expansion of the universe is the result of spacetime undergoing a transformation that continues today.



The relativity of simultaneity between eternalism and presentism

Por • 15 feb, 2013 • Category: Filosofía

The relativity of simultaneity seems to favour a block universe view according to which the universe is a timelessly existing four-dimensional world, i.e. it favours an eternalist position. In this way, presentism is taken to be at odds with the theory of relativity. In this paper I will look in detail into the relativity of simultaneity by recovering Einstein’s original approach. By clarifying the physical meaning of the relativity of simultaneity one can inform the philosophical debate. It turns out that, contrary to conventional wisdom, eternalist arguments cannot be made to stand when taking into account the relativity of simultaneity properly interpreted.



Experimental demonstration of metamaterial multiverse in a ferrofluid

Por • 2 feb, 2013 • Category: Ambiente

Extraordinary light rays propagating inside a hyperbolic metamaterial look similar to particle world lines in a 2+1 dimensional Minkowski spacetime [1]. Magnetic nanoparticles in a ferrofluid are known to form nanocolumns aligned along the magnetic field, so that a hyperbolic metamaterial may be formed at large enough nanoparticle concentration nH. Here we investigate optical properties of such a metamaterial just below nH. While on average such a metamaterial is elliptical, thermal fluctuations of nanoparticle concentration lead to transient formation of hyperbolic regions (3D Minkowski spacetimes) inside this metamaterial. Thus, thermal fluctuations in a ferrofluid look similar to creation and disappearance of individual Minkowski spacetimes (universes) in the cosmological multiverse. This theoretical picture is supported by experimental measurements of polarization-dependent optical transmission of a cobalt based ferrofluid at 1500 nm.



Relativity Is Not About Spacetime

Por • 18 oct, 2012 • Category: Leyes

Quantum measurement predictions are consistent with relativity for macroscopic observations, but there is no consensus on how to explain this consistency in fundamental terms. The prevailing assumption is that the relativistic structure of spacetime should provide the framework for any microphysical account. This bias is due, in large part, to our intuitions about local causality, the idea that all physical processes propagate through space in a continuous manner. I argue that relativity is not a guarantor of local causality, and is not about ontological features of spacetime. It is, rather, an expression of the observational equivalence of spacetime descriptions of physical processes. This observational equivalence is due to the essentially probabilistic nature of quantum theory.