![The Time Machine Factory [unspeakable, speakable] on Time Travel -TM2019](/event/2767/logo-693158660.png){kind=logo}
Exactly hundred years ago, in May 1919, Arthur Eddington and three colleagues observed the gravitational light deflection, as predicted by Albert Einstein, during a total Sun eclipse. After a historical introduction, I'll discuss the relevance of gravitational lensing as an important tool for present-day astrophysics. In the last part of the talk I will investigate in some detail the pictures...
Black holes in equilibrium are fundamental objects predicted by General Relativity. However, real black holes form, evolve and eventually evaporate, thus they are dynamical. Do they have a well-defined boundary? Where? The usual Event Horizon is global and teleological, thus not well defined for dynamical black holes. The concepts of dynamical and trapping horizons, based on closed trapped...
What would happen if you could enter inside a black hole? You would travel to the future, coming out of a white hole! In fact, the huge gravitational redshift distinguish two characteristic time for such a process: the one of the infalling observer, that is fast, and the one of an external observer, that is extremely long. I discuss how such a process is allowed by gluing classical metrics...
We study the properties of regular black holes using both test and gravitating scalar fields. The main motivation being to discover features that distinguish them from real black holes. One such characteristic is regularity of horizon which is spoilt by scalar field in spherically symmetric static cases.
Abstract
In general relativity theory (GRT) one can construct solutions which are related to real physical objects. The most famous one is the black hole solution. One now believes that in the center of many galaxies there is a rotating super-massive black hole, the Kerr black hole. Because there is an axis of rotation, the Kerr solution is a member of the family of the axially symmetric...
In calculations of gravitational collapse to form black holes, trapping horizons (foliated by marginally trapped surfaces) make their first appearance either within the collapsing matter or where it joins on to a vacuum exterior. Those which then move outwards with respect to the matter have been proposed for use in defining black holes, replacing the global concept of an event horizon, which...
General relativity allows for the existence of closed time-like curves, along which a material object could travel back in time and interact with its past self. Previous studies by Thorne and others showed that for any choice of initial conditions, consistent dynamics — even in the presence of closed time-like curves — exist. Moreover and counterintuitively, they showed that the examples with...
While the dynamics of black hole evaporation and closed-timelike-curve physics in the presence of quantum fields are to some extent understood in principle, the computations necessary to produce concrete predictions from them are often intractable in practice. Here we show how tensor-network based numerics, which assign a manageably sparse representation to certain quantum states, can be used...
I would like to explore a change in the interpretation of time. By thinking time as a cut, and no more like a lapse, there could be interesting opportunities. Particularly, with such interpretation, quantum gravity theories based on 3+1 spacetime (e.g. Kuchar or Ellis' evolving block universe) may open unexpected and fruitful views. Among the many consequences, there will be no possibility for...
