39,822 research outputs found
Jet interactions in massive X-ray binaries
Massive X-ray binaries are formed by a compact object that accretes matter
from the stellar wind of an early-type donor star. In some of these systems,
called microquasars, relativistic jets are launched from the surroundings of
the compact object. Such jets interact with the photon field of the companion
star, the stellar wind, and, at large distances, with the interstellar medium.
In this paper I will review the main results of such interactions with
particular emphasis on the production of high-energy photons and neutrinos. The
case of some specific systems, like LS I +61 303, will be discussed in some
detail. Prospects for future observations at different wavelengths of this type
of objects will be presented.Comment: 5 pages, 5 figures. Invited talk presented at the meeting: "Massive
Stars: fundamental parameters and circumstellar interactions", Carilo, Dec
200
Philosophical problems of space-time theories
I present a discussion of some open issues in the philosophy of space-time
theories. Emphasis is put on the ontological nature of space and time, the
relation between determinism and predictability, the origin of irreversible
processes in an expanding Universe, and the compatibility of relativity and
quantum mechanics. In particular, I argue for a Parmenidean view of time and
change, I make clear the difference between ontological determinism and
predictability, propose that the origin of the asymmetry observed in physical
processes is related to the existence of cosmological horizons, and present a
non-local concept of causality that can accommodate both special relativity and
quantum entanglement.Comment: 20 pages, small changes to match the version published by Cambridge
University Pres
The collapse of supertasks
A supertask consists in the performance of an infinite number of actions in a
finite time. I show that any attempt to carry out a supertask will produce a
divergence of the curvature of spacetime, resulting in the formation of a black
hole. I maintain that supertasks, contrarily to a popular view among
philosophers, are physically impossible. Supertasks, literally, collapse under
their own weight.Comment: 10 pages, accepted for publication in Foundations of Scienc
From change to spacetime: an Eleatic journey
I present a formal ontological theory where the basic building blocks of the
world can be either things or events. In any case, the result is a Parmenidean
worldview where change is not a global property. What we understand by change
manifests as asymmetries in the pattern of the world-lines that constitute
4-dimensional existents. I maintain that such a view is in accord with current
scientific knowledge.Comment: 13 pages, accepted for publication in Foundations of Scienc
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