937 research outputs found
Is Quantum Mechanics Compatible with a Deterministic Universe? Two Interpretations of Quantum Probabilities
Two problems will be considered: the question of hidden parameters and the
problem of Kolmogorovity of quantum probabilities. Both of them will be
analyzed from the point of view of two distinct understandings of quantum
mechanical probabilities. Our analysis will be focused, as a particular
example, on the Aspect-type EPR experiment. It will be shown that the quantum
mechanical probabilities appearing in this experiment can be consistently
understood as conditional probabilities without any paradoxical consequences.
Therefore, nothing implies in the Aspect experiment that quantum theory is
incompatible with a deterministic universe.Comment: REVISED VERSION! ONLY SMALL CHANGES IN THE TEXT! compressed and
uuencoded postscript, a uuencoded version of a demo program file (epr.exe for
DOS) is attached as a "Figure
Absolute spacetime: the twentieth century ether
All gauge theories need ``something fixed'' even as ``something changes.''
Underlying the implementation of these ideas all major physical theories make
indispensable use of an elaborately designed spacetime model as the ``something
fixed,'' i.e., absolute. This model must provide at least the following
sequence of structures: point set, topological space, smooth manifold,
geometric manifold, base for various bundles. The ``fine structure'' of
spacetime inherent in this sequence is of course empirically unobservable
directly, certainly when quantum mechanics is taken into account. This issue is
at the basis of the difficulties in quantizing general relativity and has been
approached in many different ways. Here we review an approach taking into
account the non-Boolean properties of quantum logic when forming a spacetime
model. Finally, we recall how the fundamental gauge of diffeomorphisms (the
issue of general covariance vs coordinate conditions) raised deep conceptual
problems for Einstein in his early development of general relativity. This is
clearly illustrated in the notorious ``hole'' argument. This scenario, which
does not seem to be widely known to practicing relativists, is nevertheless
still interesting in terms of its impact for fundamental gauge issues.Comment: Contribution to Proceedings of Mexico Meeting on Gauge Theories of
Gravity in honor of Friedrich Heh
Exotic Smoothness and Physics
The essential role played by differentiable structures in physics is reviewed
in light of recent mathematical discoveries that topologically trivial
space-time models, especially the simplest one, , possess a rich
multiplicity of such structures, no two of which are diffeomorphic to each
other and thus to the standard one. This means that physics has available to it
a new panoply of structures available for space-time models. These can be
thought of as source of new global, but not properly topological, features.
This paper reviews some background differential topology together with a
discussion of the role which a differentiable structure necessarily plays in
the statement of any physical theory, recalling that diffeomorphisms are at the
heart of the principle of general relativity. Some of the history of the
discovery of exotic, i.e., non-standard, differentiable structures is reviewed.
Some new results suggesting the spatial localization of such exotic structures
are described and speculations are made on the possible opportunities that such
structures present for the further development of physical theories.Comment: 13 pages, LaTe
The regular cosmic string in Born-Infeld gravity
It is shown that Born-Infeld gravity --a high energy deformation of Einstein
gravity-- removes the singularities of a cosmic string. The respective vacuum
solution results to be free of conical singularity and closed timelike curves.
The space ends at a minimal circle where the curvature invariants vanish; but
this circle cannot be reached in a finite proper time.Comment: 4 pages, submitted to Proceedings of Spanish Relativity Meeting 2010
(ERE2010, Granada, Spain
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