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Search Results: 1 - 10 of 201978 matches for " Rafael D. Sorkin "
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Big extra dimensions make lambda too small
Sorkin, Rafael D.;
Brazilian Journal of Physics , 2005, DOI: 10.1590/S0103-97332005000200012
Abstract: i argue that the true quantum gravity scale cannot be much larger than the planck length, because if it were then the quantum gravity-induced fluctuations in l would be insufficient to produce the observed cosmic "dark energy". if one accepts this argument, it rules out scenarios of the "large extra dimensions" type. i also point out that the relation between the lower and higher dimensional gravitational constants in a kaluza-klein theory is precisely what is needed in order that a black hole's entropy admit a consistent higher dimensional interpretation in terms of an underlying spatio-temporal discreteness.
Is the spacetime metric Euclidean rather than Lorentzian?
Rafael D. Sorkin
Physics , 2009,
Abstract: My answer to the question in the title is "No". In support of this point of view, we analyze some examples of saddle-point methods, especially as applied to quantum "tunneling" in nonrelativistic particle mechanics and in cosmology. Along the way we explore some of the interrelationships among different ways of thinking about path-integrals and saddle-point approximations to them.
Two Topics concerning Black Holes: Extremality of the Energy, Fractality of the Horizon
Rafael D. Sorkin
Physics , 1995,
Abstract: We treat two aspects of the physics of stationary black holes. First we prove that the proportionality, d(energy) ~ d(area) for arbitrary perturbations (``extended first law''), follows directly from an extremality theorem drawn from earlier work. Second we consider quantum fluctuations in the shape of the horizon, concluding heuristically that they exhibit a fractal character, with order lambda fluctuations occurring on all scales lambda below M^{1/3} in natural units.
How Wrinkled is the Surface of a Black Hole?
Rafael D. Sorkin
Physics , 1997,
Abstract: We present evidence that, below a certain threshold scale, the horizon of a black hole is strongly wrinkled, with its shape manifesting a self-similar (``fractal'') spectrum of fluctuations on all scales below the threshold. This threshold scale is small compared to the radius of the black hole, but still much larger than the Planck scale. If present, such fluctuations might account for a large part of the horizon entropy.
Logic is to the quantum as geometry is to gravity
Rafael D. Sorkin
Physics , 2010,
Abstract: I will propose that the reality to which the quantum formalism implicitly refers is a kind of generalized history, the word history having here the same meaning as in the phrase sum-over-histories. This proposal confers a certain independence on the concept of event, and it modifies the rules of inference concerning events in order to resolve a contradiction between the idea of reality as a single history and the principle that events of zero measure cannot happen (the Kochen-Specker paradox being a classic expression of this contradiction). The so-called measurement problem is then solved if macroscopic events satisfy classical rules of inference, and this can in principle be decided by a calculation. The resulting conception of reality involves neither multiple worlds nor external observers. It is therefore suitable for quantum gravity in general and causal sets in particular.
Is the cosmological "constant" a nonlocal quantum residue of discreteness of the causal set type?
Rafael D. Sorkin
Physics , 2007, DOI: 10.1063/1.2823750
Abstract: The evidence for an accelerating Hubble expansion appears to have confirmed the heuristic prediction, from causal set theory, of a fluctuating and ``ever-present'' cosmological term in the Einstein equations. A more concrete phenomenological model incorporating this prediction has been devised and tested, but it remains incomplete. I will review these developments and also mention a possible consequence for the dimensionality of spacetime.
Impossible Measurements on Quantum Fields
Rafael D. Sorkin
Physics , 1993,
Abstract: It is shown that the attempt to extend the notion of ideal measurement to quantum field theory leads to a conflict with locality, because (for most observables) the state vector reduction associated with an ideal measurement acts to transmit information faster than light. Two examples of such information-transfer are given, first in the quantum mechanics of a pair of coupled subsystems, and then for the free scalar field in flat spacetime. It is argued that this problem leaves the Hilbert space formulation of quantum field theory with no definite measurement theory, removing whatever advantages it may have seemed to possess vis a vis the sum-over-histories approach, and reinforcing the view that a sum-over-histories framework is the most promising one for quantum gravity.
Quantum Mechanics as Quantum Measure Theory
Rafael D. Sorkin
Physics , 1994, DOI: 10.1142/S021773239400294X
Abstract: The additivity of classical probabilities is only the first in a hierarchy of possible sum-rules, each of which implies its successor. The first and most restrictive sum-rule of the hierarchy yields measure-theory in the Kolmogorov sense, which physically is appropriate for the description of stochastic processes such as Brownian motion. The next weaker sum-rule defines a {\it generalized measure theory} which includes quantum mechanics as a special case. The fact that quantum probabilities can be expressed ``as the squares of quantum amplitudes'' is thus derived in a natural manner, and a series of natural generalizations of the quantum formalism is delineated. Conversely, the mathematical sense in which classical physics is a special case of quantum physics is clarified. The present paper presents these relationships in the context of a ``realistic'' interpretation of quantum mechanics.
A Specimen of Theory Construction from Quantum Gravity
Rafael D. Sorkin
Physics , 1995,
Abstract: I describe the history of my attempts to arrive at a discrete substratum underlying the spacetime manifold, culminating in the hypothesis that the basic structure has the form of a partial-order (i.e. that it is a causal set).
Quantum Measure Theory and its Interpretation
Rafael D. Sorkin
Physics , 1995,
Abstract: We propose a realistic, spacetime interpretation of quantum theory in which reality constitutes a *single* history obeying a "law of motion" that makes definite, but incomplete, predictions about its behavior. We associate a "quantum measure" |S| to the set S of histories, and point out that |S| fulfills a sum rule generalizing that of classical probability theory. We interpret |S| as a "propensity", making this precise by stating a criterion for |S|=0 to imply "preclusion" (meaning that the true history will not lie in S). The criterion involves triads of correlated events, and in application to electron-electron scattering, for example, it yields definite predictions about the electron trajectories themselves, independently of any measuring devices which might or might not be present. (So we can give an objective account of measurements.) Two unfinished aspects of the interpretation involve *conditonal* preclusion (which apparently requires a notion of coarse-graining for its formulation) and the need to "locate spacetime regions in advance" without the aid of a fixed background metric (which can be achieved in the context of conditional preclusion via a construction which makes sense both in continuum gravity and in the discrete setting of causal set theory).
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