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Jul 20, 2013
07/13

by
Olaf Dreyer

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General relativity differs from other forces in nature in that it can be made to disappear locally. This is the essence of the equivalence principle. In general relativity the equivalence principle is implemented using differential geometry. The connection that comes from a metric is used to glue together the different gravity-free Minkowski spaces. In this article we argue that there is another way to implement the equivalence principle. In this new way it is not different Minkowski spaces...

Source: http://arxiv.org/abs/1203.2641v1

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70

Sep 20, 2013
09/13

by
Olaf Dreyer

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In a purely relational theory there exists a tension between the relational character of the theory and the existence of quantities like distance and duration. We review this issue in the context of the Leibniz-Clarke correspondence. We then address this conflict by showing that a purely relational definition of length and time can be given, provided the dynamics of the theory is known. We further show that in such a setting it is natural to expect Lorentz transformations to describe the...

Source: http://arxiv.org/abs/gr-qc/0404054v1

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Sep 22, 2013
09/13

by
Olaf Dreyer

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We introduce the notion of background independent quantum field theory. The distinguishing feature of this theory is that the dynamics can be formulated without recourse to a background metric structure. We show in a simple model how the metric properties of spacetime can be recovered from the dynamics. Background independence is not only conceptually desirable but allows for the resolution of a problem haunting ordinary quantum field theory: the cosmological constant problem.

Source: http://arxiv.org/abs/hep-th/0409048v2

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Sep 23, 2013
09/13

by
Olaf Dreyer

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Attempts to quantize general relativity encounter an odd problem. The Hamiltonian that normally generates time evolution vanishes in the case of general relativity as a result of diffeomorphism invariance. The theory seems to be saying that time does not exist. The most obvious feature of our world, namely that time seems to progress and that the world changes accordingly becomes a problem in this presumably fundamental theory. This is called the problem of time. In this essay we argue that...

Source: http://arxiv.org/abs/0904.3520v1

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Sep 20, 2013
09/13

by
Olaf Dreyer

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We review an idea that uses details of the quasinormal mode spectrum of a black hole to obtain the Bekenstein-Hawking entropy of $A/4$ in Loop Quantum Gravity. We further comment on a recent proposal concerning the quasinormal mode spectrum of rotating black holes. We conclude by remarking on a recent proposal to include supersymmetry.

Source: http://arxiv.org/abs/gr-qc/0404055v2

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Sep 23, 2013
09/13

by
Olaf Dreyer

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In this paper we discuss Internal Relativity, a recent program to address the problem of quantum gravity. In our approach we change the relationship between spacetime and matter. Currently we view matter as propagating on spacetime. Einstein's equations encode how spacetime curves due to the presence of matter and how spacetime, in turn, tells matter how to propagate. In internal realtivity matter and spacetime cease to exist as distinct entities, rather, they arise simultaneously from an...

Source: http://arxiv.org/abs/0710.4350v2

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48

Sep 23, 2013
09/13

by
Olaf Dreyer

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In physics we encounter particles in one of two ways. Either as fundamental constituents of the theory or as emergent excitations. These two ways differ by how the particle relates to the background. It either sits on the background, or it is an excitation of the background. We argue that by choosing the former to construct our fundamental theories we have made a costly mistake. Instead we should think of particles as excitations of a background. We show that this point of view sheds new light...

Source: http://arxiv.org/abs/1212.0371v1

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Sep 22, 2013
09/13

by
Olaf Dreyer

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We present a new approach to early universe cosmology. Inflation is replaced by a phase transition in which both matter and geometry are created simultaneously. We calculate the spectrum of metric perturbations and show that it is flat. We then argue that as a consequence of the dynamic nature of the phase transition the spectrum is likely not completely flat but tilted. We argue that the tilt is related to $\eta$, one of the critical exponents characterizing the phase transition. This exponent...

Source: http://arxiv.org/abs/0805.3729v1

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Sep 22, 2013
09/13

by
Olaf Dreyer

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The transition from the quantum to the classical is governed by randomizing devices (RD), i.e., dynamical systems that are very sensitive to the environment. We show that, in the presence of RDs, the usual arguments based on the linearity of quantum mechanics that lead to the measurement problem do not apply. RDs are the source of probabilities in quantum mechanics. Hence, the reason for probabilities in quantum mechanics is the same as the reason for probabilities in other parts of physics,...

Source: http://arxiv.org/abs/quant-ph/0603202v1

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Sep 18, 2013
09/13

by
Olaf Dreyer

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The search for a quantum theory of gravity has followed two parallel but different paths. One aims at arriving at the final theory starting from a priori assumptions as to its form and building it from the ground up. The other tries to infer as much as possible about the unknown theory from the existing ones and use our current knowledge to constrain the possibilities for the quantum theory of gravity. Probably the biggest success of the second path has been the results of black hole...

Source: http://arxiv.org/abs/gr-qc/0401035v1

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Sep 18, 2013
09/13

by
Olaf Dreyer

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In this article we propose a solution to the measurement problem in quantum mechanics. We point out that the measurement problem can be traced to an a priori notion of classicality in the formulation of quantum mechanics. If this notion of classicality is dropped and instead classicality is defined in purely quantum mechanical terms the measurement problem can be avoided. We give such a definition of classicality. It identifies classicality as a property of large quantum system. We show how the...

Source: http://arxiv.org/abs/quant-ph/0611076v1

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Jul 20, 2013
07/13

by
Olaf Dreyer

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We review different approaches to quantum gravity in which spacetime is emerging. We discuss in some detail the proposals by G. Volovik and S. Lloyd and show how they differ in the way they treat time. We further propose an approach to quantum gravity in which the Einstein equations are derived rather then used. We call this approach Internal Relativity.

Source: http://arxiv.org/abs/gr-qc/0604075v1

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Sep 22, 2013
09/13

by
Seth Lloyd; Olaf Dreyer

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Path integrals represent a powerful route to quantization: they calculate probabilities by summing over classical configurations of variables such as fields, assigning each configuration a phase equal to the action of that configuration. This paper defines a universal path integral, which sums over all computable structures. This path integral contains as sub-integrals all possible computable path integrals, including those of field theory, the standard model of elementary particles, discrete...

Source: http://arxiv.org/abs/1302.2850v1

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Sep 18, 2013
09/13

by
Olaf Dreyer; Amit Ghosh; Jacek Wisniewski

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Symmetry based approaches to the black hole entropy problem have a number of attractive features; in particular they are very general and do not depend on the details of the quantization method. However we point out that, of the two available approaches, one faces conceptual problems (also emphasized by others), while the second contains certain technical flaws. We correct these errors and, within the new, improved scheme, calculate the entropy of 3-dimensional black holes. We find that, while...

Source: http://arxiv.org/abs/hep-th/0101117v1

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Sep 22, 2013
09/13

by
Olaf Dreyer; Fotini Markopoulou; Lee Smolin

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We argue, using methods taken from the theory of noiseless subsystems in quantum information theory, that the quantum states associated with a Schwarzchild black hole live in the restricted subspace of the Hilbert space of horizon boundary states in which all punctures are equal. Consequently, one value of the Immirzi parameter matches both the Hawking value for the entropy and the quasi normal mode spectrum of the Schwarzchild black hole. The method of noiseless subsystems thus allows us to...

Source: http://arxiv.org/abs/hep-th/0409056v3

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64

Sep 19, 2013
09/13

by
Abhay Ashtekar; Olaf Dreyer; Jacek Wisniewski

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Using ideas employed in higher dimensional gravity, non-expanding, weakly isolated and isolated horizons are introduced and analyzed in 2+1 dimensions. While the basic definitions can be taken over directly from higher dimensions, their consequences are somewhat different because of the peculiarities associated with 2+1 dimensions. Nonetheless, as in higher dimensions, we are able to: i) analyze the horizon geometry in detail; ii) introduce the notions of mass, charge and angular momentum of...

Source: http://arxiv.org/abs/gr-qc/0206024v3

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Sep 19, 2013
09/13

by
Olaf Dreyer; Badri Krishnan; Eric Schnetter; Deirdre Shoemaker

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We present a coordinate-independent method for extracting mass (M) and angular momentum (J) of a black hole in numerical simulations. This method, based on the isolated horizon framework, is applicable both at late times when the black hole has reached equilibrium, and at early times when the black holes are widely separated. We show how J and M can be determined in numerical simulations in terms of only those quantities which are intrinsic to the apparent horizon. We also present a numerical...

Source: http://arxiv.org/abs/gr-qc/0206008v2

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Sep 22, 2013
09/13

by
Detlev Buchholz; Olaf Dreyer; Martin Florig; Stephen J. Summers

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A condition of geometric modular action is proposed as a selection principle for physically interesting states on general space-times. This condition is naturally associated with transformation groups of partially ordered sets and provides these groups with projective representations. Under suitable additional conditions, these groups induce groups of point transformations on these space-times, which may be interpreted as symmetry groups. The consequences of this condition are studied in detail...

Source: http://arxiv.org/abs/math-ph/9805026v2

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Sep 22, 2013
09/13

by
Olaf Dreyer; Bernard Kelly; Badri Krishnan; Lee Samuel Finn; David Garrison; Ramon Lopez-Aleman

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Assuming that general relativity is the correct theory of gravity in the strong field limit, can gravitational wave observations distinguish between black hole and other compact object sources? Alternatively, can gravitational wave observations provide a test of one of the fundamental predictions of general relativity? Here we describe a definitive test of the hypothesis that observations of damped, sinusoidal gravitational waves originated from a black hole or, alternatively, that nature...

Source: http://arxiv.org/abs/gr-qc/0309007v1

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Sep 18, 2013
09/13

by
Abhay Ashtekar; Christopher Beetle; Olaf Dreyer; Stephen Fairhurst; Badri Krishnan; Jerzy Lewandowski; Jacek Wisniewski

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Boundary conditions defining a generic isolated horizon are introduced. They generalize the notion available in the existing literature by allowing the horizon to have distortion and angular momentum. Space-times containing a black hole, itself in equilibrium but possibly surrounded by radiation, satisfy these conditions. In spite of this generality, the conditions have rich consequences. They lead to a framework, somewhat analogous to null infinity, for extracting physical information, but now...

Source: http://arxiv.org/abs/gr-qc/0006006v2