The reliability horizon for semi-classical quantum gravity: metric fluctuations are often more important than back-reaction

Visser, Matt

doi:10.1016/s0370-2693(97)01226-4

Cited by 19 publications

(15 citation statements)

References 27 publications

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“…One of the present authors has further argued that in the vicinity of any chronology horizon there is an invariantly defined reliability horizon beyond which Planck scale physics comes into play [50]the region characterized by the existence of closed space-like geodesics shorter than one Planck length is a region subject to violent Planck-scale fluctuations, even if the expectation value of the stress-energy is small.…”

Section: Chronology Protectionmentioning

confidence: 66%

Faster-than-c Signals, Special Relativity, and Causality

Liberati¹,

Sonego²,

Visser³

2002

Annals of Physics

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193

188

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Motivated by the recent attention on superluminal phenomena, we investigate the compatibility between faster-than-c propagation and the fundamental principles of relativity and causality. We first argue that special relativity can easily accommodate-indeed, does not exclude-faster-than-c signaling at the kinematical level. As far as causality is concerned, it is impossible to make statements of general validity, without specifying at least some features of the tachyonic propagation. We thus focus on the Scharnhorst effect (faster-than-c photon propagation in the Casimir vacuum), which is perhaps the most plausible candidate for a physically sound realization of these phenomena. We demonstrate that in this case the faster-than-c aspects are "benign" and constrained in such a manner as to not automatically lead to causality violations. C 2002 Elsevier Science (USA)

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Section: Chronology Protectionmentioning

confidence: 66%

Faster-than-c Signals, Special Relativity, and Causality

Liberati¹,

Sonego²,

Visser³

2002

Annals of Physics

Self Cite

193

188

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“…As is often the case with reductio arguments, this reductio leaves the beholder searching for the explanatory force. Visser (1997Visser ( , 2003 has argued that the situation is even worse because the chronology horizon lies beyond the "reliability horizon," which marks the limit beyond which SCQG cannot be reliably applied. The "unreliable region" consists of points connected to themselves by spacelike geodesics shorter than the Planck length (ca.…”

Section: No-go Results Using Semi-classical Quantum Gravitymentioning

confidence: 99%

Do the laws of physics forbid the operation of time machines?

2008

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We address the question of whether it is possible to operate a time machine by manipulating matter and energy so as to manufacture closed timelike curves. This question has received a great deal of attention in the physics literature, with attempts to prove no-go theorems based on classical general relativity and various hybrid theories serving as steps along the way towards quantum gravity. Despite the effort put into these no-go theorems, there is no widely accepted definition of a time machine. We explain the conundrum that must be faced in providing a satisfactory definition and propose a resolution. Roughly, we require that all extensions of the time machine region contain closed timelike curves; the actions of the time machine operator are then sufficiently "potent" to guarantee that closed timelike curves appear. We then review no-go theorems based on classical general relativity, semi-classical quantum gravity, quantum field theory on curved spacetime, and Euclidean quantum gravity. Our verdict on the question of our title is that no result of sufficient generality to underwrite a confident "yes" has been proven. Our review of the no-go results does, however, highlight several foundational problems at the intersection of general relativity and quantum physics that lend substance to the search for an answer.

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“…Things become even more complicated when considering two additional observations. On the one hand, in [48] it was argued that huge fluctuations in the energy-momentum tensor are not always related to huge fluctuations in the geometry. On the other hand, there is the theorem by Kay, Radzikowski and Wald [49] which proves that for every compactly generated Cauchy horizon there are points at which the energy-momentum tensor cannot be defined and, hence, semiclassical Einstein equations do not hold because there is no sensible definition of its right hand-side.…”

Section: A Classical and Semiclassical Chronology Protecction Impleme...mentioning

confidence: 99%

Chronology Protection Implementation in Analogue Gravity

Barceló,

Sánchez,

García-Moreno

et al. 2022

Preprint

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Analogue gravity systems offer many insights into gravitational phenomena, both at the classical and at the semiclassical level. The existence of an underlying Minkowskian structure (or Galilean in the non-relativistic limit) in the laboratory has been argued to directly forbid the simulation of geometries with Closed Timelike Curves (CTCs) within analogue systems. We will show that this is not strictly the case. In principle, it is possible to simulate spacetimes with CTCs whenever this does not entail the presence of a chronological horizon separating region with CTCs from regions that do not have CTCs. We find an Analogue-gravity Chronology protection mechanism very similar in spirit to Hawking's Chronology Protection hypothesis. We identify the universal behaviour of analogue systems near the formation of such horizons and discuss the further implications that this analysis has from an emergent gravity perspective. Furthermore, we build explicit geometries containing CTCs, for instance spacetimes constructed from two warp-drive configurations, that might be useful for future analysis, both from a theoretical and an experimental point of view. CONTENTSI. Introduction 3 II. Attempts to simulate Gödel spacetime 6 III. A survey of some spacetimes displaying CTCs amenable to analogue gravity simulation 12 A. CTCs engineering through warp-drive bubbles 13 B. Generalized warp-drive regions 20 C. Misner and Misner-like spacetimes 23 IV. Analogue gravity simulations: Attempts to simulate CTCs 26 V. Chronology protection: lessons from analogue gravity 29 A. Classical and semiclassical chronology protecction implementation 30 B. Chronology protection implementation from a deeper causal structure 32

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The reliability horizon for semi-classical quantum gravity: metric fluctuations are often more important than back-reaction

Cited by 19 publications

References 27 publications

Faster-than-c Signals, Special Relativity, and Causality

Faster-than-c Signals, Special Relativity, and Causality

Do the laws of physics forbid the operation of time machines?

Chronology Protection Implementation in Analogue Gravity

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