The Lack of Observational Evidence for the Quantum Structure of Spacetime at Planck Scales

Ragazzoni, Roberto; Turatto, M.; Gäessler, Wolfgang

doi:10.1086/375046

Cited by 53 publications

(85 citation statements)

References 25 publications

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“…Thus there is a possibility [28,29] for detecting the Planck-level fluctuations predicted by the various theoretical models (parametrized by α) by using interferometric techniques to search for fringes from point sources in distant objects because of the amplification provided by the factor (l/λ) 1−α .…”

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confidence: 99%

Probing Spacetime Foam with Extragalactic Sources

Christiansen

Dam

2006

Phys. Rev. Lett.

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Due to quantum fluctuations, spacetime is probably "foamy" on very small scales. We propose to detect this texture of spacetime foam by looking for halo structures in the images of distant quasars.We find that the Very Large Telescope interferometer will be on the verge of being able to probe the fabric of spacetime when it reaches its design performance. Our method also allows us to use spacetime foam physics and physics of computation to infer the existence of dark energy/matter, independent of the evidence from recent cosmological observations.

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confidence: 99%

Probing Spacetime Foam with Extragalactic Sources

Christiansen

Dam

2006

Phys. Rev. Lett.

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“…This is clear from the ongoing debate concerning the quantitative assessment of the effects to be sought experimentally. Essentially this debate revolves around adopting the most promising phenomenological formula for the description of the gravity-induced contribution to the uncertainty in the localization of a particle after propagating over a distance x, with two (alternative) such formulas being considered most actively [15][16][17][18] …”

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confidence: 99%

Gravity's Weight on Worldline Fuzziness

Amelino‐Camelia¹,

Astuti²,

Rosati³

2012

Int. J. Mod. Phys. D

102

163

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We investigate a connection between recent results in 3D quantum gravity, providing an effective noncommutative-spacetime description, and some earlier heuristic descriptions of a quantum-gravity contribution to the fuzziness of the worldlines of particles. We show that 3D-gravity-inspired spacetime noncommutativity reflects some of the features suggested by previous heuristic arguments. Most notably, gravity-induced worldline fuzziness, while irrelevantly small on terrestrial scales, could be observably large for propagation of particles over cosmological distances.Gravitational phenomena weigh on our daily lives very noticeably, but are the phenomena whose description is most unknown at subatomic scales. A fair assessment of the present situation is that we have access to non-gravitational phenomena down to distance scales of the order of 10 −20 m (LHC scales) whereas we have so far gained access to gravitational phenomena only at scales no smaller than 10 −6 m. The challenge of quantum-gravity research is accordingly overwhelming: we have apparently solid indirect evidence (see, e.g., Refs. [1, 2]) of the necessity of a new quantum theory of both gravitational and non-gravitational phenomena with onset at a scale of the order of the minute Planck length ℓ P (∼ 10 −35 m), but any experimental guidance we could seek for attempting to describe this new realm of physics only concerns much larger distance scales.Over the last decade there has been a determined effort [2,3] attempting to improve this state of affairs by using the whole Universe as a laboratory. We focus here on an intriguing example of how this might work out, in investigations of the "spacetime-foam" scenario first discussed by John Wheeler in the 1960s [4] (also see Refs. [5-8]). In some recent studies, such as those in Refs. [9][10][11][12][13][14], the spacetimefoam intuition has guided efforts aimed at characterizing gravity-induced contributions to the "fuzziness" of the worldlines of particles. One attempts to describe the dynamics of matter particles as effectively occurring in an "environment" of short-distance quantum-gravitational degrees of freedom. And it is expected that for propagating particles with wavelength much larger than the Planck length, when it may be appropriate to integrate out these quantum-gravitational degrees of freedom, the main residual effect of short-distance gravity would indeed be an additional contribution to the fuzziness of worldlines. The idea that this might lead to testable predictions originates from heuristic arguments [9][10][11][12][15][16][17][18] suggesting that these quantum-gravity effects should grow with propagation distance. In particular this could produce an observably-large contribution to the blurring of the images of distant astrophysical sources, such as quasars [17,18].We here do not review the relevant heuristic arguments. Actually our starting point is the realization that heuristics was surely valuable for inspiring this phenomenological program, but has run out of steam as a resource ...

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“…If diffraction of light were ignored, or if we assumed a space-time with one time dimension plus one spatial dimension, our toy model would give comparable results to previous estimates on the random-walk model claimed in [1][2][3][4]. However, the diffraction of light requires us to average space-time fluctuations over all different possible optical paths that extend to all three spatial dimensions.…”

Section: Discussionmentioning

confidence: 51%

“…There have been several proposals to use extragalactic point sources to constrain the quantum fluctuations in space-time [1][2][3][4]. It was argued that, space-time fluctuations cause random phase shifts of photons, and that these shifts accumulate throughout the very long light propagation path from the point source to the earth, causing wavefront distortion from a perfect spherical shape upon arrival at the earth.…”

Section: Introductionmentioning

confidence: 99%

Photons with sub-Planckian energy cannot efficiently probe space-time foam

Chen

Wen

2014

Phys. Rev. D

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Extra-galactic sources of photons have been used to constrain space-time quantum fluctuations in the Universe. In these proposals, the fundamental "fuzziness" of distance caused by space-time quantum fluctuations has been directly identified with fluctuations in optical paths. Phase-front corrugations deduced from these optical-path fluctuations are then applied to light from extra-galactic point sources, and used to constrain various models of quantum gravity. However, when a photon propagates in three spatial dimensions, it does not follow a specific ray, but rather samples a finite, three-dimensional region around that ray-thereby averaging over space-time quantum fluctuations all through that region. We use a simple, random-walk type model to demonstrate that, once the appropriate wave optics is applied, the averaging of neighboring space-time fluctuations will cause much less distortion to the phase front. In our model, the extra suppression factor due to diffraction is the wave length in units of the Planck length, which is at least 10 29 for astronomical observations.

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The Lack of Observational Evidence for the Quantum Structure of Spacetime at Planck Scales

Cited by 53 publications

References 25 publications

Probing Spacetime Foam with Extragalactic Sources

Probing Spacetime Foam with Extragalactic Sources

Gravity's Weight on Worldline Fuzziness

Photons with sub-Planckian energy cannot efficiently probe space-time foam

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