No quantum gravity signature from the farthest quasars

Abstract

Context. Strings and other alternative theories describing the quantum properties of space-time suggest that space-time could present a foamy structure and also that, in certain cases, quantum gravity (QG) may manifest at energies much below the Planck scale. One of the observable effects could be the degradation of the diffraction images of distant sources. Aims. We searched for this degradation effect, caused by QG fluctuations, in the light of the farthest quasars (QSOs) observed by the Hubble Space Telescope with the aim of setting new limits on the fluctuations of the space-time foam and QG models. Methods. We developed a software that estimates and compares the phase variation in the interference patterns of the high-redshift QSOs, taken from the snapshot survey of HST-SDSS, with those of stars that are expected to not be affected by QG effects. We used a two-parameter function to determine, for each test star and QSO, the maximum of the diffraction pattern and to calculate the Strehl ratio. Results. Our results go far beyond those already present in the literature. By adopting the most conservative approach where the correction terms, that describe the possibility for space-time fluctuations cumulating across long distances and partially compensate for the effects of the phase variations, are taken into account. We exclude the random walk model and most of the holographic models of the space-time foam. Without considering these correction terms, all the main QG scenarios are excluded. Finally, our results show the absence of any directional dependence of QG effects and the validity of the cosmological principle with an independent method; that is, viewed on a large scale, the properties of the Universe are the same for all observers, including the effects of space-time fluctuations.

Using observations of distant quasars to constrain quantum gravity

“…1 represents trajectories for δψ versus λ that are specified by α, this reduction in halo size leads to a reduction in the limiting value of α that can be determined from observations. Tamburini et al (2011) claim that current data exclude models with α < 0.68 (a 0 ∼ 1, including the holographic model which has α = 2/3) (the "red zone" in their Fig. 5).…”

“…The diagonal lines in Fig. 1 show predictions for the size of the seeing disk for different models of spacetime foam, for a source at redshift z = 6.3, which represents the highest redshift quasar examined by Tamburini et al (2011). We note that δψ in Fig.…”

“…We note that δψ in Fig. 1 is a factor of 2π smaller than the phase, Δφ, which was used incorrectly by Tamburini et al (2011) to calculate expected halo size. In the case of a non-detection of angular broadening, the region above the diagonal line for a given α may be excluded.…”

“…In the bottom plot, we specifically show the case of a z = 6.3 quasar, as examined by Tamburini et al (2011), for an observed wavelength of 400 nm. As in Fig.…”

“…We concentrate particularly on a recent paper by Tamburini et al (2011), published in Astronomy & Astrophysics in September 2011. Some of the points discussed below were discussed in our own paper Christiansen et al (2011), which was published nine months earlier.…”