New Constraints on Quantum Gravity from X-ray and Gamma-Ray Observations

Understand

One aspect of the quantum nature of spacetime is its "foaminess" at very small scales.

• Many models for spacetime foam are defined by the accumulation power $\alpha$, which parameterizes the rate at which Planck-scale spatial uncertainties (and thephase shifts they produce) may accumulate over large path-lengths.
• Here $\alpha$ is defined by theexpression for the path-length fluctuations, $\delta \ell$, of a source at distance $\ell$, wherein $\delta \ell \simeq \ell^{1 - \alpha} \ell_P^{\alpha}$, with $\ell_P$ being the Planck length.
• We reassess previous proposals to use astronomical observations ofdistant quasars and AGN to test models of spacetime foam.