  At Planck-scale, spacetime is "foamy" due to quantum fluctuations predicted
by quantum gravity. Here we consider the possibility of using spacetime
foam-induced phase incoherence of light from distant galaxies and gamma-ray
bursters to probe Planck-scale physics. In particular, we examine the
cumulative effects of spacetime fluctuations over a huge distance. Our analysis
shows that they are far below what is required in this approach to shed light
on the foaminess of spacetime.
