Dear Deepak, because the geometry simply cannot work in the same way for sub-Planckian ultrashort distances – the usual notions of geometry break down, the quantum fluctuations of proper lengths are of order 100%, the topology of spacetime is spontaneously changing over there (quantum foam), etc. The spacetime with gravity can’t be the same or self-similar at/beneath the Planck scale. Even wrong theories of quantum gravity such as loop quantum gravity clearly imply this – in the LQG case, the proper areas can’t be nonzero but much smaller than the Planck area (quantization). Think about it. – Lubos Motl Mar 24 ’11 at 5:36

2012.01.10 Tuesday ACHK