  Due to the quasi-exponential red-shifting which occurs during an inflationary
period in the very early Universe, wavelengths which at the present time
correspond to cosmological lengths are in general sub-Planckian during the
early stages of inflation. This talk discusses two approaches to addressing
this issue which both indicate that the standard predictions of inflationary
cosmology - made using classical general relativity and weakly coupled scalar
matter field theory - are not robust against changes in the physics on
trans-Planckian scales. One approach makes use of modified dispersion relations
for a usual free field scalar matter theory, the other uses some properties of
space-time non-commutativity - a feature expected in string theory. Thus, it is
possible that cosmological observations may be used as a window to explore
trans-Planckian physics. We also speculate on a novel way of obtaining
inflation based on modified dispersion relations for ordinary radiation.
