  In the framework of inflation, scales which nowadays correspond to large
scale structures were smaller than the Planck length at the beginning of
inflation. Therefore, measurements of CMBR anisotropy or surveys of galaxies
and of clusters of galaxies could help us to probe physics beyond the Planck
scale. In these proceedings, we study how the inflationary observables depend
on trans-Planckian physics. It is found that there exist cases where
adiabaticity can be violated and the primordial spectrum of the quantum
cosmological perturbations modified. These cases correspond to rather drastic
alterations of the dispersion relation. There exist also modifications of the
standard physics which leave the power spectrum unchanged and therefore which
are compatible with the data. In this sense, the presently available
observations already constrain trans-Planckian physics.
