  We solve the Schr\"odinger equation from first principles to investigate the
many-body effects in the expansion dynamics of one-dimensional repulsively
interacting bosons released from a harmonic trap. We utilize the
multiconfigurational time-dependent Hartree method for bosons (MCTDHB) to solve
the many-body Schr\"odinger equation at high level of accuracy. The MCTDHB
basis sets are explicitly time-dependent and optimised by variational
principle. We probe the expansion dynamics by three key measures; time
evolution of one-, two- and three-body densities. We observe when the
mean-field theory results to unimodal expansion, the many-body calculation
exhibits trimodal expansion dynamics. The many-body features how the initially
fragmented bosons independently spreads out with time whereas the mean-field
pictures the expansion of the whole cloud. We also present the three different
time scale of dynamics of the inner core, outer core and the cloud as a whole.
We analyze the key role played by the dynamical fragmentation during expansion.
A Strong evidence of the many-body effects is presented in the dynamics of two-
and three-body densities which exhibit correlation hole and pronounced
delocalization effect.
