  While the transformation of flowing liquids into rigid glasses is
omnipresent, a complete understanding of vitrification remains elusive. Of the
numerous approaches aimed at solving the glass transition problem, the Random
First-Order Theory (RFOT) is the most prominent. However, the existence of the
underlying thermodynamic phase transition envisioned by RFOT remains debatable,
since its key microscopic predictions concerning the growth of amorphous order
and the nature of dynamic correlations lack experimental verification. Here, by
using holographic optical tweezers, we freeze a wall of particles in an
equilibrium configuration of a 2D colloidal glass-forming liquid and provide
direct evidence for growing amorphous order in the form of a static
point-to-set length. Most remarkably, we uncover the non-monotonic dependence
of dynamic correlations on area fraction and show that this non-monotonicity
follows directly from the change in morphology of cooperatively rearranging
regions, as predicted by RFOT. Our findings suggest that the glass transition
has a thermodynamic origin.
