[en] In this thesis, we first give an introduction to the holographic principle by reviewing the basics of bosonic and supersymmetric string theory. Afterwards, we will motivate the holographic principle and give more details about its specific realization in the context of AdS/CFT. The discussion of the physical relevance of this thesis is then divided into two parts. In the first part, we will make use of the holographic principle to model Heavy Ion Collisions (HICs) by two colliding lumps of energy in a CFT. Through the holographic principle, this is mapped to the collision of gravitational shockwaves in an asymptotically AdS spacetime. To reduce complexity we will consider shocks which are infinitely extended in the transverse direction. We will motivate that this can be seen as the first order in a gradient expansion of an off-center collision with finite transverse extent. We find that the post-collision hydrodynamic flow is very well described by appropriate averages of the symmetric collision. Chesler, Kilbertus and van der Schee give an analytic expression for the proper energy density. In a similar manner, we found an approximation which models initial data for hydrodynamic simulations without the need for cumbersome holographic calculations. In the second part, we study entanglement entropy in SU(N) Yang-Mills (YM) theory. One of the motivations for this was to test how fast the N to infinity limit is reached. Entanglement entropy, or to be more precise the entropic C-function, can be calculated both in holography (for N to infinity) and in lattice gauge theory (for finite N) which then allows a comparison for these theories. Holography predicts a sharp jump for the entropic C-function in a slap shaped geometry at some finite slap length l. In lattice simulations we find a smooth transition from O(N${}_c^2$-1) down to a value compatible with zero for this observable. Within the statistics achieved in this work, the slope for SU(4) is larger than for SU(3) supporting the holographic scenario.