Explain the fundamental premise of String Theory in the context of unifying General Relativity and Quantum Mechanics. Describe the shift from point-like particles to one-dimensional vibrating strings. Discuss how different vibrational modes correspond to different particles (gravitons, photons, etc.). Address the theoretical requirement of extra spatial dimensions (10 or 26) and the concept of Calabi-Yau manifolds. Conclude with the current state of the theory regarding falsifiability and experimental evidence.