Cosmic Bubble Collisions: Observable Signature of a Classical Transition

The theory of inflation was introduced to resolve many existing observational problems in cosmology. Inflation becomes eternal when a region of space continuously spawns non-inflation regions. This process arises from metastable vacua in a potential landscape. Our universe could be a realization of one of these many vacua predicted by the theory. In this thesis, we explored the idea that a universe can be born via a collision between two bubble universes. This process is known as a ``Classical Transition''. In this thesis, the potential observability of relics produced during the collision is studied. If a classical transition did happen in the past, its presence is imprinted on the CMB temperature anisotropy.