We study a model for gravity in 3+1 dimensions, inspired in general
relativity in 2+1 dimensions. In contrast regular general relativity in 3+1
dimensions, the model postulates that space in absence of matter is flat. The
requirement that the Einstein equation still holds for the complete spacetime,
implies that matter may only appear as conical defects of co-dimension 2, which
may be interpreted as straight cosmic strings moving at a constant velocity.
The study of collisions of these defects reveals that the dynamics of the model
is incomplete. Certain highly energetic collisions of almost parallel defects
suggest that no dynamic completion may exist that is fully compatible with the
principles on which the model was based. We also study the phase space of the
model in the continuum limit. We find that even though does not contain
gravitational waves at the fundamental level, they do appear as an emergent
feature in the continuum limit.Comment: PhD thesis, Utrecht Universit