Observational cosmologists consider the standard Big Bang model to be a good approximation to the Universe
- in spatial extent from the Earth outwards towards the observational sphere
- and in time backwards from the present towards some limiting "time=zero"
Alternatively, theoretical cosmologists have many ideas of "scenarios" of what the Universe might be like on bigger scales:
- the quasi Steady State model
- chaotic inflation
- brane models
- models including the Hartle-Hawking boundary condition in which the whole of space-time is finite
- ekpyrotic scenarios of an eternally bouncing (big banging) universe