Currently there is no theory concerning generation of the universe, as the big bang theory does not start from nothing (zero matter and zero energy).
Big bang is an physically impossible theory because it starts with a physically impossible state: singularity, ultra small, ultra high density, ultra high temperature, ultra high energy.
The universe has been generated by pairs of opposite spheric spin energies (see separate page: from nothing to universe). The pairs separated along their spin axes, so that at all positions the spin energies were compensated. This means there was no need for energy for separation. After separation the spin energies moved with same velocities to opposite directions. Acceleration also did not need energy as FPs do not have mass. (Mass is well defined by New Physics).
The generated spin energies are called fundamental particles FPs.
All FPs have same size, which means that there is just one type of fundamental particle in space.
The generation of FPs stopped as soon as the space of the universe was filled, because then energy would be necessary for generation to push away already generated FPs.
Spin orientations of generated FPs were random. After generation well defined interactions according the unique CBD-mechanism occured.
As the density of omnipresent particles in universe does not change, the size of the universe is constant. All matter in universe including matter at the limit of the universeis well defined by New Physics.