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).
In addition big bang clrarly 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.
A pair of spin energies is equivalent to an electron and a positron. As an electron can change to a positron by turning upside down, both are identical, so these are generally called electrons by New Physics and there is only one fundamental type of particles in universe.
The generation of electrons stopped as soon as the space of the universe was filled, because then energy would be necessary for generation to push away already generated elrectrons.
Spin orientations of generated electrons were random. After generation collisions occured, by which the fundamental particles tried to annihilate themselves by overlapping. The only active force in universe is that electrons intend to move to the postion of lowest spin energy. It is luck for mankind that complete annihilation is only possible in the very beginning of interactions and when the collisions are done exactly against poles with exactly opposite directions. All other collisions will just cause partly overlapping, which is equivalent to a bonding. The only passive force according to the universal principles is to maintain the current movement. This overall leads to a vibration movement with the position of minimum spin energy at the center. By this the reduced spin energy is transformed to vibration energy, so that the total energy over all times stays stable at zero. The total energy of an object (particle or body) is defined as the sum of spin energies over all bonded electrons plus the sum of vibration energies over all bonded electrons.
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 universe is well defined by New Physics.