The next step now is to explore the possibility for the Universe to have a beginning. The question that comes to mind is how an infinite Universe could begin its existence.
The first and easiest answer to this question is that time, like space, is infinite and therefore does not have a beginning nor an end. This however does not leave us with much space for discussions denying us all the fun.
Assuming that there was a beginning we can imagine the fabric of spacetime to be full of fluctuations in the same way there are waves and currents in the sea or a lake. This fluctuations of spacetime produce energy, and from energy to mass is merely a question of extending the theory of evolution, hence we would have that, in due time, energy would evolve into mass. At the end of the day mass is simply energy that is somehow locked into itself.
On the other hand, the sea is full of waves because there are currents and winds that agitate its surface (assuming that there would not be bodies in the sea). In the same way the fabric of spacetime is fluctuating because there are stars and galaxies that shake its fabric producing what we know today as gravitational waves.
If we suppose that there are no celestial bodies in the Universe, as it would be if there was a beginning, then the lattice of spacetime would have no reason for fluctuating. Again we could assume that two very distant regions of spacetime would have a slightly different potential or stretching and would one day meet to produce the first lump of energy. This assumption is, however, quite unsatisfactory as would not answer the question why there should be two regions with different stretching. The last possibility we are left with is that there was a "divine pinch" in the fabric of spacetime, and from there everything evolved to what we are today.