During the Big Bang, when atoms are forming, as the number of atom formation increasing, the rate of atom production were also increasing at par with the production. That means, if the number of atoms produced becomes 1 billion, its rate of production also increased by 1 billion times & so on. This formation with the multiplayer effect became so rapid & so fast that ultimately, it led to the inflation of the universe. This process is still going on at the edge of the universe even now & hence the universe is expanding.
During the formation of these atoms, the tiny dots surrounding it, which we usually see on television when not broadcasting & which is actually the residue of cosmic background radiation (CBR), are actually photons or pixels, which in turn during inflation of the universe transformed into empty space & attained transparency. That means early photons can be compared with pixels, later on which became empty space. That's why our universe along with its space or voids is actually bounded by lights & for which light speed is constant & highest compared to all other things.