So the subject's question should be revised to the minimum initial volume of the expansion of the universe. Where is it? What is the object that constitutes the smallest volume, and how does it produce all kinds of basic particles, that is, matter, through expansion?
Because nature is discontinuous, there is qualitative change. Our universe is only a part of nature. In addition, nature is just an abstract philosophical concept, which is infinite and an open concept; The creation of our universe is a concrete physical concept, limited and a closed object.
Therefore, according to the basic principle of human understanding, "all concrete things are limited", our universe is a closed system that exists independently relative to nature, that is, relative to its external space.
As a concrete closed system, our universe has a certain volume outside, but there must be a limited number of undivided smallest particles inside. So the smallest volume of the universe is the sum of the volumes of these smallest particles, and the initial state of the universe is the plasma state where these smallest particles gather.
As a closed system, like a balloon, whether the universe expands or not and the rate of change of the universe are all determined by the ratio of internal and external space pressures, that is, by the spatial energy density composed of the smallest particles inside and outside the universe.
The so-called space is the physical background of discrete particles. The most basic space that determines the existence of the universe is the physical background composed of the smallest particles. For this background, we call it quantum space.
Therefore, when the universe shrinks to the point where the space quantum spacing approaches zero, the energy density of quantum space in the universe will increase sharply, which leads to the reversal of the change of the universe, from contraction to expansion.
The initial expansion of the universe is very intense, so it is commonly known as BIGBANG. In essence, the smallest particles in the universe, that is, quanta, are rapidly moving away from each other, that is, the distance between quanta is increasing.
Because of the initial expansion of the universe, its expansion speed is much faster than the quantum propagation speed in the universe. So the quantum space in the universe will become more and more unbalanced with the expansion of the universe.
In this way, the local high-energy quantum will form a closed system with the help of the shielding effect of quantum motion, and produce various basic particles, that is, substances.
Thus, in the universe, from the original single plasma state, a new existing state is differentiated, that is, an energy aggregation state is produced.
Therefore, there are two different states in the universe. Discrete quantum constitutes the physical background of the universe, and closed quantum system becomes the physical object of the universe.
The former is called space, and the latter is what we commonly call matter; The former belongs to the category of energy, that is, the measurement of the movement ability of open particles, while the latter belongs to the category of quality, that is, the measurement of the spatial effect of closed particles.
With the expansion of the universe, the ratio of energy density between the internal and external quantum space of the universe will change and decrease accordingly, thus making the expansion of the universe tend to be gentle, and the expansion speed of the universe is far lower than its internal propagation speed (light speed).
In this way, the inner space of the universe will gradually become balanced, and there will be no closed system that produces quantum. Thus, in the universe, the original energy is transformed into mass, and mass is transformed into energy.
This is why what we are seeing now is that mass becomes energy. In this sense, matter is only a by-product of the rapid expansion of the universe, and it is a slow-release device of energy in the universe, which plays a role in balancing the universe and maintaining its stable existence.
In short, our universe does not exist in isolation. The universe is the smallest and exists in a wider external quantum space. The initial composition of the universe is that the smallest particle is called quantum, so the sum of their volumes is the lower limit of the universe volume.