Background: The properties of quantum particles and fundamental fields are the same all across the Universe. Each particle of a certain kind is identical to all other particles of that kind ("a certain kind" integrates every property a particle might have, including left/right-handedness, etc.).
The manifest reason for this is that the properties of quantum particles were determined in the very early Universe, mostly fractions of a second after the beginning of the Big Bang, through a series of very foundational, "mathematical" events, e.g., symmetry breakings (gravitation separating from all other forces at Planck time; strong from electro-weak at about 103 Planck times; electromagnetic from weak at about 10-25 seconds). From that one central event, the Big Bang, emerged the properties of all known quantum particles (as well as those that might exist, but were never observed, say axions or gravitons).
(Of course, there are larger-scaled, lower-energy particles which joined the Universe relatively much later, rather than being created in the early Big Bang, such as heavier atoms; in any case, they are not fundamental particles or hadrons; also, their properties, for example the amount of nuclear binding energy, are determined by those of fundamental, early Big Bang fields.)
So, there is a direct relation between the size and age of the early Universe and the physical processes which took place at that point in time, or the Compton wavelengths of the particles or phenomena being "created". See the examples above, regarding symmetry breakings and the separation of forces.
Therefore, intuitively it seems that the very early Universe "was a quantum particle-like entity" or was something similar to a single-particle system. In other words, such a small space could not have held a large number of particles, when its entire size was the Compton wavelength of a single particle (of course, as the Big Bang progressed, the newest particle was of lower and lower energy). For example, the 1080 electrons which exist today could only have come into existence after their fundamental properties (mass, quantum numbers) were determined in the early Big Bang.
Indeed, most/many fermions were created later, as the result of pair production and similar processes. However, even considering just the "parent" particles, photons, which originally held that (mass-)energy, the above holds true: not all photons could have been created in the very early Big Bang. At some point in time, the Universe had to switch from being the mathematical, symmetry breaking, small-size quantum factory that determined the quantum numbers, masses and other properties of particles and fields - to actually containing large amounts of those particles.
Question: when, then, did this switch occur? When did a large number of particles, which hold the enormous amount of energy in the Universe, come into existence? Since energy is conserved, that most probably happened very early, but when? Is inflation related to this issue and if so, in what manner?
Thanks in advance.