The horizon problem (homogeneity problem) arises due to the difficulty in explaining the observed homogeneity of casually disconnected regions of space in the absence of a mechanism that sets the same initial conditions everywhere. The size of the universe is too large for homogeneity, since thermalization faster than the speed of light is considered impossible.
I propose the simplest solution of this problem based on the proposal that the universe in its early stages was not in a hot state but in a pure, metastable quantum state:
Melkikh A.V. A pure quantum universe as an alternative to inflation
Article A pure quantum universe as an alternative to inflation
If the moving particles of the universe were entangled with each other, then these particles will simultaneously transit into their mixed state, no matter how far apart they are. This means that their further thermalization (associated with the creation and annihilation of other particles) will depend on the degree of entanglement of the initial state, but not on the size of the system.