What could be past the particle horizon? Forgive any kind of "dumb" question I may ask as this is a new interest of mine and I know it's purely hypothetical. 

If one were able to surpass light speed and the expansion of space to go beyond the particle horizon, what could be out there? Could it just be an empty void? Could it loop around to the other side of the particle horizon? I'd love to read about any kind of theories or research done on this subject.
It sounds like your question is about the single most important principle of cosmology, called the cosmological principle.  This asserts that as long as all our observations are consistent with the idea that the universe is the same everywhere at a given age, we will continue to use a model with that attribute.  There are lots of good reasons for adopting that principle, the least of which is not that it allows us to have a model in the first place.  So what this means is, our answer to what is beyond what we can see is that we don't know, but we are going to model it in a way that makes sense to us, so we will use the cosmological principle.   You have to be able to distinguish what we know in the sense of having direct information about, versus what we know about our own best models.