Thoughts on the Paranormal

I have been researching many paranormal subjects for a few years now and even though I have learned a lot since then, more questions seem to arise. I wonder how it is that ghosts get to our dimension. Do they have to actually enter a portal from their paranormal dimension to ours, or do they accidentally get here by some other means. I have read many experiences of others that seem to suggest many different situations a ghost can be in.
One situation is that the ghost does dwell in another dimension and are permitted to visit our by the higher power, probably God. Another situation is that the ghosts go and do as they please in our dimension without any authority over them. I also wonder how and why ghosts know so much about the past,present, and future. Anyway, these are just some thoughts on the paranormal I thought I would share with everyone.