The origin of UHECR’s is a mystery, notwithstanding the fact that they were discovered 100 years ago.
In my opinion UHECR’s originate from Black Holes or more precisely from the Interchange Horizons of Black Holes in cases of decreasing distances between Black Holes and their Interchange Horizons (see post 19). This can be explained as follows.
In a Black Hole the course of time is extreme slow due to the enormous gravitational pull or time-delay by the mass of the Black Hole. The increase of entropy in a Black Hole evolves at a slower rate than the increase of entropy outside the Black Hole. The difference between the process of time in the centre of a Black Hole and the course of time at its Interchange Horizon is very big. This implicates that the differences in temperature must be very big also due to the thermodynamical effects caused by the time-differences. By the same token singularities cannot exist.
If a Black Hole is subject to time-acceleration (the process of accelerating expansion of the universe is caused by time-acceleration), the process of growth of entropy in the Black Hole evolves at an increasing rate. The circumference of the Interchange Horizon decreases. The energy of rays disappearing from the Interchange Horizon into space increases (increasing wavelengths and increasing amplitude heigths). The mass of the Black Hole decreases (see also post 13).
As explained in earlier posts the accelerating expansion of the universe is accompanied by the emission of energy like the Cosmic Microwave Background Radiation (CMBR), energy emitted by masses moving away from each other.
The difference between the masses involved is the only difference between the origins of UHECR and CMBR (see also post 15).