I just felt a 'click' with my last post. Forget the concept of 'hot' at the first level: what if we reduced the model to one of 'speed'? If the base of our universe was an element moving too fast for us to detect it, and everything else built upon it that we could see 'slower', the difference between differing speeds could be the origin of what we call 'high energy' or 'heat'. This would also explain phenomena such as black holes if these were regions where, although they were created through a high accumulation of atom mass, forces became so dense that even atoms were reduced - thus accelerated - to their 'undetectable' base energy form and speed?
The above would also explain 'dark matter'.