It never crossed my mind to ask about temperatures below absolute zero. My science tells me that this corresponds to zero motion = zero energy. That is why you cannot reach it since it would require heat transfer from another object of temperature below that condition.
Cat
I don't believe zero motion is possible. In other words, energy must always be able to remain energetic to remain in existence. Any attempt to still it forces it to take the easiest available escape route. Perhaps a better understanding of quantum mechanics will provide more clues. I believe this because the conservation of energy law would otherwise be null and void. I've seen no evidence that suggests energy can either be 'disappeared' or emerge from a void.
Speaking of voids, I believe they are figments of the imagination and that there isn't a place where energy doesn't exist to manufacture the necessary space-time to remain active. I believe energy does this on multi-dimensional levels that are beyond our comprehension.
I've seen no evidence to suggest the energy within the universe is not eternal. However, there is no way to prove reality, or all of the energy in existence, is infinite. To believe there is no end to it, that the energy 'within' reality just goes on and on infinitely is a bit hard to swallow. That would mean there is no 'within' reality because there would be no end to it- no border and no limit to the amount of energy in existence. That's a lot harder for me to swallow than a finite amount of energy within reality, even though we'll never be able to pin a number on just how much energy there is and how vast reality is. The universe may have nothing more to offer than a glimpse of a far more complex reality.