I actually didn't. I am a mathematical physicist. I do research in special functions and supersymmetry. I will be publishing a paper in both areas topics by the end of summer.
Absolute negative temperatures =/= below 0K. That's all it is.
I don't know why that is is hard for you to understand. The Max Planck institute in Munich arguably the leading institute in research on absolute negative temperatures. It is one of the first things on their FAQ.
I'm well aware I'm not the most versed person on absolute negative temperatures, that's why I cited them. If the institute that is the leading edge in this research has "there is no such thing as less than 0K" in the FAQ, I'm going to take that as the truth over some douche on Reddit that took an into level statistical mechanics course that thinks he knows better than the Max Planck institute.
When I was in undergrad I had a lengthy discussion with my advanced mechanics professor who does research in condensed matter and experimental particle physics on this exact topic. My thoughts were exactly the same as yours. He looked into it for about a week and told me the exact same thing I'm telling you.
If you are just trying to get a rise out of me by trying to insult me, question my experience as a researcher, or try to teach me basic concepts from an intro level statistical mechanics course then you are going to have a really hard life ahead of you.
Remember when you learned a cross product gives you a vector back and then in a mathematical physics course you learned it doesn't give you a vector back?
Remember when you learned the equations of motion and then learned about special relativity and learned they were wrong?
Remember when you learned gravity was a force and then you took general relativity and found out it wasn't?
Remember when you learned intuitively what a continuous function was and then took an analysis course and cantor fucked your shit up?
Well I remember most of those things. I bet you are probably in the middle of most of that now. Good luck.