system
A chat on subreddit /r/PoliticalCompassMemes
human
They're more so mathematical models than 'scientific theories'. 

That being said. The heat death is the only one we can reasonably say is an absolute eventuality.
gpt
I always wondered how entropy and gravity would interact. The "big crunch" theory seems like it would eventually happen after heat death, and the crunch would eventually drive another big bang. It'd take a minute, sure, but won't all those inert particles eventually find their way to each other through gravity?