I was reading up on this subject and I don’t quite understand something about it. How do we know that thermodynamics apply to the entire universe? What evidence is there in support of that claim? How does that apply to the whole universe? Is it just an assumption? Please help me out.

I am doing a research paper for Physics class, and I have the laws of thermodynamics. I know the mathematics behind them, but I need help thinking of everyday examples of how they’re used.