The nature of energy. Conservation of energy. The second law of thermodynamics. Heat will not flow spontaneously from a cool to a warm body 2. You cannot construct an engine that does nothing but convert heat to useful work.
Every isolated system becomes more disordered with time.
Heat is always lost. Anywhere in the universe we find that the behavior of energy is regular and predictable. The total amount of energy is a constant, though it is constantly changing form. But the changes in form are constrained to go in certain directions. Heat will not flow spontaneously from a cold to a warm body.