// thermodynamics //

the theory:

total entropy of the system and surrounding always increase.

how my prof explained it:

Let's say your room is initially very neat, everything is in order.
As days passed, it becomes messier, resulting in a disordered state.
This does not require any energy.
However, to make your room neat again, energy is required.
Anyway, as your room becomes messier and messier and messier, day by day.
One day, you cannot even tell the difference of the state of your room as compared
to yesterday.
Equilibrium state is reached.

All this while, I was imagining the state of my room.
lol.
imagine! you can't even tell how messy is your room
and that is called equilibrium state!