What are you taking as your "closed system"? What is a closed system for most may not be so closed for some.
Total Eclipse
The Emissary arrives in many disguises,
A shutter that opens and closes.
Two freeze time in a frame
Of painful and awkward poses.
Two charge and recharge the battery,
Repulsed by the Earth as a rocket.
Two ride on the wings of some lofty being.
I keep my Aim in my pocket.
Picture a tunnel (a cube, if you will)
With interchanging faces.
Which side has the door
Through which I might slide?
They taught me in School of such spaces.
. ............................ Spiral of Friends
It was an extension of what merej99 suggested. The fact that we have a finite amount of energy which can neither be dissipated or more created. Only re-arranged.
That may or may not be true for the Universe as a whole - I have no way of knowing and speculation is useless. But that energy cannot enter or leave a given subsystem of the Universe as a whole is certainly not true. Take the Earth within our solar system - energy both enters and leaves the earth. Take the thin skin of biological life upon the Earth. Energy both enters and leaves it. Take the tiny sub-system of humanity within the thin skin of organic life upon the Earth. Energy both enters and leaves.
Do you see where I am going with the anologies?