Consider a glass box, full of water with a constant heat source at one end, and a constant heat sink (something to absorb heat energy) at the other. Dissolved in the water is some nitrogen and some carbon dioxide. One end of the box will grow quite hot, but as fast as the fire pours energy into this end of the system, it is conducted away toward the cooler end and out again. The average temperature inside the box is therefore a constant.

Consider the effect this will have on the thin soup inside the box. At the hot end of the box, the high-energy end, the molecules and atoms absorb this extra energy and are raised to excited states. As they drift around the system, these energized parts are free to form high-energy chemical bonds with each other, bonds that would have been statically impossible with the system in global equilibrium. A variety of complex compounds is therefore likely to form and to collect toward the cool end of the system, compounds of greater variety and greater complexity than could have been formed without the constant flux of heat energy. Collectively, carbon, hydrogen, oxygen and nitrogen are capable of literally millions of different chemical combinations. With the heat flux turned on, this partially open or semiclosed system starts vigorously to explore these combinatorial possibilities.

It is easy so see that some kind of competition is taking place inside the box. Some types of molecule are not very stable, and will tend to fall apart soon after formation. Other types are made of sterner stuff, and will hang around for awhile. Other types, though very unstable, may be formed very frequently, and so there will be quite a few of them in the system at any given time. Some types catalyze the formation of their own building blocks, thus enhancing further formation. Other types engage in mutually beneficial catalytic cycles, and form a symbiotic pair of prosperous types. In these ways and others, the various types of molecule compete for dominance of the liquid environment. Those types with high stability and/or high formation rates will form the largest populations.

The typical result of such a process is that the system soon displays a great many instances of a fairly small variety of distinct types of complex, energy-storing molecules. (Which types, from the millions of types possible, actually come to dominate the system is dependent on and highly sensitive to the initial make-up of the soup, and to the flux level.) The system displays an order, and a complexity, and an unbalanced energy distribution that would be unthinkable without the flux of energy through the system. The flux pumps the system. It forces the system away from its initial chaos, and towards the many forms of order and complexity of which it is capable. What was improbable has become inevitable.