Such a state is less ordered, or more disordered, than the original state in which all the molecules were in one half. Likewise if one side contains a different gas then removing the partition will cause the gases to mix, creating a uniform mixture of the two gases and creating a less ordered state. This is just a simple example applying to gases but in truth entropy is a rough law that applies to all systems, including those that exchange information. If entropy had its way the whole universe would be a soup of equal density, temperature and composition. The second law of thermodynamics states that, unless a system is a closed system, entropy will always increase and the whole become more chaotic.
Life is about the fight against entropy.
It does this by absorbing, or eating, energy from the surrounding environment. If Earth was too hot, we'd die, too cold and we'd freeze and also die. It appears that our version of life likes a certain temperature band. This may be obvious but it is an important point as we will see. Chris Langton is one of the continuing chain of people responsible for major breakthroughs in Alife.