Physics has a law which states waste will always occur.

This law is The Second Law of Thermo- dynamics. It says waste always occurs because of entropy.

On the other hand, physics has another law which says energy cannot be destroyed or lost. This is The Law of Conservation of Energy.

For us mere mortals trying to understand what these both mean and how they relate to waste, it's important to understand entropy. So here's a little story to help.

Imagine you are alone and stranded on a spaceship (isolated system). While you wait for help you have to stay alive by eating (receiving energy).

Unfortunately all you have is a chicken and some corn. What would you do? There are two choices.

1) Eat the chicken and eat the corn. In this case you get the maximum amount of available energy. (Your primary need.)

2) Feed the corn to the chicken. The chicken will lay eggs. You could then eat the eggs and then the chicken. But in this case you are receiving less energy because the chicken has used up some of the corn's energy by breathing, clucking, producing droppings etc. (Secondary products for you and therefore arguably waste.)

So how does this relate to entropy, the Second Law of Thermodynamics and the Law of Conservation of Energy?

No matter what you decide to do your spaceship (isolated system) will contain the same amount of energy. This is because of the Law of Conservation of Energy. However with the second choice there is a much greater amount of entropy (while there is only a little bit of entropy in the first choice.) The energy has been devalued and is of less use to your own personal energy needs. But it hasn't disappeared. The chicken has converted it into kinetic energy (to move), thermal energy (heat) and droppings.

So what are you going to do? Eat the chicken and the corn? Or store the droppings as fertiliser and keep the chicken for a while and enjoy its very existence....your companion on a lonely cosmic journey.

by Stavros Mouslopoulos (Theoretical Particle Physicist)