This is part of my Limits of Language series. These ideas can be rather abstract at times.
As you walk past by a local school, you see an eager little boy break away from his friends and run towards you. He stops in front of you with an expectant look on his face.
“Why do cars go when you push the pedal?” he demands.
“The pedal gives more gas to the engine, so it goes faster,” you reply.
“Because more gas produces a more powerful expansion in the cylinders.”
“Because the energy in gasoline is proportional to its volume.”
“Because gasoline is made up of billions of tiny molecules, and they react react individually and give the same amount of energy. More volume means more energy.”
“Because the atomic forces holding those molecules together release energy when they are broken, like a spring whipping back after being stretched past the breaking point.”
“Because those atomic forces push and pull differently depending on the distance to other particles.”
You think for a moment and finally reply.
“No reason, it just is.”
Anything which is observed in the universe can be put into one of two categories.
Fundamental phenomena are those that exist for no reason other than that they exist. They just are. They cannot be said to have causes or systems underlying them. Fundamental physical laws are like this.
Emergent phenomena are those that are an expression of smaller elements. They do not just exist on their own. They are the observable output of systems which are formed from smaller parts. These smaller parts may or may not be fundamental themselves. Unless you happen to be a physicist, everything that you understand in your day-to-day life will be emergent.
Think of a car. Cars do not work because there is some physical law that says that cars should go when you push the accelerator pedal. The movement of a car in response to a pedal is caused by the way that the smaller parts of the car interact. In this case, pushing the pedal activates a sensor which interfaces with the engine computer, which sends an electrical signal to the gasoline injection valves, which then open to put more fuel into the cylinders, causing stronger explosions in the cylinders. This makes the cylinders to move faster, thus driving the crankshaft and ultimately causing the wheels to turn.
It doesn’t end there. None of the components of the car discussed so far are fundamental. All of them are composed of even smaller elements.
For example, gasoline does not burn because of some physical law which says that gasoline should ignite and expand when heated. It burns because of the behaviour of the hydrocarbon molecules that it is composed of. We say that gasoline ignites when it is heated. What this really means is that when hydrocarbon molecules are moving fast enough, something we usually say means they are heated, if they bump into an oxygen molecule, they react to form heat and waste particles.
This reaction, however, is not fundamental. There is no physical law which says hydrocarbon molecules shall react with oxygen at a certain temperature to form heat and waste particles. The behaviour of hydrocarbons is caused by the behaviour of their components. In this case, hydrocarbon and oxygen molecules are composed of groups of atoms bonded together by atomic forces.
Most physical explorations stop here, at the atomic level. For some time, scientists did view the atom as fundamental. This is not the case, however. Atoms are composed of smaller components.
Example subatomic particles are like protons, neutrons, and electrons. Protons, in turn, are composed of a set of even smaller particles called quarks.
Don’t worry. We have finally reached the end. Quarks are currently regarded by scientists as fundamental particles. Their interactions follow a set of fundamental rules. These rules are not known to have any particular causes or sub-components. They just are. This makes them fundamental.