We humans are victims of common sense. If something is common to me then it must be common to all of us. Unfortunately, vast–and also tiny–sectors of the universe are uncommon to our senses.
The first step to develop a working knowledge of quantum physics is to abandon your belief that anything valuble should fall within the bounds of common sense. Do not worry that I will burden you with an explanation of Schrodinger’s Cat. You probably would not understand me. Honestly, I do not think I understand it. No one really understands Schrodinger’s Cat.
Quantum means small, subatomic small. The word subatomic is a self contradiction. Atom means smallest. According to its most basic definition an atom cannot be broken into smaller parts. Essentially, subatomic means smaller than the smallest.
The word atom represents an influential philosophical breakthrough. Atom arose from the Ancient Greek word, atomos. In the 21st century, we know atoms are not smallest. But just the idea that all matter is made of tiny, indivisible things was a tremendous realization.
Fundamental is probably the best word to represent these tiny, indivisible things.
We continue to search for fundamental entities. These fundamental entities are often called particles in modern physics. The study of particles is the essence of quantum physics. Unfortunately, when we observe the smallest things, classical physics breaks down.
(Classical physics is precisely predictable and mostly algebra-based. Isaac Newton revealed the foundations of classical physics about three centuries ago. Calculus applies marvellously to classical physics too, but algebra is enough to communicate the principal ideas of the subject. By the way, Isaac Newton invented calculus. Classical physics is pretty much all that is taught at the high school level. It is a bit boring after you learn modern physics, so let us get back to the more exciting stuff.)
The most likely candidates for particles of matter appear to be quarks and electrons. There are other particles of matter, but quarks and electrons will serve as excellent representatives for all matter particles during this post.
Our common sense often informs us that nature is fluid and infinitely divisible; continuous may be the best word for this apparent fluidity of the universe. Water running from a hose seems to be a continuous flow of stuff that we can keep dividing forever.
A water stream is effectively modeled using a basic mathematical concept: the number line. According to basic geometric definitions a line can be divided into an infinite number of segments. We could also say a line has an infinite number of points or positions.
A number line is an abstraction. The abstraction only applies under ideal conditions. Experimental evidence indicates that a water stream can be divided into a finite number of discrete particles called water molecules.
Those molecules are made of atoms. Atoms are made of protons, neutrons electrons.
Electrons are the smallest of the three. It would take nearly 2000 electrons to equal the mass as a proton or neutron. Electrons have a mass of 0.00000000000000000000000000000091 kg. Although there are about a billion billion billion electrons in a human, there is nothing common to our senses about an individual electron.
An electron is so small that looking at one would change its nature. We see objects when photons reflect off those objects: the photons deliver information to our brain via our eyes.
Photons are light-energy particles.
An electron is so small that when a photon bounces off an electron, the electron’s nature is changed: the reflected photon delivers outdated information about the electron to our eyes.
Classically speaking, an electron is not observable. But when not observing an electron it is not really there. An Electron is everywhere in space-time when not observed. It is more likely to be in some places and times compared to others but we can never know for certain. Once observed, the electron becomes what the observation compels!