I would like to guide you to the entrance of the quantum theory in this site. I would like to write the topics for the people who are not familiar with the physics. I hope you will be interested in quantum theory.
Double slit experiment
At first I would like to introduce the double slit experiment of quantum mechanics.
The above figure shows that one electron flies. There are double slit in the wall. This experiment is called "double slit experiment". The electrons collide with the wall or go through the double slit. What happens if we repeat it? Some electrons collide with the wall as shown below.
If we increase the number of electrons, we can see the following figure.
We can see the distribution of electrons in the following figure.
This is very mysterious. The electrons pass through the slit, one by one. Why can we see the interference fringes?
The state of the electronic is expressed by the following wave function.
This function is called "psi x".
The wave function is the function of complex numbers. In this experiment, there are two possibilities in the electronic. The first is the potential to pass through the slit of the left. The second is the potential to pass through the slit of the right. We add the wave functions Ψ₁ (x ) and Ψ₂ (x ) corresponding to the both potentials.
The interference occurs from this summation. It is called "superposition principle." Observation probability of electrons P(x ) is the square of the absolute value of the wave function.
However, how why does this mysterious thing occur?
Why the interference occurs?
Physicist Feynman described the following words in 1965 in the text book "The Feynman Lectures on Physics".

One might still like to ask: "How does it work? What is the machinery behind the law?"
No one has found any machinery behind the law. No one can "explain" any more than we have just "explained." No one will give you any deeper representation of the situation. We have no ideas about a more basic mechanism from which these results can be deduced.

So, we do not know the mechanism. I would like to quote Einstein's words of 1951 from the text book "Gauge Theories in Particle Physics".

All the fifty years of conscious brooding have brought me no closer to the answer to the question, "What are light quanta?" Of course today every rascal thinks he knows the answer, but he is deluding himself.

In this site, I would like to consider the mystery of the quanta with you.]