The following video shows the different scales of the universe:

Let's list the different scales:

• Universe: 10²⁶m,
• Galaxy: 10²¹m,
• Sun: 10⁹m,
• Earth: 10⁷m,
• Humankind: 1m,
• Blood cell: 10^-6m,
• Water molecule: 10^-9m,
• Electron: 10^-15m.

Quantum means “the minimum amount of any physical entity”. That is to say something that cannot be split again.
More generally, we say “quantum” (or quanta, the plural) when we speak about the infinitely small.

Different scales means different laws. For instance in the solar system (1,2.10¹³m) the gravity is the major force.
But at electron level laws are very different. Gravity depends on the mass, and the mass of an electron is 9,1.10^-31 kg, at this scale of infinitely small, the gravity has no effect (or almost: let's say negligible).

The question that follows is: what forces are applicable at quantum level? Well there are several:

• Strong interaction,
• Electroweak interaction,
• Weak interaction,
• Gravitation ?

Since I'm not an expert, I won't be able to describe in detail these forces. But different forces means different behaviors.

Therefore in quantum world, laws and behaviors are different than laws of our scale. In the next chapter we'll describe some of those strange behaviors.