So I've heard that when a photon flies by a atom excited enough to release a photon there's a good chance it will. Because Photons want to be together and have the same direction etc?
Is this true? And then, why is it like this?
Did you here that in the context of lasers or BEC?
Photons are bosonic particles, this is generally what people refer to when they say 'they want to be together'.
I think what you are talking about is the stimulated emission of radiation. This is part of the process that occurs in a LASER and in fact, gave the LASER it's name - Light Amplification through the Simulated Emission of Radiation. When an atom is in an excited state it can spontaneously decay to a lower energy state with the emission of a photon of a particular frequency. If a photon of that same frequency passes an excited atom it can stimulate the atom to emit a second photon in the same direction and with the same phase (and frequency) as the original photon. According to Wikipedia:
The reason why two photons can have exactly the same frequency, phase and location in space is because they obey Bose-Einstein statistics. Photons have spin 1 which is why they are Bosons with Bose-Einstein statistics. If the photon were a fermion (like the spin 1/2 electron) simulated emission would not be possible since it is impossible for two fermions to occupy exactly the same quantum state.
Any particle in a system (like a photon or an electron) can be in many different energy state. You may be familiar with the energy states of atoms, these are the states occupied by electrons orbiting the nucleus.
But electron are fermions and they don't want to be together (in fact they can't). In order to minimize the energy of the atom any additional electron will occupy the lowest energy state available (but only if this energy state is empty).
On the opposite photons are bosons and they can be together. They can occupy the same energy state as the other photons. If you consider a system with many photons, any additional photon will occupy the lowest energy state wether it is already occupied by another photon or not. This is done in order to minimze the energy.
However the answer to your first question :
The answer to your second question :
is more complicated. The answer to the question "Why photons are bosons?" is very difficult. But in a general way bosons can be seen as the way for fermions to communicate. It is true in the case of photons. Photons are the way for electrons to exchange energy and thus interact.