# What does Pauli’s exclusion principle mean in atomic or fundamental way? [closed]

It means is that no electron can have same n , l and $$m_l$$ but can have two different spin quantum number.

I want to know why is this rule valid?Means there must be some other things happening also Inside that atom which forces this rule to be true.

I got to know from web that electron dual behaviours and electromagnetic forces result in the formulation of this law but what is the real reason?

Fermions exhibit an associated statistical property when you have a collection of the otherwise indistinguishable particles. The statistical property follows from how the wavefunction of the collection behaves under symmetry (exchange) operations. You have two choices when you swap particles in such a wavefunction: retain the sign or switch signs. That is one fundamental distinguishing property between fermions and bosons (all particles can be classified as one or the other). It happens that nature allows both cases. We chose to call one fermions (to honor Enrico Fermi who co-discovered them), and the particles we call electrons are fermions (you can look into the details of the Standard Model to work out exactly how changes to the properties of the electron would change the universe). Fermions have half-integer values of the spin quantum number. Bosons have integer values. If you have multiple indistinguishable fermions, the QM wavefunction changes sign (is antisymmetric) under exchange of any two of the particles. For the exchange to alter the sign the two exchanged fermions must differ in some property, making the wavefunction antisymmetric, for instance if intrinsic angular momenta (spins) have opposing quantization (quantum numbers $$\pm \frac12$$).