No, particles with opposite spins cannot be found in identical states. This is a consequence of the Pauli exclusion principle, which states that no two identical fermions (particles with half-integer spin, such as electrons) can occupy the exact same quantum state simultaneously.
In the context of spin, this means that if one particle has a certain spin state, such as "spin up" along a particular axis, then another particle of the same type cannot occupy the same state. If the first particle has spin up, the second particle must have spin down along that same axis.
This principle has important implications, particularly in determining the electronic structure of atoms and the behavior of particles in systems with many interacting fermions, such as in solids. It leads to the filling of electron orbitals in atoms according to the "Aufbau principle" and is crucial for understanding the stability and properties of matter.
Therefore, particles with opposite spins cannot exist in identical states due to the Pauli exclusion principle, which is a fundamental principle in quantum mechanics.