Are all eigenstates of observables orthogonal?

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The discussion centers on the orthogonality of eigenstates in quantum mechanics, specifically addressing the relationship between eigenstates of observables O1 and O2. It is established that if two eigenstates, psi1 and psi2, share the same eigenvalue for observable O1, they are not necessarily orthogonal unless they differ in their eigenvalues for observable O2. The example of hydrogen is cited, illustrating that eigenstates can be degenerate, meaning multiple eigenstates correspond to the same eigenvalue, yet remain orthogonal due to differing quantum numbers. This clarifies the conditions under which eigenstates are orthogonal.

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Suppose psi1 and psi2 are eigenstates of observables O1 and O2

Suppose Value of O1 of psi1 = value of O1 of psi2

Therefore, <psi1|psi2>=1

Suppose value of O2 of psi1<>value of O2 of psi2

Therefore <psi1|psi2>=0

Contradiction!how to explain
 
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AlonsoMcLaren said:
Suppose psi1 and psi2 are eigenstates of observables O1 and O2

Suppose Value of O1 of psi1 = value of O1 of psi2

Therefore, <psi1|psi2>=1

This is not correct. Eigenvalues can be degenerate; that is, there can be more than one eigenstate for a particular eigenvalue. Example: in hydrogen, the energy only depends on the quantum number n, and not on the angular-momentum quantum numbers l and m. Eigenstates with the same value of n (and hence the same energy eigenvalue), but different values of l or m, are orthogonal.
 

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