Why the eigenvalues of hamiltonian are discrete in bounded systems (only discrete energy levels)?
1048
Discreteness of set of energy eigenvalues
77388
Differentiation operator and eigenvalues
42186
When is the Hamiltonian of a system not equal to its total energy?
11358
Eigenvalues of the Lagrangian?
6514
Prove $T$ has at most two distinct eigenvalues
70455
Why are all nonzero eigenvalues of the skew-symmetric real matrices pure imaginary?
10371
If photon energies are continuous and atomic energy levels are discrete, how can atoms absorb photons?
38878
Why are eigenfunctions which correspond to discrete/continuous eigenvalue spectra guaranteed to be normalizable/non-normalizable?
71040
If $ \operatorname{Tr}(M^k) = \operatorname{Tr}(N^k)\;\forall 1\leq k \leq n$, then how do we show the $M$ and $N$ have the same eigenvalues?
23089
Differences between symmetric, Hermitian, self-adjoint, and essentially self-adjoint operators
117010
What does it mean for a Hamiltonian or system to be gapped or gapless?
1584
Why does spin have a discrete spectrum?
123948
Why do I not see evidence of discrete energy in the spectrum?
66241
What can the eigenvalues of unitary matrices tell us?
112900
Eigenvalue of a polynomial evaluated in a operator
94004
Boundedness of general relativity Hamiltonian
127799
Eigenvalues of symmetric matrices are real without (!) complex numbers