On 7/29/2025 1:12 PM, Alan Grayson wrote:
It's true by construction that the eigenstates span the Hilbert space. "The Hilbert space" is the space whose bases are the eigenstates.On Tuesday, July 29, 2025 at 2:04:31 PM UTC-6 Brent Meeker wrote: On 7/29/2025 7:18 AM, Alan Grayson wrote:Assuming we know all possible results of the measurements of a quantum system, that is, the set of possible eigenvalues, and suppose we also know the associated eigenfunctions, and we write the wf of the system as a linear sum of eigenfunctions each multiplied by a complex constant, is it mathematically assumed, or proven somewhere (perhaps by Von Neumann), that these eigenfunctions are orthogonal and form a basis for the Hilbert space in which they reside? TY, AG --Yes, that's pretty much it. The physical system, including the ideal measurement, is modeled by a certain Hilbert space in which the basis states are the eigenfunctions the measurement. This is implicit in the concept of an ideal measurement as one, which if immediately repeated on the same system, returns the same value again. BrentBut is it proven or assumed the eigenfunctions in the sum are basis states which span the space? If proven, where, by whom; if not, then the construct lacks rigor. AG
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