From: Osher Doctorow on
From Osher Doctorow

Rigged Hilbert Space (RHS) rather than Hilbert Space turned out to be
the correct space for Quantum Mechanics, although physicists now
usually refer to RHS as "Hilbert Space" for simplicity. See:

1) Rafael de la Madrid, "The role of the Rigged Hilbert Space in
Quantum Mechanics," 31 pages, arXiv: quant-ph/0502053 v1 9 Feb 2005

and Arno R. Bohm (U. Texas Austin) Phys. Rev. D71 2005 085018 among
others.

It turned out that expectations, uncertainties, commutation relations
were not defined on the whole Hilbert Space for unbounded observables
with continuous spectrum, including continuous and resonance
spectra. The theory of Distributions was used to solve or repair
this difficulty, the word "Rigged" referring to "equipped (with
additional things)", and it has many relationships to Probability
theory.

The Dilemma in P(A-->B) - P(B|A) taking on values between 0 and 1 is a
somewhat analogous dilemma, because of the following:

2) If u and v are variables in [0, 1] and u - v takes values from 0 to
1 either inclusively (including 0 and 1) or non-inclusively (except
for 0 and/or 1), then the "variation" in a generalized sense between u
and v is as large as the range of u and of v (inclusively or non-
inclusively).

It is thus necessary to have two theories: one for P(A-->B) (Probable
Causation/Influence) and one for P(B|A) (Conditional Probability), and
to compare the predictions from each, rather than leave the question
of whether one is using one or the other "undecided" or even
"negative" (only using one of the two).

Since physics and mathematics already use P(B|A), therefore P(A-->B)
needs to supplement the former in both fields and applications.

There are 22 papers in arXiv on "Rigged Hilbert Space," from 1995
through 2006. The ending of arXiv contributions in 2006 was because
the incorporation of Rigged Hilbert Space into Quantum Mechanics was
regarded as completely solved. Wikipedia's article "Rigged Hilbert
Space" includes the de la Madrid reference, but surprisingly omits to
mention its main uses!

Osher Doctorow