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pabloweigandt
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In Quantum Mechanics, how can you justify the use of distributions like the delta functional without introducing a rigged Hilbert space? I see that some texts do not make any reference to this subject.
Ballentine talks about this in his sections 1.3 and 1.4. In summary (p28):pabloweigandt said:What I mean is why some authors avoid mentioning or treat rigged Hibert space when they suppose to be formulating QM in a rigorous mathematical context.
In short, you can do QM rigorously without rigged Hilbert space if you don't use Dirac's formalism.pabloweigandt said:What I mean is why some authors avoid mentioning or treat rigged Hibert space when they suppose to be formulating QM in a rigorous mathematical context.
Which authors do you have in mind? Also you don't have to mention rigged Hilbert spaces to use them!pabloweigandt said:What I mean is why some authors avoid mentioning or treat rigged Hibert space when they suppose to be formulating QM in a rigorous mathematical context.
pabloweigandt said:How is that "rigorous treatment" without rigged Hilbert space?
pabloweigandt said:How is that "rigorous treatment" without rigged Hilbert space?
mattt said:Just Functional Analysis, as usually done by mathematicians.
See for example the book "Fundamental Mathematical Structures of Quantum Theory" by Valter Moretti.
George Jones said:Even though rigged Hilbert spaces make rigourous the physicists' version of the maths used in quantum mechanics, it is not strictly necessary to move out of Hilbert space. Reed and Simon advocate remaining in Hilbert space. From Reed and Simon: "There has arisen an extensive literature on a 'rigorous' Dirac notation which attempts to capture the flavour of bra and kets more fully. ... We must emphasize that we regard the spectral theorem as sufficient for any argument where a nonrigorous approach might rely on Dirac notation; thus, we only recommend the rigged space approach to readers with a strong emotional attachment to the Dirac formalism."
If you want to study the Hilbert space approach (as opposed to the rigged Hilbert space approach), then I recommend the beautiful "Quantum Theory for Mathematicians" by Brian Hall over Reed and Simon, even though I like Reed and Simon. Hall is a really wonderful book, but it has "the basics of L^2 spaces and Hilbert spaces" as prerequisites. Most of the functional analysis presented in the book is in chapters 6 - 10, through which the author gives several paths "I have tried to design this section of the book in such a way that a reader can take in as much or as little of the mathematical details as desired."
One of them, "From Classical Mechanics to Quantum Field Theory", has a totally misleading title. In this book classical mechanics is not treated at all, QFT is treated only at an elementary level, while most of the book is really about mathematical formulation of QM.mattt said:the three ones of Walter Moretti
Demystifier said:One of them, "From Classical Mechanics to Quantum Field Theory", has a totally misleading title. In this book classical mechanics is not treated at all, QFT is treated only at an elementary level, while most of the book is really about mathematical formulation of QM.
https://www.amazon.com/dp/B084GMNHCQ/?tag=pfamazon01-20
(I fixed them for you. Your edit time probably expired.)mattt said:By the way, I just noticed that the voice dictation system of my mobile phone didn't spell correctly some of the names (I cannot edit my previous post to correct it, I don't know why).
The correct names are Eberhard Zeidler and Valter Moretti.
pabloweigandt said:In Quantum Mechanics, how can you justify the use of distributions like the delta functional without introducing a rigged Hilbert space? I see that some texts do not make any reference to this subject.
yes, you are right, and the rason us that it takes too long. RHS theory is very heavy: you need topological vector space theory, nuclear space theory, abstract kernel theorem, special vector measure theories, and so on.pabloweigandt said:What I mean is why some authors avoid mentioning or treat rigged Hibert space when they suppose to be formulating QM in a rigorous mathematical context.
This might be a difference in terminology, but von Neumann's theorem is not circular, i.e. it does not assume its conclusion. It does remove a certain "natural" class of classical theories as a model for QM.vanhees71 said:but be aware that the physics part is partially flawed, particularly the no-go theorem for hidden variables, which is circular, as already realized by Grete Hermann also in the 1930ies
I know her argument, but I disagree with it.vanhees71 said:Grete Hermann argues that von Neumann's assumption that ##\langle A+B \rangle=\langle A \rangle + \langle B \rangle## to be valid for the expecation values of any observables contains already the assumption that all there is to characterize the state of the system is the "wave function" (I'd rather say "the quantum state"), which was what he wanted to prove.
A rigged Hilbert space is a mathematical framework used in quantum mechanics to describe the states of a quantum system. It consists of a Hilbert space, which is a space of infinite-dimensional vectors, along with two additional spaces known as the "dual space" and the "anti-dual space". This framework allows for a more complete description of the states of a quantum system than is possible with just a Hilbert space.
A rigged Hilbert space is necessary in quantum mechanics because it allows for the inclusion of states that cannot be represented as vectors in a Hilbert space. These states, known as generalized states, are important for describing certain physical phenomena that cannot be fully explained using traditional Hilbert space formalism.
The main difference between a rigged Hilbert space and a traditional Hilbert space is the inclusion of the dual space and anti-dual space. These spaces allow for the description of generalized states, which cannot be represented as vectors in a traditional Hilbert space. Additionally, a rigged Hilbert space has a larger set of mathematical operations and transformations that can be applied to states.
The rigged Hilbert space has many applications in quantum mechanics, including the description of quantum systems with an infinite number of degrees of freedom, such as the electromagnetic field. It is also used in quantum field theory, where it allows for the inclusion of states with indefinite particle number. Additionally, the rigged Hilbert space has applications in quantum information theory and quantum optics.
There are some controversies surrounding the use of the rigged Hilbert space in quantum mechanics, mainly regarding its mathematical rigor and whether it is necessary for describing all physical phenomena. Some physicists argue that a traditional Hilbert space is sufficient for describing quantum systems, while others believe that the rigged Hilbert space offers a more complete and accurate description. However, the rigged Hilbert space is widely accepted and used in many areas of quantum mechanics and has been shown to be a powerful and useful mathematical framework.