Hilbert space Definition and 236 Threads

Dirac's bra-ket formalism implicitly assumed that there was a Hilbert space of ket vectors representing quantum states, that there were self-adjoint linear operators defined everywhere on that space representing observables, and that the eigenvectors of any such operator formed an orthogonal...

So, I've found the result that orthonormal sequences in Hilbert spaces always converge weakly to zero. I've only found wikipedia's "small proof" of this statement, though I have found the statement itself in many places, textbooks and such. I've come to understand that this property follows...

In QM a system is represented by a Hilbert Space rather than a classical Phase Space. So, system A might be described by Hilbert Space Ha and system B might be described by Hilbert Space Hb. Mathematically, Hilbert Spaces are many things, but the first thing they are, at the most fundamental...

How long does it take for newly discovered math material or physics material to be standardized into the math undergrad curriculum? Just wondering about hilbert space as well. When did hilbert space first go into the undergrad curriculum?

I am sure that my questions are stupid. If we have a Hilbert space H, what do we mean by the closed subspace of H. Also, Does every Hilbert space have an identity? :P. Could anyone please clean to me these things . Thanks!

The inner product is supposed to give the probability amplitude for state u turning into state v. Taking a little mini-universe of two dimensions in the complex plane if I rotate vector u by multiplying it by scalar a to get vector v, then I end up that a = u*v/(||u||.||v||); given that the...

Hi, I was reading a paper on control of the 1-D heat equation with boundary control, the equation being \frac{\partial u(x,t)}{\partial x}= \frac{\partial^2 u(x,t)}{\partial x^2} with boundary conditions: u(0,t)=0 and u_x(1,t)=w(t), where w(t) is the control input. The authors...

Please can anyone help me to display the meaning of Hilbert Space?

Hello, Given a system and an observable that one wants to measure in it, how does on get the (or a?) relevant hilbert space and the suitable operator in it? The examples I've come across so far seem to rely on... well, I'd call it "vague reasoning", but the word 'reasoning' seems too much. It...

Suppose T is an injective linear operator densely defined on a Hilbert space \mathcal H. Does it follow that \mathcal R(T) is dense in \mathcal H? It seems right, but I can't make the proof work... There is a theorem that speaks to this issue in Kreyszig, and also in the notes provided by my...

Rafael de la Madrid writes: - de la Madrid (2005): "The role of the rigged Hilbert space in Quantum Mechanics" Could the second paragraph be restated as: "The elements of \Phi, the vectors, regarded as equivalence classes of functions differing only on sets of zero Lebesgue measure, can...

When I was studying general relativity, I learned that to change a vector into a covector (or vice versa), one used the metric tensor. When I started quantum mechanics, I learned that the difference between a vector in Hilbert space and its dual is that each element of one is the complex...

Hi, Could someone tell me, or refer me to a reference, about what the physical separable hilbert spaces are for the electroweak and strong forces. I'm looking for a defined inner product for the theories and a rigorous account of their hilbert spaces. Thanks a lot,

Hello all, I'm currently working on a problem in which I'm attempting to characterize a centered Gaussian random process \xi(x) on a manifold M given a known covariance function C(x,x') for that process. My current approach is to find a series expansion $\xi(x) = \sum_{n=1}^{\infty} X_n...

I'd appreciate it if anyone could help me clear up some concepts, the last chapter of one of my math courses is a (highly mysterious) introduction to Hilbert spaces (very very basic): What does it mean for a function to be "square-summable"? Has something to do with the scalar product in...

Von Neumann developed the concept of Hilbert Space in Quantum Mechanics. Supposed he didn't introduce it and we didn't use Hilbert Space now. What are its counterpart in pure Schroedinger Equation in one to one mapping comparison? In details. I know that "the states of a quantum mechanical...

Hi All: in the page: http://mathworld.wolfram.com/SymplecticForm.html, Complex Hilbert space, with "the inner-product" I<x,y> , where <.,.> is the inner-product Does this refer to taking the imaginary part of the standard inner-product ? If so, is I<x,y> symplectic in...

I am reading J.W.Negele and H.Orland's book "Quantum Many-Particle Systems". I don't know how one can derive equation (1.40) on page 6. The question is For quantum many-body physics, suppose there are N particles. The hilbert space is H_{N}=H\otimesH\otimes...H. Its basis can be...

I would like a second opinion on my answer to this question as I'm confusing myself thinking about my proof. Any input is appreciated Homework Statement "Let (X, ||.||) be a complete normed linear space and Y \subsetX be a non-empty subspace of X. Then (Y, ||.||) is a normed linear...

I'm trying to understand the relationship between conserved charges and how operators transform. I know that we can find conserved charges from Noether's theorem. If (for internal symmetries) I call them Q^a = \int d^3x \frac{\partial L}{\partial \partial_0 \phi_i} \Delta \phi_i^a then is it...

I'm in Quantum 1, and the professor briefly mentioned Hilbert Space. I'm having a difficult time finding a non-technical description of what Hilbert Space is. Could someone give me a brief description of what it is physically, rather than mathematically?

I want to know the projective Hilbert space of coherent state and squeezed state.Thank you very much!

Homework Statement Much as the title says, I need to construct an example of a linear operator on Hilbert space with empty spectrum. I can very easily construct an example with empty point-spectrum (e.g. the right-shift operator on l_2), but this has very far from empty spectrum. If I...

I think this is right, but could someone confirm (or deny) this for me? While a particle like an electron - or a finite set of particles for that matter - is represented by a single normed vector in Hilbert space which is acted on by operators such as ones for energy, position and momentum...

What is the relation between Hilbert Space and space-time? Are the two disjoint or is there something relating the two?

Homework Statement Prove that for a linear set M a subset of Hilbert space, that the set perpendicular to the set perpendicular to M is equal to M iff M is closed. The Attempt at a Solution I already have my proof -- but what is an example of a linear subset of H that is not closed? I think...

Thant helped. thank you!

1. Problem description Let (e_n)_{n=1}^{\infty} be an orthonormal(ON) basis for H (Hilbert Space). Assume that (f_n)_{n=1}^{\infty} is an ON-sequence in H that satisfies \sum_{n=1}^{\infty} ||e_n-f_n|| < 1 . Show that (f_n)_{n=1}^{\infty} is an ON-basis for H. Homework Equations...

So I was recently learned that for some square integrable position wave-functions in Hilbert Space have the momentum function is not square integrable. Thus the momentum function are not in hilbert space. However, due to "Fourier's Trick" Dirac discovered for quantum mechanics, the momentum...

Homework Statement Show that \int {{f^*}(x)g(x) \cdot dx} is an inner product on the set of square-integrable complex functions. Homework Equations Schwarz inequality: \left| {\int {{f^*}(x)g(x) \cdot dx} } \right| \le \sqrt {\int {{{\left| {f(x)} \right|}^2} \cdot dx} \int {{{\left|...

I have a Hilbert space H; given a closed subspace U of H let PU denote the orthogonal projection onto U. I also have a lattice L of closed subspaces of H, such that for all U and U' in L, PU and PU' commute. The problem is to find an orthonormal basis B of H, such that for every element b of B...

Hello, I hope I am asking this in the right area of the forums. My teacher wrote the following formula down at our last meeting, and I was wondering if it was true ( \mathcal{H} is the infinite dimension separable Hilbert space): \mathcal{K} (\mathcal{H}) \approx \mathcal{K} (\mathcal{H}...

Hello, I hope I am asking this in the right area of the forums. I wanted to ask if the following formula is true (assuming H is infinite dimensional and separable): \mathcal{K} (\mathcal{H}) \approx \mathcal{K} (\mathcal{H} \oplus \mathcal{H} \oplus \mathcal{H} \oplus \mathcal{H})\approx...

Hi, I asked this question in the quantum physics forum https://www.physicsforums.com/showthread.php?t=406171 but (afaics) we could not figure out a proof. Let me start with a description of the problem in quantum mechanical terms and then try to translate it into a more rigorous mathematical...

Hi, I discussed this with some friends but we could not figure out a proof. Usually when considering bound states of the Schrödinger equation of a given potential V(x) one assumes that the wave function converges to zero for large x. One could argue that this is due to the requirement...

Homework Statement three distiguishable spin 1/2 particles interact via H = \lamda ( S_1 \cdot S_2 + S_2 \cdot S_3 + S_3 \cdot S_1 ) a) What is the demension of the hilbert space? b) Express H in terms of J^2 where J = S_1 + S_2 + S_3 c) I then need to find the energy and...

this question is in reference to eq 3.9 and footnote 6 in griffith's intro to quantum mechanics consider a function f(x). the inner product <f|f> = int [ |f(x)|^2 dx] which is zero only* when f(x) = 0 only points to footnote 6, where Griffith points out: "what about a function that is...

Let H be a Hilbert space and let S be the set of linear operators on H. Is there a proper subset of S that is dense in S?

I was wondering what is Hilbert Space exactly? I read the Wikipedia page, but its one of those situations u understand what your reading but don't full grasp the concept. I was just hoping someone could explain it to me.

In article #34 of a recent thread about Haag's theorem, i.e., https://www.physicsforums.com/showthread.php?t=334424&page=3 a point of view was mentioned which I'd like to discuss further. Here's the context: I think I see a flaw in the argument above. Suppose I want to know the...

This will sound like a very amateur question but please read: I have been puzzled for a while about the *precise* mathematical meaning of "quantum fluctuation". I know what a classical fluctuation is (as found in classical statistical dynamics). I also know what a superposition is. These seem...

Homework Statement Let f(x) be the discontinuous function f(x)=e^{-x},\text{for }x>0 f(x)=x,\text{for }x\leq 0 Construct explicitly a sequence of functions f_n(x), such that ||f_n(x)-f(x)||<\frac{1}{n}, and f_n(x) is a continuous function of x, for any finite n. Here ||\;|| represents...

Hi, I was wondering how the state vector for a particle in a 1-D box can be expanded as a linear combination of the discrete energy eigenkets as well as a linear combination of the continuous position eigenkets. It seems to me that this is a contradiction because one basis is countable whereas...

Homework Statement for what range of n is the function f(x) = x^n in Hilbert space, on the interval (0,1)? assume n is real. Homework Equations functions in Hilbert space are square integrable from -inf to inf The Attempt at a Solution I am having trouble with the language of the...

can somebody explain eigenvalues inside hilbert spaces??

In real linear space, we can use the rotation matrix in terms of Euler angle to rotate any vector in that space. I know in hilbert space, the corresponding rotation matrix is so-called unitary operator. I wonder how do I construct such matrix to rotate a complex vector in hilbert space? Can I...

When quantizing a classical field theory, e.g. Klein-Gordon theory, the Hilbert space of one-particle states is taken to be a set of equivalence classes of (Lebesgue) measurable and square integrable solutions of the classical field equation, but how do you use the classical theory to construct...

What exactly is the Hilbert space of a massive spin 0 particle in non-relativistic QM? The following construction defines a Hilbert space H, but is it the right one? We could e.g use some subspace of H instead. And what if we use Riemann integrals instead of Lebesgue integrals? Let G be the set...

We know that the Hilbert space of wavefunctions can be spanned by the |x> basis which is a non-countable set of infinite basis kets. Now consider the case of a particle in a box. We say that the space can be spanned by the energy eigenkets of the hamiltonian (each eigenket corresponds to an...

In QM we require that an operator acting on a state vector gives the corresponding observable multiplied by the vector. Spin up can be represented by the state vector \left( \begin{array}{c} 1 \\ 0 \end{array} \right) , while spin down can be represented by \left( \begin{array}{c} 0 \\ 1...