Hi everybody,
I encountered this question as an example of what a google applicant is asked:
You are shrunk to the height of a 2p coin and thrown into a blender. Your mass is reduced so that your density is the same as usual. The blades start moving in 60 seconds. What do you do?
It is...
Hi togehter.
I encountered the following problem:
The timeordering for fermionic fields (here Dirac field) is defined to be (Peskin; Maggiore, ...):
T \Psi(x)\bar{\Psi}(y)= \Psi(x)\bar{\Psi}(y) \ldots x^0>y^0
= -\bar{\Psi}(y)\Psi(x) \ldots y^0>x^0
where \Psi(x) is a Dirac...
Hi together ...
In many textbooks on particle physics i encounter - at least in my mind - a misuse of the Heisenberg uncertainty principle.
For completeness we talk about
\Delta p \Delta x \geq \hbar/2
For example they state that the size of an atom is of the order of a few Angstroms...
Hi together ...
I wonder how one can deduce the existence of antiparticles from the Klein-Gordon equation.
Starting from (\frac{\partial^2}{\partial t^2} - \nabla^2 + m^2) \Psi(t,\vec{x})=0
one gets solutions \Psi(t,\vec{x})=\exp(\pm i (- E t + \vec{p} \cdot \vec{x})) leading to E^2=p^2 +...
Hi together ...
I encountered the following statement:
Operator A is self adjoint on D(A) then A(t) \equiv \exp(iHt) A \exp(-iHt) is self adjoint on D(A(t)) \equiv \exp(-iHt) D(A).
H is self adjoint, so that exp(...) is a unitary transformation. But why does the domain transform this way...
hi.
i'm reading "quantum mechanics in hilbert space" and a don't get a basic point for bounded operators.
def. 1 a set S in a normed space N is bounded if there is a constant C such that \left\| f \right\| \leq C ~~~~~ \forall f \in S
def. 2 a transformation is called bounded if it maps...
Hi.
I just calculated the quantum mechanical harmonic oscillator with a driving dipole force V(x,t) = - x S \sin(\omega t + \phi)
I used the Floquet-Formalism. Then I calculated the mean expectation value, in a Floquet-State, of the Hamiltonian over a full Period T indirectly by using the...
Hi together...
When reading Sakurai's Modern Quantum Mechanics i found two problems in the chapter "Approximation Methods" in section "Time-Independent Perturbation Theory: Nondegenerate Case"
First:
The unperturbed Schrödinger equation reads
H_0 | n^{(0)}\rangle=E_n^{(0)}...
Hi.
I found in a book on quantum optics (Vogel, Welsch - Quantum Optics) and also in a lecture script the following statements.
A System is composed of two subsystems (say A and B) which interact. So the total Hamiltionian is H_{AB}= H_A + H_B + H_{int}.
Nontheless the states of H_{AB}...
Hi all.
I found the following identity in a textbook on second quantization:
([a_1^{\dagger},a_2^{\dagger}]_{\mp})^{\dagger}=[a_1,a_2]_{\mp}
but why?
([a_1^{\dagger},a_2^{\dagger}]_{\mp})^{\dagger}=(a_1^{\dagger}a_2^{\dagger}\mp a_2^{\dagger}a_1^{\dagger})^{\dagger}=a_2a_1\mp a_1a_2...
I thought i had a basic to intermediate understanding of quantum physics and group theory, but when reading hamermesh's "group theory and it's application to physical problems" there's something in the introduction i don't understand.
first of all, i know the parity (or space inversion)...
Hi.
I've found the following relation (in a book about the qm 3-body scattering theory):
<\Omega^{\pm}^{\dagger} \Psi_n|p>= ... = 0
where |p> is a momentum eigenstate.
So it is shown, that the inner Product is zero. Then they conclude that \Omega^{\pm}^{\dagger}|\Psi_n> = 0 because the...
hi everybody.
\textbf{J}_1 and \textbf{J}_2 are angular momentum (vector-)operators.
In many textbooks \left[\textbf{J}_1,\textbf{J}_2\right] = 0 is stated to be a condition to show that \textbf{J}=\textbf{J}_1+\textbf{J}_2 is also an angular momentum (vector-)operator. But what is meant...
hi,...
i unfortunately couldn't find a solution to this problem although it seems like a classical textbook problem...
how can i solve the (time independent) schroedingerequation for the following potential
V(x) = \infty for x<=-1
V(x) = a\delta(x) for -1<x<1
V(x) = \infty for x>=1
so at x=0...
Hi there,...
For a derivation of the Ehrenfestequations i found the following commutator relations for the Hamilton-Operator in a book:
H = \frac{p_{op}^2}{2m} + V(r,t)
and the momentum-operator p_{op} = - i \hbar \nabla respectively the position-operator r in position space:
[H,p_{op}]...