# Tagged Questions

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### Range Of An Interaction

Why is the Compton wavelength $\lambda_c=\frac{\hbar}{mc}$ used as a sensible measure for the range of an interaction, where $m$ is the mass of the corresponding mediator?
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### Interaction Hamiltonian in the interaction picutre

The Schrodinger and Heisenberg pictures make sense to me. But the interaction picture which is a hybrid of the two does not. Author of this text first splits the Hamiltonian up as ...
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### How can I explain why the weak nuclear interaction between individual nucleons is 'weak'?

By considering the energy-time uncertainty principle, estimate the range of the weak nuclear interaction at low energies. Compare this range to the size of a typical nucleon (for example, a proton) ...
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### Potential Energy of Interaction Between a Sphere and a Particle Formula Derivation [closed]

A sphere of radius R has density described by ρ=ρ(r). Derive equation for pontetial energy of interaction between the sphere and some point particle of mass m which is at distance r from the center of ...
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### How do photons mediate (or create) a force?

Is there a somewhat intuitive explanation as to why the exchange of a photon between two particles causes a force between those particles? Is there a difference in the way massless and massive ...
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### What is the phase-amplitude numerical method?

What is the phase-amplitude numerical method? I heard its used to calculate long range interactions numerically, but I cannot find any papers discussing its method of implementation.
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### What is it that Lagrangian density with only bilinear terms always corresponds to free field theory?

Is there an intuitive proof of this fact? (Maybe connected in some way to Central Limit Theorem?).
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### Why is the gravitational force $10^{38}$ times smaller than the strong nuclear force?

Also, why is the weak interaction force $10^7$ times smaller than the strong nuclear force?
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### In the context of quantum field theory, what does it mean to “couple” something?

Suppose I have the following Lagrangian density $$\mathcal{L} = - \frac{1}{4} F_{\mu\nu}F^{\mu\nu}$$ The lecture notes I an reading suggest if I want to "couple to ...
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### Force and Advanced Physics: E.g. is gravity really a force? [duplicate]

I'm kinda beginner in physics but recently I've been studying really interesting concepts like the four fundamental forces and General Relativity. I started thinking that there is a weird ...
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### How do quantum fields really couple?

The term "coupling" between quantum fields refers to certain terms in the Lagrangian (density) $\mathcal{L}$ where the respective field operators appear together, e.g. $g\phi^\dagger\psi$ with ...
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### crystal momentum conservation

Electrons on 1D chain interacting with each other $$H = \sum_{k_4,k_3, k_2, k_1} V(k_4-k_1) c_{k_4}^{\dagger}c_{k_3}^{\dagger}c_{k_2}c_{k_1}\delta_{k4+k3=k2+k1;\text{mod}~G}$$ where $G$ is ...
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### Does the surface topological order on the boundary of 3D topological insulator also have topological ground state degeneracy?

The boundary of a 3D topological insulator can be fully gapped (under strong interaction) by the surface topological order without breaking the symmetry (see Fidkowski-Chen-Vishwanath, ...
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### Why does the classical electrodynamics Lagrangian density equation have a “field” term and an “interaction” term?

On Wikipedia's page on classical electrodynamics, they state the Lagrangian density equation as follows \mathcal{L} = \mathcal{L}_{\text{field}} + \mathcal{L}_{\text{int}} = ...
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### Static fields - are properties of single objects, or do exist only between two interacting objects?

I apologize for seeming to return on a same question, but I don't have the feeling that the things are clear. In a former question, "where is the potential energy stored", the conclusion was that ...
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### Semantics: alternative word for long-ranged interaction? [closed]

I am working on wording for a report. I need to a word to describe long ranged interaction that is constant in strength. But I am aware that people sometimes use 'long-ranged' to mean decaying ...
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### Is there such a thing as an interaction radius for molecules?

My question is about estimating the radius of influence between two molecules; picture some mixture, comprised of water, oxygen gas (in small concentrations) and a molecule we denote $G$. In the ...
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### Simple example showing why measurement & interaction are different

Does someone know of a clear (pedagogical) example where one can really see(with the math) where interaction and measurement are not synonymous in quantum mechanics? I know that every measurement ...
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### Relation between wavelength and system size

We always say that when a given light wave interacts with atoms bound in a molecule, only waves with wavelength close to the inter-atomic-spacing are able to probe the system. In other context ...
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### Why does heat lose its energy as we get further away?

Why does heat lose its energy dramatically as I move back? Say I have a fire around 0.5 meters in front of me, I can clearly feel the heat, however, as I move even very slightly back, say 1 meter ...
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### Why can interactions be neglected for the Integer Quantum Hall effect?

Though the statement is made often, I've not seen any justification for neglecting electron-electron (Coulomb) interactions in the fully filled $\nu =1$ IQH state. I would highly appreciate if someone ...