# What is Interaction: Definition and 711 Discussions

Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way causal effect. Closely related terms are interactivity and interconnectivity, of which the latter deals with the interactions of interactions within systems: combinations of many simple interactions can lead to surprising emergent phenomena. Interaction has different tailored meanings in various sciences.

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1. ### I About quantum interference: space and time

Hello to all, Questions that I hope are not completely devoid of physical meaning. Firstly, about space. Let be a Hilbert space, in which we can by definition establish the existence of complete and orthonormal vector bases; and a Psi vector (state) that we write as a linear combination (a...
2. ### I Wave function collapse

Let's take the example of an electron in of a hydrogen atom . It continuously interact with the proton of the hydrogen atom . Both the proton and electron are continuous interacting with each other. It is said that wave function collapse when it is being observed or observers interact with it...
3. ### B Newton's 3rd Law interactions with 2nd and 1st Law Partners

I was over on the stack but got asked to move over here. https://physics.stackexchange.com/questions/804903/newtons-3rd-law-force-on-a-rocket I've been at it all day trying to understand what partner forces are and how you can have a change in force with regard to them, or why gravity is...
4. ### I How large is the volume of a photon interacting with matter?

When a photon interacts with matter and diffracts, the photon seems to interact with the area of its wave front, determined by an aperture even if it is only one photon. But how far does it interact in depth? Does it always "feel" the whole crystal? Can we assume the photon is reflected by the...
5. ### B Electromagnetic radiation interacting with a magnetic field

Why isn't EM radiation attracted/repelled by a magnetic field?
6. ### B Can we say a photon doesn't exist until the wavefunction collapses?

I am sure this sounds silly but.. Between being emitted and interacting, a photon gives us no information as to where it is in space. If we know both where a photon was emitted from and where it then interacted, we can say that it travelled in a straight line. But we actually dont know. So in...
7. ### Classical magnetic dipole-dipole interaction in iron

I'm having a bit of trouble with this exercise because, even if I understand the physics of the dipole-dipole interaction in an ideal classical system, I don't get to know how to approach this problem. I've got a few doubts about how this system would work. First of all, what would be the...
8. ### I Interaction of EM radiation with Glass

Hi, I wanted some clarification on the mechanism for how EM radiation interacts with standard glass, namely IR, visible and high energy (UV and X-ray). Looking online most sources seem to say the band gap is around 10eV. Since visible light is about 1-3eV visible light will be transmitted. IR...
9. ### A Scalar decay to one-loop in Yukawa interaction

I am trying to calculate the amplitude for a decay ##\phi \to e^+e^-## under a Yukawa interaction ##\mathcal{L}_I = -g\phi \bar{\psi}\psi## to one-loop order (with massless fermions for simplicity). If I'm not wrong, there are 4 diagrams that contribute to 1 loop, three diagrams involving...
10. ### B Shouldn't quantum gravity be an interaction between mass and spacetime?

Einstein showed (via general relativity) that spacetime is curved by mass, mass moves in relation to this curvature, and that gravitation arises as secondary effect. Why then are we looking for quantum gravity as some sort of mass<->mass interaction? Aren't the fundamental interactions better...
11. ### I Axion Interaction: Weak & Strong Nuclear Forces

Looking to confirm: Does the hypothetical axion interact through weak and strong nuclear forces?
12. ### A Kirkendall effect: vacancy concentration and pair interaction energy

I am reading the following article on Kirkendall effect leading to the Formation of a hollow binary alloy nanosphere: a kinetic montecarlo study. I am unable to understand or find in references the reasoning to obtain equation (1):
13. ### I About photon-polariser interaction quantum-molecular-level mechanics

I'm quite interested in the aforementioned topic, and would like to take a look at more literature about it, and to learn more about it, and would like to ask if you know more about it, or know interesting aspects about it, you can suggest the titles of the materials, or share the links to the...
14. ### A Question about dilaton monopole interaction derivation

I am trying to understand how one derives the dilaton monopole interaction. In "Black holes and membranes in higher-dimensional theories with dilaton fields", Gibbons and Maeda mentioned that one could obtain the dilaton monopole interaction as such: where the action is given by However, I...
15. ### B Exploring the Alpha Particle-Electron Interaction in Gold Foil Experiments

My current understanding: The mass of alpha particle is approximately 7340.6 times higher than the mass of electron.in the gold foil scattering experiment the deflection of alpha particle due to electron is approximately zero. The reason that is given is that since the electron is much lighter...
16. ### A Is the weak interaction asymptotically free?

Is the ##SU(2)_L## part of the SM asymptotically free like a typical non-Abelian gauge theory? I've been made to understand that confinement does not occur for ##SU(2)_L## because the spontaneous symmetry breaking scale is above the confinement scale, however I can't find any information on...
17. ### SARS CoV-2 link to Parkinson's, N protein α-synuclein interaction

While researching S protein interactions I stumbled across a couple of recent papers studying the increased risk of developing Parkinson's after a Covid infection and the possible mechanism that plays a role there. https://pubmed.ncbi.nlm.nih.gov/34860005/ here is the full version of the study...
18. ### A Question about F.Reif page 66 (thermal interaction of systems)

It was described that the thermal interaction changes average energy of each system by a different amount and the external parameters do not change at all in a thermal interaction. I do not understand how energy of a system changes without a change in external parameters.
19. ### I Potential Energy of an Electron-Nuclei Interaction in DFT

In density functional theory (DFT), electron density is a central quantity. Because of this, we want to calculate electron - nuclei potential energy as functional on electron density. If we know how potential energy varies across space, we can calculate this functional with plugging particular...
20. ### I Momentum conservation for EM-Field/matter interaction

Hello, I'm reading Feynman Lectures Vol II, and saw this "paradox" in section 26-2 (Figure 26-6), where two orthogonally moving charges can be shown to have unequal action and reactions. Later in Chapter 27, the explanation was given briefly citing field momentum. I tried to prove this...
21. ### B Unraveling the Mystery: Interactions and Properties of Quantum Objects

How can a quantum object interact with its environment before it has any definite properties? It seems like a ‘chicken and egg’ scenario to me. I can’t see how anything could interact with a quantum object which has only potential properties (what is there to interact with?), yet if I’ve...
22. ### A Faraday effect breaks photon interaction laws

I was taught that photons ( non-ionizing at least) never interact. So Its really bugging me that most info on faraday effect invokes B field as the cause of ( for example) rotation effects. Since EM-waves (IE Photons) themselves propagate a (oscillating) Magnetic field through infinite space...
23. ### A Interaction between matter and antimatter in Dirac equation

I'm new to relativistic quantum mechanics and quantum field theory and was trying to learn about the Dirac equation. Unfortunately, I got a little stumped by the interaction between matter and antimatter. It seems like the time derivative of matter is dependent on the spatial derivative of...
24. ### 2 Spheres of Charges and their Interaction

I can understand what happens with the conductor... (induction effects). But how can induction happen in insulators ? Is it due to the the induced dipole moment?
25. ### A Exploring the Electroweak Interaction: Uniting Weak and Electromagnetic Forces

What is the reason to unite weak and electromagnetic interaction
26. ### A Interaction between neutrons and nuclei during scattering

When we learn about the scattering of a particle, the context is usually a charge shooting towards a Coulomb potential. With some assumptions, we can derive the scattering cross-section pretty reasonably. Therefore, the scattering cross-section of different elements in X-ray spectroscopy is...
27. ### A Magnetic exchange interaction by first principle (Blume-Capel model)

Hi guys. I work with statistichal mechanics, applying classical spin models, as Ising model. I'm trying a collaboration with a colleague that works with first principle calculations. Does anyone know how to calculate the exchange interaction and anisotropic constant (of the Blume-Capel model)...
28. ### I Atom-photon interactions in the interaction picture (self answered)

EDIT: I'M SO DUMB! I can't believe I can't multiply matrices together. Of course the result is not zero, the matrix on the left will be: $$\begin{pmatrix} 0 & e^{i\omega_at/2}\\ e^{-i\omega_at/2}&0 \end{pmatrix}$$ So i was solving problem 3 from...
29. ### I Feynman diagram for scalar - vector interaction

The term for the electromagnetic interaction of a Fermion is ##g \bar{\Psi} \gamma_\mu \Psi A^\mu##, where ##g## is a dimensionless coupling constant, ##\Psi## is the wave function of the Fermion, ##\gamma## are the gamma matrices and ##A## is the electromagnetic field. One can quite simply see...
30. ### Photon-photon interaction, EM frequency overlap

Now from physics I read that photons don't interact with one another normally, at higher energies they might through pair production but that is besides this point. So this means that for example if we have multiple sources of EM radiation like say multiple sub pixels within a screen then each...
31. ### How to estimate the interaction time of Raman scattering?

Maybe we could use (1) uncertainty principle $\Delta E \Delta t = \hbar$ and get $\Delta E$ from the spetrum. Or (2) forced vibration model, then get the damping factor $\gamma$， and get $Delta t = frac{1}{\gamma}$
32. ### A Frustrating Problem with GUI Interaction: Is Anyone Else Annoyed?

This has been a big annoyance for me for a while. I do some GUI development and programming for some of the Manufacturing Test Fixture programs that I develop, so I'm sensitive to making GUIs intuitive and easy to use. But with many PC and phone interfaces (mainly browser-based), the program...
33. ### What is Boundary Interaction in Echolocation and Internal Body Structures?

What is a boundary and how can boundary interactions be used in echolocation and examining internal body structures?
34. ### B Is there a magnetic interaction between light and charged particles?

Light is propagating electric and magnetic fields. The electric field interacts with electrically charged particles, e.g. electrons. Is there a corresponding magnetic interaction?
35. ### A Exploring Free and Interaction Terms of L in Quantum Field Theory

With free part L=-½(∂Φ)^2 -½m^2 Φ^2 and interaction term L=½gΦ^2Any help would be appreciated, thank you.

I'm a college grad, but not in science or physics. I'm useless on the math. However, I have a solid layman's understanding of double slit experiment as well as the delayed choice quantum eraser . I also have a layman's understanding of quantum physics via reading some mainstream science...

47. ### Interaction picture of a phonon-electron coupling

What I have tried to do is to separate the exponential of the unitary transformation operator to the interaction picture into three different Hilbert "subspaces" like: $$e^{i\frac{H_0}{\hbar}t}=e^{i\omega_m \hat{b}^+\hat{b}}\otimes e^{-i\hbar\nu|1><1|} \otimes e^{-i\frac{g}{\omega_m}|e><e|t}$$...
48. ### Exploring the Interaction of Magnetic and Electric Fields

Hello, If you have an appropriately oriented conductive ring in a constantly changing magnetic field, current will flow in the ring. There will also be a magnetic field associated with the current in the ring. I understand (maybe ... ) that the current is due to the electric field which is...
49. ### I Fermi-Liquid - amount of electrons available for the interaction

I have attached the pages in Kittel's book (pages 417-420) regarding my question. My question is simply based off of the second to last photo, where e_f = 5*10^4 K and e_1 = 1K. e_2<e_f and |e_2|<e_1. So how can (e_1/e_f)^2 be less than 1? The energy of the free flowing electron is assumed to...
50. ### I Gravitational interaction between three bodies

If there are three bodies A, B, and C arranged linearly, and B is free falling towards C, will the gravitational presence of A affect the rate of free fall of B towards C?