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6
votes
2answers
173 views

What are fundamental dimensions used to describe the physical universe? [closed]

I have heard that the universe can be explained in terms of the four fundamental forces. I have also heard it can be explained in terms such as space, time, energy, mass or even motion. To further ...
0
votes
1answer
123 views

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, ...
7
votes
2answers
493 views

Can we fully simulate molecular physics?

Is our knowledge of physics complete enough to achieve fully natural simulations of molecular interactions in a computer simulation? How far off are we? Reason for question: I wonder how far we are ...
2
votes
2answers
41 views

The time interval of fundamental interactions?

I extract the below text snippet from our text book: Strong interaction is charge independent.The time interval of such a strong interaction is about $10^{-23} sec$ and it's range is approximately ...
0
votes
1answer
135 views

Gravitational force and Electromagnetic force?

I found this interesting note in one of my textbooks, The enormous strength of the electromagnetic force compared to gravity is evident in our daily life. When we hold a book in our hand, we are ...
0
votes
1answer
72 views

Force-carrying particles instead of forces

Are there physical theories in which notions of particle are used without the concept of force? I know about gauge bosons, see: http://en.wikipedia.org/wiki/Force_carrier and ...
1
vote
1answer
52 views

A problem regarding the Elitzur-Vaidman bomb tester

To quote wikipedia Step-by-step explanation After being emitted, the photon 'probability' wave will both pass through the first 50% reflecting mirror (take the lower-route) and be reflected ...
1
vote
1answer
153 views

Interaction pictures of Quantum Mechanics

I want to understand the Schrödinger, Heisenberg and interaction picture and have a few questions about them: So in general you have a time-dependent Hamiltonian $H$, as for example the potential may ...
0
votes
0answers
36 views

What equation can be used to solve an ideal string/membrane in a non-vacuum medium?

I'm interested in the eigenmodes of the membrane for various mediums, such as vacuum, air, water, etc., which impose a damping effect on the membrane. This cannot be done by merely changing the value ...
4
votes
1answer
89 views

Question about the foundation of part I in A. Zee's book

Zee says in Section I.3 of QFT in a nutshell: The functional integral $$Z = \int D \varphi e^{i \int d^4 x [\frac{1}{2} (\partial \varphi)^2 - V(\varphi) + J(x) \varphi (x)]} \tag{11} $$ is ...
1
vote
0answers
115 views

$G$-parity in an electromagnetic decay

I am looking at the decay $\eta\rightarrow\pi^+\pi^-\gamma$ and I would assume that the decay itself (ignoring the $\pi\pi$ final state interaction that is obviously strong) is electromagnetic since ...
0
votes
1answer
119 views

Quartic terms as two particle interaction?

In some lecture notes I found the sentence: [...] considering two toy models: the classical and quantum harmonic oscillator with quartic perturbation. The quartic terms $\sim x^4$ and $\sim \hat x ...
1
vote
0answers
36 views

Is it possible for quasiparticles to form charge density wave of quasiparticles?

What if the quasiparticle has fractional charge? -----UPDATE------ For example, 1d kink has e/2 charge, if view kink like electrons in 1d (we know there is 1d charge density wave of electrons), is ...
0
votes
0answers
62 views

Interactions with high helicities particles

As it can be shown, there are no interacting helicity-3 (and higher) particles (i.e., massless spin-3 or higher particles) in soft limit (small momentums of emitting particles of given helicity). Сan ...
0
votes
2answers
126 views

Does yukawa potential of two particles have effect on each other? [closed]

Okay,a novice here.Suppose two particle interact with Higgs field.Does The Yukawa potential created by each of them affect each other or the interaction in any way.If so,what is it physical ...
5
votes
2answers
188 views

Why are the “coupling constants” constant?

The coupling constants (in the gauge theory) fix an inner product on the lie algebra of the gauge group and we use it to define strength of the fields. we are using ad-invariant inner products which ...
4
votes
3answers
292 views

Could Dark Matter particles that don't couple to quarks or leptons have been produced?

With what we know about physics, is it possible that when the universe 'began', around when quarks and leptons were produced, another particle, which doesn't couple to either quarks, leptons or ...
4
votes
0answers
69 views

Why are interactions always mediated via bosons (as opposed to fermions)? [duplicate]

Weak, Strong and electromagnetic force are mediated via bosons. I've come across the Walecka-model where the exchange particles are $\sigma$ and $\omega$ mesons; bosons again. why are interactions ...
8
votes
4answers
3k views

How is it possible for objects to travel faster than the speed of sound when particles interact at the speed of sound

First of all, I am sorry if this is a stupid question but: I've heard that atoms interact with each other at the speed of sound (when you for instance push a chair, the atoms collide with each other ...
0
votes
1answer
41 views

Collision of a heavy charged particle with an electron at rest - Deduction

When I was studying Nuclear Physics I saw this formula about interaction of radiation with matter. The book mentioned that when considering a elastic collision of a heavy charged particle of mass $M$ ...
3
votes
2answers
665 views

What is an “Interaction Hamiltonian”

I'm an undergraduate reading up on some quantum physics so that I can help out more in the lab that I'm working in this summer. In the book I'm reading (Shankar's "Principles of Quantum Mechanics") I ...
4
votes
0answers
75 views

How to prove that identical particles are attracted or repelled in a given spin-s interaction theory?

Let's assume that we have integer spin interaction theory (EM field, linearized gravity, arbitrary gauge spin s theory). How to prove the consequence that in interaction theory with spin $s = 2n$ two ...
43
votes
5answers
18k views

How exactly does gravity work?

The electromagnetic force and strong and weak forces require particles like photons and gluons. But in case of gravity there is no such particle found. Every mass bearing object creates a ...
1
vote
1answer
168 views

What is the leading order Feynman diagram for nucleon-anti-nucleon annihilation into two mesons ($\psi^{\dagger} \psi \to \phi\phi$)?

I am working with a standard basic scalar Yukawa theory. I.e. the only interaction term is $-g\psi^\dagger\psi\phi$, where the $\phi$ field quanta are the mesons, the $\psi$ field quanta are the ...
0
votes
1answer
93 views

Is glass considered as a linear optical medium?

My research, which is mainly related to communication, involves the use of optical sources (mainly lasers). However, my background in photonics and optics is not yet solid, so my question might be a ...
2
votes
1answer
258 views

From a cross section to a probability

This is homework problem: Given the cross-section of a neutrino-electron scattering, what is the probability for a solar neutrino to scatter with a electron as it goes through the center of the Earth? ...
0
votes
1answer
141 views

How do magnetic objects exhibit attraction/repulsion across empty space?

Magnets will attract or repel over a distance before physically touching each other. What makes this effect possible? My best guess is that the forces generated by the angular momentum of the ...
6
votes
1answer
433 views

Why will two bubbles floating on water surface attract each other?

Two identical bubbles floating on water surface will form clumps, according to the "cheerio effect". But what's the detail about the force? It's necessary to calculate the shape of water surface, in ...
5
votes
0answers
81 views

Five-component field

Recently I was reading about 5-component field $(\varphi , \psi_{\mu})$, for which $$ \hat {p}^{\mu} \varphi = mc\psi^{\mu}, \quad \hat {p}_{\mu}\psi^{\mu} = mc\varphi . $$ This field refers to the ...
4
votes
1answer
91 views

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?
2
votes
3answers
71 views

Do molecular bounded systems shield or reduce neutron cross-sections?

When talking about neutron cross-sections, literature is usually investigating isolated cases of Neutron + Atom. Here, the abundance of hydrogen is dominating neutron fluxes through material. I ...
2
votes
1answer
1k views

How do electrons and photons interact?

Two electrons, or an electron and a proton, interact with each other because of the Coulomb potential, which can also be seen in the Schrödinger equation (which is the equation that describes the ...
3
votes
1answer
318 views

Diagonalizing Van der Waals Hamiltonian

In Kittel's Solid State Physics, he attempts to find the energy exchange due to the van der Waals interaction. He starts by writing the hamiltonian: two oscillators with coordinates $x_1$ and $x_2$ ...
1
vote
0answers
88 views

Exotic coupling

I have encountered the minimal coupling between a field and charges before $$H = \frac{1}{2m}(p-qA)^2,$$ whereby I am considering the classical case. The description minimal leads me to ask if ...
0
votes
1answer
66 views

What defines the interaction strength of a particle (massless or not) with matter?

Generally, talking about photons, the shorter the wavelength, the higher the interaction with matter. I doubt that I really understand why this happens. What about other massless particles? And ...
4
votes
1answer
217 views

Feynman rule for deriative interaction: an example

Consider a theory for a finite number of real scalar fields $\phi _i$ with interaction terms of the form $$ -\lambda _{ijk}\phi _i\partial _\mu \phi _j\partial ^\mu \phi _k, $$ with the sum over ...
0
votes
1answer
127 views

Which interaction is the responsible for long-range magnetism?

I'm taking solid state physics, subject mostly based on Ashcroft-Mermin's "solid state physics". Yesterday I sat for an exam and there was a question I couldn' t even answer: "Which interaction is ...
1
vote
3answers
256 views

Relativity and photon interactions

A particle's interaction (with anything it can interact with) can be thought of as it making a measurement of the physical quantity associated with the interaction, (e.g. electric field in case of the ...
5
votes
1answer
122 views

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 ...
2
votes
2answers
255 views

Potential in Quantum field theory

I studied free particle field like Dirac field and Klein Gordon field. My question is about interaction. How can I put a potential term in the Lagrangian density? $\mathcal{L} ...
2
votes
1answer
240 views

Why Does Knife Cuts?

Why is it that when we cut bread or anything else with a knife, the less effective way to cut it is just by pressing on it from above? And is it true that we can cut things with knife because of the ...
2
votes
0answers
78 views

In QFT, how can it be shown that the field out, ${\phi_{out}}$, is a free field if the field in, ${\phi_{in}}$, is a free field?

In the Dirac picture of QFT interacting fields, if the field in, ${\phi_{in}}$, is a free field, then I know that the field out, ${\phi_{out}}$ should also be a free field. How can this be shown? ...
0
votes
1answer
131 views

Definition: Coupling [closed]

What does it mean to say that 2 fields are coupled? More generally, what does "coupling" mean?
2
votes
0answers
97 views

Adiabatic theorem in the regime of quantum optics

I am wondering whether there is a version of adiabatic theorem in the regime of quantum optics. My understanding of quantum optics involves with the interaction between photon and atom. This ...
3
votes
1answer
704 views

Are fundamental forces conservative?

I wonder whether fundamental forces are conservative. First of all, I'm not sure if we can talk about conservative forces, since to study electromagnetism, weak and strong interactions we need QFT. ...
6
votes
2answers
536 views

How general relativity gets to an inverse-square law

I understand that a general interpretation of the $1/r^2$ interactions is that virtual particles are exchanged, and to conserve their flux through spheres of different radii, one must assume the ...
4
votes
2answers
247 views

Non-local Lagrangian contact interaction

Conside a contact interaction given by a delta function on their worldlines. Use a gauge fixed Lagrangian for two point particles in terms of their proper times $t$ and $t^{\prime}$. Is it possible to ...
3
votes
1answer
315 views

Deriving Feynman Rules (with the presence of a gluon field strength tensor)

If I have a Lagrangian of the form: $$ \mathcal{L} = k \bar{\psi} \varepsilon^{\mu \nu} \lambda^a \phi G^a_{\mu \nu} + h.c. $$ [where $\phi, \psi$ are fermions, $\lambda^a$ are Gellmann matrices, ...
0
votes
1answer
129 views

How fair is it to say that all chemistry arises from failures of the ideal gas law?

I was reading here about how the ideal gas law assumes point masses and non-interaction. Is it fair to say that all chemistry arises from failures of that? Of course, such a sweeping generalization ...
2
votes
3answers
230 views

What is the cause the light is affected by gravity? [duplicate]

I know that photons have no mass and that a photons exist only moving at the speed of light. So what is the cause that a massive astronomical object can bend a ray of light? I have two thoughts, but I ...