Use this for questions relating to the proper use of physics terminology or nomenclature.

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1answer
51 views

What is high energy physics?

Is high energy physics the same as particle physics? Does research in high-energy physics include things like quantum gravity, string theory and quantum field theory? Is unifying the four ...
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2answers
23 views

Why do people say “finite temperature” instead of “nonzero/positive temperature”? [duplicate]

This question is about terminology. The term "finite temperature" is often used to mean positive temperature, or equivalently finite inverse temperature $\beta = 1/T$. It seems to me that better ...
0
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0answers
16 views

What is the $D_{x^2-y^2}$ symmetry/channel/instabilitied referred to with regards to super-conductivity?

I have been reading various articles on Renormalization group where they compute the flow of some parameter which becomes increasingly attractive and then say that parameter is responsible for Cooper ...
0
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1answer
36 views

Is harmonic oscillator continuous variable system?

In the literature I have seen that the notions "our system is continuous variable system", "Hilbert space of our system is infinite" were used as if they were equivalent. For example for harmonic ...
0
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0answers
44 views

Terminology: Gauge stress?

When a material is loaded with a force, the stress at some location in the material is defined as the applied force per unit of cross-sectional area. If I have a material submerged in pressurized ...
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2answers
225 views

Correct terminology for combined kinematic and dynamic state

The kinematic state is defined as the position and orientation in space. The dynamic state is defined as the associated velocities. What is the correct terminology for the combined kinematic and ...
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0answers
25 views

What are the differences between logistic map, poincaré map, attractor, phase portrait, bifurcation diagram? [on hold]

What are the differences between Logistic map, Poincaré map, Attractor, Phase portrait, Bifurcation diagram Currently I became interested in chaos theory and non-linear dynamics. While ...
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1answer
45 views

What is the defintion of a current-current diagram?

Right now I am facing some Feynman diagram calculations and in the instructions I am reading the phrase current-current diagram appears quite often so I wanted to know: What is the definition of a ...
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3answers
53 views

How to tell if area is displacement or distance?

why is it not called "velocity v. time"? how do you know? If the y-value can be either positive or negative, the direction is then indicated. i think this is why it should be called velocity but ...
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0answers
28 views

What is crossover?

It is known that EW and QCD phase transitions in SM are so-called "crossovers". What is the difference between crossover and phase transition of the second kind?
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11answers
14k views

What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)?

This is a confused part ever since I started learning electricity. What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? All of them have ...
4
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2answers
199 views

Difference between locality and causality?

I ask this question as the two seem to be very closely related and are sometimes taken to be one and the same (in the notion of microcausality in QFT), which has left me confused as to what meaning of ...
0
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2answers
95 views

What is an effective potential in classical mechanics?

What is an effective potential in classical mechanics? I have read the wikipedia article and David Tong's lectures notes, but I didn't understand how an effective potential simplifies a situation or ...
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2answers
86 views

What does it mean by saying the generators of translations transform as vectors under the Lorentz Group?

The commutator of generators of Lorentz transformation and translation is as follow: $$[M^{\mu\nu},P^\sigma]=i(P^\mu\eta^{\nu\sigma}-P^\nu\eta^{\mu\sigma} ).$$ Then from this we usually say that the ...
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7answers
111 views

What is inertia of a body?

The definition of inertia is "Inertia is the resistance offered by the body whenever its state of motion is changed." What is inertia of a body? Is inertia actually a force exerted by the body? If ...
0
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2answers
60 views

Is escape velocity really a velocity?

The term escape velocity is quite common to us. But we know velocity is a dimension dependent on the direction. But the escape velocity has same value irrespective of from where it is thrown from the ...
2
votes
1answer
229 views

What was Feynman's famous formula?

In Welton(1983), Memories of Feynman, Welton mentions two formulas which he denotes as Feynman's Famous Formula (FFF) and FFF #2. Which famous formulas is he talking about? Is he maybe talking about ...
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0answers
18 views

Electromagnetic transfer function

In a paper on the superlens, I came across the term of "transfer function". I understand that the transfer function relates the output to a given input, but I've been unable to find a formula for the ...
4
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2answers
148 views

Rigorous distinction between quasiparticles and collective excitations

I would like to hear your opinion on the question whether there is an accepted distinction between both concepts in condensed matter physics. I would tend to use the word quasiparticle for dressed ...
5
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1answer
54 views

What is meant by a preliminary run at the LHC?

I am a bit confused over the meaning of "Preliminary run" when referring to the LHC experiments CMS and ATLAS. For example in this summary, Figure 2 refers to both the CMS $19.7\ \mathrm{fb^{-1}}$ ...
8
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1answer
191 views

Group representations as vectors and isomorphism between weights and matrix generators

This might be something basic, but it is unclear to me. So I am used to work with representations of groups as matrices. These matrices represent the structure of the Lie algebra by satisfying the ...
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0answers
13 views

What's the difference between frequency, spectral and cepstral domains?

I have a hard time teasing apart the conceptual difference between these three domains, and constantly mix them up in my head. I've been reading up on it, but I can't wrap my head around it. a ...
2
votes
1answer
37 views

Quadrature in quantum optics

I am reading a chapter about Squeezed state, and came across this word, quadrature, which I have never seen before in the book. Here is the quote from that chapter. " A general class of ...
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2answers
177 views

Locally flat coordinate and Locally inertial frame

I am having some doubts on myself regarding the above concepts in General Relativity. First, I want to point out how I understand them so far. A male observer follows a timelike worldline ($\gamma$) ...
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0answers
52 views

What's the difference between wave equation in PDE form and wave equation in normal form? [migrated]

What's the difference between "wave equation in partial derivative form" and "wave equation in y(x,t) form" ? Are they both same? And why "wave equation in in y(x,t) form" is the solution of "wave ...
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2answers
171 views

What is the difference between configuration space and phase space?

What is the difference between configuration space and phase space? In particular, I notices that Lagrangians are defined over configuration space and Hamiltonians over phase space. Liouville's ...
2
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3answers
403 views

Conversion of ideal gas to real gas via $Z$ compression factor

The ideal gas equation $PV=nRT$ can be converted into real gas equation by compression factor $Z$ i.e $PV=Z~ nRT)$. My question is what is $Z$ and how does it arise? Is $PV/nRT$ a compression ratio of ...
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6answers
923 views

Gibbs free energy intuition

What is Gibbs free energy? As my book explains: Gibbs energy is the energy of a system available for work. So, what does it want to tell? Why is it free? Energy means ability to do work. What is ...
2
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3answers
17k views

What is the difference between angular speed and tangential speed in a circular motion?

I was looking a long time for the way the equations of this two speeds are obtained, and i found pretty much nothing important, so can someone explain how are those obtained, and which is the ...
2
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1answer
47 views

Is UV catastrophe same as IR catastrophe?

I am currently studying quantum physics from Serwey-jewet. Where in the topic of Planck's law, infrared catastrophe is alternatively used for UV catastrophe while explaining how Plancks constant ...
0
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1answer
33 views

Do gauge bosons really transform according to the adjoint representation of the gauge group?

Its commonly said that gauge bosons transform according to the adjoint representation of the corresponding gauge group. For example, for $SU(2)$ the gauge bosons live in the adjoint $3$ dimensional ...
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0answers
30 views

What does 'easily reversed' mean in the NIST spectral database? [closed]

Cross posted to http://engineering.stackexchange.com/q/3303/ I'm trying to do some processing of optical emission spectra from sputtering plasmas, and am confused by what NIST means by 'easily ...
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0answers
60 views

How is the formula for the capacitance of a parallel plate capacitor derived?

I have seen in I.E. Irodov that if the permittivity is given as $\epsilon$ then we can find the capacitance as $$C = \frac{\epsilon A}{d}$$ but I wonder whether it is dimensionally correct or not and ...
2
votes
1answer
59 views

What operation does a beam splitter apply?

What is the unitary matrix equivalent to the operation of a beam splitter? I'm asking because I've seen different matrices used and was wondering if the term is just ambiguous or if there's an agreed ...
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5answers
309 views

Is Parity really violated? (Even though neutrinos are massive)

The weak force couples only to left-chiral fields, which is expressed mathematically by a chiral projection operator $P_L = \frac{1-\gamma_5}{2}$ in the corresponding coupling terms in the Lagrangian. ...
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0answers
46 views

Dynamics and kinematics of quantum field theory

What is the difference between dynamics and kinematics of quantum field theory? I read that in QFT there is no possibility to keep the two things distinct because of a problem with the separability of ...
2
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1answer
64 views

What does “downshear” mean?

I occasionally read descriptions such as "downshear of the vortex" in meteorological publications. What does this mean?
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3answers
423 views

In the double slit experiment what, exactly, is a slit?

I have seen and read several times about the double slit experiment, that an electron (or even a molecule (!) as I found out later) behaves like a wave that swaps over those slits. However I wonder ...
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0answers
21 views

Measurement of drag (?) tension between two surfaces

I want to know if there are (reasonably inexpensive) devices to measure the tension between two surfaces. Beware of my terminology: the first help I need is to actually formulate my question ...
1
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1answer
38 views

What is “forward peaking”?

In "Research and Development for a Gadolinium Doped Water Cherenkov Detector" the phrase "forward peaking" is used to describe a signal. This comes up in lots of other contexts too, but I still can't ...
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0answers
58 views

Is hidden symmetry the same concept as broken symmetry for the standard model?

I have recently started studying the basic ideas of symmetry and group representation in order to understand the basic principles behind the standard model. I do follow the difference between a global ...
2
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2answers
213 views

What is meant by “unique direction” in most of the arguments in application of Gauss' Law?

This term is really bothering me a lot. While explaining the radial direction of electric field of a uniformly charged sphere, my book writes: Notice the use of argument of symmetry. There is no ...
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3answers
13k views

Is time a Scalar or a Vector?

In Wikipedia it's said that time is a scalar quantity. But its hard to understand that how? As stated that we consider only the magnitude of time then its a scalar. But on basis of time we define ...
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5answers
5k views

Why and how does negative velocity exist?

Why and how does negative velocity exist? I have read on the internet about negative velocity but I still don't understand how it can even exist since time is positive and so is length. By doing some ...
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1answer
41 views

What is meant by 'a perfect dipole'?

Question What is meant by a perfect (electric) dipole? Additional information I came across the term in this question Force from point charge on perfect dipole and also in a textbook (which does ...
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1answer
40 views

Superscript on density matrix

I have been asked in homework to solve the optical bloch equation for the initial condition of $\rho_{22}=0,\rho_{12}=0$. Professor gave a hint of the general equation and let us carry it from here. ...
3
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2answers
115 views

Is kinetic theory part of statistical mechanics?

Some years ago from now I've seem some basic details about what was then called "kinetic theory of gases" where the study of property of gases was made by statistical considerations about the momentum ...
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2answers
42 views

Difference between a reversible change and a reversible process?

Question In thermodynamics what is the difference between a reversible change and a reversible process? Additional information I am new to the topic of thermodynamics and getting confused about ...
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0answers
16 views

Radial excitation and orbital-angular momentum excitation

Sorry. Just want to make sure, but what does radial excitation and orbital-angular excitation mean in the context of bound states? Just higher $n$ and $\ell$ quantum number?