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

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2
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2answers
2k views

Differences between astronomy, astrophysics and cosmology? [closed]

What is the main difference between Astronomy, Astrophysics, and Cosmology? I have the impression that astronomy is a subject that runs parallel to physics but it is outside the physics field. This ...
3
votes
1answer
111 views

Is there a scientific term for star formation?

It might be my stupidity to think that many laymen terms that most people use to describe some physics phenomena usually have a scientifically accepted term or name? The process of star formation, ...
3
votes
2answers
181 views

What is the difference between Chiral anomaly, ABJ anomaly, and Axial anomaly?

I get confuse with these three terms: Chiral anomaly, ABJ anomaly, and Axial anomaly. I can not find standard definition of these three. Is there anyone can describe precisely?
0
votes
1answer
40 views

What is “Lifetime Intensity” in photoluminescence?

I'm reading an article "Surface plasmon enhanced Förster resonance energy transfer between the CdTe quantum dots". Link The reasearchers are writing about increase in "lifetime intensity" and even ...
5
votes
2answers
522 views

What is a gauge in a gauge theory?

As I study Jackson, I am getting really confused with some of its key definitions. Here is what I am getting confused at. When we substituted the electric field and magnetic field in terms of the ...
0
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1answer
144 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
0
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1answer
66 views

De Donder Weyl theory

Im trying to get my head around what the difference is between a symplectic and multisymplectic manifold is. My understanding currently is that on a symplectic manifold time is the parameter that ...
1
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2answers
183 views

Is uniform circular motion an SHM?

I know the projection along a diameter is an SHM but is circular motion itself an SHM? If we consider the mean position to be the center of the circle then the centripetal acceleration is proportional ...
1
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2answers
123 views

Friction force in rolling motion

In rolling without slipping motion we know that the friction acting is static friction and so we treat it as an unknown while solving equations of dynamics. Question: Is the static friction during ...
0
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1answer
168 views

Simple explanation of Coherent integration radar

I have a physics background, and I'm reading some physics data analysis papers where they keep throwing around the term coherent integration. I've done the google search, but the best answer I could ...
10
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4answers
563 views

What is an interpretation of quantum mechanics?

In the sense of "Copenhagen Interpretation", what exactly is an interpretation? What purpose does an interpretation serve? Can an interpretation be tested or even be correct or incorrect independent ...
2
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2answers
238 views

X-ray diffraction analytical principle - diffraction or reflection?

I am an MSc in analytical chemistry, currently working with x-ray diffraction. The technique is called "x-day diffraction", but are not the x-rays reflected? Max von Laue discovered that x-rays were ...
3
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2answers
160 views

Covariant derivative applied to a vector vs. applied to a matrix?

I know there are (say) two different definitions/representations of the covariant derivative: one is the covariant derivative applied to a vector $F$, which reads as $$DF=\partial F+iAF$$ ...
11
votes
4answers
571 views

Is partial derivative a vector or dual vector?

The textbook(Introduction to the Classical Theory of Particles and Fields, by Boris Kosyakov) defines a hypersurface by $$F(x)~=~c,$$ where $F\in C^\infty[\mathbb M_4,\mathbb R]$. Differentiating ...
2
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2answers
122 views

How do you pronounce $\vec{A} \cdot \vec{B}$ and $\vec{A} \times \vec{B}$? [closed]

I'm French. I would like to know: How do you pronounce $\vec{A} \cdot \vec{B}$ : "A scalar B" or "A dot B" ? How do you pronounce $\vec{A} \times \vec{B}$ : "A vectorial B", "A vector B", "A cross ...
1
vote
1answer
130 views

Vorticity versus Viscosity

For a work project I need to revive my aerodynamics knowledge again. Can somebody help me with the distinction between vorticity and viscosity. If a flow vorticity is not equal to zero, the flow is ...
2
votes
1answer
286 views

Difference in “momentum” names in Lagrangian mechanics

In the context of Lagrangian formulation of classical mechanics, the following names keep occurring in most textbooks, which confuse me a lot, are they different in any way? Momentum Generalized ...
0
votes
1answer
158 views

Does graphene have a honeycomb lattice?

In my grand ignorance I would state that graphene has a honeycomb lattice. Some tend to agree with me and some others do not. I'm curious to know what members of the SE community think is the right ...
1
vote
1answer
176 views

Difference between a “source dipole” and a “force dipole”

I know quite well what a dipole is and in general what multipole moments are (in the context of, for instance, electrodynamics). What I find myself confused by is something called a "force dipole" in ...
8
votes
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 ...
0
votes
1answer
30 views

What does “shortwave radiation” mean to a meteorologist?

I'm have an empirical model developed using surface observations of radiation (400-1100nm). I tend to think of this as visible, near infrared, and a little bit of shortwave infrared. I now need to ...
3
votes
2answers
161 views

Is internal symmetry the same as gauge symmetry?

This is more a terminology question. I have seen that some people differentiate between the two types of symmetry: internal symmetry and gauge symmetry (of a field theory). Is there a difference (in ...
-1
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1answer
52 views

Angular displacement after full rotation

I was wondering is why angular displacement isn't $0$ after $n$ full rotations?
10
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3answers
963 views

Planets and Pluto? Neptune?

If one of the rules to be a planet is that it needs to clear ALL objects from their orbit, does this also make Neptune a non-planet? Since it has thus far failed to clear Pluto from it's orbit. Or ...
1
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3answers
238 views

Generic term comprising everything that can be represented with a number and a unit?

I am looking for the generic term comprising all of the following: $23.42\,\text{m}$ $200\,\text{K}$ $123\,\text{MeV}$ $ħ$ with other words, everything that can be reasonably represented ...
2
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0answers
56 views

Which scientists have managed to name their laws/terms after themselves? [closed]

It would be pretty vain for someone to name a scientific law, unit, or term after themselves. "Newtons" as the name for the measurement of force, for example, was adopted in 1948, so I don't expect ...
2
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1answer
75 views

What is the clear cut difference between isotropic and anisotropic spin exchanges?

When are spin exchanges said to be isotropic or anisotropic? I have read several articles on this and can not differentiate these concepts properly.
4
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1answer
63 views

Why is the specific notation used for term symbols useful?

This has bugged me for a long time. Term symbols describe electronic states of atoms which have well-defined total electronic angular momentum $J$ as well as total spin and orbital angular momenta ...
7
votes
1answer
140 views

Has the Nobel committee mixed up this years prizes for Physics and Chemistry? [closed]

The title of the question is tongue-in-cheek but the question remains: How does the Nobel committee delineate the fields when awarding work which is of such an inter-disciplinary nature. The chemistry ...
3
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2answers
349 views

What's the difference between hopping and tunneling?

My professor made a distinction between electron hopping (the closest wikipedia had an article on) and tunneling, saying that one (he didn't say which, but I assume hopping) was temperature dependent ...
0
votes
1answer
42 views

Why is a “Semi-leptonic” Decay Mode called so?

Why is a semileptonic decay mode called so? I mean, if there is one lepton amongst the decay products, it should be leptonic, right? If there are two, that should be called bi-leptonic or something ...
0
votes
2answers
250 views

How to understand whether potential energy increases or decreases?

I am confused by how to deal with the negative sign in the equation $U=-GMm/r^2$ in the following problem: If the distance between two masses is tripled, then the magnitude of the gravitational ...
5
votes
3answers
2k views

How is a bound state defined in quantum mechanics?

How is a bound state defined in quantum mechanics for states which are not eigenstates of the Hamiltonian i.e. which do not have definite energies? Can a superposition state like ...
0
votes
2answers
104 views

When referring to weights and mass of weights in a physics laboratory, do we use the term mass or weights?

What terminology is used to refer to weights/ mass/ weight of mass/ mass of weights when referring to the mass of weights in a physics report? My question is more of the weights that we use in the ...
2
votes
2answers
177 views

What's the symbol for the antiparticle of the delta plus baryon?

It can't be $\Delta^-$ since that is another particle also made up of quarks (not antiquarks). I can think of four possibilities: $\overline\Delta^+$ $\overline{\Delta^+}$ $\overline\Delta^-$ ...
2
votes
2answers
51 views

Meaning of SIS in accelerators

With reference to accelerator facilities, the term "SIS" is often used. e.g. SIS-100, SIS-300 etc. What does SIS stand for, in this context? (The last S is probably for Synchrotron) Google appears ...
1
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1answer
115 views

How does Dirac form this conjugate imaginary equation?

On page 30 of Dirac's book $$\xi|P\rangle = a|P\rangle\tag{12}$$ He then says Suppose we have a solution of (12) and we form the conjugate imaginary equation, which will read $$\langle ...
0
votes
1answer
61 views

Friedmann equations question

Friedmann equations for critical density is: $$\rho_c = \frac{3H^2}{8\pi G}$$ Is there any other way to write this equation? For example: $$\rho_c = \frac{3}{8\pi GH^2}$$ I saw the above form on ...
1
vote
1answer
163 views

Buoyancy / Drag Problem

Buoyancy / Drag Problem Just a little bit of help would be nice. I have a spherical particle of radius $R$ and density $\rho$, surrounded in a fluid of density $\phi$ and viscosity $\eta$. I'm ...
3
votes
1answer
119 views

Use of the term first order dependency

In a question I am doing it says: Show explicitly that the function $$y(t)=\frac{-gt^2}{2}+\epsilon t(t-1)$$ yields an action that has no first order dependency on $\epsilon$. Also my textbook ...
4
votes
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 ...
1
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0answers
71 views

Why are Lagrangian subspaces called 'Lagrangian'?

I am wondering what the special role of Lagrangian subspaces (or submanifolds) are in mechanics. Do these subspaces have some sort of special property for which we have some sort of `Lagrangian ...
2
votes
4answers
1k views

Newton's first law: is his concept of (force of ) inertia still useful and used?

The force of inertia is the property common to all bodies that remain in their state, either at rest or in motion, unless some external cause is introduced to make them alter this state. That ...
0
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4answers
48 views

Can the term «shadow» pertain to anything else than light? [closed]

Can the term shadow pertain to anything else than light? Feel free to interpret this question in the widest sense possible.
2
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2answers
248 views

Conservation laws and continuity equations

I'm a bit messed up with conservation laws and continuity equations. This is my understanding: A conservation law describes that a physical quantity $G$ is conserved with time. It does not prevent ...
6
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0answers
183 views

What does “P-wave” mean when referring to a particle?

In scattering theory, P wave means $l=1$, where $l$ is the azimuthal quantum number. However, what does P wave mean when referring to particle states? For example, in this paper (arXiv link), the ...
0
votes
1answer
36 views

Can Allan variance be generalized such that the “Oscillator model” is not presumed?

The definition of Allan variance, $\sigma^2[ \tau ]$, which relates to "stability of clocks" is described on the Wikipedia page as being derived in terms of an "Oscillator model": "The oscillator ...
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4answers
625 views

Is the Big Bang defined as before or after Inflation?

Is the Big Bang defined as before or after Inflation? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've ...
3
votes
3answers
332 views

Is it time or duration? [closed]

Taking this post: "Is there a proof of existence of time?", as a starting point. Therein was mentioned that there is confusion between: "time" and "flow of time". There was a comment (of mine) that ...
1
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2answers
695 views

Why is density an intensive property?

I am still trying to understand what are intensive and extensive properties. Possibly someone can give a pointer to a decent text (preferably on the web), as I am not too happy (to say the least) with ...