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

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2answers
76 views

What is the principle of equivalence in thermodynamics?

I've been searching for this for a while. There is a principle of equivalence in general relativity: http://en.wikipedia.org/wiki/Equivalence_principle But I need the principle of equivalence in ...
1
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1answer
47 views

Gravity force and dark energy [duplicate]

If gravity is a fundamental force which bends spacetime and dark energy is energy which stretches spacetime, what is the difference between the terms force and energy?
0
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1answer
91 views

Single-channel vs multi-channel scattering

I am studying quantum scattering and stumbled upon the "scattering channel" and "single- and multi-channel scattering" terms. However, I didn't manage to find any sufficiently formal definitions of ...
2
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2answers
121 views

Why “Dark Energy” is called energy instead of force?

The overly simplified explanation I'm giving myself right now is dark energy causes the opposite of what gravity does, that's why the universe is expanding. Now where gravity is a force, why dark ...
2
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2answers
130 views

Why is the Faraday Tensor derived from the Lorentz force?

If we start from the Lorentz force, $$\textbf{F}=q\textbf{E} +q\textbf{v}\times\textbf{B}$$ and use the four velocity u$^{\mu}$ and the four momentum p$^{\nu}$, then we get to ...
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3answers
75 views

Commutator summation notation

I have the relation $ e^L M e^{-L}=\sum_{n=0}^\infty \frac 1{n!} [L,M]_{(n)}$ where $L$ and $M$ are operators. What does the subscript $n$ after the commutator bracket denote?
4
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1answer
144 views

Which transformations are canonical?

Which transformations are canonical? Why do canonical transformations preserve the measure of integration in phase space?
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0answers
21 views

What is Fermi energy and Fermi level? [duplicate]

What is meant by Fermi level and Fermi energy? And what is the difference between the two?
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0answers
56 views

Actions at a distance vs. contact interaction

The ancestors could not imagine an action at a distance (in German: "Fernwirkung"). Today physicists don't take serious its opposite anymore (in German: "Kontaktwechselwirkung"). So my first question ...
3
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1answer
2k views

Difference between steady state and equilibrium?

In semiconductor physics, what is the difference between steady state and equilibrium. How analysis of devices varies in these processes?
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2answers
75 views

Should theory be the appropriate term? [duplicate]

Should theory be the appropriate term? I mean, for example, because of the quantum field theory we have been able to find the subatomic particles that it theorized and make the Standard Model. Why ...
5
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2answers
7k 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 ...
1
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1answer
333 views

Transparence of an infinite square well? [closed]

What does it mean by an infinite square well being transparent? I have been doing the calculation of the infinite square well and I came up with an answer $T = 1$ where $T$ for Transmission ...
5
votes
1answer
320 views

“Hard wall”/ “soft wall”

I have encountered those terms in various places. As I understand it, "soft wall" can correspond to a smooth cutoff of some spacetime, while "hard wall" can be a sharp one, which can be described in ...
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2answers
73 views

How is the set of displacement operators best called?

Displacement operators $\hat D(x,p), \ \ x,p\in\mathbb{R},$ follow a composition rule $$D(x,p) D(x',p') = \exp\frac{i(px'-xp')}2 D(x+x',p+p').$$ Because of the extraneous phase factor, the set of all ...
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1answer
59 views

Valley meaning explanation for foreigner

English is not my native language and I have some hard time translating this word. I was searching in couple dictionaries(both paper and online) and could not find it. Could anyone provide me ...
1
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2answers
112 views

Terminology for line integral of magnetic field

One of the quantities appearing in the integral form of Maxwell's Equations is the line integral of the magnetic field around a closed loop. (The relevant equation states that this is equal to the ...
1
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1answer
52 views

The exact definition of conjugate momentum density

After checking various websites, I've seen the conjugate momentum density defined as either: \begin{align*} P_r ~=~ \frac{\partial \mathcal{L}}{\partial \dot{A}_r} \end{align*} or \begin{align*} P_r ...
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0answers
50 views

Difference between RPA and generalized RPA

The random phase approximation (RPA) is an approximation method in condensed matter physics and in nuclear physics. What is the difference between RPA and generalized RPA?
3
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3answers
522 views

What does “nearly infinite mass” mean?

I am sure this is a silly question, but I was reading something that described the pre big-bang universe as having "nearly infinite mass." How can something be "nearly" infinite? The term seems to ...
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0answers
22 views

What is “thermal undulation” in the context of lipid bilayers?

What is thermal undulation in the context of lipid bilayers? Is it another word for "thermal fluctuation"?
2
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1answer
92 views

Ramsey Interactions

What are Ramsey interactions? I am researching atomic clocks and am not sure why the atoms need to be exposed twice to an electromagnetic field in order to cause excitation.
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2answers
75 views

Definition of quantum anharmonicity

I have been reading research papers in mathematical physics for some months now, and I've seen the the term "anharmonic oscillator" quite frequently. At first I assumed that given a Schrodinger ...
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1answer
26 views

Equivalent temperature: laser and cell containing Rb

What's the meaning of "equivalent temperature" related to a cell containing rubidium and crossed by laser?
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1answer
55 views

What is a phrase for testing for a certain result? [closed]

Is there a word or phrase for when someone is testing for a certain result thereby skewing his findings?
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0answers
162 views

Morphisms between chiral CFTs

This is a question about terminology. Given two vertex algebras $V_1$ and $V_2$ (= chiral CFTs), there are two kinds of maps $V_1\to V_2$ that one might want to consider. 1) Morphisms of VOAs that ...
5
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1answer
175 views

Why the speed of light is represented by $c$? [closed]

In almost every textbook, I've found that the speed of light is $c \approx 3 \times 10^8\: \mathrm{m/s}$. I wonder why it's just $c$ ?
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3answers
14k views

What is the difference between phase difference and path difference?

I have learnt that path difference is the difference between the distance travelled by two waves meeting at a point. If that is path difference,then how will one know what is phase difference and how ...
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0answers
26 views

Is there a generic term for orbital groups such as $e_g$ and $t_{2g}$?

I am looking for a generic term for sets of atomic orbitals (viz. spherical harmonics) which are grouped by crystal symmetry. The most familiar examples would be $e_g$ and $t_{2g}$ (in cubic ...
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4answers
2k views

Are quantum mechanics and quantum physics the same field?

What is the difference between quantum mechanics and quantum physics?
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2answers
486 views

What does “the ${\bf N}$ of a group” mean?

In the context of group theory (in my case, applications to physics), I frequently come across the phrase "the ${\bf N}$ of a group", for example "a ${\bf 24}$ of $SU(5)$" or "the ${\bf 1}$ of ...
4
votes
3answers
191 views

Defining left and right independent of a human body?

Is it possible to define right and left independent of the asymmetric human body? I am unable to think of such a definition without circular reasoning. Example: If you are facing east, your left ...
2
votes
1answer
68 views

Any difference between “Mueller matrix” and “Scattering matrix”?

I find in some references 4x4 Mueller matrix and in other references 4x4 Scattering matrix. Are they different or identical? If they are different, I would like to know the book or any research ...
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3answers
141 views

Direction of motion

What does the term direction of motion actually mean? Is it a direction where a particle is moving or the direction of its velocity? For example, what is the direction of motion of a projectile in ...
5
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1answer
90 views

Why are “quadratures” called this way?

In quantum optics (and hence also cv quantum information), given the annihilation and creation operators of the electromagnetic fields $a$ and $a^{\dagger}$, the "position" and "momentum" operators ...
4
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2answers
107 views

Why is it tension in surface tension?

Why is it called surface tension not surface compression?
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0answers
25 views

Origin of the names for the decay chains

Is there any reason for the names of the decay chains? As shown in this chart (larger version here): only the Thorium chain starts on an isotope of the element it takes its name from, and it can ...
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1answer
233 views

A basic question: what is accelerating voltage? [closed]

Or would it be acceleration voltage? Acceleration sounds like it makes more sense, but my paper says accelerating. What are possible ways you could go about calculating it?
6
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3answers
8k views

What is the official difference between a planet and a dwarf planet?

I'm trying to understand how objects are classified as planets, moons, or dwarf planets. Can someone please explain the differences between them? I'm really curious about why Pluto is a dwarf planet, ...
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1answer
78 views

Relativistic momentum and mass [duplicate]

Is there even a relativistic mass or just relativistic momentum? How does one reason to prefer one over another? What is the problem with saying a hot gas will have more mass/inertia to it?
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2answers
2k views

What are virtual objects, Reflection of light? [duplicate]

While studying reflection through a plane mirror, I have been told that when the object is real the image will be virtual and the image will be real while the object is virtual. What are virtual ...
2
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0answers
56 views

What is the 1/2 spin analog of the graviton called?

In some supergravities you have the gravition, gravitino, graviphoton and graviscalar. Each is analogous to each other in only sharing gravitational properties and nothing else. They differ by spin ...
4
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1answer
550 views

What is the difference between the words transparent and translucent?

Merriam Webster defines transparent as: Having the property of transmitting light without appreciable scattering so that bodies lying beyond are seen clearly. And translucent as: ...
2
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1answer
181 views

What is the name for the whistling “musical” sounds that change stepwise in pitch when a hollow tube is spun like a lasso?

You have likely heard those sounds, science museums sometimes sell Flexible plastic tubes you can whirl like a lasso. The air rushing by the end of the tube causes these sounds, which are admitted in ...
2
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2answers
239 views

What is deep Fresnel region?

If I understand correctly, it has something to do with autocorrelation function, but can someone give me a definition or exact explanation? In case of scattering, if you wish to analyze pattern with ...
0
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2answers
205 views

Equilibrium - uniform circular motion

Maybe this is a bit of a silly question, but let us pretend we have a pendulum in a ideal universe with no friction, drag, or anomalous forces there to affect it. Additionally, our pendulum is ...
12
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5answers
3k views

Does Earth have a code name?

Everything we discover in the sky get eventually a code name, like NGC 7293, Simeis 147, etc. Does Earth/Moon have a code name too? Or it is just Earth/Moon, etc.?
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4answers
190 views

Space-like and time-like: where do the names come from?

Space-like separated events are events that, in a well-chosen reference frame, can take place at the same time but never happen at the same location. On the other hand for time-like events, one can ...
2
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1answer
96 views

Term for “atmospheric ricochet” due to wrong “angle-of-attack”

I watched "Apollo 13" yesterday, and they had the "angle-of-attack" problem that had to be manually solved, to prevent the ship from "ricochet[ing] off the atmosphere like a rock skipping off a pond". ...
0
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1answer
105 views

Can the phrase “Terminal Velocity” be used to describe non-gravity situations?

According to Wikipedia: [Terminal Velocity] is the velocity of the object when the sum of the drag force (Fd) and buoyancy equals the downward force of gravity (FG) acting on the object. Since ...