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Questions tagged [definition]

The definition tag is used in situations where the question is either about how some term or concept is defined or where the validity of an answer depends on a subtle definition of some term or concept used in the question.

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7
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6answers
695 views

So is quantum entanglement actually FTL “communication” or is it mundane pre-determination?

I have to say right off the bat, I'm a little frustrated that there seem to be very contradictory answers about this, at least to a layman like me. If two particles are entangled and you separate them ...
4
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1answer
215 views

What is a definition of the trace norm?

I have found that (one?) definition of the trace norm is $$\mid\mid A\mid\mid = \sqrt{A^*A} \tag{1}$$ but now I am reading this paper where (on page 4) it says In particular, we will restrict ...
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3answers
56 views

Confusion Regarding Hookes law

I am used to seeing Hookes law in the form: $F = kx$ but in another one of my books it gives the equation: $\\ F = \frac{\lambda x}{l}$ where $l$ is the unstretched length, $x$ is the extension and $\...
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2answers
79 views

What does Dirac mean by “proximity”?

I was reading Dirac's "The Principles of Quantum Mechanics" and on page 7 he makes the following statement: "Like the fundamental concepts (proximity, identity) which everyone must learn on his ...
0
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0answers
30 views

Relation between computation of curl and divergence and their formal definitions

both divergence and curl of a vector field have a formal definition, however, we don't use these definitions when we compute the divergence or curl. so can we just derive the computations from the ...
9
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2answers
2k views

What is the difference between a neutrino and an electron neutrino?

So, what is the difference between a neutrino and an electron neutrino? Like how does the term 'electron' made a difference? Also, what is the difference between an antineutrino and an electron ...
3
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2answers
218 views

Can magnitude be negative?

My teacher told that magnitude is the positive value of that quantity or the modulus of that quantity. he also told that vector quantities have both magnitude and direction and scalar quantities have ...
5
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2answers
142 views

Is length an extensive property?

From my experience, volume, surface and length are extensive properties. Indeed : the reunion of two cubes of 1 $m^3$ leads to a cube of 2 $m^3$ the reunion of two tiles of 1 $m^2$ leads to a tile ...
3
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1answer
61 views

What's the difference between twisted light and light of circular polarization?

Circular polarization: https://en.wikipedia.org/wiki/Circular_polarization Orbital angular momentum of light: https://en.wikipedia.org/wiki/Orbital_angular_momentum_of_light From point of view, ...
3
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1answer
165 views

What is the definition of “force” in quantum field theory?

In quantum field theory, there are certain interactions that we seem to associate with the action of "forces." For example, the exchange of a gauge boson between two matter particles is associated ...
0
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2answers
86 views

These terms are so foreign to me that they feel like unnecessary jargon; what do these terms mean, and are they relatively common?

No pun intended in the title. ;) I am having trouble understanding this sentence on Wikipedia's page for Unified Field Theory: Governed by a global event $\lambda$ under the universal topology, ...
0
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1answer
60 views

What does $\mathcal{N}$ refer to in Gauge theories?

Context: I am a second-year (undergraduate) physics major applying for a summer research position. The investigator is working on Quiver Gauge Theories and in response to my inquiry email he told me ...
3
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4answers
837 views

What are the differences between specific latent heat and latent heat?

What are the differences between specific latent heat and latent heat? As far as I know, latent heat is the heat required or released during the change of state, without change of temperature. So ...
0
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0answers
110 views

What is the symmetry of a Hamiltonian?

Recently while I was reading a paper on integrability of Rabi model by D Braak. In this paper there is a discussion about the symmetry of a model and that in the case of the Rabi model it is $\mathbb{...
0
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0answers
78 views

Difference between pure and thermal states

As far as I know by inserting a harmonic potential $V(x) = \frac{1}{2}m \omega x^2$ into the time-independent schrödinger equation I can obtain the wave-functions eigenstates and eigenvalues (energies)...
0
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1answer
65 views

Should specific heat capacity be defined as “the numerical value of the quantity of heat…” or simply the “quantity of heat”?

Sorry for this vague question but I'd just like to ask a question that my teachers weren't able to give a really satisfactory answer to. In my notes the specific heat capacity is defined with the ...
0
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1answer
35 views

If oscillatory motion is not simple (or chaotic), is it then by definition complex?

I'm trying to logically deduce or show that a specific type of motion is complex. It is two-dimensional oscillatory motion that can be expressed by coupled second order non-linear differential ...
1
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0answers
151 views

Difference between Scattering and Reflection

I am confused: What exactly is the difference between optical scattering and optical reflection? To me, both terms are distinguished by where we place the observation plane. Reflection: Observation ...
0
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3answers
2k views

What is quasi-static process?

What is the formal definition of quasi static process? I am accustomed with it a bit intuitively, i want to know the formal definition of this. At some source I found the definition of somewhat ...
0
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1answer
76 views

Definition of angular velocity vector of $B$ in $A$ - Strange notation

I found the following definition of angular velocity vector of B in A at page 49 of the book "Thomas R. Kane, Peter W. Likins, David A. Levinson - Spacecraft Dynamics - McGraw-Hill (1981)": The ...
1
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3answers
94 views

$Q$-factor for damped oscillator (not driven)?

How would this be defined? Some of the Q-factor definitions I have encountered include: $$Q=2\pi\frac{Energy \space stored}{Mean \space power \space per \space cycle}\\Q=2\pi\frac{Energy \space ...
6
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1answer
91 views

Distinct choice of partition in the Path Integral

Practically all books in Quantum Mechanics and Quantum Field Theory define the non-relativistic path integral by taking one interval $[a,b]$ and breaking it up into $N$ subintervals of equal length. ...
0
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3answers
206 views

What's the difference between gravitational attraction and weight? [duplicate]

What exactly is gravitational attraction? In my textbook it was quoted " all objects both tiny and large objects are attracted to the earth. This is known as gravitational attraction, or the force due ...
-1
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2answers
76 views

Why is work defined with respect to distance rather than time? [duplicate]

The common way of finding the work done on some object is by applying the equation: force*displacement. However, suppose we apply a force of F newtons on an object of mass M for a duration of T ...
0
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2answers
99 views

Impulse as the time derivative of force

Momentum is the time derivative of force. $F = \frac{dp}{dt}$. But isn't impulse $J=Ft$, $F=\frac{J}{t}$? Can impulse be the time derivative of force too, or is it just defined as an integral?
10
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1answer
272 views

What is the actual definition of conformal invariance?

I've seen a large variety of slightly different definitions of conformal invariance. For simplicity I'll only consider scale invariance, which is already confusing enough. Some of the definitions are: ...
0
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3answers
103 views

How can we define energy other than the definition that it's a capability to do work? [closed]

It is actually a property of energy that it can do some work not an actual mean to define it because we cannot define a thing on the basis of what it is doing or what it can do.
0
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2answers
660 views

Phase Velocity Derivation

I spend few hours trying to derive phase velocity of sinusoidal wave $$\cos(kx - \omega t).$$ I know that it must be equal to $\omega \over k$ but after banging my head for few hours and trying to ...
2
votes
4answers
264 views

Why is escape velocity independent of direction of projection?

However, for any body projected with a velocity less then the escape velocity, the final maximum height will vary with variation in angle of projection. But why is this not the case in case of ...
2
votes
1answer
90 views

Is there any special significance of force field in physics?

What is the formal definition of force field? Which is more fundamental force or field? Do field exist in nature (as force do i think as per section 12-1 of Feynman lecture volume 1, and page 8,9 of ...
1
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1answer
43 views

Is there a “standard” Newton?

Basic SI units have definitions through experiments that seems to imply a pretty obvious setup. Is there a standard experiment for calibrating Newtons? The definition is the force needed to cause a ...
2
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1answer
45 views

States of classical general relativity

In Classical Mechanics a state of a system is either a pair $(q,p)$ or $(q,\dot{q})$ depending if we formulate the theory on the tangent or cotangent bundle of the configuration space. The evolution ...
1
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0answers
85 views

What is the difference between acoustic photon and acoustic phonon?

In the book Biomedical Photonics Handbook, 3 Volume Set edited by Tuan Vo-Dinh, it is written : Brillouin Scattering is caused by the interaction of the photon with the acoustic phonon. As the result ...
4
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5answers
523 views

Could someone explain what is a potential?

In many part of physics, me talk about potential (electrical potential, gravitation potential, elastic potential...). All those definition looks very different, and I would like to know how all those ...
6
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1answer
152 views

GR with Torsion: Definition of contorsion

I start doing some computations in manifolds with non vanishing torsion and things are getting a bit confused, basically because of notations and definitions. I understand that in presence of non ...
2
votes
1answer
72 views

Definition of equilibrium for thermodynamics and statistical mechanics

Is the definition of equilibrium for thermodynamics and statistical mechanics the same? From my understanding, a system is in thermodynamic equilibrium if its macroscopic variables are not changing. ...
6
votes
2answers
301 views

Is this actually the rigorous definition of the path integral in Quantum Mechanics?

Let a quantum system with a single degree of freedom be given. We want to define the path integral so that we get the representation for the propagator as $$\langle q' |e^{-iHT}|q\rangle=\int_{x(a)=...
2
votes
1answer
93 views

Time Travel, CTC and Causal Loop

What is the difference between a closed timelike curve and a causal loop? If someone is travelling in a closed timelike curve, are they also in a causal loop?
2
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4answers
158 views

Thermodynamics second law variational statement query

In thermodynamics as I understand entropy is a state function. A state function is a property whose value does not depend on the path taken to reach that specific value. In contrast, functions that ...
0
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0answers
87 views

Superstate vs superposition

Is superstate the phase space of a superposition that includes subsets? It seems like superstate is not used as a word that often, and usually seems to be a synonym for superposition. Can anyone give ...
6
votes
2answers
196 views

Will the SI units need redefining ever again?

Up until recently, there were obvious problems with the SI definitions of fundamental units, like bits rubbing off the kilogram prototypes (or mercury vapour absorption), and the water used for the ...
1
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2answers
57 views

Strange super script notation $^{(4)}R$ in the textbook Numerical Relativity

In Numerical Relativity by Thomas W. Baumgarte and Stuart L. Shapiro. There are bunch of superscript $(4)$ over $T,\Gamma, R$ i.e. $^{(4)}\Gamma^a_{bc}$ _ $^{(4)}R_{abcd}$ _ $^{(4)}R$ ... (...
0
votes
1answer
29 views

Meaning of flux 2-integral

Can someone please explain the meaning of flux 2-integral in this sentence: Mass is evaluated as a flux 2-integral at the asymptotic infinity. For asymptotic infinity, I believe it is as ...
2
votes
2answers
156 views

How to arrive at the thermodynamic definition of entropy?

My question is, how do we say that, $$dS=\dfrac{dQ}{{T}} ~?$$ How do we relate heat and temperature to entropy? Why is the temperature in the denominator? Can we replace heat by work? How does ...
1
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2answers
91 views

Quantum Mechanics Defining a field

I am currently in a basic class where I am being taught some concepts of QM.. We were taught today some field theory but we were not given the definition of field in QM. I looked around but my book ...
2
votes
1answer
322 views

A new definition of mass using Planck constant

Tonight in a italian television news channel well known internationally I have heard that almost certainly the definition of mass that we currently know will be obtained by means of the constant ...
1
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0answers
70 views

Extensors in mathematics and in physics [closed]

Could someone explain in a simple but accurate manner what extensors are as mathematical entities and how they are used? How do extensors essentially differ from tensors? Are there or could there be ...
1
vote
1answer
181 views

Ladder operators vs creation/annihilation operators

I am trying to figure out the difference between the ladder operators (for harmonic oscillator) $a^\dagger$, $a$ and the creating/annihilation operators $c^\dagger$, $c$. Are they the same? I have ...
5
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1answer
175 views

What is the general mathematical definition of wave?

What is the general mathematical definition of wave?
1
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1answer
59 views

What is the general mathematical definition of periodic motion?

What is the general mathematical definition of periodic motion? My answer : Can you say that each function is in the form $ \overrightarrow{r} (t)= \overrightarrow{r} (t+T)$. it is right?