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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Definition of conserved quantities in integrable system
This question is about the definition of conserved quantities integrable systems.
Using Algebraic Bethe ansatz,a family of commuting operators $F(\lambda)$ can be contructed by taking a partial trace (...
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Help understanding quote on theory and knowledge in Gravitation (Misner, Wheeler, & Thorne, 2017)
I came across an interesting discussion at the start of chapter 3 of MWT Gravitation. It reads:
Here and elsewhere in science, as stressed not least by Henri Poincare, that view is out of date which ...
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Meaning of electric dipole moment
what is the meaning of electric dipole moment?
Or why do we need to define electric dipole moment?
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Difference between Bravais lattice, point lattice and space lattice
I am good at crystallographic terminologies. Can somebody explain to me what is the difference between Bravais lattice, point lattice, and space lattice, if any?
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Conditions for a force to be conservative - Does the second condition imply the first? [duplicate]
John Taylor's Classical Mechanics says this...
I was wondering if the second condition already implies the first? I mean, are there situations where the first condition is violated even though the ...
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WKB method as a Semiclassical Approach
A naive question about WKB approach. It is dubbed to be a "semiclassical" method. What is precisely mean in quantum mechanical context to be "semiclassical"? Wikipedia states that ...
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Intuition for magnetic dipole moment
The definition of the electric dipole moment of a system of charges makes sense intuitively -
$$\boldsymbol {\bf p} = \int_{V} \boldsymbol {\bf r} \rho (\boldsymbol {\bf r})dV$$
describes the overall ...
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Necessity and Sufficiency of Yang-Baxter Equation for Integrability
Yang-Baxter Equation (YBE) seems to be a sufficient condition for integrability, i.e. if you have an $R$-matrix satisfying YBE, then the model is integrable. But how about the reverse? More ...
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Can anyone in here explain to me what exactly is 'Quasi-Generalised Co-ordinates'?
This comes straight up from a certain text that I was going through, which of course is in the form of a question which asks 'A solid cylinder is rolling without slipping and how many generalized co-...
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Why can the Ampere not be defined as the flow of $n$ Coulomb in $n$ seconds?
1 Ampere is defined as the flow of 1 Coulomb of charge in one second. However, I do not understand why it cannot be defined as the flow of n Coulomb of charge in n seconds.
This definition is ...
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Thermal equilibrium, heat and temperature [duplicate]
I am just studying thermodynamics for the first time and confused between these three terms
Temperature is defined in terms of thermal equilibrium (from zeroth law of thermodynamics) and thermal ...
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What exactly are resonances in particle physics?
I am very confused about this, are they an excited state of a particle where an electron is excited to an upper energy level, which seems less likely to be the case since the resonant states of ...
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What's the difference between observable and unobservable objects in a physical theory?
Both can help explain physical effects, but I'm looking for a rigorous definition of “observable” and “unobservable.”
For example, how is the experimental evidence for the existence of particles such ...
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Notion of $4$-vectors in Lorentz symmetry violating case
$4$-vectors can be defined in various ways. One very common way among them is by saying if $A^{\mu}$ is some $4$-vector, then it will transform via the Lorentz transformation rule and will obey the ...
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Difference between moment and couple
What is the exact difference between a moment and a couple? In some YouTube channels and books, they say the moment of a force produces a translational as well as rotational motion whereas the concept ...
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Exact definition of entropy [duplicate]
Sometimes it is described as a state of disorder and sometimes it is called the inavalability of the thermal of energy of the system to do mechanical work.
So
How exactly is entropy defined?
Also, ...
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Conformal manifold of a supersymmetric field theory
I'm trying to understand what exactly is the conformal manifold of a theory. If I understand it right, the conformal manifold is the space of couplings.
From that point of view, it is just a subset ...
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What are Quantum Field Theories?
Every time I read about quantum field theories, I wrongly assume and associate the theory to the Standard Model, that is, our current theory of particles and interactions.
However, it seems that the ...
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What is the difference between the strong force and the strong nuclear force?
Is there a difference between the strong nuclear force, and the strong force (without the nuclear in between)? I have heard that the strong nuclear force binds protons and neutrons together, while the ...
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What is the definition of bound state in quantum field theory?
I asked a question a while a go what is a bound state and the question was closed because there is a similar question.
Now since best description we have to describe nature in quantum field theory
How ...
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What is the mathematical definition of bound state? [duplicate]
While searching why poles of Green’s function corresponds to bound states I came across that I don't know what bound state is. Intuitivaly I know that bound
State should be a state that the ...
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Potential Difference and Electrical Potential [duplicate]
What is the difference between Electrical Potential and Potential Difference?
Please try to explain in layman language
Any response would be apriciated
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What exactly is kg? [closed]
Kilogram literally makes no sense. We say that we are 10 kilogram by using the weighing scale but according to its definition, it is the amount of matter contained in an object. So how much matter is ...
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Are all materials that have 0 electrical resistance superconductors?
Are all materials that have 0 electrical resistance superconductors?
Are all perfect diamagnets superconductors？
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What is the difference between reflectivity and reflectance?
This question is in the context of solar reflections in buildings that cause glare. The two terms are similar but they have differences.
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Difference between $\mathcal{N}=2$ and $\mathcal{N}=(1,1)$ SUSY
In supersymmetry algebra, $\mathcal{N}$ refers to $I=1,2,.. \mathcal{N} $ in $Q^{I}_{\alpha}$. My question is what does it mean to write $\mathcal{N}=(1,1)$ superalgebra?
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What is equilibrium position in a pendulum? Will there be only one equilibrium position in the motion of a pendulum?
Equilibrium position of a pendulum is defined as the position where no external force acts on the body and if no force is applied, it remains at rest. In the image, isn't gravity acting everywhere, ...
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Is the magnitude of a vector equal to its length
Suppose a body has a velocity $V =2\hat i$ metres per second. The magnitude of velocity is 2 meters per second . We can draw a vector of length 2 cm to represent this velocity.
According to the below ...
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How to understand JJ Thompson's experiment without defining charge via electrons and protons?
I am beginning to learn chemistry/physics, and I have recently read about JJ Thompson's experiment which led to the discovery of the electron. In every source that I've read, the writers note that ...
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Main subatomic particles [closed]
I've come across a question that asks what the subatomic particles are. The answer being the proton, neutron and electron. However, from my understanding subatomic particles also include quarks etc. ...
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Definition(s) of polarization of waves
Is there more than one definition to "polarization" in the context of waves?
In some cases, I've seen the term "direction of polarization", which I presume it refers to the ...
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Jackson's Electrodynamics: Green's function prefactor
In Ch. 6 of Jackson's Classical Electrodynamics 3rd ed., the Helmholtz equation Green's function is written as satisfying the following inhomogeneous equation (Eqn. 6.36):
$$ (\nabla^2 + k^2)G(\mathbf{...
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Is there a non-counterfactual definition of energy? [duplicate]
I have once heard that the definition of energy is "the ability to do work". However, that is a counterfactual definition, because a physical system can have that ability without actually ...
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Is the position vector an axial vector?
The displacement vector $\vec{r}_{ij} = \vec{r}_j - \vec{r}_i$ is of course a polar vector because it's completely independent of the choice of origin, but what about the position $\vec{r}$ which, by ...
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What is the difference between the potential energy and potential function in quantum mechanics?
In quantum mechanics, we study particles in various systems, such as an infinite potential well, a finite potential well, potential barriers, potential steps, harmonic oscillators, and so on. In all ...
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What does it mean that the metric is static?
I'm reading the paper Regular phantom black holes where in page 2 (left column) the authors write that "the metric is static where $A(\rho)>0$".
Does anyone know what they mean with the ...
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What are spherical tensors?
Following Sakurai, I know how the Cartesian components of a tensor transform under rotation, in classical physics and also in quantum physics. For example, the Cartesian components of a vector change ...
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What are the extra terms in the generalized momentum regarding the Lagrangian formalism?
In the lectures, we have defined the generalized momentum in the Lagrangian to be:
$$p_i=\frac{\partial L}{\partial\dot q_i}.$$
But with this definition, if we do not make any assumptions about the ...
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What exactly are uniformly accelerating reference frames in SR?
When we talk about a uniformly accelerating reference frame in the context of Galilean spacetime, it is absolutely clear what is meant (in a previous edit I said "linearly accelerating" but ...
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Forbidden vs. allowed transitions
In Chapter 1 of his Semiconductor Devices text, Sze gives a crash course (being generous) on solid state physics. At one point, Sze talks about two classes of transitions:
Allowed direct
Forbidden ...
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On what space of maps is Polyakov path integral actually defined?
This is a question more concerned about mathematical detail involving the Polyakov path integral.
In section $3.2$ of Polchinski's 1st String Theory book it is stated the following about Polyakov path ...
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Relation between Force and Potential in a relativistic context
In a relativistic context we define the four-force as, $$\frac{\mbox{d}}{\mbox{d}s}p=F$$ In the particle frame the four-force must have the form $$F=\left(0,\ \mathbf{f}\right)$$ As it must be ...
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Why $C^{\infty}(\Sigma, \mathbb{R}^D)$ instead of $\text{Emb}(\Sigma, \mathbb{R}^D)$ in string theory $\sigma$-model?
In most String Theory textbooks, e.g. Polchinski, Blumenhagen et. al., GSW, Becker & Schwarz, Zwiebach, the dynamics of the string is firstly motivated geometrically by the Nambu-Goto action $S_{...
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How to know whether a frame is inertial or not? [duplicate]
how one would know that the given frame of reference will be inertial or non inertial, without the use of 'accelerometers'. earlier physicst has defined this concept and I am sure that they define it ...
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Inertial and non-nertial observer
Let's assume there are two observers 'A' and 'B'. B is at ground and A is moving with an uniform acceleration ('a') with respect to B. Will A be an non inertial observer with respect to B? (As we know ...
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What is the definition of velocity?
We know that displacement is change in an object's position (here position means 'position vector'). Then velocity will be change in position of the object with respect to time, simply displacement/...
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What is exactly thermodynamic equilibrium? [closed]
As I wrote in the question, what is thermodynamic equilibrium? From what I understand is a state where the thermal, chemical properties don't change with respect of the time and there is a mechanical ...
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Inertial and non-inertial frame of reference
we know that those frame of references which are in uniform motion relative to an inertial frame of reference are called inertial frame. but the inertial frame we are using for comparing will also be ...
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The fundamental equation of a system
I was reading Thermodynamics and an I（second edition） by Callen and thinking about the problem in P92.
A particular system is constrained to a constant mole number and volume so that no work can be ...
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Is all change movement? [closed]
Is there a change in the universe that cannot be reduced to movement? One counter-example should be enough. :)
Heat is a type of change that was once thought to be qualitative, but is now realized to ...
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