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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Precise Definition of Degrees of Freedom [duplicate]
I am taking Analytical Mechanics and while reading Goldstein's and LL something bothered me: can I say that a degree of freedom is an independent (generalized) coordinate?
What bothers me is that we ...
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Defining Nuclear Reaction and Beta Decay
I use a school textbook that defines nuclear reaction in the following way. I will go through what does make sense to me, and then point out the thorns.
"When an atom changes into a different ...
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Why is entropy defined in the way it is?
In thermodynamics course we were taught that in a reversible adiabatic process of an ideal gas the entropy change is zero.
Now what I didn't get intuitively is that if the system is compressed ...
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Is there a formalization of the butterfly effect?
According to my understanding, the butterfly effect says, very informally, that even a tiny perturbation in a physical system can lead to significant alterations in future states of the physical ...
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What are relativistic particles? [duplicate]
What are relativistic particles? I got it in a question of mechanics.
So, what is it about a particle that makes it "relativistic"?
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Can the composition law of a group be defined only when considering a representation or realisation of the Group?
When we talk about, lets say, the Lorentz group, we define the action of the Lorentz transformation $\varLambda$ on
\begin{alignat}{1}
x^{\mu} & \in\mathbb{R}^{1,3},\\
x^{\mu} & \rightarrow x'^...
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In what sense is $\int (u \cdot \nabla) u \cdot u dx$ an energy flux?
Due to the nature of this question I have have cross-listed it on mathSE.
Let $u$ be either a solution to either the Euler equations or Navier-Stokes equations over a domain $\Omega$. In fluid ...
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What is the name of the transformation from one harmonic oscillator basis to another centered elsewhere?
If I have a harmonic oscillator basis centered at $x=2$, how do I rewrite it in terms of the harmonic oscillator basis centered at $x=0$? To be more specific:
If $|\Psi_n\rangle$ is the $n$th ...
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The definition on vacuum-vacuum amplitude with current in chapter of External Field Method of Weinberg's QFT
I'm reading Vol. 2 of Weinberg's QFT. As what I learnt from both P&S and Weinberg, the generating function is defined as
$$
Z[J] = \int \mathcal{D}\phi \exp(iS_{\text{F}}[\phi] + i\int d^4x\phi(x) ...
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Why isn't work a state function?
I've heard the example, that work is path dependent. But whether I climb a mountain directly or in serpentines, in the end it's the same amount of work, with the one difference that it takes me longer ...
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Equivalent definitions of Wick ordering
Let $\phi$ denote a field consisting of creation and annihilation operators. In physics, the Wick ordering of $\phi$, denoted $:\phi:$, is defined so that all creation are to the left of all ...
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Why is Wigner-Seitz cell considered primitive?
During the lecture I listened, as well as in the internet, in Wikipedia for example, unit cell was defined as the parallelepiped spanned by the translation vectors. Primitive cell was defined as the ...
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Kinetic Energy equation: Is $K=\frac12mv^2$ a Definition, or a derived Theorem?
I am trying to understand classical physics as a mathematical model. I will first specify the trail of thoughts that led up to this question. (Please correct me if anything is wrong with the reasoning ...
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Is there any difference between Wick time order and Dyson time order?
Reading A Guide to Feynman Diagrams in the Many-Body Problem by R. Mattuck, I am getting the feeling that I missed something subtle related to time order. When deriving the Dyson series for the ...
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Mathematical meaning of a position eigenbra $\langle x_0 |$
Let $|x_0\rangle$ be an position eigenket. The physical picture I have for $|x_0\rangle$ is a particle located at $x_0$. Thus it should be represented by a delta function $\delta(x-x_0)$.
For $f\in L^...
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