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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Renormalization group equation, the Callan-Symanzik equation, and renormalization group flow
I am learning about the renormalization group and I am getting confused on some terminology.
For the massless $\phi^4$ theory the Callan-Symanzik equation is:
$$\big[ M \frac{\partial}{\partial M} + \...
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Clarification regarding the meaning of Universal Time UT1
I've been reading the book "From Sundials to Atomic Clocks: Understanding Time and Frequency" by James Jespersen and Jane Fitz-Randolph which is available at https://www.nist.gov/system/...
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Why is angular momentum defined so?
We know angular momentum is defined as $mvr$. In the context of Lagrangians and Noether's theorem, this definition pops up as the conserved quantity due to rotational symmetry of the system. Is there ...
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What exactly is kinetic energy? [duplicate]
What exactly is kinetic energy? I know that kinetic energy is the energy that an object obtains by the virtue of its motion, but I need an exact answer. So, potential energy, like there are three main ...
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Definition of angular velocity in rotational motion of a non-rigid body? [closed]
Consider a particle in rotational motion with radius r and angular velocity w both varying with time, what is the relationship between the displacement u and w of the particle? $w=\frac{\partial u}{\...
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Inconsistent definitions of Entropy [duplicate]
On the wikipedia page "Entropy", entropy is defined as $S=k_B \ln\Omega$, where $\Omega$ is "the number of microstates whose energy equals the system's energy". This is what I had ...
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In physics, what is the difference between a fact and a definition?
For example, I came across this statement:
"It is a fact that the components of force are derivatives of potential energy, but it is not a definition."
What does this statement mean?
I ...
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Contracting the metric tensor with its inverse yields Kronecker delta
It's probably straightforward, but I would like to see the proof of the identity:
$$g_{\mu\nu}g^{\nu\alpha}=\delta^\alpha_\mu.$$
In the book 'Spacetime and Geometry' by Carroll, this identity is the ...
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What actually is Boyer-Lindquist coordinates?
I want to know the difference between spherical and Boyer-Lindquist coordinates. Don't they both use $r, \theta, \phi$ parameters? I've searched books and sources on the internet and there's none that ...
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Definition of quenched data set/disoprder in the context of spin glass
I cannot come across a good definition of what "quenched" means in the context of spin glass problems. I see such use as "quenched connectivity", "quenched data set", &...
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Fierz idendity (supersymmetry)
So basically I have two Fierz identities involving spinors:
$$\psi^a \psi^b = -\frac{1}{2} \epsilon^{ab} \psi \psi$$
And
$$\overline{\psi}^{\dot{a}} \overline{\psi}^{\dot{b}} = \frac{1}{2} \epsilon^{\...
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Difference between stationary states, collision states, scattering states, and bound states
A few weeks ago, I was presented one-dimensional systems in my QM class, and of course one-dimensional potentials too. Nonetheless, I'm still a bit unclear about the terminology my professor uses. ...
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Cosmology - Anthropic Principle [closed]
What do cosmologists actually mean by Anthropic Principle? What are the differences between weak and strong Anthropic Principle?
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Matter vs antimatter asymmetry per particle [duplicate]
What is called matter and what is called antimatter is just a convention, isn't it? For example, suppose we call the bottom, the charm and the down quark antimatter and we call the strange, top, and ...
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Definition of generalized force in Lagrangian formalism
In some texts (e.g. Taylor's Classical Mechanics), the generalized force is defined to be (I'll simplify to one particle in one dimension for ease of notation): $Q \equiv \frac{\partial{L}}{\partial{q}...
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