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

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What is localization length of eigenvectors?

Apology if this question is not appropriate. I was looking to associate entropy to eigenvectors for some of my work and I found the link http://chaos.if.uj.edu.pl/~karol/pdf/ZK94.pdf . This leads to ...
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1answer
17 views

What is the difference between 'Illumination' and 'Illuminance', if any?

What is the difference between 'Illumination' and 'Illuminance', if any? From my knowledge, both of them have the same unit, the lux. So are the two words used to refer to the same parameter or are ...
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0answers
20 views

Zeeman splitting of $xcm^{-1}$

I am working through some practice problems and one question says a for the ground state of hydrogen there is a Zeeman splitting of $x cm^{-1}$. There is no other helpful information in the question. ...
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0answers
33 views

Non-local cosmology

Does anyone know what exactly non-local cosmology mean? Does it have anything to do with the scale we are dealing with or is it just the idea of objects interacting with each other despite having very ...
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1answer
69 views

Uses of effective action and effective potential

Effective potential allows us to answer the question that whether there will be spontaneous symmetry breaking induced by quantum corrections. Is there any other information that can be extracted from ...
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1answer
48 views

What is the resistance force of a ramp?

I know that the effort force is what you exert on the object, the effort distance is the length you walk on the ramp, and the resistance distance is the height that I traveled (or height of the ramp), ...
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2answers
232 views

Differences between eigenstates, bound states and stationary states [closed]

I am not very clear about the differences between eigenstates, bound states and stationary states.
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1answer
40 views

Scientific definitions of “moment (of)” and “instant”? [closed]

What are the scientific definitions of "moment (of time)" and "instant"? Are they different with their definitions in everyday language? I also don't know the definitions in everyday language, of ...
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1answer
45 views

STU-model for Black holes

In string theory in the realm of black holes, what does the acronym STU stands for when we talk about the STU model?
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3answers
76 views

What is reactive power?

I am trying to understand what is reactive power. I have read that it has a relation with voltage, that is has a relation with the creation of a magnetic field in a motor, that it is coming and going ...
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0answers
46 views

What is the difference between the pressure and “pressure force”?

I am in the process of going through a question pertaining to inviscid flow over a cylinder. The velocity field is, in polar co-ordinates: $$\vec{u} = U_{\infty}(1 - (\frac{a}{r})^2\cos2\theta,- ...
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1answer
33 views

Why there are reduced properties?

In physics we frequently encounter with quantities that are 'reduced'. But why? Why there are reduced Planck constant, temperature, pressure etc?
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1answer
81 views

Quantum Gravity vs. Quantum Field Theory in Curved Space-time [closed]

I'm a freshman on Physics course, espite of this fact I have a quite interest on Gravitation. My question is: What is the difference between Quantum Gravity and QFT in curved space-time? The great ...
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1answer
60 views

What are some of the differences between (the fields of) quantum computation and quantum information theory? [closed]

I have just started self-learning quantum information theory, and have a sub-trivial question: what is the difference between that field of study and quantum computation? I have some understanding ...
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1answer
30 views

Clarify difference between Peryton and Fast Radio Burst

Could someone knowledgeable in the phenomenon help me understand the difference between the class of observations called Perytons, and those called Fast Radio Bursts. I recall the "opening a microwave ...
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1answer
57 views

What's the difference between a short circuit and a parallel circuit? [closed]

Isn't a short circuit just a parallel circuit with one path having very low resistance? Shouldn't both paths still have the same voltage across them? So why does all the current go through the short ...
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0answers
30 views

What is the name of the basis that uses objects of definite parity?

Currents to which gauge fields couple in four dimensions can be described as follows: $$ \mathcal{L} = -g A_\mu J^\mu. $$ Sometimes it useful to discuss these couplings in the chiral basis, ...
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0answers
47 views

Is energy only an idea? [duplicate]

Physicists say that energy is the ability to do work, and work is moving something against a force, like gravity. But what is energy? Is it something real? I know I will be criticised for using that ...
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0answers
30 views

What is the definition of governing equation? [closed]

What is the exact definition of the governing equation? What is its purpose? What makes it different than other equations of physics? Why they are necessary?
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2answers
43 views

SHM with acceleration at mean position

Suppose we have an equation of motion as $$\frac{d^2x}{dt^2} = -kx + c,$$ then can it be called a SHM? Since acceleration is still proportional to displacement. But then, how will we define the mean ...
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2answers
86 views

Why is it called “escape velocity” and not “escape acceleration”?

As we know, velocity to escape from an orbit is in proportional with the orbital velocity: $$v_\mathrm{escape}=\sqrt{2}v_\mathrm{orbit}$$ Since, orbital velocity decreases as we move away so should ...
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2answers
73 views

What exactly is duality?

I came across the notion of duality recently to explain a physical concept. What is duality? Why does it occur? How do I know if two things are dual?
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1answer
51 views

Why are we mentioning weight of the product in kg? Why not Newton? [closed]

I am confused using this units. Why this changes happened?
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2answers
55 views

What is the difference between the meaning of “state space” and “configuration space”?

What is the difference between the meaning of "state space" and "configuration space"? I'm only familiar with the first, and when I look up the second I can't tell the difference.
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1answer
54 views

What does it mean to say that something is “relativistic for an electron”?

I want to understand a concept better. I did a homework problem where I solved it all the way, then checked my answer with a solution set. My answer was different, so I followed the solution set from ...
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1answer
65 views

In GR what is a “source-frame mass”?

In the recent LIGO paper, "GW150914: First results from the search for binary black hole coalescence with Advanced LIGO, (LIGO Scientific Collaboration and Virgo Collaboration)", they refer to the ...
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1answer
44 views

Energy method to solving equations of motion? Why does this method work and what is it called?

Given the stated system in the photo we are suppose to prove simple harmonic motion when given an initial displacement $x$ I first considered the total energy of the system which we will call $H$ ...
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1answer
50 views

Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= ...
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0answers
38 views

Name of the fourth entropy potential

Wikipedia's "Free Entropy" page lists three entropy potentials: Entropy, $S$, with natural variables $U$ and $V$ Massieu Potential / Helmholtz Free Entropy, $\Phi$, with natural variables $1/T$ and ...
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0answers
32 views

Why is Bohr's explanation called Bohr's model and not Bohr's theory?

I have seen an answer which tells the difference between model (specific) and a theory (general). And it makes sense 'coz Bohr explained it for the hydrogen atom only. But did he not make a set of ...
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2answers
68 views

Is standing wave realy a wave [closed]

We know that at least the waves inside a flute or laser make resonance waves,and simply we know that a standing wave is superposition of two waves that are propagating in oposit direction,for example ...
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0answers
72 views

What is a Witten diagram?

Recently I heard the terminology of Witten diagram. Studying QFT, I frequently see Feynman diagrams and use them to compute scattering amplitudes, one-loop corrections and so on. In string theory ...
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1answer
76 views

How is father of physics appointed? [closed]

I've tried Google, but couldn't figured out exactly whether its Newton, Einstein or Galileo. What is the criteria for appointment of father for a particular subject?
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1answer
117 views

What does $L^2(S^1,\mu_H)$ mean?

It's a Hilbert space, $\mu_H$ stands for the Haar measure on $U(1)$, but what does $S^1$ mean? I found it in one of my quantum mechanics books which approaches from a very 'mathematical' way.
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1answer
34 views

How do we call in English scientific terms the Fermat's principle about back and forth light traversal?

We know that the path followed by the light from point A to point B is independent of the direction of propagation of light. This is what is called in French "le principe de retour inverse de la ...
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4answers
57 views

Same equation, different meanings

I went into a physics classroom today and saw this equation written on the board: $$ E = \frac \sigma \epsilon $$ At first I thought it referred to the electric field $ E $ between 2 parallel plates ...
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4answers
129 views

What is meant by an excited atom?

I want to know how an atom is when it is excited. If an atom, due to collision of another fast moving atom, becomes fast moving as well, is that also an "excited state"?
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92 views

Which scientist is this?

Okay so I was watching discovery channel, in that i saw a man cleaning live electric wires of 10k volts in the air, he was not touching the ground. They said he was able to do this because of the ...
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1answer
71 views

Doesn't linear motion include curvilinear and rectilinear motion?

From some Portuguese language textbooks, I learned the following definitions: linear motion (movimento linear): motion along a line; rectilinear motion (movimento retilíneo): motion along a straight ...
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0answers
52 views

Terminology - optical (visual) properties of a structure

I am trying to understand few terminological problems that I encounter. Without knowing keywords it is hard to perform search for literature or publications in the area. The area relates to the ...
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3answers
61 views

What is the difference between accelerating and boosting?

My professor claimed in class that there was a difference between an acceleration and a boost. I don't really understand the distinction. If you want to go to a different inertial frame of reference, ...
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0answers
42 views

What is $\mathrm{U(1)}$ vector and axial?

In hadron physics we talked about $\mathrm{U(1)_V}$ (vector) and $\mathrm{U(1)_A}$ (axial) as well as $\mathrm{SU(3)_L}$ (left) and $\mathrm{SU(3)_R}$ (right). There are certain relations between them ...
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1answer
30 views

Prompt gamma emission vs gamma decay

I understand prompt gamma emission to mean gamma emission in a time period shorter than a second. I understand gamma decay to be the relaxion of a nucleus into a lower energy level by emission of a ...
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1answer
165 views

Repeated index in covariant derivative using abstract index notation

The same index showing up twice in the charge conservation law $\nabla_a j^a = 0$, as stated using abstract index notation, highly confuses me. If we chose a coordinate basis ...
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4answers
39 views

What is the distinction between a “ray” and a “wave” in optics?

What is the distinction between a ray and a wave in optics? From what I can gather, the only discernible difference is in nomenclature, where a ray simply refers to an EM wave with short wavelengths. ...
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2answers
70 views

Distinguishing real forces and fictitious/pseudo forces in Newtonian mechanics

In understanding the law of inertia I had to consider the motion of bodies screened from the so called "real forces". What characterises these real forces? What makes us call them real? Or what is ...
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3answers
93 views

What does “fidelity” mean?

In particular I am interested in whether it is more closely related to "precision" or "accuracy". So a somewhat mathematical description might be appropriate. For example the word "fidelity" occurs ...
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35 views

Physical intuition on bivector in fluid dynamics

Reading the M. S. Howe's Theory of Vortex Sound I've ran into this exoression and equation: Let $v_A$ denote the fluid velocity at a point A at $x$. The velocity $v_B$ at a neighbouring point B at ...
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2answers
666 views

What is polytropic index?

What is polytropic index? What is the connection between it and work of an adiabatic system? I tried surfing but didn't able to find a proper answer for that.
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1answer
54 views

Difference between escape velocity and speed [duplicate]

What is the difference between escape velocity and escape speed , is their any error if we use them interchangeably?