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

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Definition of a ray?

The typical definition of a ray and the one that I was initially taught was that a ray was a line perpendicular to the wave front. However, when reading up on birefringence it seems as though there ...
4
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1answer
213 views

Regular solution vs irregular solution

My Quantum Mechanics textbook (John S. Townsend's A Modern Approach to Quantum Mechanics) mentions regular solutions and irregular solutions. It claims that regular solutions (at the origin) to the ...
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0answers
32 views

What does 'fully excited' actually mean?

In statistical mechanics you often hear the phrases such as 'when the degrees of freedom are fully excited then....'. An example would be the validity of the equipartition theorem. But what is the ...
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1answer
33 views

Bifundamental representations [closed]

Can someone give me explicit examples (in matrix form) of bifundamental representations? Illustrative would be for instance: a) SU(3) x SU(2) b) SO(4) x U(1) c) E6 x U(1) but other you may have ready ...
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0answers
37 views

Terminology for 'inferring the current state of a quantum system as it evolves and gets measured out of your control'

Suppose I hand you a quantum computer in an unknown state, but running a known program. You know the program and which part of the program is currently being executed. The program tells the computer ...
2
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1answer
40 views

Spectroscopy, interferometry and …?

Consider the case of a Michelson 'Interferometer', from what I have read: If you measure the output as a function of mirror separation that's interferometry. If you measure the output as a function ...
5
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2answers
174 views

“Randomness” versus “uncertainty”

Highly rated PhysicsSE contributor @CuriousOne regularly makes the following claim about quantum mechanics (e.g. here): There is no randomness in quantum mechanics, there is only uncertainty. I ...
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0answers
38 views

Ampere right hand screw rule or Maxwell screw rule is the more correct name of the right hand grip rule?

Wikipedia states ampere right hand screw rule Some textbooks state maxwell screw rule Which one is the more correct name in representing the (colloquial) Right hand grip rule?
4
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1answer
320 views

What's the difference between the diffeomorphism invariance and reparametrization invariance?

Can somebody tell me what's the difference between the diffeomorphism invariance and reparametrization invariance?
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1answer
44 views

Speed of light in vacuum in special relativity

In special relativity, the speed of visible light is defined as a constant. But visible light is only a small part of the electromagnetism field. So why?
0
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1answer
62 views

Physical meaning of Phase matching

Can anyone help me understand what exactly is meant by phase matching? I want to know whether momentum can be conserved only under phase matching condition or phase matching condition ensures momentum ...
0
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2answers
103 views

Difference between scattering and refraction?

I while back I learnt that when light is incident on a dipole the dipole will scatter the light, and when it is incident on a material of a different refractive index then the light refracts. From the ...
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0answers
43 views

Are there any symbols left? [closed]

I have looked through most of the symbols used in physics and math. It seems like there are none left in the alphabet and the greek alphabet. Are we screwed if we find a new constant? Edit: How do ...
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3answers
119 views

What are the units for tenths-of-a-millimeter?

I'm seeing all kinds of mixed representations for what is a SI unit that doesn't seem to be easily representable with the Latin prefixes. Generally I stick one of the nominal ones and scale my plots ...
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1answer
15 views

Does the Schottky Barrier only happen at Metal Semiconductor Interfaces?

Most references that I have come across refer to the Schottky Barrier in the setting of Metal and Semiconductor Interface. Would it be correct to use the term Schottky Barrier to refer to the mismatch ...
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0answers
22 views

Water maintains equal level in connected vessels. What is this property called? [closed]

How water maintains same level in connected tubes or vessels? Is this a specific property?
21
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2answers
3k views

Why is the cut off mass for massive stars 8 solar masses? Why can't it be 10-11 solar masses or so?

I know that stars having a mass greater than or equal to 8 solar masses are termed "massive stars". But why is the cut-off 8 solar masses?
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0answers
53 views

Does the analogous saying: “matter is essentially 'condensed' energy” have any merit?

Einstein in his derivation of special relativity came upon the equivalence of energy and matter, and given the right circumstances, the relation can go either way - matter can become energy, and ...
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2answers
450 views

What is the difference between “additive” quantum numbers and “multiplicative” quantum numbers?

What is the difference between "additive" quantum numbers and "multiplicative" quantum numbers? I think that this may have something to do with P and C Symmetry groups, but I may be mistaken. I’m ...
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1answer
83 views

What is the difference between the Lorentz force and the ponderomotive force? [closed]

I understand that Lorentz force is due to motion of moving charged particle in a magnetic field, and I imagine that ponderomotive force is mechanical version analogy to a person surfing on a wave ...
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1answer
49 views

What is the meaning of 'physical gauge'?

What does it mean for a gauge to be a physical gauge in your gauge choice of the theory, and why is it called the "physical gauge"?
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1answer
114 views

What do we exactly mean by a “topological object” in physics?

I have been working on topological defects like monopoles, etc. for some time. One think that I have not been able to understand is the physical meaning of the phrase "topological object". I have ...
15
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2answers
506 views

What is “Dynamical phase transition”?

What is "Dynamical phase transition"? It is a fancy notion now. But what exactly does it mean? What is the difference between it and the conventional phase transition?
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2answers
57 views

Characteristic frequency

Can you please give me shortest possible (bare basic definition) of the characteristic frequency of a spectrum? All that google gives me are books and articles where I don't understand a word.
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2answers
68 views

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
21 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
34 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
86 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
56 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
242 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
50 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 ...
0
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1answer
53 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
92 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
48 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
37 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
93 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 ...
0
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1answer
62 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 ...
1
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1answer
33 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
61 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 ...
3
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0answers
31 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, $J_\text{...
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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
45 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
93 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 ...
1
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2answers
79 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
52 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?
2
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2answers
64 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.
0
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1answer
56 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 ...
4
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1answer
69 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 ...