4
votes
1answer
453 views

Difference between baryonic, inertial and gravitational mass? (and relation to dark matter)

Inertial mass: determined from Newton's f = ma Gravitational mass: determined via Newton's law of gravity Baryonic mass: sum of mass of all baryons. Which ones ...
4
votes
7answers
982 views

For a theoretical (not mathematical) physicist, is there a need to learn pure mathematics?

For a theoretical physicist (not a mathematical physicist), is there a need to learn pure mathematics ?
8
votes
2answers
2k views

Why does it seem like a broken magnet's poles flip?

I just took a rare earth magnet out of an old hard drive. Lacking an appropriate screwdriver, force was used, and the magnet broke into two pieces; one about a quarter of the original size and one ...
2
votes
2answers
3k views

Electron behavior changes when observed?

I saw this video of the double slit experiment by Dr. Quantum on youtube. Later in the video he says, the behavior of the electrons changes to produce double bars effect as if it knows that it is ...
2
votes
2answers
427 views

Non-renormalizable corrections to GUT unification

While writing these answers: Hypercharge for U(1) in SU(2)xU(1) model and Is there a concise-but-thorough statement of the Standard Model? , it occured to me that the unification prediction for ...
3
votes
1answer
819 views

What is a free fermion model?

Title says it all really.. Why is the XX spin chain a free fermion (non-interacting) model, and the XXZ chain not? Is it right that $\sum_l a_l^\dagger a_{l+1}$ isn't an interaction between fermions ...
1
vote
5answers
36k views

Yield Strength versus Ultimate Strength

What is the qualitative difference between these two: As seen on the table Typical yield and ultimate strengths. I am trying to resolve the meaning of the phrase "contact yield stress" from C. ...
6
votes
1answer
92 views

Allowed states vis-a-vis allowed dynamics in generalized probabilistic theories (GPTs)

In his work on information processing in GPTs http://arxiv.org/abs/quant-ph/0508211 Barrett speculates that the trade-off between allowed states and the allowed dynamics in a GPT is optimal in quantum ...
3
votes
2answers
205 views

Timber floating in the river

There's an old puzzle (but the physical it is): Lumberjack chop wood and float it down the river. He noticed an interesting feature: in the spring, when the water is comming, timber is nailed to the ...
15
votes
2answers
293 views

Geometric quantization of identical particles

Background: It is well known that the quantum mechanics of $n$ identical particles living on $\mathbb{R}^3$ can be obtained from the geometric quantization of the cotangent bundle of the manifold ...
12
votes
12answers
6k views

Can there be black light? I mean is it possible to devise a machine that outputs darkness?

I understand there are various colours that light can have. But i was wondering why there is no 'black' light. What is the logical explanation for this? I mean I am expecting an answer that goes ...
5
votes
2answers
146 views

Is the distinction between the Poincaré group and other internal symmetry groups artificial?

For instance, given a theory and a formulation thereof in terms of a principal bundle with a Lie group $G$ as its fiber and spacetime as its base manifold, would a principle bundle with the Poincaré ...
4
votes
7answers
461 views

Is 'now' smeared over time?

Conventional physics as is usually presented in textbooks deals with the evolution of states in phase space parameterized by sharp instances in time, a real parameter. However, quantum fluctuations ...
2
votes
2answers
3k views

Metric tensor of coordinate transformation

How do you find a metric tensor given a coordinate transformation, $(t', x', y', z') \rightarrow (t, x, y, z)$? Our textbook gives a somewhat vague example as it skips some steps ...
3
votes
2answers
2k views

Hermitian operator and reality of eigenvalues

Prove or disprove: The eigenvalues of an operator are all real if and only if the operator is hermitian. I know the proof in one way; that is, I know how to prove that if the operator is hermitian, ...
3
votes
2answers
5k views

What's the difference between constitutive laws and governing equations?

I'm studying about the finite element method in a class but I don't come from a civil engineering background. Anyways, it hasn't been made clear to me what the difference between constitutive laws and ...
2
votes
2answers
759 views

Galilean transformation in relativity

Assume flat spacetime in a general relativistic framework (or special relativity for that matter) and two observers $A$ and $B$, with non-vanishing velocity relative to each other. We know that they ...
1
vote
2answers
442 views

Hydrogen 2P Probability Density Question

I'd like to calculate the probability density for Hydrogen in the $|2,1,1\rangle$ and $|2,1,-1\rangle$ states. There is an $\exp(\pm i\phi)$ term attached to the wave function for these states. It ...
6
votes
1answer
54 views

Transit of Mercury: how did he see it?

On November 7, 1631 Pierre Gassendi saw the transit of Mercury across the face of the Sun. How did he see it? I mean what instrument was used to reduce the apparent brightness of the Sun?
2
votes
2answers
815 views

How do I rearrange dE/dt to find an electron's 'half-life' due to synchrotron radiation?

I know that $-\frac{\mathrm{d}E}{\mathrm{d}t} \propto E^2$ for an electron losing energy to synchrotron radiation, but I can't find how to arrange this to give the time it would take for the electron ...
2
votes
2answers
406 views

WHy is SUSY QM important?

why is SUSY QM important ? i mean for each one DImensional Hamiltonian , can we write 'H' as $ H= A.A^{+}+C$ (or similar constant) here $ A= \frac{d}{dt}+A(x)$ and $ A^{+}= -\frac{d}{dt}+A(x)$ 1) ...
7
votes
3answers
3k views

Why is beta negative decay more common than beta positive?

In simple terms, why is beta negative decay more common than beta positive? I know it's something to do with occuring inside/outside the nucleus - but I can't find a simple, easy to understand ...
1
vote
2answers
2k views

Y Intercept of photoelectric effect graph?

In a graph of KE=hf-W (the photoelectric effect equation), why is the work function equal to the y intercept? I mean I can see why it is using the equation (y=mx-c) but conceptually, why is the work ...
0
votes
1answer
121 views

Difference between $|0\rangle$ and $0$ in the context of isospin

I know this has been asked before, but I am confused having read it in the context of isospin, where the creation operators act on the "vacuum" state (representing no particles) $$a^\dagger_m|0\rangle ...
1
vote
1answer
122 views

On a frictionless table, what is the angle at which a cue ball should hit another ball for it to go in?

Assume there are 2 balls on the table. Cue ball and another ball. What is the angle at which the cue ball should hit another ball for it to go in?
19
votes
2answers
3k views

Is the CMB rest frame special? Where does it come from?

It seems that we are moving relative to the universe at the speed of ~ 600 km/s. This is the speed of our galaxy relative to the cosmic microwave background. Where does this rest frame come from? Is ...
3
votes
4answers
4k views

Is it only red, green and blue that can make up any color through additive mixture?

I'm reading about color vision and have some trouble understanding the motivation for why the trichromatic theory was suggested in the first place. The book I'm reading ("Psychgology: The science of ...
17
votes
2answers
174 views

What Shannon channel capacity bound is associated to two coupled spins?

The question asked is: What is the Shannon channel capacity $C$ that is naturally associated to the two-spin quantum Hamiltonian $H = \boldsymbol{L\cdot S}$? This question arises with a view ...
2
votes
1answer
13 views

Are there trends in the number of meteors in a shower year on year?

Some years the Leonids are amazing, other years there are very few - are these predictable at all, following trends or at least reasonably accurate predictions?
4
votes
2answers
1k views

Why are there both Static and Kinetic Friction?

When dragging an object, there is a greater start-up force than the force it takes to keep it moving. Why is this? Why are there two different values for friction?
6
votes
2answers
133 views

Infinity of running couplings

A Landau pole - an infinity occurring in the running of coupling constants in QFT is a known phenomena. How does the Landau pole energy scale behave if we increase the order of our calculation, (more ...
3
votes
1answer
1k views

What are the polarization states of the photons in a polarized and unpolarized light?

The photons are completely polarized, i.e their polarization states can be expressed as $a|R\rangle+b|L\rangle$, where $|R\rangle$ and $|L\rangle$ are two helicity eigenstates of the photon. For ...
0
votes
1answer
816 views

Projectile motion question: vertical and horizontal graph

I've have got some vertical and horizontal distances for a projectile-like motion. In order to work out the trajectory, why is it better to plot on the x-axis, "horizontal distance^2", and on the y ...
1
vote
1answer
220 views

Are there any good audio recordings of educational physics material?

I am studying to return to school in physics and would like to start spending as much time as possible on that task. Most of my small amount of free time, however, I am either doing house work or ...
2
votes
1answer
2k views

Force on rope with accelerating mass on pulley

I have a pretty basic pulley problem where I lack the right start. A child sits on a seat which is held by a rope going to a cable roll (attached to a tree) and back into the kid's hands. When it ...
4
votes
3answers
347 views

returning to physics research?

What the the most realistic and practical ways for a PhD in physics who has left the fold to return to a career of research in physics? The traditional employer of choice, universities won't hire such ...
4
votes
4answers
383 views

Applications of recoil principle in classical physics

Are there any interesting, important or (for the non physicist) astonishing examples where the recoil principle (as special case of conservation of linear momentum) is applied beside rockets and guns? ...
7
votes
1answer
711 views

Renormalization scheme independence of beta function

I have some questions about renormalization. To my understanding, in order to deal with infinities that appear in loop integrals, one introduces some kind of regulator (eg, high momentum cutoff, ...
4
votes
3answers
2k views

What is lepton number?

What exactly is a lepton number of a particle? With the charge (eg proton is just 1, not the exact charge), I can understand because it's a physical property, put a particle with charge + next to ...
8
votes
2answers
2k views

Is the Mendeleev table explained in quantum mechanics?

Does anybody know if there exists a mathematical explanation of Mendeleev table in quantum mechanics? In some textbooks (for example in F.A.Berezin, M.A.Shubin. The Schrödinger Equation) the authors ...
2
votes
3answers
41 views

Where can I find a list of when I can see something in the sky?

My son is very keen on Astronomy but I don't know when there are meteor showers or something else that would be worth going out to the country to see. Last year we went to see a meteor shower, but I ...
3
votes
5answers
2k views

About the Ether Theory acceptance

Why was the Ether Theory refused by Modern Physics? If you please explain me, I just wanted to understand it more.
14
votes
2answers
448 views

Which CFTs have AdS/CFT duals?

The AdS/CFT correspondence states that string theory in an asymptotically anti-De Sitter spacetime can be exactly described as a CFT on the boundary of this spacetime. Is the converse true? Does any ...
10
votes
4answers
727 views

On-shell symmetry from a path integral point of view

Normally supersymmetric quantum field theories have Lagrangians which are supersymmetric only on-shell, i.e. with the field equations imposed. In many cases this can be solved by introducing auxilary ...
9
votes
1answer
114 views

Global symmetry in string theory

It is often stated that in quantum gravity only charges coupled to gauge fields can be conserved. This is because of the no hair theorem. If a charge is coupled to a gauge field then when it falls ...
7
votes
1answer
219 views

Supersymmetric Nonrenormalization Theorems

I'm looking for approaches to nonrenormalization theorems in supersymmetric QFT which are as much as possible mathematical, elegant and involve few heavy straightforward computations
0
votes
2answers
394 views

Physics textbooks reference request [duplicate]

Possible Duplicate: Book recommendations I am currently in the 11th grade (I am an Indian student) and I am looking forward to studying pure mathematics and theoretical physics in the ...
-1
votes
1answer
256 views

Is the Standard Model experimentally verified? [closed]

Has the Standard Model of Particle Physics been experimentally verified? Or is it still waiting for experimental verification? OR, What aspects/predictions of the Standard Model have been ...
12
votes
0answers
100 views

Minimal strings and topological strings

In http://arxiv.org/abs/hep-th/0206255 Dijkgraaf and Vafa showed that the closed string partition function of the topological B-model on a Calabi-Yau of the form $uv-H(x,y)=0$ coincides with the free ...
7
votes
1answer
290 views

Where is the velocity term in Dirac current hiding?

The dirac current is $$J^\mu = \bar{\psi}\gamma^\mu \psi $$ It looks weird at first because there is no derivative in the expression. So the velocity must be hidden somewhere in either $\gamma$ or ...

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