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15 views

How to prove that a $d$-dimensional Hilbert space can only have $d^2$ equiangular vectors (i.e. that a SIC is a maximal collection of that kind)?

It is an open question if every $d$-dimensional Hilbert space contains a collection of $d^2$ states, such that every two have a scalar product of $\frac{1}{d+1}$, i.e. if a SIC-POVM exists for every ...
0
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0answers
7 views

Measuring inner choke point on non-uniform silica capillary tube

I hope this is an appropriate place to be asking questions like these (google brought me here when I was searching for a solution)! I make an assembly where a small silica capillary tube (OD of 1mm) ...
0
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1answer
25 views

Representation of spin-$1/2$ operators in terms of Majorana fermions

I am reading Quantum Field Theory in Condensed Matter Physics by A.M. Tsvelik. In Chapter 20, it is claimed that introducing three Majorana fermions $\gamma^\mu_i$ on each site $i$ of the lattice (...
1
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1answer
40 views

How to get the Bertotti-Robinson metric into its conformally flat version?

The Bertotti-Robinson metric is a very nice exact solution to the Einstein-Maxwell field equations in vacuum. It is usually stated into these equivalent versions (where $r = \sqrt{x^2 + y^2}$ and $\...
4
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1answer
170 views

What fuel is J005311 burning?

J005311 is two white dwarf stars that have merged in such a way, that, well they merged instead of exploding. (Only 7 or so such mergers have been found.) Its stellar wind is blowing at 16,000 km ...
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1answer
29 views

Why do we have to introduce quasiparticles in the Fermi liquid theory

Why is it necessary in Fermi liquid theory to introduce quasiparticles? I understand the notion of system where someone can turn on the interactions slowly (i.e., adiabatically), but I do not ...
1
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0answers
56 views

Conserved quantities of a simple Lagrangian

Suppose the following Lagrangian with 2 degrees of freedom: $$L = \frac{3}{2}\dot{q}^2_{1} \ + \frac{3}{2}\dot{q}^2_{2} \ + \dot{q}_{1}\dot{q}_{2}$$ My aim is to find all the conserved quantities of ...
1
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1answer
50 views

Show for $r \in \mathbb R$, $e^{(a_1 ^\dagger a_2^\dagger - a_1a_2)r}|0,0 \rangle = \frac{1}{\cosh r} \sum_{j=0}^\infty (\tanh r)^j |j,j \rangle$

Let $ a_1, a_2 $ be annihilation operators for the first and second component in the product state $|m,n \rangle$ using Fock basis. Following "Quantum continuous variables, A primer of Theoretical ...
3
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2answers
52 views

Sequential Double Double Slit Experiment?

Let's say you arrange the double slit experiment so that there are two sets of two slits one after the other. Like so: ...
0
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0answers
15 views

What differences would be observed in the Stern-Gerlach experiment when using neutral fluorine (Z=9) and neutral sodium (N=11)

I have been working through some past exam papers for my Quantum Mechanics module, and one of the questions is what would be different about observing the results of the Stern-Gerlach experiment when ...
0
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1answer
25 views

Can we use energy–momentum relation with scalars to get meaningful result?

Does energy–momentum relation (as defined in the beginning of wiki/Energy–momentum_relation) meant to be used only in terms of stress-energy-momentum tensor but not with simple scalars?
4
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0answers
71 views

The spinor metric, basic spinor calculations and spinor indices

I'm currently reading the textbook "Finite Quantum Electrodynamics" by Günter Scharf, but I find myself stuck already on page 24. Background Scharf introduces the index-raising symbol (spinor metric)...
0
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0answers
6 views

“Directional” conductivity in linear flux-potential laws?

Question: Has the notion of "directional conductivity" been defined and used in the study of heat flow and electric current flow? Context: The table below gives three laws that describe linear flux-...
0
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0answers
29 views

Quintessential models for dark energy

Following Sean Carroll here There are good reasons to consider dynamical dark energy as an alternative to an honest cosmological constant. First, a dynamical energy density can be evolving slowly ...
0
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1answer
73 views

How can light reach its speed? [duplicate]

The mass of a photon is said to be 0, But light (photons) get attracted due to gravity of a black hole, that means photons have a mass which is very very very small. And we know that any object with ...
0
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0answers
15 views

Formulation for the fluence from energy-density

I'm struggling to find a mathematical expression for the total fluence of a traveling electromagnetic wave (through vacuum). Though its not really a physics problem rather than a problem with basic ...
0
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3answers
40 views

Why is there a 1/2 in the expression for electrostatic energy U?

The expression for electrostatic energy is $$U= \dfrac{1}{2} \times \int \rho\,\phi\, dV$$ where $\rho$ is the charge density and $\phi$ is the potential at that point in ($dV$) Let me explain what I ...
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0answers
29 views

Determining whether I hit the bed when jumping from a cliff [on hold]

For simplicity, assume a perfectly spherical object with uniform density falling from some height to a lake. How can I determine whether I hit the bed of the lake? Maybe this has something to do with ...
0
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0answers
33 views

Coordinate-free proof of the constancy of the scalar product of a Killing vector with the geodesic tangent vector along the geodesic

I would like to know if the following proof of the constancy of the scalar product of a Killing vector with the geodesic tangent vector along the geodesic is correct. I already found a coordinate-...
1
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1answer
52 views

Why is $J/\psi$ not being able to decay into $\pi^+\pi^-\pi^0$ (Ozi-rule)?

There are already (very similar) questions like What is the precise statement of the OZI Rule? and Why does charmonium (and phi mesons) not decay via quark and antiquark annihilation? but, to be ...
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0answers
24 views

Relation between current (not at saturation) and voltage in photoelectric effect

This is the question I got for an assignment. How do I determine stopping potential from this data? I can see that the relation between $V$ and $I$ seems to be linear, so can I just use the equation ...
1
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0answers
22 views

Defining Angle between Observables consistently

Problem Setup: There is a nice proof of the heisenberg uncertianty principle using cauchy-schwarz given here Stated in variance form it is: $$ \sigma_x^2 \sigma_p^2 \ge \frac{\hbar^2}{4} $$ Now ...
1
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0answers
17 views

Finding an equivalent shape for a given mass and 3 mass moments of inertia

So I apologize if this is just impossible, but I was wondering if there was a way to find say, the dimensions of a box of a given density that would have the same mass and moments of inertia of ...
-6
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0answers
48 views

Ray Theory of Light [on hold]

Can ray theory be used to explain wave nature of light? True/False ? Explain it with reason.
0
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0answers
29 views

Hydrogen hyperfine structure from H2-molecule, interacting H-atoms or independent H-atoms?

On hyperphysics the hyperfine structure of hydrogen is compared to that of deuterium: According the Hyperfine structure on Wikipedia In atoms, hyperfine structure arises from the energy of the ...
2
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0answers
39 views

Are first Integrals the same in Lagrangian and Hamiltonian formalism?

A first integral in Lagrangian formalism is defined as a function which is constant along the solutions $(q,\dot{q})$ where $q$ are the generalized coordinates; while a first integral in Hamiltonian ...
2
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0answers
30 views

Regularization methods' equivalence and the hierarchy problem

There are several questions related to this one but whose answers just raise the doubt I'm going to describe here. Some facts that are everywhere are (i) The hierarchy problem results from the fact ...
1
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1answer
46 views

3D reflection of a ray on a cylindrical mirror

I am trying to calculate the reflection of a ray on a cylindrical mirror in a three-dimensional space. To achieve this, can I apply the laws of reflection separately in xy and xz planes (as in the ...
1
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2answers
96 views

How does the Carnot Cycle work?

I am learning the Carnot cycle, which consists of four transformations for a fluid. In the first two transformations the volume of the fluid expands, generating work. This happens in two steps: ...
0
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0answers
27 views

Resonance in physics

The resonance is a physical phenomenon which manifests itself in several contexts. It is asked the general characteristics and a specific example in order to illustrate how the typical parameters of ...
0
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1answer
29 views

The exact location of normal force and friction vectors

I am struggling with a following question: "A cylinder of radius $r$ and height $h$ is standing on an inclined plane pitched at an angle $\theta$ to the ground. Given the coefficient of friction $\mu$ ...
1
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0answers
33 views

Please check my problem about SI prefixes [on hold]

2.2 A single logic gate in a prototype integrated circuit is found to be capable of switching from the “on” state to the “off” state in 12 ps. This corresponds to: (a) 1.2 ns; (b) 120 ns; (c) 1200 ns; ...
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1answer
33 views

Change of variable in 4D space-time

I was reading Sidney Coleman's article "Fate of the false vacuum: Samiclassical theory" and i stumbled upon a change of variables that i can't seem to prove. The problem is this: trying to solve the ...
5
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1answer
78 views

What kind of engine is a photovoltaic solar cell?

I have read several times here (on PSE) and there (in Google) that photovoltaic solar cells aren't heat engines. I.e. they are not working via a heat transfer between 2 reservoirs, and so they are not ...
0
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0answers
48 views

What generates physical meaning in mathematical quantum theory?

Let mathematical quantum theories be theories of Hilbert-space rays together with probability / amplitude / unitary evolution / Hermitian operator machineries. Observations essentially correspond to ...
1
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1answer
44 views

If electric field is conservative then line integral along closed path is zero, then why is potential not zero?

Here in the first image it is said $\displaystyle \int_a ^b E\cdot \mathrm dl\,$ is $0 $: Here in the second image it looks like $\displaystyle \int_a ^b E\cdot \mathrm dl\,$ is not $0$: If field ...
0
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0answers
33 views

Simulating Frisbee trajectories in Python [on hold]

So I've been trying to simulate the trajectory of a frisbee in flight thrown with different angles of attack/initial velocities. The differential equations used for the code are: $$\frac{dv_y}{dt} = ...
0
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0answers
37 views

Why is silicon absorbing visible light?

Here it is shown that silicon absorbs visible light: but the band gap energy for direct transitions is 3.6 eV which does not match to this absorption coefficient. Instead, the band gap energy for an ...
12
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4answers
2k views

What triggers a nuclear decay?

I am not a physicist but I have been wondering about this: I understand that the decay of a nucleus is a random event and one cannot predict exactly when it will happen for a particular nucleus. ...
0
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2answers
60 views

Two particles at different points on a curved manifold

Stupid question, but why two particles at different points on a curved manifold do not have any well-defined notion of relative velocity? For instance n cosmology the light from distant galaxies is ...
0
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1answer
45 views

Fractional electric charges

Since the Oil droplet experiment we are talking about elementary electric charges: Charge quantization is the principle that the charge of any object is an integer multiple of the elementary charge....
0
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1answer
36 views

What is the difference between the structure of plane and circularly polarized light?

According to https://www.azooptics.com/Article.aspx?ArticleID=65 "If the polarization of all the electromagnetic waves in a light beam can be made so that each of the electric or magnetic field ...
2
votes
2answers
89 views

What is the mass of photon? [duplicate]

I'm sorry if this question is asked before, but I searched through the site and none satisfied me. In most of the books I've come across, they just write "rest mass of photon is zero." But never talk ...
2
votes
3answers
173 views

Total force on upper block in two block system

If a block $m$ is placed on another block $M$ and a force $F$ is applied on bolck $M$. Then how many forces are acting on block $m$.(Friction is non zero) The image is taken from this site. Is ...
0
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0answers
14 views

Magnetoresistance

Why free electron theory could not explain magnetoresistance, but the two0band model could. I need the physics behind the explaination. A lot of theory have been provided, but how to physically ...
0
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1answer
25 views

Interaction between electrons in which the magnetic dipole moments interact more strongly than their electric fields

Asking a question Has anyone tried to incorporate the electrons magnetic dipole moment into the atomic orbital theory?, I was curious whether anyone has attempted to relate the intrinsic property of ...
1
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0answers
31 views

Direct Products in Coordinate Basis

I am reading quantum mechanics by R. Shankar and I was confused about how he projected the state vector onto the two-state coordinate basis. Below is the part that he wrote $\\$ Since the notion ...
2
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0answers
34 views

Event horizon area and entropy content of a black hole

I am aware that the entropy content of a black hole is proportional to the area of its event horizon, and that this can be boiled down to the bit content of a Planck area on the horizon, but I have ...
0
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0answers
12 views

Why the sum of deformations in given figure is zero?

When a vertical block is kept between two fixed support and when the bottom support is removed, it has the possibility of facing a deformation downwards which was impeded by the upward reaction force ...
-1
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0answers
23 views

Toilet Paper roll [on hold]

Why we don't replace R in formula (RT=(1/2)m(R2+r2)(a/R)) into (R,outer diameter +r,inner diameter)? Does the inner roll also rotate?

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