1
vote
1answer
176 views

Shouldn't Quantum Mechanics change in a black hole?

I recently learnt that the conservation laws are a consequence of the symmetries of space and time (the Lagrangian in Newton mechanics). Since space-time change in a black hole wouldn't quantum ...
0
votes
0answers
9 views

Refractive Index of Super Critical Fluids

I'm studying optics at the moment and I am wondering how the refractive index changes when a liquid is in super critical state? Thank you.
5
votes
3answers
175 views

Is it wasteful to use a heating element, instead of doing useful work?

Consider a computer CPU consuming electrical energy to perform calculations and consequently emitting heat. Assumption: That a CPU consuming x Watts of power, emits the same amount of heat as an ...
1
vote
1answer
57 views

Can alimentary packaging film be used to make a Fabry-Perot interferometer?

An alimentary packaging film consists on a thin plastic layer. If we put two of this films one on the other, could this acts as a Fabry-Perot interferometer? (I don't have the appropriate material at ...
7
votes
1answer
527 views

Divergent Series

Why is it that divergent series make sense? Specifically, by basic calculus a sum such as $1 - 1 + 1 ...$ describes a divergent series (where divergent := non-convergent sequence of partial sums) ...
2
votes
1answer
91 views

Does this commutation relation hold?

I was wondering whether it is true that $[L_x^2,x^2+y^2+z^2]=0$. I could not find it in the internet and therefore I wanted to ask here whether anybody here knows that this is true or false.
0
votes
0answers
24 views

Question on the Electroweak vacuum decay

Is there any current estimate of the electroweak vacuum lifetime based on the recent measurement of the Higgs boson and the top quark masses?
1
vote
1answer
119 views

Why is an exciton only observed when we excite to the conduction band and not to other electronic level inside the bandgap?

Excitons can be observed when we excite electrons to the conduction band. I don't know about excitons being observed when we excite the electrons to an electronic level that would eventually be in ...
1
vote
0answers
122 views

How does the tester screwdriver work? [closed]

How does the tester screwdriver work? If I put the tester screwdriver inside a "phase" hole of an electric socket, it lits up. If I press my finger against the metal cap on top of the screwdriver. ...
2
votes
2answers
505 views

Work done by Lorentz Force in case of motional emf

In the classical example of the slidewire generator where the rod slides on a U-shaped conductor in a magnetic field, we get a charge separation due to the Lorentz force. The way the induced emf is ...
3
votes
1answer
113 views

Laser beam position using galvanometer

In 3D printing techniques like SLA and SLS use lasers for solidifying a cross section / layer of the model that is printed. These machines, as far as I know, use XY laser scanners to project the laser ...
2
votes
1answer
115 views

Evidences against Supersymmetry [closed]

Recently, some experiments show that the supersymmetry is not realised by Nature according to the simple models that we currently have. Nevertheless, it is far from saying that the "game is over" as ...
1
vote
1answer
59 views

Mapping a given density matrix to the generalized 2-qubit state

The generalized 2-qubit state is given as: $$ \rho = \frac{1}{4}[ I\otimes I + (m_x\sigma_x + m_y\sigma_y + m_z\sigma_z)\otimes I + I \otimes (n_x\sigma_x + n_y\sigma_y + n_z\sigma_z) + ...
-2
votes
2answers
300 views

How much water from ice and after how much time? [closed]

I need two formulas in dealing with ice and water. First: If I have 2 x 2 x 2 (cm) ice cube, after it melts, how much water will there be ? Second: If I have 2 x 2 x 2 (cm) ice cube, after how ...
8
votes
2answers
204 views

Differences in the behaviour of pinching a garden hose and closing a tap

Let's say you have a garden hose connected to an ordinary water tap which is opened fully. If you pinch the end of the hose, water leaves the hose at a higher speed (and this can be useful while ...
0
votes
0answers
42 views

Eddy Currents in Metal Implants

Related: Why is stainless steel a poor conductor of electricity? I recently had a metal implant, and I'm psyching myself out- should I be considered at all with eddy currents in the implant? I feel ...
2
votes
1answer
248 views

About Poincare section for the double pendulum

I am reading Prof. Louis N. Hand's Analytical Mechanics. In the chapter about chaos, it introduces the concepts of Poincare section based on the example of double pendulum. Also, it plot the section ...
2
votes
1answer
165 views

'Fermi-Dirac'-like occupation probability at high temperature

Consider an ensemble of $N\to\infty$ free particles, each of which can assume energy states $E_i\in\{0,E\}$. Using the canonical ensemble one can compute the occupation probability for a single of ...
3
votes
4answers
221 views

Would a three wheeled vehicle be faster than a four wheeled vehicle of the same weight?

If I have a four wheeled vehicle (small wooden block with metal nail axles and plastic wheels) and apply a force X to it, would it be made faster by keeping one wheel off the ground in order to reduce ...
0
votes
1answer
177 views

Does heat increase the volume of a gas, and in turn its pressure?

Lets say you have 1 liter of hydrogen in a sealed container, at 100 psi. If 50 cm^2 of the containers surface area is heated to a 1000 degree Celsius, will the psi increase over time? What would be ...
1
vote
3answers
168 views

Non-locality and quanta

Quantum mechanics is non-local in that long distance correlations are present, though there is no signalling possible. But QFT is Lorentz invariant and contains quantum mechanics as a special case. I ...
3
votes
0answers
92 views

Functionals of quantum states in QFT

Almost every book and article I can think of represents states of QFT using the Heisenberg picture of Hilbert space vectors, but Visser in "Lorentzian wormholes" does mention that you can also ...
0
votes
1answer
81 views

Angular Momentum Conservation

There's a question I've come across that I've got some confusion on. A drum of mass $M_A$ and radius $a$ rotates freely with initial angular speed $\omega _0$. A second drum of radius $b>a$ ...
1
vote
1answer
88 views

How can I show non-Abelian CS term is a total derivative?

I want to show:$$ Tr\left (F\tilde{F} \right )=\partial_{\mu}K^{\mu }=\partial_{\mu}\left (\varepsilon _{\mu \nu \rho \sigma }Tr\left ( F_{\nu \varrho }A_{\sigma }-\frac{2}{3}A_{\nu }A_{\rho ...
1
vote
2answers
898 views

Why are there dust particles on TV screens?

My professor gave us the following reason: The screen is positively charged. When dust particles fly near it, the positive charges in the screen induce a charge in the dust particle, pulling the ...
0
votes
0answers
16 views

What is the amount of EM energy from the sun reaching the earth as a function of wavelength?

The question stems from a desire to know if more light from the sun in the infrared wavelengths has more energy than light at say yellow or violet wavelengths - at the Earth's surface. I'm guessing a ...
0
votes
0answers
73 views

Lenses and benefit of exact fourier transform

I have learned in an Optics class that a lens will "compute" the Fourier Transform of an electromagnetic wave passing through it at the focal point behind it (but with a quadratic phase). However, ...
2
votes
1answer
68 views

What is the appropriate device for measuring energy loss from collision with surface?

The surface of a running track (i.e. cinder or rubber) has an effect on a runner's performance. I would like to get some device for measuring how much energy a runner loses on each surfaces. I've ...
2
votes
1answer
64 views

Compatibility conditions of spinors and Riemannian Metrics

I came across an interesting article by Montesinos (J. Geom. Phys. 2 (1985), no. 2, 145–153.). In it, he finds that spin structures (as lifts of $SO(4)$) are not compatible with all Riemannian metrics ...
-1
votes
3answers
161 views

Can the Cosmological Constant explain an accelerated expansion?

From what I've learned so far, it appears that all models that attempt to explain the expansion of the universe are either based on Lambda-CDM or quintessence. The former support a big bang with ...
1
vote
0answers
41 views

Degeneracy and the unitarity of a gauge theory with a non-compact gauge group

The topological ground state degeneracy(g.s.d.) provides useful information for a topological field theory(TQFT), such as this post shows some example. To count g.s.d., it seems to be equivalent to ...
0
votes
0answers
166 views

How much energy does the most powerful supernova release in any form other than neutrinos?

I have read most of the supernova article on wikipedia, and there are a lot of numbers and different types of supernovae so I am confused. What I need to know is how much energy is released from some ...
1
vote
1answer
144 views

Why can't we see things swallowed by black holes?

Apologies in advance, I'm a layman with only a school-level education in physics. If an object approaching the event horizon of a black hole has its light cone progressively bent towards the black ...
0
votes
0answers
41 views

The inertia tensor is “global”, how do I make it local?

A solid cuboid has the following moment of inertia: $$I= \begin{pmatrix} \frac{1}{12}h^2+d^2 & 0 & 0 \\ 0 & \frac{1}{12}w^2+d^2 & 0 \\ 0 & 0 & \frac{1}{12}w^2+h^2 ...
1
vote
0answers
18 views

Is it possible to express “free”-ness of a time-like world line without referring to “tangent space” (but only directly to causal relations )?

I don't know much about tangent spaces, or tangent vectors, "as such"; nor about affine parametrization (which seems to be closely related to the notion of tangent vectors, as far as I understand for ...
1
vote
0answers
74 views

Inflation problem for exponential potential

I'm trying to solve the inflation problem for exponential potential. $$v(\phi) = v_0 \exp(-\alpha \phi)$$ (it's known as barrow or power law inflation) we have two main equations: $$H^2 = 8π G / 3 ...
0
votes
0answers
68 views

Born rule and Feynman propagators

Let us assume that we want to describe the full process of photon emission by electron A and absorption by electron B. Therefore electron B must be on the forward lightcone of electron A. In the ...
0
votes
0answers
97 views

Liouville's theorem on integrable Hamiltonian systems is a let down

I read a proof of Liouville’s theorem on integrable Hamiltonian systems. According to the theorem, an autonomous Hamiltonian system can be integrated in quadratures, given $n$ involutive first ...
1
vote
2answers
171 views

Classical point particles to classical fields

I often hear that in the continuum limit we can study large numbers of particles as fields. I always imagined that by removing all bounds on the number of particles (while keeping total energy, ...
2
votes
1answer
148 views

Is $v(p)\exp(ipx)$ really the positron wave function?

In many textbooks the negative energy solution of the Dirac equation is quoted as describing the positron. Actually I don't understand this. For me $v(p)\exp(ipx)$ is the wave function of an electron ...
0
votes
1answer
142 views

Infinite potential square well solutions

My question is about understanding the different solutions of the potential square well. Imagine a square well defined this way: $$ V(x) = \begin{cases} ∞&\,{\rm if} x<0 \\ 0&\,{\rm ...
0
votes
2answers
202 views

Exact definition of momentarily comoving reference frame (MCRF)

Consider a particle $P$ in the framework of special relativity with position $r(t)=(ct,x(t),y(t),z(t))$ respect to an inertial reference frame $\Sigma=(ct,x,y,z;O)$. I need to know if the following ...
0
votes
1answer
46 views

Conservation laws vs Einsteinian space-time

The way I understand conservation laws - which I am asking you to correct - is that if I observe any slice of the universe perpendicular to the time axis and count up all the mass/energy, momentum, ...
0
votes
3answers
157 views

Physically implementing quantum measurement of energy

If there were a particle in a box, how could one measure its energy? I understand the theory behind quantum measurements: the Hamiltonian operator represents the energy observable, so you perform an ...
0
votes
1answer
18 views

How can I determine a gas partial pressure knowing the flow?

I have a vacuum chamber with a pressure 10-8 Torr. Then I open an Oxygen valve with a set flow of 2 sccm from a tank with a pressure of 2 bars. The pressure in the chamber decreases to 10-2 Torr. What ...
-2
votes
1answer
55 views

Dynamics of circular motion [duplicate]

If there is a disc rotating about its centre, let the surface be frictionless and if a coin is placed anywhere on the disc (not at the center) why doesn't it fly off even though there is a centrifugal ...
4
votes
1answer
146 views

Is a Betelgeuse supernova able to neutralise earth's nuclear arsenal?

According to an article on newscientist.com, a neutrino beam could neutralise nuclear bombs by inducing a slow meltdown of the nuclear fuel. The neutrino generator would need to be more than a ...
3
votes
0answers
87 views

Trapped Surfaces. Any good articles?

I'm currently writing a dissertation on trapped surfaces as minimal surfaces. I have exhausted all of the resources I have, and the internet is pretty limited (in that it is fairly repetitive on just ...
1
vote
1answer
113 views

Smoothed Particle Hydrodynamics, Chemical Reactions and Stiffness [closed]

Dear people from stackexchange physics. I have been using SPH for quite a while to simulate free boundary flow, and just recently we tried to include some kind of (simple) chemical reaction in our ...
1
vote
0answers
68 views

Interpretation in Fourier-Laplace domain

The Green's function describing the distribution of particles sent from $\def\v#1{\boldsymbol{#1}}\def\u#1{\hat{\v#1}}\v r=0$ at $t=0$ uniformly in every directions is, in two dimensions $$ ...

15 30 50 per page