1
vote
0answers
1k views

Lagrangian of pendulum with pivot point rotating about a circle [closed]

I just would like to know If I am on the right track with this stuff. I have scanned the work I have done, sorry if it is a little messy. Disregard the top most $\ddot x$ A disk of radius ...
5
votes
3answers
377 views

Do electrons in multi-electron atoms really have definite angular momenta?

Since the mutual repulsion term between electrons orbiting the same nucleus does not commute with either electron's angular momentum operator (but only with their sum), I'd assume that the electrons ...
0
votes
1answer
86 views

Optimal methods for mapping out molecules, atoms and nuclei and their energy levels?

I'm wondering if it would be possible to map out all the different types of molecules, atoms and nuclei and their energy levels on one page (even if in a generalised way)? But perhaps I'm referring to ...
4
votes
3answers
521 views

How can a vertical force cause motion at an angle?

I just started learning physics 3 days ago and am having trouble understanding what I am doing wrong. Can someone please explain my error(s)? Thanks! We have a 1kg object on a plane at a 30 degree ...
1
vote
1answer
121 views

Looking backwards in time at yourself

If a person on Earth today is looking at a star, say, 10 billion light years away, is it possible that some of the atoms he is looking at will eventually go on to make him?
1
vote
1answer
152 views

Is there a finite unit of distance that we cannot divide past?

If distance could be divided into an infinite no of units or points, then it seems to me that motion would be impossible since a meter for instance, having an infinite no of points within it (and the ...
8
votes
1answer
400 views

How fast is the matter and antimatter reaction compared to nuclear chain reaction?

What I mean is, the nuclear chain reactions take microseconds for every generation and that is the reason that nuclear weapons exist. Because in nuclear reactors the reaction rate is much slower thus ...
2
votes
1answer
182 views

Massless Dirac equation is Weyl covariant

Does somebody know how to show that the following equation is Weyl invariant? $$\gamma^ae_a^\mu D_\mu \Psi=0$$ where: $D_\mu \Psi=\partial_\mu\Psi+A_\mu^{ab}\Sigma_{ab}\Psi$ is the spin-covariant ...
2
votes
1answer
112 views

Time taken for gravity of a distant object to interact with a newly created particle? [duplicate]

Possible Duplicate: The speed of gravity Does gravity travel at the speed of light? Imagine there is a large mass $m_1$ (e.g. a star) 1 light-year away from us. It is stable, stationary ...
0
votes
1answer
77 views

Gravitational potential energy with regards to annihilation

Given particles A, B, C and D, where: A and B have an equivalent mass C and D have an equivalent mass, both larger than A (or B) D is the antiparticle of C. A and B start close to C, but with ...
0
votes
1answer
240 views

Question about non-holonomic geometric constraints

Suppose a point particle is constrained to move on the curve $y=x^2$. This would then be a non-holonomic geometric constraint since the particle has one degree of freedom and requires two coordinates ...
0
votes
4answers
1k views

Could one argue that h (Planck constant) and $\hbar$/2 (Dirac constant) are in fact independant constants?

My question is very naive and could sound strange but it seems to me natural in so far as the Planck constant is related to the first quantization (of newtonian particle mechanics/galilean relativity) ...
0
votes
2answers
124 views

Is there a limit to the charge of a body?

Can a body be limitlessly charged? Suppose a sphere of radius $R$. Can it be charged limitlessly?
0
votes
1answer
165 views

Quantum mechanics, whats possible?

There is a thread in Physicsforums.com which states due to Quantum Mechanics, if you wait long enough diamonds will appear in your pocket, it also states its possible for all your atoms to ...
0
votes
1answer
204 views

Is it possible to charge a capacitor to any potential? Does it depend on the dielectric placed between them?

Is it possible to charge a capacitor to any potential? Does it depend on the dielectric placed between them? Or, are there other factors affecting it?
0
votes
0answers
546 views

How to calculate the force between two different magnets?

I'm doing an experiment and I need to calculate the force between two magnets with different stats, different sizes and flux density. I learned physics in high school so I know all the terms. In my ...
4
votes
2answers
324 views

What's the difference between divergences that can be corrected and those that can't

I'm confused by renormalization . If a lagrangian has a term with negative mass dimension , why can't the divergences be absorbed into lagrangian coefficients? What's the difference between ...
1
vote
2answers
1k views

Total Mechanical Advantage

How do you find the net Mechanical Advantage (MA) of two joint machines. Do you add or multiply the individual MA? Suppose I have two sets of wheel and axle connected by a fixed pulley. Each of the ...
0
votes
0answers
88 views

path integrals: how/why can the phase be identified with the action?

In Peskin & Schroeder, chapter 9 introduces the functional methods. The idea, to recall, is simply to sum over all the possible paths: $U(x_a,x_b;T) = \sum_{\text{all paths}} e^{i . ...
1
vote
1answer
262 views

In which direction is the acceleration directed in a non uniform circular motion?

Acceleration is directed towards the center of the circle in a uniform circular motion. Is it same for the non-uniform circular motion?
1
vote
1answer
90 views

Is the time of collapse of the wave function empirical?

Is the time of the collapse of the wave function empirical? Suppose there is a very long von Neumann chain of observations of a quantum system. Suppose also practically irreversible decoherence ...
5
votes
2answers
1k views

Chern-Simons term

In the literature I can only find Chern-Simons terms ( i.e. for a 3-dimensional manifold $A \wedge dA + A \wedge A \wedge A$) for odd-dimensional manifolds. Why can't I write such forms for ...
-2
votes
1answer
201 views

Cosmology: can something come from nothing? [closed]

It is often said that something CANNOT come out of nothing? Is this true? Is there a way to test the properties of nothing to make this assertion?
6
votes
1answer
246 views

Is color confinement detected?

I'm a graduate student studying QFT. I'm quite interested that is color confinement detected or proved? (both directly and indirectly) Or it is just an assumption?
-1
votes
1answer
111 views

Grandfather Paradox [closed]

This question related to the Grandfather Paradox. Assume that time travel to the past is a reality. What experiment/test could the time traveler perform in order to determine if he is in his own ...
2
votes
2answers
4k views

converting power spectrum to photon flux density

So I'm having trouble converting units and was hoping somebody could point out where I've gone wrong... It seems I'm missing something fundamental. a Power Spectrum has units $kW/m^2-\mu m$ for the ...
3
votes
2answers
504 views

Spinning spheres colliding

In an ideal environment with no friction, in a vacuum, what happens to the velocity of the spin of two spheres spinning in perfect parity at two different velocities when they come into contact?
3
votes
3answers
690 views

What is the current through the lamp?

We have the following circuit: A neon lamp and a inductor are connected in parallel to a battery of 1.5 $V$. The inductor has a 1000 loops, a length of $5.0 cm$, an area of $12cm^2$ and a ...
6
votes
1answer
727 views

Difference between $\partial$ and $\nabla$ in general relativity

I read a lot in Road to Reality, so I think I might use some general relativity terms where I should only special ones. In our lectures we just had $\partial_\mu$ which would have the plain partial ...
6
votes
1answer
944 views

Maximum Principle vs. Minimum Principle in Non-equilibrium Thermodynamics

Prigogine's Min. principle states that in steady-state non-equilibrium systems the entropy generation rate is at a minimum, i.e., a system will seek a steady-state that has min entropy generation. ...
3
votes
1answer
324 views

Does electric potential have a temperature?

When I took my first thermo class a tucked away chapter introduced Exergy in terms of electrical energy, meaning that the amount of electrical energy you could get from something is functionally its ...
-1
votes
1answer
535 views

Gravitational redshift derivation

When we derive gravitational potential it is dependant only on (rest) mass $m$, but i have seen a derivation of gravitational redshift equation placing relativistic mass $\widetilde{m}$ instead of ...
2
votes
3answers
219 views

Quantum mechanics in macroscopic systems

I don't understand the superposition principle in quantum mechanics or the collapse of wave-function (I think it's impossible for me to understand it) My question is: Is it possible to demonstrate ...
7
votes
2answers
1k views

Does chaos theory occur in quantum mechanics? Or in any non-newtonian physics?

Does chaos theory occur in quantum mechanics? Or in any non-newtonian physics? Apart from perhaps thermodynamics?
1
vote
1answer
53 views

Are the ions in a fluorescent lamps concentrated near the electrodes?

Are the ions in a fluorescent lamps concentrated near the electrodes , and just the electrons move to the other electrode or the positive mercury ions move too?
3
votes
2answers
455 views

The direction of the Lorentz Force

We have a square loop (I believe it's called) in a uniform magnetic field between the 2 poles of a permanent magnetic field (green is N, red is S). P is connected to the positive pole of a voltage ...
3
votes
2answers
1k views

Kinetic energy of a photon and Schwarzschild radius

I have read here, that $\frac{1}{2}mv^2$ must not be applied on a photon ever. If i want to calculate escape velocity $v_e$ i need to use $\frac{1}{2}mv^2$ because we say that kinetic energy ...
0
votes
1answer
384 views

Why are magnetic lines of force invisible?

We can very well feel the magnetic field around a magnet, but we can't see it. Why is that so? Also, can we cut a portion of the field and use it?
3
votes
2answers
4k views

block slides on smooth triangular wedge kept on smooth floor.Find velocity of wedge when block reaches bottom

Find the velocity of the triangular block when the small block reaches the bottom: Here is what I did: The final velocity(at the bottom)of the small block of mass m is $\sqrt{2gh}$ along the plane ...
0
votes
1answer
177 views

Dichroism in uniaxial crystals

I need a same help with it. Some books where i can find a real math explanation of this effect will be good help!! simple exp of this effect will be good too)
1
vote
1answer
311 views

Density of States for Fermi's Golden Rule

I recently read a question on fermi's golden rule posted here: Fermi's Golden Rule and Density of States However, I do not really know how you would go about obtaining a value for the density of ...
6
votes
1answer
428 views

Diffeomorphisms and boundary conditions

I am trying to find out how did the authors in this paper (arXiv:0809.4266) found out the general form of the diffeomorphism which preserve the boundary conditions in the same paper. I found this ...
2
votes
1answer
56 views

Question about linacs

Why are the electrodes of a linac connected to an alternating voltage? Within an electrode the electron moves with a constant speed, and once it is outside of the electrode it accelerates uniformly, ...
1
vote
1answer
60 views

Disregarding drag force that affects pop-up lightweight ball

Is it possible to disregard drag force of water with no viscosity that affects lightweight pop-up ball (its weight is assumed to be zero)? There is a discussion, on which I consider that although ...
0
votes
1answer
315 views

Explosion of a Neutron Bomb

Watching "The Dark Knight Rises", Bane announces halfway into the movie at the stadium that what they have is a neutron bomb. But then at the end of the movie there is an actual nuclear explosion ...
6
votes
2answers
506 views

Do the energy levels of electron orbitals change relativistically?

When an electron emits a photon from changing energy levels, the frequency of the photon depends on the difference between the energy levels. But if someone is moving with respect to the atom, the ...
37
votes
4answers
2k views

Is there a Lagrangian formulation of statistical mechanics?

In statistical mechanics, we usually think in terms of the Hamiltonian formalism. At a particular time $t$, the system is in a particular state, where "state" means the generalised coordinates and ...
6
votes
1answer
173 views

Is there an equivalent of a Galton box for a converging probability?

This is a question about probability. The Galton box (or quincunx) uses the physical process of shot moving down a pin-board, to demonstrate central limit theorem, eg: So I am interested in events ...
6
votes
1answer
167 views

What is the first appearance of the MV (McLerran-Venugopalan) initial condition?

First a quick introduction for the unfamiliar: in saturation physics (my research field), a lot of theoretical work centers on the BK (Balitsky-Kovchegov) equation, which is a differential equation ...
8
votes
2answers
453 views

Translation Invariance without Momentum Conservation?

Instead of the actual gravitational force, in which the two masses enter symmetrically, consider something like $$\vec F_{ab} = G\frac{m_a m_b^2}{|\vec r_a - \vec r_b|^2}\hat r_{ab}$$ where $\vec ...

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