# All Questions

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8 views

### Does the timeline of earth changes if Gravity exceeds 15g instead of 9.8g?

as we present a timeline to be the 4th dimensions will the dimension changes simply changing the gravity? lets say 9.8g to 15g what will be the impact on the timeline as we represent timeline as ...
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### Negative pressure in general relativity

Is there an intuitive way to understand what negative pressure means in general relativity in the same way as positive pressure can be thought to be kinetic energy of gas particles? Dark energy has ...
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### I am confused about image formation of object on itself by a system of lens and a mirror

If there is a lens and a mirror. An object is place in front of this system (nearer to lens), if final image of object( refraction, reflection and again refraction) is forming on object itself, then ...
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### The change in mass of a black hole do to Hawking Radiation

Hawking radiation which is the result of virtual particles, which are always created in pairs,(particle/antiparticle) near enough to the event horizon of a black hole, that one of the pair falls in ...
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### Which book (or article) has detailed calculation for Quantum Heisenberg Model for three or four spins? [on hold]

A I need to write a program to calculate Quantum Heisenberg Model for any number of spins (with or without external magnetic field). I know how to do this calculation for two spins. Which book (or ...
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### Heat-bath algorithm of 2D XY model

Can anyone suggest any reference where the heat-bath algorithm for the classical 2D XY model has been discussed in detail. I have found references for the 3D Heisenberg model which can be exactly ...
15 views

### Minimum calculus for Lagrangian Mechanics [on hold]

I have noticed in my classical mechanical books, the development of the motions of equation for simple systems using the Lagrangian that the main complication, if doing the work by hand, is applying ...
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### Capacitance and energy transfer

Capacitors: Using direct current I apply a voltage, Vo, to a capacitor of capacitance C. It acquire a charge of Qo. I remove the charging source and I connect both sides of the capacitor to another ...
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### Superconductivity as a macroscopic phenomena

I have been doing some reading on the formulation of BCS superconductivity. From what I understand, an additional non-vanishing term $\Delta c_{\uparrow,k}c_{\downarrow,-k} + c.c$ develops below the ...
52 views

### What exactly is a gluon doing when acting as an gauge boson?

The question is in the title. I know that, e.g., W bosons change the flavour in electroweak processes. What do gluons do?
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### As a returning adult learner from engineering and math background, what recommendations to get the basics on QM?

I'm building up the foundations to work on quantum mechanics. I am comfortable with the wave function and the PDE aspect of the field, but my mathematical background, though it covers linear algebra, ...
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### Given the action, derive the Lagrangian (Fields and non-fields)

Let us denote $L$ the Lagrangian, and $\mathcal{L}$ the Lagrangian density, and the action $S$. It is common to find the action based on the Lagrangian. Here, however, I am interested in the reverse ...
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### Initial conditions in QM

My questions are about initial conditions in QM in experiment and in lab. We consider many different initial wave functions, and we solve the problem on paper. Now, I have 2 questions about this in ...
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### There was no Big Bang [on hold]

It wasn’t an explosion. The composition of the Universe is missing 94.6% of the required material to cause a Big Bang. LIGO Satellites with 25 million mile long legs, in a rtriangular formation ...
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### Black Body Emission Curve and Self Heating [on hold]

Sorry that the original question is not as clear as it should be. How much would self heating of a blackbody (via kinetic heat energy) effect a blackbody emission curve in equilibrium? ie: Is it ...
34 views

### Schwinger paper about charge in QED

I would like to find the paper by Schwinger where he discusses analytic properties of physical values in the limit $e\rightarrow 0$ and physical meaning of $e^2$ sign. I know only that this paper was ...
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### Can temperature difference in a conductor induce charge in it?

Assume a metallic rod which is heated on its right end to maintain a constant temperature gradient in the rod. Now if we take any crossection in the rod,the right side part of the cross section has ...
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### Why is it assumed that magnetic forces arising from magnetic fields do not do work on a current carrying conductor?

Imagine a long, thin current carrying conductor carrying a current I and moving through space with a velocity $v$. If there exists a magnetic field such that there is a force on the current carrying ...
54 views

### Why is $\Delta^0$ not decaying weakly?

Given the lower decay I wonder why it happens this way. Wouldn't it be possible to decay via a weak process as well?
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### Difference between left- and right-handed, helicity and chirality

What is the difference? I know there is the (almost) same question What's the difference between helicity and chirality? but when a particle is given as left-handed. Is it helicity or chirality?
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### Symmetry reason why magnetic dipole transitions are suppressed

In the theory of light-matter interaction, electric dipole transitions between two atomic states of same parity are forbidden. This is because the Hamiltonian conserves parity. Is there a symmetry ...
43 views

### The origin of normal reaction

I want to know what actually is the origin of normal reaction between 2 objects. i have read about normal reaction from several books which generally mention it as a component of contact force which ...
63 views

### What causes objects to appear “black”?

To my understanding, the reason objects appear of a certain color is because it is the color (in visible light) that is absorbed least by the electrons in the material's atoms, and the rest is ...
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### Time travel is possible? [on hold]

Is the time travel theory of Einstein practical?If yes,then how can we travel faster than light ?
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### Kinematics problem, only energy related approach [on hold]

I read this question: From the top of a tower, a stone is thrown up and it reaches the ground in time $t_1$. A second stone is thrown down with same speed and it reaches the ground in time $t_2$. A ...
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### Is my thinking correct for partial derivatives and tensors?

So I was transforming the affine connection and I ended up with a term like this: $$\frac{\partial^2 x'^a}{\partial x'^b \partial x^p}$$ where $x$ and $x'$ are two different coordinate systems ...
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### How do elecrons move?

Do elecrons move from low to high potential or they move due to attraction by positive charge? Or is it something else, what actually happens in flow of electricity.....the concept is just so ...
35 views

### Is a force on the edge of a disk also a torque if the disk is not constrained?

Suppose you have a disk in a vacuum that is completely unconstrained (not fixed at its center). If you apply a tangential force at a point on the circumference of the disk, does the force act purely ...
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### Magnet position for maximum voltage in an ac generator (Lenz's Law)

Animated gif credit The picture above shows, that the voltage of a phase is greatest, when the magnet alligns with the coil of the phase. Why is that? To my knowledge of lenz's law the voltage and ...
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### Ignoring 2nd order terms in QM definitions of translation and momentum operators

In Sakurai's 'Modern Quantum Mechanics', he defines the infinitesimal translation operator as: $\mathcal{J}(d\mathbf{x}')=1-i\mathbf{K}\cdot d\mathbf{x}'$, and then he goes on to prove this ...
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### Does the postulate of equal a priori probability apply only to equilibrium states or to all states satisfying the constraints?

In deducing the zeroth law of thermodynamics in micro-canonical ensemble, there is a frequently-mentioned example. Suppose we put two isolated system, system 1 and 2, in contact and allowing them to ...
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### Positive Semi-Definiteness of a Density Matrix - can the eigenvalues be larger than 1?

I know that one of the requirements for a density matrix is that it is positive-semidefinite. This means that the eigenvalues are non-negative (and sum to 1, so we can assign them the meaning of ...
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### What are some of the many types of string theory and other theories? [on hold]

I've been working on an essay about string theory and other theories, and would love to know some of the others that I could research. Thanks!
Consider a Lie algebra $\mathcal{G}$ of the form $$[T_i, T_j] = f_{ij}^k T_k$$ which has an Abelian (corresponding to the Abelian Lie algebra $A$) central extension $\mathcal{H}$ of the form [T'_i, ...