# All Questions

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### Numerical Computation of Linbald Equation [closed]

Can anybody suggest me a good algorithm for the time evolution of the reduced density matrix using Linbald equation. My Hamiltonian is time dependent. I am aware about Qotoolbox and Qutip. I have ...
2k views

### What is the relative speed of two near-light speed particles headed towards each other?

I understand that nothing can move faster than light due to time dilation. I want to build upon my understanding of Einstein's theory of Special Relativity, so I came up with this hypothetical problem ...
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### What is $\hat{p}|x\rangle$?

Trying to solve a QM harmonic oscillator problem I found out I need to calculate $\hat{p}|x\rangle$, where $\hat{p}$ is the momentum operator and $|x\rangle$ is an eigenstate of the position operator, ...
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### What is Jacobian about the “Jacobian Edge” in $E_\mathrm{T}$ distributions?

Particle physicists often talk of a "Jacobian Edge" in distributions, i.e. when looking at the $E_\mathrm{T}$ distribution of $W \to e \nu$ decays at rest. How is this related to the Jacobian ...
3k views

### In the case of riding a bicycle, why can the system of the bicycle and rider be accelerated if no external net force?

According to Newton, if no external net force acting on a system then the system will keep its initial condition whether at rest or moving uniformly in a straight line. Let's consider a boy riding a ...
470 views

### Reducibility of tensor products of Lorentz group representations

Consider the statement: (34.29 in Srednicki's QFT text) $$\tag{34.29} (2,1)\otimes(1,2)\otimes(2,2)~=~(1,1)\oplus\ldots$$ Where of course, $(a,b)$ label representations of Lorentz group in the usual ...
644 views

### Quantum entropy in term of density matrix

Why in von Neumann expression of quantum entropy we have trace of density matrix expression? Why don't off diagonal term play a role?
301 views

### Feynman Rules in Momentum space

What's the difference between Feynman rules in momentum space for $\phi^3$ theory and for $\phi^4$ theory? I know it's only a slight difference and perhaps found in the vertex factor? But for some ...
106 views

### Enthalpic Excess - Regular Solution Upon Mixing

My professor, in his handout, says the following about this diagram : For $\beta>+2$ there are two minima and phase separation occurs driven by unfavourable enthalpic interactions. I ...
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### Number of Goldstone bosons in paramagnetic-to-ferromagnetic phase transitions

In paramagnetic-to-ferromagnetic phase transitions, the symmetry spontaneously breaks down from SO(3) to the subgroup SO(2) below $T_\text{crit}$. This implies that there should be two Goldstone modes ...
151 views

### Blonde hair looking green at certain angle

I have a friend who has blonde hair. And when look at an oblique angle, there's a tinge of light green in her hair. I've heard that the copper ion in pool water can make blonde hair green, but her ...
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### Are there any causeless phenomena from the mainstream physical viewpoint? [closed]

EDIT: The orginal version did not produce any answers about physics. I know what life is, I have studied that for decades. I wanted to hear how the border between matter and spirit looks from the ...
228 views

### What are some good resources for learning how to apply vectors in physics?

Although I don't have any problems with vectors when using them in Mathematics but I am having a hard time using them in physics. It is really frustrating me. Can you please recommend me some good ...
73 views

### Finding at a distance from the Earth speed of satellite [closed]

A satellite at 8000 km from Earth where gravity is 6.4 m/s^2. What is the velocity of satellite? I don't the formula to find speed of satellite.
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### Finding resistance [closed]

Two resistors when connected in parallel give the resultant value of $2\,\Omega$, when connected in series the value becomes $9\,\Omega$. Calculate the value of each resistance.
224 views

### The entropy of the universe in an irreversible cycle [closed]

Suppose we have an ideal gas performing an irreversible cycle composed by: an isothermal transformation at $T_{1}$; an isobaric transformation at $P_{A}$; an isothermal transformation at $T_{2}$; an ...