# Tagged Questions

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### Feynman's derivation of the Schrödinger equation

I'm reading the following article: Feynman's derivation of the Schrödinger equation In this article, the autor claims that Feynman derivation of the Schrödinger equation was a key aspect of the ...
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### Hawking radiation for closely orbiting black holes

Suppose we have two black holes of radius $R_b$ orbiting at a distance $R_r$. I believe semi-classical approximations describe correctly the case where $R_r$ is much larger than the average black body ...
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### Generalisation of a particle in QFT

In classical mechanics, we assumed a particle to have a definite momentum and a definite position. Afterwards, with Quantum mechanics, we gave up the concept of a time-dependend position and momentum, ...
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### Eikonal approximation in QFT

Does the eikonal approximation for calculating a scattering amplitude in QFT provide the exact result in the limit of $s\rightarrow\infty$ at finite $t=0$ ($s$ and $t$ are the usual Mandelstam ...
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### Lack of Maslov index in the path integral formalism

Introduction Consider Feynman's famous path integral formula K(x_a,x_b) = \int \mathcal{D}[x(t)] \exp \left[ \frac{i}{\hbar} \int_{t_a}^{t_b} dt \, \mathcal{L}(x(t),\dot{x}(t),t) \...
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### How to generalize the Bohr-Sommerfeld quantization condition to more dimensions?

As in the title-how to consider this condition on e.g. a polar or spherical coordinate system, with two or three dimensions? Which different methods I can use? EDIT: the coordinate system doesn't ...
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### WKB Approximation on an linear + harmonic potential

I have a quick question: I have performed the WKB approximation to find the energies of bound states in symmetric potentials (Square, harmonic, ...). To do this I just find the "turning points" by ...
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### Gravitational wave contribution of the Hawking radiation from a black hole

Black holes are expected to radiate like a perfect black radiator at the Hawking temperature, which means that they'll emit all particles according to the relevant formulas one can derive using ...
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### Why are electrons treated classically in cyclotron measurements?

As I understand , systems having large angular momenta relative to the planck constant (limit of large quantum numbers, e.g. $J/\hbar \to \infty$), can be treated as classical systems. Now in the case ...
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### How can I use a magnet to lift a paperclip?

This question has been asked already, but no satisfying answer came up. All the answers seem to push the problem further, but do not explain clearly what is going on. I will reformulate it for a ...
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### Why do we obtain classical physics by taking the limit of Planck's constant to zero?

Why if we specifically set Planck's constant equal to zero (the limit of it) do we sometimes get classical physics? I mean, what does it mean physically to set the constant equal to zero? Or to say it ...
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### Relativistic time dilation on Mars compared to Earth?

What is the time dilation in Mars, compared to earth? Can we accurately calculate it? What information is needed to do these calculations?
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### Positive energies

If the potential is bounded below $V(x)=V(-x) \ge a$ for some real number $a$, and we can be sure that as $x\rightarrow \infty$ we know that $V(x) \ge 0$ then does it mean that the energies for ...
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### Bohr-van Leeuwen theorem and quantum mechanics

Preamble: If one considers an ideal gas of non interacting charged particles of charge $q$ in a uniform magnetic field $\mathbf{B} = \mathbf{\nabla} \wedge \mathbf{A}$, then the classical partition ...
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### Classical spin viewed as $SU(2)$

In which sense is the configuration variable of a classical spin $SU(2)$? I can view a classical spin as a unit vector in $\mathbb{S}^2$ (2-dim. sphere), but it seems it is really given by a matrix $U$...
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### Is Ehrenfest theorem equivalent to Bohr's Correspondence Principle?

Ehrenfest theorem is usually dubbed as the quantum mechanical equivalent of Newton's law and Griffiths states, in the first chapter of his textbook, that Ehrenfests theorem enables us to work with ...
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