# Tagged Questions

Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy and the uncertainty principle and is generally used in single body systems. Use the quantum-field-...

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### On a measurement level, is quantum mechanics a deterministic theory or a probability theory?

Quantum mechanics is a non-commutative probability theory. As such, it fundamentally behaves differently from classical probability theories. This manifests itself most pronouncedly in the uncertainty ...
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### Express state as eigenkets

this is very basic but I just suddenly confused. Since any state can be expressed as complete set of eigenkets with discrete eigenvalues $$|P\rangle = \sum^n c_n |p_n\rangle$$ I understand above. But ...
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### Can this relativistic hack allow one to see beyond an event horizon, in principle, else why not?

Consider a lone photon. As its frequency increases, its energy increases. Taken to the limit, a sufficiently-high-frequency photon could be a black hole unto itself. But the frequency of a photon is ...
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### Two particles system

Source: http://www.youtube.com/watch?v=k3K_lyvbfOE For two particles system(09:30), why is it wave function a product of each particle's wave function? E.g.$$\psi(x_1,x_2)=\psi_a(x_1)\psi_b(x_2)$$ ...
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### Can we predict throwing a dice?

What happens if we throw a dice from same position, with same force, by creating a vacuum environment on earth? Will it be predictable now i.e. will the dice have same results all the time? If answer ...
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### Is it possible to synthesize an EMW which is not quantized?

( I initially started to ask, "since according to Quantum-theory of light; the energy of a photon, depends only on the frequency of light-wave (E = h * nu), and no-mention of amplitude. So, does the ...
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### Why is the energy expressed in an electron orbital change of state electromagnetic (photon)? [on hold]

As I understand, Schrodinger's wave equation predicts the allowable energy states an electron can have under the electromagnetic forces of a given nucleus (and I assume other 'orbital' electrons). If ...
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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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### Energy Spectrum and Gauge Transformations

There is a question in SE about the fact that the Hamiltonian isn't invariant under the EM gauge transformations. I wanted to ask about its consequences here. I know that in general, the Hamiltonian ...
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### Free particle Schrodinger equation: propagator

I am going through Shankar's Principles of Quantum Mechanics and am having trouble finding the free particle propagator $U(t)$ that satisfies $\lvert\psi (t)\rangle = U(t)\lvert\psi (0)\rangle$ due to ...
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### What's role of signal-to-noise ratio in the quantum measurement? [on hold]

Recently, I've been watching videos of MIT opencourse (http://www.youtube.com/watch?v=TcvY8Nt0ZGA&list=PLUl4u3cNGP62FPGcyFJkzhqq9c5cHCK32&index=2) taught by Nobel laureate Wolfgang Ketterle. ...
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### Is it possible to reconstruct the Hamiltonian from knowledge of its ground state wave function?

Is it possible to "construct" the Hamiltonian of a system if its ground state wave function (or functional) is known? I understand one should not expect this to be generically true since the ...
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### Is the single slit experiment a practical example of Heisenberg's uncertainty principle?

I saw some videos where a person points a laser through a slit. As they reduce the width of the slit, the diffracted image spreads out, like this: Can this pattern be viewed as a consequence of ...
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### How force get transmitted when a magnet attracts iron?

According to particle physics , every fundamental force has its force carrier particle. Photon is a force carrier particle of electromagnetic force but how does force gets transmitted when a iron is ...
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### Minimum gap between consecutive energy levels?

Assume a standard one-particle, non-relativistic Hamiltonian of the form $$H=\frac{p^2}{2m}+V(r)$$ and denote its eigenvalues as $E_{n,\tau}$, where $n$ is the principal ...
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### Simplest way to store a quantum superposition temporarily [on hold]

My understanding of the Schroedinger's Cat experiment is that, while it's an amusing thought experiment, the cat would not actually be in a superposition of states because it's just too massive an ...
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### How does an operator transform under time reversal?

We know that a time-reversal operator $T$ can be represented as $$T=UK$$ where $U$ is some unitary operator and $K$ is the complex conjugation operator. Then under time-reversal operation, a quantum ...
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### What am I missing on my thougth expierement? [on hold]

Before I say my thought experiment I wanted to state that most of my knowledge on physics and such is from college books, and not from actual instruction. I arrived at this conclusion and realized I ...
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### Possiblity for particle to be carried by a wave such as a photon or electromagnetic wave/waves in general for means of transportation/travel? [closed]

I am wondering whether it is possible for a photon/EM wave to carry a very small particle like an elementary particle or smaller on it like a highway carries a car traveling on the highway or an ocean ...
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### Switching Parity in a Superconductor

I've got a pretty simple question that's been bothering me for a while. This is the issue. Suppose we have a superconductor with phase $\phi$, and we change this to $\phi+2\pi$. One would think that ...
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### Doesn't quantum uncertainty disprove string theory? [duplicate]

String theory states that the oscillations of little strings are responsible for all the particles in and the evolution of the universe. The specific type of particle created by a string depends on ...
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### Why don't the internal electric and nuclear forces holding atoms and molecules together cause decoherence during a buckyball double-slit experiment? [on hold]

My understanding is that anything that qualifies as an "observation" or "measurement" will cause the "fuzziness" of the superposition to disappear to the local observer, and the results of said ...
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### Direct Sum representation of multiple particles in Quantum Mechanics

Suppose that I have three non-interacting spin-1/2 particles such that I can represent the combined system in a basis of \begin{align} D^{(1/2)}_1 \otimes D^{(1/2)}_2 \otimes D^{(1/2)}_3 & =(D^{(...
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### Problem with figuring out sign conventions in QFT

I have a problem with sign conventions in QFT which I have trouble dealing with myself. I self-study and mainly use Weinberg and Peskin. I will present the reasoning following conventions adapted by ...