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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-theory tag for the theory of many-body quantum-mechanical systems.

22 votes
3 answers
3k views

Why doesn't the no-cloning theorem make lasers impossible?

As I understand lasers, you start off with a few photons that are in an identical state, and other photons that are created later tend to have the same quantum numbers due to Einstein-Bose statistics. …
yippy_yay's user avatar
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11 votes
2 answers
2k views

Why were the fathers of quantum mechanics so sure radioactive decay was indeterministic?

The classic example of an indeterministic system is a radioactive isotope, e.g. the one that kills Schrödinger's cat. I get there are arguments against hidden variables in quantum mechanics, but how …
yippy_yay's user avatar
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9 votes
5 answers
970 views

Why isn't there an atom with an electron at the center and a proton on the outside? [duplicate]

I can understand that the role of electrons and protons are not interchangeable for elements heavier than Hydrogen, because there is no nuclear force to keep the charged electrons together in a nucleu …
yippy_yay's user avatar
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5 votes
4 answers
630 views

Why does a force field leave the momentum operator unchanged in the Schrödinger equation?

The reasoning leading to the Schrödinger equation goes as follows: A plane wave in empty space has the following form: $$\psi = e^{i(kx-\omega t)}$$ Einstein had previously explained the photoelect …
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2 votes

The Momentum Operator in QM

As opposed to classical mechanics, where a particle is represented by a momentum and position vector that have determined directions and magnitudes, in Q.M. the particle is in a "superposition" of dif …
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2 votes

Where does the Born rule come from?

For an electromagnetic wave, the Energy is proportional to the Electric/Magnetic Field (i.e. the wave) squared. This is a classical result which can be derived from the Maxwell equations. When photon …
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1 vote
Accepted

Why does a force field leave the momentum operator unchanged in the Schrödinger equation?

I found a proof that the momentum operator does not change when the wave it operates upon is not a plane wave: Let $\phi(k) = \frac{1}{2\pi}\int\limits_{-\infty}^{\infty}e^{-ikx}\psi(x)dx$ be the Fo …
yippy_yay's user avatar
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