Questions tagged [quantum-mechanics]

The branch of physics that relates to the behavior of objects, typically particles, on small scales. Probability is very important in quantum mechanics.

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Why Doesn't Einstein Get More Credit for Being the Father of Quantum Mechanics?

I'm not simply referring to the notion that Einstein treated the discrete emission and transference of energy (and matter) as "real" physical phenomena, but rather his major continuous role in the ...
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During the development of QFT was this theory actually used to build any invention like the MRI?

I have always wondered if the equations of quantum field theory were actually ever used in the production of some invention or device other than needed to make predictions about the Standard Model of ...
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What was Einstein's contribution to the Einstein-Podolsky-Rosen (EPR) paper?

Do we have any insight or document into theoretical development of the EPR papers both in terms of math, ideas and anything related to actual physical problem. I know that Einstein didn't write the ...
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What is the first effect demonstrating the importance (or existence) of quantum coherence?

As far as I know, in the old quantum theory, a system can only reside in a stationary state. There was no Hilbert space, and no linear superposition. Or, a system cannot be simultaneously in two ...
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Who first noted the connection between Heisenberg's Uncertainty Principle and the Fourier Transform?

This is a question about the history of Quantum Mechanics. Who first noted the connection between Heisenberg's Uncertainty Principle and the Fourier Transform?
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Etymology of 'qubit'; is there any relation to cubits?

Whilst several not-very-authoritative sources e.g. Wikipedia state that the word qubit was derived, partially, as a play on the word cubit (obviously it also stands for 'quantum bit'), is there any ...
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How Bohr guessed the quantisation rule?

We all know Bohr's Quantization rule as L=nh/2pi. How did Bohr derive this? If it is a guess, what is the reason behind choosing h/2pi and not some other constant? ...
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Did Werner Heisenberg ever agree or propose the existence of some kind of multiverse?

I was watching a video (https://www.youtube.com/watch?v=muJYTeQlvC4) where the director of a videogame company speaks about one of its most successful games. This game is set in a floating city which ...
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What is the history and motivation for the (d-1,1) notation used to describe a field theory?

Very often in the literature of research papers and other articles, and maybe text books, on topics of quantum field theory, a theory may be described as a 3+1 or 0+1, or maybe even 1+1 theory. I ...
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Did the concept of the Dirac Sea influence the development of semiconductors like the transistor?

Dirac (1928), (http://rspa.royalsocietypublishing.org/content/royprsa/126/801/360.full.pdf) explained the negative-energy solutions of his equations as holes in a sea of electrons. The concept seems ...
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What did Hans Bethe think of von Neumann's quantum logic?

Nobel laureate Hans Bethe was a friend of mathematician-physicist John von Neumann, and he once said: "I have sometimes wondered whether a brain like von Neumann's does not indicate a species ...
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Which is the physical interpretation of the “strange” constant $e \cdot c/ 4 \pi$?

This constant is assignable to charged leptons $(e, \mu, \tau)$ representing the fraction of their individual magneton $\hat{m}= e \cdot \hbar/ 2 m$ to their Compton-wavelength $\lambda_{C} = h / m ...
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Max Planck and energy quantization idea

Did Planck have an intuition behind the idea of energy quantization of atomic oscillators and radiation, or it was just a mathematical trick to drive his distribution law?
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Why is the angular momentum written as JJ in quantum mechanics?

Why is $\textbf{J}$ called angular momentum operator? Can anyone explain why the expectation value of J is angular momentum? Here is how $J$ is defined: The rotation operator $$ U(\alpha)=\exp(-i {\...
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Planck's quantization idea

First of All, I doubt there has ever been any new idea that did not involve intuition. However, most textbooks suggest that the quantization idea was just a mathematical trick, that Planck introduced ...