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 ...
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Why do electrons occupy the space around nuclei, and not collide with them?
We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
2
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10answers
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What is a good introductory book on quantum mechanics?
I'm really interested in the quantum theory and would like to learn all that I can about it. I've followed a few tutorials and read books but none satisfied my need completely.
What is the good ...
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7answers
2k views
Does Quantum Physics really suggests this universe as a computer simulation? [closed]
I was reading about interesting article here which suggests that our universe is a big computer simulation and the proof of it is a Quantum Physics.
I know quantum physics tries to provide some ...
23
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8answers
4k views
Why quantum entanglement is considered to be active link between particles?
From everything I've read about quantum mechanics and quantum entanglement phenomena it's unobvious for me, why quantum entanglement is considered to be active link. I.e. it's stated every time that ...
25
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4answers
2k views
What is spin as it relates to subatomic particles?
I often hear about subatomic particles having a property called "spin" but also that it doesn't actually relate to spinning about an axis like you would think. Which particles have spin? What does ...
10
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3answers
880 views
What really cause light/photons to appear slower in media?
I know that if we solve the maxwell equation, we will end up with the phase velocity of light is related to the permeablity and the permitivity of the material. But this is not what I'm interested in, ...
36
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7answers
5k views
Why do people categorically dismiss some simple quantum models?
Deterministic models. Clarification of the question:
The problem with these blogs is that people are inclined to start yelling at each other (I admit, I got infected and it's difficult not to raise ...
16
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9answers
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About the complex nature of the wave function?
1.
Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an ...
22
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5answers
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A list of inconveniences between quantum mechanics and relativity?
It is well known that quantum mechanics and (special and/or general) relativity do not fit well. I am wondering whether it is possible to make a list of contradictions or problems between them?
E.g. ...
22
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5answers
1k views
Hamilton's Principle
Hamilton's principle states that a dynamic system always follows a path such that its action integral is stationary (that is, maximum or minimum).
Why should the action integral be stationary? On ...
9
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5answers
2k views
Consequences of the new theorem in QM?
It seems there is a new theorem that changes the rules of the game in the interpretational debate on QM:
http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392
Does this only leave ...
15
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10answers
867 views
Why can't the outcome of a QM measurement be calculated a-priori?
Quantum Mechanics is very successful in determining the overall statistical distribution of many measurements of the same process.
On the other hand, it is completely clueless in determining the ...
10
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5answers
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Deterministic quantum mechanics
I came across a very recent paper by Gerard 't Hooft
The abstract says:
It is often claimed that the collapse of the wave function and Born's rule to interpret the square of the norm as a ...
10
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3answers
855 views
Time as a Hermitian operator in QM?
In non-relativistic QM, on one hand we have the following relations:
$\langle x | P | \psi \rangle = -i \hbar \frac{\partial}{\partial x} \psi(x)$
$\langle p | X | \psi \rangle = i \hbar ...
8
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5answers
564 views
Isn't the uncertainty principle just non-fundamental limitations in our current technology that could be removed in a more advanced civilization?
From what I understand, the uncertainty principle states that there is a fundamental natural limit to how accurately we can measure velocity and momentum at the same time. It's not a limit on ...
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1answer
287 views
confusion on quantum field theory [closed]
Having read Art Hobsons paper on Quantum field theory, he states " the field collapses into a field of atomic size" This seems to be stating that each field quanta is a different quantum field? Like 2 ...
23
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7answers
888 views
Are these two quantum systems distinguishable?
Suppose Stanford Research Systems starts selling a two-level atom factory. Your grad student pushes a button, and bang, he gets a two level atom. Half the time the atom is produced in the ground ...
14
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6answers
947 views
Why can we treat quantum scattering problems as time-independent?
From what I remember in my undergraduate quantum mechanics class, we treated scattering of non-relativistic particles from a static potential like this:
Solve the time-independent Schrodinger ...
9
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4answers
2k views
What exactly is a quantum of light?
I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a photon as a quantum of light, which it further explains as some kind of a wave-packet.
What ...
6
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3answers
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Is Dr Quantum's Double Slit Experiment video scientifically accurate?
I'm fascinated by the fundamental questions raised by the Double Slit Experiment at the quantum level. I found this "Dr Quantum" video clip which seems like a great explanation. But is it ...
20
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4answers
756 views
In quantum mechanics, given certain energy spectrum can one generate the corresponding potential?
A typical problem in quantum mechanics is to calculate the spectrum that corresponds to a given potential.
Is there a one to one correspondence between the potential and its spectrum?
If the ...
8
votes
5answers
490 views
Is it possible to recover Classical Mechanics from Schrödinger's equation?
Let me explain in details. Let $\Psi=\Psi(x,t)$ be the wave function of a particle moving in a unidimensional space. Is there a way of writing $\Psi(x,t)$ so that $|\Psi(x,t)|^2$ represents the ...
4
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5answers
470 views
Classical limit of quantum mechanics
I have heard that one can recover classical mechanics from quantum mechanics in the limit the $\hbar$ goes to zero. How can this be done? (Ideally, I would love to see something like: as $\hbar$ ...
3
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2answers
551 views
Learn algebra and interpretation of QM
I have a good undergrad knowledge of quantum mechanics, and I'm interesting in reading up more about interpretation and in particular things related to how QM emerges algebrically from some reasonable ...
2
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3answers
2k views
What is the math knowledge necessary for starting Quantum Mechanics?
Could someone experienced in the field tell me what the minimal math knowledge one must obtain in order to grasp the introductory Quantum Mechanics book/course?
I do have math knowledge but I must ...
1
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0answers
76 views
Do particles travel backward and forward in time? [duplicate]
All these classical ideas are pointless and obsolete today, because in quantum mechanics, the particles are completely different objects, defined by quantum motion of fields, not by the location of ...
8
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2answers
950 views
Proof that the One-Dimensional Simple Harmonic Oscillator is Non-Degenerate?
The standard treatment of the one-dimensional quantum simple harmonic oscillator (SHO) using the raising and lowering operators arrives at the countable basis of eigenstates $\{\vert n \rangle\}_{n = ...
37
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9answers
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Is Angular Momentum truly fundamental?
This may seem like a slightly trite question, but it is one that has long intrigued me.
Since I formally learned classical (Newtonian) mechanics, it has often struck me that angular momentum (and ...
11
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5answers
2k views
Why do people rule out local hidden variables?
I bet the automatic response to my question would be "Bells Theorem" and of course I am not disputing Bells proof, I am however uncertain of one of his assumptions.
The so called "no conspiracy" ...
13
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6answers
1k views
Quantum mechanics on a manifold
In quantum mechanics the state of a free particle in three dimensional space is $L^2(\mathbb R^3)$, more accurately the projective space of that Hilbert space. Here I am ignoring internal degrees of ...
26
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5answers
1k views
Path integral vs. measure on infinite dimensional space
Coming from a mathematical background, I'm trying to get a handle on the path integral formulation of quantum mechanics.
According to Feynman, if you want to figure out the probability amplitude for ...
12
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4answers
565 views
Reason for the discreteness arising in quantum mechanics?
What is the most essential reason that actually leads to the quantization. I am reading the book on quantum mechanics by Griffiths. The quanta in the infinite potential well for e.g. arise due to the ...
12
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7answers
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Why do people still talk about bohmian mechanics/hidden variables [closed]
I was reading the Feynman lectures in physics and after thinking about it for a while it seems particularly unreasonable to talk about hidden variables. Let us say that the electron has some internal ...
12
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8answers
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Why $\displaystyle i\hbar\frac{\partial}{\partial t}$ can not be considered as the Hamiltonian operator?
In the time dependent Schrodinger equation $\displaystyle, H\Psi = i\hbar\frac{\partial}{\partial t}\Psi$ , the Hamiltonian operator is given by
$\displaystyle H = -\frac{\hbar^2}{2m}\nabla^2+V$
...
14
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10answers
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Does the Pauli exclusion principle instantaneously affect distant electrons?
According to Brian Cox in his A night with the Stars lecture$^1$, the Pauli exclusion principle means that no electron in the universe can have the same energy state as any other electron in the ...
10
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5answers
610 views
What are some useful ways to imagine the concept of spin as it relates to subatomic particles?
The answers in this question: What is spin as it relates to subatomic particles?
do not address some particular questions regarding the concept of spin:
How are some useful ways to imagine a ...
4
votes
3answers
497 views
What is the physical meaning of a “complete” Hilbert space in QM?
What does the word "complete" means from the physical point of view?
I do not understand what it physically means to say that a Hilbert space is a complete vector space.
7
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1answer
561 views
What are the specific requirements for a do-it-yourself quantum double-slit experiment?
I was shocked to recently learn that the double-slit experiment is not only possible to do with completely ordinary equipment (with photons of course), but it actually looks rather easy. This is from ...
3
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2answers
449 views
Classical Limit of the Feynman Path Integral
I understand that in the limit that h_bar goes to zero, the Feynman path integral is dominated by the classical path, and then using the stationary phase approximation we can derive an approximation ...
6
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4answers
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On the nature of the collapse of the wave function
The collapse of the wave function by measurements is one of the most mysterious properties of quantum mechanics.
At what scale does the wave function collapse? What are the conditions for a ...
12
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7answers
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What equation describes the wavefunction of a single photon?
The Schrödinger equation describes the quantum mechanics of a single massive non-relativistic particle. The Dirac equation governs a single massive relativistic spin-½ particle. The photon is a ...
5
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1answer
252 views
Rigged Hilbert space and QM
Are there any comprehensive texts that discuss QM using the notion of rigged Hilbert spaces? It would be nice if there were a text that went through the standard QM examples using this structure.
5
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4answers
473 views
Study Quantum Physics
I'm an aspiring physicist who wants to self study some Quantum Physics. My thirst for knowledge is unquenchable and I can not wait 2 more years until I get my first quantum physics class in ...
3
votes
1answer
469 views
Schrodinger equation from Klein-Gordon?
One can view QM as a 1+0 dimensional QFT, fields are only depending on time and so are only called operators, and I know a way to derive Schrodinger's equation from Klein-Gordon's one.
Assuming a ...
2
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2answers
502 views
Why don't quantum effects invalidate the speed of light barrier?
While proving that no matter can reach the speed of light (a fact which I call the kinetic energy barrier), Einstein uses the fact that he can calculate the velocity and position of an electron. ...
1
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1answer
315 views
Schrödinger function: Separable wave function with even potential function of x
I have done the Problem 2.1 in Griffiths' quantum mechanics,
and it seems not making sense to me.
What if the wave function isn't symmetric at all?
Then obviously the proof doesn't work. The ...
0
votes
2answers
362 views
Operators Uncertainty
$\hat A$ is an operator.
The uncertainty on $\hat{A}$, $\Delta A$ is defined by:
$$\Delta A=\sqrt{\langle\hat A^2\rangle - \langle\hat A\rangle^2}$$
what is difference between
$\langle\hat ...
6
votes
6answers
610 views
What is an observer in quantum mechanics?
My question is not about (pseudo) philosophical debate; it concerns mathematical operations and experimental facts.
What is an observer? What are the conditions required to be qualified of observer, ...
5
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5answers
439 views
Linear Algebra for Quantum Physics
A week ago I asked people on this forum what mathematical background was needed for understanding Quantum Physics, and most of you mentioned Linear Algebra, so I decided to conduct a self-study of ...
3
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3answers
776 views
Popular books on QM
After some discussions with my friend about some "popular" aspects of quantum mechanics, my friend asked me whether there exist any books that could convey the basic ideas in a non-technical way (my ...
