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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13 views

Degeneracy of harmonic oscillator

Let we have a two dimensional potential for harmonic oscillator which is $\frac{1}{2} m \omega^2 x^2$. If I am asked to evaluate the degeneracy of Quantum state with energy $2\hbar \omega$ then ...
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18 views

How can electrons still occupy orbitals in metals if they are delocalised?

I was reading about why most metals are gray/silvery in colour and it said something about d orbital electrons transitioning to s orbitals and the visible spectrum not having sufficient energy to ...
0
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0answers
29 views

Speed of electrons at given temperature in non Hydrogen-like atoms

I may be somewhat confused on the topic, so please excuse me if this is really basic. For the Hydrogen atom, one can easily derive the expectation value of the electron's speed: $$ \langle v \rangle ...
4
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0answers
57 views

Solving Schrödinger's Equation for the electronic energies of the Molecular Ion Hydrogen H2+ in the Elliptic coordinate system

Electronic Energies of Molecular Ion Hydrogen $H_2^{+}$ $r_1$ is the distance between the proton $1$ and the electron. $r_2$ is the distance between the proton $2$ and the electron. $R$ is the ...
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0answers
39 views

High energies for small length scales

One of the biggest challenges in experimental high energy physics is to reach ever higher energies in order to be able to probe ever smaller volumes/distances of space! This is suggestive of a type of ...
0
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0answers
43 views

is it possible to get “100% sure” physical/chemical measurements and/or “100% clear” compounds? [on hold]

The obvious question for any serious movie fan of the famed "Breaking Bad" series is, arguably, "is the chemistry setting (e.g. the famous "Heisenberg Purity") realistic at all?". The question itself ...
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0answers
23 views

Practical uses of superfluids [on hold]

I am wondering whether and how superfluids (possibly at room-temperature, if that is possible at some point) can be of any practical use in mechanical or electrical engineering or other fields. I ...
6
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4answers
711 views

Is uncertainity a postulate? [duplicate]

I heard the standard interpretation of Heisenberg Uncertainty Principle: Just the measurement affects the position of the body because always you want to see a body (=to measure the position), you ...
1
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2answers
74 views

Has Dirac ever co-authored a paper? [on hold]

Just curious. Not counting PhD theses, books, and review papers, but regular research papers with original ideas.
2
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2answers
46 views

Proof of: if $\hat H | a_n\rangle=a_n|a_n\rangle$ then $f(\hat H)| a_n\rangle=f(a_n)|a_n\rangle$?

In Quantum Mechanics you have the eigenvalue equation: $$\hat H | a_n\rangle=a_n|a_n\rangle \tag{1}$$ where $\hat H$ is the Hamiltonian operator, $\{|a_n\rangle\}$ is a complete set of eigenstates ...
4
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4answers
102 views

How to determine the observables rigorously?

In Quantum Mechanics, as I know, if a system is described by a Hilbert space $\mathcal{H}$, each physical quantity is associated with some hermitian operator $A : U\subset \mathcal{H}\to \mathcal{H}$ ...
1
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2answers
75 views

Entanglement and coherence

I have come across a wonderful review of entanglement by Chris Drost in his answer to this post. One part that left me puzzled was: (This post is merely an attempt to understand a portion of Chris' ...
2
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2answers
83 views

Wavefunctions in different Hilbert spaces

The state of a quantum system is represented by a wavefunction usually in some specific Hilbert space, .e.g of position, spin, momentum etc. But before deciding in which of these bases to decompose ...
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2answers
85 views

Understanding the Bloch sphere

It is usually said that the points on the surface of the Bloch sphere represent the pure states of a single 2-level quantum system. A pure state being of the form: $$ |\psi\rangle = a |0\rangle+b ...
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1answer
38 views

Can quantum entanglement work like this?

Lets say you have two entangled particles (A,B) and you already measured theirs spins and know that A has z+ and B has z- What will happen if after the measurement you will set the spin of B to z+ ...
1
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3answers
52 views

With respect to the Casimir effect, why can't the wavelengths of the virtual particles between two plates just “pass through” the plates themselves?

I've read over the years that the suppression of many of the possible wavelengths between the two plates in a Casimir experiment is what causes the phenomenon (top comment on this Askscience thread is ...
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0answers
5 views

What exactly is an integral kernel? [migrated]

I am not sure if I have seen integral transforms in the right way, but given a transform like fourier transform - its actually a basis transformation right ? $$ F(y) = \int K(x,y) f(x) \text{d}x $$ ...
1
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1answer
59 views

Periodicity of function as a result of superposition in Quantum Mechanics

Say we add infinitely many waves (states of definite momentum) so as to produce a function that gives a very well-defined position, does that addition(using Fourier series) make that function ...
0
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2answers
64 views

Superposition of waves with different initial phase in Quantum Mechanics

In Quantum Mechanics, if a particle's state is a superposition of many states, then we say that its position is well-defined (by the Heisenberg uncertainty principle, because here we have ill-defined ...
1
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1answer
31 views

Question about what a simultaneous measurement of entangled spins means

I was working through a problem I found online and ran into something that is confusing me. We have a system of three spin-1/2 particles, in the state $$ |\psi\rangle = ...
0
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0answers
35 views

Addition of spins and projection

This is a calculational question but is not a homework question (rest assured I'm past that stage). Still, I don't quite know how to show the following. Say we have two $SU(2)$ spins $\vec{S}_1, ...
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0answers
19 views

Quantum mechanics Hermitian problems [on hold]

how to determine its non zero Eigenvalues and eigenfunctions how to prove A is hermitian in problem 2
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0answers
27 views

gravity and inflation [on hold]

Looking at the interaction between mass and the higgs field. Could gravity be a result of the topographical distortion of the fabric of space-time as the universe accelerates under inflationary ...
1
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1answer
49 views

How to prove that sum converges to integral using density of states?

Essentially, I would like to prove $$ \sum_k f(k) \to \int f(k) \rho dE \tag{1}$$ where $$ \rho = \frac{dk}{dE} \tag{2}$$ is the density of states and $k \to \infty$. The model is that there is a ...
5
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1answer
32 views

Why exactly do sometimes universal covers, and sometimes central extensions feature in the application of a symmetry group to quantum physics?

There seem to be two different things one must consider when representing a symmetry group in quantum mechanics: The universal cover: For instance, when representing the rotation group ...
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0answers
30 views

Can atoms exist [duplicate]

Can an atom be created from 2 top and one bottom quark together with a tau selectron? How would its properties differ from a hydrogen atom? What combinations of quarks and selectrons are possible to ...
2
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2answers
75 views

Can atoms with top / bottom quarks exist?

Do we have examples in nature or the lab of atoms constructed of 2 top and 1 bottom quark and a tau selectron? How would its properties differ from a hydrogen atom?
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0answers
12 views

Bandlike vs. Excitonic Semiconductors

What is the different between 'bandlike' semiconductors and 'excitonic' semiconductors and how does this relate to whether they are organic or inorganic? I also wonder how such bandlike or excitonic ...
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0answers
62 views

Why photon have zero rest mass?

If photon have zero rest mass then the term E=hf should also be zero because if rest mass is zero then relativistic mass is also zero and so on by Einstein mass energy relation energy shoud be zero ...
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1answer
116 views

Are black holes in a binary system with white holes, and are they both wormholes? [on hold]

What is a black hole? The general explanation is that a black hole is small region in space with such strong gravitational effects that nothing can escape and even light is trapped inside of the event ...
0
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4answers
130 views

“FTL” Communication with Quantum Entanglement? [duplicate]

Can quantum entanglement make sending a message, whether audio, video, or even Morse code, instantaneous between two points (faster than it could travel normally at the speed of light)? Let me first ...
2
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0answers
70 views

Continuum analogue of $ \langle \psi | \psi \rangle = \sum _i a_i^* a_i$

I'm learning Dirac notation, and I found the following exercise: Verify that if $$|\psi \rangle=\sum_i a_i |i\rangle, \tag{1}$$ (where $a_i=\langle i|\psi \rangle$), with $$\langle i|j ...
0
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0answers
17 views

Determining photon flux at a particular distance from a source, given frequency and transmitter wattage

I want to check my process and formulae for determining the observed number of photons per square meter per second, when the signal frequency is $f$, transmitter power is $P$ and the distance from the ...
0
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0answers
45 views

Quantum Mechanics, Free Particle with Gaussian Distribution [on hold]

Assume a free particle of mass $m$ is initially at rest, $v = 0$, which has a time dependent Gaussian distribution $V= \text{expected value of }v$. Write down the expression for the wave function: Is ...
0
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0answers
41 views

Electron double slit, different probabilities of going through each slit [on hold]

The Problem: Consider a two slit experiment where the slits are not the same. Specifically, consider the case where the probability of an electron passing through one slit is different from that of ...
0
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1answer
50 views

Possible values for $L_x$

I've a physical system with $l=1$ and I have to calculate the values I can obtain if I measure $L_x$ and their probability. I know that: the values I can obtain are $\ m=0, \pm 1$ $\displaystyle ...
3
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2answers
87 views

What all has intrinsic spin?

What does and does not have intrinsic spin? Wikipedia Spin (Physics) https://en.wikipedia.org/wiki/Spin_(physics) says: “In quantum mechanics and particle physics, spin is an intrinsic form of ...
1
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2answers
74 views

(Local) Conservation of Energy in Quantum Mechanics

Generally, we say that conservation of energy is a local law; the change in energy in some small region of space is equal to the energy flux out of that region. However, in quantum mechanics, we can ...
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25 views

Will water vapour rise in vacuum?

If I put water vapour in vacuum, will it behave normally like a gas? Will it rise up in the vacuum?
2
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2answers
78 views

Superposition in Quantum Mechanics

First of all, let $V$ be a vector space over the field $\mathbb{F}$. It is possible then to show, by Zorn's Lemma that there is a basis for $V$. The main point is that although basis are quite ...
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19 views

Best thermal (heat) radiation barrier (insulator)? [on hold]

Which material provides best insulation from thermal (heat) radiations? In other words, which material blocks most of heat radiation from escaping?
1
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0answers
25 views

Bragg Scattering of Thermal Neutrons

I'm currently reviewing Bragg scattering. The particular problem below has me slightly confused on whether I'm thinking about it correctly. Questions Is the problem below referring to the kinetic ...
0
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0answers
27 views

potential decomposition in terms of Bloch eigenstate

Given a single particle Hamiltonian $H=-\frac{\hbar^2}{2m}\nabla^2+V(r)$, where $m$ is the electron mass and $V(r)$ is a periodic function representing the lattice potential. It is defined in the ...
26
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7answers
4k views

What is Quantum Mechanics really about?

This question might sound very silly, so I'm sorry if that's the case. I'll try my best to make my point clear here. Before explaining, just to make clear, I'm not confused because of the Math ...
0
votes
1answer
26 views

What is meant by the expression “Markovian dynamics”

I know what a Markov chain is but what does it mean in physics when I say that I assume Markovian dynamics? For example in Quantum Mechanics, I read that it means that the time evolution can be ...
0
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0answers
54 views

Perturbation theory, eigenvalues and eigenvectors for degenerate case (1st order)

I was trying to understand the perturbation theory, but I was lost in the notation... I have understood that I have to identify the unperturbed kets that are degenerated and find the matrix $V$, ...
3
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2answers
245 views

State of a system in Quantum Mechanics and state vectors

I'm taking a course in Quantum Mechanics and there is something I'm not being able to fully understand. On more elementary courses on Quantum Mechanics I've been told that the idea of Quantum ...
0
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0answers
22 views

Is there a constant decay of particles that maintains the value of the Quantum Vacuum? [on hold]

By my question I am attempting to understand how the Vacuum of space remains at a constant value, (GR the universe on the large scale matches the “critical” energy density of about 8.5×10-10 J/m3) ...
3
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0answers
34 views

What quantum measurement formalism is easiest to implement physically?

As part of my studies and research, I have learned to work with three different measurement formalism which I define to avoid any ambiguity with the nomenclature: General measurements, which are ...
0
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2answers
64 views

Is the universe a Turing machine?

Reading about Computable numbers I wondered if there is any physical experiment that returns non-computable numbers or if there is any physical theory that needs non-computable numbers. Because if ...