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.
178
questions
1
vote
0
answers
19
views
Who proposed the concept of "electron clouds"?
Who proposed the concept of "electron clouds," which classifies electron orbits in an atom into orbitals (s, p, d, f, etc.) using the Schrödinger equation, and in what year?
- 445
1
vote
0
answers
277
views
Arthur Lunn and the Schrödinger equation
It is claimed that Arthur C. Lunn at the University of Chicago found the Schrödinger equation of the hydrogen atom in 1921, but the paper was rejected by the Physical Review. At the beginning of the ...
- 111
2
votes
0
answers
68
views
How did Kolmogorov's probability theory contribute to the development of quantum mechanics?
I understand that the introduction of probability theory into quantum mechanics came from Max Born, Paul Dirac, and others' papers in 1926. On the other hand, the formalization of probability theory ...
- 445
1
vote
0
answers
40
views
Who introduced the fermionic creation and annihilation operators?
It is strange that this is never mentioned when textbooks introduce the 2nd quantization formalism.
- 417
21
votes
5
answers
4k
views
I want to know the tricks to search for and find old academic journals for free
In the research of scientific and mathematical history, efficient skills in searching for and accessing old academic journals (preferably for free) are essential. However, even when using platforms ...
- 445
1
vote
0
answers
82
views
Is the first paper attempting to apply Hilbert space theory to quantum mechanics in 1926 Germany available for free online?
I would like to view the quantum mechanics paper "Über die Jacobischen Transformationen der Quantenmechanik," published in Germany in 1926 by Fritz Wolfgang London. The reference is Z. Phys. ...
- 445
1
vote
0
answers
105
views
Was Bell’s theorem historically seen as evidence against realism and determinism?
As Tim Maudlin points out in his paper:
Early on, Bell’s result was often reported as ruling out determinism, or hidden variables. Nowadays, it is sometimes reported as ruling out, or at least ...
- 111
2
votes
1
answer
143
views
I'm searching for the original paper from 1924 where Max Born first proposed the term "quantum mechanics."
I'm searching for historical documents pertaining to quantum mechanics because I aim to write a popular essay on the topic for a web magazine. Specifically, I'm seeking free access to Max Born's paper ...
- 445
4
votes
2
answers
2k
views
Use of eigenvalues of operators in quantum mechanics
My very basic understanding of Quantum Mechanics and its history is that first, some physical quantities were thought to be continuous but experiments showed that they only took discrete values.
My ...
- 399
2
votes
0
answers
122
views
Origin of Einstein quote "Quantum mechanics: Real Black Magic Calculus"
The description of the 1993 English translation of The Quantum Dice, by Ponomarev and Kurchatov, as well as one of the quotes for chapter 2 of Quantum Computation and Quantum Information, by Nielsen ...
- 121
1
vote
0
answers
136
views
What paper or papers about molecules did Heisenberg "like", and what has Heisenberg published or otherwise commented about it?
In the 2023 film Oppenheimer based on the 2005 biography American Prometheus by Kai Bird and Martin J. Sherwin, there seems to be two references to work by Oppenheimer on molecules:
RABI: I caught ...
- 2,107
0
votes
0
answers
124
views
A brief history of "delocalization" of electrons
I have been studying the concepts of "resonance" and "mesomerism" recently and a common principle of these concepts is the "delocalization" (of electrons, molecular ...
- 235
3
votes
2
answers
304
views
Origin of the name "Loschmidt echo" in quantum chaos studies
The name "Loschmidt echo" is used in quantum physics for the quantity
$$
M(t) \equiv \left| \langle\psi_0| e^{i H t/\hbar} e^{-i H_0 t/\hbar} |\psi_0\rangle \right|^2
$$
where
$$
H = H_0 + ...
- 133
3
votes
2
answers
191
views
Dirac’s debt to Hamilton
According to Tobias Hurter’s popular exposition Too Big for a Single Mind (narrated in the present tense):
Dirac makes use of an elegant mathematical tool developed by the Irish mathematician William ...
- 617
0
votes
1
answer
113
views
How did Schrödinger do quantum mechanics with wave functions?
On my way to learn about the very beginning of quantum mechanics and its different formulations, starting with Heisenberg infinite matrices and Schrödinger's wave functions, I can really not find till ...
2
votes
1
answer
2k
views
Why was the Greek letter psi (Ψ) chosen to represent the wave function?
When I was reading, the question just popped into my head after noticing that the Greek letter ψ looks kind of like a wave itself. Stylized, they look even more wavy:
$$\Huge \Psi\;\Huge\psi$$
This ...
- 189
1
vote
1
answer
220
views
Who was the scientist who first showed that helium has a bound state, and was he a nazi?
I remember from my quantum course that the first person (I believe in 1927) to show that helium has a bound state, using the variational principle, was a nazi. It was remarked by my professors that he ...
- 119
0
votes
0
answers
149
views
Did Heisenberg say free will could arise from quantum probabilistic mechanics?
I see this view attributed to him a lot during Twitter debates but I never found the source for it
does anyone know if Heisenberg actually held this view/suggested it?
- 429
3
votes
1
answer
226
views
Did any "classical era" physicist foresee that a theory such as Quantum Mechanics is logically inescapable?
I am interested in knowing if in the era preceding the observations that lead to the advent of Quantum Mechanics, anyone foresaw logically that a theory such as Quantum Mechanics is in a sense, "...
- 353
5
votes
1
answer
103
views
How and by whom was the magnetic term in the Hamiltonian first derived?
The Hamiltonian of a charged particle in a magnetic field is: $$H=\frac{1}{2m}(\frac{h}{2\pi i}\nabla-qA)^2+q\phi$$
Can anybody help me find out when, how and by whom was it first derived?
- 51
2
votes
0
answers
125
views
Whom did Sommerfeld prefer as student?
On the occasion of Heisenberg's death, Wigner wrote an obituary in April 1976 issue of Physics Today (pp. 86-87):
Sommerfeld, an excellent teacher with a wonderful overall knowledge
of his discipline,...
- 357
11
votes
2
answers
727
views
Who popularized the atom icon (atomic whirl or planetary model)
There is a symbol or icon for an atom that is instantly recognizable and is associated with nuclear physics and with chemistry. A search for "nuclear atom symbol" (on 3/23/2023) shows what ...
- 289
2
votes
0
answers
37
views
Understanding how Stern-Gerlach tests Bohr-Sommerfield Hypothesis
I am trying to get to the bottom of a few things in the Stern-Gerlach experiment. First, on wikipedia, it says
The Sommerfeld model predicted that the magnetic moment of an atom measured along an ...
4
votes
1
answer
157
views
From where did Heisenberg (1925) obtain the classical frequency equation?
In Quantum-Theoretical Re-Interpretation (1925), Heisenberg gives the following:
In order to characterize this radiation [of an electron] we first need the frequencies which appear as functions of ...
- 1,466
0
votes
1
answer
82
views
Why are the views of quantum mechanics called the Copenhagen School?
Why was the name of a group of opinions about the meaning of quantum mechanics called the Copenhagen Interpretation, relative to the Danish city of Copenhagen and not the name of a scientist named ...
- 101
1
vote
0
answers
88
views
Who first stated the three polarizers experiment in quantum mechanics?
In my experience, Dirac is most often cited as the origin of this thought experiment. However, from what I've read in his Principles of Quantum Mechanics, he never actually introduces the idea with ...
- 1,466
1
vote
0
answers
127
views
Why is 'total angular momentum' denoted by the letter $J$ in quantum mechanics?
In quantum mechanics, we say $J$ ('total angular momentum') = $L$ ('orbital angular momentum') + $S$ ('spin angular momentum').
Apparently $S$ is from 'Spin', but why $J$ for the total angular ...
- 11
0
votes
0
answers
65
views
question regarding Stern-Gerlach experiment
When Stern-Gerlach experiment was done with quantum electron , two peaks were observed rather than a continuous distribution as in case of small magnets , but how did those peaks confirm that angular ...
7
votes
2
answers
260
views
Early helium spectrum measurements and their challenge for Bohr's quantum mechanics
My understanding is that explaining ortho- and para- helium spectral lines was a key motivation for Heisenberg's new quantum theory. For example, Birthwistle's 1928 "The New Quantum Mechanics&...
- 1,252
1
vote
1
answer
145
views
Paradigms in Newtonian physics around 1900
I am thinking about the change from Newtonian mechanics to quantum physics and relativity.
I note that we have accepted the words "ultraviolet catastrophe" in connection with the situation ...
- 187
2
votes
0
answers
642
views
What did Einstein say about the Dirac equation?
The wiki article on Dirac quotes Einstein as saying of Dirac
I have trouble with Dirac. This balancing on the dizzying path between genius and madness is awful.
and
I don't understand Dirac at all.
...
- 165
5
votes
1
answer
144
views
What did Nathan Rosen (from EPR) say about Bell's inequality and its violation?
Motivated by this year's Nobel prize in physics, I was wondering whether there are recorded statements by Nathan Rosen (the R in the EPR-paradox) about the Bell inequality and its violation by this ...
- 151
13
votes
1
answer
2k
views
Why was Alain Aspect discouraged from doing his now Nobel-winning work?
In an interview following Aspect's winning of the Nobel Prize in Physics, he claims that John Stuart Bell discouraged him from pursuing his now-famous 1982 experiment on quantum entanglement. The ...
- 233
2
votes
0
answers
98
views
What are the favorite interpretations of quantum mechanics by the recent Nobel laureates in physics?
The new Nobel laureates in physics have been given the prize because of their contributions to quantum mechanics (QM).
Of course, the Nobel prize focusses more on groundbreaking work that has links to ...
- 121
3
votes
0
answers
110
views
What's the early history of the "inner quantum number"?
Pais, in his "Inward Bound", describes the early history of spin. He tells us that Goudsmit and Uhlenbeck interpreted Pauli's "doubled valuedness" as spin, while in turn Pauli re-...
1
vote
1
answer
189
views
What is the origin of the name "degeneracy" pressure and "degenerate" Fermi gas?
What is the origin of the name "degeneracy" pressure and "degenerate" Fermi gas?
I was trying to find the first paper that used the term "degenerate/degeneracy" to ...
- 13
0
votes
0
answers
100
views
According to Heisenberg, is quantum theory merely a calculation procedure for predictions?
Is quantum theory just a mathematical tool for correct predictions, according to Heisenberg's views?
What are his personal ontological commitments in relation to quantum theory (if he had any ...
- 101
2
votes
0
answers
271
views
Did John von Neumann make any comments about the Many Worlds Interpretation of Hugh Everett?
I was having a discussion with a physicist about Many Worlds Interpretation and he told me that von Neumann like the idea of having multiple worlds in quantum mechanics. When I asked him about more ...
- 307
1
vote
0
answers
172
views
Did Felix Bloch really discover Bloch oscillations?
A 1929 paper by Felix Bloch, Über die Quantenmechanik der Elektronen in Kristallgittern, is widely cited as having predicted the phenomenon of Bloch oscillations: The oscillatory motion of an electron ...
- 994
2
votes
0
answers
180
views
The original Dirac equation
In the original 1928 paper (pdf) the Dirac equation appears on page 615 in equation (9) as
$$
[p_0+\rho_1\left(\boldsymbol{\sigma},\boldsymbol{p}\right)+\rho_3mc]\psi=0\qquad(1)
$$
Using the ...
- 21
6
votes
1
answer
280
views
Does the prototype BB84 quantum cryptography machine still exist?
According to Wikipedia's timelines, quantum computing may have had some inceptions as early as the late 60's, when Stephen Wiesner invented conjugate coding.
Around the early 80's, Wiesner's ideas ...
- 243
4
votes
0
answers
120
views
Einstein's overdetermination theory
In 1923 [1], Einstein proposed an idea for a classical theory that would explain some features of quantum mechanics, via the overdetermination of the EoM, so that only certain configurations would be ...
- 905
0
votes
0
answers
72
views
On implications of Schrodingers Cat regarding macroscopic quantum states and decoherence
How exactly did Schrodingers Cat lead to development regarding macroscopic quantum states and decoherence? One often hears that the thought experiment was the initiator to the question, whether ...
- 301
19
votes
1
answer
4k
views
What did Schroedinger try to say with the cat thought experiment?
In many books one finds different explanations. Specifically popular seems to be that he "argued against the Copenhagen interpretation". But what did he really intend to communicate?
I for ...
- 301
4
votes
1
answer
203
views
Einstein's Objection to Drude Model
In Walter Isaacson's Biography of Einstein, it is stated that the young Einstein was developing his own ideas in Statistical Physics and Thermodynamics and he had found some error in Drude's model for ...
- 163
1
vote
0
answers
65
views
Who was the first scientist to give a formula for the probability density function of the position of a photon in the double slit experiment?
The double-slit experiment shows the fundamentally probabilistic nature of quantum mechanical phenomena. On Wikipedia one can read:
This type of experiment was first performed, using light, by Thomas ...
- 11
2
votes
1
answer
197
views
How did Heisenberg build the P Q matrix terms?
I learnt in some Wikipedia articles that the terms of the P and Q matrices designed by Heisenberg were composed of Fourier coefficients. Could you provide some explanation on how these coefficients ...
- 21
3
votes
1
answer
203
views
de Broglie's conception of the electron
I've been working on de Broglie's thesis (English PDF, Original French PDF) for a course, and I've found something that's been bothering me. My training is in Physics, and so I'm not particularly ...
- 131
2
votes
1
answer
163
views
Who first proposed the idea of "resolution of the identity"?
Who first proposed the idea of "resolution of the identity" as used in the functional calculus of self-adjoint operators? Was it von Neumann?
In Japanese, it translates as "resolution ...
- 445
6
votes
0
answers
137
views
What technology was used to determine the shape of the blackbody spectrum at the 19th century?
The shape of the blackbody radiation spectrum was known in the 19th century from experimental measurements, and before the theoretical discovery of Planck's law.
At those times, how did people manage ...
- 337