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.

Filter by
Sorted by
Tagged with
1 vote
0 answers
86 views

Quarks heavier than strange

Gell-Mann et al. speculated the existence of 3 quarks based on the possibility to organize baryons and mesons in multiplets of SU(3). So, starting from this strange idea, they speculated the existence ...
Matteo's user avatar
  • 11
1 vote
1 answer
171 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 ...
David Raveh's user avatar
0 votes
0 answers
34 views

Who was the first to make a Stern-Gerlach experiment with two magnets?

I'm trying to fill a conceptual gap I have in the history of physics In 1922 Stern and Gerlach make their experiment, proving that electrons have intrinsic angular momentum, however it takes a while ...
HighlyEntropicMind's user avatar
0 votes
0 answers
127 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?
Hisham's user avatar
  • 409
3 votes
1 answer
202 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, "...
Amit's user avatar
  • 343
4 votes
1 answer
91 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?
Aida Lf's user avatar
  • 41
2 votes
0 answers
115 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,...
hyportnex's user avatar
  • 275
11 votes
2 answers
392 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 ...
Karsten Theis's user avatar
2 votes
0 answers
31 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 ...
Relativisticcucumber's user avatar
4 votes
1 answer
146 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 ...
Sam Gallagher's user avatar
0 votes
1 answer
77 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 ...
user 123456789's user avatar
1 vote
0 answers
58 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 ...
Sam Gallagher's user avatar
1 vote
0 answers
85 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 ...
edpidufd's user avatar
0 votes
0 answers
55 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 ...
Astitva Roy's user avatar
5 votes
1 answer
157 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&...
David Bailey's user avatar
1 vote
1 answer
101 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 ...
Mikael Jensen's user avatar
2 votes
0 answers
334 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. ...
Adam Herbst's user avatar
5 votes
1 answer
105 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 ...
Mario Krenn's user avatar
12 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 ...
Tfovid's user avatar
  • 221
2 votes
0 answers
89 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 ...
Qfwfq's user avatar
  • 121
3 votes
0 answers
102 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-...
David Schrittesser's user avatar
1 vote
1 answer
153 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 ...
Cory's user avatar
  • 13
0 votes
0 answers
96 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 ...
Pavel Borisov's user avatar
2 votes
0 answers
231 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 ...
vengaq's user avatar
  • 297
1 vote
0 answers
119 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 ...
Carlo Beenakker's user avatar
2 votes
0 answers
155 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 ...
Trond Saue's user avatar
6 votes
1 answer
231 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 ...
Mark S's user avatar
  • 213
4 votes
0 answers
104 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 ...
Slereah's user avatar
  • 751
0 votes
0 answers
65 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 ...
manuel459's user avatar
  • 291
18 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 ...
manuel459's user avatar
  • 291
4 votes
1 answer
163 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 ...
Kutsit's user avatar
  • 163
1 vote
0 answers
61 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 ...
AdVen's user avatar
  • 11
2 votes
1 answer
166 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 ...
JCRCan's user avatar
  • 21
3 votes
1 answer
179 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 ...
Philip's user avatar
  • 131
2 votes
1 answer
134 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 ...
enjin2000's user avatar
6 votes
0 answers
133 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 ...
Solidification's user avatar
5 votes
2 answers
1k views

How did Stern or Gerlach, of Stern-Gerlach experiment, create individual silver atoms? How were they accelerated?

How, a century ago, could Stern and/or Gerlach KNOW that they had created single silver atoms? How were they moved, or accelerated?
Kurt Hikes's user avatar
3 votes
1 answer
215 views

Bohr-Kramers-Slater (BKS) theory and energy conservation only on statistically basis

I was reading Wikipedia article on Bohr-Kramers-Slater (BKS) theory, https://en.wikipedia.org/wiki/BKS_theory. I encountered two interesting points and need your help to understand the reasons behind ...
PG1995's user avatar
  • 377
2 votes
1 answer
102 views

Need quote from early 20th century about humanity probably never being able to control (manipulate, see?) a single quantum system

I remember having read a statement, I think by one of the founding fathers of quantum mechanics, that we will probably never be able to control (or manipulate or see or isolate...?) a single quantum ...
getschwifty123's user avatar
2 votes
0 answers
480 views

On the origin of "sandwiches" in quantum mechanics

The term "sandwich" and the verb "to sandwich" appear pretty common but informally in quantum mechanics. Generally when describing some kind of inner product of the form: $$\langle ...
Mauricio's user avatar
  • 2,447
1 vote
0 answers
82 views

Why are pilot waves in quantum mechanics said to be Faraday waves?

De Broglie proposed a pilot wave in connection with quantum mechanics. He was more or less forced to abandon this wave in favor of the Copenhagen view. Bohm furthered his approach in the fifties but ...
Deschele Schilder's user avatar
2 votes
1 answer
579 views

Why didn't the phase space formulation of Quantum Mechanics get the upper hand?

At university I learned quantum mechanics in or position or momentum variables. Later (in fact on this site), I learned about the phase space formulation in which both are used at the same time. The ...
Deschele Schilder's user avatar
1 vote
0 answers
56 views

What is the origin of the probability interpretation of quantum mechanics?

Born came up with his probability interpretation of quantum mechanics. But why did he think about such an interoretation? Why not thinking that a deterministic process has to lay at its foundation? ...
Deschele Schilder's user avatar
3 votes
1 answer
369 views

Why did the Copenhagen interpretation of quantum mechanics got the upperhand?

The Copenhagen interpretation of quantum mechanics is nowadays the interpretation that prevails over other interpretations (or theories). Basically, it states that all processes in Nature are ...
Deschele Schilder's user avatar
4 votes
0 answers
255 views

Origin of the recurrence relation for Clebsch-Gordan coefficients

The Clebsch-Gordan coefficients $C_{\pm }(J,M)$ arise in quantum mechanics in the problem of addition of angular momentum. They also arise in mathematics in the more theoretical (but related) problem ...
roymend's user avatar
  • 113
3 votes
2 answers
276 views

A technical and historical introduction to quantum mechanics

I am curious to understand the history of QM. In particular, how did the physicists conclude that observables can be treated as operators, or the use of complex state spaces, or that Eigenvalues of ...
user2808118's user avatar
0 votes
0 answers
184 views

Was Landau interested in the interpretations of quantum mechanics?

I am interested in Lev Landau. I was trying to find what was his approach to the interpretation of quantum mechanics, I am unable to find any particular source were this is discussed. Was he an ...
Mauricio's user avatar
  • 2,447
1 vote
2 answers
724 views

What are the definitive experiments/phenomena which motivate quantum mechanics?

The double slit experiment is usually given as the foremost example of a physical experiment that requires quantum mechanics to satisfactorily explain. However, every account i've seen of it (such as ...
pprof's user avatar
  • 13
1 vote
0 answers
32 views

Dirac's non-neglibile disturbances argument and epistemic quantum mechanics

Here is Dirac's argument about one reason to motivate quantum mechanics: "It is usually assumed that, by being careful, we may cut down the disturbance accompanying our observation to any desired ...
J Kusin's user avatar
  • 111
1 vote
1 answer
258 views

Origins of the canonical commutation relation

I have recently been reading Gunter Ludwig's book wave mechanics to get a better understanding of quantum mechanics and in reading through the book I came across the relation $$m\sum_s \{|q_{rs}|^2\...
Flumpo's user avatar
  • 121