Talk:Stern–Gerlach experiment

message: There is a nice explanation in this page:
http://rugth30.phys.rug.nl/quantummechanics/stern.htm
but I do not have time to summarize/rewrite. 
 -- ato 21:35, 1 Sep 2004 (UTC)
thread_title:  external link

message: Hey what do you think about the rewritten basic theory/description section? BeardedPhysicist 23:58, 14 May 2006 (UTC)
replies: text: pretty well written overall. nice. Mct mht 06:18, 17 June 2006 (UTC)
thread_title: Description Rewritten

message: Strange that there are no links to articles about Stern or Gerlach or even anything that says when this experiment was done! Michael Hardy 18:19, 9 Sep 2004 (UTC)
replies: text: I have added a section "Impact" where we can discuss all the related stuff that came AFTER that experiment. this will be usefull to include the links to more modern experiments or physics.   
Alain Michaud 01:32, 23 December 2005 (UTC)
thread_title: History?

message: The original edit, as of 6 September, 2004, seems to have been copied from .  I've left a note on the user's user page; I'm going to rewrite the article.  -- Creidieki 02:44, 12 Sep 2004 (UTC)
thread_title:  Original text was copied from external page 

message: For greater clarity I think the quantum number S and ms should be differentiated between.
i.e. that electrons are fermions, and therefore posses a spin number of +1/2, which is a property intrinsic to the electron, and that the electron itself can be 'orientated' to give a projection spin quantity of +/- 1/2, which is a property of a situation or specific electron in an atom.
In the experiment, all electrons, by their nature, have a spin number of 1/2, but have angular momentum projection number of +/- half when detected in a system, hence there being two possible (degenerate) quantum states for ground state silver- and the two lines.
Sorry if this doesn't make any sense! This article was recently slated by a university professor, but I feel it's content isn't wrong, just in-explicit.
Alexanderhowell 15:06, 6 March 2007 (UTC)
thread_title:  Spin numbers 

message: From the first paragraph of "Basic theory and description":
"The experiment sought to determine whether individual particles like electrons have any "spin" angular momentum."
Surely this statement is incorrect, as according to the Physics Today source  the experiment was originally conducted using silver atoms to test Bohr's theory of the atom (in particular "space quantisation", although I'm not sure what exactly this is supposed to refer to). Electron spin wasn't known about at the time and the experiment was only interpreted in terms of electron spin in 1927.
Pagw 14:46, 28 August 2007 (UTC)
replies: text: I think you are almost certainly right as to the purpose of the original experiment not being about electron spin. Rather than rewrite the sentence to talk about the original purpose, I'd suggest rewriting it to talk about the application to electron spin, which is the most talked about use for the apparatus. Teutanic 15:44, 31 October 2007 (UTC)

text: Yes, thanks. Pagw (talk) 13:55, 31 December 2007 (UTC)
thread_title: Purpose of the experiment

message: What will be if one of those magnets in image will be removed? Does there will be the same two levels quantization or only one level will remain?
More precisly, what will be if will be removed one of two magnets in Stern-Gerlach Experiment for electron spin? http://hyperphysics.phy-astr.gsu.edu/Hbase/spin.html Does spin then still be quantized in two orentations or only in one?  —Preceding unsigned comment added by Fakeup (talk • contribs) 16:06, 21 July 2008 (UTC)
thread_title:  not enough information 

message: The claim "measurement of the spin of electron" is valid in the sense, that electron is spining around the nucleus, not in the sense that the implicit spin of the electron was measured. Deflected particles are atoms, not electrons. The cause of deflection of atom is orbital direction of the electron motion interacting with magnetic field, or better, interaction of the overall magnetic moment of the atom, caused by the atom as whole.
:: Apart from any theory, it can be stated, as a pure result of the experiment, and as far as the exactitude of our experiments allows us to say so, that silver atoms in a magnetic field have only two discrete values of the component of the magnetic moment in the direction of the field strength; both have the same absolute value with each half of the atoms having a positive and a negative sign respectively (Gerlach and Stern 1924, pp. 690-691, FW)
If the atom is unique discrete system, there are only two configurations of the atom preserving its discrete properties - preserving its identity. These configurations difer in direction of rotations.
Interpreting the Stern-Gerlach experiment as implicit spin of the electron is the same as saying : the outer electron (with lowest binding potential) is draging the heavy atom of the silver, instead of being teared out from the atom. If so, than the force of draging must be less than the force that will tear out the electron ... Softvision (talk) 18:37, 11 July 2009 (UTC)
replies: text: As I understand it, it is an s electron, so no orbital angular momentum. I presume you can also S-G on ones that do have orbital angular momentum. Gah4 (talk) 21:04, 10 May 2018 (UTC)

text: I just realized that I didn't finish this. Yes, the force is small enough not to tear the electron out. Gah4 (talk) 22:41, 14 April 2019 (UTC)
thread_title:  If the element in experiment is atom, you are measuring properties of atom, not a single electron ! 

message: From the article "Even if the electron radius were as large as 14 nm (classical electron radius) then it would have to be rotating at 2.3×1011 m/s. The speed of rotation would be in excess of the speed of light, 2.998×108 m/s, and is thus impossible.[2] " - This is in error, both the value and calculation.  The classical electron radius as per wiki is 14 femtometers.  The calculation is way out.. or am I mistaken?  —Preceding unsigned comment added by 75.152.156.5 (talk) 02:03, 24 March 2010 (UTC)
thread_title:  Error: classical electron radius and calculation 

message: Suppose you had a stream of random direction magnetically polarized particles that were drifting latterly along and then entered a length of a magnetic field that had a definite orientation of the polarization direction. This encounter would result an interaction of the magnetic lines of force between the two fields such that an aligning torque would occur to both the magnetic field system and the individual moving particles. And this would result in the rotation of the orientation of the direction of the traveling particle's magnetic field so that it could continua to move in its lateral direction. And that might cause the orientation of the particle's magnetic field to change into 2 categories of orientation relative to the fixed magnetic field. Say that if the particle's magnetic field were reoriented to be perpendicular to the fixed magnetic field, then it could get through with the particle's magnetic field being oriented in either direction. But now we have the interaction of 2 perpendicular magnetic fields, with one of them having 2 directions of polarity. And that might result in a deviation in the path of the traveling particles such that they arrive at different spot locations at the end of the travel path of the moving particles.WFPM (talk) 16:09, 2 May 2010 (UTC)
thread_title: Hypothesis

message: I believe the description of this experiment is inaccurate.  The article states that the experiment shows that "  particles possess an intrinsic angular momentum...that takes only certain quantized values."  As noted by other comments and even later in the article, however, spin quantization was known to the experimenters and others at the time of the experiment.  Moreover, quantization of intrinsic spin *does not* entirely account for the results of the experiment.  The greater significance of this experiment is that it showed the *projection* of the angular momentum vector (and, therefore, the magnetic moment of the particle) onto the coordinate axis parallel to the direction of the applied B-field is quantized and has only two values with equal magnitudes but opposite signs.  This is a significant difference from the current text.   This phenomenon has been called "amazing" even within the realm of quantum mechanics and is often labelled "quantization of space."
References:
Modern Physics; Kenneth Krane, 1983, pp. 191-192.
The Encyclopaedia of Physics 2nd Edition; Lerner/Trigg, 1991, p. 1162.
"Angular Momentum Quantization: Physical Manifestations and Chemical Consequences"; Michael Fowler; http://galileo.phys.virginia.edu/classes/252/Angular_Momentum/Angular_Momentum.html  [This is already a reference to this article.]
Porcelain mouse (talk) 18:30, 5 November 2010 (UTC)
thread_title: Description Inaccurate

message: "as well as photons, W and Z bosons and gluons are spin +1 particles and have three possible values for spin angular momentum."
As far as I know we need to leave the photons out in this sentence as they are (which makes them different from the massive bosons) no rest-mass and therefor the projection of the spin angular momentum (the sentence talks about the spin angular momentum itself which is still always +1, or at least the quantum number is +1, the absolute value is sth like sqrt(s(s+1)) right?)
So anyways, the projection (depending what defines your quantization axis) might for a photon not have a possible value of 0, namely if the momentum p defines for quantization axis (see helicity for a discussion on that). For Pi light (Zeeman effect) there might be a projection of spin angular momentum m_s=0 as the b-field is the quantization axis defining your atomic level and p can be orthorganal to B.
To wrap this up: 
1) "have three possible values for spin angular momentum" is not precise, it needs to be the projection
2) photons ... have three possible values for spin angular momentum is as a general statement WRONG, as explained in above example!  —Preceding unsigned comment added by 128.100.93.74 (talk) 19:19, 26 January 2011 (UTC)
replies: text: Thanks. I nuked the rubbish in late 2012 but did not report here. Incnis Mrsi (talk) 13:09, 28 June 2013 (UTC)
replies: text: Photons are spin 1.  Spin 1 particles in general can have -1, 0, or +1, but photons can only have -1 or +1. Gah4 (talk) 21:53, 28 February 2018 (UTC)
replies: text: By the way, much of the physics of SG is the same physics as photons and calcite crystals. Calcite will separate photons by polarization into two discrete beams. You can use two calcite crystals rotated at different angles, or even more, and do somewhat similar experiments, except that the two polarizations are 90 degrees apart, instead of 180 degrees for spin 1/2. And calcite crystals are much cheaper. Gah4 (talk) 07:42, 26 June 2019 (UTC)
thread_title: Photons have three different projections??

message: Aside of the scandal above, the section makes redundant references to Δ-baryons and quarks. There were no such words in the time of Stern and Gerlach. Links spin (physics) and spin-½ will be sufficient, and references to all irrelevant particles shall be removed. Comments? Incnis Mrsi (talk) 13:09, 28 June 2013 (UTC)
thread_title:  Basic theory and description 

message: How do you create an inhomogeneous magnetic field? The strength of any magnetic field will vary according to your position within it. Seems to me the arrangement of this field is crucial to this experiment. Or are we talking about simply sending the beam closer to one pole than the other? Maybe we don't even the need the second pole near the beam. Pergelator.  — Preceding unsigned comment added by 50.43.12.61 (talk) 05:19, 8 August 2013 (UTC)
replies: text: If the magnetic field is homogeneous (i.e. the same everywhere), then the resultant force exerted on the atoms/electrons is nil. They don't move, and you simply get a dot on the screen, as if the field was not there. The expression, for a vertical magnetic field, of the force is F_z=\mu_z \frac{\partial B_z}{\partial z}, which clearly shows that B_z must vary in space. 7dare (talk) 20:38, 29 November 2017 (UTC)
thread_title:  inhomogeneous magnetic field 

message: I have undone an unacceptable edit. It is unacceptable because it is personal self-promotion of material that is not supported by Wikipedia-standard reliable sources. The editor who posted it, presumably in good faith, apparently does not know the Wikipedia policies on such matters. He could look at WP:RS and at WP:PROMO.Chjoaygame (talk) 17:18, 11 March 2015 (UTC)
thread_title:  unacceptable edit undone; reasons 

message: This new edit posts a link that says that the Stern–Gerlach beam splits into three. Not as I see it. Where field inhomogeneity is strong, the splitting of the beam into two is big enough to see above the noise. At the edges, where the field inhomogeneity is weak, the splitting of the beam into two is not big enough to see above the noise. I think the linked article is wrong in this bold claim. I think the link should be deleted.Chjoaygame (talk) 14:44, 11 September 2015 (UTC)
replies: text: This figure is correct, you can cite chapter 5 in vol III of The Feynman Lectures on Physics.Earthandmoon (talk) 16:00, 11 September 2015 (UTC)
replies: text:  and if you check history of edit this page, i just changed the dead link of this external link.Earthandmoon (talk) 16:03, 11 September 2015 (UTC)
replies: text: Thank you for this response. Yes, on reading the link again I see it is ok. I didn't read it carefully the first time.Chjoaygame (talk) 22:11, 11 September 2015 (UTC)
thread_title:  faulty new link 

message: It seems to me that S-G directly shows the quantization of magnetic moment, and only indirectly the quantization of angular momentum.  I realize the connection that we now know between them, but it likely wasn't so obvious in 1920.  The beginning of this article also doesn't make this so clear. I could just change it, but wanted to see if others have thoughts about it. Gah4 (talk) 22:47, 28 February 2018 (UTC)
replies: text: Not the case.   Magnetic moments are not quantized while angular momentum is.   Remember that in each physical situation there is a "g-factor" that relates the angular momentum of the system (quantized in units of h-bar) to the magnetic moment.   The g-factor can be calculated for simple atomic systems, but not, in general, for many-body systems like nuclei or molecules. There are tabulated values of *measured* g-factors for all sorts of systems, if you look.   Qwerty123uiop (talk) 23:08, 28 February 2018 (UTC)
replies: text: Yes, but once you set the system, which you have to do when setting up a S-G experiment, then g is fixed. S-G measures magnetic moment, and not angular momentum. I suppose you could be unlucky in a variety of ways, though. From , Ag has a nice electron configuration with only one unpaired electron in an s orbital, so no orbital angular momentum. Gah4 (talk) 01:46, 1 March 2018 (UTC)
replies: text: Sure, once you pick a measuring stick from among all possible measuring sticks, then you can measure any length in quantized units of that stick. But that is not the same as saying the stick-length you picked is in any sense "fundamental".   What stays the same in all quantum systems is the size of the angular momentum unit, that is, Planck's constant... you don't get to pick it. Qwerty123uiop (talk) 16:17, 3 March 2018 (UTC)
replies: text: OK, if you measure in sticks then it is always length. But you might measure length by the time it takes something to go that distance. Radar measures length by the time it takes a signal to reach and return from an object. Directly time, indirectly length, and the speed of EM waves as the scale factor. S-G directly measures magnetic moment, and indirectly angular momentum, with appropriate scale factor. But okay, from Electron magnetic moment the first assumption is that the mass and charge distributions are the same. From that, you only need a dimensionless g-factor.  But even so, S-G measures the magnetic moment. Knowing that it is proportional, even without knowing the constant, two values of magnetic moment means two values of angular momentum. After S-G comes the problem of measuring the g-factor, not before. Gah4 (talk) 23:44, 10 May 2018 (UTC)
replies: text: From the title of the SG paper, and even though I don't speak German: .. magnetische Moment des Silberatoms, I am pretty sure that means magnetic moment of silver atoms.  Since I don't speak German, I can't be sure that magnetische Moment doesn't mean angular momentum, but I still don't think so. They were measuring the quantization of magnetic moment. We now know, though I suspect that they didn't at the time, that that is due to quantization of angular momentum. (And, as noted, g.)  Gah4 (talk) 03:38, 28 June 2019 (UTC)
thread_title:  [[angular momentum]] or [[magnetic moment]]? 

message: In the sequential experiments section, there are no examples that put a split beam back together.  As noted, blocking one beam loses polarization on any other axis.  If you don't block a beam, and using a S-G apparatus to put the beam together again (that is, opposite polarity), there is no measurement, and no loss of previous polarization state. Gah4 (talk) 04:33, 1 March 2018 (UTC)
replies: text: I think that's wrong: the measurement happens within the S-G apparatus, which outputs two polarized beams. E.g., if you initially have a x+ beam, and you split it in z+ and z- beams using a S-G apparatus and later merge these two beams, you don't have anymore a x+ beam, i.e., if you now measure it with a new S-G polarized along x you'll get both x+ and x-.  --151.56.35.40 (talk) 10:41, 23 September 2018 (UTC)
replies: text: According to which interpretation of quantum mechanics do you believe that?  Have you done the experiment?  One of the most interesting things about quantum mechanics is when you are sure of something, but it turns out not to be true, or, as Feynman would say, "Nobody understands quantum mechanics". Gah4 (talk) 16:14, 23 September 2018 (UTC)

text: When I find my Feynman vol. III, I will see what he says about it. Gah4 (talk) 16:14, 23 September 2018 (UTC)
replies: text: I finally found it.  Read section 5-4 in Feynman's "Lectures on Physics" volume III.  The book is somewhat unusual in the way, and the order in which, it explains things. If you separate the beams, don't block them or otherwise disturb them, then put the back together again, previous state information is not lost.  It isn't so obvious that you can do this with real S-G apparatus, but is otherwise fundamental to QM. You might have to tune carefully to get the beams back together without losing phase.  Gah4 (talk) 01:57, 16 November 2018 (UTC)

text: You might want to check Ellerman https://arxiv.org/pdf/1112.4522.pdf (a revised version is peer reviewed with Springer https://link.springer.com/article/10.1007/s40509-014-0026-2) and it very nicely explains why it is wrong to assume that the S-G apparatus outputs two polarized beams. I assume this misunderstanding is pretty much widespread and strongly suggest you read Ellerman.  — Preceding unsigned comment added by 217.95.160.165 (talk) 22:20, 30 June 2019 (UTC)
replies: text: Yes. And to quote from the above: One of the very few texts to consider such a Stern-Gerlach analyzer loop is The Feynman Lectures on Physics: Quantum Mechanics (Vol. III) where it is called a ”modified Stern-Gerlach apparatus”[2, p. 5-2].  It also mentions another book that mostly gets it right, but that most books ignore this. Gah4 (talk) 18:45, 1 July 2019 (UTC)

text: For another way to think about it, consider the strong baseball principle described by Mermin, and quoted by Ivars Peterson.  This is meant to explain things such that anyone can understand them. Specifically, the baseball principle says that watching a games on TV, thoughout the season, doesn't change the results.  The strong baseball principles applies to individual games, and the very strong baseball principle to games that are rained out.  (If a rained out game, was not actually rained out, would the result have been different ...)  A quote from Mermin: "These are intrinsically quantum-mechanical data, and the lesson from these data is ... that you have to be extraordinarily careful in talking about what might have happened but didn't. In this case, the numbers demonstrate that there's no way you can make up a picture to account for what might have happened but didn't."  Yet we go through life, planning our days around what might have happened  ...  but didn't.  Gah4 (talk) 18:45, 1 July 2019 (UTC)
replies: text:  In fact, Ellerman argues exactly against the misconception expressed by 151.56.35.40 – “if… you split it in z+ and z− beams using a S-G apparatus and later merge these two beams, you don't have anymore a x+ beam”. Spatial deflection of atoms doesn’t affect their spin. Only when the atom hits an obstacle can we count for a kind of measurement of its state. By the way, IMHO all the “baseball” stuff above can be dismissed as ambiguous and cryptic. Incnis Mrsi (talk) 20:02, 1 July 2019 (UTC)
replies: text: The baseball stuff is meant to connect everyday experience to you have to be extraordinarily careful in talking about what might have happened but didn't.   There are more detailed discussions in Mermin's Boojums All the Way through.  Specifically, he uses statistics that could come from SG experiments, either spin 1/2 or spin 1 (photons), which show that no possible results of experiments that weren't done could agree with the ones that were done.  And this is all without what Feynman calls the modified Stern-Gerlach apparatus.  Gah4 (talk) 21:15, 1 July 2019 (UTC)

text: (Excuse my English if it's not good, I'm not a native English speaker.) I would like to remind you that the superposition IS an interpretation, not a fact. We have no means to know whether the spin is determined inside the S-G apparatus with the deflection of the beams or the beams are entangled and each one is in a superposition of both states before touching the screen. The literature is plethoric about thought experiments of putting a split beam back together (which can be called an eraser experiment) but there are quite few actual experiments of the situation. This is what I found : Scully is the 1st one who studied it and he made 3 experiments trying to produce interferences at the recombination of the beams. The absence of interferences express the decoherence of the beams (thus the presence of which-path information, which can be either interpreted as : both paths are superposed as to their spin characteristic but separated in space = not spatially coherent anymore, or as : each path corresponds to a determined spin). The presence of interferences proves the coherence of the beams (the absence of which-path information can be either interpreted as : there is a total entanglement between all possibilities of spin and spacial distribution or : each particle already has a spin but has not undergone spatial decoherence yet). Anyway you will never have as an output a clean beam identical to the one you got as an imput. The passage into the device does something to the beam, whether it is changing it into a mixture or into interferences. But even if you are satisfied with interference because you are only looking for coherence (and not for the impossibility to tell if a measurement was made or not, which I would rather be looking for), it is very difficult to produce them experimentally because of the magnetic field, which is not perfect and has little fluctuations (due to its quantum nature), and these fluctuations provoke systematic decoherence of the beams, and apparently also because of the constraint of irreversibility of processes (linked to the irreversibility of time). I haven't understood the techniques they tried to correct that but it appears to be still a work in process. The more complete article I found on the subject is this one : https://www.researchgate.net/publication/322355005_Realization_of_a_complete_Stern-Gerlach_interferometer (open access), he makes a little review in introduction and appears to succeed in recovering the coherence after recombination so if this article holds I think the effect is experimentally confirmed. As you can see it's very recent so I would wait a bit before being sure there is a consensus.Hellena Liseron (talk) 11:44, 25 March 2020 (UTC)
replies: text: I started the discussion based on what Feynman says in his lectures, vol. III.  How easy it is to build, is another question. But note that, other than the difference between spin 1/2 and spin 1, the same experiments can be done with calcite crystals and polarized light. (And they are commonly done that way for entanglement experiments.) If putting the beams back together is less than perfect, then the polarization of the result will be less than perfect, but maybe still measurable. This gets very close to Interpretations_of_quantum_mechanics though. Gah4 (talk) 15:59, 25 March 2020 (UTC)
thread_title:  sequential experiments 

message: hey guys, idk how to make comments correctly but the video is wrong, the diagonal magnets would be deflected towards their opposite poles  — Preceding unsigned comment added by 2600:1700:67D0:C4A0:4177:9510:C275:E59E (talk) 06:29, 11 March 2018 (UTC)
thread_title:  Video 

message: It is the component of the magnetic moment in the direction of the magnetic field, that is, \mu \cdot B. The supposed randomness is in the direction of the magnetic moment. Gah4 (talk) 07:10, 9 May 2018 (UTC)
thread_title:  ''amount proportional to its magnetic moment'' 

message: I replaced Much of the text of the caption  for the diagram of the experiment, and began to suspect that I had  duplicated at least part of the existing caption.  My best guess is that I made no error, but my tool is  an iPad 2 which makes my editing somewhat clumsy, so it's hard to be sure. The code I have about it is because of repetitious looking markup,  and I am not in a position to do a version to version compared to confirm my best guess to The effect that The repetition is intended and has nothing to do with my edit.  I apologize if I am mistaken and hope a colleague will remedy  any damage that I did. --Jerzy•t 06:52, 14 August 2018 (UTC)
thread_title:  Did my caption edit involve a bad side effect? 

message: I thought there was lacking images to show what is going on in the Sequential Experiments section, so I created a 3D model to show each of the 3 experiments a bit better. Please let me know if there is something incorrect in the image, maybe I can fix it and re-upload. Also I wasn't sure what to put in the caption, please improve on it if you can.
MJasK (talk) 20:32, 25 November 2020 (UTC)
thread_title:  New Image/3D model added to Sequential Experiments 

message: "The act of observing (measuring) the momentum along the z axis corresponds to the operator J_{z}.[specify] "
I think that the operator mentioned should be the pauli operator sigma_z
Kriesell.D (talk) 16:55, 16 January 2021 (UTC)
thread_title:  The act of observing (measuring) the momentum along the z-axis 

message: This explanation is wrong: “Video explaining quantum spin versus classical magnet in the Stern–Gerlach experiment”. The classical magnet would rotate and produce only two dots. The original experiment shows that the absolute value of angular momentum has two values - not that it has two orientations! Zyavrik (talk) 21:40, 11 July 2021 (UTC)
thread_title:  Wrong Explanation 

message: The article seems to refer to the visible image formed by a free electron on a screen in the S-G apparatus, but fails to include a photograph of such an actual image. I see this lack elsewhere as well. I think the article deserves a real photo of the S-G output, along with an explanation of why it is not a pair of separated dots or short lines as expected from theory. If this is not possible, an explanation of why no such image or explanation can be included would be appreciated. Perhaps I have missed something basic about the S-G experiment. David Spector (talk) 13:03, 25 August 2021 (UTC)
replies: text: There is an excellent image of the result from a paper already cited on the page (available here https://plato.stanford.edu/entries/physics-experiment/app5.html). I see no reason not to include it, but what do you mean by "not a pair of separated dots or short lines as expected from theory"? As I see it there are two lines as predicted by the theory, they simply taper out as you go further from center due to the nature of the magnetic field. G1butler615 (talk) 16:33, 29 November 2021 (UTC)

text: Just to be clear, the article makes no claims about free electrons. The experiment involves Silver atoms, not free electrons. Johnjbarton (talk) 18:28, 21 February 2024 (UTC)
thread_title:  Pattern image needed