Talk:Quantum eraser experiment

message: I read the entire external link article "A Scientific American article: A Do-It-Yourself Quantum Eraser" and there was no "do it yourself" experiment instructions.. perhaps consider renaming or removing the link. I was quite disappointed when I discovered there really is no "at home" experiment.  —Preceding unsigned comment added by 71.112.198.228 (talk) 08:45, 5 May 2008 (UTC)
replies: text: Really?  I've read the article and the description of how to make the apparatus. The way the article is written you have to jump around to lots of different sub-pages. Scientific American also seems to have a policy of gradually chopping away at their on-line articles.  Maybe it is gone by now.  I'll see what I can find out. P0M (talk) 20:57, 5 May 2008 (UTC)
replies: text: Dig deeper.  Start at http://www.sciam.com/slideshow.cfm?id=a-do-it-yourself-quantum-eraser and enlarge all images.P0M (talk) 20:20, 10 May 2008 (UTC)
replies: text: Still there in Sept 2015. Its awesome! 67.198.37.16 (talk) 16:41, 24 September 2015 (UTC)
replies: text: As I remember the article, it is a pretty simple experiment. Maybe simple enough that it isn't obvious that it is erasing.  It depends on how you understand polarizers and polarization. Gah4 (talk) 07:44, 8 March 2019 (UTC)
thread_title:  External link 

message: ===Rewrite===
Ouch. I just had a look at the article and the fundamental statement of how the experiment works was wrong from the time it was written. Let's get it right this time.
The quantum eraser experiment is a double-slit experiment in which particle entanglement and selective polarization is used to determine which slit a particle goes through by measuring the particle's entangled partner. This entangled partner never enters the double slit experiment. Earlier experiments with the basic Young double-slit experiment had already determined that anything done to discover by which path (through slit a or through slit b) a photon traveled to the detection screen would destroy the interference effect that is responsible for the production of interference fringes on the detection screen.
It should be:
<BLOCKQUOTE>The quantum eraser experiment is a variation of Young's double slit experiment that established that when a photon is acted upon in any way that permits determining which of the slits it has transited then it cannot interfere with itself. When a stream of photons is marked in this way, then the characteristic interference fringes characteristic of the Young experiment will not be seen. The quantum eraser experiment demonstrates that it is possible to create situations in which a photon that has been "marked" so as to enable determination of which of two slits it transited in order to reach a detection screen can later be "unmarked." A photon that has been so marked cannot interfere with itself. But a photon that has been marked and then unmarked can interfere with itself. When a stream of photons has been marked and then unmarked it can once again produce the fringes characteristic of the Young experient. The experiment has three phases: </BLOCKQUOTE>
<BLOCKQUOTE>In the first phase, pairs of entangled photons are created using a BBO device. The entangled photons are polarized and diverge in two directions from the point of their creation.  Those that go down the lower path in diagram 1 encounter a double slit and then are picked up using a sensitive scanner that sweeps across the interference pattern that they produce when they interfere with themselves. The number of photons at each step along the way is recorded, and the list thus produced is graphed. The graph shows a standard interference pattern. In principle the same procedure could be followed with the photons proceeding along the upper path as there is nothing that distinguishes the two streams of photons insofar as their suitability for demonstrating self-interference.</BLOCKQUOTE>
<BLOCKQUOTE>In the second phase, quarter-wave plates are inserted so that anything that goes through slit A gets its polarization changed into circular polarization in one direction (clockwise or counter-clockwise) and anything that goes through slit B gets  th other circular polarization. When the detector device is swept across the region of space where an interference pattern was earlier detected, no such result is observed, and it is as though only one slit were present in the photon path. This result is consistent with the very well tested observation that anything that is done that could detect which path a photon has taken through a double-slit apparatus, anything done that "marks" the path of the photon, will prevent an interference pattern from appearing.</BLOCKQUOTE>
<BLOCKQUOTE>In the third phase, no further changes are made in the lower pathway. Instead, a polarizer is inserted in the upper path so that the entangled twins of any photons going through the lower path are also changed in their polarization. Since the photons in the upper path have had their polarizations changed, the photons in the lower path must undergo the same modifications in their own polarizations. By choosing the appropriate angle of polarization for the upper polarizer, half of the photons in the lower path can be coerced to again have the same polarization. Once they have the same polarization they can interfere with each other again, or, to put it another way, now there is nothing that marks whether each of them went through path A or path B.  So they again interfere with each other. The problem for the experimenter is that the other half of the photons in the lower path get their polarizations changed also, but in their case they are still differentiated one from another. Since they have another set of opposed polarizations, they still cannot interfere with each other, or, to put it another way, their "which path" information can still be determined by measuring their polarizations. So they do not interfere with each other. Thus half of the light that reaches the scanning detector consists of non-interfering photons, and the self-interfering photons tend to get lost in the overall pattern of illumination. Fortunately, the experimenters can distinguish the two groups of photons because
only half of the photons will pass through the upper polarizer, and the photons that reach the upper detection screen are the twins of the
photons that have their marking polarizations "erased" in the lower path. By rotating the upper polarizer, the experimenters can select either the photons that have clockwise or counter-clockwise polarizations to "erase" and thus restore their ability to interfere with themselves. Whichever group the experimenters select will self-interfere, but the other photons will not self-interfere and their presence in the scanning photon detector will tend to wash out the interference fringes. However, the coincidence detector can match the photons that actually reach the upper detector with their "restored" twins in the lower path. The unmatched photons can be deleted from the electronic record and then when the numbers of photons detected are graphed the Young fringe pattern emerges.  
</BLOCKQUOTE>
<Blockquote>
Because of the way the polarizers affect light as they are shifting it from one mode of polarization to another mode of polarization, the two groups of photons that can be "restored" in the lower path will be 180 degrees out of phase with each other. The result is that the Young fringes for the two groups will be flipped left to right.</BLOCKQUOTE>
I think I've got it right now. Anybody see any problems? P0M (talk) 03:28, 15 November 2008 (UTC)
replies: text: I replaced the first paragraph listed above. P0M (talk) 23:32, 19 November 2008 (UTC)
thread_title: And it really is wrong 

message: Ouch. I just had a look at the article and the fundamental statement of how the experiment works was wrong from the time it was written. Let's get it right this time.
The quantum eraser experiment is a double-slit experiment in which particle entanglement and selective polarization is used to determine which slit a particle goes through by measuring the particle's entangled partner. This entangled partner never enters the double slit experiment. Earlier experiments with the basic Young double-slit experiment had already determined that anything done to discover by which path (through slit a or through slit b) a photon traveled to the detection screen would destroy the interference effect that is responsible for the production of interference fringes on the detection screen.
It should be:
<BLOCKQUOTE>The quantum eraser experiment is a variation of Young's double slit experiment that established that when a photon is acted upon in any way that permits determining which of the slits it has transited then it cannot interfere with itself. When a stream of photons is marked in this way, then the characteristic interference fringes characteristic of the Young experiment will not be seen. The quantum eraser experiment demonstrates that it is possible to create situations in which a photon that has been "marked" so as to enable determination of which of two slits it transited in order to reach a detection screen can later be "unmarked." A photon that has been so marked cannot interfere with itself. But a photon that has been marked and then unmarked can interfere with itself. When a stream of photons has been marked and then unmarked it can once again produce the fringes characteristic of the Young experient. The experiment has three phases: </BLOCKQUOTE>
<BLOCKQUOTE>In the first phase, pairs of entangled photons are created using a BBO device. The entangled photons are polarized and diverge in two directions from the point of their creation.  Those that go down the lower path in diagram 1 encounter a double slit and then are picked up using a sensitive scanner that sweeps across the interference pattern that they produce when they interfere with themselves. The number of photons at each step along the way is recorded, and the list thus produced is graphed. The graph shows a standard interference pattern. In principle the same procedure could be followed with the photons proceeding along the upper path as there is nothing that distinguishes the two streams of photons insofar as their suitability for demonstrating self-interference.</BLOCKQUOTE>
<BLOCKQUOTE>In the second phase, quarter-wave plates are inserted so that anything that goes through slit A gets its polarization changed into circular polarization in one direction (clockwise or counter-clockwise) and anything that goes through slit B gets  th other circular polarization. When the detector device is swept across the region of space where an interference pattern was earlier detected, no such result is observed, and it is as though only one slit were present in the photon path. This result is consistent with the very well tested observation that anything that is done that could detect which path a photon has taken through a double-slit apparatus, anything done that "marks" the path of the photon, will prevent an interference pattern from appearing.</BLOCKQUOTE>
<BLOCKQUOTE>In the third phase, no further changes are made in the lower pathway. Instead, a polarizer is inserted in the upper path so that the entangled twins of any photons going through the lower path are also changed in their polarization. Since the photons in the upper path have had their polarizations changed, the photons in the lower path must undergo the same modifications in their own polarizations. By choosing the appropriate angle of polarization for the upper polarizer, half of the photons in the lower path can be coerced to again have the same polarization. Once they have the same polarization they can interfere with each other again, or, to put it another way, now there is nothing that marks whether each of them went through path A or path B.  So they again interfere with each other. The problem for the experimenter is that the other half of the photons in the lower path get their polarizations changed also, but in their case they are still differentiated one from another. Since they have another set of opposed polarizations, they still cannot interfere with each other, or, to put it another way, their "which path" information can still be determined by measuring their polarizations. So they do not interfere with each other. Thus half of the light that reaches the scanning detector consists of non-interfering photons, and the self-interfering photons tend to get lost in the overall pattern of illumination. Fortunately, the experimenters can distinguish the two groups of photons because
only half of the photons will pass through the upper polarizer, and the photons that reach the upper detection screen are the twins of the
photons that have their marking polarizations "erased" in the lower path. By rotating the upper polarizer, the experimenters can select either the photons that have clockwise or counter-clockwise polarizations to "erase" and thus restore their ability to interfere with themselves. Whichever group the experimenters select will self-interfere, but the other photons will not self-interfere and their presence in the scanning photon detector will tend to wash out the interference fringes. However, the coincidence detector can match the photons that actually reach the upper detector with their "restored" twins in the lower path. The unmatched photons can be deleted from the electronic record and then when the numbers of photons detected are graphed the Young fringe pattern emerges.  
</BLOCKQUOTE>
<Blockquote>
Because of the way the polarizers affect light as they are shifting it from one mode of polarization to another mode of polarization, the two groups of photons that can be "restored" in the lower path will be 180 degrees out of phase with each other. The result is that the Young fringes for the two groups will be flipped left to right.</BLOCKQUOTE>
I think I've got it right now. Anybody see any problems? P0M (talk) 03:28, 15 November 2008 (UTC)
replies: text: I replaced the first paragraph listed above. P0M (talk) 23:32, 19 November 2008 (UTC)
thread_title: Rewrite

message: Or at least very misleading.
I am working on a rewrite incorporating the following complaints; I will add it here when I am finished.  The short version is that what you see on the screen never actually changes, even when interference is restored.  If this were not true, the experiment would violate causality, as you could, for example, send messages in Morse code from the future to the past by either erasing or not erasing the information, which would cause the pattern at the screen to change when the original photons arrived at the screen.  When the information is 'erased', what is actually changing is the correlation between the photon which enters the double-slit experiment and the one which does not (for simplicity I will refer to this second photon as the 'non-interacting photon', even though that's probably horrible terminology).  In the 'erased', restored interference case, we can get the following measurements results:  |R, +45> (Double-slit photon spin right circular, non-interacting photon spin +45 degrees), |R, -45>, |L, +45>, or |L, -45>.  If we get |—,+45> then we have no way of knowing whether the photon went through the upper or lower slit; similarly if we get |—,-45>.  However this misses a subtlety - the interference pattern for the |—,+45> case is opposite that of the |—,-45> case in that where one has bright fringes, the other has dark fringes and vice versa.  The effect is such that when the two are added together, no overall change is observed at the screen.  This is supported by the external link *A more technical analysis of the quantum eraser experiment and by a careful reading of the other sources (which also seem to gloss over this point).
This is a confusing enough concept that it might be worthwhile to devote a specific section of the page to it, explaining how this experiment does not violate all physics as we know it (it mystified me for a good few days when I first came across the Scientific American version, and again for a few hours when I read Wikipedia's slightly different version about a week ago).
EDIT:
I see this has already been addressed somewhat:  P0M stated that 
<Blockquote>
As I recall, the requirements for correlations, etc., are basically artifacts of the experimental design and do not imply anything significant about the reality of "erasure." 
</Blockquote>
and
The interference phenomena occur regardless of whether the experimenter can see them or whether they are "smeared out" as they are in this experiment minus the correlation counter. 
which would contradict my argument, but which I find to be highly implausible for the causality-breaking reasons I mentioned earlier.  P0M, do you have a reference for your claim that no correlations need to be present in the experiment?  Or at least an argument of your own?
I suspect some of the confusion may stem from the fact that the article is dealing with the delayed-choice quantum eraser.  I have not seen a version of the experiment which would not permit delayed choice, but I suspect it is only those versions which would not require correlation.
74.69.50.116 (talk) 05:38, 14 October 2012 (UTC)
thread_title: And it's '''still''' wrong

message: *The article already cited, http://grad.physics.sunysb.edu/~amarch/, makes the useful observation that:
One can wonder then, if this perplexing behavior is just due to a disturbance between the "which-way" detector and the photon.  The detector might be changing something about the photon which causes it to get off course to its position in the interference pattern.  The answer is, as the experiment described in the next section shows, that this is not the case.  A "which-way" detector can be designed that in no way disturbs the photon and the same phenomenon is observed.
*The article makes another observation: That since the polarization of the entangled photon in the upper part of the apparatus must be changed according to the way that its twin in the lower part of the apparatus is changed, it is possible to learn of the polarity of the lower-path photon by measuring the polarity of the upper path photon. So one can know the polarity of any lower path photon -- but this just assures in another way that the lower path photon cannot interfere with itself. The factor that "marks" the photons in the lower path is shown to be related to the polarity imposed by the quarter-wave plates, and there is no evidence for anything additional having occurred in interaction with the double-slit apparatus to disturb the photon and make it therefore unable to interfere with itself. When a polarizer is added in the upper path with the result that interference is again possible and the characteristic Young fringes appear, it is even more clear that the state of polarization of the light is the only factor that is influencing whether a photon can interfere with itself. P0M (talk) 08:11, 15 November 2008 (UTC)
thread_title: Needed additional elements

message: User:Diza added a  tag on October 31, 2009, but formatted it wrong, including the criticism "messy, repetitive and lacks a coherent overview" as part of the tag. I am correcting the tag and adding this section to record the criticism for cleanup editors. Please direct any questions or comments to User:Diza, not me. Unconventional (talk) 14:37, 12 November 2009 (UTC)
thread_title:  Cleanup-section: Introduction 

message: While reviewing the article, I noticed a discrepancy between it and the original paper. The paper gives the distance from the photon emitter to the QWPs as 42 cm, and from the photon emitter to the POL1 linear polarizer as 98 cm for the quantum eraser experiment and 2 m for the delayed quantum eraser experiment. (The distance to POL1 in the quantum eraser experiment is not explicitly given, but Fig. 1 in the paper suggests that POL1 is attached or adjacent to detector p.) Thus, the linear polarization in the double-slit path is measured between the slits and detector for the quantum eraser experiment, and after detection of the s photon in the delayed experiment. The article incorrectly describes the linear polarization as being measured prior to the double-slits, and needs to be changed. The dashed line in Illustration 2 repeats this mistake. (Perhaps the mistake was the result of the paper's Fig. 1, in which the p path appears to be shorter than the s path. But the distances given indicate that the figure is not to scale.) Unconventional (talk) 18:21, 12 November 2009 (UTC)
replies: text: Are you really talking about the illustrations that go with the Wikipedia article? I guess you must be talking about the original article. By "QWP" you mean quarter-wave plate? P0M (talk) 16:08, 13 November 2009 (UTC)

text: I just had a look at the original article again.  The wording of that article is a little confusing because it uses the word "behind" -- and whether something is in front or behind depends on the point of view of the observer.  In the article's illus FIG 1, the photons hit the quarter wave plates first and then the double slits.  That is what is shown on the series of diagrams shown above on the Talk page. The illustration for the actual Wiki article is different, and it is not as clear as it should be what the sequence is. P0M (talk) 20:27, 14 November 2009 (UTC)
replies: text: To clarify, I'm talking about two things: (1) The dashed line between the "+" symbols in the article's Illustration 2 suggests that the polarized p photon leaving the linear polarization filter affects the entangled s photon before it enters the quarter wave plates; and (2) the last paragraph of the Experiment section says so explicitly in its third sentence: "the photons heading down toward the double slits will meet the two circular polarizers after having been rotated". This is incorrect. The s photon hits the quarter wave plates and the slits (at 42 cm) before the p photon is linearly polarized (at 98 cm, or 2 m for the delayed erasure experiment). I would correct the text myself, but I'm not too clear on what effect a linear polarizer has on circularly polarized photons (nor vice-versa), and I can't fix the image because I have no means to edit SVG files. Unconventional (talk) 00:34, 15 November 2009 (UTC)
thread_title:  Discrepancy between article and original paper 

message: Isn't there something missing from the original paper? Just as the polarization of the p photon by POL1 coerces the polarization of the s photon after the slits, the polarization of the s photon by the QWPs must affect the polarization of the p photon before it gets to POL1. (But how? If s goes through both QWPs, would the complementary polarizations cancel out?) It seems to me that wasn't addressed in the paper, unless it's covered by the math (which I'm too dumb to follow). I can't guess what effect this would have on interpretation. Is there peer review criticism that should be added to the article? Unconventional (talk) 19:22, 12 November 2009 (UTC)
thread_title:  Something missing? 

message: As an interested amateur I have recently read a number of standard non-academic works on elementary particle physics (e.g. Q is for Quantum by John Gribben, The Particle Garden by Gordon Kane). I am now exploring aspects of these books via Wikipedia and in the process have come to admire the clarity of many of the relevant physics articles. These seem to follow a fairly standard format, at least as far as those dealing with well known experiments, e.g. Double-slit experiment, and Delayed choice quantum eraser. That is to say, the experiment itself is generally described in the present tense, such that the wording could be used as a recipe for repeating the experiment, while the outcome is set in the past tense, describing what the original experimenters actually observed. In this article, however, the tense in the penultimate paragraph of the section entitled  The experiment (beginning 'Next, in an attempt...') the tense suddenly switches to the future, and this tense is carried on throughout this and the final paragraph ('The next progression in the setup will...'). To me this reads as though it is describing some future experiment which could be conducted as an extension to the experiment which has already been described, together with a prediction of what might be observed as the outcome of such a future experiment. My point is not one of semantics, nor philosophy (and not pedantry I hope) merely an attempt to get clarity of concepts that for all of us (including Richard Feynman) are very difficult to grasp. I suspect that the wording should in fact be in the present tense, consistent with the earlier paragraphs describing the experiment. However, the fact that no one else appears to have raised this point makes me wonder if this is in fact based upon my own fundamental mis-understanding hence my reluctance to be bold and make the edits myself.
Inspeximus (talk) 16:13, 17 January 2010 (UTC)
thread_title:  Use of future tense in description of experiment? 

message: Since P0M and I seem to disagree on whether the correlation is inherent in the physics I am posting my proposed update here first.  I should probably update the 'up'/'down' and 'left'/'right' notation to reflect the actual directions used in the experiment, and maybe look for some pictures to help with the explanation.
74.69.50.116 (talk) 05:57, 14 October 2012 (UTC)
thread_title: Proposed update

message: I am having a devil of a time understanding the diagrams in the article.  Where do the photons come from and which direction are they moving? It seems in need of improvement, especially compared to the much more clear delayed choice quantum eraser diagram.  Ranatoro (talk) 18:11, 25 March 2013 (UTC)
replies: text: I tried to improve the image. Unfortunately, Inkscape frequently tries to mess up the arrowheads. It looks fine on my computer, and then when it comes back via Wikipedia and the web the arrowheads are rotated.   No time to try to fix things now.P0M (talk) 01:35, 27 March 2013 (UTC)
thread_title:  Diagram is confusing 

message: I have a request to delete this article. I have transferred the information to the Delayed choice quantum eraser where I merged it with other simular experiments. I think it is no useful to have a special article about one experiment. DParlevliet (talk) 16:18, 28 January 2014 (UTC)
replies: text: I disagree with most of your changes. See the recent comment by a physicist regarding the article that you have made many severe changes in.P0M (talk) 02:06, 31 January 2014 (UTC)
thread_title:  Request to delete 

message: I have deleted the recent change be DParlevliet. The citation (http://arxiv.org/pdf/quantph/9501016 ) offered as justification mentions "this experiment," but the experiment being discribed is not this one. Such irresponsible claiming of evidence to change an article without prior discussion and agreement is disruptive.P0M (talk) 17:17, 7 March 2014 (UTC)
thread_title:  Please read what you offer as proof 

message: We all know the two polarised slit experiment, that the polarization lenses are on both or one slit.
We must make the classic two slit experiment, but now the polatization glass should be not
in two slits, but in the electron gun itself, and the other experiment will be without
detectors and polarizers, also the slits will be as in the classical experiment, undisturbed.
Then we will rotate the polarizing glass of the electron gun or the lazer if we make that experiment
with light.
Polarization on the lazer gun, and rotation of the polarizing glass
has no effect on the quantum interference results. Neither the rotation of the polarized glass.
We have to see that. It will be boring, because mathematically it will be same as the classic one,
but we have to do it still  — Preceding unsigned comment added by 2.84.206.251 (talk) 16:21, 14 July 2014 (UTC)
replies: text: Wikipedia is not a place to report original research. P0M (talk) 00:44, 15 July 2014 (UTC)
thread_title:  polarised at birth 

message: Hello fellow Wikipedians,
I have just added archive links to  on Quantum eraser experiment. Please take a moment to review my edit. If necessary, add  after the link to keep me from modifying it. Alternatively, you can add  to keep me off the page altogether. I made the following changes:
*Added archive http://web.archive.org/web/20071015191251/http://www.sciam.com/article.cfm?chanID=sa006&articleID=DD39218F-E7F2-99DF-39D45DA3DD2602A1&pageNumber=1&catID=2 to http://www.sciam.com/article.cfm?chanID=sa006&articleID=DD39218F-E7F2-99DF-39D45DA3DD2602A1&pageNumber=1&catID=2
When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at ).
Cheers.—cyberbot IITalk to my owner:Online 18:39, 29 February 2016 (UTC)
thread_title:  External links modified 

message: Some people prefer the "many Quantum Erasers experiment".
Some European lotteries have 7 numbers to find, and all are decimal numbers.
Because the classic Quantum Eraser doesn't win you a lottery, people tried mentally to create a 0/1 system, so you don't try to read many data,simply if the experiment was interfered or not.
Thus you analyze each decimal number to a longer binary, and thus you need many different setups to reveal one digit - interference or non interference - not many data exist in each setup, thus you express any possible number via many simple on-off binary states of separate setups lined in order.
Of course it doesn't work for the same reasons. It is as silly as the original experiment, so of course we have to mention it because we mentioned the one setup version. 
they tried mentally to look for other artifacts, but no meaningful artifacts were found, no data could be transferred - this is also a mental experiment, because freezing particles is a hard job and we always distort their initial state  — Preceding unsigned comment added by 2.84.220.137 (talk) 01:16, 10 October 2016 (UTC)
thread_title:  The many Quantum Erasers experiment, and why you can't win the lottery 

message: As many have pointed out in this talk page before, the style of the article is not Wikipedia's summary style but instead written like a personal essay. This leads to some far-fetched proclamations, such as evidence of non-locality. I don't feel like delving into Wikipedia's cesspit of quantum physics "inaccuracies", but I feel at least like pointing this one out. Bright☀ 15:50, 28 July 2017 (UTC)
thread_title:  Non-locality and the style of the article 

message: The current description states that circular polarizers in front of each slit were used in discussed experiment. However, it's clearly visible from the original article or figures (1,2) that only quarter-wave plates were used. It's quite important because photons passed through crossed polarizers can't produce interference pattern.
I propose the following changes, but as my native language is not English, please have a look and correct the language if needed. The biggest part of "Non-locality" section is also removed as it's explaining the experiment basing on wrong understanding of setup. I didn't find the source of it's calculations either.
31.7.226.106 (talk) 12:54, 25 August 2018 (UTC)
thread_title:  Fix incorrect description of experiment 

message: I thought the experiment was done with polarization states, which are quantum mechanically equivalent to slits, but physically different.  It seems from above that some have figured out that things need to be fixed, but maybe still aren't.  I should probably get the original paper before saying more.  It is described in the book "Through two doors at once", though. Gah4 (talk) 07:51, 8 March 2019 (UTC)
thread_title:  polarization 

message: It seems that the whole article is written in terms of photons, but actually has to apply to any entangled (quantum) particles. Specifically, it also applies to electrons. In the case of electrons, it is somewhat easier to detect where one is by shining photons on it. Not so easy with photons. Gah4 (talk) 10:59, 8 August 2020 (UTC)
thread_title:  electrons