What is Double slit experiment: Definition and 481 Discussions

In modern physics, the double-slit experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles; moreover, it displays the fundamentally probabilistic nature of quantum mechanical phenomena. This type of experiment was first performed, using light, by Thomas Young in 1801, as a demonstration of the wave behavior of light. At that time it was thought that light consisted of either waves or particles. With the beginning of modern physics, about a hundred years later, it was realized that light could in fact show behavior characteristic of both waves and particles. In 1927, Davisson and Germer demonstrated that electrons show the same behavior, which was later extended to atoms and molecules. Thomas Young's experiment with light was part of classical physics long before the development of quantum mechanics and the concept of wave-particle duality. He believed it demonstrated that the wave theory of light was correct, and his experiment is sometimes referred to as Young's experiment or Young's slits.

The experiment belongs to a general class of "double path" experiments, in which a wave is split into two separate waves that later combine into a single wave. Changes in the path-lengths of both waves result in a phase shift, creating an interference pattern. Another version is the Mach–Zehnder interferometer, which splits the beam with a beam splitter.In the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate. The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles. However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen. Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave). However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.Other atomic-scale entities, such as electrons, are found to exhibit the same behavior when fired towards a double slit. Additionally, the detection of individual discrete impacts is observed to be inherently probabilistic, which is inexplicable using classical mechanics.The experiment can be done with entities much larger than electrons and photons, although it becomes more difficult as size increases. The largest entities for which the double-slit experiment has been performed were molecules that each comprised 2000 atoms (whose total mass was 25,000 atomic mass units).The double-slit experiment (and its variations) has become a classic for its clarity in expressing the central puzzles of quantum mechanics. Because it demonstrates the fundamental limitation of the ability of the observer to predict experimental results, Richard Feynman called it "a phenomenon which is impossible […] to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery [of quantum mechanics]."

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  1. V

    B Are Schrodinger's cat and the double slit experiment the same idea?

    Hello, My highest level of physics is Physics 3 for engineers in college. So I don't have the math or physics background to know this hence the question. I woke up thinking about the double slit experiment and how the simple act of observing somehow interacts or interferes with the...
  2. D

    B Has anyone ever done a double slit experiment in an electronic valve (vacuum tube)?

    i.e a vacuum tube. using the gate in a triode to adjust the amplification of the electrons. i guess you would have to have a photographic plate attached to the anode but this shouldnt effect the operation of the valve. just a thought... not sure where you would put the detector, maybe it would...
  3. Quarinteen

    B Double Slit Experiment: Dumb question that needs to be asked

    So the double slit experiment. If I understand correctly when electrons are shot through 2 slits and no one is monitoring, measuring or watching they create an interference pattern if they are being measured they create a 1 to 1 pattern. I keep seeing it be said that the mere act of monitoring...
  4. R

    B Double slit experiment, expensive gear?

    I have an idéa how to run the double slit experiment that could give new insight to whats hapening. As I understand, when the photons are observed by someone the wawefunction colapses and the photons become particles, this can be seen as the interference pattern dissapears in the experiment...
  5. Addez123

    B What is causing destructive interference in double slit experiment?

    When you do the double slit experiment with photons or electrons you get a wave pattern. At certain points no electrons are detected. This is said to be caused by destructive interference. Destructive interference of what? If we shoot single electrons, one at a time, from where is this...
  6. PeterDonis

    A Can the double slit experiment distinguish between QM interpretations?

    This paper claims that the double slit experiment can be used to distinguish between QM interpretations: https://arxiv.org/abs/2301.02641 IMO, the paper goes astray right at the start, when it points out that time is a parameter in the Schrodinger equation, not an operator, so that equation...
  7. J

    I Double Slit Experiment Mathematics

    Electrons are shot thru two slits separated by a distance s at a screen a distance ##z_0## away. The wave function for the particles is proportional to ## e^{ik \sqrt{(x-s/2)^2+z_0^2}} +e^{ik \sqrt{(x+s/2)^2+z_0^2}}## Taking the first one, we can manipulate the square root algebraically...
  8. D

    B Non-parallel double slit experiment

    Is it possible to tell which slit some of the light went through when the slits aren’t parallel (green & red boxes in option 3)? I used a Bahtinov mask to cover the aperture of my 600mm f/9 lens while observing the star Polaris. Various open slits were tested while others were covered with...
  9. Christian Thom

    I Double-slit experiment with momentum entangled pair of photons

    In Kaur, M., Singh, M. Quantum double-double-slit experiment with momentum entangled photons. Sci Rep 10, 11427 (2020). https://doi.org/10.1038/s41598-020-68181-1 and in C. K. Hong and T. G. Noh, "Two-photon double-slit interference experiment," J. Opt. Soc. Am. B 15, 1192-1197 (1998) it is...
  10. entropy1

    I Does the photon in a double slit experiment create many worlds?

    I can't find the anwer on this anywhere, so I hope I may ask it here. My question: In a standard double slit experiment, according to the Many Worlds Interpretation, does the photon create different worlds with different impact locations of the photon? So, without measuring which way...
  11. N

    B Double slit experiment combined with Stern-Gerlach

    A bit of background: I've read Derive the probability of spin at arbitrary angle is cos( ) | Physics Forums post in this forum and went into a "thought rabbit hole". It didn't make any sense to me and I think I made a wrong assumption somewhere along the way. Instead of typing everything out, I...
  12. H

    A Double double slit experiment and path information

    Hi Pfq My question is about this experiment: https://www.nature.com/articles/s41598-020-68181-1 (the link was given by DrChinese. If all the impacts are conserved no interference can be seen on the screens. but if we only take the impacts (Y, yi) where Y is always at the same position on the...
  13. H

    I Young's Double Slit Experiment: Is it Possible?

    I think that it is harder to describe the two slits Young experiment in terms of hamiltonian because the particle has a constraint: to pass through the slits. is it possible? thanks.
  14. Matt711

    B Q - Double slit experiment, delayed slit selection observation

    Do I see an interference pattern on a interference screen in Double slit experiment if there is a detector watching which slit photon went trough but the observer does not see the result of detector measurement? Thanks :]
  15. L

    I Significance of double slit experiment?

    What is the significance of the double slit experiment? When I first learned about it I thought the human observer decided the outcome. But I guess a human observer isn't even needed and therefore a conscious mind is just as irrelevant. What does it prove that an outcome is neither one thing or...
  16. S

    I Does the double slit experiment show waves collapse when observed?

    Do wavefunctions collapse when looked at? Or does observe mean something else? https://www.nature.com/articles/d41586-018-05892-6 This article is where my information is from, physicists talking about how our mind causes the collapse.
  17. M

    I David Deutsch's Many Worlds Interpretation and the Double Slit Experiment

    David Deutsch is a well known proponent of the Many Worlds Interpretation. His argument seems to be that a single photon in the double slit experiment must be interfering with one from another world. It is commonly held by physicists that the the photon, as a wave going through double slits, can...
  18. Ghost Quartz

    I Math of Electron Double Slit Experiment

    I'm looking for a good derivation of the "wave" patterns in this experiment. I suppose that if wave-particle duality is an obsolete idea, there must be a derivation from quantum mechanics that gets close results. Thanks in advance
  19. P

    B Question re photons/EM waves and the double slit experiment

    Not a physicist. Background is in electronics over many years. Have recently been "binge" watching youtube lectures on the "dreaded" QUANTUM MECHANICS by various people(Susskind, Feynman et al) and trying to comprehend the whole thing. While I can generally follow the lectures I must admit the...
  20. M

    B Double Double Slit Experiment -- Question about Variations

    emitter -> double slit -> double slit -> detector. Was an experiment ever made where two double slits are placed at some distance between each other? What kind of interference pattern would you get? What would happen if second slits were placed at the position where there is destructive...
  21. Ebi Rogha

    I Measuring Photon Intrinsic Nature: Is Interference a Factor?

    I would like to know, how can we be sure this is not due to the influence/impact/interference of our measurement, not necessarily the intrinsic nature of photons? In most reference books, it seems it is a given and it is not discussed
  22. deadbeef

    I Interference Patterns & Photon Paths: Exploring the Double Slit Experiment

    Hi. As i understand in double slit experiment photon can arrive at slits through different paths (longer and shorter) and it would still show interference pattern. My question is - if there was some path cutting device in a way of photon (on longest path after length that photon arrive at...
  23. Lexovix

    B Wave Function Collapse using faulty recording devices.

    Hey there! I have two questions regarding the Double Slit Experiment and the Wave Function Collapse. How effective does a measuring device have to be to cause a collapse? As in, say that every second the device has a 50% chance to turn off or on for one second, does the collapse still occur...
  24. B

    B How is the measurement done for the double slit experiment?

    How is the measurement of which path the particle took done for the double slit experiment? When electrons are being sent through the slit. Or when photons are being sent through the slit. Is it an active process or a passive process? I haven't seen an explanation for this and perhaps this...
  25. J

    I The Ensemble Interpretation and the Double Slit Experiment

    I am a big fan of Ballentine's book on QM and was reading the discussions about the Ensemble Interpretation. Although, I am not an expert on these matters I reject the idea of the wave function collapse as a fundamental postulate of QM. Instead, I've come to the conclusion that we don't...
  26. PainterGuy

    B Double slit experiment with electrons

    Hi, Could you please help me with the queries below? Thanks in advance! Question 1: I was watching this video. Between 8:36 to 9:44 the following is said: "But only firing particle by single particle at this barrier with the 2 openings and by recording dot by single dot where each of those...
  27. H

    B Gravitational signature of a photon in a double slit experiment

    I'm trying to think of a how the double slit experiment can detect a photon without interacting with it in theory. In principal (not reality of course) does a photon have a gravitational signature which could be used to detect which slit it traveled through during the double slit experiment...
  28. S

    I The velocity of Pilot-wave and the Double slit experiment

    Hello, Its been a while since I'm trying to understand the concept of the pilot wave theory and it's relation with the deBroglie wave. What is the fundamental difference between the two? My confusion comes from the double slit experiment. The velocity of the deBroglie wave is c^2/v so I...
  29. Axel Togawa

    I Double slit experiment and the Uncertainty Principle

    With the double slit, experiment we show the double nature of light and matter as wave and particle. In particular, the so called "which way" thought experiment illustrate the complementary principle. In my book, this experiment is analyzed putting a series of particles in front of one of the...
  30. H

    B What is the pattern in a double slit experiment near the slits?

    I am looking to this picture https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory#Double-slit_experiment it seems that fringes only appear on a screen when it is not too close to the fringes. and that the electron near the screen would give a pattern as when the path is known. Is it right?
  31. tanaygupta2000

    Young's double slit experiment

    Since slit-2 = 4 × (slit-1) Hence amplitude, a2 = 4a1 which gives i2 = 16×i1 So i(max) = i2 + i1 = 16i1 + i1 = 17i1 & i(min) = i2 - i1 = 16i1 - i1 = 15i1 => i(min) /i(max) = 15/17 but there's no such option. Kindly help me to figure out where am I doing error.
  32. wolfy

    B Has the Double Slit Experiment been Performed in a Near Vacuum?

    Where, When and Who has performed the Double Slit Experiment in a Near Vacuum Environment Cannot find it anywhere on Line Thank You
  33. S

    I Young's double slit experiment -- Question about this wavefront diagram

    Hello, I have a question about the blue waves coming from sources S1 and S2 in de next picture. The blue waves from sources S1 and S2, are those two resulting waves (interference of all wavelets, Huygens Principle) or are those blue waves two wavelets?
  34. J

    I Double Slit Experiment Question

    I'm wondering if this would be a way to interpret the double slit experiment. In other words, when we observe an electron in the present, it goes through one slit or the other as a particle. However, if we do not observe it, it goes through both at once as a wave; we only see evidence of it...
  35. B

    Finding the distance between slits in double slit experiment

    Hi so I have been struggling on a part of a question that I'm not too sure on how to solve For some reason PF is not allowing me to pose an image of the question on here so I have provided a link to it Question link: And here is what I tried to do so far, I drew a sketch of a diagram to help...
  36. A

    Number of maxima in Young's double slit experiment

    I honestly do not have any idea regarding this sum. Any help will be appreciated:)
  37. T

    I Single Photon Double Slit Experiment

    We're told that single photons passing through a double slit produce an interference pattern, but the act of observing which slit the photon passes through causes the interference pattern to show a simple ballistic pattern instead. But observing which slit the photon passes through necessitates...
  38. Davephaelon

    I Single photon double slit experiment

    My question is does the photon that is absorbed by an atom on the detection screen have exactly the same energy as the photon that left the 'gun' source? Hence, does the wave packet representing a photon lose some of its energy when it impinges on the double slit barrier, so that when the...
  39. F

    B Order of a dark fringe in Young's double slit experiment

    So the angular position for constructive fringes is d \sin \theta = m \lambda = (2m) \frac{\lambda}{2}, \qquad m=0, \pm 1, \pm 2, \ldots whereas for destructive fringes we have d \sin \theta = m \lambda = (2m+1) \frac{\lambda}{2}, \qquad m=0, \pm 1, \pm 2, \ldots I can see that ##m##...
  40. Marcin

    I Time measurement in a double slit experiment with single photons

    Assumption: Screen detector is much closer to the slits than in "standard experiment" and the small angle approximation can't be used to determine the interference fringe maxima, but the interference pattern still occurs. Is it possible to measure the time of detection in such setup accurately...
  41. Marcin

    Double slit experiment with magnetic traps

    1. Is it possible to perform the following, modified double-slit experiment with single electrons/electron beam: The slits are separated in such a way, that each leads to a separate magnetic trap. The traps have oppositely directed magnetic fields, so that the electrons entering them move in...
  42. SEYED2001

    I Relativistic energy equation applied to a double-slit experiment

    My question: How do the values for the velocity, momentum and energy of an electron in a double-slit experiment are altered by the observation? Probably,energy is altered. Given that energy is a function of momentum and velocity, either or both of these must have been changed. However, I am...
  43. UnderstandingQT

    B Questions about measurement devices in the double slit experiment

    How did you find PF?: Google Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?
  44. Spinnor

    I Photon Double Slit Experiment: Visualizing the Guiding Field

    Does the following picture which I think shows the guiding field for electron in the double slit experiment have a corresponding image when the experiment is done with photons? Thanks for any help.
  45. S

    Wavelength used in double slit experiment

    m × lambda for bright = (m - 1/2) × lambda for dark so: 2 × 708 = 2.5 × second lambda Second lambda = 566.4 nm But the answer is 495 nm. Where is my mistake? Thanks
  46. C

    Young's double slit experiment

    I know that ydse is based on interference of light when it passes through an obstacle having almost same aperture as the wavelength of light. Also they should be coherent to have a constant phase difference at every point. But I don't get why the light beams should be parallel?
  47. jisbon

    Finding Angles in a Double slit experiment

    Hello all! Having some problems understanding this question. From what I know, bright fringes means that there will be constructive interferences, whereby ##d\sin \theta =m\lambda## In this case, I know the d (separation of silts). However, what should I put in for wavelength? I went through...
  48. Adesh

    Putting a slab of some material just after the slits in Young's model

    If I put a slab of some material whose refractive index is \mu and width is D, in front of slits in Young's Double Slit model, then In the figure you can see that I have placed the slab just after the slits. So, when rays going to come out of the slab they will bend away from...
  49. ilper

    I The construction of particles in QFT

    In all books about QFT I have seen I can not find anything about what a localized particle concept is. Suddenly I found this note in Zee's 'QFT in nutshell' page 4: "As usual, we can form wave packets by superposing eigenmodes. When we quantize the theory, these wave packets behave like...
  50. N

    Exploring the Symmetry of the Double Slit Experiment

    I have no clue how to answer this question. I would imagine for (a) that half of the probability of total particles goes away with only one slit.