What is Double-slit experiment: Definition and 114 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. Q

    I Making the wave observable in the double-slit experiment

    Physicist Dr. Muthuna Yoganathan thought the wave function was just a calculation tool, which is the standard minimal interpretation of QM. But then she started doing her own versions of the double-slit experiment at home using a red laser, culminating in purchasing a smoke machine. With that...
  2. RUTA

    Insights How Quantum Information Theory Solves “the only mystery” of Quantum Mechanics

    [url="https://www.physicsforums.com/insights/how-quantum-information-theory-solves-the-only-mystery-of-quantum-mechanics/"]Continue reading...
  3. Mr Fallspring

    I Double-Slit Experiment: Does rate of photon emission matter?

    Hi there! High school physics teacher hoping to pick the brains of people who know more than I do here. I'm curious whether the rate of photon emission has any noticeable effect on the diffraction pattern generated by the double-slit experiment. To be clear: I understand a diffraction pattern...
  4. T

    I Double-slit experiment, determining which slit an electron passed thru

    I was reading Feynman's lecture on the double-slit experiment, the attempts to determine which slit an electron passes through. https://www.feynmanlectures.caltech.edu/III_01.html#Ch1-S6 And the key part is when Feynman says, "Then a terrible thing happens.", about the low optical resolutions...
  5. 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...
  6. C

    B How is energy transferred from a wave to a photon?

    This is just a curiosity to me. My interest is from the position of a layman (as you will see from my description below). In the double slit experiment it shows a wave passing through both slits and interfering with itself to create an interference pattern. This is how I understand it... From...
  7. A

    A Double-Slit Experiment: Momentum & Position

    In the double-slit experiment with two open slits, is there a fixed relationship between the momentum (p) of the particle immediately after passing through the slit and the position (q) of the impact on the screen?
  8. A

    I The probability density function for the double-slit experiment

    I am desperate. I've scoured the web for the formula for the probability density function for the interference pattern obtained in the double slit experiment with both slits open. So I want to know the probability density function and not the intensity function. I prefer not to have references...
  9. A

    I How does the double-slit pattern change depending on the slits?

    Summary:: How does the double slit pattern change in the double slit experiment depending on the width of the slits and their spacing? On Wikipedia in the article Double-slit experiment, the lower figure of the figure next to the Overview chapter shows a picture of what can be seen when two...
  10. O

    I Observing a double-slit experiment

    Do I have the proper understanding of the following three double-slit experiment situations? #1 While a standard double-slit experiment is run via a Mach-Zehnder interferometer apparatus that completely lacks which-way detectors, can an ordinary human experimenter be present and watch that...
  11. H

    Young's double-slit experiment - Bright fringes occurring

    I think the answer is E because each bright fringe is differed by a wavelength, in other words, one wavelength is equal to 2π. (For example, the first bright fringe is d * Δy/L = 1*λ.)
  12. jackiepollock

    Young's Double-Slit Experiment

    As I searched online an answer suggested that the blurry effect might be a speckle pattern. However, it still hasn't explained the reason why when my body come near the pattern gets blurry.
  13. K

    I Constant beam, both slits analyzed double-slit experiment?

    I keep seeing that it's assumed that photons interfere with each other, and there are other points of proof for this like destructive interference, etc., but I've never seen an experiment in which a constant beam is used but both slits are analyzed or the energy required for measurement is...
  14. R

    B A question about the double-slit experiment

    In the diagrams illustrating the double-slit experiment, I see waves extending longitudinally towards the the metal sheet. What if the waves were modeled differently so that they extended transversely in the diagrams? I've got the feeling that this can say something different.
  15. J

    I Repulsion before the screen in a double-slit experiment

    Consider a double slit experiment with electrons fired illustrated in the attached figure. One interpretation of this experiment is that each fired electron clones itself, one of the clone passes through one slit and the other through another slit then they reached the screen where they...
  16. 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...
  17. L

    I General Implications of the Double-Slit Experiment

    I've been reading about the sophisticated double-slit experiments currently being conducted by a team of physicists led by Tom Campbell. It's no secret of course that Campbell hopes that the findings of these experiments will strengthen the argument that our universe is a computer simulation...
  18. Krushnaraj Pandya

    How does the Double-Slit Experiment explain the strange behavior of electrons?

    I have always seen YouTube videos saying how an electron 'knows' when we are observing it but I always put that down to youtubers creating popular science (verging on science fiction) hype for more views. I suppose there is more science behind an electron behaving like a particle when we put a...
  19. Graeme M

    B The Human Eye as a Detector in Double-Slit Experiment

    Trying to wrap my head around what the double-slit experiment is illustrating, it occurred to me that one could replace a mechanical detector with the human eye. I found that this was tested with what seems an elaborate test setup in 2016, and the result suggests that while an interference...
  20. Ken Hughes

    B Interference of Light in the Double-Slit Experiment

    It is said that interference occurs when a peak (of the light wave) meets a trough and the wave cancels to zero, giving a dark band on the screen. However, if light waves are bands or "shells" of high densities of photons interspersed with bands of zero photons, then how can this be? When a peak...
  21. Wrichik Basu

    Classic double-slit experiment in a new light

    An intense beam of high-energy X-ray photons (violet) hits two adjacent iridium atoms (green) in the crystal. This excites electrons in the atoms for a short time. The atoms emit X-ray photons which overlap behind the two iridium atoms (red) and can be analyzed as interference images. Credit...
  22. fluidistic

    A The different interference patterns in the double-slit experiment

    I've read on page 107 of the pdf http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=617AE275E5CECF5F0AFD69ACBC52141B?doi= that . Thus it seems that there are three different interference patterns. 1: We do not try to detect the electron passing through the...
  23. M

    I Double-slit experiment: Alternating results

    How can the results of a double-slit experiment change just by adding a detector at the point of entrance of the split? Is it really so that if there is a detector, we will only see two lines and if there is no detector we will see interference?
  24. quantumdave

    B Observation in the double-slit experiment

    I'm not sure if there's a better category to post this in, and I'm just a casual physics enthusiast, but I'm having trouble understanding this: "Consider the famous two-slit experiment. When you watch a particle go through the holes, it behaves like a bullet, passing through one slit or the...
  25. Q

    B A view of the double-slit experiment

    Greetings. My name is Antti, I'm from Finland. My scientific background consists mostly if not only from watching youtube videos about science and Googling things that I'm curious about. So i registered on this forum to ask questions from the more educated people. So here's my understanding as...
  26. MichPod

    I Modified double-slit experiment - two photons

    On the following link https://physics.stackexchange.com/questions/183961/modified-double-slit-experiment-two-electron-sources-instead-of-two-slits there is a discussion of the modification of double-slit experiments where two electrons sources are put in place of the slits. The conclusion is -...
  27. P

    I Proposal for a peculiar double-slit experiment

    Hi to all who might respond, Consider the 'peculiar' double-slit setup below. There is a double-slit configuration such that the two slits are never open at the same time. That is: whenever the top slit is open for a certain interval, Ts, the bottom slit is closed for the same interval and vice...
  28. B

    B Double-slit experiment observed by split brain

    Hello all, Does anybody here know whether the double-slit experiment has been conducted with a split brain patient as observer?
  29. B

    B Trying to understand the double-slit experiment

    Has anyone ever thought that the wave pattern on the screen is not because the particle is a wave. There is no reason that the wave appearance could not be due to a photon being distributed in this fashion and still be a particle while both slits are open. You have a different distribution with...
  30. MadMartigan

    Calculating the angle of a double-slit experiment

    Homework Statement So, my physics professor has been behind all semester long and basically taught the entire light wave and optics chapters in a single day and explained absolutely nothing, hence massive confusion on the following problem:[In a double-slit experiment, the slit separation is...
  31. S

    Thomas Young's Double-Slit Experiment Problems

    Homework Statement Determine the wavelength of light being used to create the interference pattern in 3 different ways from the given data. -The angle to the 8th maximum is 1.12° -The distance from the slits to the screen is 302 cm -The distance from the first minimum to the fifth minimum is...
  32. Jens Lundell

    B Electron in the double-slit experiment

    Newbie here: Is the (single) electron leaving the "machine" in the famous double-slit experiment the same one hitting the screen? Please give a short explanation on how this is proved, thank you.
  33. Quotidian

    B A non-physicist's question on the double-slit experiment

    OK this question comes from a late-night discussion, er, argument, about the famous double-slit experiment. One of the interesting facts about the double-slit experiment is that the interference pattern that appears on the screen doesn't seem to be affected by the rate at which electrons are...
  34. moenste

    Young's double-slit experiment, fringe separation

    Homework Statement The distance between the 1st bright fringe and the 21st bright fringe in a Young's double-slit arrangement was found to be 2.7 mm. The slit separation was 1.0 mm and the distance from the slits to the plane of the fringes was 25 cm. What was the wavelength of the light...
  35. Tareq Naushad

    B How to make the wave collapse in double-slit experiment

    I successfully created the fringe pattern at home with a simple laser light and a black plastic sheet with two thin cut as double-slits. I then used two mobile phone cameras at two sides in hope that the wave function of light will be collapsed. But nothing happened i.e. the fringe remained...
  36. kamhogo

    Double-slit experiment: What is the speed of the neutrons?

    Homework Statement An experiment was performed in which neutrons were shot through two slits spaced 0.10 mm apart and detected 3.5 m behind the slits. The following figure shows the detector output. Notice the 100 μm scale on the figure. To two significant figures, what was the speed of the...
  37. B

    Double-Slit Experiment problem?

    Homework Statement In a double-slit experiment, the third order bright fringe is 15 mm from the central fringe. What is the distance of the first (zero-th order) dark fringe from the central maximum? Homework Equations (m+.5)(lambda) = dsin(theta) => dark fringe m(lambda) = dsin(theta) =>...
  38. sciencejournalist00

    I Does the double-slit experiment create path-entangled states

    If I try to send a vertically polarized photon through one slit and a horizontally polarized photon through the other slit, they actually go through both slits. But when I measure and find out through which slit the horizontally polarized photon went, I automatically know that the vertically...
  39. quantumdave

    B Watching the double-slit experiment affects the results?

    Sorry that I haven't done a search here, but I've searched exhaustively on the internet for a definitive answer, but I watched the Dr. Quantum video on the double-slit experiment, and he says near the end that "The observer collapsed the wave function simply by observing" with an eyeball on a...
  40. En Joy

    Thought double-slit experiment

    In Young’s double slit experiment, if we use a single electron, then the electron-wave would divide itself into two wavelets due to two narrow slits. Similarly would the electron-matter divide itself in that experiment? If it would not, then through one slit, both the electron-wave and...
  41. A

    MHB Interference in a Double-Slit Experiment

    In a double-slit experiment, the distance between slits is 5.0mm and the slits are 1.0m from the screen. Two interference patterns can be seen on the screen: one due to light of wavelength 480nm, and the other due to light of wavelength 600nm. What is the separation on the screen between the...
  42. I

    Double-slit experiment: any videos of the Observer Effect?

    Hello! I've been reading up about Quantum Mechanics, and I'm trying to understand various aspects of the double slit experiment. This is one of among many videos I've watched: Dr Quantum - Double Slit Experiment Here's my understanding so far of the basic setup (where the gun is shooting out...
  43. C

    Young's Double-slit Experiment

    Homework Statement In a KhanAcademy video, light of wavelength 700nm shines through a double-slit whose holes are spaced 1300nm apart. If a screen is placed 3m away from the double-slit, what will be the distance from the central bright spot on the screen to the next bright spot...
  44. Ookke

    Double-slit experiment and gravity

    If the particles used in double-slit experiment were massive enough and/or our equipment sensitive enough, could we use gravity to spy what path the particles take even before they hit the detector? Would this kind of "measurement" destroy the interference?
  45. R

    Double-Slit Experiment Variations List

    Hi all, first post and an amateur enthusiast here. I'm a 33 year old programmer who takes an interest in the mysteries of quantum mechanics and trying to nurture my own little theories. I've came across variations of the double slit experiment and was wondering if there's such a resource that...
  46. U

    New version of double-slit experiment

    I am trying to find a definite answer whether the following version of the double-slit experiment has ever been performed. Calculate/observe what interference pattern should appear by emitting photons individually one-by-one through the double-slit barrier and onto a detector screen behind...
  47. C

    Collapse of Wavefunction, Double-Slit Experiment

    Now I'm trying to imagine the wavefuction before and after collapse when measured at either slit. Before the particle enters the slits I imagine the wavefunction more as a planar wave with no definite position (single wavenumber and a superposition of positions). If no measurement is made then...
  48. P

    The Young Double-Slit Experiment

    I have basically two doubts regarding diffraction and interference. First of all, according to my CIE A level Physics book, while the double slit experiment results in fringes that are more or less equally separated, a diffraction grating results in fringes that are not equally separated. Why is...
  49. A

    Young's Double-Slit Experiment

    Homework Statement When two parallel slits are illuminated with monochromatic light of wavelength 632.8 nm, the angle between the center of the central maximum and the center of the second side maximum is .45 degrees. What is the distance between the parallel slits. Homework Equations...
  50. V

    What interference pattern of double-slit experiment does mean

    I have a doubt about the interference wave pattern of double slit experiment with light beam. does it mean the interference of electromagnetic wave (which tells about the frequency causing color) or Spatial probability wave (which was explained by Max Born). I am not good at math. can someone...