What is Double-slit: Definition and 187 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. O

    I Why doesn't gravity cause double-slit decoherence?

    A double-slit experiment can be run and get similar results using either photons or small particles that have mass, such as molecules. Why doesn't the gravitational field of molecules in the experiment reveal which-way information to the surrounding environment, and trigger decoherence and loss...
  2. sbrothy

    I Classic 'Double-Slit' Experiment Using Time Instead of Space

    (Not sure about the prefix. Choose intermediate to be sure.) This article Physicists Recreate Classic 'Double-Slit' Experiment Using Time Instead of Space has it's basis in this paper: Double-slit time diffraction at optical frequencies It certainly sounds intriguing but is there actually...
  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. S

    HW Question regarding double-slit interference

    A Homework Question about double-slit interference reads as such: "Finding a Wavelength from an Interference Pattern Suppose you pass light from a He-Ne laser through two slits separated by 0.0100 mm and find that the third bright line on a screen is formed at an angle of 10.95° relative to the...
  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. Byron Forbes

    I Interference in double-slit with single photons

    My question is about how the interference patterns work in a double-slit experiment when firing individual photons through either slit. Classic - there is 1 photon - it has nothing to interfere with. Quantum - even with a photon going through each slit at the same time, the likelihood of them...
  15. 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.
  16. F

    B Why doesn't the electron "wave" collapse at the double-slit?

    This is dumb question, so please bear with me. In the double-slit experiment where they fire a single electron at time, as you can see the electron gun fires a single electron. Now the electron travels as a wave. Now my question is, why doesn't the wave collapse when the wave encounters...
  17. 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...
  18. David Charles

    I Double Slit Interference Question II

    A stream of photons pass through a double-slit. The photon stream emerging from each slit then passes through a crystal which splits each photon into coherent entangled pairs. One photon from each pair heads towards a detector (D0) that "can be scanned by a step motor along its x-axis for the...
  19. David Charles

    I Double Slit Interference Question

    A laser provides a constant stream of photons which pass through a double-slit. The photon stream emerging from each slit then passes through a crystal which splits each photon into coherent entangled pairs. One photon from each pair heads towards a photosensitive screen and the entangled twin...
  20. 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...
  21. 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...
  22. 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...
  23. 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...
  24. 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...
  25. B

    I Phase shift after double-slit for entangled photons

    Hi all, I'm trying to understand how to describe the quantum state of entangled photons, including their phase, if one of them encounters a double-slit. Here's a simple example: Suppose you have two polarization-entangled photons A and B in the following Bell state: \begin{equation}...
  26. 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...
  27. 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...
  28. 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?
  29. Beth N

    Diffraction Grating Vs Double-Slit: Small angle Approx.

    Homework Statement In double slit interference , the angle between the center bright fringe and the path length (aka the angle used to find the path length difference) can be approximate as a small angle. However, we cannot assume the angles of bright fringes due to diffraction gratings are...
  30. 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...
  31. Euthan

    I Self-interference in double-slit experiments

    In a double-slit experiment, if a beam of photons is fired, an interference pattern composed of photons will result. But, if photons are fired one at a time, an interference pattern will still result. Why is this? The only explanation that I've seen is that the photon interferes with itself. I...
  32. 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...
  33. 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 -...
  34. B

    I Does Conscious Observation Affect the Outcome of the Double-Slit Experiment?

    Hello there, My question is: Is there a double slit-experiment done with all of the measuring equipment in place and all of the equipment activated but without a conscious observer? Proving there is no differentation pattern regardless of a conscious observer. Thanks in advance
  35. B

    I Concerning concioussnes and the double slit experiment.

    Hello there, I have a question about the double-slit experiment and conscioussnes. Excuse me if I don't formulate things right and might come over as a total fool for asking this (English is not my native language and i don't study physics). I just saw this video: <Moderator's note: link...
  36. 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...
  37. 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?
  38. J

    Solving Asymptotic Formula: Eq. 25 & 27

    In the following equation, $$P(x; a)= \frac{\gamma}{2\lambda L \eta} [\frac{1}{π^2N_F(a)\eta(1 - \frac{x}{a\eta})^2} + \frac{1}{π^2N_F(a)\eta(1 + \frac{x}{a\eta})^2} +\frac{2}{π^2N_F(a)\eta(1 - \frac{x^2}{a^2\eta^2})} [sin (\frac{π N_F(a)\eta(1 - \frac{x}{a\eta})^2}{2})sin (\frac{πN_F(a)\eta(1...
  39. 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...
  40. 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...
  41. 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...
  42. 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.
  43. S

    Double slit problem with glass block

    Homework Statement Light of wavelength 600 nm passes through two slits separated by 0.20 mm and is observed on a screen 1.0 m behind the slits. The location of the central maximum is marked on the screen and labeled y=0. (I only need help on the last 2 parts, but I will list all of them in...
  44. D

    I How important is light in the Observer Effect?

    How much importance does light (electromagnetism) have to do with the "Observer Effect" in the Double-slit experiment? From my research, it seems that the only successful "Observer Effects" in the Double-slit experiments, wherein, the interference pattern transitions to a clump pattern, is...
  45. 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...
  46. 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...
  47. 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...
  48. T

    I Mind Bending Double-Slit Diffraction Thought Experiment

    Hi, I studied undergrad pure maths now post grad philosophy, not quantum physics, but please consider the following experiment: Suppose you set up a double slits experiment with a photon detector attached to each slit, and the photon detector attached to a photon transmitter, so the photon can...
  49. 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...
  50. 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) =>...