What is Double slit: Definition and 822 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. J

    I How to improve the accuracy of Young's double slit experiment?

    My teacher asked me to find the separation of a double slit by finding the distance between fringes. I wonder how I can reduce the experiment error. So what can I do?
  2. H

    I Is it possible for a BBO crystal to produce an interference pattern?

    This question originated under a separate thread (see below) in an attempt to better understand what is happening with the quantum eraser experiment. Specifically, it seems that the BBO crystal which splits the photon beam after the double slit is critical in how the experiment is setup...
  3. H

    I Delayed quantum eraser: turning off sensor to bring back interference

    I've been learning about the delayed-choice-quantum-eraser experiment. To sum up; I imagine a double slit which has behind it a crystal which splits photons into entangled pairs. The crystal sends a photon to the right, from either slit, toward a single sensor (s1) which simply measures that a...
  4. bushmonk

    I Measurement and Thermal Effects Similar?

    A weak (one photon at a time) beam of laser light strikes a double slit. In case 1 the barrier forming the double slit is a mirror. In case 2 the barrier is flat black. An array of detectors surround the experiment and can detect the photon whether it goes through the slit or is reflected. In...
  5. dom_quixote

    I Double slit as a function of time

    It is known that in the double slit experiment, when successive photons are fired, the photons are statistically distributed on the target screen, as if it were a wave. What is the variable that changes between one shot of and another? Probably the slits change places as a function of time.
  6. jaketodd

    I What is the limit in size that two particles/objects can be entangled?

    What is the limit in size that two particles/objects can be entangled? With the double slit experiment, I know that there are matter waves, of large size - not just individual photons. So can a matter wave be entangled with another one, or even just a single particle with the matter wave...
  7. D

    I Double slit experiment with observer

    Hi ! This is about the well known experiment using small particles like electrons or photons - Light/electron beam passes through two slits - We observe a wave interference pattern on the wall after the slits https://en.wikipedia.org/wiki/Double-slit_experiment#/media/File:Double-slit.svg Now...
  8. 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...
  9. 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...
  10. 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...
  11. 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...
  12. 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...
  13. 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...
  14. G

    A A double slit thought experiment leading to a paradox

    Consider a Double Slits experiment in which the light source is monochromatic and each slit very narrow. There will be many fringes visible on either side of the axis. 1) If the light source is pulsed with very short, randomly spaced, pulses it will produce spectrally broadened radiation and...
  15. 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...
  16. 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.
  17. 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 :]
  18. 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...
  19. 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.
  20. H

    I Double slit fringe visibility with sunlight

    Hi Pfs, I know that Young made his double slits experiment with sunlight and i would like to know the best value of the fringe visibility on the screen. The visibility is equal to (Imax - Imin)/(Imax + Imin) thanks
  21. L

    B Double slit -- simple question

    With the double slit experiment the first thing I have to ask that is never explained, is why would an electron not always go through one slit? One does not design a gun to fire randomly over an area, but to be fairly precise and accurate in it's firing. Is there an assumption of the firing...
  22. 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...
  23. 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
  24. 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...
  25. 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...
  26. 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...
  27. Homestar1

    I Double slit - properties of slit?

    In the double slit experiment, are there articles that study different slit properties (e.g. charges, magnetic fields, current, etc.)? Curious if a wave is the property of the measurement, changing the properties of the experiment may alter the output measurement.
  28. Samina

    B View double slit from other end

    Our eyes not only detect the visible spectrum of light; they can also show the direction the photons are coming from. If, instead of a detecting screen, we use a moving camera or an array of cameras, can't we tell exactly which slit a photon / electron passed through?When viewing a light source...
  29. L

    B Double Slit & Quantum Eraser

    If you perform a double slit experiment but never look at the results could we say that the experiment never actually happened? The beginning of the experiment would show intention to find results but we believe intention does not create physical reality. Quantum Eraser could be preventing us...
  30. 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...
  31. wcjy

    Can Small Errors in Path Difference Affect Double Slit Interference Patterns?

    $$Δφ = 2π \frac{L_2 - L_1}{λ}$$ $$Δφ = 2π \frac{\sqrt{0.016^2+10^2}-\sqrt{0.014^2+10^2}}{560*10^{-9}}$$ $$Δφ = 33.659 rad$$Answer = 2.24 rad (unsure if the answer provided is correct/wrong)
  32. 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...
  33. B

    B Double slit question - how far apart can the slits be?

    How far apart can the slits be and the double slit experiment still works i.e the wave interference pattern is seen on the target screen?
  34. R

    B Questions about double slit experiments

    Firstly I’m just an interested layman who only started delving into QM and physics later on on life. So please forgive my ignorance. One of the things I’m trying to understand better is the wave / particle duality nature of objects. In the classical set up where single electrons are fired one...
  35. 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...
  36. 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...
  37. 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...
  38. 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...
  39. MichPod

    I Quantum vs Classical multiphoton interference on double slit

    For a setup analogous to double-slit experiment, do I understand it correctly that if we have two photons, one going only through slit A and another going only through slit B simultaneously (or vice versa as they have a symmetrical wave function), then there will be no interference pattern...
  40. C

    Trying to make sense of the double slit "experiment"

    How did you find PF?: A quick Google search of Physics forum gave me a link to this site. I have a good background in science (BSC Mathematics), but not specifically in Quantum theory. That happened after I left University. I have read lots, know a fair bit but wouldn't dare to claim I...
  41. 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?
  42. S

    B Double Slit Paradox: A Wave-Particle Mystery

    Let's take a pair of particles A and B that are in a quantum entanglement state, and shoot them in different directions. Along the way, one of them will pass in the famous screen of the two slits, say B. According to the known experiment, if we put a detector in one of the slits, we will lose...
  43. 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.
  44. 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
  45. 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?
  46. 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...
  47. 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...
  48. 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...
  49. 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...