Double-slit Definition and 187 Threads

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. kamhogo

    Single-sit vs. Double-slit vs. Diffraction grating

    Homework Statement Briefly state one characteristic of single-slit /double-slit/diffraction grating interference pattern that allow you to clearly distinguish one from the others. Homework Equations NoneThe Attempt at a Solution Single-slit: Taller, broader central maximum.Double-slit: More...
  2. T

    Double-slit problem with incident and refracted angles

    Homework Statement For the given configuration, the path difference between the 2 rays is given as δ=dsinθ1 - dsinθ2 Homework Equations Small angle approximation? The Attempt at a Solution I'm used to seeing a double-slit situation where only the exit angle is specified, and thus path...
  3. LegendLen

    How Do Different Wavelengths Overlap in Double-Slit Interference?

    Homework Statement In a double-slit interference experiment the slit separation is 8.40 x 10-6 m and the slits are 2.80 m from the screen. Each slit has a width of 1.20 x 10-6 m. 2 lights of wavelength 450nm and 600nm are shone on the same slits. If both of the above light sources are shined...
  4. 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...
  5. jk22

    Double-slit with half-transparent mirror

    Mentor's note: This thread has been split from https://www.physicsforums.com/threads/double-slit-with-semi-transparence.845980 What about if the wall were not transparent but one of the slits equiped with a half transparent mirror ? Then we would half-know which path was taken hence we should...
  6. Pizza

    Double-slit with semi-transparence

    Hi, I have a little question about the double-slit experiment, if this is the right place here, the right category? When the particles/waves are hitting the wall (the screen): Is that a mesurement as well? I would say Yes, it is, but would like to here a confirmation or a correction. And...
  7. DoobleD

    Constant intensity maxima in double-slit interference ?

    Third question about wave optics in two days, hope it's not too much. When we look at the intensity of light on the screen in a double-slit interference experiment (assuming negligible diffraction), we find something like this : When we look at the intensity of light on screen in a...
  8. 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...
  9. 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...
  10. VALENCIANA

    Decoherence and double-slit with eraser

    If I say that decoherence is an irreversible loss of information, then in the double-slit with erasure when initially decoherence has occurred with the measurement, and then after erasure of the information the state is again as it was at the beginning , how can this occur if the initial...
  11. 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...
  12. P

    How Does Mica Affect Fringe Shift in Young's Double-Slit Experiment?

    Homework Statement In a young's double slit experiment a thin sheet of mica is placed over one of the two slits. As a result, the center of the fringe pattern shifts by 30 bright fringes. The wavelength of light in the experiment is 480 nm and the index of refraction of the mica is 1.60. The...
  13. 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...
  14. C

    Why Are There Different Results in Young's Double-Slit Experiment Calculations?

    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...
  15. L

    Another double-slit question

    When performing the double slit experiment using one photon at a time does the single photon wave front hit both slits at the same time?
  16. 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?
  17. 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...
  18. A

    How Does Glass Thickness Affect Fringe Shift in a Double-Slit Experiment?

    A double-slit experiment is set up using a helium-neon laser (l = 633 nm). Then a very thin piece of glass (n = 1.50) is placed over one of the slits. Afterward, the central point on the screen is occupied by what had been the m = 10 dark fringe. How thick is the glass? I have the solution's...
  19. 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...
  20. 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...
  21. R

    Double-Slit Interference in Quantum Mechanics

    Hi, there Today, a friend came to me and asked the following questions and they made me confused. If the source is strong, the light has to be considered as wave, and the double-slit interference (DSI) can be interpreted, and the conditions for the DSI is (1) same frequencies, (2) parallel...
  22. R

    Conditions for Double-Slit Interference in Quantum Mechanics

    Hi, there Today, a friend came to me and asked the following questions and they made me confused. If the source is strong, the light has to be considered as wave, and the double-slit interference (DSI) can be interpreted, and the conditions for the DSI is (1) same frequencies, (2) parallel...
  23. vanceEE

    What is the correct wavelength of the light provided by the laser?

    Homework Statement In Fig. 6.1 the distance from the two slits to the screen is 1.8 m. The distance CP is 2.3 mm and the distance between the slits is 0.25 mm. Calculate the wavelength of the light provided by the laser. Homework Equations $$asinθ = nλ$$ $$w = \frac{λD}{a}$$ The Attempt at a...
  24. 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...
  25. K

    Young's double-slit interference?

    Homework Statement In a Young's double-slit experiment, a set of parallel slits with a separation of 0.102 mm is illuminated by light having a wavelength of 580 nm and the interference pattern observed on a screen 4.50 m from the slits. (a) What is the difference in path lengths from the two...
  26. A

    What Is the Distance Between the Slits in 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...
  27. 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...
  28. F

    Double-slit experiment and watching the electrons

    double-slit experiment and "watching the electrons" I'm trying to build a picture of what is happening in the double-hole experiment when you are "watching the electrons" (http://feynmanlectures.caltech.edu/III_01.html#Ch1-S6). It's mostly clear to me but I do have some questions: if you use a...
  29. TrickyDicky

    Double-slit experiment with photons vs electrons

    Both photons and electrons give the same kind of interference pattern in the double-slit experiment, but while in the case of electrons this carachteristic interference pattern is due to the probabilistic complex wavefunction of the Schrodinger equation within NRQM, for photons no such...
  30. G

    Understanding the Double-Slit Experiment: Photon Direction and Predictions

    I have been studying the double-split experiment and read different descriptions of it, but there's something I don't quite understand about the actual setup of the experiment: In the version of the experiment when photons are fired at the slits one-by-one: Are the photons fired at random...
  31. StevieTNZ

    Double-Slit Experiment With Various Energy Particles

    http://www.youtube.com/watch?v=n-7DsLR5wtk&list=PLE7AE1B2E44908250&index=7 At 1:57, James Binney describes the two-slit experiment with an electron gun. He mentions the electron gun fires electrons at one well-defined tuned energy. My question is if we fire each electron one by one to the...
  32. J

    Variation of the Double-slit experiment

    Hi Guys, I am not a physicist, just an average blue collar Joe who finds QM fascinating. I was wondering why they always use parallel slits. Has anybody ever tried varying the angle between the slits? And what would the interference pattern look like at different angles, starting at 1...
  33. T

    Non-technical answer wanted about the double-slit experiment

    Hi, I know that there are numerous threads about this, and I've also read several papers about it on the web. Still, I don't understand how the far-reaching conclusions of QM follow from the setup or results of the double-slit experiment. If anyone here has the patience to explain in...
  34. W

    Can this explain the double-slit experiment by a classical way?

    Hello. I found it very strange that matter behave as a wave and started thinking a lot... I have seen a video previously explaining this experiment and when I saw this: In red is the first path and in blue the second path. Could it be the answer? At the end of the video, in the screen of...
  35. tomwilliam2

    Double-slit experiment, thought experiment

    I'm trying to understand the implications of the double-slit experiment, and I have been considering what QM theory would predict as the outcome of the following experiment: Consider an electron gun firing electrons towards a detection screen two metres away (gun perpendicular to screen), and...
  36. M

    Double-slit quantum eraser: measured patterns on screen

    Consider a double-slit quantum eraser experiment such as the one by Walborn et al (http://arxiv.org/abs/quant-ph/0106078). The overall pattern formed by the signal photons on the screen behind the double slits is the same regardless of whether which-path information is available or destroyed...
  37. K

    Antenna Wavelength - double-slit interference

    Homework Statement The question is " Two large boulders lie between the house and Farmer Joe's favorite radio station. Farmer Joe cannot put the antenna on his house because the howl of the wind through it keeps Mrs Joe up all night. Where is the next best place Farmer Joe can put his antenna...
  38. R

    Question about the double-slit experiment

    In the double-slit experiment, an interference pattern emerges, until observed, whereby there emerges no diffraction pattern. I was thinking about this, and the following occurred to me. I was hoping someone could tell me if I was approaching a better understanding... When observed, the wave...
  39. DrChinese

    Double-slit interference pattern measurement with entangled photons

    Although it is well known that a series of individual photons will build up an interference pattern in a double slit setup, there have been few (if any) experiments where such a pattern is built up by sending photons through one at a time. Here is a great experiment from one of the top quantum...
  40. S

    I question the double-slit experiment:

    Concerning the double-slit experiment: In the basic version of this experiment, photons pass through a thin plate pierced by two parallel slits. The photons (interference pattern) are observed on a screen behind the pierced thin plate. If you change the depth of the slits does it change...
  41. E

    Double-Slit Arrangement With Plastic Sheet

    Homework Statement Consider the double-slit arrangement shown in the figure below, where the separation d is 0.280mm and the distance L is 1.16m. A sheet of transparent plastic (n = 1.50) 0.0513mm thick (about the thickness of a piece of paper) is placed over the upper slit. As a result, the...
  42. V

    Double-slit experiment questions

    I recently been reading up quantum physics including the double-slit experiments and I got two basic questions: 1# Why does the electron not act like a wave when there is only one slit? Shouldn't a single slit still result in a wave like pattern? 2# 'Measuring' the wave seems to turn it...
  43. C

    Double Slit Experiment: Home Reproduction Guide

    So I am a sophmoore in high school and i am really interested in quantum physics and i am fascinated by the double slit experiment. So i wondered, is there a way that i could reproduce the same results using common materials such as a laser pointer and aluminum foil. Any point at all would be...
  44. J

    Double Slit Experiment: Interference Patterns & Worldlines

    If we were to remove the double-slit from the experiment and have the CCD screen a light year away would we expect the same results? In other words is it the double slit that causes the interference pattern or do all particles have a worldine that is wave-like? I would think the latter.
  45. M

    What is so 'counter-intuitive' about the double-slit experiment?

    One photon produces a point on the screen. Many photons produce an interference pattern, whether the photons all arrive at the screen at once, or whether they are fired at the screen one by one. What is so 'counter-intuitive' about that? When we know that the electron shell that produces...
  46. D

    DeBroglie matter waves and double-slit

    Homework Statement A beam of electrons with a kinetic energy 1.00 MeV strikes normally at an array of atoms separated by 0.25 nm. in what direction can we expect the electrons in the fifth order? Homework Equations Ek= hf - W p=h/λ dsinθ=nλ The Attempt at a Solution i tried my...
  47. J

    Question; double-slit and wavefunction relationship

    I am having troubles finding anything online that reveals the conceptual concerns relating to the probability wavefunction in regards to the travel of a particle and then how that plays into the double-slit experiment. No math is required. I merely need to know the concepts involved. 1) exactly...
  48. B

    Question about the double-slit experiment.

    If a particle has the probability of being in two places at once, then is it possible to use a particle accelerator to accelerate the particle to a high energy and into the two slits and then place two detectors, with one at each slit, to convert the energy of the particle into electricity...
  49. I

    A simple question on a modified Double-Slit Experiment

    I guess inaccuracies in the actual experiment suggests the answer for this question. But would still ask to confirm. If instead of using a whole screen, one simply puts half a screen. That is, from a top view the screen extends upwards from the central beam axis, also right in the middle...
  50. D

    Link to description of detector type for double-slit experiment

    Can someone supply me with a link to a good article or book, or anything, that gives details on the type of detector that determines "which way" in experiments where the double-slit interference pattern is cancelled? DC
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