What is Two slit experiment: Definition and 25 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. C

    A Two Slit Interference Experiment Variations

    Examples that have references to special two slit experiments : https://sciencedemonstrations.fas.harvard.edu/presentations/single-photon-interference https://en.wikipedia.org/wiki/Double-slit_experiment If you have an opinion on what you think the experiments tend to support and what they do...
  2. C

    I Two slit experiment with different sized slits

    If the two slit experiment is performed with one slit half the width -- or 1% or 0.1% the width -- of the other, how is the interference pattern affected.
  3. Machine1701

    I Why doesn't decoherence apply to unobserved experiments?

    This is based on the Hugh Everetts interpretation of quantum mechanics, where the waveform never collapses but the observer becomes a part of it, thus experiencing decoherence of the wave form from their point of view. So, let's say someone is doing the two-slit experiment. The particles going...
  4. A

    Finding the separation of two slits

    Homework Statement How do I know what value of m to use when using the equation? Here we had to use m = 1 to find the answer. Please refer to part 3 for the problem statement. Homework Equations Please refer to part 3 for the relevant equations. The Attempt at a Solution [/B]
  5. R

    I Two slit experiment w baseballs

    Would it be theoretically possible to perform a two slit experiment with, say, baseballs? How would such an experiment need be set up?
  6. M

    B Regarding Young's two slit experiment

    regarding Young's two slit experiment 1. HOW can a light source is used to create a single photon that can be directed at 2 slits simultaneously ? I am confused as to how the light source can be aligned with both of the slits simultaneously. IF the light beam is wider than the distance...
  7. Cobalt101

    I Delayed choice two slit experiment - photon

    Is it possible that the reason the delayed choice two slit experiment outcomes occur is because for the photon, traveling at the speed of light, the past, present and future are all as one, and therefore it "knows" what is going to happen and therefore always "makes the right choice" at the...
  8. NaiveTay

    B Two-Slit Experiment And Varying Electron Momentum

    There seems to be two divided approaches in how the uncertainty principle is explained, but they seem to be explaining two different things. The first, more intuitive explanation of the limits imposed by quantum mechanics goes something like: in order for a measurement to be made, we have to...
  9. Jilang

    Two slit experiment with a wavy screen

    I was wondering if the two slit experiment has been performed with a wavy screen, the screen being modulated in such a way as to compensate for the difference in the phases of the paths from the two slits. If so what was the result in terms of the angular distribution? If not what would it be...
  10. Tom B

    Two Slit Experiment: Detectors

    I understand the two slit experiment and the outcome, but where I am confused is how the detectors work. It seems to me that a very simple explanation of the result differing due to the presence of the detectors is that somehow the detectors interfere with the path of the electrons. By...
  11. Arthurz11

    When does the photon splits in 2 on the Two Slit Experiment?

    Hello! I have questions in regards to the Two Slit Experiment. If the photon splits in two and passes through both slits at the same time and interferes with itself on the other side of the screen and then it hits on the second screen thereby creating the interference pattern. At what point...
  12. M

    How Does the Two Slit Experiment Illustrate Quantum Duality?

    A couple of days ago i stumble across the two slit vid on youtube and entanglement. before this day i thought quantum physics was just some kind time travel mumbo jumbo ... I am sure you get my level of noobieness from this :) ok questions if you would be so kind :) ( don't forget the...
  13. J

    Two slit experiment at home and interference

    Why is it possible to do this experiment at home and still see light as a wave? Isn't there loads of interference? Or does this have to do with wavelength? If you use a laserpen and 3 needles you can basicly do it at home without shielding off anything...
  14. P

    Can the Two Slit Experiment Be Conducted Without Observer Influence?

    Hi all! I heard about that the experiment had been iplemented so the observation don't effect the experiment. Because some scientists thought that the observation has an effect on the experiment and that's why the interference pattern doesn't appear at that time. My question is, how they do...
  15. V

    Young's Two Slit Experiment Question

    Question: I'm sure this is a stupid question, but it has been bothering me lately so I'll ask it anyhow. In Young's Two Slit experiment the conditions for max and min are dsin\theta=m\lambda (max) dsin\theta=(m+\frac{1}{2})\lambda (min) where m is an integer and d is the separation of the...
  16. R

    Does a Detector Alter Diffraction Patterns in the Two-Slit Experiment?

    In the two slit experiment when which path information is present there is no wave interference pattern such as would be seen with both slits being used. When a single slit is used there is a visible diffraction pattern. Is such a pattern seen when a detector forces a one slit path in the two...
  17. I

    Quantum entanglement and Two slit experiment

    Hi. Firstly, I'm not a physics student but was just wanting some answers to questions from those that are, so I thought I'd try you lot. :smile: 1. Has anyone proved that quantum entanglement doesn't happen at the macro level? 2. Regarding the 2 slit experiment and how consciousness...
  18. T

    Two slit experiment - variable detector

    I have a question about the situation with the two slit experiment where detectors are placed by the two slits to determine which slit the particle has gone through (and destroy the diffraction pattern). Okay, so what I'm wondering is what happens if the detectors' accuracy is not fixed, but...
  19. M

    Question on wavelength using the two slit experiment

    Homework Statement Red light with wavelength of 700 nm is passed through a two slit apparatus. At the same time, monochromatic visible light with another wavelength passed through the same apparatus. As a result most of the pattern that appears on the screen is a mixture of two colors...
  20. K

    Youngs two slit experiment problems

    can anyone give imput please,i have a problem with Youngs two slit experiment,if i remove the lens from the laser,you just get the 2 slits, iv got a few videos of it on youtube you might find strange
  21. P

    Bohmian Mechanics and the two slit experiment

    I am trying to understand the essentials of the Bohmian interpretation of quantum mechanics (BI),and my (many) difficulties start with his description of the two slit experiment.As I understand it,Bohm asserts that every quantum particle has associated with it a quantum potential or guiding...
  22. P

    Fair dice and two slit experiment

    The number that comes up on a die seems to be determined by mechanics - not probability; eventhough dice are used to explain probability. Is there a analogus process that determines where a photon will fall in the double split experiment - eventhough it is explained by probability?
  23. B

    Two Slit Experiment Setup and Variables

    The 2 slit experiment is common, but what exactly is the complete setup. i know the interference patterns, but there are variables in every experiment. Where is the particle fired? Is it fired precisely at one of the slits, or is it fired so that it should hit in between the two slits if...
  24. B

    Electron two slit experiment with gradual collapse ?

    electron two slit experiment with gradual "collapse"? Just read about the two slit experiment with electrons where you try to find out through which slit the electron went by "shining a light on it" (Feynman lectures on physics I-37-7). I try to summarize the statement and then have a question...
  25. D

    Two slit experiment - quantum theory - problem

    Hi, I'm new and I'm from Poland. I have problem with equation(average number of photons registered behind pinhole 1 in two slit experiment): \bar{n}_1=\langle n|a_{1}^{+}a_{1}|n\rangle=\frac{\langle 0|(a^{+})^{n}a_{1}^{+}a_{1}(a^{+})^{n}|0\rangle}{n!} using...