The Original Double Slit Experiment



Veritasium

Light is so common that we rarely think about what it really is. But just over two hundred years ago, a groundbreaking experiment answered the question that had occupied physicists for centuries. Is light made up of waves or particles?

The experiment was conducted by Thomas Young and is known as Young’s Double Slit Experiment. This famous experiment is actually a simplification of a series of experiments on light conducted by Young. In a completely darkened room, Young allowed a thin beam of sunlight to pass through an aperture on his window and onto two narrow, closely spaced openings (the double slit). This sunlight then cast a shadow onto the wall behind the apparatus. Young found that the light diffracted as it passed through the slits, and then interfered with itself, created a series of light and dark spots. Since the sunlight consists of all colours of the rainbow, these colours were also visible in the projected spots. Young concluded that light consist of waves and not particles since only waves were known to diffract and interfere in exactly the manner that light did in his experiment.

The way I have always seen this experiment performed is with a laser and a manufactured double slit but since the experiment was conducted in 1801 I have always thought that it should be possible to recreate the experiment using sunlight and household materials. That is basically what I did here. I will show the interference pattern I observed with my homemade double slit on 2Veritasium but I chose to use a manufactured double slit here to ensure that the pattern was impressive for observers at the beach.

Special thanks to Henry, Brady, and Rupert for their cameos, Glen for filming and Josh for helping create the apparatus. Thanks also to the Royal Society for allowing us to view the original manuscript of Young’s lecture and the University of Sydney for lending the double slits.

Music by Kevin Mcleod (incompetech.com) Danse Macabre, Scissors

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31 Responses

  1. Parag Patil says:

    Come on I want explaination for dual nature of light what instrument is used that used to see the entanglement ??

  2. if we send one by one proton ,but still same happen its going to next level quantum physics..

  3. Yuri Walter says:

    Can I give it 100 thumbs up?

  4. What if a detector is placed will the wave function collapse and we see only two bands of bright light?

  5. The Pragati says:

    It happens only because that light was not monochromatic . It was mixture of different colours with different wavelengths .

  6. Heisenberg says:

    Are they all uneducated.
    An 8th grader in my country knows what is light.

  7. If someone had asked this to children in Kota(place in India) a 15-16 yr old would have given the equations to it's proof and resulting intensity variation

  8. Question: Does the canceling out of the waves still prevent the energy of the light from transferring to the material or is the energy within those two wavelengths of light canceled out as well somehow? I'd imagine the energy is still there it just becomes inperceivable to our eyes due to this canceling phenomena

  9. kearnzey says:

    A wave is what something dose! so I’d be asking the question “what is waving” ?

  10. Theory of Quantum Illusion

    Or

    The Alternative Theory

    By:- Sagar A. Kathiriya

    E-mail – [email protected]gmail.com

    This is theory to understand the quantum state of any particle at any time either it’s observed by an observer or not. By this theory, we can understand “wave-particle duality” of nature. The Position of any quantum particle at any time is the result of deterministic trajectories that emerge from non-hidden Universal field disturbance (non-local, non-global it’s Universal) made by that quantum particle itself. When quantum particle made a disturbance in that filed, ripples are generated from that filed and particle follow that trajectories because any particle with mass can’t move faster than that ripples. That ripples travel at the speed of light. And so, every particle with mass must follow any of those trajectories that created by a ripple of Universal field. And so, what we find as Interference pattern is just a result of that ripples or wave trajectories that have been followed by quantum particle. The Final Position of any particle depends on size & mass of that particle and It also depends on that Fields Intensity. If the field is stronger then we get more Intense Interference Pattern and if that fields Intensity is lower then we will get low Intense Interference pattern from the Double Slit Experiment.
    So, the Only Question is what that non-hidden Universal field is?
    First, it’s everywhere in the Universe.
    Second, it’s not hidden. We already know almost everything about it and It’s first of its kind.

    It’s Gravitational Filed.
    To prove this theory we only have to perform the Double Slit Experiment in Deep Space.

    And After all, if I’m Correct then I only have to say just two things.
    First, we live in reality and Our Universe is always there, it doesn’t need our Observation.
    Second. No, God does not play dice with the Universe. Neither had we told God what to do because there is no “GOD” It’s just Our Ignorance of Physics.

  11. 6:10 but what is colour? what "colour" is it before light hits it? why does it get absorbed?

  12. Yeah, I wish that people who I try to talk to and teach this kind of stuff to would care as much as these guys did. I'm usually just met with blank stares and yawns when I get all enthusiastic about explaining science stuff that personally excite and interest me.

  13. Isn't light both waves and particles? The particles being photons and the waves being the frequency in the EMS?

  14. It is circular because it's d image of d Sun

  15. Mukund Mohan says:

    The starting shows that the Americans are dumb

  16. WTFMannyxFTW says:

    Glad this video didn't include the the "effect of observation".
    The guy in the yellow shirt would've jumped in the fckn ocean if he heard that.

  17. necromancer says:

    Don't think those people are stupid, at least they wants to know/learn.

    Most people don't even care to know.

  18. So light is a wave then but how don you explain a proton tho

  19. Jonty Bryce says:

    It’s both… wave-particle duality #higherphysics

  20. Jonty Bryce says:

    That’s just what happens when you introduce Scots to science

  21. Hema Bhatt says:

    This means only Indians have an amazing high school syllabus covering diverse facts of nature. Hit like for wave optics, NCERT PART 2, Chapter 2

  22. Dude why do you look like Elon musk

  23. Julio Gomez says:

    they should also take into account that some of the particles may come into contact with the edges, or their gravitational pull of the slits which would change their trajectory. With two slits having particles pass through at the same time with changing trajectories they will definitely have the Possibility of interactions as if waves. I'm no genius so only take consideration with my words but with two slits being their only possible way through and the edge of both slits only having only so many possibilities of changing their directions that should as I imagine having only so many ways they could end on the other side or collide and change each others direction. which could be the reason we see patterns. my point is, it may not be the atoms fault but maybe the slits that cause what we see as waves. maybe the "wave like patterns" are only an illusion caused by how the atoms pass through the slits. just like they seem to know we are observing them when we use detectors. in reality the detectors just have an effect on them.

  24. Julio Gomez says:

    They need to test this experiment on humans. this experiment should
    include hundreds if not thousands of people. Doing it one person at a
    time, you would need a room with a starting point and an ending wall,
    the ending wall will have two doors at it unknown to the person(a blank
    wall with two hidden doors) just like the two slit experiment the
    atoms/photons do not know what will be where they will hit. Tell the
    person to walk to the wall at any point of their choosing. Once they hit
    the wall take note of their position relevant to the wall where they
    stop. If the person hits a point in the wall where one of the hidden
    doors are, open the door and tell them to continue the walk through the
    newly found door till they hit the next wall. When they hit the new
    position on the other side of the door to the wall take note. I'd love
    to see what an experiment like this on humans would reveal.

  25. Julio Gomez says:

    They need to test this experiment on humans. this experiment should
    include hundreds if not thousands of people. Doing it one person at a
    time, you would need a room with a starting point and an ending wall,
    the ending wall will have two doors at it unknown to the person(a blank
    wall with two hidden doors) just like the two slit experiment the
    atoms/photons do not know what will be where they will hit. Tell the
    person to walk to the wall at any point of their choosing. Once they hit
    the wall take note of their position relevant to the wall where they
    stop. If the person hits a point in the wall where one of the hidden
    doors are, open the door and tell them to continue the walk through the
    newly found door till they hit the next wall. When they hit the new
    position on the other side of the door to the wall take note. I'd love
    to see what an experiment like this on humans would reveal.

  26. John Johnson says:

    Like the Americans make-up s*** like light is our aura or f**** god

  27. petosk8 says:

    Hi, how much in milimeters is the the gap between the slits? How can i make it? And how far is the projection spot behind the slits?

  28. RYAN SALA says:

    DUDE! THIS IS THE BEST EXPLANATION VIDEO I HAVE EVER SEEN ON DBL SLIT YO.. YATTA! TY

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