The Original Double Slit Experiment

The Original Double Slit Experiment

What is light? What is light? Light is… light is… what is light? That’s a good question, isn’t it? What is light? Isn’t it an element? Light is brightness, I guess. – We have auras?
– We all have auras. – Which are light?
– Yes, they are. It lights up the room, it makes it… not dark. – What’s the difference between blue light and red light?
– The color. It goes in your eyes and then you see stuff. The range from white to red to orange to green, it’s like the chakras of your body. – Can you see my aura?
– No, not particularly right now. – Is it too bright out?
– It’s very sunny out here today. – Does that make it harder to see someone’s aura?
– Not necessarily. If I was to explain it to a blind person, I’d… It would be… It would be the difference… You see nothing whatsoever as a blind person, whereas I see things in front of me. To be fair, the question of what light is, is not an easy one. For centuries, the greatest minds in science debated this issue. In the late 1600s, Newton proposed that light was a stream of particles or corpuscles. He proposed this in his treatise, Opticks. But at the same time, a dutch physicist named Huygens proposed that light was a wave. And this debate raged on until it was settled by the experiment I’ve recreated today, Thomas Young’s double slit experiment. To make sure I got the experiment right, I went to the original source. With a help of Brady Haran, I managed to get into the vault, underneath the Royal Society in London. We’re in! There, I found Thomas Young’s handwritten notes from 1803. I brought into the sunbeam a slip of card, about one-thirtieth of an inch in breadth, and observed its shadow, either on the wall or on other cards held at different distances. Besides the fringes of color on each side of the shadow, the shadow itself was divided by similar parallel fringes, of smaller dimensions. Wow. This is an experiment so simple that you could make it at home, and yet so fiddly that I’ve never seen it before done with sunlight. – I was thinking about doing it in a box, like a fridge box.
– And you could take it out on the street. Taking it out on the street. Could I possibly interview you guys for about a minute? We’re doing a science experiment. What I have here is an empty box, and this is a little eye piece where we can look in, and this is a hole. And I’m gonna place this slide above that hole, and if you look closely, you’ll see that there is two openings, very narrow openings side-by-side. It’s a double slit. Now, before we have a look, we need to tilt it towards the sun a little bit, so…
we want the sun to hit this double slit directly. – What are we gonna see on the bottom of the box?
-The obvious thing you think you’re gonna see is you’re gonna see two lines. Two lines on the bottom of the box. Two broad-bands. – Two little lines.
– Yeah. I think it will be one… one line, sort of two. I can expect to see the whole box lit up. – Probably a kaleidoscope, of some sort.
– A bunch of colors. Probably, yeah. Rainbow? Different colors? There, have a look. You expected to see kind of one line – is that what you see? No! I see dots. How many? It’s one circle. Oh, there’s one.. there’s one in the middle, the strongest, two either side. The two on the outside are multicolored, and the one in the middle… is just white. It looks kind of a rainbow. The rainbow of color as well. Quite a few colors and lots of little dots. And there are more dots appearing. I think I can even see more dots spreading along. Yeah, that’s amazing. Yeah, I can see tons of dots now. Not tons, but I can see dots spreading across that way. – On either side?
– Yeah, definitely. – Isn’t that amazing?
– Yeah, that’s incredible. – And that’s just nothing else apart from…
– Two slits. That’s incredible. But all we’re doing is we’re putting light through two very narrow slits side-by-side, so how does this make any sense? There’s some kind of principle involved in it that the average person’s not familiar with. That’s the only explanation. I’m really confused by it, but I’d like to find out why. People were debating: Is light a wave or is it made of particles? So what causes that? Well, if light were behaving as particles, you would expecting to go through each slit and just produce a bright spot underneath, so we would see two bright spots under the bottom of the box. But, if light is behaving as waves, then the wave from one slit can interact with the waves from the other slit. I’ve got a demonstration here on a little pond, where we can see this with water waves. I have two sources of ripples, which are basically like the two slits, when I create ripples with a single source, they travel out with circular wave front, nothing particularly surprising there. But, if I add a second source of ripples, then we start getting an interesting pattern. This pattern is created by the ripples from the two sources interacting with each other. Where they meet up peaks with peeks and troughs with troughs, the amplitude of the wave is increased, that’s what we call constructive interference. But if the peak from one wave meets up with the trough from the other, then we get destructive interference and there’s basically no wave there. And this is exactly what was happening with the light. When the light from one slit met up peaks with peaks and troughs with troughs, they constructively interfered and produced a bright spot. But, if the trough from the wave from one slit met up with the peak of the wave from the other slit, they would destructively interfere, and you wouldn’t see any light there. It’s light canceling itself out. – This is basically the same is like having two drops of waterfall in a swimming pool,
– That’s right, – exactly the same pattern.
– and then they’re going overlap As this ripple overlaps with those ripples, down the bottom, you get a series of… you get like a bright spot… and then a dark spot, then a bright spot, then a dark spot, then a bright spot. Now there is a slight complication, which is that sunlight is composed of many different colors, and they have different wave lengths. So, obviously, they’re gonna meet up at slightly different points, and that’s what caused the rainbowing effects as we go further from the central maximum. You saw the ones to the right were slightly colored, that’s because the reds are gonna meet up at different places than the blues. And that’s all that makes color differences, is different wavelengths? – Exactly.
– That’s amazing. So the difference between— So that red bin over there on the green pot it’s just… I’m seeing that – It’s a different wavelength.
– It’s just different wavelength. – And that’s how we’re bringing these beautiful colors all around us.
– Exactly. That’s amazing, I’m amazed! Thanks, man! Thank you! I have been enlightened, literally. Now, you may have noticed in that experiment that the light on the bottom of the box was not in the shape of slits, rather they were more kinda round blobs, and I want to know why that is. Can you write an answer for me in the comment section? And I’ll give you a hint: one of the videos I’ve linked kind of is suggestive of the answer. So convincing were the results of Young’s double slit experiment that the scientific community concluded that light must be a wave, there is no way it could be a particle.

100 thoughts on “The Original Double Slit Experiment

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. Theory of Quantum Illusion


    The Alternative Theory

    By:- Sagar A. Kathiriya

    E-mail – [email protected]

    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.

  6. 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

  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. Re 1:45 1/30th of an inch correctly approximates the true wavelengths of light. So Thomas Young may not have been lying…

  9. I am 67 and am sure I learned this in one of my public education grade levels. As a teenager, I used to buy all sorts of light experiments from a mail order company called Edmund Scientific. But in the 1960's our limited funds weren't diverted to X-Boxes and the like either so mail order experimental kits were among the few options. Are the schools not teaching any basic science anymore?

  10. The reason most people dislike physics & chemistry is because our school systems dont leave students in awe & amazement. I was very fortunate to have an incredible physics teacher during my early days of school & she made me see the "magic" of science. If we improved our education system we would have a plethora of scientists & imagine the possibilities if we have more great minds in science 🙂

  11. the craziest thing is the combination of red-green-blue light gives white light BUT red-green-blue paint gives black paint. which suggests light and paint are not the same but indeed opposites. an object which we see as green absorbs all the colors which are not green (meaning it's actual color is everything but green) and in return reflect green color for us to see. which means that the real world is more close to what we see on a photo film negative (if anyone is old enough to have seen one).

  12. But does the camera or measurement instrument cause it to act as a particle as the other double slits experiments?

  13. I am not so glad to see and hear, that people twice and trice my age don't know almost any scientific definition of light, or don't still remember anything about light-wave lenght or light particle name…
    I guess, they had no time because of their work, that may be not related to science, so, I don't blame them.

  14. Uhm a bunch of particles with low friction act as waves whats the big deal here? 😀 water is made up of particles yet many of them bunched up together act as a wave. so a bunch of photons together will act as a wave..

  15. Life is a longitudinal pulse perturbation transmission it's in the electromagnetic spectrum there are no particles involved in the electromagnetic spectrum zero none get used to it

  16. Is there a way we can make an on/off system of observation? Like, the atoms behaving like an wave, make the system of observation automaticaly turns on, if they behave lika a particule, immediatelly turns off? the atoms and the reality would get crazy

  17. I like how the guy in the yellow shirt is so incredibly amazed by such a trivial physical fact, that I would have seen as common knowledge.
    If you then told him about the quantum eraser regarding the double slit experiment he would have had a crying mental break down.

  18. Veritasium
    My idea is as follows :
    The light at bottom of the box was not in shape of slits, but instead circular in shape because of diffraction through the aperture of slit, the edges of slit bend light waves in a way that they deviate from their actual path and form blurry circles;
    It is according to Rayleigh's Criteria that when two maxima almost coincide we cannot differentiate between its images and it is not "resolved".Due to this many rays of light coincide at slit points and thus form one image that is blurry as explained. It is due to the resolution power of our eye that we are able to see so many points that are lit up.
    This is purely what i understand from my research, i dont have a PhD.*

  19. Light is everything and anything that we can see And light is the only thing that makes us able to see COLORS.

    The color Dark or darkness is what we can’t see. Pretty much pitch black you don’t know where the hell you are going.

    It’s like the void. I believe once your in a complete calm state of mind in any pitch black area. You’ll hallucinate crazy stuff. So be careful

    But yes that’s my answer.

  20. Thumbs down for not demonstrating the 'which-path' information that 'collapses the waves'. Also, we still don't know what light is with your descriptions.

  21. Light is particle and wave but we haven’t been able to observed both at same time.
    For the question why we have seen round blobs is we are seeing it through certain angle but not parallel to the slits
    In that case we are able to observe interference of two peak waves as a round blobs i guess.
    Can any one comment the correct one if this is not.

  22. I was going here to find out why the light creates a new, spreading wave after the slit. But you never even mentioned that

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