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. What i don`t understand is when you shoot one electron at a time, how can it interfere with another one in order to create an interference pattern if there is no other electron with which to interfere. How can there be an interference pattern?

  2. Well good question, because nobody on this planet knows what light actually is. We could say it's a "quantum particle" – some sort of particle that shows properties of a wave and properties of a 'normal' particle. But that only pushes the question one further: "what is a quantum particle?". We don't know, but at least we can describe how it behaves.

  3. I wish this video existed when I was in high-school trying to understand waves during my physics class ¯_(ツ)_/¯

  4. Go ask any 17-18 y/o from India you'll get whole answers from diffraction to polarization to interference everything damn, I used to think that we people are dumb but I was wrong these people are dumb, what is light? We know about light since high school.

  5. ive seen this guy.. hes always at the beach with those green balls and he bobs them in and out of the water for hours every day and hums like a monk the whole time. sometimes hes there before i go to work and then i see him there after work as well

  6. I love how you don't judge people for their lack of basic SCIENCE knowledge..!! You stay absolutely respectful.😂😂

  7. So, if you did this experiment during an solar eclipse, I think the dots you mention would be crescents. Therefore, to answer your question at the end, are the dots caused by a reflection of the shape of the sun?

  8. when did you do this? the people look like they don't even know about the double slit experiment. but it was uploaded in 2013, so that makes no sense. was physics not taught at all back then?

  9. its so good to see people fascinated an curious about science. and yet its sad to see all the pseudoscience being propagated.

  10. thanks Derek… this helped me understand young's double slit experiment much better than what my teacher taught me!!

  11. Atheism is so senseless. When I look at the solar system, I see the earth at the right distance from the sun to receive the proper amounts of heat and light. This did not happen by chance.
    Isaac Newton

  12. I understand the particle aspect of photons, but how is it a wave? I thought waves can only be created in a medium, ie a slinky or a jump rope or water.

  13. #answer 7:12 so according to me that might be because of diffraction of light from the edges and converging at some point which we see circular .

  14. lol, the answer is right in front of his face and he can't grasp it. use a light that is
    the same shape as the slits and you will not see the pattern, use light that is shaped
    like a circle and you will. lol, science, super smart people, lmfao, yeah, no.

  15. I'm sorry, are you touching original manuscripts with your bare hands and talking all over them at a couple inches with no chinstrap on?

  16. I was wondering when we put two polarized glass on top of each other with 90 degree rotated, why we dont see any light ? We should be seeing many small dots like this

  17. There is no such thing as a ‘photon’. Light is a wave function of resonant subatomic frequencies in an electrical field. The double slit is merely a harmonic.

  18. Maybe it a polychromatic ray (the sunlight ) that's why it appeared as colorful blobs if we do with monochromatic light then it will form the pattern we all saw in our books

  19. I remember this experiment from physics in high school. But I believe we also learned that if you fire photons individually through a double slit, they will still create the interference pattern after firing a few thousand photons. Would be nice to learn how exactly that works. If I recall correctly, the photon is like a wave and somehow goes through both slits at once, but my memories are hazy.

  20. The earth is flat. Outerspace doesn't exist. We live in a simulation. The double-slit experiment is proof of the Creator, of God. Theoretical science does NOT have all the answers about why we are here.

  21. Thanks Sir for demonstrating the interference experiment of light in such a nice way….it actually helped me a lot to understand much better….about the wave nature of light

  22. Bruce B Petit

    1 second ago

    Can I translate the experiment like this, retaining essential qualities of the wave function??

    In the spirit of mathematicians "just do it".

    #1 Say: you have a field of many dimensions.: you mathematically manipulate the whole field to be represented in one dimension: you move a particle through the field: The particle will show up up intermittently in the single dimension: the single dimension is "packed" with directions the particle does not take: Field has X,Y,Z,I, C,M coordinates. one dimensional representation would be "packed" say XYZICMXYZICMXYZICM : For simplicity say the particle is only moved in the X direction : The particle would only show up in the x packets and skip the other packets: Is it easy to see a wave function with angular momentum developing out of this?

    # 2 Say: I have two fields with two dimensions each,. [FS] and [FT]. Each field has a "static" and an "active" direction at 90 degrees to each other. [FS] & [FT] align static axis with active axis ie at 90 degrees to each other: The fields are pretty local:

    # 3 Say: A particle is accelerated in a line towards a screen: a moving particle collapses the fields to one dimension creating a two dimensional plane(simplified) : The particle moves along the [FS] active axis in [FT] static time: The particle exists somewhere along the one dimensional [FS] active line depending on how the the field has been "packed": The particle while moving along the [FS] active axis is also moving along the [FT] "static" axis so no time occurs. The detector stops momentum and "collapses " the field back into its multi dimensions and the particle appears on the detector:

    # 4 Say: the double split causes the plane to "flip". The [FS] static/ [FT] active axis is now aligned between the gun and the detector : The particle does not (???) along the The [FS] static/ [FT] active axis but time exists: The [FS] "active" / [FT] static axis is aligned parallel to the detector. The detector will "collapse" the [FS] active / [FT] static axis to all its dimensions: Assuming the packing of dimensions follows a function although each actual direction is packaged according to a probability function the particle appears on the detector as per wave function, gap, chance of particle, gap , chance of particle etc.

  23. Its a little misleading. Your experiment and conclusion was that light was a wave end of story. But since Light is both a particle and a wave I feel you only told half the story.

  24. It would be great if you could explore this theme further by using also polarizing lenses. There seems to be a debate if polarizing lenses would work as a model for testing Quantum Mechanics. Cheers

  25. You cant look at light from 1-2 dimensions light may be a particle that resonates through space & time in a Helix, Spiral, or Vortex the assumption its a wave could be just its side profile? Its more of a 4 dimensional physical object at minimum? Each wavelength vibrates at its own resonance & or speed producing color? The assumptions need reviewing. Radio waves/helix or expanding diminishing spiral, light waves could actually be Helix miss identified that has a very slow decay rate? Everything moves in helix, spirals & or vortexs vibrating through space & time at there own resonant frequency? DNA strands Helix, planets following our sun through space & time at its very own resonance?, snail shell formations, sometimes life mimics the patterns? What if magnetic fields had more than just + & – they have a weak rotation to them? Our planet spins after all & magnets interact with each other in a spin before they combine. What if the double slit experiment was wrong because of the assumption light particles move in a fundamentally flawed wave form? Helix Ill say it now assumptions are the mother of all f**kups. On that note i hope anything ive said holds weight lol. Helix looks like a parralel constant (But dose light have infinite far reaching energy? We know gravitational fields can bend light Black holes) A spiral seems to fade to centre or outward ever expanding dependent on your end perspective (Radio waves seem to diminish rapidly?) Vortex reminiscent to storm cells (Or polar magnetic fields?) Are they all part of the same spectrum or am i confusing my parralel assumptions as my brain starts to melt? Who would have thought you need to go round the bend to find pertinent or the most

  26. U said if u create a disturbance using a ball in the water it forms a circular wavefront but it’s actually a spherical wavefront which is quiet different

  27. Young’s double slit experiment forms an interference pattern with both constructive interference and destructive interference

  28. They both have different wavelengths red has higher wavelength than blue light cause their energy levels r different Blue has higher energy level than red light it comes from the formula E=hC/λ where h=6.626*10^_34Js(Planck constant) and C=3*10^8m/s and λ is the wavelength of photons emitting from respective colours and E of course is the Total Energy of the photons hitting the surface which is TE= KE+PE

  29. What if you for example bring a very very very small camera and put it on the light after the double slit and turn it to the double slit and not to rhe pattern

  30. I just explained the double slit experiment, read the description.
    There is another experiment I need to do to further prove something else about the multiverse.

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