Young's Double Slit Experiment

[eightsides]

Loved your video!

[pijanecX]

there is an interference in single slit because the original experiment shoots only one photon or electron at the time, not a lots of them at a same time...laser beam shoots a lots of them stimuntaleously...therefore there is interfecence at single slit...physics wins again!! :)

[starbizzleable]

Schrodinger's Cat on the laptop

[platipusoj]

hey the "some reason" is that even when there is 1 pencil lead you can look at both sides as the slits and the lead as the gap between them. Have a nice time playing with physics

[molenini]

Actually it was triple and tetra slit experiment.

[pijanecX]

@molenini you are also right there, beam goes also around those sticks... :)

[RTRVII]

ur name is jack maxwell? are you related to james clerk ??

[star58ify]

this is a good experement as you did with photons not electrons and atoms but still cool

[OldDirtyRatbastard]

This is just diffraction. And that laser looks like it emits much more than a few photons at a time.

[dirac17]

OMG you discovered that you can get interference from a single slit. You should get a Nobel prize for this!

[florinandrei]

With a single slit (2 leads) it's not interference, it's diffraction on a small aperture. Check out the wikipedia page on diffraction for an explanation.

[Microglia1]

highly unscientific

[MrPlaiedes]

@Microglia1 Bet you wouldnt say that if Michio Kaku did it. Easy to be a critic. Plus he did exactly as his video described. So really your critique is the only thing qualifying as lacking any real scientific credibility. Regards.

[flobber238]

@MrPlaiedes Thank you Mr Plaiedes, if that is your real name..

[krishields]

@MrPlaiedes

Exactly... The original Young's experiment used a prism to create a coherent source and then used a thin piece of cardboard to split it. Highly "unscientific" right? lol... A piece of cardboard is responsible for ALL of QM...

[mathfreak123]

Single slit causes an interference pattern through Huygens' principle, which states that every point along a wavefront acts as a source for another wave.

[superfahd]

im a bit rusty on physics now but i think the interference caused by a single slit is because of diffraction. light diffracting over the edges of the 2 pencil leads, (not sure inner edge or outer) interferes and causes those effects

[zDSpider]

I sure some of the 99 commenters have point out the flaw(s) but I'd just like add one thing: the double slit experiment shoots single particles of light (fotons). What you have there is probably the equivalent of a football stadium filled with canons.

Anyway, mad cat you have there.

[ramirocmr]

Hi, at the end of the video you said you didn't know why with one simple slit you can still see the interference pattern, well that is called diffraccion and it's caused when you split a beam with an small object. Just for you to know I still believe this experiment is quite simple and quite awsome!!!

[Hannsfeld]

Yeah, and you were looking right at it (even filmed it on video) and it didn't collapse the wave function. I have never seen an indication of what the "measurement device" is supposed to be, and am still skeptical that interaction from it is causing the collapse.

[flobber238]

@Hannsfeld Hi, a measurement device isn't accurate. It's when the light interacts with the molecules on the wall. They act as a measurement device. Then the wave fn is collapsed.

[Hannsfeld]

@flobber238

I am not following that comment about wall molecules. The whole "spooky quantum" business is supposed to be advertised as the wave collapsing from "being observed". I have always found this dubious. I feel like the act of measurement of something on this scale necessarily has something to do with the measurement device interacting on a level more physical than mere observation.

[Abs9106]

@flobber238 So wait. The first exp with the one slit wasn't showing a wave pattern? And then through two slits it showed an interference pattern of a wave?

[ashtair]

@Hannsfeld Looking right at it does not mean observation, because you still can't tell which photon went through which slit. If you can tell it, that would make the wave function collapse.

[Hannsfeld]

@ashtair

You are making my point for me. You are stating that it is a specific "measurement" action rather than "observation" that collapses it. If it is required by the "measurement device" to perform an action that interacts with the particles to tell which slit it came from, there is your action that collapses the wave and the "spookiness" goes away. Example: If a scanning electron microscope must bounce an electron off the particle to measure where it "was", it just deflected it.

[xenoepist]

@Hannsfeld When they say they are "looking at it" they do not mean really looking. If you were to look at a photon, it had to go to your retina. What they mean is that they wanted to know what slit did the photon(or electron) go through, but in order to see it they had to disrput it in some way. In this case, you are not looking at the photons as they go through the slits, you are looking at the photons as they go into your eyes after they reflect frm the wall. I hope I helped

[jrswordfish1]

@Hannsfeld During looking/filming the eye/cam is interacting with the reflected photons which are part of the fringes and this will not collapse the wave function prior to the fringe formation. The act of observation of photons as they pass through the slit involves active interaction with the photons and hence collapses the wave function resulting in 2 bands instead of multiple fringes. I think thats the difference.

[jrswordfish1]

Although how the interaction collapses the wave function should be an interesting read. If someone can shed some light on it here.

[flobber238]

@jrswordfish1 yeah I think that's like the final frontier of physics, how functions collapse, and what it even means.

[nuclearheadache]

@Hannsfeld: You're being dismissive, and yet you have no idea what you're talking about. It's not the mere fact of observing or even filming the experiment itself that collapses the wave function. It's when they specifically tried to detect which slit the particle went through that it alters the experiment. If just observing the experiment collapsed the waved, how would they have ever known this in the first place? Don't be a dunce.

[Hannsfeld]

@nuclearheadache

A) This was a question, not a dissertation from me. But I am so glad you are here to declare how I don't know everything and do some name calling. It's so refreshing on YouTube because we don't get enough of it.

B) What has your comment done to provide any clarification? They do imply that observing collapses the wave function, that was the point of my original comment.

C) Don't be a douche.

[flobber238]

@Hannsfeld @nuclearheadache Play nice :)

[nuclearheadache]

When they say "observation", they don't mean observation of any kind. They're not talking about just seeing the experiment. They're talking about trying to take a measurement of which slit the particle is going through. If the mere act of seeing the experiment altered it, how would anyone ever know? Nothing in this video shows any attempt at measurement, and making the video wasn't a measurement, so "looking right at it" and the fact that he "even filmed it on video" doesn't prove anything.

[1simonmatthews]

@nuclearheadache Hi, regarding the double slit experiment and how the wave function is collapsed by taking a measurement of which slit the particle went through, do you know how they actually take this measurement? I notice you said that it has nothing to do with observation as we think of it, so I was wondering if you could explain how this measurement was taken. I've looked at a few videos and they only show the experiment without the measurement. Just thought you might know. Cheers.

[matthias2986]

@nuclearheadache right, when you observe what actually is happening, thats when shit gets strange, anyhow, im thinking it has something to do with consciousness.

[Dompiestompie]

the only thing i use a laser now is to play whit my cat :p he is going crazy when i use it , let him lose some weight xD

[burakasno1]

think the song is from Neopets key quest music btw

[tecnocubeguy]

Now you just have to use the cat at the end for Schrödinger's cat experiment, and you're all set!

[Golie9285]

The light stretching and creating interference with one slit is actually a form of heisenberg's uncertainty principle. Look it up there is a good video demonstration of this principle by Walter Lewin, a profesor of Physics at MIT.

[Wittgensteinism]

Awesome!

[Ravenpulse]

i think the single slit causes interference because the leads are slightly reflective and are not creating a perfectly sharp edge

[zjeraar]

I'd like to repeat brownie003's question: why does also the single slit cause interference?

[Hannsfeld]

@zjeraar

I think that because there is not a barrier to either side of the pencil leads, there are actually three "slits" due to their being a path through the slits, plus two paths around the slits. This would cause an interference pattern. This assumes a beam of coherent light wide enough to do this.



[sharhalakis]

What you are seeing is light diffraction which is also caused with just one list (that's why you see it). Interference happens inside each band of light that you see. However, you'll have to (at least) prevent light from going around the two slits (around the pencil leads) to test it, but I'm not sure if it will be visible to the naked eye.

However, if you use a camera and point the laser to the camera instead of the wall, it may be visible.

[GimilitheGreat]

what was the music?

[42DuckyDuckers]

There's another way to describe this phenomenon. It's called the QED theorem. The QED theorem says that light goes in every possible direction, and it is just by probability that light usually goes in a straight line. It's weird, but the QED theorem describes the behavior of light *exactly* with its equations.

[Wittgensteinism]

@42DuckyDuckers That is strange (about QED and light). So does QED describe a light "cone" still as the most probable?

[TheEvilCommenter]

Why does it seem that everyone who owns a webcam and computer also owns a cat?

[91jgphonecall]

that was really cool, how'd you think of that?

[flobber238]

@91jgphonecall I was just playing around wit my new laser :)

[Tartersauce101]

that...was honestly a complete waste of a minute 10.

i mean is this really it? you shine a fucking lazer through some pencile lead...and conclude that that causes interference with the lazer?? only reason i bother to comment is that i am shocked this video has more likes then not...i mean really?

[starstarstar42]

@Tartersauce101

Umm, I think you don't understand what this all means. Read on wikipedia about the "Double Slit" experiment to realize why it is downright spooky. To put it in really simple language,the light beam from the laser is reading your mind. No, I'm not kidding. The photons can tell whether you are looking at them or not and they do different things depending on whether they are being watched. Read the Wikipedia article and see.

[Tartersauce101]

@starstarstar42

not quite sure how to respond to that. i know about the experiment. this was not it. nor did it represent it in any way. this didn't represent anything at all. if he were to set up the laser, and the lead (be a little professional and have it secured down so the laser and lead are not moving around in his hand as it was in the video) and THEN set it up remotely and find a different result when not being observed...you would have something.

[starstarstar42]

@Tartersauce101 Granted, the poster showed a very simplistic way to demonstrate the phenomena, but how can you say it did it NOT represent the experiment? Perhaps the poster can weigh in on this...

[Tartersauce101]

@starstarstar42

yah, i guess i was a little harsh...it does represent the experiment just... poorly. i suppose the fault might be mine of having too high of expectations when i clicked the video :/

[flobber238]

@Tartersauce101 yeah I wasn't exactly trying to publish an article in a journal with this... the point was that you can see interference by doing stuff with things lying around at home :) and I wasn't thinking I had stumbled upon irrefutable proof of quantum physics either :D

[brownie003]

why does the single slit cause interference??

[aenigmate]

So nice experiment...

[incessear]

tats coool... jus wt i wntd 2 c...

[YouSpamTard]

it seems nobody has mention the obvious variable of ricashae

[vampired305]

Well.. based on the actual experiment, if the protons and neutrons etc are being observed/measured/monitored, they should actually behave as if they were physical matter. Weird it doesn't occur here.

[hoticewater]

@vampired305 depends on your definition of physical matter. Schrodinger's cat. Best explanation to date? ..Each individual photon (physical partical/matter) is actually going through both slits at the same time without splitting. It is, for all means and purposes, in two places at once. Atm tho, it's impossible to prove this is what's happening. Interference has been shown with photons, protons, electrons, nuetrons... even molecular compounds.

[vampired305]

@hoticewater Thanks for the explanation :)

[HungryGuyStories]

The light is simply being bent at the edges of eaxch slit, causing it to scatter. No big mystery there.

[starstarstar42]

Won't lie, read the title and honestly thought I was going to see some teenage bi-curious girl on girl pron.

[flobber238]

@starstarstar42 sorry to disappoint you.

[haneyenah]

@starstarstar42 /sigh...



[RonBurgundy161]

@starstarstar42 Lol!!

[littlebigman52]

@starstarstar42 I'm actually surprised this is the first time I've ever seen someone make a joke based on the obvious double entendre.

[asim18]

I have the same laser!

[flobber238]

@asim18 Awesomme!

[HomerJ666]

you can see an interference patter at the first try too (1 slit)... is this because the laser is going through the slit AND on the other sides of the pencil leads too?

[flobber238]

@HomerJ666 hehe nice idea. The truth is that it's photons interfering from opposite sides within the one slit.

[HomerJ666]

@flobber238 thanks, that would mean if you would shoot photons or electrons one at a time (without observing them, i.e. through a vacuum) there wouldnt be an interference pattern with just one slit?

Btw thanks, i didnt knew i could do it at home too HA! :D

[flobber238]

@HomerJ666 Haha not so lucky- a single particle interferes with itself !?! Cos it literally is a wave before it hits something. When it hits something, then it remembers that it's only one particle :D but til then it interferes like a water wave spreading through the gap.

[HomerJ666]

@flobber238 ok so if one single electron/photon/whatever-is-sm­all-enough goes through the slit (ONE slit) and doesn't hit anything, it would "bend" around it like a wave, not creating an interference pattern, but still spreading horizontally?

[flobber238]

@HomerJ666 Erm well it Would make an interference pattern. Google images "single slit interference" if you wanna see the idea. And you got the bending round bit right though.

[HomerJ666]

@flobber238 yes, sure, but it does not state shooting electrons or photons one at a time, one after another.... it's clear to me they create an interference pattern if they interfere with each other, but as far as i know they cannot interfere with themselves, right? :p

[flobber238]

@HomerJ666 Ah well no. You see when it's in wave mode, it's not like a water wave made up of particles. It's actually called something like a probability wave. When there are loads of particles making an interference pattern, it's the result of each individual particle interfering with itself. They never interfere with each other :) 

[HomerJ666]

@flobber238 yes i got that :) still i cant see why a single slit should have more than one density point, just thinking of a wave going through one slit.... i'll just believe it then ;)

[YamiPoyo]

@HomerJ666 They can, They leave the start as 1 electron hit the slit as 2 and bounce off each other/themself on the other side.

[HomerJ666]

@YamiPoyo you still try "imagining" it. in fact, they dont act as 2, they act in their wave function. the wave function collapses by interfering with it, such as measuring the position or the "state"..

[HomerJ666]

fucking awesome!

[nickharvey7]

Photons only seem to exist when the light waves comes in contact with an object. Then the wave function collapses forming a discrete or quantized form of energy in the shape of a photon. If this is a universal and continuous process could it be forming the passage of time? Because each new photon will have a unique position in space and time that the light waves never had before they made contact with an object.

[flobber238]

@nickharvey7 Yeah I like it. When I get an MSci I'll check it out for you :D -just give me 4 years!

[akrivera]

@nickharvey7 no

[tehlegend88]

My condolences for your cat.

[TakesTwoToTango]

No need friend. Yes it's dead, but it's alive too so it's ok :)

[bobbymcgeorge030566]

Nice music, what is it?

[flobber238]

@bobbymcgeorge030566 I think it's by Andrew Baron (in credits :D) and I got it from the Rocketboom website. Don't know what it's called but it pops up on TV and videos all over the place.

[bigmurph762]

...so here is the problem...when you observe the experiment with a comera, eye, whatever, its not going to behave like a wave. This video is useless.

[flobber238]

The laser light is only observed on the wall, before which point it would have behaved as a wave. Any photon that did hit an air particle on its way would have stopped being wave-like, but most photons did not.

[DocHackenbush]

@flobber238 Great Video! I thought about this problem a while ago. Isn't the use of the term "observer" misleading and gets sometimes abused (e.g. in Bleep)? When I look at something with my eyes I'm not changing the state of the photon. The photon has to interact with something that also can be interpreted as observing. But just looking or filming isn't interacting with the particle. It's just processing its light-echo on my retina. Or am I wrong? Strange that no docu is clear on that point.

[HomerJ666]

@DocHackenbush i'm not sure, but i guess you cannot observe a photon with your eye, unless it hits your retina. "observing" things with your eye means shooting photons on some object which reflect and go on your retina. The photons you observe with your eye in this experiment reflect on the wall, therefore you observe the wall. photons hitting air particles or whatever BEFORE they hit the wall, will not create an interference pattern imo. can someone tell me if i'm right?

[brucealmightyakshay]

single does cause of diffraction of light waves....

[Cheuvin]

as someone pointed out, having one pencil lead is not like having one slit, it is like having two massive slits that are so large that you cant see their other ends'. What is important is that the space on the left is seperated from the space on the right by an occluder. Light bending around the edges of this occluder causes interference patterns.

In order to repeat the double slit experiment, you actually need a slit.

[Jurojin]

@Cheuvin Then again, he was using two and then three pieces of pencil lead.

[krishields]

@Cheuvin

These are diffraction patterns. But, if it is aligned just right, then, no, you don't. You don't even need any slits to produce interference patterns. A linear beam ( laser level ) through a desktop magnifying lens does just fine. In fact, it is more useful because you can see by rotating and moving the lens around how the alignment is critical and watch how the interference pattern builds as the diffraction patterns cross.

[capetorial]

...reflection?  Try another material, just to be sure. Cut slits in paper?

[insectism]

hey, can you try to make the laser line vissible (with powder?) so u can get 2 lines in the background??

[OlehChaplia]

Cool!

[tlast2012dude]

this is fake, show the laser and you holding the sticks and all in the same plane and i will belive this

[netsoj]

Not fake... Far from it... Besides it's not hard for you to get 3 pencil leads and a laser and try it yourself...

[tlast2012dude]

i did and i see 2 points only

[netsoj]

You are doing it wrong. This does in fact exist. That would mean that there has been a conspiracy for the past 100 years....

[moegreen2]

it was not really a singel slit, was more like two very big slits

[cooldude99901]

single slit causes due to diffraction...

[nickharvey7]

Good video I like the cat

Good Video!

But could it be that Time has symmetry and geometry? Newton believed Time was a thing in itself and connected to motion and Einstein believed there was something missing from quantum mechanics. In my video The Paradox of Schrodingers Cat an artist view it is Time that is the Hidden Variable.

[AndrewCedricThe2nd]

What if we alter the width?? What would happen to the separation and the intensity of both the dark and the light?

[upcycle]

try it with sticks made of material with different light absorbant properties.. see if any difference in intensity of pattern effect.. be sure to match the shape of the sticks as to give better comparison.. I suspect some of the interferance is from the laser light bouninc off the round glossy surface of the graphite sticks, one or two times before continuing to the wall.. kind of like shining a laser off mirrors.

[Chortleclips]

im guessing the cats name is schrodinger...

[flobber238]

lol

[MacManLtd]

and the look on its face says, it doesn't want you to try any experiments with him :p

[BYMYSYD]

and this only works with coherent light, bicause if the wave's were not in sync, then there would be no or very little cancellation.

[flobber238]

Thanks duuude that's cool.

[BYMYSYD]

and the single slit makes an interference pattern because, the light also bends about the other side of the graphite stick (no just through the middle.)

[BYMYSYD]

Thanks for the post!~!!!! Nothing's better than doing the experement yourself. I tried this out myself and i confirm it works.

[cherissalim]

wow this is so cool. thanks :)

[zuzzo661]

PERFECT... I was just tryng to figure out how see the interference pattern of light. I was thinking about calculate the distance between the slits to make the pattern appear by considering the lenght of the lightwaves, but after a little search on youtube, I found this wonderful experiment... Now you just have to demonstrate that measuring in a singli slit, the interference pattern disappear.. :) Thank you for this

[OneCoolDude08]

Thanks for posting this. Everyone else posted animations. I never could figure out how to do this experient myself. Much appreciated!

[ronaldpettersen]

Wave pattern with 2 and 3 pencils leads. The laser sends too many particles out at once. And even if you could find a laser to shoot one particle at a time you wouldn't be able to see it, it'd be much too small.

[FadieZ]

The single slit produces a pattern because the laser is not a single point source, but many point sources next to each other. they still interfere with each other whether there is one slit or one thousand. You can even put a single lead in front of the laser and notice some interference with the right size and distance.

[ExternalDingus]

Is it possible that gravity is causing the wave pattern? I am thinking that the photons are so small and lighweightt that even the small amount of gravity created by the pencil lead is enough to warp the path.

[check86]

If that were true, then you could keep the gap the same and measure how far the light spreads using pencil leads or wires of different densities. Of course, it doesn't matter if you use pencil lead or paper or tin foil or uranium to make your gaps, the light spreads the same, which means no, gravity is not responsible for the wave pattern.

[pmarceau]

nice to see a practical demonstration of this experiment.

A version I can actually verify first hand.

[y0u73b3r9]

i dont rly c it :/

doesnt the normal experiment happen becus the light travels in waves moving outward

but a laser is just waves moving in a straight line,

[flobber238]

The laser wave just goes straight, yeah. But when it goes through the little gap, it diffracts like a ripple. The two ripples interfere then.