Delayed Choice Quantum Eraser - Quantum Physics

Quantum physics at its most profound: Delayed Choice Quantum Eraser experiment and its implications.

[@EugeneKhutoryansky]

To see subtitles in other languages: Click on the gear symbol under the video, then click on "subtitles." Then select the language (You may need to scroll up and down to see all the languages available). --To change subtitle appearance: Scroll to the top of the language selection window and click "options." In the options window you can, for example, choose a different font color and background color, and set the "background opacity" to 100% to help make the subtitles more readable. --To turn the subtitles "on" or "off" altogether: Click the "CC" button under the video. --If you believe that the translation in the subtitles can be improved, please send me an email.

[@WackyJackyTracky]

Why do you first say it is about the "which-way" information beeing somewhere in the universe that let the interference pattern collapse, but later call it observation and "if we watch".

[@JoeOvercoat]

Not a subtitle suggestion, rather just the thought that the script might want to say “equally possible” at 20:47

[@sensen4582]

Terima kasih.

[@tom_something]

It's kind of amazing that we're even able to conduct an experiment like this. We're "stuck" inside of a universe governed by these rules. Being able to peer into these rules while also being governed by them is almost like an eye looking at itself without a mirror. It's possible, if not likely, that there could be something even deeper, more "source code-ish", than these wave functions, that we'll never be able to observe. When expressed mathematically, there is very little difference between space and time. Yet to our experiences, they are easily distinguishable. This could be because they actually _are_ very different, or it could be that the universe we see is a limited projection of something deeper that we can only measure through conjecture. A classical analogy might be comparing the scientific discoveries and technological developments of two equally-intelligent beings: one that lives on land, and another that lives underwater. It is quite trivial for the land-dweller to conduct chemical experiments that require water, as well as experiments that must be done in the absence or near absence of water. But the aquatic species has a much greater challenge. Even very simple experiments, like mixing baking soda and vinegar, become much more difficult when you're under water. How do you get these chemicals in isolation in the first place, before mixing them? If a chemical reaction requires a flame, how much work is involved in making that happen in the underwater environment? Further, how much longer would it take the aquatic species to even observe fire in the first place, let along master it? Consider also experiments in electromagnetism. You would have to produce a non-conductive environment before you can even get to work putting conductors in it. In this real-world, classical analogy, there are solutions, because it is possible to leave the water and even bring air into the laboratory. But when it comes to quantum mechanics, our observable universe itself might be the water. Even in a perfect vacuum, even with materials at absolute zero, our experiments might be tainted by the nature of our universe.

[@jonbigeffortthegoodness7437]

(Kind) Wisdom very intelligent prose (prose is a talented writing) wisely stated

[@ramifakhry4049]

I like the fact that you pose for 5 seconds between the sentences. It gives me time to think about what you just said. Keep up the good work.

[@EugeneKhutoryansky]

Thanks.

[@the_sophile]

Actually that is the only thing I don't like about this channel. There is a pause button in KZbin. It is more convenient to use it compared to skipping it and missing some portions

[@harshavardhan9399]

@@the_sophile there is playback speed button in youtube, which allows you to change the running speed of a video

[@truthisthenewhatespeech9572]

True, I love that!

[@lozD83]

It's too slow for the average person, I'd say. Certainly not done to lengthen the video, I'm sure

[@MouseGoat]

It's the same in school. when the teacher isn't looking the student's actions become alle random and unpredictable, but if the teacher decided to look, the student's will be hard at work. ^^

[@arthurvin2937]

Except when teacher decides to set up a hidden camera and he actually will be able to see all the unrelated actions without them knowing about observance. Quantum world is far more complicated. But have you ever noticed or felt weird sense of being watched by somebody else? In fact this phenomena is also from quantum world and some people even have this 6th sense developed so good so that they can instantly tell that somebody is watching spying on them, and it is quite easy to learn by anyone and experience quantum world in reality.

[@ratbullkan]

Yeah that being watched feeling phenomenon would be quite cool if it wasn't faulty.

[@sulmaenya]

Made my day, after 2years

[@oomphffoomphff4604]

Arthur Vin soooooooooo true ..... I was a second grade teacher being evaluated on video and a student was dancing behind my back and I never knew until I saw playback video....

[@kumardigvijaymishra5945]

We are made up of quantas of unpredictability from quantum world. This gives us 6th sense, and it will always be unpredictable. Act of observation does affect physical measurement. In classical mechanics, observation does not affect to the extent it does in quantum world because quantum world is so tiny.

[@TheACG22]

Shrodinger's cat looks happy that she's not the object of this experiment.

[@TheLordSod]

+Austin Geary she also *is* the object of this experiiments.

[@conniejurgs9427]

Maybe you should train the cat to respond to which detector the particle went thru. Then if the experiment only responds to a human measurement, the cat could have the real answer to the question posed by this video. Would the results then change if the cat could signal the information to a human? Someone else probably thought of this before.

[@UkrainoTV]

@@conniejurgs9427 Castrated cat WILL NEVER cooperate with human being, therefore it won't respond to your answer. LOL.

[@conniejurgs9427]

Well then, that would mean that the interference pattern would remain in place according to quantum theory. We had a cat like that once. It was also declawed on the front. Poor kitty!

[@ishworshrestha3559]

Hmm

[@davidchung1697]

Of all videos in the Internet, this video gives the best explanation of the DCQE experiment. Most accurate, as well as comprehensible. Not easy to explain something complex in a field that one has been working on for perhaps decades, to layperson. Incredible.

[@EugeneKhutoryansky]

Thanks for the compliment about my explanation.

[@ExternusArmy]

This is hands down one of the most amazing pieces of information available on the Internet. What is nearly an incomprehensible topic explained so clearly that boggles the mind with its ramifications. You take your time with us so each sentence is really digested by the viewer. Great work Eugene

[@EugeneKhutoryansky]

Thanks for the compliments.

[@mireazma]

@@EugeneKhutoryansky The way you construct the ideas when you explain the notions tells about the way you structure them for yourself and this is something to thank for as well.

[@EsdrasOlivaresPcmasterrace]

Except it's incorrect... Retrocausality is not possible we've known that for a while so not really amazing, there's plenty of crazy theories. Time doesn't even exist it's just something that exists in our minds, a tool we created to keep track of things, just like political laws don't really exist, I hope we can move forward beyond Einstein and his spacetime it's time to grow up already and quit playing around and solve the cosmology crisis and quit eating time with "beautiful" theories like string

[@EugeneKhutoryansky]

In case, you have not already seen them, I also uploaded several other videos recently. As always, for each video that you like, you can help more people find it in their KZbin search engine by clicking the like button, and writing a comment. Lots more videos are coming very soon. Thanks.

[@JamesSmith-ek1or]

Huge fan of your videos Eugene. I have shown them to my professor and he was impressed, particularly with the ones pertaining to the visualization of mathematics. The work you do truly impacts my life and I am very grateful. Never stop spreading knowledge, it makes the world a better place.

[@dsinghr]

Logan Retamoza Eugene has a very special way of explaining things. Even this video is mind-blowing.

[@ZoeTheCat]

Eugene Khutoryansky This answered a longstanding question that I've had. I always wondered if the shear act of measuring was collapsing the wave-function. This proves that it is NOT the measurement itself, but merely the fact that we KNOW information - which leads us all down the path of madness ;-) QM is truly absurd.

[@alexandrugheorghe5610]

Eugene Khutoryansky Brilliant! Brilliant! Brilliant! Bravo! I loved it, this answered some questions raised from previous video on QM as well as tons and tons of other material I watched over the years on the subject. And raised a lot others.

[@RiadhBoukratem]

By using the beam splitters we erase information from which detector we want it to detect the photon.

[@EugeneKhutoryansky]

You can help translate this video by adding subtitles in other languages. To add a translation, click on the following link: kzbin.info_video?ref=share&v=SzAQ36b9dzs You will then be able to add translations for all the subtitles. You will also be able to provide a translation for the title of the video. Please remember to hit the submit button for both the title and for the subtitles, as they are submitted separately. Details about adding translations is available at support.google.com/youtube/answer/6054623?hl=en Thanks.

[@studmalexy]

so..if I jump of a really high building with my eyes closed?....

[@anandsuralkar2947]

I hypothised a future pridictor using this

[@sandeepwolfman9845]

Music name till 2:25???

[@user-sm9yg8sr1l]

How can I communicate with you?

[@sandeepwolfman9845]

@@user-sm9yg8sr1l ??to whom..

[@threemonths8826]

Mind = Blown, or least I think, I haven't observed it yet to confirm...

[@giovanniandreani2124]

Eugene, you posses a very unique and effective view of the pedagogical approach needed for a gradual explanation of these phenomena.

[@EugeneKhutoryansky]

Giovanni Andreani Thanks for the compliment.

[@new-knowledge8040]

This is a very interesting "reverse" variation of the Yoon-Ho Kim, Rong Yu, Sergei P. Kulik, and Yanhua Shih Delayed "Choice" Quantum Eraser. In the above video, the entangled pairs are created within the crystal photon detector. What is even more interesting, is that the experiment has both particle and wave behavior occurring simultaneously, and which state it is that you wish to view is determined by which "emitted photon" detector it is that you wish to monitor.

[@alexvolk8942]

That was a very creepy cat, but this is probably the most well-made video I have ever seen. It made an extremely difficult and non-intuitive topic relatively easy to follow and understand. Great job and I hope to see more like this!

[@Berniebud]

Not really. Nothing about this intuitive especially with the strange cat animation acting as though the mere act of looking at a detector changea reality

[@slevinchannel7589]

@@Berniebud Hi. May i recommend you; a science-youtube-fan; some more science-youtuber?

[@jacky9575]

@@Berniebud The cat is very important

[@MissNorington]

The cat's creepiness was needed to kinda erase the multiple questions from each fact, to not block more information 😁

[@cottonheadandtheninnymuggi3698]

Even if I never fully understand this experiment, I will continue to watch it for the cat. You know that it's not real and that it is just an assembly pixels, yet you still acknowledge it as a cat, wanting to see something less eerily false because your mind has convinced you that it is supposed to be something which it is not. A curious thing. 😵

[@deathtoy101]

Dammit i told you the universe wasn't ready for offical release yet.

[@mikkel715]

It doesn't show any programming bugs in this one. I'll say it works perfectly. Just doing the math algorithms, only when necessary.

[@FocusReborn44]

Now's a good time to get my bong out

[@alexandroochoa5858]

FocusReborn So you won't remember most of the important points? What you should do is watch the video first and understand it, and THEN take a bong rip. Once your high, let your imagination wander.

[@FocusReborn44]

I like the way you think.

[@cdlogans]

+Alexandro Ochoa Me too!

[@JohnDoe-ln7ei]

+Alexandro Ochoa I find that THC helps me concentrate. If I were sober I probably wouldn't have paid full attention to the whole video.

[@professorschuler]

after a dessert of shroms

[@CreationTribe]

This has got to be one of the best explanations for the Delayed Choice Quantum Eraser. Thank you :)

[@kevdog261]

my mind is in a superposition of blown and confused

[@fukcg00gle95]

Welcome to the club...🤔

[@travisdraper2411]

My brain wasn't ready for this. Amazing stuff. Thank you.

[@chaitanyamc]

Oh my god! That was hands down the best explanation I never came across in my life. Thank you!

[@EugeneKhutoryansky]

Thanks for the compliment about my explanation.

[@stlkngyomom]

Chaitanya kumar Try Tom Campbell.

[@oleg5730]

Thank you for keeping up these videos, for me this is the best explanation

[@aroseland1]

The 5 second delay between sentences is killing me

[@rd0769]

+aroseland1 fast forward , video speed 1.25 .

[@walterprunzik6202]

5 seconds quantumlly erased

[@ceestimmerman9785]

Watch at double speed and read the captions.

[@ceestimmerman9785]

Watch at double speed and read the captions.

[@matthewcragg3607]

The background music is a distraction too.

[@andreadedomenico1479]

As always, great work Eugene.

[@spiros252]

Eugene, congratulations for your fabulous videos! The way you present quantum phenomena is unique. I can understand the great effort required to do so. Especially I want to congratulate you for that: You enter into the essence of the concept - the nature - of observation, something many others avoid thoroughly.

[@skoar8321]

jeez, the universe is so troll

[@BlingSco]

Bohr is the fucking troll. He was a fucking idealist. Check out pilot wave theory or Bohmian mechanics.

[@Luisitococinero]

@@BlingSco you are a Physics noob. Or worse, a Physics troll.

[@starseed96]

@@BlingSco Bohemian mechanics are the best.

[@EricJaakkola]

Are the speech pauses to allow time for information to travel backwards through time?

[@paulcallahan3897]

The clarity and precision of the English voice-over is exceptional which give even more value to this extra-ordinary video.

[@EugeneKhutoryansky]

Thanks for the compliments.

[@marcuspradas1037]

Another great lecture. It's amazing how Theoretical physics is yielding such good communicators.

[@matheusadornidardenne8684]

@14:30 This is called a Von Neumann Chain. The detectors do not collapse the superposition, but becomes entangled with it, also becoming a superposition, so the whole system will share a common wavefunction until an observation is made. For example: What would happen if we conducted the Schrodinger's Cat experiment inside another bigger box containing both the box with the cat, the scientist and another mechanism to kill the scientist (this is our eraser... haha) if the cat is found dead? The scientist's state would be entangled to the state of the cat, which would be entangled to the state of the radioactive particle, so the whole system would share a common wavefunction which would not collapse until someone from outside the system observe it. Now to blow our minds: What if we conducted this experiment with everyone in the world? Billions of boxes, one inside another, containing a person and a mechanism to kill that person if the previous was found dead? The system's wavefunction would only collapse if it is observed by outside the system. This has two solutions: or the system is never collapsed, what would mean that no one would actually be dead, but both dead and alive, even if the cat was found dead by the first scientist (a sort of solipsism, where the state of the "whole world" depends on you), or there is some sort of "omnipresent cosmic observer" which looks down at us to say we are alive or dead (a sort of theism). This is the Wigner's Friend Paradox.

[@SteelBlueVision]

+Matheus Adorni Dardenne The problem is that we can observe the cloth pattern BEFORE we decide whether to quantum erase or not (i.e., say the photons must travel an hour before they hit the beam splitters that erase the path information). In this case, since we have already observed the cloth, we know whether or not the wave function collapsed and can use the information to choose to erase or not erase, breaking down this whole system, it seems.

[@matheusadornidardenne8684]

SteelBlueVision The crazyness of it is that whatever answer we observe on the cloth always correlates with our decision to erase the data or not. This is why some (like Wheeler) argue this experiment implies in retrocausation.

[@SteelBlueVision]

+Matheus Adorni Dardenne But, our decision to erase the data or not comes much later in time than our perception of the cloth. This creates a paradox, because our decision can intentionally be the opposite to what we see on the cloth.

[@matheusadornidardenne8684]

+SteelBlueVision it can't, what we decide in the future will correlate with what the cloth shows. How can I put it; the pattern in the cloth is always incomplete until the other photon hits the detector, when it does, the sum of both patterns becomes the final result... we cannot see on the cloth what the decision will be on the future, it seems "ambiguous" until then, and corresponds both with the predictions of wave-like and particle-like behavior.

[@SteelBlueVision]

+Matheus Adorni Dardenne Sorry, but this doesn't make sense to me. What it sounds like you are saying is that the pattern on the cloth does not form until the photon's information is either revealed or erased. But there are four particles at play here, the photons which head off in their own direction and their corresponding larger particles which head for and are detected on the curtain. However, in my thought experiment, the larger particles hit the curtain first (in time), thus forming an interference pattern (or not) on the curtain. This happens > before already formed long ago < on the curtain 2) The curtain pattern changes > retroactively < based on what we decide to do with the photons (also a paradox of sorts?) It then appears to us that even though we had the intention to do the opposite, for some unexplainable reason we chose to act with the photons in a way that corresponds with what appeared on the curtain. We try again, and again, inexplicably, we decide to act with the photons in a way that corresponds with the curtain pattern instead of in contradiction to it. 3) The pattern on the curtain reflect what we will do in the future with the photons and once we see it, try as we might, we will only deal with the photons in a way that is compatible with the curtain pattern.

[@Navak_]

Please someone explain to me how this isn't true: Say you have your double slit in your laboratory on Earth. Each gate has a photon-emitting crystal detector as shown in this video. The photons from the detectors are amplified and then beamed into space directly toward a Mars laboratory. Say Mars is 10 light minutes away. You activate your double slit at precisely 3:00:00. You have a prior arrangement with the astronaut in the Martian laboratory that he will choose to either insert the mirrors and erase the data (stripe pattern) or omit the mirrors and collect the data (collapse the wave function) at, say, precisely 3:09:59, one second before the light from your experiment reaches him from Earth. Wouldn't you already know at 3:00:01 which action he is going to take judging by which pattern appears on the wall behind your double slit on Earth? Couldn't you use this to communicate with him faster than light? What if he also had a double slit and you also had an eraser/detector setup, couldn't you then communicate across infinite distances instantaneously?

[@ioctane2891]

Nice twist :)

[@annedejong13]

Nice thought! I may have an idea why this isn't true, but do note I'm new to this subject. I'm thinking if the Martian 'chooses' whether to insert or omit mirrors, the wave function collapses. It's no longer probability. If instead of choosing it was a probability, then it can't be used for communication. Right?

[@shruploads]

without the information from the detector, you won't be able to tell the difference between patterns. The blue and purple pattern you see is only formed by matching the data from the beam splitter with the wall.

[@Yurikeukens]

You say you would already know which action he is going to take at 3:00:01, but that's not true. You already know it before that because of the prior arrangement. If you didn't make an arrangement, he would have to send his data back to earth, otherwise you wouldn't be able to recover any pattern... I think.

[@Luisitococinero]

You can't erase the information after the particles hit the cloth, therefore, you'll never observe a stripped pattern.

[@Cazanu417]

Still blows my mind as it did 7 years ago,love your channel

[@EugeneKhutoryansky]

Thanks.

[@MissNorington]

The pause between important information, as well as the 3D cat, helped more to understand this very difficult topic. Big thanks to the animator for making things basic!

[@EugeneKhutoryansky]

Thanks.

[@MissNorington]

@@EugeneKhutoryansky 7 year old video, and a reply within minutes!? 😊 I wasn't prepared for that!

[@ICEMAN3rdID]

The creepiest cat I have ever seen

[@ioctane2891]

It's the quantum cat. Everybody recognizes her.

[@Doomroar]

at 11:29 i started thinking that a bunch of hunters had it with its creepiness and were after its head.

[@wesjohnson6833]

The cat is stressed out by 80 years of rumors of having his life threatened.

[@Deshammanideep]

that is a shrodingers cat.. 🐈

[@vitreo1363]

This is what happens when a cat is both alive AND dead at the same time...

[@josemartini8982]

4:10 - 4:25 ... according to my calculations: in order for the experiment to work, we must kill the cat. 🐱

[@cyberloopy]

A huge thanks for your videos. I have wanted to have something in-depth like this for a good while.

[@EugeneKhutoryansky]

Thanks. I am glad you like my videos.

[@dionsilverman4195]

Fantastic soundtrack, and great animations. I particularly like the cat looking very inquisitively at the little puffs of wave.

[@EugeneKhutoryansky]

+Dion Silverman, glad you liked my video.

[@bluesrock2008]

25:27 revenge of the Shrodinger's cat?

[@maxorbit357]

So, that MUST be Schrodinger's cat, right?

[@EugeneKhutoryansky]

Yes, that is Schrodinger's cat. He makes appearances in many of my videos.

[@truthisthenewhatespeech9572]

@@EugeneKhutoryansky 🤣🤣🤣🤣

[@KarmicBeats]

I have sen this experiment described in a different way and I am wondering if it has been done in this way. Particle detectors are put on each slit. The date from the particle detectors goes into a computer and no one sees them until later. Photographic plates are used. The experiment is run multiple times with the particle detectors turned on each time. The plates are developed and fixed. Nobody looks at the plates until two weeks after the experiment. A that time no one has seen either the plates or the results in the computer. Now the computer randomly picks half the experiments and erases the results. When the data is looked at the results for each experiment that had the detector data erased shows an interference pattern on the plates and the ones for which the particle detector data was kept show the pattern of individual particles. Has this experiment ever been done? Could it be done?

[@markmerzweiler909]

Thank you for these wonderful videos!

[@stuffintaco]

is that the quantum eraser send information back in time or is it that the particle is deciding after passing through the quantum eraser ? It seems to me it about the timing of the choice being made, not that the "eraser" is doing anything at all...

[@edmclaughlin4923]

So if a tree falls in the forest, and no one is there, does it make it sound?

[@stuffintaco]

The Bigger question Ed is does that tree even exist whilst no one is there to observe it and are you just data in my universe till the day I observe you and materialize you into form...you exist in yours whilst you observe yourself, but how about your face and back side ? your not observing those right now ... :p *as Ed reaches round to grab his butt and check if he is real* :p

[@Feynstein100]

Quantum mechanics makes my brain hurt.

[@BlingSco]

And a million other people, check out the other interpretations -particularly check out pilot wave Theory. also don't think of this as some kind of abstract mathematical construct, that's exactly what Bohr though of it, he thought of the wave function as some kind of abstract mathematical construct which only exist on paper which is utter bullshit. Mathematics was invented for real physical political economic purposes and reflect how materiality in actuality how the world works why thesis pieces of material world external to human beings and the antithesis of human brain and body interpreting the world leads to synthesis of mathematics. or in other words mathematics is a real fucking material thing and you are a real material fucking things made out of matter. Read anti during by engels

[@tommarchner]

This is an excellent video. Part of an excellent series. Some of the videos in the series have explained things I've been trying to understand for a long time.

[@TheCrow01]

I really love your quantum science videos. I am so glad you are going to make another one.

[@EugeneKhutoryansky]

space laser dank raccoon Thanks. I am glad to hear that you love my quantum videos.

[@amadeobordigahitsquad]

What exactly qualifies as observation?

[@EugeneKhutoryansky]

Pseudo That is a matter of considerable debate, and no one knows for sure. Any detector consists of particles which are also described by wave-functions, which don't seem to collapse until they are "observed."

[@mEPknuser]

Eugene Khutoryansky Isn't it more about our knowledge of the system rather than observation? As I understand it scientists use some kind of measuring device to measure which slit the particle goes through. So if you don't put a measuring device in front of the slits you'll get an interference pattern, but if you do put a measuring device in front of the slits to measure which slit it goes through you get that clump pattern instead. So, what would happen if you just placed your own two eyes in front of the slits instead of the measuring device? Wouldn't that be an observation too? But then again, your eyes wouldn't be able to see which slit the particle goes through since it's so tiny for us to see, so my prediction would be that if we placed our eyes in front of the slits instead of the measuring device we would get the interference pattern since our eyes can't really see which slit it goes through, hence why I think it's more about knowledge of the system rather than observation. So just by looking at the slits with your own eyes without any detectors/measuring device would NOT qualify as an observation. Am I correct or what, Eugene? What I'm trying to say is that the Delayed Choice Quantum Eraser Experiment shows that it isn't the detectors themselves which cause the wave function to collapse but rather that an observation of a conscious being that does it. So if you know which path the particles took which means you know which slit it went through the wave function collapses e.g. you get a clump pattern. But if you don't know which slit the particles went through you get the interference pattern. But what if a cat were to look at the data instead of a human? I've made the assumption that it's the knowledge of the system which causes the wave function to collapse. (You know which slit the particle went through, therefore the wave function collapses.) But since I would call a cat a concious being, what would happen if a cat were observing the data from the detector instead of a human? I would assume the cat doesn't know anything about the experiment, what it is, what it's all about, which slit the particle went through even if it looked at the data etc. So since the cat doesn't have the knowledge of which slit the particle went through, but is at the same time a conscious being, what would the cat see? Would the cat read something different out of the detector than we would do? Would the cat only see the interference pattern/read it out from the detector since it doesn't have the knowledge of which slit the particle goes through?

[@SteelBlueVision]

+Eugene Khutoryansky The problem is that the decision to "erase" can be made years after the particles have landed on that cloth. That is, whether or not beam splitters are employed can be really really delayed into those futures, so those photons travel for a very long time before the information contained within them is erased. In this case, what is the pattern on the cloth? Since it is formed before the choice of whether beam splitters will be employed to perform quantum erasure.

[@spiros252]

+mEPknuser "I've made the assumption that it's the knowledge of the system which causes the wave function to collapse. (You know which slit the particle went through, therefore the wave function collapses.)" Yes, you are correct. Its the case. Think about entanglement. If the other particle is to the opposite side of the universe, if you measure the one that is here, you automatically know the status, the reality of the other. Because the two particles, are one system, they are under the same wavefunction.

[@Argonova]

+Eugene Khutoryansky I have two questions about this video that seem most appropriate to ask in this reply thread. 1. If I understand correctly, a "Quantum Eraser" is essentially an array of reflecting mirrors placed in front of the two detectors/holes to allow for the possibility of the photon passing through either. It would seem then that for this to work, it must be functioning at the time of the experiment itself. How would one "activate" such a device after the fact when the photon/wave has already completed its journey past the point of the detector and through the two holes (or to phrase it perhaps more accurately, "done whatever it has done")? 2. I would also very much like to know what qualifies as an observation. If I understand the information you have presented correctly, it seems as if objects do NOT qualify, but living, thinking observers DO? Or am I misunderstanding? Would a computer recording the event count as an observer if the data on its drive was erased before anyone had the opportunity to look at it? I love your videos, and I thank you very much for making them! These are very difficult concepts to grasp for the uninitiated (people like me).

[@thomasslone1964]

im thinking this is more about how mass, space and time are tied together than wave particle duality

[@jorgepeterbarton]

Because from photon reference frame without rest-mass, there is no causality and all events happen simultaneously from the photon pov. Light speed is causality speed so as instantaneous as you can get. Not from outside inertial frame however (they appear to move lightspeed). Move interactions are physical interactions with another inertial frame so appear to obey causality. This experiment is NOT it is the photon's information being changed, its knowledge and not a material process. It must some how know its own wave function, or pilot wave as an informational omniscient thing...

This channel is simply the best for me. A lot of channels illustrate complex concepts like this one, with fancier animations but for inexplicable reasons, this makes actual intellectual undestanding simpler for me. Thanks for the good work!

[@EugeneKhutoryansky]

Thanks!

[@pendalink]

I think this is one of your best. I look forward to seeing your next masterpiece when it comes out :)

[@EugeneKhutoryansky]

pendalink Glad you liked it. Lots more videos are on their way.

[@primeobjective5469]

This video scares me. What in the world in going on at the Quantum level?

[@CompleteMeYT]

sounds like just like a videogame, things aren't rendered if there are no players around.

[@fckinnonstick9919]

That cat is far more stranger than quantum mechanics ^_^

[@hintzofcolorconcepts]

I kept wondering if it was supposed to be Schrödinger’s or if the narrator is a serious cat lady.

[@kakolisarkar1537]

Cat catter cattest

[@half-soul8393]

I'm so glad this video talks about the very fundamental concepts and I think this is the only one I've seen so far which has explained "What erasing of information means", I've been quite confused about it in the other videos which just seem to mention it without really explaining clearly. Thank you!

[@EugeneKhutoryansky]

Thanks.

[@hlexjava]

Love how amaze science is!

[@MrGriff305]

okay, so it's not so much that the information is observed by a conscious mind, because the wave pattern drops when a detector is turned on regardless of whether a human being ever looks at the result of a detector. Instead, what collapses the wave function is if the information is simply available to the universe by way of entangled particles that can only behave a particular way as a particle if its "partner" is behaving in a particular way as a particle. Then again, maybe the system collapses if observed by the detector, despite the fact that the detector is not conscious. In any case, it seems that human observation is not what collapses the function if simply turning on a detector without looking at the detector result causes humans to observe the no interference pattern on the screen.

[@jorgepeterbarton]

THIS. thank you. quantum mysticism gets on my tits and this business about consciousness needs stopping. 'observe' ah its a word, a different definition here, totally. following on from the uncertainty principle which talks about observation, how do you observe without interfering when the particle you use is equal in importance to things being observed and cant be divided. (although technically this experiment isnt uncertainty priciple, its observer effect, similar things really)

[@jorgepeterbarton]

@boi detectors dont know anything because they are detectors not people. i dont quite understand the point you are making. a ball doesnt 'know' which angle to bounce, it just does it, its not that different.

[@bindaredundat-uv6wz]

YES

[@jmanc3]

Quantum physics is so crazy! Very good video.

[@EugeneKhutoryansky]

jmanc3 Thanks for the compliment about the video.

[@AwesomeFaceOver9000]

Nice vid. I love the cat so please keep him/her around for the future quantum videos.

[@EugeneKhutoryansky]

+9009Hayden, thanks. And yes, the cat will always stay alive and healthy for future videos.

[@chikeezebilo6545]

+Physics Videos by Eugene Khutoryansky phew...

[@NyteMunkey]

+Physics Videos by Eugene Khutoryansky Just don't let that Schrödinger guy around him. If you do, you'll never know what could happen to him

[@AwesomeFaceOver9000]

NyteMunkey XD

[@blake301987]

Thanks for the new video Eugene, ever since I heard about physicists at ANU doing this experiment I have wanted you to make a video on it to allow me to understand it better. Great job, love all your other videos too!

[@EugeneKhutoryansky]

blake301987 Thanks. I am glad that you liked this video, and all my other videos too. Lots more are on their way.

[@maxdoubt5219]

Thank you so much. The animation really helps. Quantastic!

[@EugeneKhutoryansky]

+Deacon Verter, glad you liked it. Thanks.

[@aroseland1]

especially that cat, this video would be pointless without it.

[@juangreen8194]

This is a tough one. Will rewatch.

[@shreyashipaul1378]

The more I watch his videos the more surprised I get. Love your work as always Eugene

[@EugeneKhutoryansky]

Thanks!

[@steviegroovie]

I really like the creepy cat please never abandon him and let him stay in your vids

[@fhjfhdgh]

14:32 So this means that there is a difference between a conscious observer like us and and an unconscious observer like the detector? That question is on my mind for quite some time now, does the universe differentiate between consciousness and "non-consciousness" ? Wouldn't that mean that without consciousness there cannot be a definite reality? Hmmm this was probably asked by so many people, what do you think of this? edit: okay i just finished the video, should have waited to ask that question since it is mentioned at the end :D hopefully you will adress this kind of stuff in the future videos

[@EugeneKhutoryansky]

niv skillsurf Whether or not consciousness makes a difference is a matter of debate. There are a number of different philosophical interpretations of Quantum Mechanics. One of them states that a wave-function collapses when it is observed by a conscious observer. The other interpretations have a different explanation. And yes, as you said, I plan to eventually make a video that addresses the different philosophical interpretations.

[@khaledyasser8293]

There is no reason to assume Consciousness has anything to do with it when you entanglement I don't think. You could just say we only see the wave function we entangle with

[@John77Doe]

niv Gnasherus The detectors aren't doing reading. The detectors have to be read by a recording device. Once that happens, the quantum wave collapses. In the real Delayed Choice Quantum Eraser experiment photons are hitting the screen or the detectors at a rate too fast for humans to decide whether or not to read a detector. Fast processors are implementing software to record no not record through which slit the entangled photon and it's entangled partner that hit the screen earlier in time. We can only play back the recording and match entangled particles. From the recording, we see that when it is known through which slit a photon passes, the photon hitting the screen acts like a particle. From the recording, we see that when it is not known through which slit a photon passes, the photon hitting the screen acts like a wave. There is no human consciousness involved. Quantum entanglement appears to break distance and convey information faster than the speed of light, instantaneously. Quantum entanglement appears to break time and convey information backward in time. Three years after this video,I have seen no papers that can satisfactorily tidy up this mess. A decision in the present causes an outcome in the past. 😖😖😖😖😖

[@classicalmusful]

​@@khaledyasser8293 We do have a reason to assume consciousness is at play because the primary variable in this experiment is knowledge of how its set up.

[@danmatt44]

I really enjoy your videos. I would like to just make a comment about the music selection though. I think it would be VERY impactful if you choose darker music. Much of the "happy" major songs seem to take away from the awe-inspiring effect your videos generally leave upon a person. I see you use music form the Audio Library of KZbin. If you choose more music from the Dark category (Classical and Ambient are usually the best of the dark genre), music more abstract and maybe even a little disturbing, I think you could greatly enhance the quality of your videos and add a uniqueness factor to your videos (All of the commercial industry already uses happy ukulele songs, you should avoid doing that). If you add this dimension to your videos (haunting music with awe-inspiring physics revelations), I believe you could gain a cult following. I with you the best with your channel and I hope you consider my suggestion.

[@luajimbar]

Hey Daniel. I really enjoy the background music to be honest. I was wondering where is he taking it from. Do you know? Thanks in advance mate!

[@bobbyfeatherstone2834]

music is william tell overature, the lone ranger bit is at the end.

[@Gritaremos]

Thanks so much for these videos!

[@louiscipher5861]

I looked at myself in the mirror and my spin collapsed to be up. Incredible!

[@CurbsideJimmy]

Here is the problem. To be an observer one must be conscious. But, we don't know what consciousness is so we don't know what an observer is either. Since we don't know what consciousness is we can't say for certain that that the particles themselves are not conscious. If the particles are conscious, they may change the way the mind perceives the patterns they make.

[@rever4217]

+CurbsideJimmy Haha lol. Everything is alive and watching you. They are keeping tabs on what you do whether you like/know it or not. c:

[@lukapopovic5802]

Curbside Jimmy No, an observer can be an nonconscious thing such as polarisation glasses

[@rg7535]

Steve Bergman How so? It seems to me one of two possible things happen in this scenario 1 - Consciousness - meaning the awareness that some event has taken place - causes the "rest" of the event to also materialize, in the sense that if a particle is measured at a given point, it must have traversed through a certain path to get there, or 2 - All the events have been laid out in advance as an infinite set of possibilities, and when observation - or just the mere fact that an event has taken place - "forces" the event into existence in its entirety. That, however, would imply that time is only a dimension we travel through, and everything that ever was or will be was "created" instantaneously before even the first ever event to take place in our universe. Seems to me like both scenarios imply the existence of consciousness, either within or outside the system. In the first scenario, the universe would be the consciousness I'm referring to. In the second scenario, an outside consciousness would have "created" the entire set of possibilities and then set it in motion. What am I missing?

[@charlesmcmillion5118]

Ha! Schrodenger's cat's person.

[@gershoma5538]

it's creepy how much like a video game this makes real life sound; things the user doesn't observe are not rendered, just abstracted to save processor resources

[@ffreshblood]

This is seriously what thought but it is not exactly same. Observation changes result

[@dragovian]

Guys seriously, am I the only one that wants to try or see someone else perform the following experiment?(I call it 'The opposite way experiment") : 1) We take the simple splitter variation, with A and B detectors 2) We position them open at 1.798754748× 10^(10 ) meters distance. (This is according to google the distance light travels in 1 minute). That means that the photons will reach 1 minute after the first ones hit the screen 3) If we see see no interference pattern (meaning that we ''measured them'') WE WILL CLOSE the detectors. or if we see interference WE WILL OPEN them. Essentialy doing the exact opposite of what will happen on the screen(which is whether we will supposedly measure). Keep in mind we have 1 minute to act upon. 4) Checkmate universe. Really eager to see whether the universe has a default mode, for any of this (my guess would be no interference if it behaves like this).. or it would change the pattern on the screen :P ( not a plausible solution) or it would collapse of the universe xD

[@steveball4444]

We would have to communicate the information as to whether or not to close the detectors over that 1-light minute distance. That communication would travel at the speed of light and take one minute to arrive. Thus there would be no time left to change the state of the detectors.

[@CaptainJadde]

First of all I would like to say that I think your videos are absolutely fantastic. Except the two about quantum mechanics. You really make it seem like consiousness has some important role in the double slit experiment, which is definitely not the consensus by physicists. Im not sure if you really believe that or if it is a mistake by my part from interpreting the video, but you unfortunately make it look like it (a lot of youtube videos do) for example when the cat is closing its eyes and the results change. "Observing" in quantum mechanics does not mean "consious beeing observing". I believe interfere or disturb is a better word to avoid confusion.

[@bartkwezelstaart9306]

Andreas Henriksson I also thought that consiousness had nothing to do with it, but how can it then be that the wave function does not collapse by measuring, but only by the information that the measurement produces? (As shown by the use of a quantum eraser) Khutoryanski already promised a video about the phylosophical concequences of this.

[@EugeneKhutoryansky]

Andreas Henriksson There are a number of different philosophical interpretations of Quantum Mechanics. One of them is, in fact, the idea that the wave function collapses only when a conscious observer observes it. There are also many other interpretations of Quantum Mechanics, where consciousness does not play a role. However, all these other interpretations have to explain why the data makes it seem as if consciousness is involved. In my videos on Quantum Mechanics, I leave this as an open question, and I only state that it "seems" as if consciousness plays a role. I never explicitly state whether it does or doesn't, as this is a matter of debate, and no on really knows for sure when or how the wave-function collapses.

[@CaptainJadde]

Eugene Khutoryansky Yes, there is a number of different philosophical interpretations of Quantum Mechanics, and one of the more unpopular (by physicist) and silly ideas is the idea that consciousness plays a role - an idea often used by new-age people and such who misuse Quantum mechanics to fit their own view. What counts as consciousness? can a toddler collapse the wave function, a chimpanzee? dog? insects? This obviously creates some ridiculous problems (and its actually quite arrogant to believe that we humans possess a special ability to collapse the wavefunction..) And I do not agree that the data seems as consciousness has something to do with it, just that your explanation of the problem make it look that way ;) As a matter of fact I have never heard of any physicists that believe in this interpretation (Im a physics student, and have asked my professors about this) I know you never explicitly stated anything, but you sure emphasized this very disfavored interpretation.

[@EugeneKhutoryansky]

Andreas Henriksson All I am doing is leaving open the possibility that consciousness plays a role, without stating whether it does or doesn't, as there is presently no way to prove this one way or the other. Also, I think that the percentage of physicists who think that consciousness plays a role might actually be higher than you think, though they would disagree with each other over what counts as consciousness. In any case, the biggest issue I see for the view that consciousness plays a role is the question of what the Universe was doing before there were conscious observers in it, such as before any planets had yet formed in the Universe to support life.

[@davidflores909]

Andreas Henriksson You are not considering that, maybe, consciousness has something to do. I am not by far instructed at quantum mechanics but using the logic that my knowledge in programming has granted me I can take a shot at it. This is that maybe our "consciousness" is like a system that kind of constructs a solid experience through the possible quantum outcomes so we can actually be self aware of our existence. I mean if you try really hard to think what consciousness is you will realize that it is way beyond understanding; it is like trying to see the back of your head in a place with no reflective surfaces. So what I'm trying to say is that maybe the Universe, time, space, and all energy and particles make no sense and are not correlated at all but our consciousness (which I think might be created by the way the particles in our brains are set up) is so complex that can make everything make sense among the quantum chaos and make us feel, well, conscious.

[@starwarsjk99]

That cat gives me nightmares.

[@geoffmulberry]

Eugene, your animations are great. I especially love the videos with cats.

[@EugeneKhutoryansky]

Geoff Mulberry Thanks. I am glad that you like my animations, and that you like the cats.

[@antonnym214]

This is a great video. nice explanation, and WEIRD stuff!

[@HeriJoensen]

Any talk of the content of human consciousness being the deciding factor of whether or not "reality" is real is obvious nonsense! There is something fundamental that we have not understood

[@morgorththered9040]

why?

[@MrMcKlain]

Here is my opinion. I don't think human consciousness is the deciding factor, but the fact that the information of the experiment exists somewhere in the universe. It can be registered on a sheet of paper, a hard drive or a brain. It looks like we are also entangled with the whole experiment.

[@scottkuhn4026]

I agree. It's very suspicious that this experiment is so accepted among prominent thinkers. The blind jump from physics to philosophy is obscene. Physics has something to gain as does philosophy. Very politicized.

[@tiagofranca2660]

Very great video!! I just loved your explanations, you've helped me a lot! Please keep these videos coming!!

[@EugeneKhutoryansky]

Theenerd ジェームズ Thanks again for the compliment. I am glad that you love my explanations, and that they are helpful. And yes, lots more videos are on their way.

[@SciStone]

great explanation, very insightful, good work as always!

[@EugeneKhutoryansky]

Anon Ymous Thanks for the compliment. I am glad you liked it.

[@straightedgerc]

Any entanglement demonstration involving a choice illustrates that the subjective experience of scientist A making a choice, only he knows, violates locality as observed by scientist B, and so the subjective experience of scientist A does not occur in a finite box. Therefore, the human mind cannot be said to be inside a finite box such as the brain, the brain and body, or the body and the local environment regardless of how entanglement works.

[@hanshanshans78]

nice video, I am excitedly looking forward to your video about the interpretations of the experiments! best regards

[@EugeneKhutoryansky]

Hans HansHans Thanks, and I am glad to hear that you are looking forward to my video on the different interpretations on Quantum Mechanics.

[@jojolafrite90]

The French hymn behind is perfect. He he. Well done mister Aspect.

[@ramprakash1562]

This is one of the finest videos on this channel...😍😍😍😍

[@NathanielRossol]

Just one question: Why is the blue striped pattern skewed to the left (yellow detector) and purple to the right (towards the green detector) instead of vice versa?

[@geetsuri123]

Eugene Sir, what is the name of the music in the starting? it perfectly blended with your beautiful presentation

[@EugeneKhutoryansky]

All the music in this video is from the free KZbin audio library, and the names of the songs are the following. Stale Mate William_Tell_Overture_by_Rossini 1812_Overture_by_Tchaikosvky

[@JustinStLouis-jm1zn]

We create our own reality.. it's whatever we make it and how we perceive it.

[@arcstur]

Mindblowing. Excellent video, as always

[@EugeneKhutoryansky]

+AC Souza, thanks.

[@RubberJunk1]

Have you made the video for the different philosophical interpretations of this experiment yet?

[@douginorlando6260]

This is well done, especially explaining how no information is transmitted faster than c. However, I had to wait for the description of the test configuration near the end to see the context. Without the context it is nearly impossible to connect the first half to physical reality. Please and thank you, Next time start with the context and then explain the results. Thumbs up for the best explanation on the internet.

[@EugeneKhutoryansky]

Thanks for the compliment about my explanation.

[@JoeOvercoat]

No cats were hurt in the execution of this mind experiment. 😻🥰😻

[@NeverMetTheGuy]

I'm not even in a field that has anything to do with this directly, in any way. I've been watching these videos since last week and it's fascinating.

[@EugeneKhutoryansky]

+NeverMetTheGuy, I am glad that you are enjoying my videos. Thanks.

[@lisagoodwin6623]

Fascinating! As someone who never had any more schooling and basic math and science, I've been fascinated at learning these things now when I'm 55! So please don't laugh at me, but, what if these experiments were performed in many different places at the same time and all the documented info was recorded together at the same time to see if these particles somehow communicate with each other elsewhere in place/space and time? I don't even know if that makes sense but if the process of just looking changes things? Wow, what a mind blowing experiment that might be!

[@myyoutube945]

Thanks for these!

[@EugeneKhutoryansky]

BigBad Wolfe You're Welcome!

[@xCorvus7x]

What are the limitations of the quantum eraser? Does it still restore the interference pattern if we endow the photons emitted by one crystal with another certain property (say, a specific polarisation)? Is the result of that the same, if the four final detectors for the photons measure not only light, but also polarisation?

[@trout3685]

Does the two slit experiment need to be done in a vacuum in case the air in the room interacts with the particle therefor theoretically you could figure out which slit the particle went through? Or on a different scale, don't particles cause gravity so theoretically you can measure the particles gravitational wave effects somehow and determine which slit it went through? In that case you wouldn't really be affecting or touching the particle as it flies through the slit? I'm trying to think of a way you might theoretically detect something without actually disturbing it.

[@B_D__]

Thx for the video, you provided a easier way to understand this difficult and strange phenomenon

[@EugeneKhutoryansky]

Barry D Glad to hear that my video made this phenomena easier to understand. Thanks.

[@caejayllaga1713]

In the delayed eraser double-slit experiment, if they have a video camera looking at the detector data, instead of the scientist, and the scientist erase the detector data before looking at it, will they see a diffraction pattern or a two lines on the screen? If they see the diffraction pattern and then look at the footage from the camera and then look at the screen again will it change to two lines? If they see two lines but decide to delete the video before watching it will it change to a diffraction pattern?

[@AlexHop1]

Thanks, Eugene, another fabulous video--and I'll be re-watching this one more than a few times. Some videos on physics feature narrators who talk really fast--possibly to sufficiently engage attention. I love it that your narrator talks at a normal pace with lots of pauses and sometimes repetitions to allow me to absorb the ideas. Your music and animations do the engaging. And, of course, the animations often help with visualizing. This is a brilliant and unique approach. I wish other video makers understood this.

[@EugeneKhutoryansky]

+Alexandra Hopkins, thanks for the compliment. I am glad that you like the video, and the pace of the narrations. And thanks for the compliments on the animations.

[@new-knowledge8040]

+Alexandra Hopkins -- the fast ones that I despise, are the ones where they finish the video and then edit out the small pauses between sentences/paragraphs. Thus it becomes just one endless no pause nightmare.

[@dsinghr]

thank you for this amazing video !

[@EugeneKhutoryansky]

bannajirocks You are welcome. Glad you liked it. Thanks.

[@Dannafilms96]

I love this cat and your videos!! So good!

[@brettvollert9913]

hats off to anyone who sat patiently and listened to the painfully slow pace of this video

[@jucapeloso]

What if when the electron passes through the cristal, it gets itself entangled with the photon that is emitted? So when the photon is measured, it "passes the information" instantly to the electron that created it, then the pattern instantly colapses to a wave-like pattern or a particle-like pattern (depending on whether the quantum eraser was activated or not), even though they have already passed through the detector, forming the four possible patterns that overlap (as shown in the video). Does it make any sense?

[@RiadhBoukratem]

Does the Quantum Eraser is just another probability, of the 4 detectors, Of the 1/2 of the two holes and to the same of the beam splitters?

[@Moregnan]

I did execute this experiment in a lab as a physics student, with many photons at the same time but I still don't actually understand it properly, hopefully this video will help a bit.