Down The Rabbit Hole Of The Delayed Choice Quantum Eraser | Answers With Joe

this video is supported by dashlane there's a quote that's usually attributed to richard fineman and it says if you think you understand quantum mechanics you don't understand in quantum mechanics but like most historical quotes it may or may not have been him there's just not actually a record of him saying this everybody just heard somebody else say that they heard him say this you know but it does sound like him it's got a certain Fineman astute now he did once say that he didn't think that anybody actually understood quantum mechanics we do have a recording of that although that he may has been joking there it kind of feels like a lifeline of course some people think that this line should be attributed to Neil Bohr who did once say anybody who is not shocked by quantum theory has not understood it but regardless of who said what the reason these lines sort of resonated amongst people who study quantum mechanics is because it is intrinsically kind of impossible to understand it's just a world that plays by entirely different rules and truly the more you understand about quantum mechanics the weirder it gets it's like every experiment we do seems to bring up more questions and answers so today we're just gonna go down that rabbit hole of quantum experiments that one at a time chipped away at our understanding of reality until we get to the one that breaks time itself the delayed choice quantum eraser experiment there were many mysteries of the universe that the ancient philosophers used to debate over wine and leg of lamb but perhaps the one that troubled them the most was the nature of light what is it how does it work what's it made of how much does it weigh theories range from being part of the divine to part of matter and the things that make up matter to being particle to being waves the last two were the ones are really stuck like for a long time because sometimes light would act like a particle and sometimes would act like a wave it just didn't seem to want to make up its mind what it wanted to be and one of the cases where it definitely acted like a wave was the double slit experiment when you shine light through a single slit what projects on the wall behind it is pretty much do you expect just kind of a cluster of light but when you shine it through two really small slits something very different happens you don't get two beams of light you this this is known as an interference pattern it's called this because as the light passes through the slits as waves the photons fan out from the slits on the other side and interfere with each other the peaks of the troughs colliding to form this pattern which also corresponds the various levels of probability that a photon would land there so light definitely seems to be working as a wave in this instance but good science leave well enough alone of course not so the next big question became what if you put through the photons one at a time that way they don't have anything to collide against would you still get this interference pattern or would you get something that you would expect from a single slit they didn't know so they tried that and they still got an interference pattern which makes no sense how could these things be interfering with something that's not there unless they're interfering themselves are the photons literally splitting into passing through the slits and then colliding with each other on the other side cuz that's kind of bananas it was decided that no that's not what's happening here that the photon was actually in a superposition of states as it passed through the double slit a superposition that was determined by the wavefunction the particle is like sort of its own system really and when it goes through the double slit it's in a superposition of all states at once so some of those states do collide with each other on the other side and form this interference pattern okay so now we know that quantum particles exist in the superposition of States sort of in all places at once until the wave form collapses when its measured in this case when it gets measured is when it hits that back screen this alone kind of changes our understanding of reality doesn't it because it's not just photons that do this it's electrons it's protons it's some whole atoms that are in this superposition and only collapse the wave form and become real once they're measured everything that we understood up to this point said that that was impossible and yet experiment after experiment after experiment showed that this was the case but as it turned out we had not yet begun to melt our brains because now scientists wanted to find out if they could measure which one of the slits it was going through so they put up a detector on one of the slits because that should clear things up right nope this experiment called the whichway experiment because you're figuring out which way the particle went resulted in no interference pattern on the screen no traveling in waves no superposition of states once it goes through this slit it behaves like a particle in other words the waveform that puts it into superposition collapses because it's being measured at the store so this is where a lot of woowoo creeps into this thing because it does beg the question how does this particle know it's being watched and a fundamental misunderstanding comes up at this point because a lot of people take this to mean that it's human consciousness that collapses the waveform in other words our thoughts are affecting the physical world enter the secret enter what the bleep do we know and about a thousand other new agey you know you control the universe with your mind kind of theories that have sprung up and look I'll come clean here I had been guilty of this too it's really easy to get caught up in the whirlwind of what all this could mean you know it's empowering this idea that you can control the world you have some kind of agency in the world just by being conscious and just by being you I'm not gonna lie feels good man I mean not to mention isn't it a great feeling to know that there's more to reality than we think that there's more to heaven and earth than are dreamt of in your philosophy and you know what we're still discovering crazy things every single day so that may still be the case but not necessarily in this case it is not human consciousness that brings a particle out of superposition and into reality it's just the act of measurement human consciousness not required now some of you may hear that and ask you know what's the difference fair question basically what it means is that you can't measure the particle without affecting its properties it's like imagine a swimming pool with a ball floating on the top of the water and a big huge swimming pool and there's a button on the ball that when you press it will measure its position the problem is you have to get into the water in order to get to the ball and there's no way to get into that water and move closer to the ball without disturbing its position you know the closer you get to it the more you disturb the water around it and the more it moves away from its original position does that make sense here's another analogy because you can't have too many analogies am i right it's someone who has spent a lot of time behind and in front of a camera I can tell you unequivocally there is no such thing as truth on film not really because when you point a camera at someone they change they just do they talk differently they stand differently they were you two things differently you know what it's like do you think that you act exactly the same when there's nobody around as you do when there's people around you of course you don't I bet 10% of you right now have your hand down your pants watching this so do i my own pants not not you this is gonna be demonetised I get people telling me all the time that I come off really real and genuine and natural on this channel and I take that as a huge compliment because I actively work to put something that sounds and feels authentic out there this is not my normal state though this is nowhere near my normal state the point is the act of observing a person changes their behavior even if it's just a camera and the camera is not conscious same thing the act of measuring a quantum system changes that system no consciousness required anyway the whichway experiments went a long way to explaining the nature of quantum systems and the nature of scrambled brains but if our brains were scrambled by all this so far a new experiment came along that basically made a brain omelette because then we started to wonder how would quantum entanglement play into this I mean we know that if we measure our photon before it hits the back wall then the waveform would collapse and we would lose the interference pattern but what if we measured an entangled particle as I covered in this video right here quantum entanglement or spooky action at a distance as Einstein was fond of calling it is the thing where two particles share the same properties and if you measure the properties of one particle you know the property of the other particle so if you could split a particle in the double slit experiment you can make it so that one particle goes towards that back screen and the other particle goes towards a detector and that's what they did they added a crystal right behind the slits this crystal splits the photon into two entangled photons with half the energy of the first one these entangled photons travel in different directions one to the back screen and one to the detector if the photon travel through slit a it would be picked up by detector a if it went through slit B it got to detector B so you know which slit the entangled photons went through but you're still not physically measuring the photon that hits the back screen so would measuring the entangled photon change the waveform state of the other yes yes it did there was no interference pattern on that back screen let's just take a second and consider how bonkers this is no seriously take a second because it's about to get weirder particle physicists were determined to find a way to measure a particle without collapsing its wavefunction come hell or high water so what if we move those detectors back a little bit that way the particle that hit the back screen would actually get there before the entangled particle reaches the detector so done deal right I mean there's no way to collapse the wave function before it hits the screen so it's got to be an interference pattern because I mean that information can't travel backwards through time take that quantum physics this idea was called the delayed choice experiment it was brilliant it was genius it was foolproof and it didn't work no interference pattern what the hell somehow measuring the entangled particle affected the wavefunction of the other particle in the past quantum physics you are such a bit that's not how this works that's not how any of this works except I guess it does okay that's it said the quantum physicist for the purpose of this video I will find a way to outsmart the quantum particle so what if we measure the particle and then erase the information would we still get an interference pattern as if we never measured it this is where the quantum eraser comes in so take the delayed choice experiment as we had it before with a splitter and two sensors a and B now let's add two more sensors C and D only C and D are arranged in such a way that the beams get scrambled together and you can't tell which slit the photons went through then put specialized mirrors between a and B so that 50% of the photons bounce and 50% pass through basically making it so that half the photons are measured and the other half are not measured or at least the information of their measurement is lost and sure enough when you look at the photons just went to C or D you got Anna Faris pattern even though it was measured and erased after the in tango particle hit the back screen this is crazy it's like where the particle ends up determines the path that it took to get there it's like effect determining cause in classical physics an object's destination is determined by its initial conditions its position its velocity its direction that kind of thing that's what sets the path in quantum physics it seems to work backwards it's the closing of that wavefunction the collapsing of the wavefunction that the destination that it ends up at that seems to set the entire path of the particle this experiment known as the delayed choice quantum eraser is one of the biggest headaches in physics because it seems to indicate both nonlocality and non temporality nonlocality because the entangled photons effect each other across space and non temporality because they seem to affect each other across time some of the greatest minds in history are struggling to this day to reconcile this including those who rely on pilot wave theory but even pilot wave theory relies on hidden variables to work hidden variables are almost like cheats but not really it's like they take a look at the math around all this and they say well you know if you add this equation or this algorithm right here then the whole thing works so let's just call that a constant and add that into all of our equations and we're good to go but then we're like yeah but what's causing the constant or maybe it's more like the theory that there's a planet nine out there in our solar system because they're disturbances in the orbits of the outer planets and there's a series of comets that seem to all be on a similar trajectory and the only way that really makes sense is if you insert some kind of planet or some very large masked object out there you insert that it all works and maybe someday we'll find that ninth planet maybe someday we'll discover this constant but outside of things like pilot-wave theory the best anybody can seem to come up with is just to say you know they're just different rules in that world and that of course leads back to the big fundamental question of physics how do we reconcile the relativistic world that we live in with the quantum mechanical world that comprises the atoms makes up everything in this world two different realities with a completely different set of rules coexisting in the same reality and even relying on each other somehow it's enough to make you say now there have been plenty of theories of everything out there some of which I've talked on this channel I'll put links to others down in the description but none of them have been unequivocally proven but until we find that theory of everything let's try not to fall into that trap of inserting magical stuff into the gaps of our knowledge I get it it's it's easy it's clean feels good it's just not science and if there is a theory of everything out there it has managed to keep itself secret from us from the 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Channel: Joe Scott

Views: 650,146

Rating: 4.9274755 out of 5

Keywords: answers with joe, double slit experiment, quantum physics, richard feynman, neils bohr, quantum entanglement, which way experiment, delayed choice experiment, delayed choice quantum eraser, quantum mechanics

Id: spKlpexL_Hg

Length: 16min 32sec (992 seconds)

Published: Mon Nov 25 2019