What is Schrödinger's Cat? | Neil deGrasse Tyson Explains...

Transcript

[Music] so chuck i never give you a chance to ask me a question for one of our explainers anything been eating you lately well i mean since since you asked how about because this is something you hear all the time especially in jokes believe it or not really sh yeah schrodinger's cat wait you have a quantum division of the joke department well i don't think that the comedians know what schrodinger's cat is but it's such a uh it's such a ubiquitous reference yeah that they make reference to it a lot of times it's intercultural it's interesting it has interculture i don't know why they don't call it schrodinger's dog okay all right so all right so it dates back to irwin schrodinger uh who irin yes and he was a physicist right they're all one nobel prize is all these people who contributed to our understanding of the quantum right and quantum mechanics is what it's officially called but i like just calling it quantum physics because it's an entire branch of physics that deals with the small small things in the universe uh all that so you do sweat the small stuff yes you do i see precisely precisely and uh the schrodinger's cat relates a little bit to what people have called the observer effect okay where if you observe something you change it so i can respond to both of those in the same in the same pop if you allow me okay so let's do the observer effect for the moment so it's unfortunate that somebody called it the observer effect because then new age folk and other people who were basically scientifically illiterate were thinking it's your consciousness that affects what you're observing and oh my gosh there's a consciousness field and they go running off in a you know off the cliff see what you don't understand is that like particles are totally alive okay and the reason why there is a collective consciousness in the universe is because like all of these particles that are spinning what they're actually doing is conducting thought and consciousness they're thinking they're things they're thinking man rocks think trees think more than rocks right so let me let me cut through all of that and simply say that you're sitting there and i can see you because in fact you're illuminated by if not sunlight through an open window an uncurtained window but artificial light within the room all right that light hits your face bounces off your face goes through the computing system and i see you okay that light carries energy every photon of light that strikes your face carries energy and then they they most of them reflect others uh get absorbed actually depends on how dark your skin is it's getting very dark it'll absorb most of them if you have that because you know photons they want to be a part of this baby let me give something let me give you guys i see where we're landing [Laughter] yes just to be more precise about chuck's excursion there uh darker skinned people absorb more sunlight than lighter skinned people and it's your albedo it's a it's the percentage of incident energy that you absorb relative to what you reflect very important calculation for the earth because what earth absorbs drives our climate whereas what earth reflects back to space just goes back to space from the sun and so glaciers reflect light cloud tops reflect light oceans reflect light that sort of thing so for climate change to solve it we just need to get a bunch of white people in one place just reflect the light to reduce the do us a favor guys sunbathe everybody just sunbathe right here reflect out the sun okay all right i'm sorry i had to do it man all right don't write don't write don't write but it was good that was that was funny yeah that was a good one yeah i mean if you if the earth is getting hot you just just um increase its albedo to increase the reflectance of it so right yeah so uh instead of chuck's solution everyone could just wear white clothing and that would sure even better right that's [Laughter] so so here's the thing if i made you tinier and tinier and tinier right so you're no longer a macroscopic human you're a microscopic particle there's a particle size below which when you open the curtains and shine light on you that light will hit you and pop you into another location so i'm smaller than the photon then what the your whatever your your capacity to move to a different state of existence that the energy that that is required to make that happen correct energy the same as the energy of the light that's hitting you gotcha so you hit me with in order in order to see you right and then you pop somewhere else and i say where'd you go right what are you doing so am i there am i not there well we'll never really know because you're hitting me with something that makes me not there once you're exposing me to it correct and and since it happens on the moment you're exposed not the moment i see you right i will never know what you were doing exactly okay if you're small enough for that light energy to to affect you in that way so that's why we don't think about this in everyday life because we're too big for light to pop us into other states of existence exactly but particles electrons atoms nuke all of this it happens all the time and this was a very disturbing discovery in the 1920s we're in the centennial decade of the discovery of quantum physics in the 1920s because you discover this i want to see what you're doing oh my gosh you're not going to let me see what you're doing because the light i shine on you in order to see it is so so it's really uh it's not so much an observer effect it's a measurement effect exactly okay get the human brain out it's just the device to measure you you you can't know it okay right so so let's get on to so it has nothing to do with consciousness so let's get on to schrodinger's cat by the way it's from an era where people spoke lightly of doing bad things to cats okay oh no peter you know yeah but peter wasn't around so so i'm a little disturbed that they picked cats right they could have picked dogs they could have put worms but cats are lovable and they'll fit in a box right um and so because cat house cats don't come as large as house dogs do just think that through right can you imagine yeah a box for a dog is called your living room right so here's what happens you say to yourself um you put a cat in a box and if the cat is a quantum cat with two states states of existence it's either dead or alive while it's in the box you have no idea which it is and so the way we describe this in quantum physics if you do the experiments okay so some percentage of the time you open the box the cat will be alive others the cat will be dead and so you what we say is that the the cat's existence is a superposition of being dead and being alive i gotcha it's a superposition of those two states because it's in the box it's in the box and you're not looking at it and you're not looking at it and that's why the superposition exists correct and it's a quantum cat not a microscope it's not a it's not a it's not maru the internet cat that people love to see jump out of a box okay all right it's a hypothetical quantum cat by the way do you know cats on the internet uh took a steep rise the same year the cats on broadway closed the music really yes check your data on that that is a weird little so we need somebody we need somebody to investigate that because where did those cats go is what so it was like 1990 you know early internet you know uh and cats closes on broadway and so i think people needed their cat fix and they landed on the internet but anyhow so here we go now the superposition the details of that experiment are a more intricate thing than what i'm describing to you because what they wanted was to have like a something that's radioactive that would decay and then that would then trigger a gate that would open the box you know it's a little more rube goldbergian than what i'm describing but just to be clear if you don't look in the box you do not know if the cat is alive or dead so the schrodinger's cat is you're talking about something that you don't know about until you actually investigate it and then you'll end up the movie seven i didn't see that that was a movie that came out many years ago with morgan freeman and the beautiful man i forget his name oh god he's uh he did 12 monkeys he's done uh thelma and louise what's his name brad pitt thank you brad pitt of course brad pitt so brad pitt is stalking a serial killer who is looking who is using the seven deadly sins to kill people long story short the last murder he puts the head of someone in the box and brad pitt wants to know what's in the box and morgan freeman says don't look in the box there's no reason for you to look in this box and brad pitt goes what's in the box because he knows that it's his wife's head that is completely morbid like what what i don't know but it's perfect it should be called schrodinger's cat it should be called brad piff's white's wife's head and chuck that is the most morbid analogy to this example i have ever heard oh oh cause a dead cat is perfectly fine oh no okay so so this actually in a way applies to quantum computing which you might have heard snippets about or at least bits of headlines that are uh making the news so if you think of regular computing is like a zeros and ones bits right and all calculations are done in this way well quantum computing the i a bit a quantum bit otherwise known as a qubit can be either a zero or a one or anything in between okay it could be eighty percent one twenty percent zero fifty fifty eighty percent zero twenty percent one or anything on that continuum and so so the qubit has more computational versatility than a regular bit that can only be either a zero or a one and and the and the when i say you can be anywhere between a zero or one statistically you can have that bit represent eighty 80 ones 20 zeros uh 50 it can be any combination of those two in the service of the programming that you're introducing to the computer so all of that schrodinger's cat your dead wife's head in a box right from this morbid movie that now i'm never going to see um you were so excited about it too because it's so much better than schroedinger's cat okay it actually represents something that is consequential that you know i mean never mind it doesn't really make a difference [Music] it's i mean it doesn't make any difference once you're in the quantum it doesn't make a difference but it's just a much cooler reference right right because it's not a quantum head it's not a quantum head so it doesn't make a difference you know once you're in the quantum it's not a it's not a cat it's a quantum cat and it's not a head it's a quantum head so all right i see what you're saying it was never really a cat to begin with right it was a fictional quantum cat and the same way it's a it's a quantum head exactly exactly the world according to chuck that's so funny you're like chuck uh go have another bowl and get back to me so chuck there it is that's like you know schrodinger's cat 101. he could have should call it schronger's coin is it heads or tails right right exactly it's just is this is the quantum state only have two possibilities right in that description and so once you open the box and and thereby gain access to information that is otherwise hidden from any observer or any uh device that would make the measurement coin is actually the best representation since if it's a superposition like we said or like you said like i said right please look at me look at me taking credit for quantum discoveries however that means it's always a probability so probability correct it's always a probability so that means quantum coin is actually you came up with the best one why why you got to do that why you got to best me i come up with a head in the box and then you still got it you still got to outdo me really we our fans with a head in a box version of this i'm sorry and just to be clear the the quantum state doesn't have to be one or the other right it depends on the atom and or the circumstances but it can be any number of different states that each have a probability of being true exactly and in fact the wave function of the particle extends outside of the box oh so the probability dropped rapidly across the border of the box but it still exists in a little bit outside the box so what's inside the box has a probability of spontaneously disappearing from inside the box and appearing outside the box that's called tunneling and it does that instantaneously like faster than the speed of light another spooky freaky thing in quantum physics and that relates in part to quantum entanglement because you can have two different particles whose wave functions interact on a way that where you do something that one particle the other one knows about it instantly because their wave functions communicate this is quantum 101 it's like fun parts of quantum that is crazy so we should do a lot of these about quantum physics this was like an overview i could spend a whole explainer on each one of these things because this is the decade in the 1920s was a watershed decade in physics where hubble discovers that we that the milky way is not the only galaxy there are other island universes they were called um in andromeda is another galaxy containing 400 billion stars and four year three years later in 1929 he discovered that the universe is expanding and we apply einstein's relativity to show that we've got possibly a big bang which would later would make 50 years before we had the supporting data and most of what we now know understand and love about quantum physics was discovered in the 1920s and we knew all of that before the neutron was discovered and before texas instrument actually made a calculator uh yeah [Laughter] and why is that because that means these guys had to work that math oh i should just say okay before anybody made a calculator right right exactly uh exactly by the way i had a friend who had the very first texas instrument scientific calculator and he knew it was the first because it didn't even have a model number on it wow it predated model it would ultimately become the ti-35 but we i remember we all crowded around it staring at it it was one of those moments that you never forget okay i just love the visual of a bunch of nerds cradling around and then you know you think they're looking at a magazine or something and then you part the ways and they're all around a calculator like whoa look at that can you believe this thing welcome to the geek verse the cosine do the cosine again now i'm a tangent man myself [Laughter] so i chuck we got to call it quits there all right we ran over the clock on this one but quantum physics deserved a few extra minutes we gave it i think absolutely all right all right till next time this has been a star talk explainer just for you neil degrasse tyson keep looking up [Music]