Why Everything You Thought You Knew About Quantum Physics is Different - with Philip Ball

we'll just get that combination. Any other combination of currencies other than both. Putting in 2 pounds will produce 2 rabbits or 2 dogs. I'm just stipulating these rules now I want to know what the inputs are and we have to be. to satisfy you, a pound analysis produces a rabbit, okay, a pound in Bob produces what well, let's think about that, in fact, we have a lot of these answers, so we already know, okay, the pound analysis box Alice produces a rabbit, okay. Well, if you think about it, that means that whatever Bob puts in a pound or two pounds has to produce a rabbit because he could only produce a dog if they both put in two pounds, that's one of our rules, that It is the second. govern so that we

thought

I already had all the rules, all we need to know now is what happens when Alice puts down two pounds.

Well, we know that if Alice puts in two pounds and Bob puts in if Alice puts in two pounds and Bob puts in two. pounds we know we have to have a dog and a rabbit, okay, that's our third rule, that means if I put in two pounds, Bob puts in and two pounds we get a dog, that also means that you know that in this case we will also have a dog. Alice puts in two pounds, she gives you a dog, okay, the problem here is that this doesn't work because we're not meant to have a dog and a rabbit in this top case, only in the bottom case, where they both put in two pounds. so one is wrong now, what it was, what it means is that we can only follow those rules three out of four times, we get a 75% success rate, maybe we can do better, no matter how much you try to juggle and see If there is If there is any other combination that works, you will see that it does not.

This is the best you can do. You can only follow these rules three out of four times. Okay, but what if Alice and Bob's boxes could change? They are out, but depending on what. the other position, then it's a

different

matter, you know, then we could say maybe Bob from Alice. Alice's box gives a dog when Bob puts in two pounds, but a rabbit when Bob puts in a pound, well, that could work, so the thing is that we have to know what one has put in before the other box, plus what is going to output, so we need to have some communication between the boxes, so we need to connect them and they will send a signal between them and then us. you can do better, well okay, but this signal has to travel through the wire and it can only do that at the speed of light, okay if they are here, that takes virtually no time, but it takes some time and in In fact, even at the speed of light, if Alice's box is here and Bob's box is in, say, Fiji, on the other side of the world, it takes a tenth of a second for the signal to travel there, so so we have to wait that long before Bob puts on. on his coin um his before Alex puts his coin in any direction we do so we can't do any better than this instantly if Baba now puts on his coins instantly so we're kind of stuck you know ?

This communication will not work if we look for how to solve this problem instantly. However, these are classic boxes. Now what if they are

quantum

boxes? Well, then we can do better because it turns out that the rules of

quantum

mechanics allow us what seems like a kind of communication between the boxes that happens instantaneously and that would allow the boxes to share information with each other without any physical connection between them. I'm going to say something more about this quantum effect that allows us to do this, just take my word for it the moment quantum mechanics allows us to do it well, then we can do it better, then what Bob puts in his box can instantly seem affect what Alice puts in her box and then we can, we can, we can do it better, it does too. that means then that we can satisfy these rules all the time, we can actually calculate using quantum mechanics how well we can do it in that case and it turns out that if your quantum box is that we can't get a 100% success rate, we can get precisely well, not exactly, an approximate success rate of 85 percent using this quantum, which looks like communication between the boxes.

Now, what I just told you about this mysterious quantum bond is the quantum phenomenon called entanglement and I wanted to do it without any mass, without any Schrodinger equation. and wave-particle duality even without particles just with Sylvanian x' okay, I'm into what's going on here because doesn't Einstein's theory of special relativity say that you can't send signals faster than light? The speed of light is the maximum. cosmic time speed limit, well that's true, but what's happening here is that Alice and Bob can't actually verify that they have this eighty-five percent success rate without exchanging information about how their box is produced and the only way they can do that is by communicating with each other in some normal way by email, by carrier pigeon, by letter, whatever it is, however they do it, they can't do it faster than light and it turns out that in reality this is what special relativity prohibits.

I can't verify that you have this faster than light success rate and what that effectively means is that Alice and Bob can't use this quantum entanglement to send information to each other faster than light, which turns out to be fine. With special relativity, well entanglement was discovered in 1935 by Albert Einstein and two younger colleagues named Boris Podolsky and Nathan Rosen, who were perhaps ironically trying to show that, in their view, quantum mechanics had a flaw. , so Einstein Podolsky and Rosen came up with an idea. experiment that they believed revealed a deep paradox at the heart of quantum theory and that could only be resolved by adding something else to it and this

thought

experiment was later reformed brilliantly and clearly by physicist David Bohm and that's the way I'm going to talk now and what Bohm imagined was something like this: you have a box that spits out two particles in opposite directions and they are entangled with each other, the way they are produced means that they are entangled, what that means is that there is some relationship. between the properties of one and the properties of another and that's thinking in terms of spins so that you can entangle them in such a way that if the spin of one of these particles is up, the other one has to be down, okay? and then if So if we do a measurement on one of them, when we see that it has an up spin, we know that the other one will have a down spin, so now they're correlated, maybe you can see that this is a little bit like these two paintings. here, but in the sense that the measurement here plays the same role as when I put coins and what we see going up or down is a binary choice, like getting a rabbit and a dog, so this was really an experiment of entanglement.

This correlation may seem unremarkable to you because you might say, well, we could do this with a pair of gloves, say a left-handed glove and a right-handed glove, we could send one to Alice in Melbourne or something and one to Bob, you know in in Shepherds Bush and then as soon as Bob opens his package and sees that he has a left-handed glove he instantly knows that Alice has a right-handed glove and he instantly knows that that must be true because they started out as a pair so what happens? Well, here's the big problem, according to the Copenhagen interpretation, the direction of these up or down spins for these two entangled particles, unlike the direction of those two gloves, is not actually determined until we observe them until that we make a measurement and if that is Then this experiment from our Podolsky and Rosen Entertainment seems to be saying that making a measurement of one particle somehow instantly fixes the other, as if the result of that measurement is eerily communicated to the another particle instantly.

This is what Einstein called creepy. action at a distance and again said that it can't be right because special relativity seems to prohibit it. For a long time no one really

knew

how to solve this paradox. Do you know what the error in the reasoning is or what the problem is? The problem was, or maybe Einstein, Podolsky and Rosen were right, no one

knew

what to do with it and it was swept under the rug, which changed in 1964 when an Irish physicist named John Bell, whose day job was something like the John, I guess, was a particle physicist at CERN in Geneva, but in his spare time he turned around the Quantic annex and here before reformulated the Einstein-Podolsky-Rosen experiment in a way that showed how a measurement could be made to try to figure out what was going on here in In fact, what he drew on the board is basically a diagram of the experiment that he thought of and this experiment, this procedure is a little bit analogous to these black boxes here because what John Bell basically showed was that if you make some measurements and you find that there is a certain amount of correlation, in fact, in your case again, a 75% correlation, then you know that the rules seem to be obeyed 75% of the time, then it shows that you have something like classical

physics

or, in fact, something like that. like what Einstein Podolsky and Rosen thought, which was basically saying that those spins must have been fixed all along in some way by some variable that is hidden that we can't see and we can't measure, that's fine, but if you get a better correlation than that between the two spins, if you obtain this 85% that quantum mechanics predicts, then Einstein's image does not hold true.

Quantum mechanics must be right. You should get this weird thing that looks like communication and well, these experiments were done, they were first done in the 1970s. they were first done with a little more rigor in the 1980s, after having been done countless times since that every time they found the same clear result that quantum mechanics is correct, you get a better correlation than any kind of classical

physics

or any kind of Einstein hidden variable picture. So entanglement really happens, but what was wrong then with Einstein's reasoning in this experiment? Well, he made a perfectly reasonable assumption, so reasonable that we didn't even realize it wasn't an assumption that we can call locality the idea that the properties of a particle of an object located in that object, I mean, is logical that its blackness is in the robot, what would it mean to say that the blackness of this box is also partially in this box, but in quantum mechanics I seem to have to say things like that, it seems that the properties of quantum objects when they are entangled can be non-local and only if we assume that this locality assumption is that

everything

that has to do with this object is fixed. here in this location it is only under that assumption that we have to start thinking about spooky actions at a distance and this kind of instantaneous effect through space, what quantum mechanics really tells us is that there is something else, something loosely called non-quantum locality. which means that there is a kind of mixture of these two things that is very difficult to put into words, but it means that there is a non-local influence that means that, in effect, we can no longer think of these two boxes as separate objects, that It is what is intertwined. it means that they have somehow become part of the same quantum entity, so quantum nonlocality is not spooky action at a distance, it is the alternative to the spooky action or distance now, when you made dinner when you saw what Einstein Podolsky and Rosen had said that he recognized this Montague phenomenon at the seventh angle, which was quite central to what quantum mechanics was really about and, in fact, entanglement is what happens all the time when any quantum particle interacts with any other, they have to be entangled, that's the only thing that can This happens according to quantum physics and what this means is that when a quantum object begins to interact with its environment, you could say its quantum, or you could say that if it is in an overlay, your overlay begins to extend into the environment and becomes harder to see. that quantity, that superimposition on the original object itself, spreads like a drop spreading in water and what that effectively means is that the quantity begins to disappear, this entanglement leads to a loss, technically the word is a decoherence of quantum properties and that seems to be what ultimately leads to quantum objects behaving like classical objects when they start interacting with their environment, so what that really tells us and what we can say now is that there is no situation weird thing where little things like atoms obey quantum rules and then for some reason big things like semi-classical rules are just

different

things, actually now we can say that this is what quantum mechanics looks like when you're 6 feet tall, that the weirdness we have that is talked about in quantum mechanics is simply the way in whichhow the world works and in fact, you know it's a little strange for us because when quantum mechanics gets to this scale, it looks different than it does when you talk about photons. and electrons why quantum mechanics only allows us 85% success why it doesn't allow us 100% Well, it turns out the answer really is about how efficiently these boxes can share that information about, in this case, which Queen he put himself in them.

It's about the efficiency of information sharing, if we can make use of quantum entanglement then we can improve the efficiency with which information is shared between quantum objects like qubits and that's really how quantum computing gets its power from sharing information. information more efficiently between the different bits of the system that we can use when we use classical bits like the small transistors in laptops and what it also tells us is that what makes quantum mechanics quantum at its root really has nothing to do with the notions of wave functions. and maybe and particle wave-particle duality is really about what you can and can't do with information.

Let me give you an idea of ​​where that takes us because it means that some researchers feel that we could rebuild quantum mechanics from scratch. getting rid of things like the Schrodinger equation of waves and particles, but just using some simple axioms about what is and is not allowed with information, how it can be encoded, transferred, shared and read. I want to give you just a taste of one of these that are now called quantum reconstructions this is one there are many this is one suggested in 2009 by Borya vade deca CH and cassava Bruckner at the university of Vienna and they proposed three what they said were reasonable axioms from which we could try to construct quantum mechanics, so here they are, they probably don't seem that reasonable or even that necessarily intelligible to you, but I'll just briefly say what they mean: information capacity was the first thing they said.

Suppose that all the things, all the basic entities, whatever they are, that make up the world, can encode only one bit of information. They're like those spins, they can just be up or down and that's it, that's all they can hold. Suppose also that they now call this assumption a locality. It's a little confusing because I just talked to you about quantum nonlocality, but in this case locality. means something a little different, what it really means is that there is nothing hidden behind the scenes that allows things to be done with information, there is no secret device underneath what you know here that allows these boxes to communicate and lastly , this about reversing this idea. of reversibility, they said, suppose these bits you can know contain just one bit of information, they can be reversibly interconverted, you can go from one to zero, from a spin up to a spin down and vice versa, okay, they said which showed that with just these three rules about what you can do with the information that guides you, you get two possible types of physics, one is classical physics and the other is quantum physics, but only these rules, what's more , if you modify this third axiom a little bit to let's say that to do this reversible type of spin change, suppose you can do it continuously, you can continuously rotate or spin up to one spin down, it's okay if you assume that you get quantum rules If you assume it has to be just one or the other without this kind of continuous rotation, so it's like flipping a coin heads or tails, once it's down there they go heads or tails and you can't interconvert them, so you get the classic rules , Well. find that kind of extraordinary, you can get so much out of what seemed so little and the point about these axioms about information is that they can by themselves lead to what appears to be quantum behavior and

everything

that we get from quantum mechanics as superpositions and entanglements and some researchers think that these reconstructions could lead us to a completely different perspective on quantum theory, perhaps one in which the physical meaning of all this seemingly strange behavior is clear - well, that remains to be seen, but it What is already illuminating is how they focus. in this question of information about how the answers or the results of measurements depend on the questions we ask, just as the result of these brats is what comes out of these boxes, it depends on what we put in a pound or two pounds and I think that this is the most productive way to think about quantum mechanics and there is a very nice metaphor for this perspective that was suggested by John Wheeler and John Wheeler was a study that he studied with Bohr and in fact he had had Fineman as a student and there was this wonderful metaphor for how our answers about reality can emerge from the questions we ask in a perfectly consistent, rule-bound and non-random way, without requiring any pre-existing truth about how things were and whether this is how they work.

It is based on the 20 questions game, so this is the game. I'm sure you all know where you know someone where everyone picks, say, one person, okay, one person leaves the room and everyone else picks one person and then one person has to go back and find out who that person is by asking questions. and they have to be questions that only have a binary answer of yes or no, as you can see, this is actually a quantum game. Well, let's say it plays like this person goes outside, we all decide on one person and well, we'll all know how to do our thing and then the person comes back and starts asking questions and this time the person who came back and you know it starts like this Normally, she says is this person alive or dead and what is not, she should say is this dead person, yes, okay, this person is a man, yes, okay, and so on, except that the interrogator discovers that in actually asks more and more questions. the answer takes longer to come, the person you ask has to think about it for a while before giving the answer, which is a little strange because you know that surely one thing and the other is true, why do you have to think about that ? anyway the game continues and finally she thinks she's getting closer to who he is and finally says I know it's Richard Fineman and everyone says yes it's Richard Fineman and everyone laughs and the game ends why did it take you so long time?

They already know each other. At which point I was asking more and more questions - - to answer and they all explained that they had played the game a little differently they decided that they weren't going to settle on one person, they were just going to make sure that any answer from each The individual they given when asked was consistent with all the other answers in applying at least to someone, ideally someone, someone famous, so as soon as the first question you know is that this person is dead was answered yes, all of the answers from the other people had to be consistent. so it had to be a dead person they were thinking about and then it had to be a dead man they were thinking about and so on, but the first person could equally have said no to that first question and then it would have converged on another person who wasn't. was Richard Fineman, so the options became more and more limited as the questions went on and it took more and more time to figure out who it is until it will work, who will be consistent with all of these answers so far and everyone was forced. by the nature of the questions to converge on the same person, if you asked different questions you would have ended up with a different answer, so context mattered, there was never a predetermined answer, you created it in another way that was totally consistent with all the questions you asked, what's more, the very notion of there being an answer only makes sense when you're playing, it doesn't make sense to ask who the chosen person is in that situation without asking questions about them, and quantum mechanics is a bit of a theory.

In this way I think about what is and what is not knowable and how those knowledges relate and how they emerge from the questions that we ask and I would like to think about this in terms of a distinction between a theory of business and a theory. from Ethne s: Quantum mechanics does not tell us how a thing is, it tells us what it could be and this is crucial along with a logic of the relationships between those codes and the probability that it could be so if this then that and what this What it means is that to truly describe the features of quantum mechanics as far as is possible at the moment, I think we should replace all the conventional isms of quantum mechanics that I started with at the beginning with statements, e.g., I didn't say here that is a particle, there it is a wave, rather we should say that if we measure things like this, then the quantum object behaves in a way that we associate with particles, but if we measure it like this it behaves in a way that is like a wave, We shouldn't say that the particle is in two places at once, we should say that if we measure it, if we measure it, we will detect this state with probability is what we have come to associate with science, we are used to science telling us how things are and if that is the case, it is simply because we don't know enough, we are partially ignorant about how things are, but in quantum mechanics it seems that those "ifs" are fundamental, well, fine, but what is Ness about quantum mechanics?

Obviously, it doesn't tell us anything about it and all we have now are clues and guesses and we try to bring them into sharper focus is a complicated task, which I think means that sometimes we have to use an almost poetic level of expression, the kind of thing that will make many physicists run for cover, take this attempt, for example, by physicist Chris Foote, he says that maybe the world is sensitive to our touch, it has a kind of spark that makes it fly in ways it doesn't. they were classically imaginable. The entire structure of quantum mechanics may be nothing more than the optimal method of reasoning and information processing in light of such a fundamental concept. wonderful sensitivity and what people mean here is not the mundane truism that the human observer disturbs the world, but rather they are saying that quantum mechanics may be the machinery that humans need on a scale intermediate between the subatomic and the galactic to attempt to compile and quantify information. about a world that has this incredibly sensitive character, so it embodies what we have learned about how to navigate well in a place like this, in any case, I think it is vital that we understand that this, if not, does not imply that the world, our world, ours. the home is hiding something from us it's just that classical physics has prepared us to expect too much from it we have simply become accustomed to asking questions and getting answers getting definitive answers of what color it is how heavy it is how fast it moves forgetting The almost ridiculous amount that we don't know in detail about most things around us, we think we just keep asking questions and getting answers, it had smaller and smaller scales when we discover that we can't, we feel let down by nature and utter It's strange, well, that no longer works.

Nature does the best it can and we need to adjust our expectations. We need to go beyond the strange. Thank you.