So Quantum Mechanics, is the subject of the discussion here tonight. And look it’s the year 2014 And the first glimmers of the Quantum Mechanics really came on the scene on the early part of the 20th Century. Certainly by 1930 or so the basic framework of Quantum Mechanics was place and yet, today right some 80 years later there are still questions at our right for discussion at the foundations of the subject questions that are still controversial, and we’re going to discuss one of those controversial questions here tonight so you’ll see various perspectives on that. At the same time, quantum mechanics of all the subjects of modern physics has really been embraced by the culture of at least the language of QM has been embraced by the culture I mean, just to give a couple examples right it’s there from hollywood, right we have quantum thrillers right we also have, you know, quantum sporting goods right, golf clubs, quantum bowling balls, quantum baseball we’ve got quantum cartoons right “Oh Alice, you’re the one for me” “But Bob, in a Quantum world how can we be sure” and the we have physicist talking dirty right you fiinsh I’m not going, I, I… It’s a family program here right so we also have quantum healthcare right so this one, Quantum herbal canker sore gel, nothing to do with the previous cartoon, completetely seprarate We have the Quantum Pendant, which protects the body against any harmful rays I like this one, we got the QuantumVet right Use your cellphone to instantly diagnose and medically treat your pet at home and I love this tagline that you see at the bottom, Don’t take me to the Vet, use QuantumVet which makes use of the famous of all adages which is a sure fire way to get words to rhyme, is to use the same word [laughter] now this, this one is absolutely my favourite the Quantum Sleeper protection from bio-chemical terrorist attack, kidnappers, stalkers, bullet-proof and look how… look at the loving couple over there about to enter the sarcophagus over there right so, so QM in this sense is certanly out there in the world but of course, this is just a word quantum is this really quantum bullshit right so, um, we’re gonna talk about here tonight is the real Quantum Mechanics and what I’m going to do here for just about 10-12 minutes is run through the basic ideas of Quantum Mechanics again I think that it’s probably familiar to many of you but just to make sure we’re all on the same page and that’ll actually lead us into the issue for tonight’s discussion which is this quantum measurement problem okay so for the basic premier on Quantum Mechanics the key experiment that really gets the ideas of Quantum Mechanics across is the Double Slit Experiment and I don’t know if any of you go to Spooky Action last year just by any chance. Yeah, so a handful of you so you may recall that we actually did the Double Slit Experiment on the stage last year we’re not going to do it again this year we don’t have enough time rather these animations will give you the essential ideas and if anyone doesn’t believe the animations, just ask someone whose hand was up cause they saw the real experiment done last year OK. So, what is a Double Slit Experiment the idea is this imagine that I have a gun that’s firing ordinary pellets like BBs at a barrier that has two openings now you’d expect that those BBs that’d go thru the left slit will land aligned in a band on the left those pellets that go thru the right opening will land in a band aligned with it on the right and indeed we’re to do this experiment that is the result you’d find now, what we’re going to do is imagine dialling down the size of those pellets, those BBs making them smaller and smaller until they are the size of little tiny particles, let’s just call them, electrons imagine we’re doing this with electrons you would expect that if you ran the same experiment again those electrons that pass through the left opening will land in a band and aligned with the opening on the left and similarly, for those that pass through the right that is what you would expect should happen and the thing is, many of you are familar, this is not what happens when you do this experiment instead if you do this experiment you get results that look rather different they look like this you get a bright band next to a dark region next to a bright region next to a dark region next to a bright region and so forth and that data, that strange data is really what impels us towards now that data is strange because it’s not what we’d think should happen we expect to get two bands and we get more but it turns out that that pattern bright, dark bright, dark is a familiar pattern to most physicist and we’re trained from birth to recognise that pattern right if you’re to go to any physicist, 3’o clock in the moring shake that physicist, wake them up, and tell them “I got this data, bright band, dark band, bright band, dark band ” The very first thing they would say to you is, “What the hell are you doing in my room at 3 o’clock in the morning” [laughter] But after that, they would say, “I know what that is, that’s an interference pattern” that is the hallmark signature that there is some kind of wave phenomenon Some kind of wave phenomenon taking place right to understand that, let me just give you a little visual here, where we are looking at water waves Imagine I throw 2 pebbles The first one over here it makes these circular ripples, and now I throw in a second one… and look what happens when the waves overlap, in some regions they work together, but in other regions, the peak of one wave is crossing the trough of another causing the wave to cancel out, and those are those dark regions that you see on the screen So this is exactly the kind of data that we are encountering, and to make that point a little more clearly. Let me show you an animation, same idea Imagine you got water waves going toward the barrier with the two openings and again regions where the waves work together the water is very agitated regions in between, where the peak of one wave crosses the trough of the other they cancel each other out, and if on the back screen I put bright regions associated with very agitated water, Dark regions with not agitated water Look what I get, Bright Dark Bright Dark Bright Dark and again, just to remember that is the data that we find in this experiment So this suggests, that there is some deep connection between these particles, these electrons and this other idea, a completely separate idea, of waves Now, at first sight, that might not seem all that surprising Right? Because water has water waves, but we all know that water is itself made of little particles, molecules, H2O molecules So certainly we know, if a large collection of molecules, behave in a choreographed manner those particles can yield a wave. So maybe what’s going on in the experiment is just that, you’ve got a lot of electrons and maybe they are behaving in a choreographed manner and in that way, yielding a wave just like H2O molecules yield a water wave. Now how would you test that idea? Well you could run this very experiment But only firing particle by single particle at this barrier with the 2 openings. and by recording dot by single dot where each of those single particles lands on the detector screen So let’s run that version of the experiment and see what happens. So again, Particle by single particle, we’re recording on the back screen the history of all the landing locations. And this is what happens in this experiment. Dot by single dot, we build up the same pattern, the same interference pattern, the same data. That suggests to us That there must be some kind of wave like phenomenon involved to yield this interference pattern. So this is where things get really strange. Particles, electrons little tiny dot. That is the image that we always have in mind. Waves are these spread out entities. How could a dot particle and a spread out wave somehow be connected And this was the puzzle that physicist faced In the early decades of the 20th century And many tried to figure out what could the connection between a particle and a wave be. The natural suggestion that you might throw out as you know maybe particles somehow are kind of …kind of smeared out in some way there are kind of spread out the way we didn’t realize that deal out it doesn’t really work. Because whenever you measure an electron you find all of it if it was truly smeared out. You find a piece of it here and a piece of it there And the idea ultimately was settled out the part came from the mind of the physicist–Max Born. without the way they think about the wave associated with the particle is this . This is a new idea. The wave is a wave of probability. The wave is telling us the likelihood of the probability that the particles at one location or another. They show you a little visual of that. Imagine this is the wave associated with a particle like an electron. Where the wave is big, that is a likely location to find the particle. Where the wave is small, an unlikely location. Where the wave is absolutely zero, that is the place where you simply will not find electron at all. That’s the picture that comes forward. Now how would you test this idea to see if it’s actually describing reality how the world works. For the first thing is you need some kind of mathematics equation that allows you to understand how this wave evolved how it changes over time. And that equation came to us from over Schrodinger. Whether you understand the mathematics symbol or not, it doesn’t matter.But it is good to see that there is a bona fide rigorous mathematical equation behind all of the imagery that you will be see here tonight. That is the equation that describes how this wave this probability wave evolves over time. That’s step one. So now you understand how things change in time. But the test is while you said yourself this look.Yep. At a given moment in time, I’ve got this probability profile for where a particle should be located. where I tested it, I run experiments of searching for the particles over and over again in identically prepared situations. And I count the number of the times that I found it in one of the location or another. And if the theory is correct, you should find the particles more often where the wave is big, and the less often where the wave is small. Qubism. So we’ve heard this word a few times mentioned. Ruger tell us what this approach is about. OK. I brought a Quantum System to experiment on So I just flip this Quantum System Ok, what is the probability of “heads”? 100 % by the “many worlds” approach. Sorry. I will play along. 50%. Stick with a 100% So, I have 0 %. My point being the probability, you have a different one from me. So this is actually about you, it is not about me. So the probability actually is your belief or my belief about what you will see if I show it to you. I can show it to you, you see. He’s right. So, probability in this is used in ??? ??? probability theory which actually is a model on full account probability which is used in widely in Statistic Economics in some parts of physics So, this is a respected and very useful and I believe is the only really fully consistent approach of probability. Probability is a believe of what you will experience of what you will see. Now Qubism says that, you do not need to modify the probability of Quantum Mechanics. So, even Quantum Mechanics Probabilites are personal degrees of belief So the probability ??? a measurement outcome is my expectation of what I will experience from the experiment The point is the Probability is not a property of the coin in my hand, the Probability is actually my belief. Now, Quantum States, are equivalent to probabilites. Quantum States determine probabilities of outcomes Quantum States are fully mathematical equivalant to probability distributions. So in that sense, Probabilities are an experiment on agent’s expectations Quantum States encode an experiment on Agent’s expectations for experimental outcome. Now, what this says about the measurement problem is it just dissolves. Exactly, I experience an outcome and I update my own expectations for the future. This forth approach is the dart is going and the idea is if we are not looking if we are not actually yet doing the observation there is nothing really we can say until the observer looks, so if we bring our observer and then you look, you take in the observation, you update your understanding of the world based on your observation. In science, what are we doing? We are making predictions and we test this predictions in experiments So this is really what Qubism talks about Quantum Mechanics, this must be the reason that most physicists are not interested in the potential of Quantum Mechanics. because Quantum Mechanics is a tool they can use for predictions, to design experiments to build machines, Quantum Mechanics has transformed the world in a way that is unprecedented In all these experiments, experimental designs, predictions, including cosmological predictions You never actually need to talk about hidden variables or spontaneous collapse You just apply Quantum Mechanics as a tool to make predictions And that works, and this must be one of the reasons physicists are not interested in the interpretation of Quantum Mechanics. When you look at Cosmology, what do you base Cosmology on You base it on what you observe or experience now What are the Cosmological predictions or your conclusions you draw, well they are about your future experience You will never stop at just saying “Oh well, I have explained all things I know because So, even Cosmology is about taking your present and the few past experiences and Using the Theory, using Quantum Mechanics as you know it to make predictions about future experiences. In your approach the spookiness evaporates if I understand it, can you describe to us where it goes. In the Qubist approach these correlations,, this situation is very much like ???’s socks. He used to wear different color socks and when his colleague so him coming in, when he saw one foot, one sock, he knew immediately what the color of the other sock would be, namely different. Nobody would call that Spooky action at a distance What Qubism says here is, if I have a belief about this is a belief about what I will see experience when I am making the experiment on that particle here. What happens is, if I make a measurement on this particle her I see it spins down and then I update my expectation on the other particle here. No, it is always about me and the world because Qubism emphatically says that it is not all about the subject nor is it all about the world. Any measurement is an action, subject and observer, physicist, system take on the world. So measurements are active processes they are actions Any measurement is an action on the world and it needs subject and the object, it needs… is where the experience and the world meet. But that experience is something that the individual ,the observer has,that’s the point ?Yeah good ! So,what do you think ? David ?