Right. Good afternoon. I'd like to talk a little about individuals and interactions over processes and tools. This is a tagline that gets thrown around. It's kind of listed as the first value, first comparative value in the Agile Manifesto. And this is a big question as to what does it really mean because in many cases I find that when people are pursuing Agile, either specifically because they have something in mind or even broadly just we're doing Agile because we feel we ought to because other people are, so not necessarily a good reason. There is a surprising reliance on the second category. For some people Agile development seems to be associated with a very strict interpretation of process. For other people there's a little thought bubble that goes on. They think of the tools. They think of their testing frameworks. They think of their continuous integration frameworks. They tend to associate it with these various mechanical features. Now these are useful. These are good. I'm not going to say they're bad. That's definitely not the idea of the comparative. But there is this question about understanding a little bit more about the individuals and indeed how they interact. So I want to explore that a little bit. I guess a brief bio. My brief bio is I'm Kevin Henney and I walk around the stage a lot so I'm moving this out of the way because otherwise there will be damage to me and this. Right. And my back, that's just done the right thing. Okay. So I've been involved in software type stuff. Probably the most relevant things here are a long term interest in patterns and the relationship that patterns have not simply to design but the way that people reason, discuss and view and frame problems and their solutions. And curiously enough this crowd source open source book 97 things every programmer should know which as the editor I managed using everything I'd learned from agile development. How do you get a bunch of disparate volunteers who've never met one another to contribute and write well. This is an interesting problem. And it turns out that a number of the techniques that I learned were very relevant to this. However, let's go back to this which I hopefully has everybody has good site recognition of understands the message. But that first one individuals and interactions. We have to appreciate the relationship between these people, the tools that we're talking about, particularly when we push really, really hard. I had a chat with Brian Marrick, one of the original segmentaries a few years ago. He made a point and I think he made it again in a blog or elsewhere that he felt that the first one value should with hindsight have emphasized teams more. I'm going to come out and say I know what you're saying but I disagree. Because teams are made up of people. And that's where teams come from. They come from individuals and interactions. And whilst we do value the team, unless you understand why a team is a team and why things that aren't teams are not teams, you'll be forever perplexed. Individuals and interactions give you dysfunctional teams. Individuals and interactions give you self-organizing teams. They give you all of these. If you don't understand the parts, you have no chance of understanding the whole in this case. So I think the emphasis is correct. But then we are confronted with some things. This is the standard presentation of the scrum process taken from Mike Cohn's site. We've got elements of artefact. We've got elements of time boxing and process. And it's a nice simple picture. It's a very simple picture. That is its value, its simplicity. When people draw pictures that are hard, they tend to turn us off. They tend to lose communication rather than increase it. However, there is clearly more to scrum than just this. If everything was this simple, it would be fantastic. If this is simpler than a clock, a good old-fashioned wind-up clock, people are not this simple. Organizations are not this simple. Products are not this simple. So this is clearly a simplification. We have left something out. And it turns out that scrum is a very interesting game. It's a very challenging game. Let me step outside scrum for a moment and briefly compare it to a game of chess, which is not like scrum at all. I'll come back to that in a moment. Chess is very simple to describe. The rules are very simple. My seven-year-old can play chess. Fortunately, I can still beat him. But that's the point. What makes a great chess player? It's not just the rules. There's clearly something about how you work the rules. It's the spaces between the rules and how you flow through them. And this we see often with scrum, sort of flat scrum, which is the basic interpretation. Here are a set of practices. Here are the artifacts we focus on. Here are the time boxes. Versus the subtlety. And the subtlety will be different in each case. Now, we're then confronted with this rather interesting challenge that there is a certification scheme for scrum. And Mike Cobmire put this rather well. Scrum can't have its cake and eat it, too. It can't be a simple framework that is not prescriptive and then start certifying people on how to do this stuff. There is a contradiction. How can this be true? If all the subtlety is scrum, if scrum provides you with a framework in which you improvise, explore, and do these various things, then clearly the bits between the rules and beyond the rules are immensely subtle and are going to likely be very highly context specific. How do we certify people on that? Certification plays a very particular role. It plays a role not of competence but of guaranteeing a certain level of minimal basic knowledge in a domain. Quite frankly, with scrum, that's one side of A4. Everything you can write down that is consistent and constant. All the other stuff you can fill books with. And that's not two days. It's not three days. It might be three years. It might be three decades. I'm not entirely sure. But it's difficult to certify. It doesn't mean that there's not knowledge to be had, but it's not that kind of knowledge. So clearly we have a little bit of a challenge. Taking it from the source here, Ken Schraber made a very, very good point, which is kind of in contradiction to certification. But the challenge that we face in software development is that we do not undertake defined processes. Actually, that's not strictly true. I'll come back to that in a moment. Defined process control model requires every piece of work to be completely understood. Given a well-defined set of inputs, the same outputs are generated every time. We know this. They're called compilers. I put the same code in. I get the same stuff out. It does the same thing every time. That's a solved problem. The problem is we don't actually know what the inputs are for a software development project. We're not entirely sure of what lies within the box. And we're not entirely sure about the outputs either. It's very not defined. Now, I will say that I did work on a project that could be considered a defined process. But it's worth understanding the conditions under which it operated. First thing, four days long. Not four years, not four months. Second thing, one developer, me. Third thing, strong customer interaction. She was called Yvonne. And she was about that far away from me, where we sat in desks. Probably about 20% of the time spent discussing stuff. Fourth thing is the domain. The problem that was being solved was a defined problem. A lot of GIS data in one format, a desire to have that GIS data in another format. In that four days, the formats did not change. The staffing did not change. Company politics did not change. It was massively defined. It's a very rare occurrence. But you cannot scale that four days to four months. You cannot scale one person to 10. It doesn't work like that. Most of what we undertake in software is not that simple. It is inherently undefined and better tackled through empirical process models. Expect the unexpected. Frequent inspection and adaptation. Keep your eyes on what you're doing. Don't assume you're going to know everything. Whenever you offer something in the true spirit of empiricism, be empirical about stuff. The purpose of a sprint is not the delivery of story points. It's not the delivery of features. That is a purpose, but it's not the purpose. Each sprint offers you a period of time under which you are confirming a hypothesis. And that hypothesis, if you go for traditional scrum where you have a scrum goal, that hypothesis is that you can achieve the goal of the functionality, if you've chosen to split it out into stories. Given what we know, with the people we have, the tools we have, and the time available, we can do this. That's a hypothesis. At the end of two weeks, you get some feedback on that. That hypothesis may be confirmed. It may remain unproven. It may be contradicted. You're then invited to consider, what else might work? Do we need a change of design? Do we need to change of practice? Do we need to back off a little bit from our feature driven or feature obsession? Do we need to redefine our relationship with our customer? And so on. I don't know what the solution is. That's the point. It's not defined. I can't tell you why it is that it didn't quite work out the way you expected or hoped for. But it's not a failure. It's definitely not a failure. Because what you did is you formulate a hypothesis. Now, if scrum projects are run like this, I think I'd hear a lot fewer scrum failures, but most are not run like this. They are run as delivery engines with no sense of confirmation, no sense of observation. The idea we're going to posit something and then seek confirmation through the process. What does it tell us? Does it confirm it? Deny it? Is it neutral on it? So it's an experiential thing. There is this idea that there's a lot of subtlety here, because you can't tell everything in advance. Now, why is scrum and indeed any other agile approach not like chess? And what distinguishes? This is a question I was asked a few years ago, and this is the answer that I offered. What is the difference between approaches that are iterative and or incremental and agile approaches? Haven't we done this all before? I said, I think the difference is not simply the fact that certainly different agile approaches differ in their degree of incrementalism and iteration. It's not so much that they are all based on this to some degree or another. It's this bit, whether or not they're nomic. Now, nomic is a peculiar word. If you've not come across it before, the real reason I put this up. Peter Suba in the 1980s created a game called nomic. And he did this because he wanted to explore something. And he included a very particular rule. The rule is that you can change the rules of the game. One of the rules of the game is you can change the rules of the game. We don't do that with chess. We don't do that with poker. Oh, there are a lot of variants with poker. But for each variant, there's very definitely a set of rules. And when you don't play them, you find out very rapidly. Okay. These games are still complex in one level in terms of the behavior they can create. But they are bounded in a way that constitutions and political systems, legal systems are not. That's what Peter Suba wanted to do. He wanted to explore, just as with a legal system, a legal system can change its own rules for how it interprets its own laws. He wanted to do this. And his original intention, his original intention was that the original nomic you can find the rules online is a very boring game. One of the first things you'll want to do if you play it is change the rules to make it more interesting. So can you see the comparison with Scrum? It's a very boring game. It's really simple. It's a basic idea. It's a starting point. It's a framework. You're not supposed to end up with that. It's a starting point. Your job is to find the game that works best for your product and your team.  In other words, you're not being nomic. So the process involves its own change. That's what makes a thing agile. It's not the speed. It's not the brandings. It's not any of this stuff. It is the fact that it is self-adapting. That's a very important but overlooked element. Now, it turns out that people are part of this. So how are people going to learn? Well, I want to dispel one thing, first of all. This one keeps coming up. It annoys me. Failure is a far better teacher than success. Where was this from? Financial times. So respectable paper. But this is wrong. Failure is a lousy teacher. It's a terrible teacher. It's a shockingly bad teacher. This does not mean that failure does not have a role to play. But as a teacher, I'm not impressed. If you're going to learn a musical instrument, how do you learn a musical instrument? You don't learn just by failing. My older boy, a while back, he was learning the piano. He's now going to learn the guitar. It's quite easy to get things wrong, particularly on a guitar. There are lots of people who can't play the guitar. They fail all the time. Most people who pick up a guitar get taught very badly. There is a way to learn a guitar, a ways to learn a guitar, that are built on success. Failure is only meaningful when it is given a background, a backdrop of success. So the way that, you know, how not to teach a child to play a musical instrument, piano. Here's some sheet music, but I can't read music. It doesn't matter. Just, you know, hit the keys as you see them. Bank wrong. Bank wrong. Bank wrong. Are we learning yet? Bank right. Brilliant. Which one was that? We have no context. We have no meaning there. Now, I can't really play the guitar particularly well, but a couple of times when I've sat down with Stefan with the guitar, one of the things we've done is we've listened to the original piece. Then I've played it through, then he plays it through. He knows what success looks like. He knows what its characteristics are. He knows when he's not doing it. I'm disinclined to call that failure.  That's probably failure, but getting something wrong during practice. I don't think that's failure. And again, I think this is a dramatic word, an overly dramatic word for the simple notion of the nudge that errors can give you, particularly when you have an idea of where it is you know what you want to be. Now, do we have any other sort of observations on this? Well, again, advice that gets peddled. Christopher Walken, great actor, terrible pedagogically. If you want to learn how to build a house, build a house. Don't ask anybody to just build a house. I don't think so. How much complexity is there in a house? How many ways can you get a house wrong? It turns out it's also, it's one of those cases, you built this house yourself.  There is this other thing that also happens when people, when they learn or when they do something themselves and when they are classically self-taught, as in they have had no mentoring, they have not sought advice. The fact is there is a vast body of knowledge out there about house building. It turns out we are not alone. And I'm going to say the same for software development. It turns out that one or two people have done this before. We know stuff. Our challenge is how do we get other people to know it? Not by denial. Of course, this, we have to let people experiment a little bit, but this is not the right kind of experimentation. Building a house, first of all, there are issues of safety critical concerns. You know, is it safe? But there's another thing, something I've noticed. It took me a while to notice. When people are self-taught, without having had any outside input, any form of feedback, any form of guidance, they often pick up some really weird ways of doing things. I think we may have all seen this in code somewhere. We may all know the person's name. They pick up really weird way of doing stuff. And they often say, well, you know, it works for me. It's how I do it. It's part of their personal style. In other words, that becomes part of their personality. It's part of the way they do it, her style. I'm kind of breaking away from the mainstream and all those boring standardized doors. What happens is you become attached to your mistakes. They become part of your expression. You are reluctant to give them up. So I find this a little bit concerning that we have, as a profession, we spend a lot of time being concerned about the propagation of knowledge. And then, I'm citing Christopher Walken, who is an actor and not a software developer, because somebody tweeted this a couple of years ago, somebody I respect very much, as a software developer. And I said, that's terrible advice. We've got lots of developers that do this already. We need fewer. This does not mean that we don't want to let people do their own thing at some level. But this is not the best way to start. Now, so in other words, we need to understand how individuals work. So let's go inside the brain for a moment. The assertion we can learn something from every failure is often hurt. Studied by Miller and colleagues at MIT, test the notion by looking at the learning process at the level of neurons. The study shows how brains learn more effectively from success than from failure. Brain cells keep track of whether recent behaviors were successful or not. When a certain behavior was successful, cells became more finely tuned to what the animal was learning. After failure, there was little or no change in the brain, nor was there any improvement in behavior. This is really important because it does mean that we are, by default, not hardwired to learn from things that do not work out. Now we may often say, well, hang on. What about retrospectives? What about reviews? What about all this reflection that is so commonly emphasized within the agile community? Well, that's why we do it. If it were part of our wiring, we wouldn't have to say it. If it were naturally in there, the fact that we can have books and talks on things like retrospectives and how to offer constructive feedback and how to learn and how to get a group of people learning tells us that it's not one of the things we're necessarily good at. It tells us we are capable of it but not in a vacuum. That's the point. We can help each other. I find the idea that we should not help each other rather peculiar. You can fail and I'll tell you I told you so. What did you learn from it? It's very easy to learn from failure where things are very constrained. In other words, where there is a right answer. Software development is not a domain like that. It is a complex domain. It turns out that we are equipped to do something with failure, just not quite the way we hoped. Now, I thought I'd go to the other extreme and give some redemption. I haven't listed it there but this is also from the Financial Times. It has become a commonplace to suggest failure is good for entrepreneurs. In this view, a failure that comes early in a founder's career can teach some important lessons about doing business and harden them up for the next startup attempt. This is orthodoxy. This is standard belief. Laws in different countries are arranged to allow people to fail based on this belief. It turns out the reason those laws work is not because of the belief. It's for different reasons. But this is standard orthodoxy. If you try and challenge this, I think if I were doing, if I were, if this were a conference of economists, I'd probably be booed off the stage at this point. I'm challenging orthodoxy. However, it's good to get some numbers here. I've got the exact numbers but in the UK the evidence is that novices are neither more nor less likely to be successful. So if you've had a failed company, it doesn't mean your next one's going to be any more likely. Because what you'll probably do is, as a friend of mine, he ran a failed company, there is that belief as you come out of it. You know what? That didn't work. I think we're doing, you know, we just need the right people in the right time. We just need to do everything just a little bit harder. We'll just do the same thing but with a lot more emphasis. There is, in other words, you narrow down instead of broadening out. I like the fact that more thorough work has been done in Germany. It's clear that those whose business had failed had worse performing businesses if they restarted than the novices. So basically we're saying that somebody who has no background in doing this is actually better off from a probability perspective than somebody who has a failed company behind them, regardless of what the reputation of that company might have been. So it turns out that there's a whole bunch of other stuff on the fact that we can of how we learn. There are certain behaviors, certain situations in which we end up with an error-correcting feedback but the default assumption no longer stands. Now why does this matter? It matters because we're the individuals with the individuals at the heart of the process but also a few years ago I noticed the language of scrum shifting. This is taken in the scrum primer. Scrum works by making visible the dysfunction and impediments that are impacting the product owner and the team's effectiveness so they can be addressed. The good thing is the paragraph does sort of talk about resolving problems in short cycles and experiments. This is good but there is a challenge I want to make to that idea. Making visible the dysfunction. If you've ever been in a long-term relationship has that ever improved your relationship by making visible the dysfunction of your partner? You know you're doing that wrong and you can do it slightly more subtly but you know that really doesn't work and how good are we at picking this up? Making visible the dysfunction. Turns out we are shockingly bad at it. Shockingly bad. Projects can fail in very consistent ways and the people inside the projects are still oblivious to why such failures occurred because they are human beings. They are naturally drawn towards a particular world view. So a project I had some technical involvement with a few years ago which ultimately failed for reasons well beyond the technical though they certainly contributed. I remember thinking that had the project involved public money I think I would have been inclined to either back away or blow the whistle. There was no way this project could be successful but the guy who got me in the process guy he was very optimistic and we both worked together on another project but this was a different political climate and every two weeks they fail to meet their sprint objective. Every two weeks they had technical challenges they had team challenges. Now I don't know about you but that sounds like feedback to me. You are being told this is not working. We may not know what's not working but we know that something is not right. There is a suggestion that continuing in other words the experiment the experiment that hypothesized given the people that we have with the skills that we have the architecture that we have the feature set that we are going to undertake we are doing it right this experiment is going to work let's try that out and every single experiment was coming back no no that's not right that's not working for you. Eventually the management decided to pull the plug on this project or other pull the plug on the agile process based on the fact that they did not sit there and go you know what dysfunction is highly visible we need to solve it they said we don't like hearing bad news every two weeks. This project overran to twice its original one-year length what you want all your bad news in the second year you could have it used to have it early used to have it every two weeks telling you you can't do it like this this isn't going to work this isn't of course that we don't like to hear that but that's the nature of the individuals in the whole process because that's how people think you don't like to hear bad news why would you like to hear bad news why would you like to have your work criticized even by something as abstract as a process yeah that's not how you read it you read the situation and you misattribute it to other things so it turns out people unfortunately matter why does it why is that unfortunate because people are really difficult so observation from Nassim Tower people overvalue their knowledge and underestimate their probably the probability of their being wrong this governs us in all walks of life it governs us in software development when people talk about estimation it also influences our ideas of the precise nature of the architecture that we might adopt for a particular system it's all over the place but at the same time if you get people right they can turn out to be surprisingly smart now the phrase wisdom the wisdom of crowds gets thrown around an awful lot the book came out ten years ago it's worth reading before you quote it or quote the title because it's a good catchy title James sir wiki is very very careful and very clear to outline what he considers to be the precondition for an intelligent group of people because we also know that a group of people together can act with remarkable stupidity the stupidity kind of an individual would never undertake so how can a group of people be so diverse well it's to do with the interactions diversity of opinion if you end up breeding a monoculture if your team is filled with people who think the same way then you're not going to get the wisdom of crowds because you are all fairly close to one particular point of view you've already started down the group think vote now that may mean for things that are right you are right it will also mean that you are very weak at recognizing incorrect assumptions friend of mine ran a startup and it was really interesting the way that he interviewed he interviewed basically for people like him and the other founder they went out of they went out of business eventually because they got I remember a couple of times where they where I met him in the pub and he'd say oh we just got we just had to let somebody go oh why because well he was a bit different to the rest of us and he had these other ideas and I'd seen the work the work was good but clearly just didn't fit in in why but he didn't he did not fit in because he was a bad person I think like that it wasn't because he was toxic to the team it's just that he didn't quite agree he countered he challenged some of the design decisions and the approaches you know that turns out to be surprisingly healthy independence and people do have to be thinking in a way where they are not massively influenced by other people when you operate when you get people in a group and you ask them something for example I'm not going to do it now but for a show of hands of something people to look around if you ask for group estimation I got a group of people together I get five people together and I say how would you reckon this feature is going to take to implement whoever says that whoever whoever breaks the silence first has the greatest influence and if they happen to be the most senior person at the table they're massive influence other people don't realize that they don't think oh you know what I'm going to think independently from him that's not how humans work we immediately are responding if somebody says I think that's going to take two weeks people don't immediately think independently I was thinking it was one day or one month they are now thinking do I think it's more or less that humans work in pair-wise comparison turns out we're very good at comparing the value of two things but we're not very good at giving off in you the absolute value of something out of the blue and we are also influenced it's a priming effect we are also influenced by other people priming effect is related to something known as the anchoring bias and there's a beautiful experiment a few years ago I forget the details but it was of the influence of numbers arbitrary numbers on our subsequent use of numbers and I think it was probably to lots of these Americans these experiments are done on American first-year undergraduates so we know a great deal about psychology of American first-year undergraduates but I was along the lines of exposing people to a series of numbers whether they were interest rates or numbers related to something utterly unrelated to what they were then asked the question they were then asked is how many nations in Africa are members of the United Nations and it turns out that when people were exposed to numbers that around 10s and 20s and 30s they gave their estimate of the number of countries in Africa that were members of the UN is around the 10s and 20s and 30s when they were given higher numbers in the sort of 60s 70s and 80s as their priming set they gave numbers of countries that were of that order in other words we are influenced by numbers that are entirely unrelated if I remember correctly the answer is 45 or 46 I can't remember that includes South Sudan but I'm sure some people check in on Wikipedia but it was right in the middle we are easily influenced we don't like to acknowledge it and we don't believe we do it but we are so some degree of independence decentralization the idea that people are able to draw on separate knowledge bases separate experiences the separate background that's really quite important if everybody has gone through not it's not simply a case of independence or it's not simply a case of diversity of opinions actually genuinely people actually look out to the market in different ways if you're looking at if you're looking at product development for the mobile phones you don't just want people on your team who are pure software developers but you also don't want pure software developers who are only interested in mobile phone products you want people who have interests all over the place and if you're doing Android development make sure you get an iOS person on the team because they're really annoying but they will give you something else and vice versa and aggregation none of this means anything unless you have a way of bringing it together otherwise you end up with these islands of opinion and knowledge so in other words the wisdom of crowds is a very delicate creature if you wish to harness that intelligence you have to be very careful because time and again we have discovered there is little correlation between a group's collective intelligence and the IQ's of its individual members we have seen super bright teams fail however one interesting observation which may come as a surprise to many of you but not a few of you okay it would be nice if it came to be less of a surprise this was a side effect of some very different research it wasn't the original intent of the research to prove or disprove or discover this but it was a it was an observation the experiment was sufficiently carefully run that when they looked at the results wait a minute this is interesting and I have to say ever since reading this a couple of years ago whenever I'm running workshops I have certainly made sure I've divided up the team is very differently as a result of it I think it's unfair for the women to get an advantage so they have to help the other teams but really what I believe what I believe is going on here is to do with the styles of communication you are necessarily including a very different style of communication or to be precise there's a whole bunch of stuff that you might say that you won't say what you won't say you would say styles of communication matter and this changes the landscape so it's a very subtle observations again this is not something you can get certified in so let's go to something else here let's talk about this other thing working software it turns out I want to go back to this question over the way that people often focus on value creation now of course if you're not if you're not developing software because it has business value then it probably has some other kind of value otherwise you wouldn't be doing it probably has some kind of intrinsic motivation it might be open source software that's a very different effect you might be doing it for a number of other reasons but I am a little concerned when people just say the only you know that's the most important thing here value creation is that really why we get out of bed in the morning I mean I can't really say that I got into software development because I was looking forward to adding value to somebody else's product and it just doesn't sound right it doesn't sit well with me that's not like how human beings talk this is how this is kind of how business people are supposed to talk in a caricature of business people it's not even how they talk but one of the things I thought was interesting was this observation client stakeholder value is the only thing is important add our methods balance two things one is maximizing a value creation the other thing is maximizing the chances of actually delivering something that's a very subtle distinction in other words what you are trying to do the group people is to actually try and deliver something and it may be that the thing that has the greatest value is the thing that has the lowest probability of being delivered in other words there is massively high risk so there is a balancing act here and the observation is that these two are sometimes in conflict this is why I've in the past I have I must admit I've had a little bit of a gripe when people talk about prioritization by business value okay how do you prioritize by business value how do you know what the value is how do you know in advance what the value is going to be it's an estimation exercise like any other estimation exercise is prone to error we believe that if we add these features we will get more users well that's a belief it's certainly one that we can go out and try but it's still an estimate it's an estimate that it'll be worth this much it could be worth this much it might be worth nothing nobody will buy it so in other words so basically prioritizing by an estimate of value is a different thing and then it gets more interesting is that the only way we can prioritize should be prioritized by risk as well in other words prioritized based on reducing risk prioritized based on things that we know are minimal effort minimal risk but potentially big wins well let's prioritize those there they may not be as big a big wins as other things but the idea is there is a balance here those priorities don't form a line they're not they're not linear there's a landscape now that sounds really hard and that's because it is there's a landscape that balances many factors and business perceived an estimated business value is only one of them now this idea of actually delivering something I want to refer to this thing a friend of mine Alan Kelly directed me to a couple of years back it's called that's not actually that good it turns out our costs our spending goes up our growth well doesn't it shrinks on the other hand if we try and become better at let's do this IT thing let's do this software thing let's become better at doing software improve our skills improve our infrastructure if you take a team of people that are currently as it were shielded from the flow of the organization and so they're not particularly aligned with the organization and they're not particularly effective in what they're doing and you throw them in the path of the oncoming train the alignment train it turns out they flounder they struggle they're not really given an opportunity to learn they get plenty of that failure we were talking about earlier but they don't actually get a chance to improve they're in constant firefighting mode it turns out firefighting is very expensive activity which is indicated there it turns out that they're now being rather than moving in elegant short feedback cycles they feel like they're being constantly harassed they never have time for anything they lack the time to consider well how would we do this right every deadline is sitting there like a vulture over them on the other hand if you continue main take so as I said not doing the wrong thing better continue whatever it is that you were doing but just try and do it a little better the way that we deal with the rest of the organization but let's see if we can improve something else continuous integration testing team togetherness meetings how we've laid out the tables socially whatever it is let's have some lunchtime learning sessions because clearly not everybody is up to speed because people don't have skills doesn't mean they can't have them so there is this idea that when you get a group of people who are incredibly skilled eventually at this when you ask them you know that wasn't quite the right requirement they're able to change it easily it turns out it's easier to change a lot easier I had experienced this one recently it's easier to take a well structured code base that is you know tested and all the rest of it easier to take a well-structured code base that does slightly the wrong thing and make it do the right thing then is take a messy code base that does slightly the wrong thing and make it do the right thing in fact it turns out it's easier to do the first case than it is to take a messy code base that somehow manages by luck and good fortune to do the right thing and now you want to do another thing with it well that's a big ask it turns out that's a very expensive thing to add it's a very precarious balance so it turns out that the concentration the emphasis on skills the ability to increase the probability of actually delivering something has a reflection in the way that we want to emphasize skills and learning now there is another interesting observation how do people get motivated Dan pink makes this observation if you want people to perform better you reward them but that's not happening here he makes an observation based on specific experiment but we also have some very interesting confirmation from the financial sector you've got an incentive designed to sharpen thinking accelerate creativity and it does just the opposite it dulls thinking blocks creativity turns out the people who are in knowledge work have a very different reward system once they reach a particular level of remuneration it's no longer money that matters the thing that people do care about is comparative remember I said earlier on people are very good at pairwise comparison so within an organization software developers look across at UI designers they're getting paid but they'll get pissed off but they won't look across the software developers in another organization make necessarily the same comparison so it turns out that money is not the driver once you reach a particular point another study had something to say on this one this was a study of six hundred managers across a number of companies for the engaged in knowledge work so not necessarily software development some very interesting things what they ranked the highest was recognition okay recognition for good work that was number one sadly they're wrong when they asked the people what they found is that progress is the most meaningful what motivates people is progress coupled with a sense of purpose and some degree of control over their own work autonomy when you sense that you are making progress if you've ever been on a really large project that hasn't got any obvious progress indicators you feel like you're stuck in the doldrums literally the project is going nowhere you like to feel progress either problem solved or other forms of progress this is why half of the things that are advocated in the name of agile development reason half of them work because they are visible indicators of progress there's a profound satisfaction in moving a card from one part of the board to another especially this one says done there's progress you actually got up and physically did it you run some tests that was good look I've got more tests than I had yesterday this progress and they're green today which is even better in fact sometimes you may notice this is an interesting one people undertake quite a lot of testing if they been away if they test if they're talking about a test suite that runs fast if they've been away from their desk for a while when they come back they sometimes just rerun the tests if they've left their IDE open they will rerun the tests I've done this a number of times because I mean what could have changed in the last few minutes nothing but there's a satisfaction look progress I've done something and it's more than what we had before all of these are subtle indicators of progress now you have to be very careful with certain indications of progress let me pick on burn down chart and you're very careful about how you apply this so take me because clearly this gives a formal progress okay so amount of work left to do and time you see progress if you don't make progress in the amount of work left to do then it stalls sort of but there's a couple of other things you need to take into account to make this work we have to avoid some of the very common pitfalls I noticed a few years ago that there was a strong recommendation that people should have estimates of items that they had fed into that they were actually going to burn down so in other words the current backlog they have to have estimates in hours now I regard hours as unnecessarily precise for something that I don't know about it turns out that when you use a particular unit of measure people will estimate and measure according to that measure give you a very simple example if I say I will see you tomorrow or I see you in a day you kind of know what I mean if I say I will see you in 24 hours I'm not actually saying the same thing if I say this will take about a month I reckon it's different to saying this will take 22 working days this will take about a year versus this will take 250 days or something like that in other words there is a difference there in how we do this if you're saying ours then people are if you say this will take this many hours people will track you by ours and it seems as I say unnecessarily precise given our inability to estimate correctly but I there's something else I want to draw your attention to the graph if we're measuring time in days and we're measuring work left to do in hours what's this graph a graph of it's a graph of time against time if you did a numeric degree and I'm sorry mathematics doesn't quite count computer science certainly doesn't one of the things you had beaten into you was dimensional analysis check check you check what you're doing this stuff with what's time against time what is that actually a measure of I mean currently based on my inertial frame of reference I'm currently undertaking approximately one second per second through space time but I don't think we're talking Einsteinian relativity here what we're talking about is utilization because if you say a standard working day is eight hours then I would expect on an individual level for a hundred percent utilization a bad idea that everybody's burning through eight hours a day and if they're burning through less and I obsess about numbers and I might get worried so what's this a measure of it's not really it's not it might be a measure of the goodness of our estimates it's not entirely sure what it's not entirely clear what we're doing with this particularly when sometimes people will actually put this like this they will say ours estimated and they will subtract the hours worked I estimated this was a 10-hour task I've worked five hours on it therefore I am halfway through it is entirely possible I estimated 10 hours I've worked five hours on it and I've got 12 hours to go good grief how did that happen well reality struck I'd have been better off saying I estimate a couple of days I've done a better part of a day and I still for I still think it's a couple of days it's the work remaining but it's easier to measure the work that you've done so I found some people micromanaging this one and obsessing over the numbers there so a more meaningful one is this one hours of work remaining looks different however it turns out that if I have a number of stories say 10 stories and equate a story to a task for a moment it turns out I can do 80% of my estimated work across all of them and still have finished nothing which is kind of a problem we need to solve it turns out that really strictly speaking you shouldn't mark it up until you've done it until it's reached done now what I'm describing here is very common failure modes that I've seen when people have not really understood the questions that a burn down chart is supposed to raise and the values that it's supposed to show and I've taken a very isolated set of very isolated environment I'm worried about requirements creep I'm worried about re-estimation to a great degree and yet still we are we find that there are problems with the current visualization the way that people normally exercise it for me I always find a build-up chart is slightly more positive because the graph goes up now people are people got to the habit of calling these burn-up charts a few years ago which I think is terrible you know I'm I'm both a father and someone interested in space travel and in both contexts burn up is really bad if a child is burning up it means they have a fever if a spacecraft is burning up oh that's really bad you don't want that so build-up is more positive we build up yeah it's a much better connotation now again there is the orthodoxy that assumes that although this is a progress indicator that a straight line is the right thing humans aren't very good with straight lines we struggle with them but also if we go back to the idea that we are not doing if we are undertaking a new development is genuinely new it's not like a new system that's like an old system that we did it's not like continued work on a system that is well understood if we are undertaking new work we're actually you know what we have no idea so one of my clients really interesting one of the things we did was separate out things that are familiar and we have some kind of confidence in versus we really have no clue we don't even know the answer to the question because we're not even sure what the question is so we separated those out so those did not sort of sort of one number didn't mess with the other and that's quite important because when you're doing that kind of work in the second category we actually have no idea whether or not this optimization this technique this feature will work is implementable or has any appeal to any of our AB testers we have no idea it's a complete experiment genuinely open and we can't tell you how long it's going to take and it's very very likely that your natural profile should look like this should have a kink in it or in fact even a curve like that because your learning slowly you tend to work a little better don't rush things explore a little bit you're not making any meaningful progress in terms of functionality but you're probably gathering a lot of knowledge there's a lot of time spent thinking around things the progress you're making is not as visible perhaps as other forms of progress but then if you measure the functionality in terms of delivered work then it'll rise as you get the knowledge so it's a very different anatomy to the way that people if you like reason and in full awareness of the fact that I am about to go over time I'd like to consider one more element of how our views on our practices are often distorted it's a thing called hyperbolic discounting organisms tend to value the present far more than the future in other words you take a reward that is immediate rather than a long-term benefit that is abstract if it's immediate and concrete you will take it this affects us in a very obvious way can back highlighted this if all you could do is make a long-term argument for testing you can forget about it some people would do it out of a sense of duty or because someone was looking over their shoulder soon as the attention wavered pressure goes no you test get written everything falls apart in other words even though you may have instilled in people the reason that you know long-term testing long-term is a good idea if that is the only thing you have been able to do and you've had to do it by active supervision and boxed box ticking it is very likely that people in spite of intellectually knowing that there is a benefit they will take the short term over the long term I love this quote from you scientists economists dislike hyperbolic discounting because it is irrational they prefer exponential the fact that it's what people do doesn't seem to disturb them which might explain an awful lot about the economy but the very fact that it is uncomfortable is something we need to take into account it is normal for people to not value long-term abstract gains especially when we are coupled when they're coupled with probabilities so on that note I'd like to end with an observation from Helen Sharp from the Open University she undertakes quite a lot of research on as it were the people side of stuff and she gave a keynote a few years ago at a conference where she just simply titled it software development a social activity with technical practices and that draws us right back to the emphasis on individuals and interactions the processes and the tools help us glue they also come out as byproducts but without the emphasis on the individuals and interactions we will be left in a constant state of mystery thank you very much


Just go over some of that material. It's not really very much to say to finish it off. And then be done with the same amount of that. So in particular, it's fairly easy. It's quite easy actually to find the energy shifts in the case of a weak field. Weak magnetic field. And the form given here, it's a gourmet, a ton of tons of magnetic field, multiplied by some dimensionless numbers. And the hard part of evaluating this is to make yourself a spin operator, as you can call it a spin. These quantum numbers here represent the quantum numbers of an atomic state of an atom with a single electron. So hydrogen or an alkali atom is the idea. This is the usual quantum numbers for that. So it's evaluating this final matrix element that we use in the projection theorem. Now, I think last time I did an all right job of explaining how the projection theorem is derived from Dirac's identity. I didn't prove the identity, but if you believe it, then it's fairly easy to derive this result here from the projection theorem. This is written in general terminology in which gamma, J, and M are elements of a standard angular minimum basis for an arbitrary system where J is a total angular momentum. And then, so we have to change the notation to identify whether the quantum numbers of the same above are specific to the same artifact. But what I'd like to do now, something I didn't have time for last Wednesday, is to explain why it's called the projection theorem, because that also helps you understand the theorem you need to remember in case you're on the decimal line. There's rather some time it can't remember it. So it works like this. The first thing to notice about the projection theorem is it's actually a fairly special result in the way I presented it, because it's not an arbitrary care of standard angular momentum basis factors in the two sides. Rather, it's required that the J value is in the two sides to be equal. However, as far as the gamma and the M's are concerned, those are allowed to be different. So, as I say, it's rather a special result. There is a generalization of this theorem that allows also the J value to be distinct, but we won't need it for this course, and it's more complicated than so I won't go into it. You can find it and cut it in shortly, if you want to look in that book. In any case, the J then is the same on both sides, and the other quantum numbers are different. So here's a classical interpretation of this that helps you remember it, and also helps you understand why it's called the projection theorem. The operator A, vector operator A, and the other one is J, as if they were just classical vectors.  Now, if you wanted to project A on the J, what you usually do is you've got the perpendicular down like this, and let's call that projection, let's call it A parallel, meaning the component of A is in the same direction as J. Geometry, A parallel is the same thing as A dotted into J, multiplied times J, divided by J squared. J over J squared, J over negative J is just the unit vector in this direction, and all you're doing is taking the component of that unit vector and then multiplying by the unit vector itself. That's just what this means. So this is just a simple vector geometry to see this. Now, one mechanical projection theorem says that the matrix elements of the original vector between angular momentum states where the J value is the same on both sides, so it's a subspace that fixes angular momentum is the same thing as the matrix elements of the projection. The only thing you have to remember is that the classical J squared that appears here needs to be replaced by J times J plus 1, which is the usual quantum mechanical eigenvalue of the operator of J squared. And then you see this is what you get at the right hand side. Often, it's much easier to find matrix elements of J than it is of the original vector than this usual trick you can do to take care of the dot product. So, just as an example for the S and Z here, what this says is that what the projection theorem says, if I apply it, is that this matrix element, and now what we need to do is to identify the gamma here, and if we get an L, the J is the same as the J here and the N is the same as the NJ. It's a change of notation. So, by the rejection theorem, this is the same thing as NLJ MJ on one side, and then we have S divided into J, and then we've got JZ. I've taken the Z component of this general formula and identified A with a spin, that's what I'm doing. And then NLJ MJ on the other side, and then this is divided by J times J plus 1. In this particular used application of projection theorem, the NL of one side is the same as the NL on the other side. Although the formula of NLJ again, we have a problem with a lot of these things. It's the same thing about the Emsen imprints. Emsen imprints, by the way, are the same in this formula here because the JZ commutes with the perturbation in Hamiltonian so it's diagonally in Emsen-J's interpretation. But once you've got it to this stage, then the JZ part is easy because that just brings out an MJ that's acting like a eigenstate in itself. So as far as S dot J is concerned, you use a trick. You write the orbital angle when L is equal to J minus S like this. But then you square both sides and you get L squared is equal to J squared plus S squared minus twice S dotted into J. So you concoct it so that you get a particular dot product you're interested in. And then so solving for S dot J is 1 half J squared plus S squared minus L squared. And so this S dot J can be written this way because it says this operator 1 half J squared plus S squared minus L squared. However, this operator is now sandwiched between states which are eigenstates of J squared L squared and S squared is a constant operator. So it just turns into a number which is the same thing as 1 half of J times J plus 1 plus S times S plus 1 minus L times L plus 1. And S times S plus 1 turns the same thing as 3 quarters because of the force of the spin of the electron so it's 1 half times 3 halves. So in any case, you now just put the algebra together and you get the landed G factor. This is the outline of the of the application of the projection theorem for these weak fields that I like back. Sorry, can I ask this question? Yes, sorry. I've lost track of the overarching theme from one lecture to the next. So I have no... Yeah, I'm sorry. Maybe you wouldn't have remembered it if I'd come on a Friday. No, it's just that so I have no recollection of like a business student. Yeah, so this isn't the end of the same artifact but if you look at the notes on the same artifact this is like 9 to the end of the notes. Now I think it's actually all explained in the notes but this is the weak field same artifact which in some sense is the most difficult of them all. And basically you have the energy the eigenstates are degenerate. They're basically they're just characterized by the angular momentum value or the mj is what the degeneracy is it's 2j plus 1j. And so this is an example of the degenerate perturbation theory but as it always seems to happen to get by with not the degenerate perturbation theory because the matrix is a this case a styrofoam of instant j. So I'm indeed I skipped steps leading up to this but those were done in the last Wednesday's lecture. Right. We'll take a look at the notes because you'll see it's I think that part of the notes explains it. I don't recall that but then now we're saying okay so now we have somehow from that we have like a theorem that you generate the variables and things more. Yes. In fact I'll show you in just a moment if we have time. I'll show you several more applications of the projection theorem but the this matrix element is difficult to evaluate because the j and j involve Clepschordian coefficients combining ordinal and spin random momentum and s and z only refers to one part of that. So if I were to expand the amount of Clepschordian coefficients I'd get a linear combination of terms for each one of these and then indeed it would be the easy to let s see act on them because each term would be an eigenstate of s and c but then you get a whole bunch of terms of Clepschordian coefficients multiplied by things so that's a lot of algebra to do it. So this is actually much easier so do this way this allows you to transfer the z component from s over to j which helps because you have eigenstates of j and z. Okay.  The new topic is going to use the projection theorem in a fair amount. I want to turn to the subject of the deuteron and do just a little bit of nuclear physics. It's really quite interesting. So to begin with, the deuteron is a balanced state of the proton of the neutron if I color the neutron dark it looks like this so it's a proton of the neutron each of these, of course, is a spin on half particle and the deuteron is a balanced state of that. Now, the proton and neutron are held together by the strong forces and so let me say something first without the strong forces and how they contrast with the electromagnetic forces. One of the main differences is that the electromagnetic forces are considered long range that's because the Coulomb potential falls off as whatever are it doesn't have any natural scale in the sense the scale is infinity and it's also considered a rather slow slow decay of the force. And even the nuclear forces are roughly speaking fall off exponentially. I have to say roughly this is only a crude statement because it's the idea of the potential falls off exponentially and in fact as we'll see the interaction between the proton and neutron is only roughly described by potential if you push the accuracy it's not even a potential. Unless it's useful to think that way about them. So it has an exponential decay and therefore a scale length which is the scale length of the decay. What is that scale length of the nuclear forces? It's roughly about one Fermi. One Fermi is defined to be 10 to the minus 13 centimeters and the so anything involving the range of the nuclear forces comes out as a small multiple of one Fermi. Notice that this is about 10 to the fifth time smaller than the size of the matter and so the nucleus is of that relative size its volume of the force is that Q so it's 10 to the minus 15 which is a really very small volume in the atom. Fortunately the higher density the density is 10 to the 15th higher for the density of the atom which is approximately the density of ordinary matter. Nuclear matter is much much more dense than ordinary matter. So that's actually what the forces tell. For example, just to give you an example of what this means. By studying experiments that have studied electron scattering of protons to probe the internal structure of protons it determines what's called a form factor and allows you to get information about the charge distribution inside the proton. When this comes out with an RMS charge radius for the proton it's something like about 0 for the Fermi. The RMS value so the sense of charge continues out beyond that out to something above 1 Fermi but it gives you an idea of the order of magnitude. So those are some facts about the strong forces. Here's some more facts. The strong forces are strong. That means they're stronger than the electromagnetic forces. One can see this for example in the case of the alpha particle which of course is a nucleus of helium that has two protons and two electrons. That's two neutrons. Neutrons are neutral but the protons are positive so they repel each other by the Coulomb force. Now the electric force that goes as the inverse square of the distance and since this distance is 10 to the fifth times smaller in the size of an atom it means the force which repels pushing those two protons apart is something like 10 to the tenth times as large as the attractive force of the electron and the hydrogen atom. It's really quite a strong force. It just remains as a short distance and nevertheless the alpha particle is a valid state and it is so because despite that strong repulsion the nuclear forces are even stronger and hold the proton and the neutrons together than the alpha particle. So this is the sense in which they're considered strong. Alright. Now specifically about the oh yes one more thing I should say is that the strong forces as it turns out are actually independent of the distinction between the proton and the neutron is sometimes referred to as this charge state which is a neutral one and the other one is positive but the strong forces between these two particles are in fact independent of the charge state. So the force between two protons is the same as the force between a proton and a neutron the strong forces don't care about the difference between those two particles. Of course the electromagnetic forces do and in fact the analysis of such a phenomenon electromagnetic forces are often taken as a small perturbation on top of the strong forces. Alright. Anyway the quality of the nuclear forces between protons and neutrons is the beginning of isospin symmetry which I won't have time to go into when it's a basic a structural fact about nuclear business. Alright. Now to turn to the deuterons specifically let me give you some experimental facts about it since it's a balanced state of the two we can picture as the two kind of stuff together like this it obviously has a charge of proton which is one half heavy isotope of hydrogen the we can guess that the average separation between it is on the border of a faring as it turns out it's actually somewhat larger than that because it's only in the classical region. There's some more experimental facts it turns out that the spin of the deuteron which is normally denoted, the operator is normally denoted by I the spin of the deuteron is actually physically speaking it's the sum of the spins of the proton and the neutron plus the orbital angle mentioned between them by the way the masses of the proton and the neutron are almost equal so what you have is a picture of the classical of the two nearly equal mass objects rotating around each other like a dumbbell turning about its common center of mass which is halfway between the two the two particles so in any case in general there's both orbital angle and the spin and we can write the total angle of the deuteron in this way as L plus let's call it S1 plus S2 or 1 and 2 refer to the proton of the neutron this is the spin operator let's denote the eigenvalue around the quantum number of the operator I squared by I so that the value of I squared is taken as I times I plus 1 now it's an experimental result that the spin of the deuteron is 1 as to say that the quantum number I is equal to 1 but the operator I squared goes into 1 times 2 which is 2 it has a numerical value of 2 alright this means this means so if the numerical the value of the total spin is equal to 2 we can now use the rules for addition of angular momentum to get some idea on the restrictions of the quantum numbers for L squared S1 squared and S2 squared by the way let's do this let's write S to the total spin is equal to S1 plus S2 it's the total spin of the proton plus the neutron so that we have I is just equal to L plus S like this in simple equation so the total values of the quantum number S I'll call it lower case S I'll probably make it small because the lower case S can either equal 0 or 1 because you're combining it half of the half the 0 is the singlet state the 0 is the singlet state and the 1 is the triplet state if you count the number of magnetic substates this is in concerns of the total spin so the total spin quantum is therefore either 0 or 1 and then L takes on the usual orbital angular momentum values so if I make a table here of the different allowed L and S values and the one I've read is quantum numbers of all times S and first of all S could be equal to 0 just based on the rules for addition of angular momentum S could be 0 and if S is 0 then we must have L equals 1 in order to get a value of I which is equal to 1 that's the only way you could get 1 out of the spin 0 however if the spin were equal to 1 if you're in the triplet state then the orbital angular momentum could either be 0, 1 or 2 in so far as the rules for addition of angular momentum are concerned because that's what you have to need in order to reach the final value of 1 for the total angular momentum so this is a table of possible L and S values based purely on the rules for addition of angular momentum see in a moment these get restricted by further considerations and it ends up there's a fewer set of possibilities in the other table here's that so this is as a result of the consequence of the experimental value of the spin of the neuron here's some other experimental facts the ground state of the neuron has an energy of about minus 2.2 mV this is actually a rather small binding energy for a nuclei that's considerably more energy to remove a nucleon from an alpha particle so in a sense from the standpoint of nuclear physics the neuron is trying to weaken bound another experimental fact is that this is the only bound state that the neuron has it has no excited states if you try to no bound excited states if you try to excite it all you do is break it apart and it turns into an unbound proton and neutron which is a negative state for the system so unlike hydrogen because of infinite number of bound states of the neuron the most simple nuclear problem has over one alright and finally here's another experimental fact it has the neuron has a g factor g sub e which is equal to 0.857 determined nicely by magnetic resonance experiments where high accuracy is possible what this means is that the magnetic moment operator for the neuron is equal to g sub e times the nuclear magneton times the total spin operator total angular momentum operator for the neuron divided by h bar whereas the nuclear magneton as usual is equal to e h bar divided by twice the chrome time mass times the speed of light this is the standard unit for magnetic moments of nuclei okay so what I'd like to do now is to take these experimental facts and then try to gather as much information as we can about the wave function of the neuron in the quantum mechanics using the rules of quantum mechanics alright so in the first place it would be a simple guess that the interaction between the proton and the neutron is described by a potential that would have to be a central force potential in order for the system to be vocational to vary it and if that's so we'd have a simple central force Hamiltonian e squared over 2m plus potential v of r this is really a Hamiltonian for the relative motion so the linear is really nearly as the reduced mass of the proton neutron system but anyway let's take this as a guess as a starting point for what the interaction might be we don't know what the potential of v of r is let's see what some of the consequences are well here's one of the consequences if you look at the radial wave equation as you know the potential the effective potential is the sum of the true plus the centrifugal the true potential must be some kind of a well in order to do the bound states so let's just sketch a well here the centrifugal potential depends on the angular momentum but it's always positive it's L times L plus 1 divided by 2 mu r squared so it's always a positive potential that goes plus infinity as r goes to 0 if L is equal to 0 the centrifugal potential vanishes and then you just have the true potential that's all but in any case you can see that when you add the true potential to the centrifugal potential we've got a curve that comes down like this and it's made up below 0 and then it's been an asymptote to 0 like so create a well like this in that well it's going to be some bound state that looks like that, some energy but the fact that the centrifugal potential is an increasing function of L means that the absolute ground state of the system is always going to be an S-way it's going to be one force L a k 0 this is true for a central force Hamiltonian of course we know it's an S-way for hydrogen but you see the general argument applies for a central force Hamilton and since a deuteron has only one bound state this is the ground state that ground state must be an S-way that follows inevitably from this assumption of a central force Hamilton actually we'll see in a minute that this is really not adamant to describe the deuteron there's more to it but if we accepted this then it must follow that we have an S-way and so what we conclude is that L must be equal to 0 but if L is equal to 0 then this pin must be 1 and the total angle of member has to come from just the spin part because the L is not contributing since I is equal to 1 and S must be equal to 1 and we're in a spin triplet state that's what that means so in particular we need a wave function side to side to look like this it would be a radial wave function that's called r of r and then a y 0 0 of omega because that's L equal to 0 and then what you have is the total spin where I could operate this S-square with an S and C you'd have part of numbers 1 and m sub s we look like this the m sub s is the same thing here as m sub i since L is 0 and this gives us a state of total total angle of member 1 which is the same spin part now the next question I'd like to turn it to most of what I'll be talking about in the next 45 minutes is magnetic moments so let me turn to the magnetic question of magnetic moments the magnetic moments of the proton and neutron can be measured separately as separate particles and for the proton the answer is g is g factor is 5.588 and the g factor for the neutron is minus 3.823 negative this means that the magnetic moment for the proton is equal to the g proton times the nuclear magneton times the s1 over h bar over s1 I'm going to start setting h bar equals to 1 so I'll just put an s1 here s1 refers to the proton and likewise the magnetic moment of the neutron is the g factor of the neutron times the nuclear magneton times s2 yes the question is can we understand the experimentally measured value of the g factor of the deuteron 0.857 in terms of the g factors of the proton and the neutron to make it up this is the magnetic moment of the deuteron coming purely from the combined magnetic moments of the two constituent particles so how can we analyze that? well if we have our proton and neutron in orbit around each other and we put the system in an external magnetic field and there's going to be a delta H perturbing Hamiltonian involved in the field and it's going to be this it's going to have two terms it's going to be minus the mu dot v but one from the one from the proton one from the neutron right here going into minus mu sub n this is probably the factor of mu n and then there's g proton s1 plus g neutron s2 dotted in the magnetic field v or if we put the magnetic field in the z direction then it becomes the magnitude of v times mu n which of course is an energy and then we get gp times s1z plus gn times s2z and now if we wish to find the the the energy shifts in the magnetic field these will be the perturbing Hamiltonian sandwiched around the eigenstates of the Deuteron, the ground state eigenstates well those ground state eigenstates under the conclusion we reached earlier they've got a fixed radial wave function in any given one and the only thing it changes is the s squared sc and s squared by the way is the same thing as i here because l is equal to zero I think I'll call these ground state wave functions i in sub i but i would say that i is the same thing as i would say the total s so this is really the same thing as s, s and z referring to total spin so this is now you see i is just equal to s1 plus s2 since l is equal to zero so what is this matrix settlement you see it's going to be minus the use of nuclear random times the magnetic field and then we've got i mi on one side and then gp times s1z plus gn times s2z times i mi on the other side so we need to evaluate this matrix now this is straightforward to evaluate by spanning up the i mi in terms of classical equations and then just view force charging through it but it's easier to use the projection theorem so let me do that for you let's focus on the first of all the matrix settlement of s1z which is the z component of this home time so let's look at this matrix i mi sam from s1z now by the projection theorem this is used to i mi sandwiched around the total operator i dotted into s s1 times i i cz divided by i times i plus 1 using the projection theorem the i z part is now easy because it just becomes mi brings out the magnetic field of number the ground state of the deuteron is 3-fold in general because of the magnetic quantum numbers as far as the i di s1 is concerned here's what we do let's take the i there this formula applies in the case of an L is equal to 0 let's solve for s2 so we get s2 is equal to i minus s1 and if we square both sides we get s2 squared is i squared plus s1 squared minus twice i di and thereby you see we get the dot product v1 up here that's what s2 squared and the squares and the spin operators so the protons and the neutrons those are constant that both of them are 3-quarters because it's a spin focused spin those two terms cancel and what we get to something is that i dotted into s1 is the same thing as the one half of i squared and so this thing goes over into one half of i squared which because it's acting like an i-space of i squared turns out to be one half of i times i plus 1 and the ii plus 1 cancels the denominator and the overall result of this whole thing is it's just become one half of i so that's the expectation of how you get s1z and by very similar analysis with s2z you get a good factor and a half there as well and so the result is is that this becomes minus-neutral and unique times one half of gp plus gn times s of i and what this shows you is is that the g-factor of the neuron if it is indeed coming purely from the spins and the protons and the neutrons it would just be the average of the g-factor for the proton and the neutron so where are my numbers here's the numbers for the proton and the neutron if you do them you add them up and divide by 2 here's what you get and you get 0.883 which as you see is close to the experimental value 0.857 but it's too large it's off by certainly no and so what this indicates is that the this conclusion follows inevitably from the assumption that we have a simple force Hamiltonian because that led to the conclusion that the neuron state is an s-wave and then once you've got that then the magnetic moment has to come to just the spins and it turns into that value rather than the experimental value so this calls in the question whether this is the correct Hamiltonian in fact it turns out it's not there's more to it it's not just the simple force Hamiltonian by the way there's another wide of argument that shows you that it cannot be just a simple force Hamiltonian and here's the reason it's because there's no spin dependent terms in this system it's like dealing with hydrogen but leaving out the spin orbit terms so if we leave out the spin orbit terms so we just have a simple force Hamiltonian like this then the energy does not depend on a spin state but we know that the ground state to do wrong is a spin triple s equals it is if it's an s-wave the fact that these two numbers are close together means that it's not too bad to make this assumption but it's not perfect and it means that it's a crude model we can indeed think of the way function as being an s-wave but there's more to it than that so based on this crude model we can say that it's mostly an s-wave but with some kinds of corrections well if it was purely an s-wave and if there's no spin terms of the Hamiltonian the triplet state and the singlet state spin states would have the same energy this is just like in hydrogen if you ignore the spin-spin interaction between the proton and the electron in the spin-triple and spin-singlet state would have the same energy in fact in hydrogen they very nearly do this is called a hyperfine splitting it's a very small splitting it comes from the orientation of the proton and electron spins it's responsible for the this will be my first lecture next semester but this is responsible for a splitting of the ground state this is the 21 centimeter line and so important in astrophysics but now here it's more of the 21 centimeters which is actually quite a small energy in the scale of hydrogen energies because what we can see is that by flipping the spin by going to spin singlet state it must raise the energy by at least 2.2 MeV because otherwise there would be another bound state that would spin singlet of the ground state so in fact if there really were no spin orbit turns or any spin dependent turns then you'd have a degeneracy here because of the ground state because of the 2-spost spin values ok so this is all a bunch of indications that this simple potential is not completely added it's a second force model for taking the new one it's not completely accurate now so what do we do what I do now is I'll tell you about I'll tell you about another experimental fact which appeared in 1939 and this is the fact that the denom possesses a quadruple moment like a quadruple moment let me remind you of the quadruple moment tensor you have a single particle it's the coordinates of that tensile integral the coordinates of that particle let me call it x i x j the coordinates minus double i j r squared in the case of the Deuteron there's only the neutron doesn't contribute to the quadruple moment because it's neutral so these coordinates are really the proton coordinates let me remind you also that there's a dipole operator this is for the single charge particle when we were looking at the start we considered the question whether energy eigenstates could have a parallel electric dipole moment let's talk about dipole moments for simplicity so in size of the energy eigenstates the position operator are multiplied by the electron if you're talking about a single electron pattern this is the average of an electric dipole moment operator and as we saw this is all equal to zero because energy eigenstates are eigenstates of parity and the position operator is odd of a parity now however if I go from a dipole operator to a quadruple moment operator this story changes because this is quadratic in the position of that force even in the parity and so the quadruple moment operator is a parity and so there's no parity in conservation between exclude electric dipole moments of energy eigenstates now here's another issue which arises is as I mentioned the deuteron has a i equal to 1 as the total angle of the system that means that the ground state is a irreplaceable subspace under rotations of dimension 3 and negative one number still 0 minus 1 plus 1 and it means that on that subspace the ground state subspace in the deuteron system it means that the possible irreplaceable tensor operators or if I write them as tkq they're a useful notation they allow values of k and only be 0 1 and 2 that comes from adding a cross of 1 cross 1 which is a 0 plus 1 plus 2 and the one here goes from the state of the deuteron so this is part of the homework problem the maximum k that is allowed is going to give you a subspace like this it's actually twice the state so in particular your useful tensor operators are going to make this too far allow any spin limit a spin limit system they're not allowing a spin limit f system that means that for example the proton or the triton which is the third, the heaviest oxygen of hydrogen the triton has got 2 neutrons and 1 protons that's kind of like this one step up through the deuteron this actually has a spin of 0.5 not spin 1 SPI half integer it turns out to be 1 half and since it's 1 half the maximum irreplaceable tensor operator maximum regular irreplaceable tensor operator for the triton system is 1 the triton kind of can and does have a magnetic moment but it does not have an electric quadruple moment deuteron however is allowed to have an electric quadruple moment and it was discovered experimentally by Robbie in his room in the late 1930s that in fact it does they found this by looking at the energy levels and saw that it was necessary to have have a quadruple term included alright now given the fact then that the deuteron has an electric quadruple moment we can say about the wave function what this means is if I take the wave function whatever it is the sandwich is one of the quadruple moment operators we have to get another 0 answer well the quadruple moment operator is a T2Q operator as we know P equals Q and if psi were purely an S wave so that this had L equals 0 also it's a purely orbital operator it's the only involved orbital degrees of freedom then by the figure of that card there we see the matrix so it has to be 0 this has to be equal to 0 in an S wave because you can't probably get 0 with 2 you get an answer with 0 with 0 see 2 cross with 0 just equals 2 so the answer the answer is 0 therefore in order to get a non-vanishing quadruple moment it's necessary to have a higher values of L and so the ground state wave function of the neuron must include not only L equals 0 but also higher values of L so let's do this let's take the ground state let me call it psi as the ground state of the neuron let me write it as an expansion over L L equals 0 to infinity of some coefficients I'll call A L and then psi is L the idea here is that we take this state psi we project it onto the subspaces of angular momentum L and so like this you project it onto the subspace like this and psi L is a normalize factor inside that subspace and the coefficient gives us the magnitude of the projection so this is a really understanding of psi L psi L is equal to 1 then the ace of Ls are the expansion coefficients by probability conservation by the sum of L A L adds to the value of square less to be equal to 1 now we turns out we can get some restrictions on which L values are allowed by considering further symmetry principles let's look at parity it's quite easy to look at if I take parity and allow it to act on the ground state the ground state must be an eigenstate of parity so the answer has to turn out to be plus or minus 1 but it has to be one of those two choices of whole-plated psi on the other hand we take this expansion of the parity the states of the angular momentum L are parity of minus 1 to the L so this now becomes a sum on L of minus 1 to the L times the same coefficient of A L times these projected vectors psi L like this we know that A0 is not equal to 0 and this is our original model which we had central force Hamiltonian led us to the conclusion that it was an S wave and even if it didn't work perfectly it worked pretty well so there must be a strong component of an L equal to an S wave in the dunon wave function even if that's not all there is so in particular the A L equal to 0 term ends up in a plus sign here and the only way that can equal so we find the dunon as a parity plus 1 is even parity if there is something else that happens too if we look at the L equals 1 wave then the minus 1 to the L is a minus 1 and that's not consistent with this expansion unless those terms vanish so what we conclude by a conservation of parity is that A L is equal to 0 as well as I now, boom, so some has to be only over even an S wave and then a D wave and doesn't go on well the answer is it does not go on because we can't have L greater than 2 if we had L equals 4 for example then the maximum spin we can get is 1 and if you combine them together the minimum value of I would be I equals 3 but this is wrong because we know I is equal to 1 and so in fact the sum terminates at L equals 2 so what we conclude and I'll put it right here is that the ground state of the Deuteron must be some coefficient let's call it a 0 times a normalized vector of the L equals 0 subspace plus a set of 2 times a normalized vector of the L equals 2 subspace it's a combination of an S wave and a D wave and that's all now the question is what about these 2 coefficients if you don't have time to finish this I'll just go ahead and get on it I'll show you how by using this magnetic moment data there will be this disagreement here between the simpler model where it's a pure S wave not what we're going to do is improve on this and consider this linear combination of S waves and D waves and see if we can make the magnetic moment by using the experimental which is not going to erase this was the theoretical result on that simple model having a more sophisticated model that includes a D wave to try to determine what the coefficients are turns out you can't get the coefficients themselves but you can get the squares you can get the squares of the whereas the a0 and the a2 of these on the 2 are no longer a mystery all right so let's work on this now so yes it's actually a relative wave function of course it's a semi-nasa wave function too that's true so the we'll do it like this we'll again use magnetic moment information let me remind you that in the same effect in the single electron single electron atom we had a perturbing Hamiltonian we call it delta H for the interaction of the magnetic field I think previously I called it the same I called it Hc which is which was which was this, it was use of dv and then this was multiplied times else is the plus plus s is the the orbital spin angular momentum momentum contributed unequal proportions to the magnetic moment using this there's an effective g-factor of one for the orbital motion and a g-factor of two for the spin as this is too early as this is the g-factor of the electron the electron spin the direct this is for the this is for the case of a hydrogen atom now in the case of the deuteron it's going to look like this it's going to be first of all nuclear magneton times the magnetic field there's also a minus sign which is particles of positive charge and it turns out to be the following in the first place there's an effective g-factor not of one but rather of one half and the reason it's one half instead of one is because the hydrogen and proton is massive so the electron is moving around and the proton is mostly stationary so in the deuteron both protons and neutrons are orbiting around each other and the distance from either particle to the center of mass is one half of the distance between the particles so there's an analysis one can go through in which you transform from the laboratory to the center of mass variables the lack of time that will go through this but when the smoke clears you find that there's a g-factor of one half for the orbital angular momentum in the case of the deuteron and as far as the spin is concerned these are the same things we wrote down earlier it's g proton times s1z plus g neutron times s2z and now what we want to do is to sandwich this this Xamon Hamiltonian between the psi here which refers to the ground state wave function which refers to this linear combination up here to check for the two angular momentum states to be a little more specific about those two angular momentum states psi 0 and psi 2 let me write them out so psi 0 allow me to allow me to write states this way in terms of the following quantum numbers l, s, i and m sub i let's let those be the quantum numbers then psi 0 is a quantum number in which the orbital angular momentum is 0 that's what the 0 here refers to the spin has to equal 1 because that's the only way you can get the total total experimental spin of the deuteron to come out when l is equal to 0 i is equal to 1 that's the value of the spin of the deuteron as far as psi 2 is concerned this is a d-wave so l is equal to 2 the spin is still equal to 1 you can buy 2 with 1 or you can get a normal total value of 1 like this if you prefer to think about this in terms of wave functions the first one is the same wave function I wrote down earlier which is not disappearing this is let's call it r 0 r as a regular wave function times y 0 0 even for the spins what we've got is s where m sub s is equal to m sub i the same thing of the 2 sides and the s is equal to 1 so s and e sub s are the triplet states that are made out of this the 2 spins are the particles added together now then in psi 2 what we have is we've got a different wave function r 2 of r and now we need to use clutch Gordon coefficients to combine orbital and spin angular momentum with orbital 2 and the spin 1 to create a total final argument of y so I'm going to write this this way as the sum on l l and s of y sub 2 l of the sum on angle k to the phi when the spin state will be the spin of 1 and then m sub s so this is equal to the spin and then we have clutch Gordon coefficients good grief a lot of time we have clutch Gordon coefficients which is going to be 2 1 l m s in the final shape i values are i or i here is equal to 1 like this so explicitly in terms of adding orbital and spinning angular momentum these 2 states we're taking probably another half hour we're going to take this all the way through let me just say that when you finally do this you can actually calculate we need to use the projection there about 3 or 4 times and then we're going to evaluate the citizenship of the deuter on in the presence of the external magnetic field including the orbital wave of their effects we're taking to a complex linear combination of 2 different roll values and then you're going to have an equation when you solve the first which you've got 2 squared is equal to 0.956 and you get 2 squared is equal to 0.044 so in general the wave function has about a 4% probability of being in a d-wave about 96% of the wave this is the ok, well work i have a couple of announcements i have here a memory statement that is


From VOA Learning English, this is the Education Report. Last year, 200,000 Chinese students studied in the United States. That was a 23 percent increase over the previous year. The Institute of International Education in New York reports that 26,000 US students were in China in 2011. They included 15,000 people studying for academic credit and 11,000 taking part in other educational activities. A program called the 100,000 Strong Initiative is trying to increase the number of Americans studying in China. The State Department launched the program in 2010. The goal is to send 100,000 students to China during a four-year period. Last year, the non-profit 100,000 Strong Foundation was launched. Project Peng You is one of the groups the Foundation supports. It connects American students who have lived or studied in China. Project Peng You is based in Beijing and led by Holly Chang. She says personal ties formed while studying abroad can have an effect on relations between the United States and China. She says there is still a huge amount of misunderstanding between the two countries. The Chinese government has offered 20,000 scholarships to Americans under what is known as the U.S.-China consultation on people-to-people exchange. The 100,000 Strong Foundation has no official relationship with the Chinese government. But the Foundation says it works closely with Chinese government officials to encourage more Americans to seek these Chinese scholarships. The goal is to give more Americans a chance to get a taste of Chinese culture. For VOA Learning English, I'm Laurel Bowman.