One of my main concepts is that through touch, through listening, through watching, that you can have a connection to the place that that material come from with poetic indicators of where the work is trying to take you. Durande, I'm at Ushia. I am an interdisciplinary artist and member of the Tel-Tan First Nation. When I was 18, I went back to Canada after about a year of traveling and enrolled in Getamax School for Northwest Coast First Nations Art in Hazelton, B.C. I studied there for two years under Master Carver Vernon Stevens. I wanted to go to Emily Carr. It was the only school that I applied to, and I went into sculpture to really determine my direction. I was mentored by Brenda Crabtree. She was very influenced on my practice. In Emily Carr, I took the opportunity to explore in different materials, ceramics, printmaking, doing some further exploration in paint. It really opened up that door for what materials speak. My work has always been performative. One of the pieces of fabrication was a bit of a replication of a regalia piece made from dentellium shells, and I was really thinking about questioning value in the work because I was fabricating a kind of ancient currency. On a model or on a form, it was very void of the kind of meaning that I wanted to give to the work, and so it needed to be on my body. What I'm doing differently in my practice from Emily Carr, it's specialization, and I also built conceptual foundation, and that foundation is what I drew upon when I went to grad school. And now, a lot of my practice, I call it conceptual because it doesn't matter what material that I use, as long as it's talking about these really important issues that I want to speak about. And right now, it's to do with mining, with decolonial design. And then I also work in a real material connection to industrialized land and body. When I was at grad school, I started to make the right rock rattles. They are meant to be machine, a way that they were activated by the people who were playing them and listening to them and, you know, feeling the vibrations or a way to hear the land. There was a book that came out about this ethnographer who had visited the Tel-Tan people. It really exposed me to a new kind of Tel-Tan art, and I've been pursuing and revitalizing Tel-Tan art practices and styles since 2008. I'm doing a lot of research right now on abstract Tel-Tan shapes. I've used them now for a few projects that I'm calling Tel-Tan Futurism. When I'm beading, I'm working out bigger picture ideas through making and through my hands, and so that's one of my grounding philosophies. Some of the best advice that I got while I was at Emily Carr is to make the project suit you. My advisor, Julie Nagam, is co-curator for the Insurgents Research and Show at the Winfrey Park Gallery. A piece that I submitted is called Agenda, Push It. Moose High, that's connected to a contact mic, so people can touch it. They can resonate the land. I'm trying to talk about this indigenous perspective and also place the indigenous body in the conversation.


People talk to us and ball about don't give an answer to me, because nobody has a higher position in this country than you have. President Eisenhower? Take this one. Hello? Yes, Mr. President. I'm so glad to hear you. Well, God bless you. How are you, sir? Doing pretty good. That's fine. I don't want to keep you too long, but I have been talking to Bob Anderson a little bit, and he told me he's going to see you soon. But I just wanted to speak to you first about a subject that bothered me very much. And I don't want to be in the position of second-guessing art, and I don't talk about it publicly, but it's this. Our position in Rhodesia. This thing, of course, I've read nothing on it. I have no briefing on it. I just read the papers. But participating in this embargo, and with Rhodesia having been a member of the British Commonwealth, I just didn't know. I couldn't, I didn't know the reasons, and I just, rather than try to get into the State Department and let them think, God bless them, I'd ask you. I wonder if I could have the general see you sometime the next day or two and go into that with you. And why we have gone along with Wilson to the extent we have, and how we've done it, and how we've tried to keep away from it as far as we could without completely sacrificing other entries. Are you going to be free any time next day or two for me to have? Well, I need to, I need for him to do it for two reasons. First, I wish you'd tell him, too, when you see him as a little service to me. I think I have some higher things in mind for him down the road. I'm going to be here a little while longer, and I don't know anybody that has been of greater service to me than he has since the day you told me what you did over here. Tell him, number one, I'm looking, I'm bearing that in mind, but number two, that the man that needs him most right now is the President, and that I may have to call on him to serve me a little more personally than I have in the past. And I know that any soldier is responsive to that request, but you prepare him for it a little bit because in the days ahead I'm going to have to get him to be coming in here a little more than he has. Mr. President, I'll tell you my absolute conviction. There's no man around you or that, that I know of any, whose comprehension of all of these complex subjects is better, and whose advice will always be absolutely objective. That's what? Nothing to know, nothing to see, that you don't have to fear that he has a partisanship, slays him in the slightest, he has not. He just wants to serve. I believe that when you told me, and he has confirmed that, and I know he wants to go to the top with his military career, and I'll try to see if he does that. But I have to rely on him to kind of serve me on overall policy that something besides just being Chief Staff of the Army or something like that during the next few months because this is pretty serious. I'll have him get in touch with you on two things, the complete story from beginning to end and together with the dangers we see and the problems that present in the Rhodesian thing, and number two, the Vietnam thing as of this moment because it's been too long since I had any suggestions. I will tell you, I will be delighted that he can come anytime, I'll make the time for him because I just like him as a friend of those things.  That's right. No one will ever have to be jealous of him because he doesn't think that kind of thing. He just wants to be helpful. Well, you inherited things here from a different party when you came in. I came in and I inherited things from my own party. Now, there have been adjustments and there have been changes and there have been problems and I have become a good ear closer to him since you were here and we've tried to handle things differently. I want to bring him in more than I have before and we have some adjustments. Some people that have been here are leaving and I need to make some adjustments accordingly and you can't do everything. It takes a little time and I had an election on my hands. I had to get that behind and then I had a first session of Congress. I had to get that behind and I found that we were involved in a lot of things that I've been trying to find ways and means of extricating us from. So no one's been more helpful to me than he has or you have, but I will have him get out there in the next day or two. I'll be delighted. I'd like to talk that over with him. How are you feeling? Well, I'm a gaining strength each day. I'm not playing golf yet. That is not hitting a long ball yet, but I bought another 10 days. I think I'll be playing with golf. Please watch yourself. Please do it. My love to Ms. Eisenhower. That I will. Thank you. Please kindly do it. Sure will. I'll have the general call you. Thanks.


Good day, fellow investors. Today I want to share with you my two latest financial mistakes. I will discuss what I did, why I invested and where I was wrong. I think it's essential to always look back at your investments and your investments mistakes. Because when you analyze the mistakes it could prevent you from making further mistakes in the future. So this video will also be a guidance for me not to make financial mistakes anymore or not to make that kind at least of financial mistakes. If you have made any financial mistakes in the past, please share them below in the comments. We can only learn from such shareings. This would be probably the best way to learn. So please share with us in order to enrich our knowledge and hopefully enable us to make glass mistakes in the future. As you probably know I don't make that many investments over a year. If I buy one or two stocks over a year I'm not happy. When I exaggerate, when I start buying three or four stocks in a year then it usually comes out as a mistake. So let's see what were my two latest mistakes. The first mistake I made, the last one and probably the most recent one, very discussed, very notorious is Teva Pharmaceuticals. This was Teva's stock price when I analyzed the company in order to see if it was a buy. You can see how I saw okay there were two peaks, there was a bottom range and then again the price was close to these historical bottoms. This gives me okay. It could be that the stock price will be at its lowest. So from a value perspective, fundamental perspective, I thought it was a buy. Of course I'm not buying on a technical reason ever, but I'll show you my fundamental analysis. Checked the company, the revenue breakdown, the guidance was positive, the Octavis acquisition should bring more revenues and synergies. But that was one point. Revenue, geographic diversification, mostly in the US, Europe, rest of world. What the Octavis acquisition brought was one of the largest generic pipelines in the world. So many more drugs coming online which should have brought the benefits to Teva. This was also one reason for the acquisition different geographic footprint. So now it could be synergized by selling all over the world different drugs. Then many thought that Teva paid too much for the acquisition and that's what sent the price down. Teva issued 25 billion of debt, used 8 billion of its own cash and diluted shareholders by 10%. Of course when Teva's stock price was at 55, 60, now then I can understand that they paid too much. Now that the stock price was 30, I thought okay, debt acquisition is calculated in the price if it was overpaid. Then I looked from my fundamental base, when is the debt due, what is Teva's expected free cash flow and what is the potential that the dividend would be sustained. Here was my first mistake, Teva's cash flow came in at 4 billion for this year, so it won't be 6 billion or 5, 6 billion. So if you put this line lower you see that there won't be any more dividends, but Teva will probably stay alive as it won't go bankrupt. That easily, especially as it has low debt repayments for example in 2022 or still 2018, 2 billion, 3 billion. So they will be able to cover that, but the dividend is probably gone. The plan was to repay the debt. Of course the last news destroyed that plan, but still Teva will try to repay with the free cash flow. They are still very free cash flow positive. I even looked at the management's 2009 projections to see how accurate they were in the projections and in 2009 they were pretty accurate for the next three years. So I thought okay, management what they say they actually do, I was wrong there. I looked again at Teva's estimates for 2015, how much wrong they were, was there a problem, free cash flows pretty correct, long-term projections, what are they going, how much money are they going to make per share, was again very very positive. From the fundamentals I switched to a pharmaceutical market outlook, looked how the healthcare ETF stopped growing suddenly because of all the issues with generic pricing. Nevertheless I saw that the market continues to grow, the demand for pharmaceutics continues to increase, so that was a bonus. What I especially saw is that people around the world and that was unfortunately some even happy that I lost because I invested in a negative karma stock, people around the world are unfortunately getting more and more sick and they need more medicine.  On top of the growth in the world people are aging, more medicine, more medical attention, more whatever and people want cheaper drugs and generics are usually much cheaper than the branded counterparts. Generic, the fastest growth in the last 10 years at more than 10% per year and expected to continue to grow that fast. What happens when a patent a company has on a drug expires, well you can see how fast that brand loses its market share to generics and that's what's happening to Teva's Copaxon when they use their patent. Nevertheless I looked there are many patent explorations, there will be more business for Teva, prescription sales drug growth is also expected to grow and Teva is the leader in the generic market. I even made a table with analysis of Teva compared to Pierce which is the best pharmaceutical company to be exposed to pharmaceuticals because pharmaceuticals don't fall that much in a recession. Price to cash flow yield was here from Teva and Teva had this dividend of 4% which was very attractive. Depth to equity again my mistake 1.05 because the equity was intangibles which they impaired recently. Analyzed dividend here you can see how was the story for Teva's dividend constantly up up up and up and then stabilized recently so I thought okay so I have a dividend while I wait for the situation in pharmaceuticals to improve. Going back to Teva's guidance I saw earnings per share of around five dollars giving me a price earnings ratio of seven cash flows from operations around 6 billion free cash flows of 6 billion which was very very attractive. This is now 4 billion and then it completely destroys my initial investment thesis. The investment thesis 80 plus new product opportunities 30 billion brand value so really really positive news for Teva and they deliver they really launched lots of drugs in the last few months and year. Again going back to the recession proof investment pharmaceuticals fall much lower than normal stocks this is the comparison between the US pharmaceutical ETF and the SAP 500 in the two years around the financial crisis. As you probably know Teva lowered their guidance missed earnings impaired 6 billion of assets and the stock price went from 30 to down to 25 immediately in the first day when I see a dividend cut I sell immediately because I know dividend investors are a little bit slower to digest the news and they will keep selling for a longer period of time. So that move was correct and now the stock price is around 19 as I'm filming this. Am I going back into Teva? No because I broke one of my rules and that's don't trust intangibles as book value so practically if I move the intangibles away from Teva there is no book value. What you can see here is the impairment from $31 per share in book value now we are at 24 and free cash flow has significantly decreased in the last quarter. As you can see here Goodwill is now 40 billion on Teva's balance sheet almost 50% of assets was 45 in the previous quarter so it was 50% of assets was Goodwill and then on top of it you have another 21 billion of intangible assets. So as a value investor I should have known that intangible assets don't give a margin of safety so that was my mistake I accept the mistake I accept the loss fortunately it was my 15th investment so the loss isn't that material for the portfolio nevertheless it was a mistake and I'll be more careful in the future. All right for my second investment mistake we have to go back to 2015. As you know I don't make lots of investments so I make even less mistakes so back in 2015 I invested in Whole Foods Market. I checked Whole Foods prices sales price earnings ratio and compared everything into a plot I saw that earnings per share are growing continuing to grow but the market reacts very volatile to what's going on so you can see here a similar pattern that was there with Teva. Price earnings ratio also dropped while the number of stores increased the 365 Whole Foods shops were getting opened around the state so there was a lot of positivity I thought the Whole Foods had a good business model and will continue to grow. Of course I made the mistake to buy in at the price earnings ratio of above 25 which is again something that a value investor doesn't do. So then of course the retail conundrum in America stock price fell from 14 to 28 increased to 33 I saw there so I took so I took a loss why did I sell because I bought at the valuation that was too high and Whole Foods simply stopped growing. If we look here I bought a growth company that then became no growth company and earnings per share went from 1.48 I expected those to continue to grow at 10% a year there are now 1.22 per share. Book value was also down operating cash flows were still up so it's still a positive from a company but the company's fundamentals weren't in line with what I expected and I also found better investments in other places so both my mistakes were I had money I didn't know what to do with that money because I didn't want to be overweight two free stocks I said let's buy the fifth stock let's buy Whole Foods market it's a good investment eventually turned out a good investment if I would have kept it for two years I wouldn't have lost anything I would have made a small 10-ish percent with a dividend 10-15% profit on the investment which would be good however I sold earlier because I made a mistake in my approach to the company and I think I made my money on other stocks more than 15% nevertheless it was still a mistake I bought the company expecting growth that didn't come so I as a value investor bought a growth company and I got burnt Teva similar situation I bought the company that I thought had a margin of safety it still has it's still an interesting investment but I think I can find better investments I just have to keep myself to investing maximum in two free stocks per year and waiting that they evolve so really investing the best stocks I do a lot of research so I should follow my research and my criteria thank you for watching share your comments share your ideas share your failures and looking forward to your comments and I'll see you in the next video


I hope that in the next 15 minutes or so, we will sort of start to see light at the end of the tunnel. We will get to understand what this wave function is all about, what can it tell us, what kind of information it can give us and what are the properties that it has to satisfy other than simply being a solution of a differential equation. What else, what is the physical significance and all that thanks to the work of this brilliant physicist Max Born. We are going to talk about Born Interpretation of this enigma of a wave function. So, Born Interpretation essentially says this. In classical wave equation remember Schrodinger equation started off as a classical wave equation of for de Broglie waves. In classical wave equation the mod square of psi denotes intensity of the wave. If you say psi can be imaginary also. So, if you multiply psi by its complex conjugate then you get mod psi square which is the intensity this was known. So, Born started thinking along this lines that we have this wave function which can be complex can be real all right. It is great that all possible information can be derived from psi but what is the meaning of intensity here? We are saying that this psi is the amplitude of matter wave. So, square of intensity of matter wave what does it mean? Intensity of matter wave Born realized would be the something to do with probability what does that mean? I look at some kind of a matter wave. In some region I see lots of intensity. In some region I see less intensity that essentially means that in the first region it is more probable to find the particle. In the other regions probability of finding the particle is less. So, intensity is related to probability and what I said was that this mod square of psi is really the probability density which is written as rho of x. What is the meaning of probability density? See it is at a point right psi is defined at some value of x, y, z or some other coordinate. So, you cannot really talk about probability at a point you have to talk about a region. So, if you are working in one direction we can say that we can talk about probability of finding the particle between x and x plus dx where dx is a very small increase increment in length. So, Born said that if you multiply mod psi square by dx then you get the probability of finding the particle between x and x plus dx. So, what is dx that is also important and you will see this is going to become most very strongly manifested when we talk about hydrogen atom wave functions later on. So, Born interpretation essentially says that mod psi square is the probability density and that is what makes life a lot simpler. So, now we realize that we do not have to worry about matter waves forget matter waves now we are worried about what we can call probability waves. And at this point let me stop for a moment and pay my gratitude and respect to our respected teacher Professor Balaichand Kundo who we unfortunately lost last year Professor Kundo was our teacher he was an inorganic chemist he taught us this portion when I was in college Presidency College Calcutta many many years ago and what I say now is merely a repetition of what he had told us I do not know whether it is written in as many words in any book. So, with my deepest respects to Professor Balaichand Kundo what we have now are probability waves right away the situation becomes much less disturbing I mean we can breathe easy we do not have to worry about why we are not seeing matter all around we are why we are not seeing matter wave all around us probability waves. Okay what about three dimensions in three dimensions probability of finding a particle at any point defined by xyz will be psi at xyz and t mod square of that multiplied by d tau where d tau is the volume of the small element that we get in Cartesian coordinates we get it by increasing x to x plus dx y to y plus dy and z to d plus dz. When we talk about spherical polar coordinates later we will see we get a little more interesting expression but the crux of the matter is psi tells us or rather psi psi star psi star psi is what theorists like to call it psi star psi is your probability density please do not forget the density part it is going to be very important later on. Now what you can do is you can find out things like average values because from classical treatment of mathematics the mean value is defined as integral when I say minus infinity to plus infinity I essentially mean the entire range of x when you integrate over the entire range of x then the function the average value of the function is whatever is the population distribution of probability distribution multiplied by the function you want to work with that gives us the average value of that function. So, average value of x is integral minus infinity to plus infinity x multiplied by p of x integrated over dx of course and average value of x square is x square multiplied by p of x where p of x is the distribution function how is the population distributed you can say or how is what is the probability distribution x square multiplied by the distribution function integrated over the entire range of x. So, that is exactly what we have written here what is the average value of a to know that first of all how do you find a you have to make a hat operate on psi. So, then in order to find the average you have to multiply by psi star integrate over all space. So, that is how we get the average value of any quantity that we get we are going to work out a at least one problem maybe in the next module while revising that is where this meaning of this average value and later on most probable value these will become much clearer I hope. So, this is how remember we calculate average value now what we have written here is the expression for well let us let us take a check on that we will come back and say it later. Next thing that we want to discuss is normalization of a function. So, if psi star psi is probability density when you integrate over all the entire range of your coordinates what should you get the particle has to be somewhere or the other right. So, integral of psi star psi over dx dy dz if you are working in Cartesian space is equal to 1 this condition is called the normalization condition. So, obviously divergent functions they cannot be normalized look at the function here cannot be normalized naturally look at the function here cannot be normalized it is becoming infinity at least at one point. So, what we see is that some of the values of psi which may be absolutely valid solutions of the wave equation. They are not going to satisfy bond condition and if they do not satisfy bond condition then they are what we call unacceptable. Acceptable values are acceptable wave functions are those that satisfy bond condition all right we will come to the remaining bond conditions also first condition we have said is normalization you should be able to normalize it to 1. These are some examples of acceptable wave functions well let us say what it should be what are the conditions of acceptability first is one it should be normalized what if I give you a wave function that is not normalized if I give you an unnormalized wave function something like psi which is say not normalized we can always say that I will normalize it by multiplying it with n what do I mean I mean that I n has to be chosen in such a way that n can be actually complex quantity also. So, n star multiplied by n integral psi star multiplied by psi d tau that has to be equal to 1 this is really the normalization condition. So, if I give you a non normal unnormalized wave function no big deal you can multiply it by some constant and you can normalize it is something that is doable we are going to encounter several examples of normalization in subsequent classes. Second condition that we that is very very important is that it has to be continuous third condition is this del psi del q I will write the first derivative that also should be continuous. Now, these come from the requirement not so much from bond interpretation, but these come from the requirement of the differential equation per se right. So, there is a little bit of difference between these two and the first one. See we are working with something like del 2 psi del q 2 second derivative. So, these are the conditions for the second derivative to exist as you will see that this condition number 3 especially is often violated we are going to see some examples. And the last condition I want to talk about is that it must be single valued. What is the meaning of single valued if you have a function which has more than one value at any given x then what is the probability density at that point? You cannot have more than one values of probability density at a point right that is a problematic situation. So, it must be single valued in order to satisfy bond condition. So, this is a perfectly acceptable condition you can think is it actually not perfectly acceptable. What about this it is continuous single value everything is fine look at this point at this point there is a discontinuity of del psi del q, but as you will see this is taken as an acceptable function in some cases that we are going to discuss. So, so this del psi del q is a condition that is not so strange. What about this let me write the functional form of this one I think this is sin theta by theta at first look you might think that it is not acceptable why because what is the value of sin theta by theta for theta equal to 0 denominator is 0 numerator is also 0. So, 0 by 0 undefined however if you look at the function if you zoom in zoom in as much as you want what do you see at value very very small values of theta if you approach from the right the value is going to be nearly 1. If you approach from the left then also the value will be nearly 1 and the limit exists because from both sides you approach the value of 1. So, what we do is we set this value sin theta by theta and write like this at theta equal to 0 is equal to 1. What is 1? 1 is essentially the limiting value of sin theta by theta for theta tending to 0. So, the value of sin theta by theta is defined to be 1 and this is called a removable discontinuity. So, this is acceptable. Let us show you some examples of unacceptable wave functions this one is unacceptable why because it is not continuous. It is like sin theta by theta but the same value is not obtained if you approach from left and from right. So, it is unacceptable. What about this? This is also unacceptable because del psi del q is not continuous but given the system something like this might become acceptable as we will see. This is definitely not acceptable because it is multivalued it is not single valued this is what I was saying and this is not acceptable we have discussed this already because psi goes to infinity. So, what we see is that there are several restrictions on the wave function that arise out of born interpretation and these restrictions give us what are called boundary conditions and these boundary conditions bring in quantization as we are going to see. So, all these conditions that are there they bring in restrictions and these restrictions eventually bring about quantization. So, the origin of quantization lies in born interpretation. So, even though in Schrodinger equation we do not see any quantum number quantum numbers are going to arise the moment we try to apply these boundary conditions and this is something that comes out beautifully when we discuss a free particle and particle in a box that is what we are going to take up next.


I'll start with a quick review of what we had so far. And so we started in the first lecture by talking about the connection between entropy and area for black holes. We talked about the example of the Schwarzschild black hole. And we said that in ADS CFT, we could understand this connection between entropy and area by saying that the area of the Schwarzschild black hole was actually equal to the microscopic thermodynamic entropy of the CFT. And then we had a different way to understand that as entanglement entropy, so on the geometry side, there is a maximally extended version of the Schwarzschild black hole. Maldesina proposed that this maximally extended black hole could be understood as being dual to a specific purification of the thermal state of a CFT, known as the thermal field double state. So this is where you have two CFTs, and they're entangled together similar to this formula. And so in that case, the thermal entropy of the CFT is, we can think of that as the entropy of the single CFT subsystem, or equivalently, that's the entanglement entropy between the two CFTs. And then we moved on to say that if you now consider just a single CFT, what we understood is that even the vacuum state of a single CFT, so as an example, consider the CFT on a sphere, so even the vacuum state, which is a pure state of the single CFT, if we consider a subsystem of this, and specifically I want to consider a ball-shaped region on the sphere, so we consider the subsystem B and its complement, then there's an entanglement structure, which is just like what we had for the two CFT state describing the extended black hole. So this is now just the ordinary vacuum state, but we can still understand it as an entangled state between this ball and its complement. So the fact that it's entangled corresponds to the fact that here we're summing over some set of product states. So it's not a, even though it's the vacuum state, there's lots of entanglement across the surface. So specifically what this means in this case, so we can write it in a way that looks like this thermofield double state, but these energy eigenstates, they correspond to eigenstates, not of the full Hamiltonian on the sphere, but of some symmetry generator that generates, this is a symmetry of the CFT. It's associated with a conformal killing vector, so a time-like vector that acts within the domain of dependence of this ball-shaped region. So there's this time-like coordinate that I'll call theta generated by some Hamiltonian h, theta, and I'll tell you exactly what that looks like later on in this lecture. And so what we're talking about here is some set of eigenstates of that Hamiltonian. And over here, similarly, we can define states of this side, and those would be eigenstates of Hamiltonian generating a symmetry in this region, which is the domain of dependence of this complement of the ball, or this other ball, which is the complement. So this is all happening on the boundary. For now, we can ignore the middle of it. So the structure of the vacuum state, if we make this arbitrary choice, and we say this is one subsystem, this is the other, it looks just like the structure of this thermofield double that was dual to a black hole. And so we can carry over a lot of what we learned about the black hole. We can now think about this in the holographic context and say, if we make this choice and we split up the boundary into these two parts, we can think of the density matrices describing those two parts. So each of these are density matrices that look thermal. And we can say, well, the whole vacuum state is dual to this ADS. But now we can ask, what is just this density matrix dual to? What part of the geometry does this contain the information about? And so even though there's not, from the start, any obvious decomposition of the geometry, once we make this choice and focus on this region, we can, there's a naturally associated wedge of the full geometry that we could say is dual to this density matrix, or we can argue is dual to this density matrix. So this wedge is basically just the region of the geometry. One way to define it is the region of the geometry that I can communicate with. So I can start at some point in this domain of dependence region for B and send a signal and then receive the signal back. And so that defines some wedge of the geometry. It's actually also another way to understand it is it's a Rindler wedge of ADS. It's the region of ADS that if you have some accelerated observer that starts here and ends up here, so this is some constant acceleration trajectory, this is the region of the geometry that that observer can see or that can communicate with, can send signals to and receive signals back. So this is like a, it's like the ADS version of Rindler space. So OK, so it's natural to say that this density matrix for the region B, that's sort of, that's dual to the gravity in this wedge region. And similarly, the other density matrix is dual to the other region. And then I was saying that these third and fourth regions, well, they must be, the information about those must be contained in, must be the information in the state which is not contained in these two density matrices. So that information is in the details of how the two are entangled with each other. OK, and so finally, so all the similarity with the black hole case suggests that maybe the entropy also, so the entropy of the subsystem should have some relation to an area in the bulk geometry. And in the black hole case, that area was the area of the horizon, which is the area of some, so some spatial surface separating the two sides. So this is a space-time diagram. But if I just draw the space for the black hole space-time, then it was these two asymptotic regions connected by some wormhole. And the area is just the minimal surface, an extremal surface separating the two sides from each other. So the black hole entropy was just equal to the area of that surface divided by 4. And similarly here, then we might guess that the entropy of this subsystem would correspond to the area of this surface separating the two sides of ADS from each other. And in this case, we can actually calculate what this entropy is in some CFT. We use a cutoff to get a finite answer and compare it with this area. And one finds that indeed, this formula is true. And so then this motivates further generalization, which is by Ryu Takayanagi and a covariant version by Huberni-Rangamani and Takayanagi. And they said, now consider some more general state of the CFT. So some state psi, which is not the vacuum, but not the thermal state either, could be something more general, which is, we assume, is dual to some asymptotically ADS space-time. And now instead of the ball-shaped region there, consider some more general region. So this is the space that the CFT lives on. And A is the subset. And so again, we can consider the density matrix. So starting from the state psi, we can describe the subsystem A by a density matrix or by an ensemble. And in general, this will have some entropy. And so Ryu Takayanagi, the entropy of the subsystem, would correspond to the area of something in the bulk geometry. And their conjecture is that what you want to do is define a surface A tilde in the bulk. So we can think of this as living on some spatial slice of the bulk. But actually, in general, it's not clear which spatial slice. It's not clear initially what spatial slice you should pick, because now there might not be any kind of special symmetry or any special time fulliation. But what they say is you want to find a surface here, which is an extremum of the area functional. So I should just write that down. So the area functional is just this. So this spacetime M has some metric. And then it's the usual definition. You would pull back the metric to the surface and take the square root of the determinant, integrate. So explicitly, this is the functional we're talking about. And so you want to find a surface A, which divides the space into these two parts with boundaries A and A bar, where A tilde is an extremum of this functional. It might be that there are more than one. It might be that you find multiple extrema. In this case, the prescription is that you should choose the one with the least area. Generally speaking, you will just find one extrema. And so their conjecture is then that this is the surface whose area corresponds to the entropy. Yeah, yes. Right, so the question was, in order to check this in detail, do I need to know how field theory parameters are related to gravity parameters?  So I think the original point of view was just suppose you have some existing ADS-DFT, like n equals 4, and super Yang-Mills theory with large lambda. And we think this is dual to type 2B string theory on asymptotically ADS. And in these existing examples, we would have some specific relation between parameters of the field theory and then parameters of the gravity theory. And then on top of that, so this would then just be an extra thing. I mean, then we could just check this directly, because we already know, based on other calculations, how these parameters are related. If this is the only thing, I mean, another viewpoint that I'll take a little bit later on would be to say, just start with the CFT, and then you can ask. You can calculate entanglement entropies, and then ask, is there some geometric way to represent those? And then I guess in that case, you could do one particular calculation to fix this relation between G Newton and the field theory parameters. So say I calculate the entanglement entry for some specific ball. OK, then maybe I need to fix the coefficient using that one, but then I can check the infinite number of other possible regions and see if it works. I said it last time, but I'll say it again here. This is a little bit of a funny formula, because in the way that this is written, both sides are divergent quantities. So when you calculate entanglement entropy, I can think of a field theory as being regulated somehow, where you say as a limit of some discrete system, balls and springs or something. And in the regulated theories, you can always focus on some subsystem and calculate the entanglement entropy, and it's some finite quantity. But typically then when you take a limit where the regulator goes away, in quantum field theory, this entanglement entropy is divergent. In a 2D CFT, for example, in the vacuum state, if I compute the entanglement entropy of some interval, there's actually a universal result, and you get a logarithmic divergence. And then higher dimensions, typically, then you have a lot more choice of the shape of the region. So then there's a divergence which is proportional to the area of the boundary of A times, so area of the boundary of A times the appropriate power of the UV cutoff to make this dimensionless. So one way to interpret this formula is that you should calculate things with an explicit UV cutoff in the field theory and then compare them with quantities on the gravity side, which have an IR cutoff. So on the gravity side, the area here is infinite because it's an infinite distance to the boundary of ADS. And so you could try to work with a UV cutoff in the field theory and work with a cutoff in the gravity side and then compare things. I find it a little bit more sensible just to do what we normally do in field theory and try to define quantities which are actually finite. So a less ambiguous kind of comparison would be between not the entanglement entropy itself but other quantities derived from the entanglement entropy. So I'll mention a couple of things if you have various combinations of entanglement entropies, so the simplest being this combination. So we consider some state and the entanglement entropy of this subsystem, the entropy of this subsystem, minus the entropy of the combined subsystem. Then what we notice is the divergence here, which is proportional to the area of the boundary of this plus the divergence there, cancels with the divergence here because the boundary of A plus the boundary of B is the boundary of A union B. And so this quantity is typically finite for well-behaved field theory states. This is the mutual information. This is called the mutual information between A and B. So it's literally how much entanglement there is between A and the rest of the system plus the entanglement between B and the rest of the system minus the entanglement between the union of A and B and the rest of the system. So roughly speaking, what this picks out is some entanglement between degrees of freedom of A and degrees of freedom in B, entanglement or correlations. So that's one finite quantity. Another one is just to look at vacuum subtracted quantities, entanglement entropies. So if we're interested in some state psi, which is not the vacuum state, then you can calculate the entanglement entropy for some region but then subtract the entanglement entropy for the same region but in the vacuum state. And this quantity is also typically finite. So this is often what we would do with, say, the stress energy tensor in field theories. I already mentioned some of the evidence for this comes directly from calculations for ball-shaped regions in the vacuum state of a CFT. You can check that this agrees. In 2D CFTs, there are more detailed calculations that you can compare. You can do the calculation for intervals in thermal states or for multiple intervals and see that it's correct. Other pieces of evidence are that this definition of Ryu and Takinagi obeys various properties. It can be shown to obey various properties that entanglement entropies are known to obey. So for example, this mutual information, in quantum mechanics, you can show that it must be positive, not negative. And there are a list of similar inequalities. And so one can check. One can ask, given a reasonable spacetime, if you define the entanglement entropies using this formula, if this formula is true, do the entanglement attributes you calculate obey the various constraints. And so there are a number of non-trivial checks that have been done of that form. And I'll probably say more about this later. And then actually in the case where the spacetime is static, then there's actually, I mean, more or less a proof, maybe not a rigorous proof, but some fairly convincing argument by Lukowitz and Maldesina. And that starts with the idea there is that in the field theory, there's some way to calculate Renyi entropies. I think I mentioned in the discussion yesterday about some path integral way of calculating, of representing the density matrix. So there's some path integral way of calculating these Renyi entropies, or more specifically, trace of rho to the n as a quantity that one can give a path integral description of. So this thing, using the standard ADS-CFT correspondence, you could map this over to some gravitational path integral. And so we essentially know a correct answer for how to calculate what this corresponds to on the gravity side. And so starting from that connection, Maldesina and Lukowitz made an argument. So to relate these to entanglement entropies, you have to take some analytic continuation and take a limit where n goes to 1. So Maldesina and Lukowitz made a formal argument that using this ADS-CFT connection between the two path integrals and taking this limit, one can actually recover this result. And that's so far for the static cases. So I'm going to talk about some implications of this. One more point. So this formula as written, it's understood to be, so this is the CFT entanglement entropy. It's understood that this is a large n type formula. So if we have holographic theories, there's typically a parameter which is the number of degrees of freedom that's large. So it's just the rank of the gauge group in n equals four or the central charge in 2D CFTs. And so this CFT quantity here is understood to be, so it has some expansion in the inverse of the parameter, a one over n expansion. This area here is understood to be supposed to be equal to the leading large n, so the leading term in that expansion. And there are other, so other corrections have been discussed if you look at the sub leading terms in this one over n expansion of the CFT entropy, then they correspond to other things. So just mentioned specifically Faulkner, Lukowitz and Maldesena said that the next term, the first term is the area of this extremal surface and then that gets corrected by a term which is actually a bulk entanglement entropy. So a quantum correction in the bulk which is the entanglement of the perturbative bulk fields on one side of the entangling surface and on the other. But mostly I'm going to focus on this leading, this sort of large n limit of this expression and think about the consequences of that. Okay, so implications, okay. So the first one is that now that we have this connection between entropy and area, not just for simple states or the whole system but for arbitrary subsystems. So this gives us a huge number of relations between entanglement and between the geometry. And because we have now so many connections there, I think we can plausibly reconstruct, so given a state which has some holographic dual space time, we can plausibly reconstruct the geometry at least, at least the part covered by some of these extremal surfaces calculating entanglement entropy. So so far there's not a general formula for how to do this but you can imagine that prescription is that someone gives you a state of which they assure you has some gravity dual geometry. Okay, and now you want to figure out what geometry is encoded in this state. So you just go ahead and calculate the entanglement entropy in the field theory state for lots of different regions. So you think of all sorts of different regions and you calculate all these entanglement entropies. And then you just ask is there an asymptotically ADS space time where the extremal areas reproduce all your answers? So is there a space time where the areas of the extremal surface with boundary, the same as the boundary of A, matches with all these entanglement entropies that you've calculated? And the point is that this is a highly over constrained problem. So if we think about the space of functions, so you think about well how many possible regions are there that I can compute the entanglement entropy of? I mean there's some enormous space of these regions. This is subsets of Minkowski's Euclidean space or subsets of a sphere. The space of functions on that space of subsets is much larger, the space of asymptotically ADS metrics. Okay, these are functions of some small number of variables, so this is a handful of functions of some small number of variables. This is a function of subsets of a space. And so the picture is basically like this if I'll draw it as a low dimensional space asymptotically ADS metrics. So given any asymptotically ADS metric, you can compute all of these areas for the various subsets and that will map you on to some point in this space of functions S of A. But it's a tiny measure zero subset. So let's say someone just gives me an arbitrary state of some arbitrary quantum field theory and I go ahead and calculate all the entanglement entropies for all the regions. So I'm going to end up some place in this space of functions, but it's very unlikely that all those entanglement entropies could be reproduced by some geometric prescription like this. Okay, you won't in general, if someone just hands you one of these functions or some set of entanglement entropies, you definitely won't be able to find some geometry which reproduces those. Okay, the space of geometries is much too small for that correspondence to be one to one. Okay, so the fact that you're told that this is holographic from the start. Okay, so if I know I'm on here somewhere, then I should be able to find, I should be able to find the spacetime. Okay, so the, I mean, one caveat that I have in brackets over there is that there could be parts of the spacetime where none of the entanglement, none of the extremal surfaces reach, and then I'm not going to be able to reconstruct those. Okay, so just to draw one more picture, the idea would be, if I want to, here's my, think of the geometry, if I want to reconstruct the metric in a region there, I mean, there's, I think of some surface passing through there and then I can make all sorts of perturbations to the space. So there are many, many, many, many surfaces that pass through this region, and if I know the area of all of those, then I can imagine inverting. Of course, it's a challenging mathematical problem to do this inversion. Okay, so just summary only, very special entanglement structures will be consistent with a geometrical description. So this is actually a really interesting question, just to understand better, I mean, what properties of a field theory state will guarantee that I can find a geometry that captures the entanglement entropy? If we can understand that better, I mean, this is, this should help us understand which field theories can have a gravity dual. So if we can understand which states have their entanglement entanglement entropies captured by geometries and then understand, say, you know, what kind of Hamiltonians do those states, are those states, say, the ground state of or the low energy states of, that could probably really help us understand why ADS-CFT is working or which theories have gravity duals. Yes, that's right. So specifically, specifically, you could definitely have a part of the geometry, sometimes people call it the entanglement shadow. You could have a geometry where some region in the middle is not covered by any extremal surface. So this is kind of interesting. So actually, regions behind black hole horizons, for example. Okay, so that's why I said that. You're obviously not going to learn about this part of the geometry because these areas don't give you any information there. By the way, in two dimensions, for two-dimensional spaces, it's a mathematical theorem that you can do this reconstruction and the only obstruction would be parts of the geometry where the geodesics don't cover. Okay, so, yeah, any more. But yeah, the question was about the quantum corrections. And, right, so if we think of the gravity, what do these quantum corrections mean? If we think of the gravity theory, so this is supposed to be, the CFT is to some quantum theory of gravity. And so on the gravity side, there's a classical limit, which is what I'm mostly talking about. But then we can think of there being quantum corrections to that classical limit. And the simplest quantum corrections you can understand by thinking of perturbative quantum fields living on a fixed spacetime background. So you have some geometry and then on top of that, I guess the next approximation would be, instead of just having a geometry or some classical fields, you can think of there being a geometry and then also some quantum state of the various supergravity fields. So the first correction that I was talking about, so instead of just learning about the geometry, if you look at the entanglement entropies and also care about the one over end corrections to those, then you'll also learn about the state of the fields in the geometry as well. So the connection is not just with geometry. Once you include these quantum corrections, you learn about the bulk fields as well. Okay, well since there's this more or less complete information about at least parts of the spacetime contained in the entanglement information of the field theory of, sorry, yes. There was a paper by Aaron Wall and someone else, maybe Netta, Engelhardt, that specifically addressed this question. It's called, maybe entanglement shadow was in the title. Oh, sorry, yeah, Extremal Surface Barriers, okay. And so I would recommend that you have a look at that because they have, yeah, they've spent the whole paper kind of looking into that. And I think it's a little bit more general and they have some general results about when it can happen. Okay, so since we're understanding the geometry as being contained more or less in the entanglement structure in the field theory, we can be even bolder now and ask whether you can, so understanding how gravity emerges, I'd be part of it as understanding how spacetime is encoded in your field theory. But then we can ask, I mean, can you actually see some sort of spacetime dynamics or can you learn about something, about gravitational physics by understanding properties of entanglement in the field theory? And so let me, oh, I erased the picture. So let me reproduce what I just erased. So we had this map between asymptotically ADS metrics. And then this was the much larger space of functions S of A. And so, and that mapped into some small measure zero set of this space. Okay, so there's an interesting point which is that not all of these functions S of A could actually correspond to the entanglement entropy of various regions in a consistent theory. So the entanglement entropies satisfy various, must satisfy various constraints. And these are constraints that you drive directly from quantum mechanics. They're just linear algebra properties about eigenvalues. So it's impossible to violate them. Okay, so I think I mentioned one already. You have two regions, A and B. I defined this mutual information which was S of A plus S of B minus S of A union B. And it turns out this has to be positive. This is actually a good exercise. So this has to be positive for any quantum theory. There's another one that's similar but involving three regions. Okay, so you can show, and it's much more difficult that entanglement entropies for combinations of these combinations of three regions have to satisfy this inequality. This one is called sub-additivity. This one is called strong sub-additivity. And then there are more that I'll talk about. There's one called the positivity of relative entropy and the monotonicity of relative entropy. So there's a number of these constraints. And on this picture, what it means is that part of this space of functions, let's say, these are typically inequalities. So there's only certain functions, S of A that could actually be entanglement entropies. Okay, there are some, if you have some function of regions where you find one of these to be violated, then that function can't possibly be the entanglement entropy, describe the entanglement entropy for regions in some consistent quantum theory. On the other hand, if you start with a metric, so if I start with some asymptotically ADS metric and then compute the areas of extremal surfaces using the Ryutaki-Anagi formula, I don't always end up in this good region. For some metrics, I end up in the region that can't correspond to a consistent quantum state. Okay, so these ones here, these violate entanglement constraints. And what you find is that some of the space times, some of the asymptotically ADS times I start with, I calculate all of these extremal surfaces, I find that they're in the allowed region, they satisfy all the constraints. But other ones, I write down the space time, I start calculating extremal surfaces, and I find that this function violates the constraint. Okay, so what does that mean? I mean, it means that this geometry here, it can't really be physical. It can't actually, if it were physical, some physical consistent asymptotically ADS geometry, which is an allowed state of quantum gravity, which would be dual to some allowed conformal field theory state, well that must satisfy all these. And since this one doesn't, it's an unphysical geometry. And so by kind of mapping out this space, the green region, we'll be able to learn about something about constraints on geometries based on these fundamental quantum mechanical constraints. So the question was what do I require for these to be true? So most of these are just true about any quantum systems where A, B, and C are arbitrary subsystems. So I think that even, I mean, I have in mind local quantum field theories, but it's likely that even for more general theories, as long as I can isolate some subsystems, as long as I, where they, where you have some degrees of freedom and then some independent degrees of freedom, then they should be satisfied. Yes. Yeah, I think, let's see, I mean, you could choose them. I think in this way of writing strong subjectivity, normally we imagine them to be distinct, but I think I could write this in another way where they would be allowed to be overlapping. Yeah, actually I don't remember, maybe this is more, maybe this is okay, generally. Yes, yeah, we'll see, I'll go through some of these results, yeah. So I'm running, let's see, I'm running out of time. What I'm gonna do is set up, so the next lecture, basically the plan for the next lecture is to explicitly derive it and tell you about some of these constraints. So I'll just set that up by mentioning some of the specific constraints that I'll use. So what I'll do is start with geometries that are close to ADS. So ADS, for pure ADS, then this is okay with all the constraints, if I just have that, but even if I perturb away from ADS a little bit, then what we'll find is that some of the geometries actually violate some of these entanglement constraints. And so if we start, okay, so if you think about these small perturbations, we can ask what are the constraints on states which are close by the vacuum state? So if we start with small perturbation to the vacuum state of a CFT, then there's actually a simple constraint on entanglement entropies that you can derive directly from the definition. So we can recall the definition of entanglement entropy in terms of the density matrix. And now we just imagine taking the state of the whole system. For us it's going to be the vacuum state, but this is so far it's more general. So take the state of the whole system and perturb it and see what happens to the entanglement entropy. And so what we find is that we have the variation of this that gives minus trace of delta rho, dog, rho. And then there's another term that you would get by varying the logarithm, which would be basically just this, but it vanishes because these density matrices should all have unit trace. So if I vary the state, then the trace of delta rho is just going to be zero because all of the rows always have trace of one. So this is a formula for the variation of the entanglement entropy. And now we make a definition. I'm just going to rewrite that by defining the modular Hamiltonian. So HA, the modular Hamiltonian, is just defined to be minus the log of the unperturbed density matrix. It's just this quantity that appears. And the reason that we make this definition is, so then now I can rewrite the right hand side here as the change in the expectation value of that operator. So the change in the entanglement entropy for my small perturbation is equal to the change in the expectation value of this operator. And this is useful, I mean, in many cases, this HA would be very complicated, but there are cases, if we have a starting point where we know exactly what this density matrix is, then this will give us a useful formula. So I'll just end with one example that we're going to use next time. Okay, so if we have a system where the density matrix takes a thermal form, so if rho A is equal to one over Z, e to the minus beta H for some beta and some H, then this one gives us that delta of SA is equal to one over T or beta times delta H. And so this one here is this whole thing, it's just like the first law of thermodynamics. I mean, in fact, it's sort of a quantum version. It is the first law of thermodynamics, but it's actually a nice quantum generalization. So what it says is that if I start with some system, I mean, looking ahead, what I'm going to have in mind is a ball-shaped region of a field theory in the vacuum state. And we remember that we could calculate the density matrix explicitly for these ball-shaped regions and they took a thermal form. And now what it says that if I make a perturbation, if I vary away, say from the vacuum state in this case, that for any variation, the change in entanglement entropy is going to be equal to one over T times the change in the expectation value of this Hamiltonian operator. So it relates the change in entanglement entropy to the change in energy. In the field theory, that's going to turn out, this side will be able to write in terms of the stress energy tensor. Okay. And so this is the basic constraint that you get for small perturbations to the vacuum state for entanglement entropies. And next thing, we're going to translate that to the gravity side and get a constraint on geometries, which are close to, which are close to ADS. And what we'll find is that this exactly gives the linearized Einstein equations. So you actually, directly from this thermodynamics of entanglement, sometimes people call this the first law of entanglement entropy, we're going to see that you just translate it mathematically starting from the Ryu-Takyunagi formula over to a constraint on geometries. And it says that the consistent physical geometries are the ones that satisfy the Einstein equations to a linear order around ADS. So we'll do that. And then we'll talk about a non-perturbative, well, we'll talk about constraints at second order and then kind of non-perturbative constraints. And then you learn things about sort of non-linear, non-linear gravity, again, coming directly from quantum mechanics. And that'll be on Monday. You have a question? Yeah, this is, so I had this Rindler Hamiltonian for the wedge. And then you map that using a conformal transformation to a Hamiltonian that generates a certain conformal transformation, a conformal killing vector in the domain of dependence of the ball. And next time I'm going to write explicitly what this modular Hamiltonian is. Yeah, okay, so I'll stop there.


Hello. Hello everyone and welcome to the 730 to 8 a.m. session of the 2023 Open Simulator Community Conference. In this session, we are pleased to introduce the presentation. Lone Wolf has been programming since he was 16 for over 40 years. He has built a number of major systems and Wolf Territory's grid is one of his biggest. Please check out the website found at conference.opensimulator.org for speaker bios, details of the sessions and the full schedule of events. The session is being live streamed and recorded so if you have questions or comments during the session you may send tweets to at OpenSimCC with the hashtag pound OSCC23. Welcome everyone. Let's begin the session. Hi there. It's a real pleasure to be here. I feel a bit out of text by the first session, which is really interesting. So I'm the owner of Wolf Territory's grid and I'm going to talk a bit about what it is. We are the largest by land area OpenSim grid since last month. We are now, we're about 96% the size of second life in terms of land area and I've just bought this building. Cloud storage, which is quite to avoid space problems with assets and we're running in a very big Proxmox cluster. So just to give you an idea there, you can see that when it comes to storage we're using 0% of our available space. But it's not as simple as all that. So this is another little diagram just showing about how we're doing it. We have about 26,000 equivalent second life regions and our whole grid is joined together. So you can actually get from one end to the other. You can sail or fly generally. It sort of works from one end to the other. It's very, very fast. So it doesn't matter how it doesn't matter what sort of vehicle you've got. Some vehicles of course have something in the script that stops you going. We have and we can sort that out. Anyway, 26,000 regions joined together. You can spend hours getting lost and exploring. I'm always really excited when our users, we have 800 users and when they build something new and that happens a lot where they can't go alone. You should have a look at this. So but to do that and to have that infrastructure is required some rewrites of some parts of it. Our asset services, for instance, we don't use the built-in asset service. We have our own asset services that talk to Cloudflare. Some of the assets that you get directly from the grid will actually be delivered from a local server to you. So if you're in the States when you first request certain things from the grid, instead of it coming, it'll come from our service in Germany and then it will be bounced off servers in the States. So that makes it real quick to get things down. So on top of the whole base of OpenSim, which is incredible and it's really an honor to be here with the guys who are basically behind it, we have a whole stack of other things as well because obviously to manage the amount of servers we have takes a lot more than just the standard OpenSim package or even using anything else. Of course, all our regions are running on Linux. Our whole grid is running on Linux, mostly Debian 11. We use Subaboon 2 servers as well for certain things. So we have the equivalent of 26,848 Second-Life Sims. We get about 4,300 visitors per month, but that's going up all the time. And I think we're about 200 visitors a month behind OS Grid, but we've only been going for three years, which is why we haven't got that many registered users. We have a web control panel, which you can see on the right-hand side of this slide, and that has some real cool tech in it. So our users, for instance, when you buy a region, you can go into there and use the terrain generator and click and click, and it will randomly generate a terrain for your region. You click a button and bang, you've got beautiful mountains and they're all unique because it's randomly generated. It took me about three months to write that. The other things you can do is, through our control panel, you can do things like changing your region name, we have Globits and Podex, so you could choose a grid currency, you can change the physics engine, you can scale your region. So if you need more resources, you can see how your region is doing in terms of user RAM and processor. You can restart your region, you can update your map, you can see the console of your region, but it's all done through a web control panel. And that's actually more complicated than it looks because obviously, we've got all these servers, so being that we've got like 11 region servers, one your region will be sitting somewhere on one of those servers. So when you hit like update map or restart region, the grid infrastructure has to go and go and find your region on your server, log into it, act, do what you need to do and then leave it there. It has taken an awful lot of crying and pain to do that. And getting the latency going for this type of grid has been very, very hard. There is a point where you cannot just run with standard open seam because when you get above a certain number of regions is what we found. When we got to about 400 regions, I started having all kinds of problems and latency issues and things were really slow. We had issues with region crossings and teleporting and actually it was all down to one thing. I thought it was down to the actual regions themselves because it wasn't all the regions, it was down to database latency. So what we have is we have three database services in a cluster and what that basically means is that two of them can blow up and the other one will still carry on. And the way they run, they also get backed up every night obviously onto the cloud storage, but it just means it's really, really stable in terms of database latency, but database speed, the speed at which your grid access to the database affects everything else. And that was the one thing that took a long time to learn because it did look, we have a region on our grid with 120,000 prims and he's got about 16,000 scripts running on it. And he said it's the first time he's ever had and it's actually an 8x8. And he's the first time he says, first time in 10 years, we've had it running properly. So that was really interesting. So good. Okay, next slide. Next slide, there's a button there. Okay, so a bit about our asset service. So the beauty of having Cloudflare R2 storage is that our assets are stored on masses and masses of servers. I don't know how many, Cloudflare don't tell us. But that gives us about 10 petabytes of available space if we ever need it. You pay by the amount of space and transfers you do. In the first month, we ran our Cloudflare asset storage. It worked really brilliantly, but it cost $280, which is an awful lot to store your assets. So I rewrote the asset service so that it actually utilizes the way that object storage works. If you've not heard about object storage or what it is, it's a really cool way of storing things where you write it once and read it a lot of times. So for instance, YouTube videos, YouTube music, and different types of storage and assets are perfect for it because of course, we write them once and we read them a lot of times. By redoing that, we use DNS load balancing. What that means is we've got a pile of asset servers and it just randomly chooses one because it's a very fast movement. So yes. So we are using Cloudflare's Constance Delivery Network. Bobby, Bobby, Bobby. Okay. So Crystal Frost viewer, for those who don't know, we're involved in that. We, Bobby is helping me as well. Bobby is an RIR robot. He's actually part of the infrastructure. I'll talk a bit about him in a minute. We are a part of the developers group with Crystal Frost viewer, which is something coming out and they've got, and also we've got, we are working with, it's a tiny weenie web company called Dream Hosting AC, but she has direct links into the data center. So we get our stuff. We can spin up servers very quickly. We get really amazing support. And so we are all, everything's just really cool. I remember when she first arrived, I was running my, when we started, we only had like 100 regions. I was running on like nine servers at Contabo and anyone who's used Contabo is absolutely brilliant until you have to raise a ticket in your servers down. And she arrived on my region and said, would you be interested in moving to my little hosting company? Because I've got, you know, I've got direct contact with the people in the data center and I can look after you. And she's been absolutely brilliant. And we moved to her due to a disaster because we all know what they're like hosting disasters. Okay, so next thing. Okay, so Bobby, Bobby is our chat GPT-4 AI. Now he's, it's not quite as simple as just connecting the grid to chat GPT-4. We have a big database and all kinds of things going on in between him to maintain contexts because normally with chat GPT-4, if you, you, you connect something to it, it won't remember things that you've said to it before. So I'm going to just talk to it now. So Bobby, hello. Now, the other thing about Bobby is Bobby knows all about the grid. He won't work properly on this grid. As you can see, he's lying down for some reason. I don't know why. We actually have our opens in modified to support him. And he's very tired because he's had a long day. So let's, Bobby, so Bobby knows all about all territories grid. Okay, we do actually sell Bobby to other grids, but there is a price for him because we have to do a lot of coding and teaching him all about your grid. So Bobby, where should I buy a Ford Mustang? Okay, so we're going to ask him a simple kind of question. I have no idea why he's lying down. He's never done that before. Silly boy. So you can ask him a question. He does take a little while to think about it because obviously it's AI. So he suggests Blindside Motors, which is a fantastic place to buy them. And he even gives you how to search in Firestorm and where to get the data. And in fact, that link at the bottom there is actually him saying it. So what we can also do is say, Bobby, tell me that in French. Okay. And he'll remember what he just said to me and that I'm talking to him about this. So if you go and talk to him today and come back tomorrow, he'll remember what you talked to him about to an extent. Obviously, you won't remember everything. It depends. We will expand that in the future, but for now, that's what he's doing. So there he goes. So he's now told me the same thing in French. So now, yep, if you ask him a question. So he's just gone to Rhiannon because she's asked a question. So he's now thinking about that in the middle of my demonstration. Rhiannon. Right. So he writes scripts as well. Bobby, write me an LSL script to, okay, guys, if you, yeah, there you go. So he's answered your question. He is on a percentage, of course. But Bobby actually does some stuff with the grid itself. Okay. But if you want to try Bobby out, you can go to our welcome area. And there's one there for you. He's there. You can have a lovely chat with him. Okay, good. I'm going to move on. I might show you, there we go. So you can see he stacks the questions, poor love. Overworked and underpaid. Okay. So I'm going to go back again. I just wanted to show you in writing scripts to chain, build a box, let's see, to change the color of a box. So you have to tell him what language you're writing. He has been used, Jimmy Olsen's got a huge space area on our grid. We have huge sci-fi area. It's like 150, 130, no, 160 second life regions made. It's different people who've got sci-fi regions, and they're all kind of together. And he had a problem with the script, and he asked Bobby to fix it, and he did, so which was kind of exciting. So there you go. So this is a little script here that he's just written. And I could, it's just very simple. I'm just going to quickly raise a little box, make a new script. I'm going to grab the script that he's just written, and I'm just going to paste it in there. It's save. It's a really simple script. He'll write more complicated scripts if we need it to. I'm just going to click on it, and there it randomly changes color. So there you go. So that's a bit of Bobby. And Bobby is part of our infrastructure. He actually monitors the grid as well, and he knows, for instance, which are the busiest regions, and he knows where to find things. So you can ask him questions about that sort of thing. And he is trained to learn about our grid as people use it. So that little box there, that was, that script was written by AI. And I can even do things like, Bobby, how do I make an omelette in the style of Yoda? Okay, because he knows all that Star Wars, which is really good. I don't know why he's lying down. He's never done that before, but I think it just might be, it might just be because he's tired, poor love. He's had a long day, and he's come a long way. So chilling. Yeah, he's chilling. I don't know why he's never done that before. Just wait a second for him to do that. So talking a bit about how he's going to be working in the future is he's timed out. That's partly because of he's running on a foreign grid, and he doesn't have the stuff he needs to do it. So I've got five minutes remaining. So I'm going to do any questions. Any questions? Well, Lyra asks the question I just asked him. He will answer it. But the time out thing is because we have to set a thing. So are there any questions? Do come and visit us at Wolf Territories Grid. The website I'll put in chat is HTTPS, go to wolfgrid.com, and the land is at grid.wolfterritories.org 8002. Yeah, he's probably, he probably needs, so he probably is, he hasn't got, it's complicated. There's a reason why he's doing that to do with the region itself. But do come over, you can come over to the grid itself. That's a very good question. I know what you think, Seale, even tell you what to feed me. Yeah, that we have, it is beautiful. Some of the regions there are really, really huge, and Lunas go and see Luxor as well. Luxor is incredible. It's something I always take people to see. I go and visit it about three times a week. There's Luxor, there's Lunas store as well, which is where we're visiting Wolf Mountain. There's the whole science fiction area, Europa, which has been built by Jimmy Olsen. If anyone has trees on the region, the chances are Jimmy Olsen made those. We've got the Wild West area. So yeah, basically, you're right, Mel, thanks for that comment. So basically, we've got some AI that actually generates the mesh, the landscape terrains. They're not mesh. They are actual real terrains. And you have to go and stand on top of a mountain in the middle of nowhere. You can do that in our grid. Just go and land there. Go for a walk. You can get a free horse. And they're quite well behaved horses, even for beginners. And you could just ride for miles. There's trains running all over the place across regions. There's shopping. If you hit search, and we've got a destination guide as well, you can see what's going on there. You can ask Bobby what events are on, and he'll tell you where to find out. There's all kinds of things to do. And it's really grown. And we've just got some amazing people who've joined the grid and have built some just beautiful, beautiful things. He'll answer that as well. I'm not sure what he's going to say to that. So yeah, we've got the National Park up north. Rhiannon, yes. Basically, so what happens is, when you click on a...  It goes off and does a load of AI and maths and things, and then comes back with a terrain, and you click next, and you just keep doing it until you find the one you like. Hit apply, and literally it's on your region there, and then mountains, rivers, everything. It's pretty unique. I mean, it took a lot of writing. And the main issue actually was not so much the maths, but more the speed of it, because the original one took about half an hour to actually generate the terrain. So, okay, I've got a minute left. So any other questions? I am always available. I'm quite friendly, really, if people want to friend me and ask questions, that's cool. Otherwise, I think it's done. Ah, you wonderful session. I love Bobby too. We'll give him a round of applause. Thank you, Lone Wolf, for an informative and interesting presentation. We'll have to come out and visit. As a reminder to our audience, you will want to check out theconference.opensimulator.org to see what is coming up on the conference schedule. You won't want to miss our next session, which will begin at 8am in this keynote region, and it's entitled Open Simulator WordPress Interface with W4 OS. Also, we encourage you to visit the OSCC 23 Poster Expo in the OSCC Expo 3 region to find accompanying information on these presentations, and to explore the hypergrid resources in OSCC Expo 2 region, along with our sponsor and our crowd funder booths, located throughout all of the OSCC Expo regions. Thank you again, Lone Wolf, and to you, the audience.


In this video, you will see the construction process for a concrete block abutment timber deck bridge installation. All these projects are replacing failed and failing culverts, and a lot of them which were perched, which were blocking fish passage with bridges. A lot of these culverts are starting to fail, and they're starting to plug from the upstream end. And for 25 years, the streams up above haven't been used for spawning habitat. And so now we get a chance to kill two birds with one stone, so to speak, by not only removing those failing structures that are a long-term maintenance cost for us, but also opening up spawning habitat that hasn't been used for 25 years. This type of construction consists of non-reinforced concrete block abutments, steel or timber girders, and timber deck bridge. Typically this construction can be done with a medium size to large excavator. Installation involves site preparation, excavation, and placement of the abutments, girders, and rock stabilization with an excavator. The steel girder assembly can be partially prefabricated prior to delivery to the site to minimize any onsite fabrication. The installation of the timber deck consists of basic carpentry work. A concrete block abutment timber deck bridge is typically used for smaller stream crossings on private land roads or other roads that have a lower traffic volume. Abutment heights are limited to 6 feet for the concrete blocks. Span width openings are typically 20 feet or less, however, up to 40 foot spans are possible using steel girders. These bridges are usually for one lane of traffic. They can be designed for a wide variety of loading requirements depending on the anticipated traffic over the bridge. We have a lifespan for our practices in this particular practice. I think this was, it was either a aquatic organism passage or stream crossings, had the same effect. In both of those, when we have bridges or culverts, we have a 25 year lifespan. Certainly the 25 years here, if anything, all they have to do is replace the deck. The abutments and the steel girders, they should be here. There's no reason they shouldn't be here 5,100 years from now. The steps for this project and all stream smart road crossing construction projects include the following, a review of the construction plans, water control, onsite preparation prior to construction, initial excavation, setting the abutments and establishing the stream channel, installing the bridge deck, channel shaping and adjacent road backfill. Construction Drawings Review Plans Before construction starts, a design needs to be completed that shows enough detail so the bridge can be installed properly. For a bridge, the key components are the location of the bridge, the bottom elevations of the abutments and the design channel through the bridge and the bridge opening width or span. This drawing shows a cross section of the bridge as well as the elevation of both the bottom of the footings and the design channel elevation through the bridge and the bridge opening width or span. The location of the bridge, in comparison to the location of the existing culvert to be replaced, is also shown. All elevations are established from a benchmark that was set during the initial design survey. The benchmark description is provided on the construction drawings. Other sheets of the construction drawings for this site include specific details for the assembly of the bridge components and the specific requirements for water, erosion and sediment control. The construction drawings should be provided to and reviewed with the contractor prior to construction. Water Control Water control typically consists of diverting all existing stream flow around the working area of the construction site. Any groundwater encountered in the working area of the site that picks up any sediment or is dirty water is pumped from the site and run through some type of sediment basin before the water is returned to the stream. The bridge was installed in August of 2013 when flows were low. Typically, a cofferdam is constructed both upstream and downstream outside of the anticipated working area of the site. The water pooled behind the upstream cofferdam is pumped around the site back into the stream below the downstream cofferdam.  A downstream sump was used to collect any groundwater encountered at the disturbed construction site. Water collected in this sump was pumped into the woods far enough from the stream that the sediments in the disturbed groundwater were filtered out before returning to the stream. For sites where the groundwater flow is higher, a temporary sediment basin may have to be constructed somewhere offsite for the disturbed groundwater to flow through before entering back into the stream below the site. Due to the low surface and groundwater flows during construction, a small pump at both the upstream and downstream sumps were adequate for all water control needed. Scheduling construction at low stream flows is ideal for minimizing the difficulty of water control. Note the fish block nets used to keep fish from entering the work area. So primarily, we're keeping the clean water clean and then any of the dirty water we try to get it clean before we go back into the stream. On-site preparation prior to construction, delivery of materials. Prior to construction, as many materials and equipment needed for the bridge construction should be brought to the site in order to minimize the time actual construction takes. This is important in order to minimize the time the road has to be closed and can be critical if there are higher stream flows and water control is more challenging. For this site, precast concrete blocks were used for the abutments with steel girders and timber components for the bridge deck. The steel girders were preassembled in two sections in order to minimize on-site fabrication time. Required earth fill or gravel fill needed for the backfill of the abutments and road construction associated with the bridge should be stockpiled on site as much as possible. There are typically on-site storage limitations. However, stockpiling at least some of the earth fill or gravel fill can save time during the installation, especially if the fill source is a long distance from the site. Construction start, initial excavation. If carefully done, a large portion of the excavation can be done before the water control is initiated as long as sediments can be kept out of the stream. Here's the pipe prior to the start of excavation. A portion of the road fill over the existing pipe was removed prior to dewatering being initiated. Dewatering was not needed up to this point as all excavation was kept away from the stream. Here the dewatering has been initiated since the excavation is getting closer to the stream. All flow through the pipe has been stopped and is now being pumped around the work area. The pipe is left in place to allow for a working area for the excavator to install the far side abutments. This is important as there is only one excavator on site, so all work has to be done from one side. On larger sites, an excavator may be needed on both sides since all of the work area cannot be accessed from one side. Setting the abutments and establishing the stream channel. The excavation for the abutments is dug down to the bottom of the bedding required for the concrete block abutments. Typically six inches of coarse gravel or crushed stone is placed under the abutments for the bedding material. So the excavation has to be dug at least six inches below the design elevations of the base of the abutment. Here they are excavating for placing the bedding material and then placement of the bedding material up to the elevation of the base of the abutment. The bedding material should be placed approximately one foot wider than the abutment concrete blocks for adequate support. Prior to the final excavation and placement of the bedding material, the final alignment of the abutment is set for the proper place of the bedding material and concrete blocks. Now both abutments are in place along with the rock, rip, wrap, reinforcement. The channel elevation and shape has also been established. The center of the channel through the bridge is one foot higher than the base of the abutments. Placing the base of the abutment one foot lower than the design channel bottom and placing the rock, rip, wrap, reinforcement at the base of the abutments will prevent the undermining of the bridge abutments. We get the footers, what we anticipate down to at or lower than what we would anticipate in a channel scour, so we just want to keep the footer stable. In between there, the channel underneath the bridge, if that will form a low flow channel, we've even seen gravel bars form underneath the bridge, as long as we keep those footers stable, however, whatever dynamics happen in the channel, that's fine because channels do that anyhow. Installing the bridge deck. A steel girder system was used for the bridge deck. For smaller bridges with lighter load requirements, wooden girders are sometimes used. For this site, the steel girder assembly was preassembled in two sections prior to delivery to the site. The preassembly helped save time for the girder placement and provided it for better precision in girder assembly. Here they have installed the two sections of the steel girders. Now the entire steel girder is in place. Next is placement of the transverse timbers. The upper portion of the bridge deck consists of 8 inch by 8 inch cross or transverse timbers with 3 inch thick running planks nailed to the transverse timbers. These are typically spaced 1 inch apart and are held together with 3 inch thick travel surface or running planks that are nailed to the transverse timbers. The entire wooden deck is then fastened to the steel girders with a steel plate, bolt, and channel iron assembly. Here is the completed bridge deck. And then the road backfill is even to the top of the travel surface and running planks. Completed bridge channel shaping and adjacent road backfill. Here is the completed bridge and adjacent road backfill. The backfill behind the concrete block abutments is placed in 6 to 12 inch lifts that are mechanically compacted with a hand compactor. The backfill for the road beyond the abutment backfill is typically just compacted with larger equipment such as an excavator or bulldozer. Even though the road fill beyond the abutment backfill is not mechanically hand compacted, it still should be placed in lifts no greater than 12 inches with adequate compaction between lift placements. This will help to minimize settling in the road surface especially closer to the bridge. Note the channel shape as it is slightly concave in the center section of the channel to ensure an initial low flow channel under the bridge. The amount of rip-rap reinforcement against the abutments should be limited to only the amount needed to minimize encroaching on the stream channel bottom. If the opening for the bridge is properly sized, sediments will be deposited upstream, downstream and under the bridge to form a continuous natural low flow channel. With a properly sized opening, the natural channel continues uninterrupted under the bridge and can adjust according to storm intensities and sediment transport loads. Support for the production of this video comes from Poland Spring, the Sewol Foundation and the USDA Natural Resources Conservation Service. StreamSmart is a collaboration of the following partners. Thank you to the following organizations and individuals who helped make this video possible.