So we'll start the second lecture of this morning. So it's quite a different subject. Le son sur les hypothèses cosmogonyques. Poincaré's view of solar system formation. What remains valid today by Alessandro Morbidelli. Please. Thank you and thank you very much for this invitation. It's an honor for me to be here in this meeting and honor the memory of Poincaré. So I will speak about this book, Le son sur les hypothèses cosmogonyques. So essentially it's origin on hypotheses and models, lectures on hypotheses and models on origins. Poincaré gave a series of lectures on origins at the University of La Sorbonne. And actually the book is not written by him. It's written by Henri Verne on the basis of Poincaré's lecture notes. But Verne is essentially just a scriber and when you read the book it's essentially Poincaré speaking. And Verne is not at all showing up. So Poincaré was a mathematician, was not an astronomer. So he doesn't really have his own theories. So in this book it's like a broader view of the models and the theories of the time that Poincaré describes with his mathematician touch. So he describes all these models with some uniform level of formalism, which sometimes goes well beyond what the original authors have done. And it's nice to see some puns, like for instance this one on Maxwell, where Poincaré writes that his work, his ideas, monk de rigueur, mm de clarté, so lack of rigor, and even of clarity. And so he writes everything with mathematical formalism so that the ideas are properly laid down. So although Poincaré doesn't have, oops, his own model and theory to defend, when he describes the theories of the others, of course he says explicitly where he agrees and where he doesn't agree, he doesn't hesitate to criticize some of these models so we can get through the book what actually Poincaré was thinking at the time. So the book is on origins, which means a little bit on everything. So the first part is on the origin of the solar system and the planets. And then it goes to discuss the interior of the planets, the origin of the heat inside the stars and the planets, the origin of stars, and the origin of stellar clusters, and even at the end something towards the galaxy. So because I'm a planetary scientist and I work in planet formation theories, I'm biased. And so here I will only describe the first part of the book where Poincaré discusses about the models for the origin of the solar system. So the basic observations from which astronomers at the time were starting from was that the eight planets of the solar system orbit the sun all in the same direction and its direction is the same as the direction of rotation of the sun. So the orbits are all progred. The orbits of the planets of the solar system are basically circular and they are basically co-plated. And so these three facts, the progred orbital rotation of co-planarity and circularity, suggested that maybe these planets formed from a flat circular structure like a disk. And of course astronomers knew from Saturn's rings from very early on. And it's always said, even today, when you read the review papers and books, that the idea of the protoplanetary disk, the disk surrounding the sun from which the planets formed, comes from Kant and Laplace. And so indeed Poincaré devotes the first three chapters of the book to Kant and Laplace. So Kant, what did Kant think? Kant think thought that in the beginning there was an ebule at rest, no rotation, basically uniform. And with some slight density fluctuations. And by gravity, the gas started to accumulate around one of these density fluctuations, reaching so higher and higher density there. And by coming together towards the center, the gas was colliding with each other. And these random collisions eventually gave to the nebula some rotation. This is of course wrong because there is angular momentum conservation. So if the nebula is at rest at the beginning, it should be at rest always. And there is no way that collisions, random collisions, gives a global rotational motion to the nebula. So this is a fatal flaw in the thought of Kant, which completely disqualifies Kant in the eyes of Poincaré, who is very, very critical in his right sentences like this. No mathematician would ever buy this stuff. And obviously Kant is a philosopher. He doesn't belong to the mathematician club. So it's not that very well respected. In just six pages, Poincaré closes the chapter and moves on. Oh, that's very funny to read. Laplace, instead, is a totally different story. Laplace is a mathematician. He's highly respected by Poincaré. So it's Poincaré champion, Poincaré hero. And his theory is what clearly Poincaré likes the most. He describes it in two chapters, 60 pages total. The most developed description. And he also proposes some amendments to Laplace's theory but always moves in the framework of Laplace's ideas as a sort of mentor for him. And as we will see, actually the original Laplace idea are quite different from a modern view. This was discovered for myself as well because typically people say Laplace got it all. And actually as we will see in a second, the ideas of Laplace are relatively different from the current ones. So what did Laplace find? Laplace's theory was based on two assumptions. So that there is a nebula. Here represents spherical at the beginning. Here represented by this green circle. And this nebula has a central condensation whose boundary is here represented by this red circle. And there is a lot of mass here in the central condensation compared to the rest of the nebula. This is the first assumption, central condensation. The second key assumption is that the nebula is rotating because Laplace knew angular momentum conservation. But Laplace did not know about the work of Kant. And when he quotes some precursors of this idea he puts other people and not Kant at all. So the second assumption is that the nebula is using rotation and it's in a uniform rotation. So the rotational frequency is the same wherever you are from the spin axis. And this top plot here is on the same scale as the bottom drawing. So this is the radius. Zero is at the center of the central condensation and one is the initial radius, outer radius of the nebula. And the white line shows the frequency of rotation. As you can see it's the same, whatever the radius, whatever the distance from the spin axis. And I also report for reference because it will become important this red curve which is the centrifugal equilibrium. That means that if the rotation rate is that of the red curve, a particle is in orbit because the gravitational force is counterbalanced by the centrifugal force. Okay, so this is the start of Laplace idea. And then Laplace imagine that the central condensation contracts because of its gravity and by contract it spins up. That's again angular momentum conservation. For those who don't know, I don't know if anybody, somebody cannot know this, but angular momentum conservation is that law so that for instance when a skater spins with the arms open and then closes the arms, it spins faster. And so this is exactly the same thing. When the central condensation contracts, it's like for the skater to close the arms so we start to spin faster. And so as you can see here, this rotation rate goes up compared to beginning, beginning was here and now it goes up. But it's instantaneously propagated by viscosity flow out to the nebula. So not only the central condensation spins faster, but the entire nebula spins faster. That's key in Laplace model that at any time the nebula rotation rate is uniform. So then the central condensation contracts even further so it spins up faster. And we reach a point where at the extreme of the nebula, the rotational rate is exactly the centrifugal equilibrium rate. At this point, the outer surface of the nebula, which is an equipotential surface, starts to be distorted. It's not a circle anymore. It starts to become ellipsoidal. As the central condensation contracts even further, again the frequency rate goes up and now it intersects the centrifugal equilibrium at some radius, which is smaller than one. That means that the gas beyond this location is now at centrifugal equilibrium, is detached from the nebula, is in fact in orbit around the central condensation. The equipotential surface of the nebula now stops at this point where the centrifugal equilibrium starts and all the gas that, so it becomes more contracted and all the gas that is now outside of this equipotential level has to slide along the equipotential level and come down on the plane. And as the central condensation contracts more and more, as you can see this intersection point between the rotation rate and the centrifugal equilibrium curve moves inward and inward. That means that the surface of the nebula shrinks, this point moves to the center and more and more gas is left in orbit beyond the limit of the nebula. And so you can continue like that and you get the central condensation more and more dense, which eventually forms the sun and accumulates a lot of heat by contraction and the nebula becomes small and the disk becomes extended. So this is basically the idea of Laplace that Poincare describes in mathematical terms using these equipotential levels and the equations for rotating nebula and so on in a very, very clear way. So is this all? Is this the solution of the problem? No, because for Laplace and I think also for Poincare, it was inconceivable that you can form a limited number of planets, eight planets out of a uniform nebula. Why something uniform should give origin to a discrete set of objects? So Laplace and Poincare were after an idea, a different idea that not to form a continuous homogeneous disk but rather to form a set of rings with gaps in between rings so that each ring would then give you origin to one planet and so if you have eight rings you get eight planets at the end. How to get these rings? The original description of Laplace is a little bit hand-waving and so it's formalized in Poincare's book following actually the formalization provided by Mr. Rosch, which I'm trying to explain here. So the idea is like, the beginning is like what I showed before for Poincare, for Laplace. So the nebula, the central condensation contracts at some point the rotational frequency becomes equal to the centrifugal equilibrium frequency at the border of the nebula. So the next step, the contraction of the central core we start to form the ring. Now the idea is that when the ring forms and the gas outside of the equipotential surface slides down to go to the plane then the gas that is now at the surface was inside the nebula before and now it's exposed for the first time to vacuum. So because it's exposed for the first time to vacuum it's not blanketed by the gas that was originally beyond it now it starts to irradiate heat away into the vacuum and by irradiating heat it cools down and of course by cooling down the pressure inside the nebula decreases and the pressure is what keeps the nebula inflated. So by cooling down and decreasing the temperature then the envelope of the nebula shrinks. But when the envelope of the nebula shrinks the rotational frequency doesn't change because essentially the angular momentum of the entire nebula is due to the central condensation and it's propagated to the entire nebula by friction, by viscosity. So even if the nebula would like to speed up by shrinking essentially it has to stay at the same rotation frequency of the central condensation. So this shrinking without changing the rotational frequency doesn't leave any gas behind and that's how a gap is produced. And then the central condensation will keep contracting and when it contracts it speeds up the whole thing and so new gas is left behind beyond the new surface of the nebula. But then new gas is exposed to vacuum so it irrigates heat, decreases the pressure the atmosphere of the nebula contracts again without changing the rotational frequency which leaves behind another gap. And then the central condensation contracts and this leaves behind gas in orbit and then the nebula contracts and it's another gap and so on and so forth. This is really bright. But, and so this forms a discrete number of rings depending on how many times the nebula cools relative to the central condensation shrinking. Starting from the Titus Baudelot that describes geometrically the separation of the planets Poincaré even computed the times at which the atmosphere had to contract to leave behind the rings and gaps. And he concluded that the times at which the atmosphere contracted had to increase with a geometric progression. So if T0 is the time at which first the atmosphere progresses, the atmosphere compresses then the next one T1, T2 will be two times T0 T3 will be three times T0 and so on and so forth. So in Laplace model even in this variant to form the rings as you have seen it's crucial that the nebula is in uniform rotation and that this uniform rotation is the rotation frequency of the central condensation. So for Laplace the reason for that is viscosity is friction and so the nebula is forced by friction to rotate like a rigid sphere essentially. Cannot have any shearing because shearing exerts friction. Now Poincaré in this chapter mentions that Helmholtz computed that if one uses for the nebula the same kind of molecular viscosity that characterizes the atmosphere of the earth it would take something like 10 to the 22 years for a nebula extended up to Saturn to Neptune sorry to acquire a uniform rotation rate which is the rotation rate of the Sun. So this is sort of enormous number and so Poincaré says that but for him is not really a fatal stop to the theory essentially thinks well then probably there is some other mechanism to make the uniform, the nebula rotating uniformly because this is really required in order to form the disk and the rings and in this so the fact that Poincaré in some sense ignores this problem is actually very modern because we still have this problem today. Now we observe a protoplanetary disks and we observe even the accretion of material onto the stars that we can measure. And so from these two observations one can deduce the viscosity in these disks and the viscosity in the protoplanetary disks is many, many, many orders of magnitude larger than the molecular viscosities. And so we still have this discrepancy of timescale even today in modern times and the solution of astronomers has been to invent a concept of turbulent viscosity so it's not molecular viscosity that actually drives the evolution of the disk it's this turbulent viscosity due to the turbulence in the gas. The viscosity is very, very enhanced but it's still a very open subject of research to understand what generates turbulence and what actual viscosity turbulence can generate. So this is an open problem even today and doesn't stop us from believing in accretional disks and so it's very conceivable that for Poincaré it was about the same. So as I think you have understood the Laplace idea in particular is very different from the modern idea of a protoplanetary disk. And actually there was someone not very known in the history of science to Viscont de l'Igonde to which Poincaré devote chapter five and pretty developed chapter of 33 pages who actually imagined the formation of a protoplanetary disk in a much, much more modern way compared to Laplace and actually went very, very close to what we think today is happening. So and it's a curious that this person is essentially disappeared from the history of science. So for instance if you do a search on Wikipedia of all the names I'm quoting this is the only one that doesn't have a page of his own. So and I really found out about this person reading Poincaré book so that's very interesting. So L'Igonde said that, okay, initially starting thinking that at the beginning the nebula is a uniform rotation doesn't look like very realistic but probably a very rarefied nebula a just random motion in the gas but if you do the sum of all the velocities you will get some total angular momentum which would not be exactly zero. Why should it be zero? Zero is a very specific number would be very non-generic number to get. So the nebula despite it's chaotically moving in all directions has some non-zero angular momentum. Due to the inelastic collisions of gas particles and that was also a concept that he introduced that the molecules lose energy and by losing energy they fall towards the center of the nebula and start to form a central condensation. This is not exactly right the reality is a little bit more complicated because when two molecules collide they lose energy so they emit photons but these photons can be reabsorbed by other molecules which are accelerated. So actually in a modern concept we should worry about the gas opacity and the optical depth. But okay, the idea is about right if you think that the nebula is optically thin. And so by the gas falling to the center by angular momentum condensation it starts to speed up. Also this nebula because of this inelastic collisions has to become flatter and flatter and damp on a plane orthogonal to the total angular momentum of the system. And this is easy to understand by this is the angular momentum vector and this is the orthogonal plane by definition of angular momentum and orthogonal plane it means that if you take all the velocities of all the molecules along the z direction the arithmetical sum of all these velocities is zero. And so by colliding and damping the velocities between elastic collisions of course the z component of the velocities decreases, decreases, decreases until it becomes zero which means that the nebula becomes flat on the plane orthogonal to the angular momentum. So by this concept of inelastic collisions Ligunde could explain from an originally rarefied chaotic nebula the formation of the central condensation which eventually forms the sun the formation of a flat structure around it everything conserving angular momentum. And then again that was the issue why how to form eight planets out of the disk and Ligunde thought that rings form but rings form because of sort of gravitational instability not because of this game of cooling and contraction that I showed before from Laplace. And this is actually extremely modern. What I'm a little bit surprised about is that Poincare describes all these ideas does not criticize all of them because I think cannot be criticized but is not particularly enthused by that it presents this like a model among others and maybe sentimentally is more still more attached to Laplace uniformly rotating nebula and ring model maybe because it's more mathematically defined and you can do more you can really write equations to describe the evolution of the neighboring Laplace model and these equations are those from which I did the movies before the animation before whereas this is more qualitative you know and so in the chapter from five most of the chapter is devoted to dynamics of a medium where collisions are inelastic and comparing the evolution so the contraction to the conservation of entropy and to what the conservation of entropy predicts. Okay, so what we know now about protoplanetary disks before going to the formation of the planets well disks exist and now we can see with the most powerful telescope stars forming in the star forming regions and the young stars are all surrounded by protoplanetary disks some disks are seen phase on and so they appear like dark circles on a bright background which is the giant molecular cloud which is ionized and bright other disks are seen from the side so they appear like a black horizontal band over again a bright background some disks are bright themselves because they are undergoing foot evaporation so they are highly ionized so it's quite amazing that actually basically the idea of the protoplanetary disk is right and that the people from Laplace even can't could just by imagination imagine something like that imagine that the star forms by central condensation central accumulation of gas so the basic lines are definitely correct and we now have the proof these are not models anymore this is reality on how the nebula actually contracts and speeds up and forms a star and forms the disk things are a little bit different certainly the more much different from what Laplace envisioned similar to what Ligon de envisioned now we can do this kind of calculations using numerical simulations obviously numerical simulation made by Matthew Bate so in the simulation you will see the nebula forming so the density is represented by this color scale at the beginning the density is very very low so it's all black and this image is on the plane orthogonal to the total angular momentum of the initial nebula okay so the disk will be flat so let's see the movie so the gas starts to go towards the center that's why the density increases and increases because of angular momentum conservation this thing at the center spins faster and faster until it becomes rotationally unstable it develops a bar and then this bar launches a spiral density waves the spiral density waves extract a transport angular momentum and that's the reason for which new gas can still go and feed the star and we can observe the gas being accreted by the star using like an alpha emission lines and at the same time a disk is formed due to the gas that still has too much angular momentum to go to the center and if you wait longer and longer most of the gas accretes eventually onto the center by viscosity so as you can see there are no rings and there is also no uniform rotation really except at the very beginning when the bar forms now let's go back to Laplace idea of the rings because this is what von Karay buys and let's see how the planet could form the idea is that the planet with the gas cooling the oops sorry with the gas cooling these rings contract both radially and vertically so that the density increases and eventually the planet is formed and in Laplace he doesn't question himself of why one ring should give one object and not several on the same orbit this is something that von Karay details and Laplace didn't now the idea that the disk uh... by cooling down becomes narrower and narrower is actually wrong because we know now that if one takes into account the viscosity of the gas then actually you have viscous spreading not contraction the idea that the disk contracts radially is unfortunately not correct the big issue of the time was to understand not really why a planet forms because that was considered uh... conceivable if the density becomes high enough but why the prior planets have a prerogative rotation this was a key question at the time and for Laplace again friction tends to make uniform the angular velocity of the ring for Kepler laws the angular velocity of the inner part of the ring is larger than the angular velocity of the outer part of the ring but because of friction eventually these two rotational velocities have to become the same like in the original uniform rotation rate of the nebula and when the two rotation angular rotation rates are the same the linear velocities of course larger here than here because the radius is larger and so the planet that eventually forms by this uniform rotating gas will have a prerogative rotation because the outer velocity is larger than the inner velocity will actually be synchronous relative to the sun so we have one rotation in one orbital period but the synchronous rotation is indeed a prerogative rotation so this is the only idea of Laplace that Poincare criticizes explicitly saying l'explication de Laplace est un suffisant the explanation of Laplace is insufficient and the reason is that Laplace didn't know this but Poincare knows this after the work of Maxwell which was not clear and not rigorous but he wrote it again that if a disk has an intensity which is large enough larger than this quantity where omega is the rotational frequency of the disk then the disk becomes unstable gravitationally unstable and so it has to clump and form a self-gravitating clumps of gas and also not from just a unique planet but a number of of self-gravitating clouds of gas now modern astronomers use this criterion which is called Tumorist criterion for gravitational instability and when you read books the Tumorist criterion is given like this so it's not the volume density it's the surface density that has to be bigger than omega Cs is the sound speed but actually if one thinks about the sound speed is the product between omega and the scale height of the disk and sigma divided by the scale height of the disk is just two times the density so if you do the transformation you'll find exactly the same thing so the modern celebrated Tumorist criterion actually was worked out well before by Maxwell so because of this then as I said the ring will not become infinitely thin and infinitely narrow and to form only one planet unlike Laplace and Vision it will eventually start to break down in self-gravitating sphere of gas and so you will have several self-gravitating sphere of gas on similar orbits but not quite identical and because the inner guy, the inner self-gravitating sphere of gas will orbit faster than the outer self-gravitating sphere of gas when these things will collide they will merge forming eventually one unique planet but because the inner one's orbit always faster than the outer one the final planet will turn like this not like this so a planet formed by this mechanism should always have a retrograde rotation and not a prograde rotation unlike what is observed so this issue of the prograde rotation was the real big question of the time but first before going further and see the explanation for the prograde rotation let me review the observations of the time what did the people believe so for the astronomers of the time they thought that all the inner planets are all prograde including Venus that's which is retrograde and probably because Venus is quite a uniform atmosphere they couldn't observe the clouds and so they could not figure out that Venus was retrograde so all the planets Mercury, Venus, Earth, Mars, Jupiter and Saturn were all prograde but then they believed that Uranus and Neptune are retrograde now Uranus in reality the spin axis is essentially horizontal the obliquity of Uranus is 98 degrees technically it's retrograde but not really spin down like Venus but Pankare never mentions that actually so he considers it like a retrograde planet Neptune in reality is perfectly prograde but why the astronomers thought it was retrograde at the time because the surface of Neptune is very uniform so you can't detect any rotation just by looking at Neptune but in 1846 the major satellite of Neptune Triton was discovered a Triton is a retrograde satellite it turns in a retrograde in the opposite direction relative to the spin of Neptune and at the time the astronomers knew that all the major satellites of the giant planet Jupiter and Saturn orbit the planet in the same direction of the spin of the planet so for Neptune they could not measure the spin of the planet but they could measure the orbit of Triton and by analogy if Triton turns clockwise they thought that Neptune was turning clockwise too so in a retrograde direction and so this thing first six planets are prograde the last two are retrograde is very very important in the conceptions of the theories of the time so the first explanation of why the planets are prograde I have a prograde rotation comes from Phi who actually was the director of the institute the mechanics analyst here in Paris and Phi proposed that the planets form still inside the nebula when the nebula is still uniform before it develops the central condensation why? because if you are inside the uniform sphere of material then the orbital speed instead of decreasing like one over square root of R increases like R and so that means that in the scheme the outer planet the outer self-gravitating sphere of gas orbits faster than the inner one and so upon emerging this will give a unique planet on a prograde rotation and so the central condensation and the formation of the star has to occur later after planet formation at least after that Jupiter and the other planets form so Poincare dismisses this idea as crazy because when the center condensation forms that means that the mass inside the orbit of a planet increases enormously and if you increase the mass of that attracts that changes the gravity that the planet feels then the orbit of the planet migrates inwards and so Poincare computed with an easy math that in Phi's theory the Earth should have formed that 13 AU is the current distance between the Sun and the Earth so 13 times further than the Earth actually is now and Saturn 22 times further Saturn now is at 9 AU and he considered this crazy of course so this is the reason for dismissing Phi's theory in Poincare's book chapter 4 there is actually a positive side in Phi's theory that Poincare mentions is that in Phi's model the planets form before the Sun and this was appealing because at the time the age of the Sun evaluated from cooling times was only 100 million years but the geologist by looking at sediments and fossils and so on had deduced that the Earth at least had 200 million years so the Earth looked older than the Sun and this theory would explain why but Poincare doesn't really believe any of this dating that the activity was being discovered it was obvious that anything about heating and generation of heating and cooling was going to change so he thinks this is all nothing to think about so and this argument is much more solid so Phi is disqualified so the idea of Poincare solution of Poincare and this is really his own solution actually written in the book this is my thought and for the progressive rotation of the planet is based on tides the theory of tides was very well developed in those years by this person George Darwin who was the Sun or Charles Darwin also died 100 years ago and a really great man understood a lot of things in particular the evolution of the Moon and the origin of the Moon and his ideas are now being reconsidered more and more so then Poincare says okay tides are important and tides are particularly extremely efficient when the protoplanet is still an extended sphere of gas for these are the tides exerted by the Sun on the planet so the planets form like hot and extended clouds of gas they are retrograde because of the way they form but they are very affected by the tides and as George Darwin showed the tides have the effect of slowing down the retrograde rotation of the planet until it is synchronous so that it has one spin in one orbit but the synchronous rotation is actually a progressive rotation and then the cloud the cloud that is the precursor of the planet contracts because it cools down and this has two effects first it frees the planet from the tidal grip because the narrower is the planet the less sensitive it is to the tides raised by the Sun so eventually the tides from the Sun weakens and the planet can become asynchronous and also by contraction due to angular momentum conservation and understood it it speeds up so the rotation frequency will become faster and faster so it will be asynchronous but because it starts from a synchronous rotation which is prograde it will be a fast and prograde the rotation this is very clever Juan Carré brings forward three observational evidences for this theory being right so the first one is that the inner planets the first six are prograde and the last two are retrograde and Juan Carré says great this is because tides becomes weaker and weaker with the distance from the Sun so Uranus and Neptune felt tides which were too weak to ever become synchronous and so the reason to turn from retrograde to prograde there's something to do with something that has to become more and more prominent with the distance decreasing distance from the star from the Sun exactly like tides do then the fact that the satellites of the planets have orbit have prograde orbits so they spin around the planet in the same direction of the rotation of the planet of course Laplace and Juan Carré and everybody thought that the formation of the satellite is just repeats the same process as the formation of the planets around the Sun when the planet contracts it leaves behind the disk and from this disk the satellites form and of course the disk around the planet has to turn in the same direction of the rotation of the planet but the most distant satellites are actually retrograde and Juan Carré says this on the basis of one observation which is Phoebe Phoebe was discovered in 1899 is the biggest irregular satellite of Saturn we call irregular satellite the satellites that instead of having a coplanar circular orbits have eccentric inclined orbits and some of them are retrograde and Phoebe the biggest one has a retrograde orbit and it is the most distant the irregular satellites are much much more distant than the regular satellites which are very close to the planet so Juan Carré says great this is the proof that the most distant satellite formed early when the planet was still retrograde before becoming synchronous and before becoming prograde and so this sequence the outer satellites are retrograde the inner satellites are prograde is the proof that the planets form retrograde and then eventually they are turned into prograde okay what do we know today about planet formation actually the idea the Juan Carré and the others were after is actually very similar to one modern concept of planet formation which is gravitational instability a mechanism for planet formation which has been resurrected by the works of Cameron or Alan Boss and others so there is this criterion this gravitational stability criterion that says that when the density is bigger than the rotation frequency squared then the disk is gravitationally unstable so in the outer part of the disk where omega is small indeed a disk can fragment in self-gravitating clumps of gas but these clumps typically are very massive much more massive than Jupiter and this happens only far away when omega is small actually what people at the time of Juan Carré did not understand is that it's not enough to wait long time so that the disk becomes thinner and thinner and raw increases so that eventually raw can be larger than the rotational frequency whatever whatever is the rotational frequency so at any distance from the star the reason is that the major source of heating in the disk is viscous heating and that depends on their density itself so you can't increase arbitrarily the density without increasing internally heating which makes the disk thicker and decreases the density so the density cannot become arbitrarily large in the disk but it's self-regulated by the viscosity so this relationship can only be true farther out in the disk when omega is small and so the theory of planet formation by gravitational instability actually seems to work but predates only very massive planets very far away from the star we might see this kind of planets for instance the system HR8799 which is a system imaged with telescopes show this so this is the central star which has been cancelled using modern coronography techniques and the star is surrounded by three planets the masses are not very well known but from their brightness it's about from five to ten Jupiter masses and they are very far away 24 AU, 38 AU, 68 AU from the central star remind you that Jupiter is at five and Saturn is at nine so it can work but for other worlds not really ours for our solar system we think things are different and the modern concept of planet formation envision of course a protoplanetary disk but consider the parallel evolution of the gas and the dust and the solid component so inside the gas component there is the solid component that sediments in the midplane of the disk the inner part is dominated by rocks because it's hot the outer part is dominated by ices because the temperature is low and then the solids accrete with each other forming solid bodies which are bigger and bigger and eventually if a solid body becomes massive enough and there is still gas around then it can start to attract the gas and form the gaseous atmospheres that characterizes the giant planets like Jupiter and Saturn so this curves around from Pollack's model so this is the mass of the solid component of the planet which increases up to about 10 Earth masses and then once 10 Earth masses are reached the planet starts to attract the gas so this is the total mass of the planet gas plus solid so the difference is the total mass amount of mass in gas and this eventually goes into a runaway accretion fashion and the planet of hundreds of Earth masses like Saturn and Jupiter can be formed in this model so first formation of the solid core and then accretion of the gas the progress rotation of the planet is no mystery it's enough to look at the dynamics of the gas in the vicinity of the core of the planet so this is the direction to the Sun this is the orbital direction of the planet and these are the streamlines of the gas so you can see the gas comes in like this and turns like this something you can easily understand by solving the equations of the heat problem and so the accretion of the gas necessarily gives to the gaseous planet a progress rotation for the terrestrial planet is a little bit different because there is no gas and the rotation of the terrestrial planet is due to the collisions between the rocky bodies and because the rocky bodies can become eccentric actually it's expected that the final rotation of the terrestrial planet is a multirangle so in Poincaré books actually there is no mention of the physical differences between terrestrial planets and giant planets and actually people at the time thought that even Jupiter was solid that Jupiter was understood to be gaseous planet mostly gaseous planet only 1933 and they knew the differences in densities but they just thought that these were differences in heat and so there is no distinction that terrestrial planets and giant planets somehow must form differently or take two different evolutionary paths there is no distinction between the dynamics of gas and solids the idea is that everything forms like a cloud of gas and then upon cooling any gas eventually would become solid and so there is no need, no discussion the need about to remove eventually hydrogen and helium because hydrogen and helium would never become solid at the conditions of temperature and pressure all this old acid so to conclude three take home lessons by reading this book the first one is that science really evolves by standing on the shoulders of giants it's quite impressive to see how these people like Laplace, Poincaré and so on were the brightest minds at the time were still relatively far from the modern concepts that we have and science has evolved astronomy planetary science has evolved enormously since and this is not because there was a super genius after Poincaré where it would revolutionize the entire field just because of a community effort and the piece after piece, brick after brick the edifice has been built and also a lot of observations have come in in planetary science it's an observationally driven science there is no doubt the second one is a lesson of humility of course even if because of the standing on the shoulders of giants and building an edifice brick after brick by definition I would say the modern models are the best models ever made in the history of science doesn't mean that they are good doesn't mean they are correct we still have a lot of problems in understanding some things and we are aware of that but I would even go further maybe something that we think we understand is not correct Laplace fought to understand the origin of his rings and of course he was not correct so it's probably the same thing and given that I do planet formation models myself I question myself what will be my models in 100 years from now and I'm lucky if they can last 100 years they will be eventually be looked like naive and superficial I'm sure of that and the last take home message is that even the brightest minds can be misled by bogus observations so this is a pun for our friends or enemies the observers but this is actually interesting so I'm referring of course to the fact that Neptune was fought to be retrograde and Venus was fought to be prograde and Feebe was fought to be satellite like the others and this is something actually we should keep in mind today because with the discovery of extrasolar planets we are bombarded by new data every day and there is a tendency in the community to try to write down and publish theories to explain the data as they come in forgetting that these data are still very confusing very partial, very dominated by observational biases in some cases even wrong and so we should learn these lessons and I mean a good theoretician should not start thinking until he really feels that the data are solid and robust and of course it's a skill to understand when this occurs because if you wait too long then the others do everything you have nothing else to do so but there is one thing on which Poincaré is really modern and I would like to end on this is this text which is actually not in any chapter it's in the introduction of the book that Poincaré wrote and it says this which I translate in English I can read it anyway it's too small it says Poincaré says that Laplace did not mention explicitly the possibility that other of other planetary systems but clearly implicitly thought that they should exist and they should all be more or less the same because they come out of a universal formation process which is the formation of the disk and the formation of the rings and then Poincaré says that the recent progresses of stellar astronomy does not allow us to still think the same and because telescope has discovered such diversity of stellar systems of course extraterrestrial planets did not well not know that we did not expect and then Poincaré goes on saying if the stellar systems are so diverse on each other there are individual stars, double stars, triple stars massive stars, dwarf stars different temperatures are different there is no way the other planets will be like our own the same kind of diversity that we see in stars will be also in the planetary system and this is of course perfectly right in 1995 the first extraterrestrial planet has been discovered since we've found a thousand there is a huge diversity of planetary system this is shortly summarized in this diagram which shows the distance from the central star and the eccentricity of all the giant planets discovered today and as you can see giant planets can be at any distance from the sun not just very far from the star like our Jupiter and Saturn can have some, some have even orbits much much smaller than that of Mercury some have circular orbits like our own planets but others have very eccentric orbits like the comets in our solar system and in terms of masses everything has been discovered from 10 Jupiter masses down to one Earth masses with a continuous mass distribution so really there is a huge diversity Poincaré predicted it it was totally forgotten and that's why astronomers were sort of shocked when this diversity of planetary systems came out from telescope surveys but this is what Poincaré already expected thank you very much this beautiful lecture and Shakespearean conclusion so maybe there are questions yes, please thank you very much for this lecture it was extremely interesting I have a question regarding the magneto-hydrodynamic aspect of this problem the fundamental equation existed we arrived at the same period and Poincaré doesn't mention any of these effects no, exactly and do you have any comments on that? I think so, of course Maxwell equations were known but the idea that magneto-rotational, magneto-dynamics could give rights to turbulence and solve this problem of the viscosity is much much much more modern and I think they did not have really the tools at the time to figure that out maybe not even yeah, I mean there was this realization that the molecular viscosity was not enough to keep the Nebula uniform but they did not really try to go further than that but it's true so when I said that we have the same problem today and so the molecular viscosity is not the cause of viscosity of the disk we think it's turbulent viscosity then the question is what gives origin to turbulence in the disk and magneto-rotational instability is considered by most of the people in the community today the main driver of turbulence in the disk which explains the viscosity that is indirectly observed by the Stellar-Akrician way so Alessandro, so thanks first for this the magnificent lecture because I had the book for a while in my shelf and I've started to read it a little bit but never dare to really go through and I should thank you for that my question is, did you look to what was the following of this book did it have any impact or not or was it totally forgotten did you look to that or not really but my impression is that so Laplace ideas and remained in the community certainly and at least the idea of the disk and things started to progress later when star formation was revisited and with the first computer simulations and this was in the 1950s more or less but the idea of the disk was never a question so something that actually went into the common culture of the astronomers at any time and then the fact that Jupiter is gaseous was discovered in 1933 and I think boosted a little bit the idea that some planets at least can start from the gas component and also pointed out that there are two clearly different categories of planets in the solar system and so everything has to be much more complex than what was explained at the time and sorry, perhaps it's a stupid question but what for the asteroid belt I'm not sure, was it already discovered by this time and if yes, well the asteroid is small so I'm not sure, what did they think of them and what do we think of them now for the information? Okay, so the first few asteroids had been discovered in 1901 was the discovery of Ceres, so here we are in 1911 so I think 10, 15 asteroids were known thinking if Juan Carreira mentions them I think he mentions them in passing and he says that there was this law, the Tizus Bode law describing the distance of the planets from the Sun and they had a gap so the fact that they found four or five bodies at this place was considered like what the proof that something was there and probably exploded and I think he mentions that in passing in the introduction and not in the chapters anymore and now we believe that asteroids are more the leftover of planetary formation they never formed the planet probably because Jupiter formed earlier and disturbed the region preventing further acquisition of the region. So thank you again. Thank you.


So hello everyone, we welcome you on our new show Rise in Stars which profiles the emerging talent in the music industry and today on our first episode we have with us a very versatile and talented singer Alina Rehan Khan. We welcome you on our show Alina. Thank you so much Oji, thank you so much for having me here. So Alina, my first question to you is tell us about your musical journey so far. All right, so my musical journey has been very very interesting because there are a few things which you choose for yourself and there are a few things which happen to you. All right and your career is is not one of the things you always tend to think you know that my career is something that I will choose it is not something which happens to you but it's very ironic because I always see this that I did not choose music and music chose me. It was back in 2018 when I had started uploading covers and my first cover online ever bent viral organically hitting almost 11 million views and you know people from all parts of the world started texting me that we're listening to you sing and you've got a very nice voice this and that and slowly one by one one by one you know a lot of opportunities open and I was studying my bachelor's in architecture so I was meant to be an architect but mid college something like this happened and when yeah it's a big shift and it was very unexpected because I never in I was passionate about singing but I never thought of picking it up as a career it was always just a hobby but then yeah I think God always has his perfect plan and you know he somehow picked me up from there. True true true and it was unexpected but I nevertheless I'm grateful every day I can't thank God enough that I get to do what I get to do and yeah it's been amazing. So who inspired you to become a singer any inspiration particularly? The inspiration would be so I was born and raised in Kuwait all right and but I am a Desi I'm as Desi as it gets at heart all right and I am an Indian so back in Kuwait back home like I would really hear my mom while she would be kitchen you know cooking in the kitchen she'd be singing Lata Ji's songs and Asha Ji's songs so there are so many songs so many Bollywood songs that I've never really heard in real life but I've only heard my mom sing them so yeah and those songs are like very very special for me so I would say that my mom my mom is the one who's inspired me to sing. That's great that's great. So how do you approach writing new music and do you have any specific process for it? So I always feel like the best of content is what comes to you spontaneously and at least for me it happens this way like if you tell me Alina you have to make this song and if I sit with that mindset it does not come to me but I could be in the most random places you know I could be having a shower I could be sitting with friends and a composition just clicks me yeah and I take out my cell phone and I start recording sometimes it's it's very annoying for my friends also yeah they're like what are you doing yeah but then I think that's the thing about creative field you the creativity it can hit you anywhere anytime and yeah so many a times so I work in two patterns many a times I have a beat all right and I try to compose something on it and then turn the composition and write lyrics onto it many a times when I'm sitting idle I get a thought I start writing about it and then I compose it so either way that's great that's great that's a quite draw process and a simple one yeah and also I think because I've not had any formal education in music like I've never gone to school and I've never learned so it's it's very spontaneous and it's very all over it's all jumbled up and it's very very confusing but I think I really enjoyed because it's unique to me I know because I have no formal education like no one else can make this because it's just coming out of my heart and out of my soul so how how do you prepare for a live performance do you have any rituals and routines for it yeah so live performance is something that I'm very very peculiar about because making a song is a very personal process I feel but doing live shows is a very very it's a process more about the others than it is about me obviously when I'm on stage I like to have fun but I also want to ensure that the audience has more fun than I am having so for live shows actually live shows as the more you will practice for a live show behind the stage the more it will look effortless on the stage so I think for my live shows I do a lot of practice I have to put in a lot of practice and my band and I although I'm based out of Chandigarh my band and I meet regularly in Delhi for the practices and to keep keep jamming oh wow that's great so who are your biggest musical influences any influences you have yeah this is such a tough question yeah this is a very very because I think the world has produced such great artists India has produced such such great artists there's some crazy artists from yeah from Pakistan like if I I think I could have peculiar you know like if I see just performance wise it could be maybe Michael Jackson yeah because they're great performers yeah and there are some performance who just captivate like the people who have written crazy stuff maybe Nusrat Fateh Ali Khan Sam so I mean it's crazy you know yeah like and they're those type of people used to be different genres also true true true true true but currently like in India or in Bollywood because so I because I sing a lot of Bollywood I practice a lot of Bollywood all right but when I'm alone or when I'm when I'm a bathroom singer I like to sing a lot of jazz jazz is my jam I love singing jazz um it coming to artists yeah if you say that one artist that I really look up to in India or his process of working would be A. R. Human oh yeah I yeah like his H. E. Song is a masterpiece and if you learn the process of how he's made a song I think there's so much to learn from it that's very true that's very true so you have come up with your new song right Papi Girl so tell us about yeah all right so again there are so many songs that you write all right and like I feel like there are songs that I've written which are very very emotional and probably I would want to release them so there's a very funny story behind Papi Girl so one day you know I had like a few songs then I was getting no direction because the thing with being an artist is your journey can either go uphill or it can be stagnant you know there are a lot of highs and lows so one day I was just sitting idle all right and I was thinking how do I release this song how do I make a good song so I randomly texted Iqqa and I told him hey bro um I'm an artist and I've made a few songs and I would want you to guide and mentor me on these songs so he was very kind he was very polite he replied back like this is my email Iqqa and please send me the songs I'll listen and I'll tell you what we can do so I sent him five songs and amongst those five songs some of them are very close to me I feel like they are my best written songs okay and and then there was this one song Papi Girl all right and yeah trust me would just be Papi Girl is this song just friends are sitting around and fun fun me mazzak me you make something so it's a song which was made within 20 minutes in a very very rough dummy scratch version and I sent it to him so that was also one thing I sent but I thought this is though I'm just sending the four other songs were main songs he immediately replies back he's like Alina this song Papi Girl that you've sent me is like it's my vibe it was so random because sometimes your own product which you believe leased in it could be the best for someone else because so that's when because now now generations like very peppy songs and very catchy lyrics and very viral songs so yeah correct correct correct so even even the lines in Papi Girl like there's a line where say to whom a kaafi gharelu par club ja ke a chalakta hai peena it is something that everyone relates with related to young yeah because our generation is yeah our generation is very homely also like we will do all our errands we will do all our chores we will be responsible but we like to go out and party and have a good time once in a while so I think it's a few lines in the song yeah which are very real but people connected with it so touch what the song is doing very well that's great all the very best for your song so can sing two lines two lines yeah okay yeah first of all favorite nice I love you baby I'm a party girl wow that's that was amazing I would say and go very viral I hope so it was very well so yeah bro like only 10 days and already you know we've completed like 100,000 streams on Spotify almost one million streams on all the audio streaming platforms two million viewers on YouTube people are making a lot of reels so it's good to see organic response so any your favorite song you like to perform and why specifically why any of your favorite songs you like to perform and so there's this one song I don't know if you've heard I mean I'm sure you must have heard it the mother must have done that obviously everyone yeah everyone knows it and yeah and it's one of the song which I feel it's very spiritual also all right because it is like you're talking to your creator yeah yeah it's a Sufi song yeah it's very spiritual also but on the same it's very powerful all right you need a lot of your vocal energy and energy from all of your chest to sing that song and I feel it has never gone wrong like every time I perform that song in my schedule people dance to it yeah people dance to it people lose their minds and they dance to it so I think I think yeah that's one song I really like performing so any any Sufi songs lined up for you we can have so I have so I have written I have written all kinds of songs like sad songs happy songs party songs Sufi songs but then um yeah but I want to collaborate with more and more of artists because like I told you right I'm not I have not done or learned professionally so like like just on papi girl I got ikka bhai on board and to have him on board was um you know I got a mentor on board yeah there was so much to learn in the process and right now I feel like I'm at a tender age and I want to learn as much as possible so no matter who I'm meeting like even if I'm having this conversation with you I am learning from you to be a patient listener you know so there's so much to learn and I just want to keep learning so how has your music evolved over the years your music um yeah so my music over years again I think earlier um earlier I was very afraid to write my own music I was afraid to write songs because I was always a cover artist so I would listen to Bollywood songs and try to cover them but somehow I believed uh that I cannot write my own songs or I do not have the capacity or capability to put my emotions into a song right but over time that has changed and uh I think that changing has had a very positive impact on me because when you feel like that you know what you are writing people can relate with it yeah I think I think it's nice so I I feel like there is uh I have evolved and my song writing has gained more confidence I'm more confident with my writing that's great that's great so can you describe a particularly memorable performance or recording session which you enjoyed the most um so so a very very very few people know this but um in 2019 uh I went to Bombay all right and I interned with the meath grows for a year wow yeah so um I think that is majorly from where I've learned music because I had no practical knowledge no technical knowledge you know how the studios work how to sit in a studio how the recordist works how the artists come and dub so one year in meath grows I've had the honor to um listen to some of the finest artists dub over there for meath grows like Johnita Gandhi uh Kanika Kapoor all right there's Akhil Sajdeva uh um Kumar Sanuji from old to new life my favorite yeah sorry he's my favorite Akhil Sajdeva oh yeah he's he is very good so you know you have to learn so much just by listening to them and just by being present in the studio technically I had no job I was just there but to have that honor and to have that experience to be able to witness something like this I think in itself is life changing so that I would not uh want to say any one particular artist or particular session but definitely that one year where I interned with the meath brothers that was life changing and I'm ever ever so grateful to them to give me that experience and they're they're like family for me yeah sure but what do you learn from them any any particular a small thing only what have you imbibe from them I think one thing one the first thing which I learned from there that singing is nothing but vocal acting yeah if you can anyone can say like this this is just singing but putting acting into it yeah the moment you put nakhra the moment you put expressions into it it's everything it's everything so one would be that singing is nothing but vocal acting and second would be the patience and the discipline which you require in a studio room to function as an artist a artist or a chair artist make a difference so that that's what I've learned in working with meath brothers that's amazing so uh my next question to you is that how has the music industry changed since you first started and how have you adapted to those changes that's a that's a very very nice question that's a brilliant question and it's a very relevant question in today's time um like I was just telling you back in 2019 I went and I interned with the meath bros because they were doing some of the biggest movies in bollywood back then and till date like touchwood they're doing very good work but I have realized like that was before COVID right since and after COVID I think a lot of new indie artists have come up yeah you don't need yeah you don't need a label right now you don't need a a bollywood play back right now you just need more values and you just need Spotify exactly these are the only two things which you need you need reals and you need Spotify you're good to go viral you know there are kids who are like 16 17 18 who have home studios and they're making music at home and putting it out and they're going viral uh I think bollywood nowadays is only taking famous singles remixing it and then giving it to the public yeah so I think it is the best time for an indie artist to be alive because um um I think it's great because you don't need labels big I don't name any labels but you don't need these big labels who could bully like mafia yeah you have a lot of power in your own hands that's right so you talked about remixes so in your concern that remix is trend is is what you say it's okay with you or they are doing justice justice to the old songs or what um see every everything is okay um till it's done in a limit yeah over doors is of anything is exploitation over doors yeah I think having too much money also for a person that can also be toxic so you know having being too kind can also be toxic so anything in extreme is bad yeah you take a song once in a while you remix it it's nice I think it's uh it's to give it a fresh aspect to a very iconic song is very very nice but once you start doing that to every song and you feel like that nothing original is coming up it can be a little upsetting so any advice for budding singles aspiring singles from you I mean um I think I I myself am still budding you know and yeah and I want to keep this thing in mind like no matter where I get I will always be a budding singer myself because there's no end to learning the learning that's yeah but um yeah but I one very most important thing is because I've also learned it recently so I would love to give it you know out there that you will always have the urge to quit you know there will always be that urge to quit once in a while but the key is not giving up yeah do not give up yeah your success or that one hits song or that that one day which just changes your life is closer than you realize the key is just don't give up that's amazing that was really insightful and what's lined up what are your future goals any new in your music career what next what's next any new song lined up I have a couple of songs lined up actually and uh uh touch for their all collaborations you know because I told you right now I don't want to work I will give out solo tracks also but just like how I got a cow on board for this song I want to keep working with a lot of artists so there are some very good names which I can't just use right now but we'll get in touch soon and you'll know I have a couple of collaborations lined up because the idea is to grow more and more as an artist with the mentorship of these artists so yeah actually I'm also very excited I'm also thrilled you know that these songs are going to be out wow so so happy for you and all the very best for your future so thank you so much for your time it was our pleasure to have you on our show thank you so much it was it was my pleasure to be here and you've been very kind and very very patient with me I want to go on record to say this you've been very kind and very patient with me thank you thank you see you soon


okay so we are going to discuss now how we can take care of the situation for Wheatstone bridge in capacitors okay so draw this Wheatstone bridge of capacitor let us say this is C1, C2, C3, C4 and C5 now when C5 will become useless or when the capacity so it's like water it just goes out so it can't store anything these two point is zero this capacitor will not store any charge so effectively capacity potential of this point is equal to potential of that point relation among C1, C2, C3, C4 for that so assume if this q charge how much charge this plate will have so some of the charge this plate has no charge so this will have minus q this will have plus q this is minus q okay let's say this is q1 so this is q1 and suppose q2 charge okay this stop talking this is minus q2 this will have more charge plus q2 and this is minus q2 fine now this is one loop and this is other loop can you write down that your loop rule equation for these two so I'm going from I'm decreasing my potential so it will be minus q1 by C2 okay 1 is equal to 0 for equation now in second loop let's go from A to this point D q2 by C4 is equal to 0 so q1 by C3 is equal to C4 this is the second equation so again this is a very simple looking expression C3 by C2 is equal to C4 by C1 when that happens this capacitor you can just throw it away because it has no meaning it doesn't store any charge it's 6 I by 6 this is I by 6 by 6 and this one also becomes I by 3 okay in this loop this one that's tunnel 1 see what you get is equal to 0 so V is equal to 6 5 so equation basis is 5 by 6 this one one or two more questions like this you're showing some question right yes so whatever these two and these two minus I by 3 are is equal to 0 so V is equal to 2R by 3 times pi or V by pi 2R by 3 same answer 2R by 3 what is 6R by 7? 4R minus 5 so and this out I2R minus 2R by 3 I2 is equal to 0 so V minus 3 to the 6 this is 8 to R by 3 is equal to 0 so I2 will be equal to 3V by 8R yes this current the same as that current has to be so this current is not splitting here whatever this coming here goes like this


Hey everyone, I'm Charlie Harrison, a software engineer working on the Privacy Sandbox. The Privacy Sandbox is a set of proposals to satisfy third-party cookie use cases without third-party cookies or other tracking mechanisms. I'm here to talk about one new API we're developing to enable conversion attribution for ads without the need for third-party cookies. So what is conversion attribution? This is all about measuring which ads lead to things like purchases or other valuable actions on an advertiser's site. This is effectively measuring the efficacy of online advertisement, and it can answer questions like, how well is a particular ad campaign performing, or is the campaign a good return on investment for advertisers? These are questions advertisers and ad tech companies need to answer, and we know this information is critical for a functioning ads ecosystem that helps fund the open web. Without it, advertisers and publishers are completely in the dark, and it could even lead to perverse incentives where ads optimize for clicks rather than actually providing value to the people who click on them. The Privacy Sandbox is a project about making the web more private by default while still supporting critical use cases like conversion measurement, and more committed to making this use case possible. However, before diving into the technical details of the API, it's useful to recap how this is done today using third-party cookies. Conversion attribution at its core involves connecting two events, an ad being served to a person, and a future event when that person later converts or buys something. With cookies, this is easy. As long as the same party observes the ad served and the conversion, they can use a cookie with a unique ID to link the two events together on their server. In this example, the ad tech company can use the cookie to see that the very same person that saw the ad on the news site later purchased the shoes on the shoe merchant's site. As Ma discussed in her talk, we're working to improve the status quo here. The information cookies provide is so powerful that it can be used to track a person as they browse across many websites. In the example here, the ad tech platform that uses the cookie learns detailed information about both the ad event and the conversion event joined together. That's the kind of data that could be used to build a profile based on a person's browsing history. In particular, we risk linking auxiliary data about each of these events. Let's say on news.example, I use one email address to log in. And to purchase shoes, I use a different email and also share my shipping address. With the power of a cross site identifier, it is possible to link up all this information to build a profile of me online. Now how could we improve things here and allow for this important use case in a more privacy preserving way? The biggest change we can leverage in a new browser API to preserve privacy is to perform attribution between the ad click and the purchase all on your device locally within the browser as opposed to in a server using a cookie.  Firstly, instead of the advertiser learning what conversion happened after an ad click, we can limit the advertiser to learning only a little bit of information about that conversion. Unlike with cookies where you can learn an ad ID alongside an associated purchase ID, in our API we drastically limit the amount of information you can learn about a purchase, the conversion data to only a small enum that describes it, like what type of conversion it is or maybe a broad product category. This protects by default your identity on the advertiser site from being revealed to the context that served you an ad and avoids the problem cookies have where arbitrary information can be linked. Secondly, the browser can decide to sometimes randomize that little bit of conversion information. The goal here isn't to mislead the advertiser, in fact, we'll tell them exactly how often we plan to randomize, but they won't know exactly which conversion reports are accurate and which had some noise added by a random number generator. This will let advertisers see the big picture without them being sure about any one particular action any person did. We understand analyzing data with this kind of noise in it can be challenging, so we've uploaded a script in our repo which illustrates a technique to correct noisy data. Third, we add a delay before sending out information in conversion reports. This helps us further disassociate information about the ad click from information about the conversion or even what day a conversion occurred. All of these mitigations help us provide conversion measurement as a capability of the web platform via a new purpose built API designed to provide the right amount of information while ensuring robust privacy guarantees on a technical level. Note that currently the API we've built only supports attributing conversions to clicks and not yet views, but this is an enhancement we're working on supporting. Here's a diagram showing the overall flow of the API. The API allows the ad on the publisher site to register its impression with the browser and for the conversions to be registered on the advertiser site. All this information gets stored internally by the browser and sent in a report at a later time linked together. Here's some code pointers for how to enable impression and conversion registration. Impression registration involves adding a few new attributes to the anchor element leading to the ads landing page and conversions are registered by responding to HTTP requests with a redirect to a special URL the browser recognizes. We'll go over these in more detail in a quick demo. Remember the two key pieces needed to use the API are configuring ad creatives and conversions such that the relevant data can be registered and stored by the browser. Let's start on a publisher page which embeds an ad iframe. Within the iframe there's an anchor element that controls navigating to the advertiser's landing page. To configure this ad for measurement this element needs a few new attributes. The impression data specifies an identifier for this ad that will show up later in reports. The conversion destination specifies the intended destination of the resulting navigation from clicking the link. The reporting origin specifies which origin should receive the report in the result of a future conversion. When someone clicks on an ad with these attributes specified event data is stored in the browser and eligible for attribution. For debugging purposes these ad clicks can be seen in a special internal page built into Chrome at chrome colon slash slash conversion internals. Ultimately at some point in the future there will be dedicated developer tooling but for now this Chrome internals page gives us what we need. It displays all the information from the API that is stored in the browser. Now let's convert on the advertiser's site. We can check out as a guest. Clicking on the buy now button takes us to the order confirmation page. This page includes a hidden single pixel image from the reporting origin. In other words once our purchase is complete a request is made to the reporting origin confirming that a conversion occurred. To signal a conversion the reporting origin servers need to respond to this request with an HTTP redirect to a special URL recognized by the browser. We can see this in the network panel if we look at the request for this pixel. This signals to the browser internally and any impressions targeting this advertiser's site are marked as converted with the conversion data set to two. Just like for the ad click you can view the conversion in the conversion internals page two. Here you can see all the information that will end up in the report. As you can see these quick conversions that occur right after the ad click will be delayed two days from the click. For debugging purposes however waiting this long is pretty inconvenient. We built a mechanism within the internals page to send reports manually. Let's do that. At this point Chrome has sent reports via an HTTP request to the ad text servers. Let's navigate to a page that displays all the received reports. Here we can see all the information embedded in the report. The impression data, the conversion data and some browser-provided attribution credit essentially whether the ad was the last clicked on or not. And there you have it. At this point the advertising platform can say that the ad associated with the given click ID led to a purchase. Maybe they'll use this information to show more ads on the publisher's site. If you're interested in trying this API there's a few things you can do. First you can test this out locally in Chrome today by setting a few Chrome flags listed here. The demo shown here should also be publicly available along with open source code on GitHub. If you want to run this in a production experiment you can register for an origin trial. The conversion measurement trial also supports our new third party origin trials. Please try out the API and give feedback. We'd love to hear how the API works to enable your measurement needs using attribution on your device without the need for cookies or other tracking techniques. And we welcome engagement on issues in our GitHub repo. For more information and documentation take a look at our web.dev article and check out our GitHub repo for future enhancements we're working on like support for view-through conversions and aggregate measurement. Thanks very much.


You know it's it's it's been coming more to the public's awareness the issue that's happening with Palestine and Israel right now and like I was already you know getting like invested and worked up over that but then you hear something like this happens here in Burlington so that just like adds a whole new layer of like yes I knew there were people who like indulged in that hatred for Palestinians and like kind of didn't have the right right mindset about things but then to see that something like that like is actually happening here as well. I mean the same as that it is definitely disappointing we're both from Vermont so we've kind of known what it's like to live in a progressive and inclusive state for the most part our entire lives and I'm from a rural place in Vermont so being in Burlington I'm even more expecting of community togetherness and support for people who are oppressed and it is definitely disappointing. I'm really honored to be here I'm grateful to have been able to participate in this I think this is a very important demonstration of the fact that it is solidarity and community and love that really defines this place Burlington far more than this terrible terrible thing that we're all here expressing sorrow about and sadness about. You know I think it's great that folks are coming out to reflect and to offer support to the families and the young men that were so brutally attacked and it's time for all of us to just remember that Burlington is not immune from hatred and violence and we need to say enough's enough you know I'm just overcome by emotions of feeling appalled and horrified and sicked by the violence that's taken place initially in the kids in Israelis then in Gaza far too many people have been killed. I have always been under the impression that Burlington is a very accepting and safe place for everyone and this past weekend showed that we need to make some more improvements in that area and it's nice to see people coming together for vigils and protests over the last month but more definitely needs to be done it is important for and crucial during these times for our community where such instances like a shooting takes place for us to come together and show that we are not in support of that and that we're going to be doing something about it but more needs to be done above community-scale support and it comes with awareness and education and vigils and protests like this to show that we hear you and we see things that are happening and we're aware of it and something's going to be done and that their support. Well said I completely agree with all of the points you made I think you know we hear time and time again I think a big phrase of the Burlington community is hate has no home here and well that's true I think you know hate does exist in all parts of the world and in all corners of the world even in Burlington and it's very important that we use the privilege that we have as Americans that we use the privilege that we have as educated college students and as people with voices to not only speak out about situations of injustice and violence but also you know words only go so far and I think that actions are even more important so you know just like Lucia said attending protests vigils marches calling and contacting your local representatives and voting for changes I think the most important thing we can do and we are very saddened to know that there was such a violent and awful situation in our you know community


Good morning everybody, the GLF community and all our friends online and here Yeah, I've been tasked to say or something about how do we reach the sustainable finance tipping point if there is such a thing We know that the financial sector has been a key driver Responsible to the multiple crises that we are facing today Climate change land degradation by diversity laws But we also know that the finance sector has the potential to be an important part of the solution of this crisis Because any of the solution for solving or mitigating or adapting to the major crisis that we are facing namely climate change by diversity laws growing inequity inadequate food system conflicts we require some massive uptrend investment and And sustained financing before we reap the benefits for the environment society and financially We know that the possible solution for this above mentioned crisis Are those that will induce positive tipping point if applied at scale like moving out of silk fuel based Economy into a circular bio economy Removing perverse incentive reducing inequities conserving and restoring ecosystems For all these political will and investment are needed at all scales So we need money Unfortunately, this money is currently spent elsewhere So we have seen positive development in the political agenda as national and international level Latest of these have been the CBD COP 2015 Which also the finance day for the first time and adopted the global by diversity framework This new global by diversity framework includes key targets to increase finance for natural and biodiversity There was also some good progress made during UN FCCC COP26 and 27 With some modest progress in funding the fight against the climate crisis and addressing for the first time the question of losses and damage The financing sector is also showing change in the right direction still there are many Issues remaining and and they all relate to a specific color, which is green So let let me tell you a brief story about various shades of green and and the first of this is a greening of finance We do acknowledge that sustainable finance standards are going in the right direction But it is still too slow and mostly focused on the short term and gearing stored maximizing present profits at the expense of the future The year 2022 was particularly bad for sustainable finance the North American Bank dug in on fossil fuel And pressure the gifas to capulate and dexon manager slow worked on the net zero More than eight trillion dollar were removed from sustainable investment early and the list continues the year 2023 Seems to offer new ops with the UK and European banks leading on net zero The new Biden act in the US, but the jury is still out The other shade of green is the financing green And here despite significant progress. There is still a great finance David Divide this list developing country and able to respond to crisis and invest in sustainable development What 60% of the less developed countries and other low-income countries are no access at high risk of debt distress double the 30% of 2015 we also know that the finance law to that your best solution currently has 150 billion dollar per year is less than half of the 480 something needed by 2025 and only a third of the 480 billion needed in 2030 and Then last point about the green color is the green washing Major finance giants are actively funding economic sector responsible for the Amazon deforestation while adhering officially to Deforestation free pledge. They are that's thrown out many of the carbon offset program based on scientific evidence At if I craft we believe that natural best solution is a sound investment And while the best time to plant a tree was 20 years ago, the next one is now and We have shown to our combined experience that the genetic ecological and social science tell us that selecting three species is good and help and It means that agricultural principle academic agroforestry regenerative agriculture and other Development could work in improving our food system and agriculture overall We believe that taking a system approach Brings many many feet and and we have the proof of concept I mean for an investment of 800 million dollar in the forestry and agroforestry program We have managed to Ends the protection of about 100 million hectares of forest We have reduced about 70 a gigaton of our avoided CO2 emission About 25 million hectare of land brought under restoration if you add all these even at the US 10 dollar a ton The 800 million dollar that were invested in FTA. They translate into 240 billion dollar in Economic returns avoided losses so we can do it if we really want The question that we have to ask is said do we really want it. Thank you very much