okay hi everybody again well we live in unusual times and so I'm doing this unusual thing of trying to answer whatever questions you may come up with about science I've been studying and working on science for most of my life and learnt a few things so we'll see we'll see how I do on answering your questions I did one of these last week and this is kind of back by popular request okay gosh we've got questions already we've got physics coming already all right I'm going to do so got a couple of questions here so let me let me start off Thomas asking what are protons neutrons and electrons made of okay well the story is a bit different for so first of all let's remember what where we where we run into protons neutrons and electrons so atoms are have a nucleus which contains protons and neutrons and they have electrons which are kind of sort of orbiting outside the nucleus they're kind of hanging around outside the nucleus so it's a different story electrons are a different kind of thing than protons and neutrons in the language of physics electrons are examples of things called leptons and protons and neutrons are examples of things called baryons or hadrons those are fancy words which probably get used if you study physics in college or graduate school and maybe don't get used by anybody else um but there's sort of two different families of kinds of things okay so let's start off with protons and neutrons so it was discovered in the 1960s early 1960s that protons and neutrons weren't just sort of point things they were things that have a definite structure inside and actually they have they they're there well they have a the diameter of a proton is about 10 to the minus 15 meters which is otherwise known as what's if I can do the conversion 1,000 trillionth of a meter so very small but not zero so what's inside protons and neutrons inside protons and neutrons there are things called quarks and that was kind of quarks were originally person I knew well actually kind of came up with that idea back in the early 1960s that there might be something inside protons and neutrons so roughly inside protons and neutrons each one of those has three quarks inside it and like a proton has two up quarks and a down quark and a neutron has one up quark and two down quarks and that's kind of what makes those types of particles different is they have different quarks inside them now one of the tricky things is you might say well why haven't I ever why don't I have you know like why aren't there bottles of quark surround why you know protons neutrons are very common why why do we not have quarks that we can actually see well it's a very tricky thing so quarks are these little particles which seem to be more or less point particles they more or less have zero size not quite we'll talk about that in a minute but the question is why do they never get out of protons and neutrons and the answer is there are these things called gluons which are another kind of particle and between these these quarks are kind of bound together by gluons their goo ones that are being exchanged between quarks and the gluons are pulling very hard on these quarks and so far as we can tell it's not possible to get a quark outside of a proton or neutron you can't ever pull it outside so what happens roughly is this so if you if you look at for instance some the if you look at let's say the force of gravity you might know as as gravitational masses get further apart the force of gravity between them goes down it's actually an inverse square law so if you so if the distance between the objects is R the force between them is is proportional to one over R squared okay it's the same thing actually the same exact force law for charged particles particles that have electric charge they also have a force law that goes like 1 over R squared so as you make them further and further apart but force between them gets less and less okay so gluons make a force between hawks and the really weird thing is that the force between quarks actually instead of going down as you pull the quarks apart it actually goes up it goes up roughly roughly as the distance between them is it goes up if the force increases as you make the distance go up it's roughly proportional to the to the distance between the quarks the forces so that means that you try and pull these quarks apart it gets harder and harder and harder to pull them apart so if you try and actually get a quark all the way out of a proton you can never do it so so what's inside protons and neutrons is this kind of soup of quarks mainly three quarks and a bunch of gluons that are holding these quarks together it's a little bit confusing there there's a whole kind of cloud of quarks and antiquarks when you talk about anti quarks and antimatter different time but roughly it's it's the sort of cloud of particles inside protons and neutrons so that that's the story about what's inside protons neutrons so you might also ask well what's inside quarks what's inside gluons well the answer is nobody knows you can ask the same question about electrons as far as anybody can tell electrons are perfect point particles it's like they have no if you say what's the radius of electron an electron what people have always said in physics is the radius of an electron is zero it is like a perfect geometrical point now I personally think that isn't correct and actually I happen to have been very recently working on kind of understanding what might be sort of underneath fundamental physics and I actually think that in the end it's going to turn out electrons are actually not point particles they actually have a size it's actually very very very small but and they what's inside electrons I think is related to kind of how space works see space normally we think of sort of the universe we say we can put position things any way we want we can say we put this electron at this particular position if we specify by a number it might be you know position you know one point two three seven five eight two four six four cetera teller teller we could just go on as many digits as we want we can precisely say we're going to put this electron at this precise place in space I mean how we actually do that with an experiment when might not be sure but at least when we're doing theory of physics we can say we put this electron at this precise place okay well that would work fine so long as space isn't it so long as spaces itself continuous if space was instead some grid where you could say oh we can only put an electron at this position on the grid or this other position on the grid or this other position you wouldn't be able to do this thing of saying you can put it anywhere you want well I actually think that in the end it's going to turn out space it isn't quite a grid it's more like a network and in fact electrons correspond to these kind of features of the network it's kind of almost like little knots where you have little little threads of network that connect pieces of space and electrons are kind of like little knots in that network and in fact that that means that in a sense when you say what's inside an electron what's inside an electron is a kind of space but a funny kind of space but it's all that that's I mean that's kind of a that's that's physics that doesn't yet exist because it's physics I've been working on that there wasn't for this pandemic I would be telling people much more about the only way so that's that's kind of the story of electrons is that the usual theory in physics says there's nothing inside electrons they just point particles I think that isn't correct there they actually have a small extent and sort of what's inside them as a special version of ordinary space same with with quarks in ordinary in physics as it's been thought about for the last 50 years or so it's the idea as quarks are also point particles with nothing inside them but again I don't think that's correct okay long answer to that term there question let me go back here and I can also I might also say when you start asking about very small things like electrons there are lots of tricky phenomena that happen and maybe we'll talk about them some more later about this thing called quantum mechanics that kind of is all about the fact that you can't when you think you know where the electron is maybe it isn't quite there you can't quite localize it and so on long story alright let's come to some other questions here ok there's a question at the beginning if neutron stars are just made of neutrons how come they produce light I don't think they usually produce light they produce radio waves if they produce so let me explain a little bit I think I talked last time a little bit about neutron stars so when a star billions of years from now our Sun for example will kind of run out of fuel and it will just become a smaller a smaller star but some other stars a bit more massive than the Sun and can end up having these giant supernova explosions and what gets left over after that explosion is often a neutron star which is kind of something about the mass of the Sun but compressed into something maybe five miles across so it's a very very dense object it's actually very much like the nucleus of an atom except very big like a five mile across atomic nucleus all made of neutrons so the question is how do you even know that there's a neutron star there because like a neutron it's just this big lump of of stuff that is like an atomic nucleus how would you know it's there okay well turns out that so one of the things that happens but this is some complicated physics like we trying to explain it so you probably know that the earth has a magnetic field so that means that's why compasses work so the earth has a north and south magnetic pole it's like it's like a giant bar magnet the earth the earth acts like a giant bar magnet and that's why a compass needle can be can you know point towards the North and South Poles and so the earth the earth is kind of has this magnetic field what produces the magnetic field it's probably produced by essentially electric currents in the liquid core of the earth it's not completely clear how that works and one of the things that's weird is you think that the North Magnetic Pole is to the north and it is right now at the North Magnetic Pole is somewhere in northern Canada right now but over the course of history the magnetic poles of the earth actually move around and it's not been many hundreds of years since they've been actually in quite different positions than they are now so that's probably because of changes in the flow of the kind of molten rock in the in the center of the earth that's changing and causing the magnetic field to be in a different orientation but anyway so the earth has a magnetic field the moon for example does not have a magnetic field Jupiter has a big magnetic field the Sun also has a magnetic field and it's thought that most stars have magnetic fields and so that means that there are essentially electric currents in the Sun that are producing this magnetic field it's like a giant bar magnet okay so what happens is when when this star has a supernova and it kind of compresses down to this to this neutron star then the magnetic field can't go away the magnetic field has to be that it had when it was a big sort of a large star is still there but it has to be sort of compressed down to kind of fit around this little tiny neutron star and so then ends up with a pretty intense magnetic field and so what happens is this thing is like a bar magnet a really quite strong bar magnet and boy this is some complicated physics okay so what happens is that electrons spiral around the the magnetic field lines of this bar magnet and the same thing happens for the earth actually there are electrons that come from the Sun for example that spiral around in the magnetic field of the earth near the North and South Poles and so for example that's what causes the aurora the aurora you know if you go to the northern far up north and it's good weather and you let your eyes get dark adapted and so on you'll see this really cool it's usually red green all kinds of other colors sort of curtain like pattern in the sky that's the aurora and that's produced by electrons that originally came from the Sun spiraling around the magnetic field of the near the North Pole of the earth and causing particularly things like oxygen in the upper atmosphere of the earth to to produce light of different colors in kind of the same way that a fluorescent light bulb produces light it's sort of the same rough idea of how light is produced in the upper atmosphere and on aurora but anyway so that's a place where you're producing in that case it's producing light because these electrons are hitting oxygen other things in the upper atmosphere okay in a in a with a neutron star electrons can be can be kind of made they spiral around and magnetic field and they spiral around really quite fast and one feature of electrons that are spiraling around like that is they produce they they emit radio waves and that's true in general if you have you know when you have a radio antenna the way the radio antenna works is that it's making electrons go up and down up and down up and down a certain frequency like a typical cell phone it might be 2 billion times a second five billion times a second that kind of that kind of thing the electrons are going up and down up and down in the antenna that's on the side of your cell phone so it's the same type of thing when electrons in magnetic field of a neutron star going around really fast and they're kind of being made to go around in these circles and that produces the same effect of making radio waves that happens in something like a cell phone but those radio waves are pretty intense and we can we can detect those radio waves even though these neutron stars may be a thousand light years away or really far away across the across the galaxy and so the the result of that is okay so I have to explain one more thing gosh I'm I don't get to explain this kind of stuff very often so I'm I I never I'm not quite sure how much there is to explain but let me keep going so another feature of neutron stars is they they typically spin around very rapidly and that's kind of for the same reason that the that the Sun is spinning at a certain speed if it were to be compressed down to a neutron star it would spin much faster in order to conserve its so-called angular moments angular momentum so okay so anyway this neutron star it's spinning around very rapidly it has electrons that are that are producing radio waves and what happens is as the as the thing spins around it's essentially producing as it because the the the way the electrons got a little complicated in the magnetosphere of a pulsar which is the kind of the kind of sheath of magnetic stuff around the Pulsar it's not quite uniform and so they'll typically one direction where it is producing more radio energy radio waves than in other directions and so the pulsar turns around and as the Pulsar spins around cheated here I already told you the answer so this neutron star is I should have said just neutron star is spinning around it as it spins around it'll send this beam of radio waves in in a particular beam of radio waves that it's producing will spin around as well and so if we're over here and the earth as this neutron star spins around every so often its beam of its radio beam will point towards the earth and so if we are listening on the right radio frequency we'll be able to essentially hear that radio signal coming from the neutron star okay so back in 1968 people were doing radio astronomy they were trying to use telescopes that kind of detect radio waves and they discuss this strange phenomenon that they were hearing pulses in radio pulses that were coming from particular stars in the sky particularly the Crab Nebula is one one famous one and so it's like what was this I think I mentioned this last time but but the you know you you hear this kind of pulse and it's sort of regular pulse and the first guess was gosh that must be a beacon of some extraterrestrial civilization that's saying hello we're here you know it's like a navigation beacon or something from an extraterrestrial civilization and that's what for the first two weeks I think people thought that's what that might be and then they realize no actually it's a neutron star and those things are called pulsars pulsing stars and they pulsars produce these sort of pulses of radio energy I don't think that they produce I don't think there's visible light that gets generated if there is visible light it comes from a different phenomenon of accretion discs where there's matter that's kind of being dragged into the into the neutron star but I don't think that happens with neutron stars it happens with black holes I don't think it happens with neutron stars but I might be wrong about that um but any case the the pulsars we now know a whole bunch of pulsars around the galaxy and they're there they're there they're really cool objects because though these they're these whole stars that spin around like they're even millisecond pulsars which means they spin around a thousand times a second the whole star is spinning a thousand times a second and producing producing radio signals that is about a thousand times a second we hear a pulse from it and you can do all kinds of weird things like for example let's say you wanted to work out how to do GPS in space so GPS is you know how we find how cars and planes and other things find their position on the earth and the way it works is there are satellites orbiting the Earth the constellation of how many it is these days maybe 6070 satellites orbiting the Earth that each produce pulses with a known interval and so when you're your GPS receiver can tell oh yes the pulse I got from satellite number 17 took exactly 21 milliseconds 21.125 864 something or something milliseconds to arrive because the pulses are they have a certain code that tells you when the pulse when the GPS satellite produced that particular pulse and you know when you measured that pulse so that allows you to work out because you know the speed of light you can just work out um how far away the satellite was and that tells you what you're if you know three satellites you can triangulate to find your position okay so one of the questions is if we were in space if we were doing some you know we were going off and we were sending up spacecraft to to Pluto or something was far away from the GPS satellites that are orbiting the earth they're not gonna do us any good and telling us we're app where our spacecraft is how can we what's the kind of inter interplanetary or even interstellar version of GPS that we could use and so one people one thing people have thought about is to use pulsars as kind of an interstellar GPS system because we know where all these pulsars are each pulsar has a definite series of pulses that it produces and so you can use that to figure out how far exactly how far away are you from this from all these different pulsars and that gives you a way to get a kind of location in interstellar space that gives you sort of a way to do that I mean a more simple-minded way to do it which is what a lot of deep-space probes do is to just have a little telescope and they look for different stars and they say when what what what is the orientation of you know where what what direction do I have to be pointed in to see this star and that star and they do things that way all right long answer to that question all right we've got lots and lots of other questions here um let's see come on improve mathematical and scientific analytical thinking um bucks to read and so on I'm not a huge expert in what exists right now you know I think you know the main thing I was like to do is when I see stuff happen in the world that I hear about stuff I just try and learn how it works and you know the web has lots of good sources of information about sort of how things work and you know try and read those ones you don't understand try and figure out you know what were the sort of underlying concepts and try and get to understand those I think that's a that's a good place to go when you really want to know sort of how things work learning how to tell a computer what you want is a is a really good way to do that I mean I've spent a lot of my life building this kind of computational language to have us humans be able to explain to computers what we want and I I always find that the time when I really think I understand something is when I can write a little program that does the thing that I'm talking about um that's kind of my test for whether I actually understand what I'm talking about and I find that it's a really good way to kind of organize one's thoughts to but kind of explain it to a computer it's also good explaining it to other people like I'm trying to do right now um I mean I'm gonna under script to some more of the science questions here I can talk maybe a different time about more kind of computational thinking kinds of things okay so the question from MC is how the magnets work okay well there are the all right magnets like lumps of metal that make magnets I can explain how those work you can also make magnets by using electric fear by using electricity and in the end magnets like lumps of metal work in kind of the same way as magnets that are made without lectricity but it's a little bit tricky to explain exactly their correspondence so let me start off by talking about magnets that are made a piece of metal so the most common kinds of magnets bar magnets made of iron the three chemical elements iron cobalt nickel which are next to each other in the periodic table which means that they have adjacent numbers of protons because the periodic table just is this table of all the different possible kinds of atoms where each one is arranged from hydrogen helium lithium beryllium etc each one is hydrogen has one proton helium has two protons etc that's that's how the periodic table works in one part of the table is iron cobalt nickel um and those that's the most common thing that magnets are made of they're also things called rare earth magnets which are actually much stronger magnets most common let's see I think gadolinium europium samarium I think a common examples of rare earth magnets those are those are also elements in the periodic table they're also metals um and they produce they allow you to make stronger magnets okay so how these magnets work well basically a big magnet like a big lump of iron that's a magnet the way it works is it has a lot of really tiny magnets that are all lined up inside those tiny magnets are actually iron atoms and the iron atoms are themselves little tiny magnets and the big thing that makes the big lump of metal act like a magnet is that all those little tiny magnets are all lined up so here's the thing not to do with a magnet that you want don't put it in an oven and because if you put it in an oven and heat it up there's a temperature it's called the Curie temperature at which it loses its magnetic field it loses its magnetism so what happens is just like if you take a block of ice that's you know solid all the atoms are all lined up in the block of ice and you heat it up eventually it'll turn into a liquid and the atoms won't all be lined up they'll all be you know running around all over the place the same thing happens in a magnet so an ordinary magnet when it is magnetized and it is a ordinary room temperature the the atoms inside that magnet all have what are called their spins that little tiny magnet magnets are all lined up and so that means you'll have trillions and trillions of little tiny magnets all lined up and they all line up in the same direction and so they make a big they make the whole thing act as a big magnet if you heat it up it essentially the magnets kind of it's it's like they like they melt and it doesn't it's it's long before the lump of iron actually melts long before the the actual atoms and the iron get separated to the point where the iron becomes a liquid long before that the the alignment of the little tiny magnets that these iron atoms are that gets broken down and so your magnet will lose its magnetic field so if you care about your magnet don't heat it up to that point because it will lose its magnetism now the good news is you can always give it back its magnetism if you if you put it in a magnetic field again it will the the iron atoms will line up again and you'll make a magnet again although you might make a magnet that's in a different direction than the magnet that you had before so so the way that um the way that sort of things like bar magnets big magnets and things work is they have these little tiny atomic scale magnets and they all get lined up and that's how you get one of these big magnets and it's only certain metals that um certain materials that have this feature that their atoms can line up in this way um it's still the case that if you picked out an individual atom of almost any element it could act like a tiny magnet itself but it's only in certain materials that all those little tiny magnets can get lined up to make what's called Ferro magnetism it's that's the that's the name for the phenomenon where where all the all the little tiny magnets line up to make a big magnet so anyway that's the way that magnets that's the way things like bar magnets work the the way that you can make a magnetic field without having any of these atomic magnets you do that by having the electricity a magnetism are closely related and it turns out that if you have for example a loop of wire and you have electricity flowing through that loop of wire in it will produce a magnetic field so maybe I could explain another time how that really works but basically when when electrons that make electricity are moving around in a circle they produce a magnetic field and that is goes sort of sort of perpendicular to the circle and that's so that's how that's how electromagnets electromagnets work and they're very convenient like for example if you have a you know a door that's supposed to be locked or not locked you can do that by having a what's called a solenoid which is one of these electrode it's an electromagnet and that means that when if you have if there's an electric current if there's electricity flowing through this coil then it will produce the magnet and if there isn't electricity flowing through there it won't make a magnet so if you have two two of these things next to each other for example you can say okay there's electric going through these so they make a magnet so they're held together oh you switch the electric field off open oh break apart so that's a very convenient thing because it means you can have magnets that you can kind of switch on and off just by switching electricity on and off now the the tricky thing that's a little bit more complicated is in some sense the magnets that are these atomic magnets are actually made from something analogous to a loop of wire because what's actually happening is that the electrons in inside the atoms are kind of going around the atoms just like the electrons go around that loop of wire but it's like a little tiny loop of wire the size of an atom and that's kind of how the magnetic field gets made in in just at the level of the individual atoms in iron for example now okay in in sort of to be really exact there is another thing that happens these individual particles like an individual electron actually is like a tiny bar magnet and so I was telling you earlier electrons are either of zero size or at least very very small and so there's a there's kind of a question of how how an electron manages to have what it takes to make a magnetic field just by just as a thing itself and nobody knows how that works it's I think this new theory that I have for how fundamental physics works probably explains that although I don't yet know how that works I mean if you if you're interested in there's a phenomenon called spin which is a feature of of particles again I'd be happy to talk about it it's a it's a it's an interesting and complicated story electrons have spin 1/2 photons have spin 1 all these different particles have a certain spin which and many of those particles when they have an electric charge and they have a spin they'll they will be act like little magnets so ok long long answer to that question all right let's see why is their ultimate speed limits of the speed of light well it's a good question the inn well the ultimate answer is we don't know it's a feature of our universe it's a very important feature of our universe um and we don't know why it works that way now having said that in for example my new theory of how physics works we can understand well that's some yeah we can understand a little bit more about why there's a maximum speed so so the speed of light maximum speed that anything can go out in our universe how big is the speed of light the thing that's worth if you're gonna remember one of these factoids about light goes one foot in one billionth of a second so in one nanosecond light goes one foot so that means in in one second light goes a billion feet um and it takes so for example to give us some sense of scale it takes light eight minutes to go from the Sun to the earth it takes light what is it about a couple of second notes gosh I have to work it out um maybe a half a second or a second to go to the moon so light goes fast but not an infinite speed um and to go across our whole universe takes a time that's about the age of the universe about fourteen billion years actually it takes even longer than that to go all the way across our universe but that that's sort of a first approximation to how how long it takes to go across the universe but then so what light the speed of light governs the maximum rate at which we can send signals so for example when you I don't know like when we're using when we're using the internet for example it's often called the ping time on the internet so one computer will ping another computer there's a in low level operating systems there's usually a command called ping and you say ping and then you say the name of a computer then it will say up it took 200 milliseconds two hundred thousandth of a second to send a signal to that other computer and get it back again okay so the the the ping time is is this time for signal to go from your computer to another computer and get back and tell you how long it took and so a question is is that in fact is that time that's sort of a that tells you how long it takes for information to go from your computer to another computer and in a first approximation that is at least limit well it's certainly limited by the speed of light you'll never be able to get your computer to ping another computer faster than it would take light to go from your computer to another computer now how is the actual signal sent well often a lot of signals now are in fiber-optic cables so fiber optics is like normally you know you shine a flashlight or something and just shining it through the air but you can also get light to go through glass and you can make these fiber optics where the light goes into this fiber and it bounces off the edges of the fiber and keeps bouncing off the edges of the fiber and the light will just keep going through this fiber and so you can actually have a single fiber that can be like probably these days a hundred miles long and you can just shine light in one end of that fiber and the the glass is in the fiber is sufficiently pure that the light will just keep going keep going it'll bounce off the walls but you won't lose any light and you'll still be able to get and you'll get the light out at the other end and so a lot of the internet is built with fiber optic cables where the the speed of light where where it's light that's transmitting the signals that's telling you know that's going from from my computer camera two onto the the Internet and so on and so on and so on now actually a little bit of a footnote to that light the speed of light that you hear about you know one foot and a nanosecond and so on that's the speed of light in a vacuum it's very close to the speed of light in air the speed of light in air is a little bit slower but the speed of light in other materials is considerably slower like in water it's 33% slower than in a vacuum and in glass it's typically about 50 percent slower well it's the it's called the refractive index which is the ratio of the speed of light in a vacuum compared to the speed of light in the material so for glass that's between 1.5 and 1.7 usually um and so that means that when when light is going through glass it's not going at its full speed of light speed it's going at one-and-a-half times slower than that speed why does that happen reason it happens is that in something like glass the light is continually getting absorbed by an atom re-emitted by the atom so what happens is the light hits an atom it makes the atom it puts the atom in a new state where the atom says I just absorbed a photon of light and it takes the atom just a little bit of time to remit that photon of light and so it's like it's playing some kind of relay type thing where the light is falling on one atom takes the atom a little bit of time to emit that light again and keeps going and that's how light gets transmitted through something like glass um and that's why the light is not going at the official speed of light in glass anyway so the ping times on the internet roughly roughly determined by the speed of light in glass now it's that's not the whole story because what happens is the it's not just going through this one cable it also has to go through electronics that tell it which cable to go through and figure out how to switch things and so on and actually a lot of the time the lot of the time that's taken and communicating between computers is actually inside that switching stuff rather than the actual trans mission along the fibers but the actual transmission along the fibers does take some time and you can you can detect that as you look at you know web sites that are further away from you physically and you'll find that it takes longer to the ping times will tend to get longer all right um was a question here can you ask about the corona virus only about sounds I can talk about grown of iris what I know about it um the okay oh boy we're going to so somebody's got to ask the question what is spin which I let me avoid talking about that question I'll I'm happy to talk about that sometime but beome shall I try it alright I'll try it okay um okay you want me to you want me to tell you what it actually is I'll tell you just because fun to hear the words so the a particle like an electron has a each electron has a certain mass all electrons have the same mass and the well the official definition of spin it is which irreducible representation of the prank or a group does the electron transform equipment I can use all the fancy words I'm not going to use these fancy words because this is absolutely useless um let me try and explain so those fancy words tell us that spin is something that is sort of understood in terms of mathematics and in terms of fairly abstract concepts so I I have a guess about what spin really is in terms of the way that space is built and so on I don't yet know if it's completely correct but let me tell you kind of the the standard realm we tell your mixture of kind of what spin is so so roughly you can have an object let's say I don't know if you know like a top a top can be spinning around right top spins around and one of the things that happens with the top is it just like ski likes to keep on spinning just the way it's been spinning and that's similar to if you throw something it will tend to keep going in the direction that you threw it at least until gravity makes it turn turn in a different direction that's so the reason it does that one way to explain that is it's conservation of linear momentum there's this idea of momentum when things when things are moving it's some it's a mass and velocity combined together make momentum and so a massive object going in some direction will tend to keep going in that direction there's a in in physics there's a conservation of momentum so things starts going in that direction it will keep going in that direction the okay so that's linear momentum there's also a conservation of angular momentum when you start something spinning it will tend to keep on spinning okay if you have a top for example the top will eventually stop spinning and the reason for that is there's friction if the top is just spinning on a little point there's friction between that will tend to slow down but friction for example between the points and the table or friction because the top is moving in the air that will tend to slow the top down but if there wasn't any friction if you had this top spinning in space the then then the thing would just keep spinning around it would keep spinning kind of forever that's conservation of angular momentum okay I have to tell you a story a friend of mine who's a astronaut used to be an astronaut had an experience with space in space that was was a was a one of these figure out physics and real-time kinds of experiences so he was on the space station called mer which was a Russian space station was a pretty Assessor of the current international space station and he was on the space station and the space station was some there was some accident on the space station and that caused the space station to start rotating to start spinning and in fact because there wasn't any air to slow it down there was nothing to slow it down the space station just kept on spinning and so it was a was a big question how should they stop the space station spinning and in fact my friend was used our Mathematica program to to figure out in it you have to be a very kind of cool cucumber of an astronaut to be hanging out in a space station that's spinning around and to get out your computer and start writing down differential equations and solve the equations and things and figure out yes if we fire this thruster in this direction then we'll we'll stop the space station spinning but he succeeded in doing that and figured out figured out just by using the math equations how to stop that space station spinning and then of course the the story be much better if he'd been able to implement what he what he figured out and that it worked but in fact the Russian ground controllers who were you know in charge of what happens to their space station were like no you can't do that that's not our procedure we have a procedure for what to do well we don't know exactly what it is but anyway after after a day or so they managed to use some other procedure but it was kind of a shame that the differential equations for for solved in real time to stop the spinning space station never actually got able to be implemented but any case so so in in large-scale objects there's this idea of angular momentum and there's a conservation of angular momentum okay when you have a very small object like an electron electrons also spin around but when you have a big object like a Space Station you make it spin faster or you can make it spin slower when you have an object like an electron for reasons that we don't yet fully understand you can effectively only give it one particular amount of angular momentum so all electrons have in the units of angular momentum that's used for electrons they have half a unit in angular momentum so all electrons have half a unit of angular momentum they can actually be essentially they can be either plus half a unit or minus half a unit that whole story is a little bit complicated with quantum mechanics but but roughly I think it's fair to say an electron has half a unit of angular momentum a proton also has half a unit of angular momentum photons have one unit of angular momentum gravitons the particles that make up gravity waves they have two units of angular momentum and the number of units of angular momentum that a particle has has a big effect on how the particle works and that the most important effect is if you have an integer number a whole number of units of angular momentum your thing called a boson if you have half a half integer number of units Langan events Amir I think all the fermion okay what's the difference what's the big difference between bosons and fermions basically bosons are super social and like to clump together and fermions are kind of super anti-social and like to stay apart okay why do we care well the reason we care about fermions staying apart like things like electrons and protons and so on is that most matter that we deal with atoms and things are made of fermions and the fact that they like to stay apart is what causes matter - not all collapse so there's a thing called the exclusion principle that basically says when you have fermions things like electrons things with half integer spin they will never want to be sort of all stuck together in this in the same place they'll always want to be B be sort of forced apart and that's what it's a large part of what leads to the stability of matter that leads to having actual objects that don't sort of collapse okay so that's what happens with half and you just spin things with with whole integer spin things I mentioned that photons have spin one photons are examples of bosons photons are the particles of light they're examples of bosons and bosons have the property that if you have one boson it really wants to have other bosons be right there in the same state right on top of it okay so you might say well so what well the main so what of that is that's how lasers work lasers the word laser stands for light amplification by stimulated emission of radiation and what's happening there is that in a laser you're trying to get lots of photons to all be in exactly the same state all being going in exactly the same direction all shine out of the front of the laser so to speak and it's because photons are bosons that it's possible to these electrons really like kind of clumping together and all being in the same state and all making this coherent laser light that you produce in a laser so they're these two so the spin is this property of particles that has to do with angular momentum and it really matters whether things have half a unit of spin or one unit of spin and that um that's a very well if you study theoretical physics in graduate school you might hear about a thing called the spin statistics theorem which is a which is the which is the piece of mathematics that shows that there's a connection between the spin of a particle and whether it wants to be clumped together or a stayer part I could mention one more thing about that which might be too complicated but well okay just a a thing if you're curious can look up there things called spinners and normally when we have something in ordinary three-dimensional space and we rotate it around we rotate 180 degrees it's backwards we rotate it 360 degrees it comes back to where it started from again okay um turns out for things like electrons they don't work that way they actually you turn them around by by 360 degrees they don't come back to where they started from you need to turn them around by 720 degrees you need to turn them around essentially two full revolutions before they come back to where they started from again and that's a weird and interesting phenomenon that I could talk about some other time okay let's see okay so question here boy you guys are asking about physics a lot ah let me see um gosh lots of great questions here um what should I try and a bunch about physics let me let me try and talk a little bit about math um since there's a question here about math it's a question about statistics let me see all right let's talk about statistics well I think for that I have to get my and actually do something with a computer let me do that hold on a second here okay all right let's see what we can do with statistics I'm kind of looking at my screen here so I might be looking up in a rather strange angle that sorry about that um okay well where should we start I think a good place to start is talking about averages so if we say let's say we make I'm gonna make a bunch of I'm gonna make 50 numbers between let's make them between 1 and 10 I mean I 50 random numbers between 1 and 10 so one question you might ask is what's the average of those numbers so let's say for example those are I don't know distances you throw a ball or something like that you could say what's the average of those numbers and so they're they're various ways to work out that average maybe actually let me let me do something slightly different here let me make my room numbers a slightly different way um let me say this oops I wanted sorry okay so here I've got a bunch of numbers and I want to say what's the average of these numbers okay so one convenient thing to try to do is to make histogram so a histogram let me just make it here so a histogram says let's put these numbers in in buckets let's say how many numbers are there between zero and two how many numbers are there between two and four how many numbers are there between four and six so this is saying for each bucket like this is the numbers between zero and two this is saying that I can't read this off here but there but maybe 16 numbers between zero and two same 16 numbers between two and four some I don't know how many it is six numbers between 4 and 6 and so on okay so we have numbers in these various buckets and so this histogram we can say if we want to say given these numbers what's the chance if we were to pick it okay let's imagine that we we wanted to say what's what's the chance that one of these numbers is between let's say zero and four what we'd have to say is what how much stuff is there that falls between in these buckets between zero and four compared to all the other stuff and that will give us the so so let's imagine I mean let me give a slightly different example but let me let me keep going on this let me let me show you let's say let me do a few more of these let's say we do 500 of those and let me make the same histogram again so I'm just I'm just using um so now I'm going to ask the question let's imagine that this is the this is heights of different what can what's about that height I don't know pet grasshoppers that are different no I don't think there are negative height pet grasshoppers bad idea uh what could this be this could be [Music] distance snail walks towards a piece of lettuce in a few minutes and sometimes the snail walks backwards so it's a negative number okay but anyway so now we want to ask something like what's the average distance that the snail walks towards the lettuce and so how do we work that out from this well what what do we think the average is what we might say what's the if we if we were to cut this out as a piece of paper and we would try to balance it would say where where would we put the balance that would make it be sort of an equal amount of paper to the right and to the left so that's one one way that we could sort of decide what's what's the middle of this what's the what's the what do we count as the average of this of this set of distances the snail might go and that that way of working things out is called the mean of the distribution another thing we might do is we might say I want to I want to say let's make sure that half of the and this mainly not the best way to explain it I think I should have them so there are these different kinds of averages there's mean median mode so the mode is an easy one to explain the mode is what's the most likely what's the most likely value so that would be this bucket here so they're these different different kinds of kinds of averages but but in general this sum so like this might be a distribution that it's the same shape distribution there's a very common shape of distribution it's called a normal distribution or Gaussian distribution or bell curve sometimes and a lot of things follow that distribution so for example for human Heights they follow that distribution for any given age etc you'll if you work out what's the distribution of heights and I'm sure I can do this if I if I pull up with malphur let me um let me do that yeah a [Music] go let's um let's say let's say I don't know girl age 12 height so and you can do this with Syria and things like that which are powered by wolf knife ride pretty sure they they give you this information now that's not good let's let's ask it let's say um oh I see okay there we go so this tells us for girls age 12 this tells us if we looked at lots and lots of lots and lots of kids this shows us the distribution of their heights so it tells us the most probable height seems to be well it's a little bit under 5 feet here and this tells us the the the this tells us what the distribution of heights is so if you were to have a bunch of kids and and you were to measure all their Heights and you were to put them in in bins of you know who is between this number of inches and that number of inches the number of kids would correspond to the different bins here so that's the that's the distribution of human Heights so for example you might say let's say you are you know 4 foot of 5 inches tall you might say oh boy that makes me really weird I must be you know there must be so few people who are my height ok this curve tells you how many people are less tall than you are and more tall than you are all you have to do is work out the area under this curve so the number of people who are less tall than you are if you're 4 foot 5 inches tall the number of people less tall than you are is the number of people in this in this tale here and the number of people taller than you is the total number is the total area above you and so when so for example this actually says the 95 percent range corresponds to four foot five to five feet five four foot five point six inches so what that's saying is 95 percent of people 95 percent of girls age 12 are between four foot five point six inches and five foot five point three inches tall okay and you can read that off from this distribution that's telling you the area ninety-five percent of the area 95% of the if you pick a pick a kid at random then 95 percent of the time they will be between the site and the site and about five percent of the time they'll either be shorter than that or taller than that okay so you might you might ask I mean not all not all things are distributed like this so for example I know oh yeah we have a plot here the weight distribution human weights have a different distribution they actually have a thing that's called the log normal distribution roughly so that means that there are there's a there's a tail here where there are people who are larger and heavier and there are more of those than there are people who are lighter and so it's a slightly different set up and if you look at different kinds of things these distributions you get different kinds of distributions so for example if we look at oh I don't know if we look in the stock market at the prices of stocks their prices bounced around owner let's pick a company let's see um how about Apple see what's been happening with them um so that's their poor Apple um that's their stock price and this is showing the distribution this is showing what they're the middle is their average stock price and this is showing how their stock price differs what what the chance is that you will find us a price if you look at different days or different hours of the day that is 10% higher 19% lower and so on and so this some it's again that this distribution is roughly for stocks very roughly also a normal distribution although stocks tend to have tails and there all sorts of terrible things that happen so for example the the distribution might say what gosh you can go down to have there's a certain probability to have a negative stock price but actually there can't be a negative stock price the company wouldn't be in business if there was a negative stock price so that means it can't be exactly that distribution but so that's a that's a little bit of a micro introduction to a little bit of statistical stuff so one thing that happens like when people talk about medical tests and they say things like they talk about p-values and they talk about you know this test works X percent of the time and so on or this the value of this thing is such and such with a 90% confidence interval a 95% confidence interval just means that the distribution 95% of the time the values will lie between the VAT what what is if you say this this the value of this thing is between -2 and 4 with 95% confidence interval it's saying that 95% of the area of the statistical distribution lies between minus 2 and 4 now unfortunately because I think I might say because people who are you know racing to do frontline medicine and so on don't always know or learn as much math as they might sometimes that gets a little bit messed up and people end up quoting these kinds of things like these things called p-values they quote them and they say it's this value to this value based on some experimental data and they assume that it follows one of these normal distributions and actually it just doesn't um and so that that leads to some some things that are kind of hard to figure out and it's it's usually better to look at the actual distribution so for example if we look at some what's a good example let's see what would be an example of well for the for the old folk um let's see say okay this is this is more for the for the parent crowd if you if you measure that's as cholesterol measure cholesterol in a male age 40 again you get one of these distributions this is telling you what the chances are this says the most likely um okay so this is saying ninety-five percent of males age forty if you measure that LDL cholesterol level it will lie between 65 and two hundred so and this one Sigma means 68 percent lie between 92 and hundred and sixty one of these units so there's another one of these distributions and a lot of the time people will quote oh you have a normal cholesterol level okay what does that actually mean well it often means that you lie within the 95% confidence interval sometimes it means you lie within the 68% the one Sigma confidence level and so on anyway that was a really micro introduction to some things and statistics side there's statistics is a big subject and I'm really not doing it justice here but that was just a little sort of micro micro discussion there all right let me go back to our stream here if I can work this properly let's see um all right okay so there's a question here about did humans evolved from monkeys okay so the first statement to make is there's this whole phenomenon of of evolution there's this whole tree of life that's existed on earth and maybe it started I don't know two and a half billion years ago maybe that the first living organisms existed and ever since then we've been and the even from the very beginning probably well probably not the very very first living organisms but fairly soon DNA this molecule that is essentially gives us the program that specifies how to build an organism pretty soon organisms started using DNA to specify the program that would be used to build them and like you know our DNA has six billion base pairs essentially six billion well six billion times two bits of information that specify how to build us and they specify how our cells should make should turn our food into proteins and and make make everything that's us okay so back in the you know when when when life first of all done Earth probably it didn't actually use DNA probably it used I don't know there's some theories that it used things in clay and clays and other other kinds of ways to sort of keep information about how it should be built but roughly what's happened is that over the course of time the program for building life for building organisms has gradually been refined and refined and refined and refined and refined and every time there's a new generation of organisms their programs are a little bit different than their parents programs and what happens there's this phenomenon called natural selection that was discovered in the about century and a half ago now and that by Charles Darwin um and with various input from other people but but um again don't get me started I'm talking about history of science I can give you a long long discussion about that but let's state it stick to the point so what is natural selection so there are each organism is specified by a program the children of the organism get programs that differ just a little bit from the the programs of their parents in the case of us humans and organisms that have sexual reproduction we always get a mixture of the programs from our mother and our Father and so like with humans we have 23 chromosomes and the each and each one of those there'll be stretches that are your father's DNA your mother's DNA and so on they're usually about I think it's five or six crossovers per chromosome so you'll get you know if you have siblings for example you'll be able to see oh that section of chromosome five we both got that from our father for example um and then it will cross over and you'll get it from the other parents and so on and because the program on the DNA is so jumbled up it's not the case it's not a well-organized program so to speak so you're like the the piece of the program that might encode how you know I color how one part of our eye color works maybe on a completely different chromosome from the part that encodes on another part of our eye color works and so it's not the case that just because you know you have sort of sections of DNA that come from one parent or another it doesn't mean that the traits are necessarily very correlated but any case the so different organisms gradually as as you you compared to your parents have slightly different DNA one reason for that is because of this phenomenon of the mixing of DNA from from sexual reproduction another feature is that when DNA is is replicated there are some errors in replication and those errors some of those errors are corrected by proofreading enzymes and things but some are not and so each of us probably has about 700 thousand unique base pairs unique places on our DNA that nobody else got that just completely unique to us okay so then what happens well over the course of time some of those unique mutations some of those mutations will turn out to be a really good idea so for example I don't know let's pick gosh let's not go for humans let's go for let's go for the classic thing that Darwin studied which was a type of bird that had different shapes of beak um and so and he looked at birds and the Galapagos Islands and the different islands there and on some islands the there was what was it some kinds of seeds I guess that existed where if you had a particular shape of beak you'd be more successful at cracking open that seed I may have that slightly wrong what the actual different functionalities of these birds is but it's roughly that and that certainly one one can imagine um so you know if you have a beak of a certain shape it's gonna be really good for cracking up in that seed okay if you have that shape of beak you'll be a more successful bird you will live longer you will have more children and so what then happens is that the this process of natural selection of selecting out birds that aren't so successful and selecting in birds that are successful as that continues through generations you'll tend to get evolution towards for example a bird that has a beak that's really optimized what it's trying to do now natural selection and evolution can be good and it can be kind of bad and so for example one case where it's bad is in things like viruses they they have natural selection and evolution as well well let me give you the example of bacteria so one bad example there is antibiotic resistant bacteria so bacteria are you know we have antibiotics antibiotics kill bacteria but so if you're an out if you're a bacterium and you're reproducing and you're in a place where they're a bunch of antibiotics and antibiotics kill you then you won't reproduce but if you sudden blood by some mutation manage to be a bacterium that survives the antibiotics then you'll be the winning bacterium and you'll reproduce and they'll be lost copies of you and so that's that's the thing that happens is that the the the the antibiotic will provide sort of work force that will select for bacteria that aren't killed by the antibiotic and so you'll evolve bacteria that are antibiotic resistant in that case okay so in the history of life on Earth we have evolved all kinds of different life forms that are successful in different places so for example there's there's life that lives in volcanoes there's life that lives we actually don't know how far down life lives inside the earth but there's life that lives deep deeper inside the earth we don't know quite how deep there's life that lives in very cold places very hot places places with this feature that feature and those different forms of life the ones that survive and that are naturally selected for are the ones that because of mutations ended up being successful in those particular environments well back in the time of Charles Darwin he actually thought that it was a sort of feature of natural selection that it would force one to have more and more complex organisms organisms as more and more elaborate features over the course of time that turns out not to be true it is not the case that more elaborate organisms are always more successful organisms I mean in the situation we're in right now it'd be really good if that was definitively true because we're we're significantly more complex organisms than this nasty virus that's attacking us you know for example we have it's not a great measure of this but we have six billion base pairs for a human the virus has twenty-nine thousand base pairs very tiny compared to us but the it so it so Darwin thought that that gradually life would get more and more complex and that the more successful forms of life will be more complex that doesn't seem to be the case you can have quite successful life forms that are quite simple but so so then one of the questions is so another another question sort of what evolves from what and you know we the best life-forms that have ever evolved and how does that how do you measure that and how do you think about that um the I think the specific question were here was do we evolved from monkeys the okay so first question is how would you tell so the way that people used to tell what evolved from what is to just look at the organisms and say gosh that you know humans look quite a lot like monkeys you know zebras look quite a lot like horses you know etc etc etc and they tried to arrange the tree of life just based on what organisms look like and they're about roughly 10 million species that are now and now a large fraction of which are things like beetles that exist in the Amazon rainforest things like that but anyway they're there many they're quite few mammalian species now and I think ooh how many are there maybe 10,000 maybe less than that mammalian species that are known the quite quite small number but in any case of all these different species that are known well we have so you can try and group them together you can transfer reconstruct this tree of life of what evolved from what by just looking at what looks similar to what and so you know one of the things that has been observed as they're fossils which show what what organisms that have existed in the past looked like and so we can try and piece together what was the kind of historical tree of life by piecing together well this fossil looks like this one and looks like this one we can try make a chain going all the way back and sometimes you know a lot of fossils we can make those kinds of chains there are some wonderful fossils like from the Cambrian period let's see a couple to three hundred million years ago I think that there are fossils from from well actually the Precambrian period where they're really weird-looking organisms that don't look anything like the organisms we have today there were kind of things that in a sense evolution tried out and they turned out not to be very good ideas or at least for whatever historical accidental reason they didn't make it so for example just like we have five fingers and a lot of organisms that have fivefold symmetry there were organisms at that time that have you know seven folds symmetry and all kinds of other things and for whatever reason the the five folders one out okay so so one way that we can tell kind of what evolved from what is just look at the shapes of the organisms and try and sort of piece it together another thing that's become possible more recently is to look at the DNA sequences the programs for these organisms at least the ones that exist today sometimes we can get some some DNA from from ancient organisms the sort of a hope we might get term you know there's good science fiction from getting dinosaur DNA and things like this that hasn't been successfully got yet but um but it might be possible but we can also just time the deuce from if if we know the DNA of this organism looked like this and we know it's a small change from the program of one organism to the program of the organism that was the results of a bunch of mutations from that organism we can kind of try and piece together this tree of life also by looking at the level of programs so people have tried to do that for humans I'm not a huge expert on all the things that have been found but it's clear that there were a bunch of species that existed couple of million years ago I think modern humans are maybe fifty thousand years old or something um but there were a bunch of species that existed and they had different characteristics some of them probably only went extinct I think there's one Homo florensis that I think may have existed until five hundred years ago there's a very kind of hobbit-sized human-like organism that and and there were also in the and earth all the and earth ours which were different species the Denisovans which were another species I think there's actually very recently the last couple of months there's a there's a discovery in Africa of probably a signs of yet another species and all these different species were pretty similar and they they they interbred and in fact for example for us like we have signatures of the Neanderthal species for example in us I think um blue eyes for example I think of one of the contribution Neanderthals to to modern humans and so on so we can kind of try and piece together what came from different species and how that worked um but so that's uh and it's it's always a question of when when there were a particular sort of innovations that were made in history like you know what species first had language what species first made art and though there's a that's a thing that's actually pretty actively discussed these days you know did the Neanderthals make art did they have what kind of language did they have it's it's often hard to tell you know you can look at the vocal tracts and things like that the structures inside the kind of the floats and things of in skeletons of these of these organisms and you can try and guess do they have that they have the kind of thing it would take to have you know to make different different sounds and so on I'm not sure that's a totally convincing way to do it if you're lucky you'll find a cave painting or something or an artifact it's it's even that's a hard business to because the artifacts that we find like like flint knapping one of those things that I suppose got taught in school back you know ten thousand years ago but it's kind of been lost since then it's like how do you take a flint piece of piece of rock you just keep knock-knock-knock on the flint and eventually you can make it sharp and that's a good thing if we're trying to make an arrowhead and so back in the day you know in ancient history of our species you know that was a that was a super useful skill is how to make um you know how to make sharp points out of Flint's um and uh but you know if you find a an arrowhead that was made with flint knapping it's pretty hard to tell that you know it's a it's a we okay we know how flint knapping works because kind of flint knapping sort of survived until modern times but if we found some rock that was you know seem to be chipped away in some weird shape to know that that was something that was done purposefully by some distant ancestor of ours is a tough thing it's a tough thing to know you know did they like like we know from archaeology and things like that um we know what um when we look at sort of ancient monuments we say what was this for and it's often hard to tell all right let's see um the AH gosh look at some of these [Music] whoo this is one I don't know the answer to I'm sorry I'll tell you the question but I don't know the answer it says why does an egg turn into rubber when put in vinegar well I know it doesn't actually turn into rubber um but it may turn into a rubbery substance I'm gonna I can guess the answer I the you know an egg has protein in it and proteins are very long long molecules and what and the kind of the consistency of these long molecules and that's how rubber works actually is is affected by by how how much how far these molecules are kept apart but I'm I'm sort of guessing here um and so let me let me not Tim I'm sorry I don't know the answer to that um all right there's a question here is there a maximum temperature okay that one I can answer um okay so let's talk about what temperature is I actually talked about that in the last one of these a little bit so when you have a bunch of atoms temperature is basically the energy with which those atoms are bouncing around roughly the speed would routes to the atoms are bouncing around so in air we take let's take water in steam the atoms are running around really pretty fast it's a gas you cool it down the atoms are running around a bit slower and they're kind of being stuck together a bit and that makes liquid water if you cool the atoms down even further they'll tend to just be they'll tend to not run around very much at all and they'll be kind of locked in place and that makes solid ice okay so temperature is it's actually the the the average kinetic energy the average energy of motion of motion of the atoms or molecules in a substance and or whatever is making up the substance um so that's so temperature is associated with these microscopic motions in in a material and the the so that means there's a there's a an absolute zero or a minimum temperature because there's a temperature at which you've taken all of that energy of motion out and the atoms are just staying completely still and so I think I mentioned last time the so that means most materials turn into solids when you take them down to absolute zero of temperature absolute zero is minus 273 point one six degrees centigrade so it gets very cold and for example you know as you so for example when you cool air down air there's mostly nitrogen and oxygen becomes our minus 170 degrees centigrade is that right I have to look that up I think that's the temperature at which air becomes liquid um and um I see so many seven kelvins I think so right no I'm forgetting sorry um I have to look that up I can type it into an alpha and look that up um but okay so there's a temperature at which air becomes liquid there's a temperature below that at which air becomes solid those those temperatures correspond to the molecules getting slower and slower and slower okay all right is there a maximum temperature okay so well when you heat stuff up the what's going to happen the molecules are going to go faster and faster and faster boy this is actually tricky this is this is graduate level physics sorry I it's some okay so what time you put more and more energy into these into these atoms well first of all as you put too much energy and the atoms will fall apart and it'll just be because when you the atoms are held together by a certain amount of force and when you when you try and when you put in too much temperature the atoms are sort of torn apart so what happens in fire and things like that it makes a plasma where the atoms are the electrons are torn out of the atoms okay but when you make things hot enough everything gets torn apart even atomic nuclei get torn apart when you make things even hotter even the the quarks and gluons inside protons and things get sort of torn apart um but so when everything is really really hot things get torn apart but these particles electrons whatever they are quarks whatever they can just keep going and you can just pump more and more and more energy into those particles so actually in the usual theory of physics there is not a maximum temperature you can just keep on pumping more and more and more energy into inter particles there used to be a theory that there was a maximum temperature and that came about ah let's see how to explain this okay basically the idea was we know about protons and neutrons and electrons but they're actually a whole zoo of other kinds of particles most of those particles are unstable they decay and millionths of a second or trillionth of a second or trillion trillionth of a second most in they're unstable but there's a whole giant zoo of other particles they have names like the Sigma hyper on the lambda hyper on the cascade hyper on the K on the PI on the F mez on the G Mazon as a whole giant zoo of these things but when I was a kid I was really into these kinds of particles and I used to know all about these things I am it was some I have a decent memory so I still remember you know the masses and properties of a bunch of these particles it's a little bit um they'd been measured vastly more accurately than they were known when I was a kid um but in case there's a whole zoo of these particles okay and it used to be thought that maybe as you increase the temperature of something instead of the temperature instead of the energy going into producing producing making particles go faster instead that energy would go into producing more kinds of particles and actually if you've heard of string theory it's one of the kind of mathematical theories that's thought about a bit in fundamental physics string theory the original version of string theory came out of a theory of particles in which there were just a whole zoo of more and more and more and more particles so it used to be thought at one time that there was a maximum possible temperature at which you would be producing new kinds of particles rather than the same kinds of particles going faster that theory turns out not to be correct it's an interesting question whether in my theory of physics whether there is ultimately a maximum temperature umm Baba what is the answer to that the answer is that there will be um let's see yes actually I okay let me answer to two different related questions here so one place where things got really hot was in the very early universe when the universe was was just started there was this Big Bang nobody knows why that happened but was a sort of giant explosion that started the universe and when the universe was very small and very young it was also very hot and as time has gone on the universe is cooled down it's cooled down it's cooled down at this point be sort of if you just go into space space is not at an absolute zero of temperature space is at about three degrees Kelvin three kelvins which is minus 270 degrees centigrade three degrees above absolute zero that's that that's the effective temperature of space and the reason it's not at Absolute Zero is that it still has sort of the the remnants of the heat that came from the Big Bang in the at the beginning of the universe is still is still there in the in the in essentially the the well photons the microwave the the radio energy in the universe that still sort of a relic of of the Big Bang although by now because the universe has expanded a lot it's really cooled down so it's only three degrees above absolute zero but in the in the very early universe the universe was really really really hot in fact probably in some sense infinitely hot now you're going to ask me to do some kind of advanced physics in real time of physic theory that is is not yet fully developed but I think in my theory of fundamental physics there isn't and there is a maximum temperature and I think that that maximum temperature let me think about this for a second yes yes there will be a maximum temperature and it will be let's see the reason there's a maximum temperature I mean the maximum temperature will be unbelievably huge compared to anything that we can observe in the universe with the possible exception that at the edge of a black hole one might see some phenomenon associated with that I have to think about that that is a good question thank you that that's my homework I think is to figure out in my theory of how space-time works how maximum temperature works so I somebody somebody who's paying attention to live stream from my team take a note of that that's my that's my homework um let's see let's see um okay here's another question is there a maximum location accuracy for a GPS system um the okay okay first of all let me four people let me explain again a little bit about how GPS works GPS the global positioning system that's a American network of satellites and there's actually a European one and there's a Russian one I think that but the the GPS is the is the most commonly used one okay so one big question is how do you know where you are on the earth that was a big issue when people were you know particularly on the oceans you know if you're trying to figure out where am I and I'm you know near where I near my house or something it's like oh I know that that's you know I recognize that landmark but on the ocean there aren't any landmarks to recognize so it's much harder to tell where you are and so what time so the main way that people used to tell where they were is by navigating by the Stars and the reason that that will tell you where you are is the stars as the Earth rotates the the stars will be at particular the Stars stay at a fixed location and as the Earth turns you can you can basically see where the stars are now it turns out that if you are to know your latitude that is how far you are from the north pole or from the equator the how far north you are basically that's something you can figure out just from angles of stars as the Earth turns you know where the north star is which is roughly aligned with the North Pole and you can you can figure out by seeing what angle the north north the Polaris the the north pole star is at or a corresponding thing in the southern hemisphere you can figure out what latitude you're at it was a big problem for many years to figure out the longitude because to work out longitude you have to know what time it is you have to know to know you know this star is overhead okay great but what time does that correspond to and so is a big issue of hiking and accurate enough clock to be able to know what time it is and so there was this big thing to find to create a marine chronometer and the big issue is clocks used to be well they were made with pendulums which swung back and forth well they're made with them with escapement I guess these these sort of Springs that that um but essentially it's little pendulum type things and the problem is if you're in a ship and it's on an ocean and you're being thrown around all over the place it's really hard to get the clock to keep accurate time and so people invented these whole elaborate systems to kind of keep the clock from being bounced around too much in the ocean and keep it keeping accurate time and eventually that problem was solved but that was a that was sort of so that was you know the earlier nerely system for navigation ok so then when when airplanes started flying it was there was a need for navigation for planes for planes as a different scheme that was used for planes there are radio navigation beacons in the US they usually called vortex VHF omnidirectional radio beacons and the way they work they're kind of clever actually you can see them sometimes they're there you can see them they're often near airports sometimes they're sort of on hillsides and things they're kind of these things that have a they usually have from kind of this kind of shape um they they're radio beacons and they produce a so if you are flying a plane you back in the before there was GPS you would try and get a fix on a radio beacon and you would say this radio beacon is at this angle to me and actually these radio beacons have a clever feature that they actually had two different radio frequencies and as you go around a circle around that radio beacon the relative these two relative frequencies would change as you go around the circle just by the construction of the radio antenna in the radio beacon and so that allowed you to tell what angle were you at relative to that radio beacon and that was a that was a method of navigation that was used in fact still the airplanes might think airplanes can go anywhere in the sky but actually they tend to follow these these particular sort of Airways which typically are flying from one radio beacon to the next radio beacon in straight lines if that eventually is going to get figured out how to let planes use GPS and take arbitrary paths and that will save some fuel and other good things but Tim but any case so that was a another scheme and then GPS was invented and GPS is a different idea GPS is using satellites and okay so how does GPS work basically the the satellites so first fact is once you put a satellite in orbit you can compute just with math really pretty accurately where that satellite will be at every moment and so you know if you type into off now for the name of some satellite or the International Space Station or something it will predict for you where the International Space Station is going to be three days from now and it can do that quite accurately because the the physics of orbits and things is such that you just work out these equations differential equations and they tell you sometimes of kind of complicated but they tell you just by math where the thing will be now the math all breaks down if you have if your think fires a little rocket thruster then you can make it change its orbit but assuming it fired no thrusters you can assume it fired no thrusters assuming it didn't hit the upper atmosphere hit the top of the atmosphere and start getting slowed down by that assuming no those weird things happened you can just by physics and math you can predict where the thing will be to pretty really very high accuracy okay so that there are these GPS satellites and they're orbiting the Earth and they you can predict where any one of those satellites will be okay so then if you want to know where you are you have to say well how far away am i from those satellites so if you want to work out if you say where am i if I'm somewhere on a line and I know I'm this distance from one end of the line then I know where I on that line and if I if I want to work out in in if I if I knew in two-dimensions if I if I knew I was somewhere on on a flat plane and I know I'm this distance from one I know in this distance for let's say I know I'm ten miles away well that's be more realistic let's say I'm a thousand miles away from this point on the plane well what points are a thousand miles away from this point the answer is it's a circle the the set of points that are a thousand miles away or is is a circle with a radius of a thousand miles around that point okay so let's say I now know I'm a thousand miles away from that point and I'm 800 miles away from this other point over here okay so where am i if I know that I'm a thousand miles away from this I know I'm somewhere on the circle around that point I'm eight hundred miles away from this I know I'm somewhere on the circle eight hundred was radius eight hundred miles around that point okay so I've got these two circles and that means that with with these two circles if I want to know if I know I'm a thousand miles away from this one 801 I can work out where I can be the answer is I must be on the circle around this point and the circle around this point and so my I must be on the intersection of those two circles so if you have two circles generically they will intersect in two points okay so just from two from knowing how far away you are from two things you can work out at least with between two points you can say where am I relative to those circles well if you want to break the ambiguity of those two points you need a third fix you know third you know the distance to a third point and given those three points you can work out where am i exactly so that's kind of the idea that GPS uses it tries to work out how far away are you from three satellites usually it's five satellites or more that actually get used in a typical GPS receiver and the somebody's asking how far away am i from the GPS satellites all right let me let me let me ask off alpha here class of satellites it'll give me the if we type this in here I'll just show you [Music] hold on we just bring this up okay yes and so of malphur this is showing me apparently there are 39 GPS satellites and the okay so this is telling me the all kinds of details of GPS satellites so it's telling me that the transmission delay from me to the GPS satellites 186 milliseconds round-trip to that GPS satellite so if I pick one of these GPS satellites I'm sure I can get a picture somewhere here of where all the GPS satellites are but um let's let's pick Navstar - eh - twelve let's see whether it knows where that satellite is oh it's probably computing it busily here okay that satellite is currently over the southern ocean southern Indian Ocean it is thirty thousand miles altitude the transmission delay is 224 milliseconds the satellite is going that term that's actually interesting instantaneous oh that's because it's not in low-earth orbit okay this confused me because a satellite in low Earth orbit is always going at 17,000 miles an hour but this is not so low to the earth yeah it says it's medium Earth orbit okay so this is telling me that satellite was launched 1993 okay so it's telling me the distance to that satellite okay you really want me to work it out I can work out the actual distance to that satellite um but this is telling me the round-trip time to the satellite from where I am right now but I could work out and see what is this called now star 2a - 12 all right let's try typing that in Navstar 2a - 12 see if this works he's looking very dangerously here okay let's try typing under whether we have a let me just work out what says I need to know I'm actually probably if I just say where is it where is it where is it I want the out the position um where is it position there we go okay all right this is really living dangerously but let's do it okay so this is going to tell me the position of that satellite okay so that tells me right now that satellite is at latitude - 38 degrees that means it's in the southern hemisphere longitude 81 degrees that means it's somewhere over on the east so to speak and this is the altitude and meters of that satellite okay so let's say where am i I'm in Concord Massachusetts so let's at least get um I'm not going to give you my precise GPS coordinate but let's just use the center of Concord Massachusetts so let's say the Geo position of the center of Concord Massachusetts and that's going to give that now I can work out at least on the surface of the earth it's easy for me to work out the Geo distance from that Geo position to the Geo position that the satellite was at when I asked the question because the satellite remember is moving at 8,500 miles an hour so it's actually going to be in a different position by now okay so the satellite is is some about ten thousand miles from where I am right now and we could work out um I think that might not be the slant position if I want to get that I can say that I am at I think that gives us let me see that gives us see this is where things get kind of complicated um okay this is that number there is probably the distance to the center of the earth for the position of the satellite and the sea 1 times 10 to the 7 yes it probably is okay so what I'm gonna do here if I really want to know how far away that satellite is I'm really gonna let's really get this right let's do this and then in here I want to say radius of Earth I'd sure I want to whoops I'm gonna just use this quantity um okay this is this is where how folks like me try and actually work stuff out um all right let's see that was the distance there okay let's put that in this is so this is going to give my position on the earth and now I should be able to say geo distance from my position on the earth to the position that satellite had at least when I asked for that position which was a few minutes ago um see here and okay already works it out correctly okay it already got that right it was already calculating it based on me being on the surface of the earth so there's the answer um okay so the question that was actually asked here I think was what determines the accuracy of GPS okay boy you guys are complicated questions all right okay the GPS satellites so one question is when did your GPS receiver has to work out how far it is to each of those GPS satellites the way it does it is actually a pretty clever the way it does it is the GPS satellite is producing a sequence of zeros and ones it's a very particular sequence it is a what is it called huh shift register sequence yeah um let's say that might not be that might be too long let's do um okay the satellite is producing a thing called a shift register sequence and it actually is producing one of these that's millions of bits long and one feature of this sequence it has a very interesting mathematical property if I were to look at some block of digits here that block of digits only occurs once in the sequence up to a certain length so it's saying if if I see one zero zero one zero one one I know where in this sequence I am so just by by seeing the block of digits the piece of the the piece of radio pulse that I see from the GPS satellite I know we're in the sequence of the GPS satellite I am okay so every GPS satellite is sending out a shift register sequence and those sequences repeat let's see the longer ones repeat every few months I think the shorter ones repeat every day or two maybe but within that time interval you can tell exactly because there's a it's no one it's it's every GPS receiver knows when the GPS satellites are going to generate a a particular part of that sequence so they see oh 1 0 0 1 0 0 1 1 1 that means we are at this particular part of the sequence that means we are this particular nanosecond in time relative to when the sequence started because the sequence is repeating that each bit is being delivered at um takes let's see around a few nanoseconds I think corresponds to each bit now actually I mentioned earlier the speed of light is roughly 1 foot per nanosecond so if you can tell how long it took light to get to you from the GPS satellite to within 1 nanosecond you can tell where you are - within an 1 nanosecond by knowing if you know if you can predict the orbit of the GPS satellite so you know where the GPS satellite is you know how far away you were from 3 GPS satellites you know that - within a nanosecond - within a foot then you can triangulate to work out your position within a foot so in principle GPS can it's really limited by how how fast these bits are being transmitted and that's limited by the radio frequency that's being used and and so on but there are some other limitations there are in fact for a long time there was a thing called P mode GPS the precision mode of GPS and the precision mode of GPS was actually blocked for a long time because it was used for military purposes to be able to have precise homing for things and the civilian GPS was accurate only - no it was 20 30 40 feet something like that um the actually during during the Gulf War was the first time that P mode GPS was unblocked um and the butt then a few years ago the US Defense Department decided to open up precision GPS and so everybody can use it and that term and that allows GPS receivers to to know positions to within a few feet and there's a thing called differential GPS which tries to use the tries to kind of use extra information from looking at UM looking at differences between satellite signals and things to work it out even more accurately than that so that was a that was a LAN so you guys ask complicated questions but I think that it was a fairly the it was a fairly fairly decent answer to the is there a maximum location accuracy the answer is I believe it's ultimately limited by the frequency of of this of these signals being sent it is a good question whether it is limited by the accuracy with which we can predict the orbits of GPS satellites and I'm pretty sure it's not pretty sure that we can predict the at the the satellite positions to really very high accuracy there um okay let me see you just go back here hold on one second I'm I'm confusing myself ah there we go okay we keep going here I just have to rearrange my screen so I can see what questions are asking um okay is it true that all objects in Cuban living things emit radio waves oh that's interesting okay okay what are radio waves radio waves are otherwise known as electromagnetic waves they are the result of whenever you have a charge a piece of an electrically charged thing like an electron electron is the smallest unit of electric charge and electric currents and wires and things are made essentially from the motion of electrons moving electric charges through wires makes electric currents whenever you movement whenever you accelerate an electric charge it will produce a radio wave it will produce an electromagnetic wave now it's a very tricky thing because there are many ways to accelerate a charge so for example one thing you can do is by using voltage voltage is kind of the force with which you're pushing electrons through a wire for example and and current is the number of electrons that are flowing through the wire so as you change the voltage you you you reverse the voltage you keep reversing the voltage you're pushing the electrons like back and forth inside an antenna and that will cause the electrons to accelerate as they go the accelerating one way then slow down they turn around it's alright the other way every time they accelerate they produce electromagnetic radiation and so any time there's an accelerating charge there's electromagnetic radiation um the okay for physicists okay so it's a slightly fancier story okay math fact it's actually X dot X triple dot rather than X double dot squared is the is the actual rate of radiation it just produces some weird effects that let's not discuss here um but any case in a first approximation the whenever there's an accelerating electric charge it produces electromagnetic radiation if it is being accelerated and wiggled around at a frequency of let's say a billion sort of Wiggles per second it will produce microwaves radio waves if it's if it's wiggle the trillion times a second it will produce visible light if it's wiggled even much much faster than that it will produce x-rays um but in general anytime you sort of accelerate a charge it will produce actually that radiation okay the question is does that mean that there is electromagnetic radiation produced by produced in for example in living organisms usually the answer I think mmm it's a good question I mean there's certainly a you know an electric eel certainly succeeds in producing an electric current and it succeeds in producing electric radiation in kind of the okay so sort of tricky fact is that there are electrons that are being whizzed around atoms those don't normally produce terminal radiation if you good question do is there anything in us that in the normal state of affairs will produce so much more radiation oh yeah yeah yeah yeah yeah I'm sorry I'm not thinking straight yes okay so whenever so the way our muscles work okay the way our nerves work they're sending electrical signals so a nerve like we'll have a nerve fiber that will go I don't know up you know some part of way up our arm then there's a repeater and then there's another nerve fiber it goes our brain it goes to our spinal cord then goes to our brain and so on those are like little wires and they are transmitting electric signals and those electric signals usually they're in little pulses maybe a thousand times a second and the rate of so for example when you when you touch something the touch sensors in your fingers are producing our little nerve endings that produce that use electrochemistry they use kind of chemical processes to produce an electric electricity that then flows through the nerves and then our brains detect that and inside our brains there's there's lots of nerves that are sending electrical signals all around and that's kind of what our processes of thinking consist is those electric signals and all the different interactions in the hundred billion or so neurons nerve cells in our brains so whenever we whenever we sort of you know the way our muscles work is we have nerves that go from our brains and they go on our muscles and when an electric signal comes from our brain through the nerve when that electric signal is is applied to the muscle there's this protein called actin which is a long filament type protein and when that when there's a little electric signal applied to that it will tense up and that's what causes our muscles to tense up and so what happens is that and that electric signal so every time we are moving out you know as I move my arms around whatever you know what's happening is an electric signal is going from my brain and it's causing some muscle the good the electric signal goes to the actin filaments in my muscle which is then tensed up and then causes my my arm to move so that electrical signal you can absolutely detect that you can measure surgical M eg much that stand for the in any case you can you can measure electrical signals from from the nerves when you tense up muscles and things like this in fact in our brains you can measure the electrical signals in our brains that's what EEG is doing electroencephalograph alog Rafi and we can you know in our brains normally there's there's these various rhythms the neurons in our brains tend to tend to sort of operate in a somewhat collective way and so there's a rhythm around nine point eight cycles per second that is a big the Alpha rhythm of the brain which is sort of a collective collective electrical effect of our neurons which we can detect by putting a little electrons on our electrodes on our on our head um and so--that's and by the way there are other electrical signals in humans like the heart for example is a as a muscle that's you know pumping blood and so on and it is the the when it contracts and so on sort of the signal to tell it to contract comes from nerves that come from the brain and they and you can you can you can measure that you can also measure the electrical activity associated with the actual actually you're mostly measuring in EKGs you're mostly measuring the actual muscle the effects of the article effects of the actual heart muscle I think and that again is another place where us humans produce electromagnetic effects there they're very I mean you have to stick electrodes on yourself normally to be able to detect that there are very sensitive I mean there is there are electrical signals that will be that will be traveling through space you know through through from us humans and for example the magnetic analog of EEG you can effectively detect that from a distance although you have to be in a very very place with very little electromagnetic interference um okay I think we should we should wrap up soon here but um let's see other questions let's see okay this tation about the nature of scientific thinking that'd be fun okay um something to try alright um there's a question here okay I'm gonna maybe two more I'll answer one [Music] let's see [Music] somebody's asking what is plasma and one is fairly easy let me do that one and I'll do one more um the okay plasma so normally there are three famous states of matter phases of matter solids liquids gases there actually are other phases of matter that people don't talk about quite so much that that for example gels I mean for example we are not obviously either solid liquid or liquid with kind of mushy stuff and that's kind of more like a gel and that's a typical thing you get with long complicated molecules that you don't get with them with just sort of single single atom kinds of materials and things but okay plasmas are something different plasmas are what you get when you heat up any material normally the atoms have protons in the nucleus and so an atom depending on its atomic number depending on its atomic position in the in the periodic table it will have some number of protons so hydrogen has one proton helium has two protons and so on in the normal state of that the atoms the number of electrons is the same as the number of protons in the atom so hydrogen ordinary hydrogen has one electron one proton ordinary helium two electrons two protons but you can do what's called ionize these substances by if you heat them up if you pump enough energy into them you'll pull the electrons away from the new place you'll you'll be able to overcome the electrical forces that hold the electrons close to the nucleus and you'll be able to tear them away and then you'll have a so-called ionized atom which doesn't have its full complement or electrons and so that ionized atom is what you have in a plasma that's what you have in fire for example it's what you have in the surface of the Sun these are these are these are plasmas that have that don't have that have electrically charged things in them not ordinary neutral atoms you know when you have chemical compounds the atoms also become ions but the I cancel themselves out so the whole molecule can be electrically neutral but the individual pieces like in a sodium chloride table in ordinary salt that's what happens it's na + CL - that's because it's it's acting like one of those things has an electron missing one of those things has an extra electron and that produces this force of attraction that kind of holds the sodium chloride together but when you heat things up you'll get atoms that aren't electrically neutral that have their electrons removed and they have all kinds of weird properties they have all kinds of properties about um the way that they stop electromagnetic radiation they stop radio waves things like that kind of the most the most famous plasma in a sense in the universe is the plasma that used to be throughout the universe back when the universe was very young shortly after the Big Bang the whole universe was hot enough that was all a plasma and actually it stopped being a plasma a hundred thousand years after the beginning of the universe and so back at the very very early parts of the universe it was so hot that there weren't just ordinary hydrogen atoms there were separate electrons and protons running around and it was essentially a plasma of hydrogen gas and so that meant that it was so one of the consequences of that it was it was kind of glowing like fire glows and it was also you couldn't see through it like you can't see through a piece of fire so the that was so hundred thousand years off at the beginning of the universe the universe was all a non see-through glowing plasma so question is what happened to that plasma okay so this is a okay let me so here's a question if you look you know you know that it takes light a certain time to come from let's say a different star or different galaxy like takes light eight minutes to get from the Sun it take like light it takes light for years to get from the nearest other star Alpha Centauri it'll take two Oh like you know some other galaxy it might take a million years for light to get to us so as we look out in the universe we see light that started its journey towards us a really long time ago and so one thing you might ask is if you look out your notes and there's no galaxies in the way and just look out to the edge of the universe what do you actually see well what you see is light that came to us from essentially what you're seeing is that plasma that existed a hundred thousand years after the beginning of the universe because and it's a little bit the geometry is a little bit complicated but essentially the light that you see in any direction comes from the comes from the the kind of the the the reduced the the the kind of cooled down longer wavelength version of light that started from the plasma that existed a hundred thousand years after the universe began so in every direction that we look out in in the universe we see the kind of this thing that's called the Cosmic Microwave Background it started off as visible light but because of the expansion of the universe it's now turned into microwave radio waves and we see in every direction in the universe we will see that that that that radio signal and actually what happened that was originally discovered in 1964 I think by a couple of people at Bell Labs the company that operated the u.s. phone system the precursor AT&T the they they were using satellites and things like this early communication satellites and they wanted to get they were they were measuring the radio emissions and they wanted to get really sort of low noise radio emissions from their satellites they were measuring you know how much you know could they how how well could they sort of listen to the radio signals from the satellites and they were very frustrated but there was a background there was a radio noise at very low intensity radio noise at this very specific thing that corresponds to a temperature of about three degrees above absolute zero and that they were sort of very frustrated they just couldn't get rid of that radio noise and eventually it was realized that actually that radio noise is just a feature of the universe it comes from it is the sign of the of the it's the the sort of signature of the Big Bang and it's what we what we detect from that so that was some no I'm forgetting what question I'm even answering here gosh that was terrible oh I was talking about plasmas yeah I was saying that that's the plasma that term the plasma from the early universe the sort of last vestige of that plasma is the Cosmic Microwave Background okay so last question I'm going to answer here um the what's the likelihood that there's another universe exactly like ours out there that's a very interesting question it's it hard for us to know um let me tell you something that really has surprised me so let's imagine that we know the exact laws of physics the exact rules that determine how our universe works okay so we know these exact rules we can you know then we've solved the sort of fundamental theory of physics we know the rules for the universe we can say this is how our universe works anything we want to work out about a universe if we had a big enough computer and big enough might mean a computer bigger than our universe which means we're out of luck because we don't you know the best we can do is use a computer that's in our universe so we wouldn't actually be able to work out what our universe will do but at least in principle we'll be able to work out what our universe would do if we had a big enough computer even though we couldn't actually have that the computer that big but so if we know the rule for the universe then we can in principle work out everything about our universe so then the immediate question is okay we know the rule for the universe and actually I'm I'm galloping along getting close to being able to find that rule and the okay so we know that let's say we know the rule can we you know hold it in our hands we put it up on our computer screen here's the rule you know it's some particular mathematical like thing it's the rule for our universe so the next question we'd ask is okay why did we get this rule why will we assign why was our universe assigned this rule I mean there might be an infinite number of other possible rules why did we get this rule and not another rule okay and I thought that question will be unanswerable that is I thought that there will be no scientific answer to that question um but I just had this sneaking suspicion that there might be a scientific answer to that question okay and his roughly how it works and it turns out it looks like there is an answer um the here's the thing if you are an observer a creature an organism a brain whatever in the universe you are observing that universe but the rules the laws of physics that are governing how your brain works are the exact same laws as the laws that are governing how the universe that you're you're observing works so there's this kind of funny interplay between you as the observer of the universe being governed by certain rules and the universe that you're observing being governed by the same rules and so I just had this sneaking suspicion that it might be the case that essentially every universe every possible set of rules to an observer who operates according to the same set of rules will in a sense look the same so if you were outside the universe and you didn't operate according to the rules of the universe you would say oh this universe works such in such a way but if you are embedded in that universe you might say of two different universes two universes different rules you might say oh those universes work differently I can see that from the outside but if you're embedded inside that universe operating yourself according to the rules of that universe you don't get to see that you can't tell and actually it's it's for physics types it's it's similar to the way relativistic invariance works and the the independence of I can talk about seventy some other time um but term in any case so the surprise thing that I figured out about a month ago actually is some that it really looks like we're it there's only one in other words all these different possible rules that you might use to describe the universe are all to an observer within that universe all in a sense looks the same so it turns out that there's a bunch of footnotes to this as a bunch more complexity to exactly how this works but in some sense every universe that works according to rules that are even vaguely like the rules of our universe is equivalent to an observer in that universe to the exact same universe so to my surprise I think there's a scientific argument that says there's only one universe now to say there's an exact copy of our universe yes we can't tell that we can't tell the difference between those things but to say oh there are different universes and they operate according to slightly different rules I think that's not that won't work um now there is a footnote to that and it's and for another and perhaps after I have a chance to describe my whole big physics theory but but the footnote has to do with what kinds of computations can happen in the universe and whether we can do hyper computations and other such things I think that's a topic for another time and be really happy to talk about it and you guys are asking such fun questions I'm really you know I hope you find it interesting and I hope well we're all stuck um with them that nasty twenty nine thousand base pair sequence attacking us and trying to replicate itself we can at least have some fun talking about science so I'm I'd be happy to do another one of these um I can talk about science I could talk about technology and how some technology could try and answer questions about how various kinds of Technology work and so on I will be great to get some feedback from folks who've been here to tell us what things I was talking about that were just boring incomprehensible you know kind of what people were interested in and so on um now on my effort to always do something different that I've never done before I'm actually going to do another session on Thursday and it's going to be about math and I'm going to try and talk about fun with math and that will be aimed at I think like let's say ten and up folk I hope I have things to say that will be a little bit surprising even to people who are who know lots about math but I I think I'm I'm going to I'm gonna aim it I hope at um if you if you kind of understand arithmetic decently well you should be able to understand what I'm talking about and the UM it's some so I will be doing that on Thursday and I will try to try to explain some fun things about math and so um I hope you hope you enjoyed this I had a good time and maybe I'll see you all again I'll probably do another one of these probably next week and as I say math on Thursday okay thanks for joining us and see you another time
