Science & Technology Q&A for Kids (and others) [Part 133]

hi everyone welcome to another episode of Science and Technology q a for kids and others and I see a variety of questions that have accumulated here so let me try and uh take a few of these um there's a question here from Jimmy could we be inside a black hole can biological life survive inside a black hole well so first of all what is a black hole a black hole is something where there's so much gravity that even light can't escape from that area so what happens is when you have the Earth for exa

mple if you shoot a rocket up from the earth if you don't shoot it up fast enough the gravity of the earth will just pull it back and it will crash down on the Earth again if you shoot it faster than 25 000 miles an hour up from the earth it will escape the gravity of the earth it goes fast enough it has enough momentum that it can break away from the the gravity of the earth and just go off into space every different kind of object depending on its mass and how big it is will have a different e

scape velocity so for example the sun has an escape velocity of maybe a hundred thousand miles an hour our galaxy has an escape velocity of I think about a million miles an hour and so on but what happens is if there's enough mass and a small enough volume the small enough sized object the escape Velocity eventually becomes higher than the speed of light so that means because it seems to be a fact about physics there are some footnotes to this that come out of our our new models of physics but b

asically nothing gets to go faster than the speed of light and so if you have something where the the escape velocity is the speed of light or larger that means that even light even something which goes as fast as light can't escape so that means that there's this region of space where anything that tries to get out will be sort of pulled back in and can never Escape so in particular in a black hole there's this thing called The Event Horizon which is this this place in space where it turns out

that any light that originates inside the Event Horizon will always get pulled back inside and will never escape and everything outside the amount of horizon can escape and uh the it was very confusing to people when black holes were first uh kind of thought about the the equations that describe the structure of space-time the equations of general relativity that were invented in 1915 by by Albert Einstein um those equations kind of describe how mass and energy deform the structure of space-time

and that deformation of the structure of space-time is what leads to gravity as soon as you kind of change the shape of space you change kind of the the the shortest the ways that things go on shortest paths by deforming how those shortest paths go it's deflecting how sort of objects move through space and that's kind of has the effect of uh is is the is the thing that leads to the force of gravity but in any case those the equations of general relativity implied that you could get these funny

singularities these funny sort of one over zero type things going on and people were very confused actually Robert Oppenheimer was one of the people involved with this in the 1930s 19 to 19 early 1940s um trying to sort of unravel what was really going on in these cases where there were these kind of one over zero Infinity type singularities in in the sort of structure implied for space-time and people at first thought that well you have this event horizon that as you if you were in a spacecraft

that was kind of Falling Towards a black hole you went through the eventual eyes and people sort of thought oh something terrible is going to happen at the Event Horizon turns out that's not true turns out you wouldn't even notice going through the Event Horizon the only thing that would happen is that the signals you send out you wouldn't know you you'd be waiting forever and ever for as you you get close to the event horizon a signal you send out is kind of pulled back a bit so it takes longe

r to get out than you might expect but eventually you might send some signal out to some other spacecraft or planet or whatever and eventually somebody might reply and you get get the signal back what happens is you go inside the Event Horizon is that the time for your signal to reach its destination becomes infinite you'd never get an answer back you wouldn't get you wouldn't your signal would never would never be able to reach the sort of the uh the the sender but but you wouldn't notice as yo

u go through the Event Horizon you wouldn't really notice anything bad happened you'd it would only be if you waited for signals to come that you'd sent out to come back they wouldn't ever come back so this question was what's it like to be inside a black hole well as you pass through the Event Horizon nothing much happens it's only kind of in the Long View of history that you would realize you were now kind of nothing you said could ever be heard outside so to speak but then as you sort of uh y

ou're sort of falling into this black hole now there's a bit of an embarrassing feature about black holes which is the mathematical theory that describes black holes kind of tells you how event Horizons work and things like that they're not really tell you much about what happens inside the Event Horizon in fact as far as the mathematics is concerned it doesn't really matter if there's anything inside the Event Horizon well pretty much anything inside the Event Horizon in reality a black hole is

formed when a massive star collapses and is pulled by the force of its own gravity into this tiny area and that's produces enough kind of mass and a small enough volume that you get larger than speed of light escape velocity and you get a black hole but so inside the Event Horizon of a black hole you would normally you would think in physically that what would happen is what the way it will be formed is that there's a collapsed star and there's all kinds of stuff from the collapsed star inside

the Event Horizon but because you can't find out what's happening inside the Event Horizon from outside the Event Horizon because no information about what's inside can get out you don't really know there's a collapsed star inside you might know from the past that oh yeah we saw the star it was collapsing now now that must be what's inside this event horizon but you can't know that from just seeing the Event Horizon of the black hole so that's that's sort of a uh so in the mathematics of what go

es on the structure of the Event Horizon all those kinds of things is quite independent of what's inside it could be this this you know there could be this whole civilization that's going on inside there could be they could have a whole you know it could be the thing that's this shape it's that shape it doesn't matter outside it all just looks like this kind of sphere of Event Horizon well it's even more bizarre than that because in the usual mathematical Theory there can just be vacuum inside t

he Event Horizon with one exception there has to be some kind of puncture in the structure of space-time there has to be a single point at which the structure of space-time has changed a single point at which for example the curvature of space-time becomes infinite now in our models of space-time things are not nearly as pathological as that and our models there's there's this kind of network that represents the structure of space and space is ultimately composed of these just individual points

related by The Edge business Network and so when we say that what happens when you make an event horizon for example is certain features of that Network are actually the certain features of the way that Network progresses through time uh work in a certain way and the what happens at the center of the black hole where you have this singularity in space time um and and sort of the the traditional view of space as a continuous thing the only way you can deal with that is to say there's a hole punch

ed out of space-time where there just is no space time there it's just a it's just an infinitesimally small hole but there's a hole so in our models it doesn't quite work that way you could have something much more structure you can actually see the structure of the network is different as you get in towards the singularity at the center of the black hole but one feature of that Singularity is for the simplest kind of black hole at least is that time stops so in our model of physics what's happe

ning time is this sort of progressive computation of the state of the universe the next state of the universe the next state of the universe always being computed from the previous state and in in sort of structurally what's happening is you have this giant graph and at every step all the different pieces of this graph are being Rewritten and so sort of the progress of time is the progressive rewriting of this graph and another thing in the universe is a feature of this graph every electron ever

y whatever they're all just features of this of the structure of this graph and so time is this progression of sort of the rewriting of this graph okay so what happens at these singularities in the simplest kind of black hole non-rotating black hole in the simplest kind of black hole what happens is time just stops so what does that mean it means that at the center of the black hole there are pieces of the network where no more rewrite Supply there isn't another rewrite that gets done it just st

ops so it's um uh it's if if you were sort of part of that it's kind of like your mind just stops running your brain stops running you you won't it's not like oh I'm realizing I just froze you don't realize anything there's no thinking going on there's no there's no mind there's no experience happening it just time just stops and in the uh so what happens in the sort of traditional view of things is the spacecraft that fell through the Event Horizon eventually is led into that Singularity at the

center of the black hole at which point time stops and it it always after a limited time the spacecraft always ends up at that singular point at the center of the black hole in our models it's a bit more explicit what happens um but the end result is uh at some moment you the time is Frozen nothing ever happens anymore so you don't know what happened because time is Frozen for you as it's frozen for everything else so in this question of of can you sort of lead a happy life inside a black hole

well up to a point eventually you die so to speak eventually there's no more kind of there's no more experience that happens um that that's the that's the case for the simplest kind of black hole with the other kind of black hole you get a more bizarre thing still in rotating bloodhouses that effectively are rotating you get uh so the thing I just described is called the space like Singularity um there's another kind of Singularity called the time like Singularity where instead of time stopping

effectively space has has stopped what does that mean it means that the normally in space you can move back and forth you can move around it's there's extent to space but in a time like Singularity there is no extent to space space is infinitesimally small and you are sort of Trapped in this infinitesimally small region of space where all that can ever happen is the same thing keeps on happening over and over again through time and and that's kind of a different so so there time is infinite but

space is is is infinitely small so that's a different kind of Singularity that can happen but in both of these cases it's kind of not like you'd notice anything really bad happened because you don't get to notice anything because you're kind of your mind is kind of Frozen at that point so but uh in in terms of of can can there be a uh a sort of uh if you uh often a limited time everything comes to an end now for our universe could be the same thing it could be that in our universe we expand for

a while and then gravity pulls back the expansion of the universe and eventually it goes crunch in a in a big crunch that doesn't seem to be the path that our universe is on based on the speed at which the universe is expanding and other kinds of things we can measure it seems like we're just going to get to the point where we're just eventually coasting and going and we're not we're not going to um we're neither going to speed up in our expansion nor are we going to sort of turn around and Crus

h down again but if we did it can still be the case in in both scenarios that um uh sort of you can end up with a situation where again for the whole universe time eventually ends and where sort of we keep going for a long time and then eventually it's all over and time has ended the the possibility where the universe just sort of expands Forever at an increasing rate you can get into a situation where it expands forever but the rate increases and eventually everything gets so far apart that at

least in the traditional model the uh so far apart that kind of nothing very interesting can happen anymore I actually now that I think about it in our models uh it doesn't it would not really work that way it would no longer it would not be the case that that would be an approximation and if you look below that approximation and you look at the actual structure of space-time there will still be features of the actual structure of space-time that it won't be the case that the thing has become so

rt of uniform and boring um and and in fact in our models again uh even with the sort of the Big Crunch scenario um again it won't get as it won't get the same way as it does in kind of the the older models of physics where the thing just sort of compresses to a point and there's nothing more going on there it's a little bit more structured than that so that that's uh uh a little bit of a discussion about could we be you know what's what's inside a black hole can things survive in a black hole t

he answer is yes but only for finite time typically but we are you know our universe may only survive for finite time as well and there's an awful lot of time before you know let's say our universe survives for a trillion years we're about 14 billion years in and we can lead happy lives for an awfully long time even if the actual lifetime of the universe is quotes only a trillion years so we're kind of existing in what one can think of as kind of a we might think we're existing in sort of the tr

ansient before the real outcome of the universe is known um I don't think in our models for example this idea that Things become very different uh when the universe is either crunched down or gets very big or whatever else it doesn't it's a little bit of a subtle thing because what it means to an observer like us today you know we're roughly a meter tall give or take one and a half meters tall whatever it is and to an observer like us if we imagine what the universe might be like when it's crunc

hed down or it's really big or whatever we say oh that that doesn't look very interesting that looks like nothing nothing that we can kind of engage with but that's because we're a meter and a half tall or whatever and we have certain things we can measure if we imagine sort of projecting the future of uh humans not really humans are very likely you know a trillion years from now and we say well what do we sense then well we're probably not a meter and a half tall and made up with you know biolo

gical molecules and things like this and with a different kind of Observer the structure of the universe as it might exist at that time in the distant future can be perfectly exciting and interesting even though to an observer like us it isn't interesting so it's uh that there's uh and the same through a lot of these different kinds of things the question of of is there kind of a uh what's one's impression of what's going on well it depends on what one is like as an observer um let's see oh boy

a lot of black hole questions all right let's let's take a look at some of these um death sauce with something Trapped In The Space Between The Event Horizon and the singularity eventually be able to escape uh black holes the things I explained there's actually more to the whole story of black holes and one thing that happens is quantum mechanics leads to yet more bizarre effects around black holes uh in our models it gets a little bit clearer what's going on uh but it's a bit complicated to exp

lain in our models there are many different Paths of history for the universe and that's what kind of corresponds to quantum mechanics and what happens in a black hole is there's an event horizon for things moving through physical space there's a different what one can call entanglement Horizon for things for sort of things that correspond to different parts of history and it's there's a slightly longer story to explain the picture but essentially what the the well the end result is when you thi

nk you formed a black hole where nothing can escape there's sort of quantum mechanical things going on that allow things to escape and in the if you wait sufficiently long you'll end up with the the sort of the the thing where no black hole ever really formed being what comes out so one way that one sees that is with Hawking radiation which is a quantum mechanical effect which kind of a picture of what's going on is in the vacuum in quantum mechanics there are continually particle anti-particle

pairs being formed and being destroyed again at every moment everywhere in space space is full of particle antiparticle pairs they form they do get destroyed they form they get destroyed all the time uh and smaller and smaller scales Etc et cetera et cetera in our model to physics that is really the there's this giant Network and particles are features of that Network and so as that Network gets updated you can think of those updates in terms of particles getting formed particles getting destroy

ed but in the end it's just a network getting updated and that because it goes all the way down even below the level where you can kind of identify particles and anti-particles and things like that so in fact in our models it is the activity in this network that knits together the structure of space if it wasn't for that activity two different places in space would have no relation to each other they wouldn't have there wouldn't be any sense in which these things were connected in which we could

imagine motion that goes from one to the other and so on so in any case the this idea that there's kind of this continual particle anti-particle formation or continual sort of updating of this network that one can think of in terms of particles and antibarticles happening in the universe in around a black hole kind of a a typical picture would be that these particle antiparticle pairs get informed and what happens if let's say the antiparticle falls into the black hole it gets formed and it's g

oing to annihilate again but before it denialates again the antiparticle falls into in through the Event Horizon and can no longer escape again so that means that the particle is just left hanging on its own and that emerges as a piece of radiation coming out from the black hole because its partner that it would have annihilated with again uh got trapped inside the inside the Event Horizon of the black hole so that's a kind of a sort of radiation that emerges from black holes and eventually it w

ill sort of uh mine the mass of the black hole and eventually all of it will turn into radiation that's a kind of a strange picture of what's going on I think a better picture which is a little bit harder to understand perhaps it all has to do with uh let's see at the as you get to the event horizon of a black hole two yeah this this is where things get kind of complicated in terms of what you feel like as you're falling into a black hole this is what what folks outside of it think you're doing

so what happens is if you're falling into a black hole you're just going along and you're you're thinking a certain amount of times elapsing it's not too much Etc et cetera Etc but to an observer far away you seem like you're slowing down and slowing down and slowing down you know what if you had a clock that was ticking on your spacecraft and somebody was observing the ticking of that clock from far away far away from the black hole it would be as if that clock was ticking slower and slower and

slower and slower and slower until eventually you just freeze to an observer to the on the outside you just freeze sort of at the at the surface of the Event Horizon so for you you're like oh I just fell into the Event Horizon to an observer outside it's like well it's an infinite amount of time the The Observer is stuck the the spacecraft is stuck at the Event Horizon and that's kind of the flip around of the fact that when you send a signal out you it is a a limited time for you but that time

it's sort of an infinite time for the outside world and that's kind of why your signal never actually gets out so to speak it's why for example in black holes words term invented in the 1950s 60s I guess um by an American physicist called John Wheeler in in Russian physics black holes were called Frozen Stars because of this effect that as you kind of get to the outside it looks like sort of everything freezes so okay that that's what happens so to an observer on the far outside it freezes at t

hat level now there's another bizarre thing that can happen which is that um when you think about these different threads of history that originated that exist in quantum mechanics the big thing that happens when we so the universe looked at sort of from outside the universe there are many paths of history in the universe but to an observer embedded inside the universe like us our minds are also branching just like the universe is branching into many parts of History so we have this question of

what does a mind that's branching think is happening when observing a universe that is itself branching and we have the idea that definite things happen so it's as if in our minds we're conflating together all those different parts of History it's a non-trivial fact that we don't get lots of confusions and inconsistencies by conflating those things together but we conflate those things together and that's kind of how we go from the sort of underlying Quantum many possible parts of History to the

definite things happen kind of kind of situation well the ability for us to knit those parts of History together and conclude that something definite happens shouldn't be taken for granted and in fact what happens at the entanglement Horizon as we call it around a black hole and this is part of things that have emerged from our physics project um understanding all of this stuff that at the entanglement Horizon what happens is that an observer can no longer knit together in finite time all of th

ese different Paths of History just like one can't kind of connect uh one can't send signals out and so on one also can't kind of come to a definite conclusion about which path of History one was on so it's it's as if for us we can say yes we're going to conflate these parts of History we're going to say a definite thing happened but to an observer at the entanglement Horizon around a black hole the the entanglement Horizons are probably outside of the Event Horizon um at that when the Observer

reaches that they get to the point where they can no longer sort of form a classical thought they can no longer conclude with any definiteness what happened and I think that's what's going on when one looks at kind of a black hole it sort of forms but sort of one is if one's an observer right there one kind of isn't really sure it Formed because one can't form the sort of classical thought to know what happened and eventually that what the black hole has disintegrated again and it's like well I

don't really know what happened because I couldn't really form a classical thought to know what happened and that's that's roughly the picture of what goes on there let's see um Christian asks uh about the stopping of time in a black hole is this the case also for string theory um so there is a uh one of the things that was discovered actually by a friend of mine um when was it 20 years ago maybe um was that um in string theory there's a way to sort of if you think about the analog of a black ho

le in string theory there's some uh a way to understand the properties of a black hole in terms of the structure of strings so maybe I should explain what what strength there is and how how strings work um let's see string theory has a weird weird history because it's basically had three different epochs where the same mathematics was used for three completely different purposes so it's rather confusing as you start talking about it but in a first approximation let's talk about how how String Th

eory works so in theory of in Quantum Mechanics for example one of the things one wants to talk about is how do particles behave what's a particle an electron a photon a quark these are particles that have where we have a sort of picture that there are all these many parts of History we have this way of of representing what is the sort of amplitude roughly probability for a particle to be found in different places in space and so on in the end uh what happens for these particles is that one has

certain rules for how particles can move through space so that these things called wave equations for example and different kinds of particles obey different wave equations like an electron a bay is a thing called the Dirac equation which is just some mathematical equation which describes how sort of the amplitude of these different parts of History which assign different positions to the electron how that amplitude evolves through time and in space and for example a photon has a different wave

equation that it satisfies they're different because the particles are just they have a different intrinsic Spin and that kind of the spin determines kind of which kind of wave equation they satisfy but so that's kind of this theory of how particles work in terms of these wave equations and if you look in Space the particle an electron for example in traditional physics not in our models but but in traditional physics an electron is a point particle it has absolutely no extent it's infinitely sm

all same with the photon same with the quark a proton for example it's pretty big a proton is measurable size we know how big it is an electron so far as any experiment has shown so far the electron is infinitely small in our models the physics the electron is not infinitely small but it's really really small compared to anything that we can measure with particle accelerators and so on today so an electron is essentially a point particle in space if we look at it through time it traces out what

one can call a world line if one just says it once if one looks at sort of Imagine space is two-dimensional and we just make a stack of configurations of space going down in the third dimension with time then the path of a particle will just be a line in the space-time structure so particles make lines and space time and okay so that's that's a fine thing so now the question is well what if we had something that wasn't a point particle what if we had a bigger object what if we had something that

was extended somehow in space-time well for many many years there were was a lot of difficulty understanding what that could possibly be like because a lot of the rules about quantum mechanics and relativity and so on they get very very confused when you deal with extended objects I'll give you an example of of how things get confused you've got an extended object you've got an arm and the arm it's an extended thing it's swinging around and but it's a rigid arm kind of swinging around in space

you say well let's make it longer and longer and longer arm but it's rigid well eventually that arm the tip of the arm if it gets long enough will be going faster than the speed of light but that can't happen that's not how things work so then you have to say well what happens to this arm well the answer is in reality it can't be rigid the the mechanical forces that would build up to make the tip of the arm go as much as fast as the speed of light are such that the arm could never stay together

if it's made of a metal or made of atoms or made of some carbon nanotube or whatever whatever it's made of there are infinite forces that get developed and the thing could never stay together so there's sort of you can't think about an extended object that's kind of like a long arm or something rigid thing that doesn't end up being compatible with relativity Theory and uh people had a long a lot of difficulties seeing how do you deal with extended objects okay so it was realized that um you coul

d have a kind of a string that was an extended object in in the space that kind of where sort of the the the pieces of it sort of all go at the speed of light and this string just as a particle traces out a line in space this time a string traces out a world sheet in space-time and so then the question is well okay that's that's well and good can we make that can we make kind of a wave equation like thing for that string that's you know kind of moving at the speed of light and the pieces of it a

re moving at the speed of light and so on can we make something a consistent kind of wave equation like thing and this is where things got complicated and people realized that well actually uh no you couldn't really quite do that but there was this cool thing that happened if the University of space happened to be 26 dimensional oh in some cases 10 dimensional then it did work out that you couldn't get see what what ended up happening was that inevitably as the string moved through space-time th

ere would be kind of uh features of the string that move faster than the speed of light that turned out to be an inevitable feature but somehow that because of the way the mathematics works out in let's say 26 Dimensions the the sort of the things that lead to those those kind of uh fast and the speed of light pieces they somehow cancel out and so it's like well maybe actually the universe is 26 dimensional and maybe those extra you know 24 Dimensions or so 20 22 Dimensions or whatever maybe or

23 Dimensions depending on how you're counting things maybe the reason we don't see those is that those dimensions are curled up really small that they're that and that all that happens is that in those Dimensions it's kind of like that that time like Singularity I was talking about earlier in those Dimensions space isn't really Extended space has just curled up and it's only in the three dimensions of ordinary space that it's extended and we can move around so that that's kind of the um uh that

's sort of a a basic um picture of um uh of kind of the setup now there are a lot of details about this and about different kinds of strings and different kinds of um uh the the strings that like to live in 10 dimensions and in 26 Dimensions the strings that correspond to kind of a bit like a generalization of a photon versus the strings that correspond to a bit like the generalization of an electron there's this idea of supersymmetry uh so gosh well you know they're things that are symmetrical

like you take a sphere and you rotate it and however you rotate it it's always going to look like a sphere if you have a cylinder instead well you can rotate the cylinder around its axis but if you turn the cylinder not around its axis it's not the same thing anymore so there's lots of kinds of Notions of symmetry like that one of the more interesting kinds of symmetry is that is a uh well there are symmetries that are associated with kind of the the uh features of of particles and so on um for

example well let's see in um uh well there there are cases where well for example particles versus antiparticles you can think there's sort of a discrete symmetry transformation instead of a with a sphere where you can turn it to any angle you could say well let's say we've got a square for example and we can reflect the square as it's a discrete thing it you know with that discrete transformation or we can turn it through 90 degrees with that discrete transformation it turns into itself again w

ell there's a similar kind of thing with particles and antiparticles you can kind of apply charge conjugation turn a particle into an anti-particle applied again the antiparticle turns back into a particle again and when I say apply I just mean consider applying it there's no machine that will apply charge conjugation there is a machine that will turn something so to speak through a certain angle but there isn't these these kinds of things that um these so-called internal symmetries they're not

things where a machine like that can make that transformation it's actually a little bit more subtle than that because the interaction uh this is a a subtle mess about how gauge theories work and so on but let's not go down that particular Rabbit Hole the um but in in a there is this idea of super symmetry in which things that are like photons which um sort of turn into things that are like electrons just as sort of a a particle could turn into its anti-particles so there are these Transformatio

ns that turn one of those into the other and that's they kind of relate things like photons to things like electrons and kind of that story plays into the kind of string generalizations of things like electrons and things like photons and uh that makes a very lovely theory that has a lot of very interesting mathematical properties uh we kind of suspect that in the end certain features of that theory correspond to features of our models of physics and uh there are um let's see it's kind of a ques

tion of boy This is complicated um well in our models of physics we talked about how there's this kind of giant Network that's progressively getting Rewritten according to certain rules but in the most General case you can use any rule you can imagine you can just apply all these different rules you make this thing we call a rouliad which is this kind of entangled limit of all possible computational processes and the the tricky thing is that we are embedded in this ruly ad we are observers withi

n the rouliad observing the rouliad and that sort of self-observation when we are observers with certain properties causes us to believe certain things about what we observe and the things we believe correspond to laws of physics the way in which we kind of parse out what we're observing in this kind of entangled limit of all possible computations there are different ways to pass that out we could say well there's this state of the universe and then there's another state of the universe at a suc

cessive time there are particular rules for the University being followed there are these different rules followed at the different possible rules we can follow and so on there are different ways to slice up the rouliad our guess is that string theory corresponds to an approximation to one way to slice up the rouliad and that this when I talked about these kind of compactified dimensions and so on that's a particular kind of way to uh to sort of arrange the things in the rouliad so that we can o

rganize them to to kind of compress the amount of information associated with them so that we can kind of say oh yes we can see what's going on it's not just this big complicated mess and our guess is that there are certain conditions about how in order to get consistency in the way that slicing works that corresponds to these things that lead to these implications about particular dimensions and string theory and so on that's sort of still somewhat of a guess and there's lots of mathematical ph

ysics to work through to see exactly how that works boy this got kind of complicated um let's see okay Technic is asking a rather technical question what are the implications of a naked black hole one without an event horizon okay so I mentioned that in the center of a black hole in the traditional view of physics the there's sort of a an infinitesimal Point punched out of space-time now normally you can't tell it's there because it's hidden behind an event horizon and people have believed that

there will be no naked singularities that it wouldn't be possible to set things up so that you could form the singularity but not form an event horizon there was discovered maybe 15 years ago that there is an elaborate procedure where you can essentially carefully orchestrate what happens in space-time so that you form a singularity but you carefully avoid forming an event horizon now there's a lot of tricky aspects to this because event Horizons are really you don't know whether you've formed a

n event horizon until an infinite time has passed they're really a story of infinite time uh it's an infinite time question because you could say well you know I didn't really get an event horizon just if I waited long enough I'd be able to get through it's a it's an infinite time question whether an event horizon is formed and this this question about whether you can form this thing which has no event horizon or just a singularity it it seems to be the case that sort of the formation of a naked

Singularity is something similar to making something of zero temperature so normally you have all these molecules bouncing around and in a material and if you try and do reduce the temperature what you're trying to do is make all those molecules you're trying to just stop every molecule you're trying to you know do something where you pick every molecule and you stop it and there are different ways to do that more in bulk but what's known the third law of thermodynamics basically is the stateme

nt that there's no way to get to Absolute Zero by a finite number of steps you know every time you've kind of you know you've stopped one molecule or you've got to stop another one you've got to stop another one Etc et cetera et cetera there's no way to with a sort of in in my way of thinking about this with sort of finite computational ability effort to stop all the molecules you'd have to sort of predict where every single molecule was and zap everyone to stop it well I think the same thing ha

ppens with the formation of naked singularities that basically it's the same kind of thing that you'd have to be able to break out of kind of all the computational complexity of the structure of space-time to be able to carefully orchestrate things so that you wind up with this pure naked Singularity and so I think what happens is that in in space-time you have all this sort of bubbling around of all these rewritings of this network and so on and you'd have to kind of orchestrate it so that you

just carefully navigate things so that you have exactly the right set of rewritings so that you have this pure place where time stopped and there's nothing sort of around it and the claim is that you can only do that you can't do that with a finite amount of computation that you'd have to kind of be dealing with every individual atom of space separately and sort of computing how it works the problem is we're embedded in the universe so the only way we get to do those computations is by using the

stuff of the universe to do it and so we never get to have enough computational ability to be able to sort of untangle things to the point where we can get to that naked Singularity so that's my guess is that it's kind of like in thermodynamics like the inability to get to something like absolute zero you similarly can't get to a thing where just in the universe at Large there's a place where time stopped and you can kind of I mean it it's you know where and you can sort of get to it so to spea

k now even even when you imagine a place where time stopped you know by the time you get to it time has stopped for you so you never get to get out of it so it's all a bit bit difficult to to untangle but I think that's the basic idea let's see Marcus comments um about uh when a black hole eats more stuff it gets bigger so where's the singularity so the singularity is at the center of the black hole the in the traditional view of physics it's a vacuum solution to the Einstein equations the the t

hing that this most simple simple description of a black hole but what happens is there's this sort of place punched out of the universe right at the center um and uh it's the the um the sort of well sounds very silly doesn't it they say there's an amount punched out of the universe but there can be more punched out of the universe but it's still an infinitesimal point the mass parameter of a black hole is a parameter associated with that thing that got punched out of the universe it's kind of a

weird setup in our models of physics it's much cleaner it's much more there's a much more direct interpretation of the fact that the mass associated with the black hole has to do with essentially the activity of uh of this rewrites in the network inside the black hole so what's happening in our models is there's kind of the presence of a large amount of mass is the presence of many rewrites spaces being sort of intensely uh sort of bubbling around in a very intense way getting knitted together

in a very intense way that's what mass and energy are and that's what in the end that a different mass of black hole is one where there's different amounts of that activity going on in the in the structure of space inside the Event Horizon ah let's see um uh buildings comments that mass and matter and antimatter both have positive Mass um so why doesn't Hawking radiation increase the mass of alcohol where it decreases it because because whether you are emitting matter or antimatter you're emitti

ng positive mass and so that that comes off the kind of balance sheet of the black holes mass and you're decreasing the mass of the black hole because things are escaping away a question of how small from storen how question how small can a black hole be well we don't know in our models of physics black holes can be really small because they can be little features of space so here's the thing that I suspect I suspect that electrons are basically black holes and that an electron is essentially a

feature of space-time just as a great big black hole is a feature effect feature of space-time an electron is also just a feature of space-time it has nothing in it other than being kind of this this lump of space-time it's kind of like in a fluid like water you can have an Eddy just water circulating around and there's you know you can point to that Eddy and say oh it moved around but there's nothing in the Eddy other than a bunch of molecules that happen to be kind of coherent coordinated in t

he motion that they're going through and that's what I think things like electrons are and I think there's a very close analogy between a black hole where there's sort of this definite structure the space that that forms the cement Horizon and so on an electron where I think there's also a definite structure to space and kind of traditional physics electrons are Point particles where there's just no internal structure I don't think that's right I think there is internal structure and but one of

the things that's interesting is that to the outside world just like in a black hole the outside to the outside world all you see is Event Horizon The Event Horizon sort of featureless and that means all you know about the black hole is things like what it's masses what it's effective angular momentum spin is and things like this you don't really know it's not like you can say well that's a black hole that is this shape or that shape no they're all kind of the same they're all the sort of perfec

t shape to the outside world one of the things that's always been mysterious about electrons is that they all seem to be the same it's kind of like there's only every electron in the universe seems like it's the same they can have different energies momentum things like that but otherwise they're all the same they all have the same mass they all have the same you know other properties and so on and you know one of the more bizarre theories about why that might be the case uh theory that um was c

irculating in the 1940s was the theory maybe there's just one electron in the universe and maybe that electron is going forwards in time then zipping backwards in time and going forwards in time again it's just sort of knitting through and we are existing at a particular time and the electron is just sort of zipping back and forth in time and there's just one of it kind of like in in computer science you talk about Turing machines where this is one head where where activity happens that might be

the case with electrons turns out that theory doesn't really work but so you still are left with the question why is there only why is why is every electron in the universe the same well you know I think in in our models that what's happening is it's kind of like you can say well I'm not I make a knot in a rope I can make the rope in lots of different configurations but it's a definite kind of knot there's a definite structure to that knot even though the Rope may have a slightly different form

when I kind of pull on the ends I can see it's it's ultimately the same kind of knot it has the same topological structure and we suspect that that's sort of in some sense why kind of all the electrons are the same is because even though their details might somehow be different particularly inside some analog of an event horizon that at some sort of large topological scale they are all the same and so if you ask what's the smallest possible black hole it might be that basically an electron is s

uch a thing but in any case in our models of physics you can have things like black holes on a pretty small scale I think uh that that are pretty you know comparable to the the distance the elementary length you know the the uh a proton for example is maybe uh a um uh 10 to the minus 15 meters a um a million billionth of a meter across um so but an electron is certainly smaller than 10 to the minus 20 10 to the minus 21 meters and in our models of physics it's probably more like uh 10 to the min

us 80 meters across so very very tiny and the elementary length might be 10 to the minus 90 meters so in a single electron there might be 10 to the 10 sort of uh Elementary lengths in space there might be all that structure inside an electron which kind of suggests there might be some particles that are even smaller and lighter than electrons and that's a separate story about about what might what might happen there but um let's see I think the so in some sense there may be little tiny black hol

es being um it's uh you know that that the whole structure of space-time just as there are a little particle anti-particle pairs that are being formed all the time you can kind of think about there being little sort of black hole kind of anti-black hole pairs being formed that's kind of you know one way to describe the kind of bubbling around with face time now you know what black holes are you know is there a for example in the early Universe could there be a whole spectrum of black holes a who

le distribution of sizes of black holes formed almost certainly the answer is yes there was recently an experiment based on looking at the timings for pulsars and kind of watching gravitational waves uh that might have uh existed from the early Universe kind of go through and affect different pulsars for I don't know 20 pulsars or something and as the gravitational wave goes through it changes the timing of the Pulsar just slightly and by correlating all those timings you can get a sense of of s

ort of uh primordial gravitational waves that might be sort of existing in the universe today um and um that's a um uh but but you can imagine a whole spectrum of black holes formed from the in the early universe um lucky us do you think it will ever be possible to reproduce a black hole in a lab for practical research and experimentation people there are all kinds of mathematical analogs of black holes that are quite easy to make actually in fluid mechanics and quantum mechanics and so on there

there are analogs but if you say can we take a piece of space-time and kind of curl it up to make a black hole or maybe electrons are black holes in which case we've got plenty of them um I think sort of being able to make a black hole from in the most traditional kind of black hole I don't see a path for being able to make that in in a kind of a lab setting that's probably just as well because even a very small black hole kind of going through the Earth would make you know would wreak havoc on

everything and the Earth would just get sucked into the black hole and so on so it's probably just as well that that doesn't seem to be doesn't seem to be a feasible thing to do in the current Universe unless it turns out that particles basically are black holes in which case there's a whole different story and the question of whether we will eventually be able to simulate I mean we what we've been doing recently in recent times is simulating the structure of space-time in our Network models of

space and seeing how black holes work in those in that situation and seeing how we can get very very tiny black holes that we can simulate you know kind of on a laptop and a black hole that has you know 10 000 nodes of space 10 000 atoms of space in it absolutely you know ridiculously small compared to real black holes that make might have 10 to the 200 atoms of space in them but we can see many features of sort of big black holes already at this uh these black holes that are very tiny that's a

sort of laptop simulatable and we can see these black holes merge as we know they do about once a week in our universe us and produce gravitational radiation Etc et cetera et cetera let's see um Philip asks what is spinning in a spinning black hole it's a can of worms the it's really just a mathematical parameter when we talk about things spinning the it's as far as the actual black hole itself is concerned it's just a mathematical parameter but that mathematical parameter has a consequence and

as a consequence it's a phenomenon called frame dragging and what happens is oh boy you guys ask me non-trivial questions here um the um what happens is in in a black hole there's a question of sort of where are the gravitational field lines what what what effect does the gravitational field of a black hole have on a material object like a like a a drop of liquid for example well sometimes the um uh let's see how to think about this well essentially there are tidal forces just like there are on

the Earth from the Moon and the Sun and so on that elongate that drop the the there's kind of there's a there's more gravity kind of on the inside and there's less gravity on the outside and so the blob will kind of elongate and roughly what happens is that in a black hole the so-called cursed solution to the Einstein equations that has this this spin parameter usually called J um in that solution what happens is that instead of things being sort of uh symmetrically pulled in they are kind of d

ragged so that they get so that they get kind of um so they get uh so it's as if they were kind of spinning around the black holes it's actually a little bit more complicated than this what happens is the um the paths for light rays end up uh you can think about kind of plotting and space-time the parts that light rays go this form so-called light cones where you can have a light rays are produced at some point and they go outwards in space and they if you're plotting them with time they go outw

ards kind of in a cone that you form a cone in space-time and so what happens is that cone gets tipped in um uh near a black hole and the way it gets tipped is kind of like it's getting tipped at different angles as you go around the black hole it's sort of as if it's being dragged around as a black hole is rotating but there isn't really there's nothing about the black hole itself that's rotating it just makes things around it rotate in some sense Michael asks black holes have a charge can the

effect of the charge propagate out of the black hole the photons cannot escape the answer is black holes can have a charge just like they have a a j parameter that is like an angle momentum they can have a charge parameter as a thing called the ryzen Nordstrom solution to the Einstein equations which is a black hole that has charge um the how does that work well essentially what's happening is just as the gravitational field so you could say if you know in my kind of picture of how a black hole

Works where nothing escapes the black hole because there's nothing goes faster than the speed of light and and the black hole sort of pulls back in things going going even at the speed of light you could say if you wanted to be difficult but what about the gravitons that make up the gravitational field why aren't the gravitons pulled back into the black hole just like everything else is pulled black into the black hole well that's subtle it's really this picture of things escaping from black hol

es and and so on really isn't quite the right picture black holes can a better thought about as as just these features of the structure of space-time and that's just sort of a picture for how to think about them and so you know just gravitons are not pulled back into the back hole and Nora photons in that at the type of photon that makes a static uh electric field just as okay so a graviton if you were to have a gravitational wave that in that started inside the black hole it would get pulled ba

ck into the black hole just like a a photon that starts inside the black hole gets pulled back into the black hole but okay now it gets a bit subtle because a static gravitational field a static electric field these are sort of formed from gravitons and photons but they're formed from virtual gravitons and photons and they don't have the same feature that you can kind of Trace them in space and time they're things that uh it's really how to think about this some level it's a kind of a feature of

quantum mechanics but in there isn't the same kind of idea that there's motion of the photon when you have a static electric field you can think about the electric field as being associated with the exchange of virtual photons and virtual photons going from one charge to the other charge and so on but it doesn't have the same character of being kind of a thing moving from here to there it's kind of subtle and I'm not sure I actually haven't thought about this uh with any Clarity let's see um ho

w to explain this I'm not sure I'm going to I mean in the in the mathematics of what goes on it's rather it's fairly straightforward but I'm not sure there's a there's a picture like this that really Nails it in a in a good way that sort of connects these virtual particles that exist sort of independent of time with these things that have emotion that happens in time so to speak let's see uh Emery asks is a kind of a history of Science question why are they named black holes not after the people

who found discover this phenomenon well you know it took a long time for the for this phenomenon to become clear what the heck it was and people really were confused I mean the original discovery that there was this particular solution to the Einstein equations came in 1916 um but it wasn't until the 1960s that people understood uh kind of something about what the phenomenon of the black hole was and that was a very slow process involving many different people and sort of a long progress of of

mathematical development uh let's see well I I think I almost ran out of time but we've been talking about black holes all this time we were kind of dragged into the into the eventual rising of a black hole or something um let me just try and address a couple more questions um Aaron asks we're going very different kind of question could lasers be used to display an advertisement or perhaps a clock or something else on the moon um can high bandwidth internet connections be bounced off reflectors

on the moon so the answer is you can see laser light that has been reflected from the Moon in fact the Apollo Astronauts put Luna laser retro reflectors on the moon that have little uh glass spheres in them laser light falls on the reflector it gets reflected back here's the problem lasers you should shoot a laser from the Earth the beam of the laser gradually spreads out so even though it was a very intense laser that might have had a spot that was just a centimeter across on the Earth by the t

ime it gets to the Moon it'll be a couple of kilometers across I think the best lasers right now the spread by the time you get to the moon is on the order of a kilometer so there's much less intensity in the light by the time you get there if you could keep the laser light kind of um well collimated uh you know really keep it together until it gets to the moon and then you're Illuminating Moon Rock and you know the well if you hit the laser that's a reflector you'll get you know you'll get the

laser reflected precisely back but mostly you'll hit lunar regolith just Moon soil so to speak moon rock and that consists of these tiny little sand like granules and when light hits those it hits in One Direction and it's it's uh it's a it's like like many kinds of surfaces that aren't mirrors it's it's a so-called lambushing reflector it's um it light comes in and the light that comes out is kind of spread in all directions that's a typical thing and the Albedo of the Moon that is if you send

in a certain amount of Light how much light comes back out as I think about one-tenth so you shine in a certain amount of light the surface of the Moon is pretty black only one tenth of the light comes back out you know if you have a mirror it's Albedo as one because any light you shine on the mirror if it's a perfect mirror comes right back out again um and uh different materials have different albedos the Moon is actually pretty pretty pretty black um but one tenth of the light coming from the

Sun being reflected back to us makes the Moon look bright in the sky at night so it um so what happens is that you have a laser you shine it on the moon you've got a two kilometer sized spot it's hard to have enough intensity there to to really be able to see anything from that for example the naked eye what limits the um uh the the amount of how unspread a laser gets has to do with the the way a laser cavity works and um uh let me see the in a laser you've got kind of light bouncing back and f

orth and the way a laser works the word laser stands for light amplification by stimulated emission of radiation roughly you have this cavity with with mirrors at the at the ends and so on and light is bouncing backwards and forwards in this cavity and it's gradually getting Amplified uh through a process we can talk about it's related to Bose Einstein condensation uh there's this quantum mechanical process by which photons kind of like to all be in the same state and you can kind of uh you can

do this phenomenon of stimulated emission where the presence of photons gets there to be more photons in the same state but anyway bottom line is you've got these photons bouncing backwards and forwards in this cavity that makes the laser and the sort of best thing you can get is a single mode of the electromagnetic field so so it's like you have a string and you can pluck the string and you can get the string to have just sort of one peak in the middle between the places where you're holding it

or you can have two peaks or Three Peaks or Four Peaks there's a different harmonics um they make for a different you know frequency of sound if you made sound from the from the string and so on but it's the same kind of thing with light you can have just sort of a single mode of light in the laser cavity and that's the thing that will get you the best uh the the least spreading of laser light but then the amount of spreading is determined by features of the cavity and there's a certain inevita

ble amount of spreading I mean the fancy math version of this these are I guess you can make so-called gaussian um gaussian modes and there's a certain spreading rate that is determined by the process of diffraction and light that determines how much the the thing will spread out um and I don't know exactly what's involved in making maybe if you have a bigger cavity you can make there be less spreading it's kind of like a like the reverse of a telescope where um the uh the the spreading angle is

proportional the wavelength divided by the size of the telescope so you can get a a better a more precise telescope by having a bigger telescope there's less diffraction limit for the telescope if it's bigger and I think maybe the same thing is true with lasers so if you have a big enough one maybe you can get the thing to spread less but so that would be the way of kind of doing skywriting on the moon I think it's sort of nearer term people think about uh putting things in Earth orbit and havi

ng things that re-enter the Earth's atmosphere and burn up just like micrometer meteorites burn up but you can kind of you know release something from a satellite and you can have this whole kind of uh collection of pieces of dust that you can see as they enter the Earth's atmosphere because they will burn up and they will they'll emit light as they burn up and if you change the the chemical uh constitution of of those things you can get for example different colors and you can imagine that if y

ou have sort of the satellite that's laying stuff out that um uh you can kind of skywrite in in Earth orbit so to speak actually there was a company that was trying to make that work because it's like six seven years ago I'm not sure exactly who you have to get approval from to um uh to write a big message in in space because the um uh kind of the the sort of the airspace of a country for example doesn't extend infinitely far out so there are various outer space treaties that I don't know exactl

y how they apply to advertising in space or exactly who would get upset um if you start writing your ad in space so to speak um let's see um let's see well I should probably um oh M rudos if the moon is responsible for tides on the earth can the Earth be responsible for movement of moon dust the answer is yes the the Earth raises a tide on the moon just as the moon raises the tide on the Earth but the tide on the earth most of the tide on the Earth is obvious because there's water on the earth a

nd that water can actually be raised up on the side of the earth nearer the moon and it goes further away on the side of the earth that's further from the Moon there is also a solid tide on the earth that same effect of kind of the squishing of the earth happens to the solid rock of the Earth but it's a much smaller effect than the uh than the tide on um uh and that you can see in the liquid water on the Earth on the moon the Earth raises a solid tide on on the moon and so the Moon is continuall

y kind of squished a bit by the tides that are raised by the earth now there's a satellite of Jupiter or Saturn which has strong enough um uh solid Tides associated with I think it's a moon of Jupiter now I'm going to show my lack of astronomy noise I think it's maybe IO not sure that has strong enough uh solid tides that they actually produce Heating in the in the in the in the moon and that heating produces volcanoes and all kinds of stuff so you can have enough squishing from tidal forces to

have those kinds of effects but for the moon uh we don't have that kind of the earth doesn't have that kind of effect if you ask the question does uh you know if you leave your footprint on the moon is it going to stay forever is it going to be there billions of years from now the answer is it seems that the answer is yes it isn't the case that the little pieces of dust on the moon move around now there is an effect that the solar wind uh there's a stream of particles just like this light that c

omes from the sun there is also a stream of protons and electrons that come from the Sun and those things stream into the atmosphere of the Earth um they are ultimately responsible for producing um things like the Aurora but on the moon they're continually sort of bombarding the lunar surface Moon doesn't have an atmosphere so all those particles just come crashing down to the surface and that seems to kind of bleach the surface of the Moon um progressively over time it doesn't have the opportun

ity to move around actual particles of kind of Moon dust but it does seem to sort of in a sense chemically or physically bleach those things and so if you see kind of features of the Moon that have been created recently like places where a spacecraft crashed into the moon um the you know as a little crater over the course of a few decades there will be sort of a bleaching that happens there well you can you can tell that there was a there was so when the spacecraft crashes into the Moon it expos

es layers of moon rock that have not seen the Sun or anything for billions of years and those turn out to be sort of a different color but over the course of decades they get sort of bleached back into the same color so there is an effect like that but it's not one that can I think move around the actual particles of moon dust and so you put your footprint on the moon unless some tourist comes and erases it uh you know it's going to be there for a really really long time uh side comments buying

an ad that burns up upon re-entry sounds incredibly wasteful well you know it seems like you might say buying an ad that disappears uh you know when you uh click somewhere else is also wasteful you know I think it's all about um uh what people notice and I suppose you know you would hope that the kind of the ad that says I don't know what the ad would be an ad for I don't know what people advertise for these days I'm not in that many venues where there's tons of advertising um or if I am I kind

of block it out which is terrible but any case um but you know if it the the classic will be buy coke or something and I think one can be fairly certain that if somebody did a a giant buy coke visible in the sky you know at night from all over North America that people will be talking about that for a long time they might be complaining about it for a long time but they'd be talking about it for a long time for sure so there would be even though it burnt up in a matter of uh 15 minutes or someth

ing it would still be a subject of conversation for um for many years to come let's see all right maybe one or two more questions here Stephen asks would the tea dumped into the Boston Harbor during the Boston Tea Party have affected the underwater ecosystem it's an interesting question I don't know how much tea they dumped in I mean let's assume it was a few crates of tea so the question is how dilute does that mean the T gets in uh you know in in the Boston Harbor and the next question is do f

ish like tea you know it's always a funny thing that different different kinds of animals respond in different ways to um uh to chemicals so caffeine for example I don't know what caffeine does to fish uh you know one one knows that there's some weird cases like some particular kind you know like cats I think do very badly with Tylenol um I think because the kidneys of humans uh kind of filter that out of our bloodstream but that doesn't work with cats and so it gets to some kind of poisonous le

vel I think um but you know even with things like spiders you can feed them all kinds of different drugs caffeine or some other kinds of drugs you can see they make different shaped webs depending on what you know even though they have very very tiny brains the effect of the brain function the effect of neuron firings and things associated with those different chemicals is enough to make them make completely different uh sort of uh whether they you know you can make a drunk spider will make a we

ird looking web so to speak so I don't know what what um what tea does to fish in any concentration one thing that's very confusing is that usually you would think with a dilute enough concentration it's just not going to have any effect but we know that there are some chemicals some drugs uh I think LSD is a notable one where just a single molecule can have an effect on on on something uh you know on a on a on uh I don't actually know how that works now that I think about it because a single mo

lecule can have an effect on a single synapse and a single connection between nerve cells but we've got 100 billion of those and so you know how that has a more Global Effect as a more complicated story I suppose it may be something a little bit like the story of black holes and things where you can have some some thing where there's sort of a a propagating effect from that one uh one place where there's an effect but so you know this question of well how dilute does the does the T have to be be

fore the fish no longer care that there was tea dumped in the ocean I don't know the answer to that and it may not be that the dose response for whatever is in t will be any kind of sort of linear dose response you might say see another thing happens a lot with with drugs with Pharmaceuticals of various kinds is there's a non-linear dose response if you take you know one tenth the recommended dose it might do absolutely nothing it doesn't do one-tenth as much as if you take the recommended dose

it's non-linear and it's not often not very well understood why that happens you know examples of why that can happen are things like well if you put enough of those molecules in you'll eventually block everything you know your block a whole pathway it'll prevent anything from being transported through some cell membrane or or being you know participating in some reaction but if you only block 10 of it there's still enough that can get through that whatever a process it was that was the big proc

ess that was happening can still happen and you know if you some immune response or something there's still enough immune cells that can get through until you block 100 of it um it doesn't really work and so that that's how you can have sort of a non-linear dose response you have to put enough in that you get to the point where you're blocking a hundred percent and blocking anything less than that really doesn't have much of a qualitative effect and so that's how you can end up with these nonlin

ear dose response kinds of Curves and and so I don't know whether that happens for for the thick kinds of things which are in tea um and I also don't know to what extent uh you know there are ocean currents and there's sort of a continual swirling of the ocean and I don't know how quickly there's mixing of water into different parts of the ocean I mean I know that in general there's there's quite rapid mixing between throughout the oceans of the earth I mean the famous example of this was when u

h nuclear tests were done in the Pacific Ocean in the 1950s they produced tritium radioactive isotope of hydrogen which kind of substituted for the hydrogens in water in the Pacific in a you know some a few of the the water molecules in the Pacific and within just a few years you could detect tritium in water all over the Earth so there was enough mixing between the different water in the ocean and the Pacific and in every other kind of water on Earth that um uh that that that would occur I have

to say that the tritium was generated in the 1950s bomb tests as pretty much all decayed Away by now when I was a kid the amount of tritium that was sort of said to be in a typical piece of water was higher than it is today because of that effect effect um a very weird phenomenon um let's see I think Kappa is asking how would biologists tests for this I'm not sure that this might be the effect of um of some molecule caffeine or something on a fish you know I think that uh does it affect the bra

in well you can start making measurements from about the the firing of individual neurons or you can just see what a fish does and you can say you know you have a a fish maze or something and how does the fish go through the fish maze or how does the uh you know you see certain behavioral aspects of fish and you see how much effect it has it's not an easy thing to measure really um all right maybe one more question here one from frost Frost why are the elements on the earth not more homogeneous

why are there areas and Minds abundance with certain Metals is the heterogeneity of elements increasing or decreasing on Earth is it the same for other planets other galaxies interesting question I've been curious about this question in fact I've been curious enough I've asked a bunch of geologists and astrogeologists this exact question so I can tell you some sort of distribution of world expert answers kind of converging on one thing in fact one version of this question that I've asked is coul

d there be a golden asteroid you know people say well we can go mine minerals Metals whatever from asteroids but different asteroids will have different Metals in them and I've asked you know could there be an asteroid that's all gold answer is probably not so I think what people generally believe so first point is why are there like gold mines on Earth why is that you know gold has a rough abundance of one part and 10 billion of of all the atoms in the universe it's like one part in 10 billion

well all the atoms that near us it's one part in 10 billion of gold but in the earth there's a lot of concentration of gold into particular places uh on the earth you know particular places where we make gold mines so gold like all Heavy elements is pretty much has to be made in supernovas exploding stars or processes related to those uh the what happened in the very early Universe mostly the universe was just hydrogen and helium uh the uh you know just individual protons making hydrogen or heli

um nuclei roughly the universe is one quarter helium the rest is hydrogen and then there's a trailing amount of of other elements some bit which were made in the in the Big Bang in the early Universe the heavier elements particularly ones past iron in the periodic table are pretty much all made in exploding Stars and so the fact that we have things like gold on our planet is a consequence of the fact that our sun wasn't a first generation star there were other stars that lived and died before th

e sun I mean the sun has a 10 billion year lifespan we're at about the four billion year point in that lifespan of about halfway uh there are other stars particularly bigger stars that live on him a few million years like Betelgeuse there's one such star near us and so there are there are stars that kind of come and go and that produce supernovas produce heavy elements that's where all the stuff all the gold that we have came out of some other star that exploded at some time in the past so when

the earth was formed what happened is that there was this kind of uh region of of dust and so on that was gradually being pulled together by gravity it Formed an accretion disk it was spinning around that's how we ended up with planets kind of more or less in a plane all orbiting around in the same direction um it formed this this disc and different parts of it would Clump into a planet and other planets and so on well depending on lots of details about the density of things and this and that an

d the other exactly how far out they were in this disc you know how did things get sort of vacuumed up by one thing that was kind of a massive object that was pulling in other massive objects I think in the end the Earth as it was formed as this kind of giant amalgam of different kinds of objects that were formed at different distances out from the Sun and so on and whose orbits were not just circular but whose orbits were more comp located and things would gradually sort of crash into each othe

r and all make make themselves into this Big Blob of of stuff now then what happened is well the Earth uh that that sort of it's it's the fact that the Earth is kind of a clump together of all these different pieces that I think is the first step in making it not heterogeneous now the second thing was perhaps a little bit confusing is when the moon was formed the current best theory for how the moon was formed is something very bizarre it's kind of a two-step thing it's well first the earth was

formed and then some other little thing crashed into the Earth and it's you know a thing maybe a little bit smaller than Mars or something crashed into the Earth and that kind of disrupted the earth a lot and it made the Earth kind of uh you know turn liquid and so on and then another it kind of that that ejected this big piece of stuff from the Earth which wound up then forming into the moon and actually the Moon unlike the Earth the Moon is not very homogeneous the Earth is is reasonably if yo

u look at the gravity of the earth you have a spacecraft going around the earth it kind of orbits at room more or less the same height all around the earth the moon that's not true one side of the moon is denser than the other side there's kind of a it's like the Moon is two things that got stuck together and that's probably from this big Splat that happened when the moon was formed or at least that's the theory of it so the moon really has a very inhomogeneous there's two very inhomogeneous pie

ces stuck together the Earth probably melted at one point and then re-frows again it's still molten and the core of the earth is still molten and probably there are sort of detailed processes associated with the motion of of of the molten core of the earth and so on that had a different effect for some uh depending on the densities of materials and things like this and eventually there are chemical processes that will and to concentrate things in one place rather than another so in the question

of whether that's true you know if we go mining on the moon or we go mining on Mars we find the same kind of oh there's a tantalum mine here and so on that's an interesting question actually I have not specifically asked that question um whether the big Splat will have had an effect on the homogeneity of the earth I don't know and the fact that the Earth has a liquid core might have an effect Mars does not have a liquid core the moon does not have a liquid core um well Mars might have a tiny one

but the moons doesn't seem to have one at all and uh that's something we know from just like from earthquakes on the earth we can tell that when there's one place on the Earth where there's big earthquake we can see how the seismic waves propagate through the Earth and we can see that the that in the core of the earth there's something liquid because different kinds of waves go through liquids then go through solids and so on the moon uh there are little Moon Quakes that happen they're smaller

than earthquakes but we can see from that that there doesn't seem to be anything that it seems to be that they propagate through the moon as a solid object so that that's kind of the um the story of of um uh uh yeah that's so so I'm guessing it's an interesting question I'm sort of guessing the first approximation they'll be mining on Mars like there's mining on Earth second approximation it might not be the same because of the big Splat and things like that um and it might very well be that um

and some of these planets and moons that get continually so squidged by by tidal forces and so on they may have kind of separated out different materials and and different minerals and so on in different ways it's a good question as you can tell I thought it's a good question because I've asked it a bunch of people trying to get to a definitive answer but I'm I'm telling you that the best I know so far all right I gotta go to uh something for my day job but thank you for a lot of interesting que

stions and um I hope people found that interesting and uh look forward to chatting with you another time bye for now