Thursday, May 26, 2022

Science & Technology Q&A for Kids (and others) [Part 11]

Okay hi everyone back for another episode of science and technology q a for kids and others happy to answer all kinds of questions here um looks like we still have a few from uh lost time left over we have one from anders here .

What is dark matter well let's see when we look out into the universe we see lots of stars that we see uh producing light and so on question is is there other matter out in the universe that exists but that isn't producing light that's .

Dark and how could we tell if it was there so we can tell if other things are there is by looking at the gravitational effects that they have so gravity makes things uh is a force that pulls things together so for example gravity is what causes the .

Earth to go to stay in orbit around the sun it causes our galaxy to stay together to the hundred billion stars that are in our galaxy to to have them hang together and just go around in a slow spiral uh in this slow rotation that they that they undergo uh .

But but hang together gravity is what makes them hang together so the question then is can we tell from the amount of gravity that we see can we tell how much stuff is there gravity the force of gravity is depends on mass depends on the total mass of stuff and so can we tell what the total mass of .

The stuff that's keeping the stars going around our galaxy is and then when we look at that total mass if we compare that with the number of stars that we see how do those compare okay so there's been this problem in astronomy for oh probably four decades maybe maybe a .

Little bit more than that that when you look at the rotation of galaxies there seems to be more mass that's holding in the things on the outsides of the galaxy than we can account for by just looking at the stars in the galaxy and uh so that so that that sort of .

Other stuff that seems to have a gravitational effect but that doesn't seem to be showing up as stars we can see that are producing light it's called dark matter question is what is dark matter uh first question is is it really there one thing that looked like it might be .

True for quite a while is that maybe we got something wrong about the way that the force of gravity works but there are some examples where for example we see galaxies colliding going through each other where it seems like there's a thing that got left over that's dark .

Matter that's producing a gravitational effect but that isn't um that isn't something that has stars associated with it so what kinds of things could dark matter be well maybe it could just be additional gas that's hanging out between stars and and .

Just not lit up maybe it could be little tiny black holes maybe it could be some other some kind of particle some kind of matter that isn't like uh ordinary protons and neutrons and electrons that make up our ordinary atoms we don't know for sure uh there are lots .

Of different experiments that people try to do to see what dark matter could possibly be and there's evidence and counter evidence against various kinds of things what seems to be the case is that whatever dark matter is it seems like it's not interacting much with ordinary matter .

Because if it was then we would likely see you know if it was little tiny black holes then maybe we'd settle places where there are ordinary matter that are somehow interacting with that black hole those kinds of things it seems like dark matter is something doesn't interact much at all so there are a bunch of .

Experiments that get done where people are trying to look for oh maybe dark matter is going through even deep in the earth it's kind of going through some detector that's under two miles of rock or something it's still getting through there or maybe dark matter can be seen in this place .

Maybe it can be seen in that place maybe dark matter is something like a um uh it's it's some kind of of a new kind of particle that has a mass if it doesn't have a mass well could have a gravitational effect because of its energy but but doesn't really .

Doesn't have the kind of gravitational effect that it looks like dark matter has so it probably has a mass but we don't know what its mass is and uh that's sort of the challenges to figure it out now for example in in our recent theory of physics .

There is some suggestion about what dark matter could be um because the theory kind of suggests that there can be lots of different kinds of particles like electrons and muons and tore leptons and so on we know about oh around um 20 different kinds of of particles that .

Are currently thought to be elementary the quarks the the uh the things like photons and z bosons and and so on we know about 20 of these kinds of things um and uh this theory suggests that there probably are a bunch more and particularly ones that have masses .

Very small compared to the masses of things like electrons that we see today and so one possibility is that those very low mass particles i call them oligons because they're oligos in greek means few and uh they're particles that have a very small number of sort of atoms of space in them .

And so these oligons would be a candidate for what dark matter might be um but we don't know whether that's really what's what's what's happening right now uh quite possibly the dark matter that we that exists in the universe is dark matter that got created in the very beginning .

Moments of the universe during the big bang that happened 14 billion years ago that started our universe and started the expansion of the universe um that was a time when sort of any kind of stuff that could be produced would be produced because in the big bang things were the universe was sort of infinitely hot .

And that means that particles of all kinds were getting produced um in in substantial numbers among them whatever dark matter might be and the dark matter could have been produced and interact with things in the extreme heat of the very early universe but ever since then it's been not .

Interacting with things uh so the um the question of of um and so so some things get left over from the very beginning of the universe for example the cosmic microwave background if you look in any direction in the sky um you'll see .

Uh the the the sort of the photons that were coming to us from from the very early moments of the universe well from about 10 000 years after the beginning of the universe hundred thousand years after the beginning of the universe um are uh uh that are that are the sort of .

Leftovers of the sort of heat of the big bang same with neutrinos and same probably with dark matter so that's the that's the current state of dark matter and there's some interesting kinds of physics that people are doing to try and detect the presence of dark matter .

And to try and see when there's things where it's just you just don't see anything there you see some effect from energy conservation momentum conservation or sometimes gravitational effects but you don't see any other thing there and that would be what one might call dark matter now it's always suspicious .

In science you know if you say well what fraction of the matter in the universe is dark matter well it's about 90 percent and that's always it's always suspicious when when one comes up with conclusions like that it's like saying you know 90 percent of the brain is unused 90 of the genome is unused .

Mostly these kinds of science statements end up not being true in the end um that actually there is some uh that there's there is some real thing that's there um we just didn't know how to look for it there's another thing called dark energy which is a little different from dark matter .

Um dark energy is a weirder thing it's almost it's kind of like a negative mass kind of matter that is potentially leading to the acceleration of expansion of the universe and it's a slightly more uh controversial kind of thing .

Um also has a a potential source in our models of physics all right uh let's see um got a bunch of questions here's a question here which i'm afraid i don't know the answer to uh oh maybe i do know the answer to this question is why is the sun's corona .

Hotter than its core um okay i will attempt this one see this is where it's very unfair because i'm i'm if i was like allowed to use the web and things but i'm not allowing myself to do that because otherwise this isn't a good conversation so i'm doing all of this kind of cold um .

The temperature of the center of the sun i think is 10 million degrees centigrade the temperature of the of the luminous part of the exterior of the sun is only about 6000 degrees but the corona which is sort of the area around the sun is is uh is hotter i don't actually know .

The temperature it's always a little bit tricky to define the temperature of a sufficiently rarefied kind of gas because normally what is temperature you know when we say this block of metal is at this temperature this air is at this temperature what we mean is we're looking at all .

Those little molecules in the thing the block of metal the air whatever and all those molecules are running around and those molecules have a certain average energy they have kinetic energy associated with the motion that there that they have running around .

And temperature is simply defined as the uh in terms of the average kinetic energy um it's there's a constant called boltzmann's constant after a chap called ludwig boltzmann who lived in the late 1800s um and he was the person who kind of uh uh worked on on making the connection .

Between the microscopic uh properties of matter and notion of heat and temperature and so on and so that constant k it's usually uh is named after him and and basically whenever there's a a thing in a material that can move around in a certain direction there's a half .

Kt of of average kinetic energy where t is the temperature that is associated with that thing at that temperature so for example a thing that can move around in three dimensions there's three halves kt of average energy average kinetic energy associated with .

That thing at temperature t and uh so so in in the case of the the when there's a sort of rarefied gas that is what is the corona of the sun um i i don't um i think that the heating of that is associated with so so normally when you have a .

Uh just some object out in the world and you say uh it's it's hot whatever how did it get its heat how did that energy that's making all those molecules run around come to it well there are several mechanisms for things to get heat one is conduction just you have a big let's say you have a .

Block of metal here you have another block of metal and the block of metal you just added the second one is much hotter than the first block of metal well you can conduct heat from one block of metal to the other what that means is that the interface between those two blocks of metal .

There are little metal atoms that are running around a very high speed and they hit metal atoms in the other block of metal that are going more slowly and they impart some of their momentum to the other metal atoms and so those start moving faster and gradually after every .

All these atoms have run into each other and the thing has come to equilibrium you will have taken the heat from this one side and you will have spread it equally across all the parts of this metal object and that's that process of of of spreading heat by just having uh sort of physical contact between the .

Materials and um that's the process of conducting heat conduction that's one one way in which heat gets transferred to things another way in which heat gets transferred is through radiation so what that means is uh you can for example .

Light from the sun can hit something and those photons that are coming from the sun they have a certain energy and just like the uh the other atoms can hit atoms and and give them energy so those photons from the light from the sun can hit an atom and give it some energy and therefore .

You can increase the temperature because you're increasing the average energy because there's there's energy from the light that is being imparted being put into the energy of the individual atoms and that's some that's increasing temperature that way and so the kind of radiation that .

Can produce heat um is well uh pretty much any radiation um but among electromagnetic radiation um not only visible light but also for example infrared radiation um infrared is is what is typically associated with sort of radiant heat it's it's .

It's the typical uh frequency of photons that is given off by things that we heat up to maybe a thousand degrees centigrade or 500 degrees centigrade or whatever the thing that causes heating elements on a oven or something like that to be um uh to glow .

Um red we're seeing just the visible light part of that but most of the photons are infrared photons that our eyes don't register but those are still photons that are con that have energy associated with them and they are what will heat up let's say a block of metal or something .

When those photons those infrared photons hit the metal they will kind of kick the atoms to go faster and that's what heats up the block of metal so that's the second kind of way in which heat is transferred is radiation now that kind of radiative heating photons are one way to get things hot .

Another is if you if you've broken off an electron you've broken off a proton and you're just accelerating that proton and it's something that happens uh the solar wind for example is from the sun is is an example of a place where where electrons and photons and protons rather .

Are accelerated by magnetic fields in the sun and they stream outwards from from the sun and that's another kind of different form of radiation and that form of radiation can heat things up too and i think that's what's happening in the solar corona is that um it's being heated by .

Uh the the energy associated with um uh with these particles that have been made to get to this to the speed that they get to by magnetic fields by being accelerated by magnetic fields rather than by just being heated up by standard uh as a standard .

Uh question of of the temperature of the fame uh just to round that out there's a third kind of way that you can transfer heat to things and that's convection and convection is something that happens when when something is in a gas and you say convection is .

Uh that there are atoms in the gas molecules in the gas that get heated up but those those molecules actually move around so you might have hot air a block of hot air here and hot air has a lower density than cold air so hot air tends to rise and so if we looked in this room we'd .

See these little plumes of hot air going up cold air coming down that's the process of convection that is the transfer of heat because you actually take these hot molecules these molecules are running around quickly and you're physically moving them by this sort of stream of air is moving .

Them around and that's able to transfer heat because the hot stuff is moving to somewhere where it can then transfer its heat to something else and so that's that's convective heating is when you're when you heat up air and then that air is physically moving .

Somewhere else to heat something up that it comes in contact with and um in general you know when you when you ask about uh a block of material or something and you say oh how quickly is it going to cool down i've got my my cup of hot chocolate or something and i'm waiting for it to cool down .

What's making it cool down well the the number one thing that's making it cool down is convective cooling it's that there are molecules of air that um uh get that moving around in the air they get in contact with the hot chocolate the hot chocolate heats those molecules up and then off those .

Molecules go taking away the heat from the hot chocolate and more molecules that are colder come in and and they get heated up again and so that's why when you blow on the hot chocolate you're kind of getting more molecules to move past the hot chocolate to get .

Heated up by it um and uh um that uh and that's cooling it down so in fact there's a there's a thing called newton's law of cooling it's named after isaac newton which says that the rate at which something decreases its temperature is proportional to the difference of .

Temperature between the thing and the the outside environment when you that's what happens when you have so-called free convection when you just have the thing and there's just in still air and the heat of the of your of your hot chocolate .

Is causing some air right above it to get hotter so that air has lower density so it rises and transfers away the the temperature the heat associated with the hot chocolate then new cold air comes in and then it gets heated up and transferred away and newton's law of cooling applies to .

That situation if you blow on your hot chocolate you can actually i think you get a 5 4 slaw where the where it's the temperature difference to the power 504 um so it it cools down faster if you blow on it and that's kind of why it cools down faster if you blow on it i .

Mean this this process of convection is common all over the place i mean for example inside the earth there are convection currents that are associated with the mantle of the earth which is the liquid core of the earth has convection currents in it and .

They're moving it goes they go quite slowly it's very viscous rock but it's it's molten rock in the center of the earth um and the convection currents in the earth are presumably what lead to the magnetic field of the earth they are they're moving things around .

And they're they're presumably uh like they they move also charge around and they produce a magnetic field that is the magnetic field that we detect when we have a compass or something like this the sun also has convection currents inside it um there's a .

A convective layer inside the sun it's associated with stars of a certain size sometimes you see really bizarre effects i mean for example if you have convection uh so so when you when you look at the flow of a fluid um if the fluid is flowing slowly and you've got an object and fluid is flowing .

Around it if it's flowing slowly the fluid will just sort of slide around the object and you'll see if you were to look at kind of streams of fluid you'll see that they're sort of smooth streams of fluid flowing around the object that's called laminar flow um when the flow of fluid is faster you'll start getting eddies .

Little vortices coming off behind the object and when it gets even faster you'll start getting this turbulent wake where the where the fluid just looks kind of random okay in the case of um uh of that's what happens when you just have an object and you're pushing fluid past it at a certain speed .

The other thing can happen is that this convection process can cause fluids to move let's say you have a a pan of of water or something and you're heating it from below that heating from below will cause convection to occur because again just like with air the water that has .

Higher temperature is a lower density it will rise the water of of uh that's colder will have higher density it will fall so you'll get these little convection current convection cells going where you'll have water going up coming down going up coming down .

And in the regime that's like the regime where fluid is flowing past knowledge and just sliding past and laminar flow there's a similar regime for uh for convection and actually there's some really cool effects like for example you can have this hexagonal collection of of convection cells where you look at the top of the .

Fluid and you'll see these little regions which are little uh hexagons packed together that correspond to uh the convection cells associated with little areas where where the fluid is going up down up down et cetera .

Um and the same thing is it's um uh when just like in fluid flow past uh an object when it goes faster eventually you get turbulent flow the same thing happens in um uh in convection you eventually get turbulent convection um and there's all sorts of issues about the rate of heat transfer and turbulent .

Convection versus non-turbulent convection and so on can talk about how heat exchangers work um all sorts of things like that but anyway that's the basic story the original question here had to do with the temperature of the surface of the sun .

Versus its corona um but uh i mean just to say a little bit more about the how the sun works um the sun is powered by nuclear fusion um and uh it's it's powered by the by ramming together hydrogen nuclei which are protons and releasing lots of energy associated .

With fusion um the uh uh it takes a long time for even a photon to get from the center of the sun to its is i think about 10 million years for us our star it's very it's it's it's very slow because the photon keeps on uh it like hits something it hits .

Something else it hits something else and takes a long time for it to uh after all those collisions for it to wind its way to the surface so to speak neutrinos uh go from the central sun much more quickly and the nuclear reactions that take place in the sun also produce these .

Particles called neutrinos which are particles that have that don't interact much with mata um they can a lowish energy neutrino can go all the way through the earth without ever interacting and they're hard to detect but the fact that they go so far without .

Interacting means they can come even from the center of the sun and they are like a form of radiative cooling they can take energy from the center of the sun and they just take it all the way out because this neutrino which has energy is like going all the way out of the sun it doesn't it doesn't do sort of the .

Convective process like the photon would do where it's transferring energy to something uh just by moving itself the neutrino is just like i'm out of here and it uh it exits the sun and um uh and then then goes off into space all right that was a long um answer to that .

Let's see um uh all right there's a question um here from uh sarsa um are white holes theoretical or are they real um uh what about black holes uh what happens to the light and matter that goes into a black hole .

Okay so what is a black hole how does this all work so black holes are all associated with gravity so gravity is the force that causes things to just fall towards the center of the earth they fall full towards masses so gravity is what causes uh .

Massive objects between them when we're dealing with the earth something the earth will fall towards the sound of the earth okay if you dropped something from a long way away from the earth and it was going faster and faster and faster and faster and faster .

Um and uh there wasn't any atmosphere to slow it down or anything eventually it would go at about 25 000 miles an hour before it hits the earth and the other way around if you want to take something if you want to fire a rocket from the earth and have it escape the gravity of the earth it has to go at .

About 25 000 miles an hour to escape the gravity of the earth so what happens with a black hole is you have enough mass concentrated in a small region so that the escape velocity is effectively more than the speed of light the speed of light is the fastest anything can go .

In our universe and so that means that if the escape velocity is is faster than the speed of light that means anything that gets close to the black hole gets pulled into the black hole and can never and and it doesn't that nothing can escape from the black hole so that's kind of the basic picture of .

How black holes work now then things get complicated because the theory of black holes is to do with einstein's general theory of relativity and it took people 50 years to understand even that the mathematics that came from einstein's theory actually implied this phenomenon that .

You could have this area of space where things would kind of fall in and not come out okay now there's a lot of i mean we understand quite a bit more about this from our new theory of physics but essentially what's happening in uh this picture of a black hole um .

Of of sort of things fall in and nothing can get out because to get out you have to be going faster than the speed of light that's more or less a correct picture um the uh let's see how do i get into this one of the tricky things is that in the mathematical theory of black .

Holes the thing that's significant is the so-called event horizon that is the the the thing that the point of no return once you fall into the event horizon you can no longer escape again now the question is is that really produced by .

A collapsed star inside that's producing a lot of gravity or can the theory of gravity itself have a sort of self-sustaining event horizon like that and it's a little tricky because in the traditional theory of gravity the mathematical equations say you can .

Have this thing that just exists in the vacuum it's just associated with the curvature of space in the vacuum the gravity that exists in the vacuum and all that has to exist at the center of the black hole is one point that has sort of an infinite mass .

That's a very weird thing and the mathematics of it is similarly weird it's a space-time singularity at the center of the black hole that's all you need in order to get a black hole in order to get an event horizon now in actuality in our universe when an event horizon forms it probably forms because you have a .

Collapsing star and there's a lot of other crud inside the black hole other than that uh potential space-time singularity but you can get a black hole just from that one point space-time singularity you can also get it by just having a lot of mass inside but because there's an event .

Horizon around it you think well doesn't really matter what's inside all you see is what's going into this event horizon well there's a whole big complicated story in the theory of gravity about whether there can be naked singularities whether there could ever be a singularity in space-time .

That doesn't have an enclosing event horizon and it's now known that such things are possible um and they but only in rather restricted complicated circumstances and very weak singularities but uh so you're kind of asking the question um in a black hole uh okay so what happens .

In the center of black hole the space-time singularity if it really has a space-time singularity what is it what is that space-time singularity like it's a very common kind of singularity for a so-called schwarzschild black hole and non-rotating black hole is um uh um a uh uh yeah that's a space-like singularity .

And so uh what what does that mean what it means is if you fall into the black hole and you're falling falling falling in you're inside the black hole this is kind of a weird thing to understand but but basically you always fall towards the space-time singularity and every path that you might take .

Inside this black hole leads to the space-time singularity and you always reach the space-time singularity in finite time it can in your perception of time it's like you only survive a certain amount of time and then you reach the singularity what happens with the singularity .

At the singularity time stops now in our models where we're thinking about the the progression of the universe as kind of a computational process it's kind of like computation just stops it's like you were a computer and the computer died and its brain just stopped the computations in it just .

Stopped so it has no perception of time passing because everything in it just stopped and that's what happens in the center of a in the space like singularity at the center of the most common kind of black hole and as time simply stops uh the other thing can happen is a time like .

Singularity where essentially you are you are doomed to repeat things infinitely repeat exactly the same thing forever but i think the more generic case is probably that time simply stops so the perception for anything that falls into the black hole is time just stops .

Eventually um and okay so that's in a standard black hole you can kind of see a movie of a black hole forming and all the stuff is falling in and eventually this eventualizing forms and then you have a black hole okay now you can ask yourself uh the standard laws of physics that determine how things work .

Are reversible in time so just like you might see you know if you could see a little movie of of atoms colliding with each other you could see a movie where these two atoms come in and they bounce off but the the reverse movie is equally valid where those two atoms come in and they bounce off the other way .

When we look at things on a very large scale we don't see that kind of reversibility that's a whole different story of the second law of thermodynamics effectively what's happening is that even though we start with something that's very organized the actual process of all these .

Molecules hitting each other is like doing a computation that sort of encrypts what we fed in and so we see something that looks kind of random but but that's not what's happening at a microscopic level in physics in physics in a microscopic level people things are basically reversible .

So if there's a process where things can fall in and make a black hole you might say well isn't there a process where things can well we can have the exact time reverse of that where we make a white hole where the thing is spewing out stuff um uh like uh in the time reversed .

Version of a black hole well yes you can have that according to the equations of of gravity theory you can't have that now the question is can you actually form a white hole in practice in our universe well that's a whole different story and the answer is probably not you can .

No more form a white hole then you can make something where you have you know if you break an egg the egg will be ill and or you shatter a piece of glass the glass will all be in pieces and that's something you can see happen but you don't see the glass spontaneously forming itself from all .

Those shattered pieces into a nice organized piece of glass that's the phenomenon of the second order thermodynamics law eventually increase that's what tells you that doesn't happen almost certainly there's a direct analog of that that says that white holes don't spontaneously form in our universe .

So a black hole of things sort of coming together that's kind of like uh that's that's like standard thermodynamics running sort of things forwards a white hole will be kind of like the reverse of that and it probably doesn't happen in our universe now there are things which could cause .

White holes to exist so for example in our theory of physics um the fact that the universe the universe is more or less three-dimensional has space that's three-dimensional i can move you know forwards backwards left right up down that's the three dimensions of space in principle space could have six .

Dimensions or it could even have 2.7 dimensions or whatever in our theory of physics the dimension of space can actually vary with positions so there might be parts of the universe that effectively have slightly different dimensional space we haven't seen that yet i just actually .

Was inventing a possible way to do experiments to be able to see things like that um but any case the uh so one of the things that could happen imagine there was what i'm calling a space tunnel which is basically a a lump of space that has more dimensions .

Than three well it turns out that in that case what you would see is basically one one end of that space tunnel would be a black hole the other end would look like a white hole it will be pulling in matter at one end and spewing stuff out at the other end .

Now if you ask what happens to the matter that goes into a black hole what is the fate of stuff that goes into a black hole well there are a lot of gravitational forces in there which grind things up but it's like do you actually get rid of this matter or what what happens to it well at first it seemed like everything .

Just fell into a black hole and then it would stick there and never come out then uh well uh various people jacob beckenstein stephen hawking other people uh kind of figured out that there would be radiation from things like black holes where .

Not only is um is there this was in the early 1970s this was figured out that uh quantum mechanics would imply that there should exist would suggest at least that there should exist uh sort of radiation things that come out of black holes .

As well as everything falling into black holes more or less the reason for that is in quantum mechanics in a sense there's a certain amount of uncertainty in everything and so among other things there's sort of uncertainty about where particles are and there can be uncertainty about oh if there was this pair of particles that .

Got produced did one of them is are they both on one side of the event horizon did one of them go on one side of the event horizon one of them go on the other side of the event horizon that presence of uncertainty will lead there to be particles that sort of end up sort of randomly outside .

The event horizon and able to to go off and not not get pulled into the not not just get sort of ingested into the black hole so it's been sort of a mystery uh how the ideas of quantum mechanics relate to the ideas of the formation of black holes it's a thing called the .

Black hole information paradox that you can have sort of uh information about about mata going into a black hole but then it never comes out again that seemed quite mysterious and there are slowly starting to be a few possible solutions in our theory of physics there's a very .

Clear solution to this this paradox um it's a little complicated to explain i mean i'll say the words that go around it there's an event horizon a so-called causal event horizon there's also what we call an entanglement horizon which is a different thing the entanglement horizon is the thing .

That kind of limits the propagation of quantum information and the point is that the entanglement horizon can be outside of the event horizon so it can be the case that there are things that are trapped that sort of matter that we don't we're not we're not .

We can't detect because of this various features of this entanglement horizon and there's also this event horizon beyond which we really really can't see what's going on but there's there's this region between the event horizon the entanglement horizon that can sort of maintain the .

Information of what went into a black hole and when things are getting radiated out of a black hole it's believed that at the end of the life of a black hole eventually everything is radiated out and the thing has a big explosion as so it gets faster and faster as the black hole gets smaller and smaller .

And poof eventually there's no black hole anymore um and that's as a result of quantum effects but in our kind of model that happens because there is the the information that went into the black hole is trapped between these two kinds of horizons and so it can kind of happily come out .

Again when the when the black hole evaporates that entanglement horizon is a strange quantum phenomenon that comes out of our models and it's a place where uh it's a little bit of a strange thing it's something where if you were an observer if you were hanging out near .

This entanglement horizon what would happen is that in quantum mechanics one of the issues is that quantum mechanics says many different possible things can happen but we have the idea that we can eventually we decide we measure a particular outcome .

But that process of measuring an outcome takes a certain amount of time and at this entanglement horizon the amount of time it will take to measure an outcome from a quantum measurement goes to infinity and that means that we can sort of never decide we can never .

Make the measurement we can never definitively decide did the particle go into the black hole or not and that's that's kind of how that works ah let's see gosh um uh well let's see all kinds of questions here all right we got a question um from thoth asking .

About is it possible to clone a dinosaur um and how might that work okay first of all uh what would it mean to clone a dinosaur well all life on earth is specified by dna sometimes it's a virus just rna but dna this molecule that is basically gives a program .

For how to construct for example us so like i have a copy of my genome the uh the sequence of of pieces of dna molecules that exist in all the cells in my body it's about six billion base pairs long base pairs of these agct uh groups of of atoms that exist .

On this long strand of dna which is is the thing that encodes that information so what happens is this dna this program for humans six billion base pairs long this program basically says how to make the molecules that we're made of the proteins and things that we're made of it says uh each gene .

And there are about 30 000 genes in humans um where each gene is a certain piece of that long six billion base pair sequence in our dna and it says some genes are bigger than others like there might be one that's uh one megabase long one million bases long .

And that or there might be one that's only a kilobytes long or even shorter than that um but these genes are basically specifying okay make a protein that has units a g c t t t g a c t t et cetera et cetera et cetera and that that protein is made the protein is made .

In with the amino acids the about 20 amino acids that are sort of the building blocks of proteins and those those base pairs specify the sequence of amino acids that will be put together to make each kind of protein and so we have many .

Kinds of proteins you know actin in our muscles um cytochrome um uh atp i mean lots of different things that do different have different functions um the uh the um uh so so what our dna is doing is specifying make these particular proteins .

And then these particular proteins are when we grow those are the proteins that are being produced to uh to make all the different things we have the you know skin bones eyes etc etc etc okay so our particular um uh so that's the the program that sort .

Of specifies how to make us so when we talk about cloning things what we're talking about is taking that program and using it to build a a new organism so if you were saying you know let's clone this cat for example you would take the dna .

From your cat and you would just take a complete copy of that dna and you would say let's make a new cat based on the program for that particular cat now the other thing to say is between different humans there's always a variation in our base pairs there's .

Millions of out of the six billion base pairs there's many millions of base pairs that differ between humans and we typical we all have about 700 000 base pairs that are pretty much unique to us us as particular humans because when .

When our dna was originally uh produced the um when when uh you know when when each new organism is is conceived the the dna the process of making that dna has a certain number of random mutations in it um and that and we also get half the dna from uh mother half from .

Our father and so on but there's also random mutations that happen even beyond the mixing from parents um so we each end up with a certain amount of completely unique dna that nobody else will have exactly like that okay but between if between all humans most of our six billion base .

Pairs are exactly the same if we look at a dog for example x six billion base pairs will have all kinds of differences from ours now it's actually a little bit embarrassing that i don't know what fraction is for a dog but it's quite possible 90 95 percent of the dna maybe maybe a little less than that .

Um is shared between us and dogs there's a lot of basic functions of living organisms that have very much shared and have been pretty much the same in the history of life on earth for a billion two billion years uh some of the basic things about how living organisms work .

Are really the same across many different organisms but okay so let's say we wanted to make a dinosaur well what we would have to do is get the program for making a dinosaur we'd have to get the dna of the dinosaur how would we get the dna of the dinosaur well dna is actually a pretty robust .

Molecule and it is conceivable that dna could be maintained in uh uh not decay over the 65 billion years since dinosaurs disappeared um and not um and that we might so there was a kind of an idea that wound up in in the jurassic park movie i think .

That was that maybe a mosquito would bite a dinosaur suck the blood of the dinosaur then the mosquito would get frozen in amber uh type of type of rock and it will be stuck in amber and but that molecule the molecules from the blood of the dinosaur containing the dinosaur's dna .

Will be in the mosquito that have been sort of uh embedded in the slump of amber and we'll be able to break the thing open take out that molecule and it's like hello here we have a molecule a dna program from a dinosaur okay that's one possibility there's another possibility was just .

Look at all the different organisms that have evolved in the history of life on earth dinosaurs pretty much what were dinosaurs became birds in the history of life on earth or so it seems so the things you know gradually there's evolution uh the one organism will gradually uh give rise to another organism as sort of this .

Moment when a separate species breaks off um it's kind of like an event horizon forming in the physics of black holes or something they're there for a while everybody can interact and everybody can interbreed and then then there's this kind of separation .

That happens as uh some members of a species become the as you get a separate species of things become different enough to break off um and not be able to breed together anymore but anyway so if we look at the history of life on earth there's this big complicated tree of life .

Where all these different species all these different organisms came into existence one thing we can do is say okay let's look at everything that was the successor of the dinosaurs and let's try and figure out from all these different things that came out from the dinosaurs .

Can we work backwards to figure out what the dna of the dinosaurs must have been given that they led to this kind of bird over here this kind of reptile over here this kind of thing over here you know let's pick put all those pieces together and see what the common ancestor that was the dinosaur must have been .

But okay so let's imagine that we've successfully got and when we got decent idea these days about what some aspects of of dinosaur dna must have been like but over time we'll probably get more ideas about that um as we are able to sequence more organisms as we're able to you know maybe we'll find that magic .

Mosquito i don't know but um at least we'll be able to do this sort of backward inference of what dinosaur dna must have been like okay so let's say we've got the program for a dinosaur how do we actually make a dinosaur well it's a little tricky because let's say you're cloning a cat .

For example and people have done that i think there's a there's a there's a certain tendency to call that a copycat so to speak um the uh um but in any case you you basically you take well the first kind of organism that was cloned a mammal that was cloned was a .

Sheep called dolly um and uh dolly the sheep was this was in um the 1990s um it's an interesting thing that for many many years before that time people had said cloning a mammal is impossible and i i used to ask why is it impossible explain to me why it's impossible .

People always say oh it's just too difficult there are all these things that can go wrong etc etc etc the final procedure for cloning a mammal was really weird i mean it involves basically electric shocks to to cells and things like this it's kind of like in the frankenstein .

Uh you know story or something but in any case it was there was a procedure found for cloning even mammals uh and probably work for humans too although people don't want to try that um the uh uh the sort of more junior versions of that with with making uh human organs and things that are that .

Are more interesting but um uh the the thing that um uh the thing that you do then is you you have the program for dolly the sheep and you want to actually make a sheep from it well the good news is we have other sheep so we can take that uh dna that we have from dolly the sheep .

And we can make that into the the fertilized egg um that will be injected into a you know this is in vitro fertilization for a sheep so to speak um you're putting the uh the dna from dolly into the the fertilized egg uh that is going to grow into another sheep .

And you inject that into a sheep and it grows inside the sheep and then you get a young dolly the sheep um from from the you know you had original sheep and then you were going to make an exact copy of that sheep by taking dna out of the first sheep and putting it into sort of in vitro .

Fertilization of another sheep and then getting the results out okay so notice there is an important piece to this which is you you have a fertilized you know sheep egg and into that you put this particular dna that made dolly the sheep but you have this fertilized sheep egg .

So one of the problems is for a dinosaur we don't have a dinosaur you know if we try to make a stegosaurus we might um well uh we might say well what's the what's all the stegosauruses because they're reptiles had actual external eggs they had eggs that sat on the ground and eventually hatched .

With little stegosauruses coming out um and uh so you know what about the rest of the stegosaurus egg you know do we have the wherewithal to make the rest of the stegosaurus egg can we make um uh and and um and that's a more challenging thing we might be able to deduce backwards what the dna of the stegosaurus was like .

But do we have the egg so what people have tried to start thinking about is could we take for example a chicken which is a bird and um could we take kind of a chicken egg and could we somehow put our guess about what dinosaur dna must be like and somehow put it into a chicken egg .

And and maybe the chicken is sort of similar enough to a dinosaur that the baby stegosaurus can happily grow inside a chicken egg as it could grow inside a stegosaurus egg and if that worked then eventually we'd have hatching stegosauruses and then we would have uh successfully .

Cloned dinosaurs uh do i think this will eventually happen yes i do uh we will definitely eventually have cloned dinosaurs um and they will be uh uh you know it's an interesting question how um you know what good or bad things will happen as a result of doing that .

Um but yes i think they will eventually be cloned dinosaurs and and yes you will probably whether you'll be able to go to a pet store and buy a uh you know i don't think a stegosaurus would be a great pet to have they got they got really big um but they were little dinosaurs too .

Um and so uh uh you know it's it's uh i think um the obstinate stegosaurus pet would be a bad thing to have a friend of mine has studied a lot the dinosaur motion of dinosaur tails and he's pretty sure that some dinosaurs could whip their tails around at supersonic speeds .

So you don't want to be near a dinosaur that isn't happy about what's going on um but uh uh anyway that that's um so yeah i think that's a um that's something to look forward to in the future um oh my gosh so many questions um there was a question here from icy .

About how do we tell i'm not sure if this is a good one so really cover but um there's a question here about how do we tell the difference between science and pseudoscience uh you know people call things pseudoscience when they believe that they're nonsense .

Um sometimes things that seemed like they were pseudoscience turn out to actually be science and actually be true and sometimes things that people thought was pseudoscience turn out to be as people expected nonsense and it's uh it's often quite challenging to tell the difference .

Because somebody can have an unlikely theory for something but it can turn out to be true and it was just unlikely because everybody was off thinking something completely different was true um so you know there are so there are there are particular areas where people .

Uh will say oh that's pseudoscience so i'll give you one example it's not so popular in the in modern times but it's popular in the past is um things like extra sensory perception and telepathy and so on so what's that about so you know we communicate by talking to each other we say .

Something somebody else hears it we can communicate by gesturing around and people can see what we gestured but there was an idea at one point that it was popular in the in in up until oh probably 20 30 years ago that there might also be direct brain to brain communication that might be the case that the .

Something associated with the thoughts that we were thinking would be transmittable to another brain directly without us talking without anything else maybe it's some electrical process maybe it's something it's not clear what it is so so that was a that was a thing and people studied it and the people did .

All kinds of all kinds of things where they would have one person in a room who was looking at cards and they would have another person outside the room who was trying to think very hard and try and imagine what card the other person was seeing by by virtue of this kind of extra sensory perception this telepathy and so .

On and there was a lot of study of that and how that worked and you know was it what people guessing the cards more often you would expect by chance and so on and in the end that looked like pseudoscience because there was no sort of significant effect that was .

Found but if we ask the question could there be brain to brain communication could it be the case that the electrical uh signals that are produced by our brains are somehow detected by another brain is that absolutely physically impossible no it's not impossible i mean you know after all we can perfectly well if if we .

Measure our brain waves we put an electrical sensor on our heads and we measure brainwaves well we can you know there's a thing outside of our brains that is sort of extra sensorially uh detecting what's going on inside our brains it's a big jumbled mess right now we .

Can't really tell there's no good way to say oh let's put an electrical uh detector on our brain and say okay i'm now thinking about a dinosaur type thing we can't read out the information yet about what our brains are thinking although i suspect eventually we'll be able to do much better at that .

Although one thing to realize is that what's happening inside our brains is probably really different for each person you know in human language the way human language works is that we're all saying the same word to kind of mean the same thing language is this kind of social thing .

Where everybody has to agree that the word camera means the same kind of thing but what's going on inside our brains there's no reason for the kind of way that i represent knowledge inside my brain to have anything to do with the way that somebody else represents knowledge inside their .

Brain there's nothing that is causing us to communicate directly the internal representation in terms of electrical signals and so on of knowledge from brain to brain but is it possible that there could be some sort of brain to brain communication sure it's possible um is it uh uh and you know when we look at .

Computers again if we looked at you know if you if you take a radio and you put it an old-fashioned like am radio or something you put it near a computer and i haven't done this for a few years i don't actually know what happens anymore but it used to be the case that you would hear .

On the radio detect you'd be able to detect the kind of the thought processes going on in the computer you'd hear nasty sound weird sounds and as the computer does different things uh you'd hear different uh different signals and you know you can you can often tell if you if you make your computer do a lot more .

Work you'll hear the fan come on because the computer will be using more power and its fan will automatically try and cool it down and things like this you can you can there are similarly electrical signals that differ depending on what this is what the computer is doing just as presumably there are things in .

Our brains that are different we certainly know that there are things in our brains that differ when you go to sleep things like that we have different uh brain waves and so on so yeah so that's an example so telepathy extra sensory perception is an example of something .

That is today firmly in the bin of pseudoscience will it turn out that it's a real thing will it turn out that you know ants really have that as well as being able to lay down chemical trails for each other will they in fact will it be discovered that you know the brain of an ant can .

Communicate directly with brain of another knight it's possible right now people would say that pseudoscience whether it will stay pseudoscience i don't know sometimes there are things that are in in science so to speak that turn out to be total nonsense .

Um and that people have believed for a long time i mean there are a lot of things around um uh this pandemic where we're we're getting uh you know more aware of a lot of things in immunology but people have said it never works that way but actually it does and we're .

Discovering that it actually works that way and so on so there are a lot of things where people would have said oh no no that's a that's a kind of pseudoscience theory but actually turns out it's not so there's a it's a it's a bit of a more complicated uh .

You know interchange between sort of science and pseudoscience than one might think and sometimes things can be believed as science for 50 years 100 years and it just turns out to be nonsense i mean you know it was believed for a long time that you know the shape of one's head was an important .

Determiner of one's personality i don't think people believe that anymore but there were all kinds of scientific studies that showed that and uh you know it turns out to be nonsense um uh or to a large extent nonsense and just like there are other things where people believed that you know .

The germ theory of disease the fact that there was some invisible vector that was causing disease to happen that seemed like pseudoscience that seemed like nonsense for a long time until it turned out to be true so it can be a complicated thing to tell the difference between science and pseudoscience .

I would like to say that after all the years of experience that i've had in in doing science and trying to tell the difference i i do better than the average probably in that i'm trying to think of an example where i've been wrong um about uh how things would come out there um .

There have been cases where i sus where i thought the theory was a little bit crazy but it turned out to be right i wasn't sure the theory was wrong but it seemed more complicated than i would have expected to be to be the kind of theory that would turn out to be right and it turned out it was .

Right all right let's see gosh so many questions here and i'm running out of time um ah let's see um oh there's a question here's a quite a simple one in convection what drives the flow of air and fluid in the first place .

What drives it is simply that hot fluid is lower density than cold fluid so it floats on top of the cold fluid so it's it's it pulled up by by the um uh by the cold fluid and and convection starts up when fluid is heated on a surface and then then starts rising .

Um let's see um all right there are questions here about some a few quite fairly simple ones is there any possibility for the creation of dark matter in a fusion reactor like a tokamak um we don't know for sure but i'm guessing .

The answer is no and why do i say the answer is no if dark matter was going to be produced you would see processes go on so dark matter has mass it has momentum it has energy so what you would see is you'd see particles coming together and they would uh particles come .

Together they have a certain amount of energy and particles go out and then there'd be missing energy there'd be something where you don't see what comes out but you know it has energy because total energy is conserved the energy coming in is equal to the energy going out but you only see some of the energy coming out .

It'll be like a miniature version of what we see in galaxies when we see sort of the presence of dark matter although that's more gravitational effects this would be the fact that there's energy that is disappearing and it sort of seems dark now historically this kind of happened .

Before because there were nuclear decay processes nuclear beta decay where we precisely saw things like um uh you know another nucleus would be produced an electron would be produced and it'd be whizzing off in some direction and it's like how is momentum conserved .

In this case we've got this electron whizzing off in this direction and there's nothing compensating for it sort of going the other way well that's what led to the invention of neutrinos the the realization that there was another kind of particle it was just something we couldn't see .

It seemed like kind of a dark matter kind of thing i it's a particle that has no charge it doesn't interact electrically it has only uh so-called weak nuclear interactions um and neutrinos are very weakly interacting things they can often go all the way through the earth for example .

Um and so that's an example of of something like a sort of previous version of something like dark matter that um uh existed uh that exists in the universe and so people have certainly looked for dark matter where it's like some process happens .

With particles colliding and have a certain amount of energy and whoops we missed the energy people have looked for that and haven't seen that so that's a that's evidence that doesn't happen often at least so i think that probably is not a process that can make um dark matter but um i i you know it's an .

Interesting question and maybe it can make it as small um uh at a small rate all right i am supposed to go to something completely different now but um i am just this is so much fun i'm i'm um uh oh gosh there's so many questions i want to .

Uh want to answer here so there's one from william here why is the moon the same size as the sun when seen from the earth that is really a coincidence uh eventually it will be smaller the moon is gradually moving away from the earth and eventually it will uh not be you know right now you .

Hold out your thumb i don't know whether this is uh and you can more or less cover both the moon and the sun uh with the with the angle that you get to um you know in um uh i think in babylonian times they used to measure angles on the sky by such and such a number of fingers .

Um you know when you hold your hand out at a certain at that sort of uh your fingers are a certain size there's a certain angle there but any case so right now for we are the unique planet in our solar system where the um actually i don't know this absolutely i think we're the unique planet where a moon .

Of ours and we only have one moon uh just exactly covers the size of the of the disk of the sun which is why when you see a total solar eclipse i've seen two in my life they're really cool worth going to see them um the you know the the moon when it moves in front of the sun .

Just exactly covers the the sun they more or less exactly match in size um if we're on mars for example the moons of mars phobos and demos are tiny compared to the disk of the sun on mars um and uh the um uh so in time so be be glad you live at this time in history .

You know in another uh in another probably even another 50 million years 100 million years uh you won't be able to see nice total solar eclipses on the earth that that same way because the moon will move too far away but i think it's sort of a coincidence of current times .

But that's what we see uh all right well i'm so um oh boy there's a question here this one's easy to answer uh the question what do you do for fun for me this is a good example of what i do for fun this is fun for me uh it's uh .

Um uh what else do i do for fun i i do science for fun um i uh i do i'm a tech ceo for fun i kind of like to do the things that i like to do so to speak and i've kind of tried to arrange things so i get to spend as much of my time doing things i like as .

As possible and usually i at times i develop various kinds of hobbies and somehow almost every hobby i've ever developed has eventually turned into a real thing so i kind of had hobbies of studying history and i've written some some some books about kind of um uh .

You know the book of like a book of historical biography and things like that and i you know that ends up becoming a thing that i do um i don't know what's going to happen to this particular hobby that has been uh sort of originally i i started doing these um .

Q a's uh because i wanted to uh uh uh help out in in the pandemic but they're really fun and um this is what i an example of the kind of thing i do for fun and um i'd better go and um uh do some day job tech ceoing because that's the next thing that's up on my agenda .

Actually talking about um uh um an initiative that um we are going to be pursuing as the pandemic continues uh in education and maybe i'll talk about that another time all right well thanks very much uh see you again next week and um i'll try and uh cover some of the .

Questions that came in here and i didn't get a chance to to go through next week so please tune in again thanks okay bye-bye

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