In Class With Brian Cox 2018

welcome to in class with Brian Cox I'm Alan Duffy lead scientist of Australia's Science Channel Professor Brian Cox is here with us for ABC stargazing live of which I'll be apart but you can be too if you join in the Guinness world record attempt for the most people stargazing at one time on Wednesday night you can also catch Professor Brian Cox in 2019 during his Universal world tour now we're joined by thousands of students in hundreds of schools streaming on Australia's Science Channel many of you have asked incredibly good questions and I don't know that we're going to get to them all today but we're gonna try our best so let's get started Brian we have questions from year two in Salisbury primary school Shakira asks how the moon was made that's a good question as often is the case with science questions there's not a complete agreement but there is a theory that with which most people agree which is that it was made in an impact so very early on in the life of the solar system so let's say four and a half billion years ago or so we think that a planet about the size of Mars collided with the youngers and although a glancing blow actually which caused a lot of rubbles to go out into space formed momentarily a ring around the earth somewhat like the rings around Saturn but then that ring very quickly coalesced into the moon so we think that the moon is made of mainly bits of the earth and also bits of this other planet that glanced off it about and that should be exactly I think something like four-and-a-half billion years ago it's very very early very soon after the earth formed I think maybe two three hundred million years after after we were beginning to form yeah all right Cameron also in year two wants to know if you can describe how big the biggest star in the universe is oh that's a good question and so I I don't know that the figure for the biggest star but the one of the biggest you can see and with the naked eye actually is Betelgeuse orbital goes in Orion and that so that's the red star and in the constellation of Orion to say but I can't because the orientation is different here but it's a top-left but it's not it's gonna rotate it over the head straight till your head find Bethel goes it's a red star in Orion the shoulder of Orion and what's interesting about that is you put it where the earth is then it would extend out pretty much to the orbit of Jupiter I think even beyond the obvious of Jupiter so you imagine how far it is to Jupiter that will be all waiting inside the star and it's so big that we can see sunspots on the surface with telescopes here on earth it's a vast star but that dad isn't that's a star at the end of its life that's swollen up that isn't however the biggest and so what we should probably do is that an I should go onto the Internet I don't have in my head the number for the most massive star or the biggest star but there are stars that really literally the size of solar systems there maybe even the pop three stars I was thinking those early very first stars yeah ten thousand times the mass of our Sun but absolutely enormous objects but we've not been able to see them yet yeah well they have very short lifetimes that's the thing so that the more massive the star is so you're talking about you said a star let's say 10,000 times the mass of the Sun then it has to burn its fuel extremely quickly to stay up against the force of gravity and so they live millions of years actually the lightest I'm not not billions of years so they're very very very short-lived they're really massive stars in the universe okay so lots of students from around Australia have asked how many stars there are in the universe but as a follow-up how many do you think we will be able to see on the stargazing live attempt ah so the the number of stars you can see first of all is actually only a few thousand I think it depends obviously depends on how big the telescope is that you have all of the stars we can see here in our galaxy the only thing you can see beyond our galaxy well there are three things in the southern hemisphere you can see the Magellanic Clouds which is satellite galaxies of the Milky Way and you can also see Andromeda with the naked eye and that's pretty much all you can see beyond our galaxy without binoculars or a telescope you some good binoculars and you start to see tens of galaxies or in a small telescope you can start to see tens or even hundreds of galaxies out there and the number of stars in the universe that's a so there are something like between 200 and 400 billion stars in our galaxy and you might think that's why it's not because I don't know it's because nobody knows it's quite hard to count actually so it changes how the design the estimate but let's say conservatively 200 billion that's 200 thousand million stars in our galaxy and the current estimate for the number of galaxies in the observable universe which is a bit we can see is around 2 trillion so that's 2 million million yeah that's right two million mate so we have something like let's say 2 million million galaxies that we can see in principle and each one of those has 200 thousand million stars let's say on average so you have to multiply 2 million million by 2,000 so that's a 6 and they're saying that's 18 19 20 21 so it's something like let's say 4 with 21 knots after it we're checking that to 2 trillion is 2 million million so that's a 2 with 12 knots after it and then we have a let's say a 2 with 9 knots after it so it's a 12 and a 9 so that's 21 knots and probably 4 or 5 so let's say 22 so let's say 1 with 22 knots after it's something like that however that's the bit of the universe we can see in principle it's called the observable universe we very strongly suspect that the universe extends way beyond the bit we can see it does for all intents and purposes and we don't know how big it is so it could go on forever we just don't know and so you know these are big numbers ozzie kids are very curious about alien life we have many questions on this students from Clapham primary school have asked probability favors the existence of aliens why haven't we observed any so and what you mean by probability favors the existence of aliens I guess you mean and I'd agree with you that the universe is so big I mean we just said there is something like one with 22 knots after it stars in the observable universe we now know that most of those and have planetary systems and certainly if you look in the Milky Way at which we can do in our own galaxy basically everywhere we look we find planets around the stars so let's say that most of them have solar systems so it is inconceivable that there will not be life and that I think civilizations out there amongst the Stars and but the question becomes first of all what form does that life take so in the solar system we know there's only one place earth which has complex life and certainly a civilization like ours it could well be that there are microbes below the surface on Mars today or there may have been microbes on Mars in the past when Mars had rivers and lakes and quite possibly oceans for a few hundred million years and so there could have been Martians but there would have been little microbes or bacteria like things at best I think and on the moons of Jupiter and Saturn like Europa there are oceans below the surface and we think the conditions are rights for life's who have started but we don't know because we haven't been there so if there are aliens in our solar system there were little single-celled things waiting for us to find them some of you might discover them actually because we are building missions to Mars will be sending humans to Mars certainly in your lifetime and one of the things you'll be doing is looking for microbes below the surface so maybe we'll find Martians but if you mean aliens in spaceships that means civilizations and we don't know we've looked a bit we've listened for radio signals from other stars we found nothing we have no evidence of alien civilizations at all that might mean we haven't looked hard enough because we haven't looked particularly hard the galaxy is very big but it might also mean that civilizations are rare and the one thing I would say is if you speak to biologists they will be more pessimistic about discovering civilizations than astronomers I think astronomers tend to say though they give loads of planets loads of planets there must be some but biologists say well but if you look at life on Earth it began we have good evidence it was on the planet let's say 3.8 billion years ago so let's say it may have begun even four billion years ago after the planet settled down in the oceans first formed it took four billion years let's say to go from the origin of life to a civilization which is about a third of the age of the universe and if you start to say well if that's typical and we don't know then it may be that there are very few solar systems and planets and stars that are stable enough for that long to allow for evolution to do its work and for the single-celled things to go to multicellular creatures and plants and make an oxygen atmosphere and and then make a civilization you know get some things that are clever enough I mean you think about there are clever things on earth besides humans dolphins for example but dolphins are not going to build spaceships because they can't have any electricity because they live in the sea and so you know it can hey could be but quite typically if things with big brains tend to be under the water then they're never gonna build radio telescopes and spaceships there won't be astronomers if they can't see the water stuff well that's right though the ice bond aliens if they exist in Europa yeah they have no idea of the universe around them no and and and you can't need you try to do electronics underwater [Laughter] underwater hydeia good fine we try to invent I mean try to invent it yes you will not build a teleological civilization yeah if you're intelligent being in a sea I guess there's a very quick follow-up from Mandurah Baptist College Brody has asked if they did it did exist could we contact them so if civilizations exist then yes we could and again the distances are important if you think about our galaxy it's like say hundred thousand light years across or so that means that it would take a radio signal 100,000 years to go from one end to the other so it would be a very slow conversation I mean even our nearest star and Alpha Centauri the nearest star system with planets around it we think is four light-years away or so so that means that a conversation would take eight years so he said hello you have to wait for eight years before they said hello back and that's our nearest star system so the distances tend to make conversation difficult toby creamer from Sunshine Coast grammar school and the class of six ale from Dane Bank school have asked when the Andromeda and Milky Way galaxies collide will their black holes merge or will they remain as two separate entities and what does actually happen when two black holes meet so the first answer is I don't think we know when the Milky Way and Andromeda collide whether the black holes will merge I mean we certainly know there's an interaction between the galaxies we know they will the galaxies will merge so I may be their own my guess not actually knowing the latest researches they probably would eventually I think but it depends on the angle that they hit each other and so on and so on and also the timescales I mean it may be that they'll inevitably merge in trillions of years for not billions on there eventually they will but yes it could be billions it could be aliens yeah so right so so maybe the consensus here is that they they will do eventually but it depends what you mean by eventually it yeah and but we do know what happens when black holes collide because we've observed it so and our latest detectors which deserve so called gravitational wave detectors which detects unbelievably ripples in the fabric of the universe ripples in space and time from the collision of objects like black holes are now working beautifully and we've seen several occurrences in the universe where black holes have collided with each other emerged and so what we know is that they form a black hole they lose some energy when they collide but they do form a black hole with an area an area surface area which is bigger than the two holes that collide and that was a prediction from Stephen Hawking this so-called area theorem and that's been proved so and the prediction of how they collide and how they merge and what you get afterwards is in absolute accord with Einstein's theory of general relativity which was published over 100 years ago and Einstein didn't know that there was such things as black holes when he published a theory he certainly didn't know that we'd ever see them collide together he certainly didn't know that there were ripples in the fabric of the cosmos although he predicted that slightly later they would carry the the information just like light carries the information from distant stars so the ripples in the universe can carry information from collisions of black holes so we've in the last couple of years we've entered a new age of astronomy where we can watch black holes collide so reverse Stephen Hawking's area theorem which seems to have been proved by these collisions now says that if you collide two black holes together then the the area of the horizon around the new black hole has got to be bigger than the area of the horizons of the two little black holes and that seems to be what we've seen what is that thing the event horizon is the area around the black hole from which light can't escape so if you if you go into a black hole she could do if it's sufficiently big or sufficiently massive you could fall in through this point there's this sort of region of space around the hole and you wouldn't you could easily fall in and happen when you fall in is that you could never get out again and you couldn't even even send the signal of light out of the black hole because the gravity is so strong that the light can't escape and the region from which the light can escape is called the event horizon or inside this event horizon and that's what you see you at the black hole if you could float around and see one you wouldn't see anything because it would be blank but you would see this this sphere or this shape in space from which no light would emerge and around which all the light from the distant stars and the galaxies would Bend and curve and be warped so that's it there's a very strange thing to black hole and I should also say we don't know what happens right in the middle so it's called the singularity that's where our physical theories break down and that's another thing for you lot to go and do what probably someone of your generation will work out how to how to do the physics to say what really happens in the middle well it could be Andrew year six at Basin primary school and Tia from year six at Mark Oliphant College who are curious about what's in the black hole the singularity is it they ask is it a highway to another dimension or are there different universes inside well so first of all what what happens in there so let's say the ones by the way the supermassive ones are the hearts of galaxies we don't really know how they form it's one of the the things that end the Square Kilometre Array mainly north of Perth here in Australia is going to look at the formation of the first stars and galaxies to try to see to understand how those enormous things you know many millions of times the mass of the Sun get into the center of galaxies and but the smaller ones the little ones but said the ones we've seen collide which had about 30 times the mass of the Sun the big ones we've seen two collide those formed by the collapse of massive stars so what happens is a star is holding itself up against a pull of its own gravity she's trying to squash it down because of the nuclear reactions in the core of the star so because the star shines and that produces a pressure if you like the Holzer thing up but it can't keep burning its fuel forever and when it runs out it will gravity will take over again and in the case of the most massive stars there no known physical process can stop the collapse so gravity wins so it just collapses and collapses and collapses as far as we know forever so you get an infinitely dense point of what I can't even call it matter it's gone really all there is left is the gravity in some sense now we don't know whether that's true because we don't know the physics when these things get so so dense and so so tiny we don't know what the physics is so it may well not be just this infinitely dense point we we just don't know but so we give it a name the singularity but all that's left that you can observe in the universe is the gravity all the matters can have gone into this so it's one of the great questions in physics and it's very strange that strange things happen for example you can we can work out what the the circumference of the black hole is so that so we go round the event horizon and say well it's so big but if you say what's the distance from the event horizon to the center it can be infinitely big as far as we can tell so it's like it's hardest inside in some sense inside a black hole so we just don't really know but it can be it can be a lot the radius can be a lot lot lot lot bigger than the circumference would suggest because of the curvature and bending of space and time so they're really weird basically year 12 at kep knock State High School ask about the gravity of the black hole since gravity pulls things into a black hole why can't light which has no mass escape oh so and you're kind of correctly thinking about gravity in terms of the way Newton described it which is that it's a force between massive objects and bloody nine Stein's theory which is better than Newtons it isn't that it what it is really is that you say we imagine the universe really you can imagine space and time as our fabric it's often called the fabric of the universe and the the sub picture that many people use which is quite a good picture if you imagine putting something like a bowling ball or a cannon ball in the fabric then it curves it and maybe so you can imagine this sort of curved so well in the fabric which goes down so where the heavy thing the massive thing is and maybe imagine rolling a marble or something around there then it's not gonna go in a straight line it's gonna bend around and that's the same for lights as well the the light waves or the the particles of Lights if you like called photons follow just paths through the curved space in the same way that massive objects follow the path through the curved space so Einstein's theory naturally predicts that light is bent in the same way that the path of light is bent in the same way as a path of anything else through through the curved space the students of year 10 T from Saint Peter's Lutheran College want to know what do you think is currently the most exciting area to study in cosmology and why I think it's black holes which we've been talking about a lot and I'll give you two a couple of answers but black holes are interesting and they're interesting just because they're interesting who talked about them they're really weird but that the point is that also to describe them properly and to describe the collisions you start to need to get a better version of Einstein's theory and so Stephen Hawking is probably most famous for something called Hawking radiation which is the idea that black holes have a temperature and radiate because they have a temperature they can radiate energy and particles back out into space again that's merging the laws of what we call quantum mechanics but the laws of how atoms and molecules behave with Einstein's theory of gravity and that's one of the probably the biggest challenge in theoretical physics is to merge those two things together no one has been able to do it yet but the first steps were taken by thinking about black holes so that's one of the reasons black holes are fascinating and that really links in it's that language we also would need to describe the origin of the universe so the very origin of the universe so the Big Bang or maybe what happened before the Big Bang did questions like that ultimately we need better theory that Einsteins and the black holes are probably the testing ground at the moment for such a theory okay John from year 12 at comet Bay College asks do you have any advice for an aspiring theoretical physicist and I love this did you follow that advice or do you wish you had oh so my advice is to practice mathematics that honestly that's a maths is I don't know about you but it's it's not something that comes just completely naturally to most if not the majority of physicists and never mind mathematicians I think and what it is is I always think of it as playing an instrument or learning an instrument or a foreign language actually which is the only way to do it is practice and the more you practice the better you get at the language and as Galileo said mathematics is the language of nature so you have to do it and it becomes fun but it becomes fun and really exciting when you practiced it so that you know the language and I wish I'd followed that advice because I it took me quite a while to him to realize that actually the only key to mathematics is is just it's just practice yeah very similar and actually I didn't quite fail but very nearly the group Theory class that was my mathematics ceiling at university Manchester yeah because I didn't do enough practice and it just escaped me yeah it's it's it's really important I think Einstein once said famously that when he was young he was no Einstein he what he meant was that it's not you know there's this kind of idea that you there's some kind of freaky genius type people who become scientists and it's not true it's just people are interested in astronomy or biology or you know collecting butterflies or anything and then do the practice and want to do that as a job and that's it's all about being interested isn't it absolutely and then and then doing a bit of practice okay carlo in year 5 has a brilliant question about exploring planets with different properties to earth and he's asked as Jupiter is made of gas could you fly a rocket straight through it no but it's a great question so you could you could fly a rocket through the upper bits of its atmosphere and where it's not quite as dense but if you go down in towards the core of Jupiter that the pressure becomes so high and the temperatures become very high we think there are all sorts of exotic materials we don't really know what's at the center of juice so we have a spacecraft called Juno at the moment which is orbiting around Jupiter to answer that very question trying to work out what is actually in the middle within there exotic things called metallic liquid hydrogen and all sorts of really strange materials for them if you tried to fly a rocket through the center it wouldn't get very far it would get squashed and crushed and melted and then it may well hit something very solid indeed in the core but we that's these are great questions that's such a good question that NASA built a spaceship to go and try and answer your question which is there at the moment as we speak okay Gordon from the gap senior high school and chungee in year 10 at Keys borough Secondary College want to know what advances are needed for humans to be able to colonize another planet like Mars how many years is it likely to before this becomes a reality and will it involve terraforming so the answer is that no technological advances are required for us to go and colonize Mars to visit Mars first and then colonize it we have the technology now that Mars is it's an easy it is well it's actually the only planet other than the earth that we will ever colonize I think it's fair to say if you think about it Mercury's too hot Venus is really too hot and the rest of them are made of gas so perhaps the moons around the other planets we could so Mars Mars is the only planet will colonize beyond Earth but it's an easy planet to colonize it's got water in abundance below the surface we're sure or frozen in the ice caps it's got all the minerals that we need to build a civilization we have the technology to go and extract the water and turn the water into oxygen and hydrogen for us to breathe and to make rocket fuel and let twist see all the things we need there's lots of iron there plots all the stuff you need to build a civilization so we know how to do it so it's just whether we want to or when we want to we have the rockets that can take us there and so any one of your generation could walk on the surface of Mars and I think you will if you want to because because we can do it I think we will do it and I think we'll do it within the next anyone go there in the next 20 years so when you're about the right age to be working on those missions actually and I think we'll have permanent bases there I don't know probably probably at that point the most of the plans I've seen to go to Mars involves setting up the base first with robots and then going to the base so it's almost we build the base first and then we go and move in and I think that's what we're going to do do you think we need to terraform well so terraforming is changing the atmosphere of the planet and that's a longer-term goal but we we can and we know that we could do it in principle and ultimately you'd want to grow plants on the surface when when you made it hot enough I should say that there's a place called Hellas Basin on Mars which is a big almost certainly an impact crater it's a well impact Basin actually and it's so deep that we stand on the edge of the rim of the helis basin it's nine kilometres down to the floor so that means that although it's so big you couldn't see it if you forever ax stin the middle you could look down on the summit from the edge you couldn't actually could the summit of the over the horizon because it's such a big thing it's a quite a big part of the planet but it's so deep that the atmospheric pressure is so high at the floor of the crater that liquid water can occasionally exist to the floor so already although Mars is atmosphere is very thin there are places that are so low in altitude that the pressure is high enough the liquids who exist momentarily they're even now so you can see that the atmosphere of Mars doesn't need a lot it needs things like greenhouse effect carbon dioxide and things thrown into the atmosphere but then you can imagine growing plants and the planets would produce oxygen and the waters for them to do that and so you could imagine at some point in the future that we end up with a an atmosphere on Mars again again because it did have one once karinna at curtain grammar school asks do you think that one day we will use wormholes to time-travel oh it's a great question that I should say what they are so they're a bit like black holes actually they're they're a place where space and time the fabric of the universe is very curved and you but you what the picture is he's not just like a black hole where it's curved and it goes down to this singularity whatever this is and by down you know what I mean I think you have to imagine four dimensions and we don't to do that anyway but wormholes would be you'd picture them as instead of stopping at the singularity they'd come and open out again to another bit of the fabric of the universe so the analogy would be so I came to Australia last week on a plane from London so and I had to fly all the way around obviously around the surface of the earth which took about 20 hours but you could imagine taking a shortcut drilling a hole from London to Australia and then I could get here quicker because that's a shorter distance and having to go all the way around a wormholes work like that and it's one of the big questions in theoretical physics whether those things first of all can exist they do they can give an Einstein's theory people can imagine that kind of geometry if you like but there's a question about whether they would be stable so there's a question about whether if you tried to send information through them then they would collapse and it's a big debate at the moment actually Stephen Hawking used to paper and which is you guys got a fancy name called the chronology protection conjecture now that means in fancy words what your question is like could you use it's a time machine to go into the past and I think most physicists think not they think that the whilst they could exist they would be unstable and collapse again and so you'd never be able to send information through let alone a person even one little light signal wouldn't get through it into the past but we need as we said before then the more unbalanced theory the quantum theory of gravity to be sure so there is still a bit of a debate but I think it's fair to say I don't have you'd agree I think it's fair to say that most theoretical physicists think well although we can't prove it yet we think that they won't exist it just gets messy if if they do exist if we're used for time it does just get a bit messy people think about little ones those subatomic sized wormholes that really might exist and really might be the key to understanding the laws of physics and in a better way than we do at the moment so it could be that on a subatomic scale space and time are covered in these little wormhole e things that go around and that might have something to do with the world that we see today but on the big ones no who knows who knows the interesting debate to be had yeah maybe you can help answer that actual question Dylan in year 8 and ty in year 9 are curious about multiple universes and they want to know what do you think the chances are for that parallel universes exist and is there actually any proof for the multiverse theory so first of all there's no proof and and secondly there are lots of different versions of what you mean by parallel universes the multiverse though the one that and one of the ones that's interesting to physicists is something called the inflationary multiverse so what is that well the idea is our best theory of let's say the way that the galaxies are distributed in the sky so we can map that so if something we can observe we can look at where the galaxies are then we have a big map it's called the Sloan Digital Sky Survey of where the galaxies are and when you look at them then there'd a random in a sense but there's also some pattern to it and and in particular they tend to roughly speaking lie on circles in the sky so they're not completely randomly distributed and we can trace that all the way back to patterns that we see in the oldest light in the universe which is the light that if we look as far as we can add into space then we're looking back in time you might be ready to participate in the record event so go in the stargazing world record to go and look out at the night sky and get the most people ever looking out into the night sky at the same time you could also likely I think see the Andromeda galaxy not quite sure about the time when it's gonna be open but look at the Andromeda galaxy you've seen light coming from it which has traveled for 2 million years so you're looking back in time 2 million years because you've seen the underarmor galaxy as it was 2 million years ago we can look so far out into space that we can see the light from just out to the Big Bang about 380,000 years after the Big Bang actually and in that light before there were stars and galaxies there are also patterns which patterns that match on to the way the galaxies are distributed in the sky today and then where did those patterns come from well the best theory we have is a theory called inflation which says that before the Big Bang in the sense that before the universe was very hot and very dense it was still there and it was kind of cold and empty but expanding very fast and then that very fast stretch of the universe came to an end slowed down and in the slowing down the universe got heated up and all the particles at which the stars and galaxies are made were created so that's called inflation and many physicists think so there's good evidence for that and now many physicists think that that inflation doesn't all stop at once but stops in little patches and so you have a little patch of this extremely expanding universe it slows down and makes a big bang and that would be our universe and then the rest of it carries on another little patch slow down stops and you get another big thing and that would be a different universe and another it starts to get a big bang in a different universe and so on so that's called the inflationary multiverse which is what was in your question a multiverse a load of bubble universes if you like essentially an infinite number and that could be our reality it really could be that our entire universe which is much bigger than the universe we can see with two trillion galaxies in it is one bubble in a multiverse of bubble universes and then is there any evidence for that and there's evidence for the inflation bit which slows down and stops there's no evidence for the other bubble bits so could we ever see evidence people speculate that you could perhaps in the in the most ancient light in the universe see a pattern that suggested that maybe there was a nearby bubble that formed at the same time but we haven't seen it yet and or it could be that the theory becomes so well developed and it describes things so well that we see in our universe that you start to think well the theories suggesting that this is the only way things could be and but we're a long way from that so the simple answer is after all that is no there is no evidence the multiverse is in that sense but it's plausible because the theory that sort of predicts them also predicted the stuff that we can observe Michaela Lacey's year 7 class at Christian Brothers high school wants to know how do we actually know that the universe is expanding oh so that's a good question and this is a really simple observation you can you can almost do it yourself actually and you can with a bit of quite advanced amateur astronomy kit but not a big professional telescope you can do this so what you do is you look at the light from distant galaxies so you have a big enough telescope that you can see a galaxy that's quite a long way away and you look at the light from it what you find is that for all galaxies that are not too close then the light is stretched so you think of light as it as a wave a bit like a wave on water so it peaks and crests then the distance between two peaks gives you the color and so red lights has got a big distance between the peaks and blue light has got a smaller distance and what you find is that from all galaxies that are further away than the closest ones that the light is stretched so that the colors of the light from the galaxies are a bit redder and what you find is the more distant the galaxy the more the stretch so that's the observation and that's exactly what you'd expect if the galaxies were riding along on a stretching fabric the fabric the universe if you like that means that the further away the galaxies are then the the more stretch the light will be why because it's been journeying through the stretching space for longer so it's got more stretched and that set it's called the hubble law actually it was the first observed in the 1920s by Edwin Hubble so it's a very simple and direct observation okay some more general questions just to wrap up Morgan from the Charter tars school of distance education asks topic very dear to my heart what is dark matter something easy to finish I don't know and so why do we think it's there so the observation is there are many observations actually one of them is just that galaxies and spin round faster than they should essentially so and if you think about something going around very fast then the thing that keeps it in orbit is gravity and so if you look at how fast some things going around like let's say a star on the edge of a galaxy you can see how fast the galaxy is rotating and that allows you to calculate just using newton's laws how much stuff there is in the galaxy and what we always find with virtually every galaxy I think apart from one that was seen recently is that there's much more matter in there than can be accounted for by all the stars and so that that's the the observation that there's some dark matter stuff that you can't see shining are stuff that isn't gas that the absorbs or emits light that's in the galaxies and and that so you do that for lots of galaxies you find about the same amount you can also look at the way galaxies orbit around each other and you see that you need more stuff there and you can also look at the expansion rate of the universe and all sorts of things and you see that you need more stuff there's just some sort of matter but some sort of matter that doesn't interact with light doesn't glow doesn't clump together into big blobs so almost certainly or the best model for that is that there's some kind of particle subatomic particle out there which outnumbers the subatomic particles out of which we and the earth and all the stars and galaxies are the stuff that shines in the is made of some different kind of thing which is we shout numbers this stuff by about five to one and so that's the that's the the observation and so as I said its most physicists think it's likely to be some kind of particle but actually to our surprise I think we haven't found such a particle at places like the Large Hadron Collider a particle accelerator in Geneva so that either suggests that these kind of particles are rather exotic perhaps very very massive indeed and beyond the capability of the Large Hadron Collider to make or it could be that it could be that our Theory's wrong and there isn't some kind of other particle out there there's something else going on but that's less likely and I think so my guess would be some kind of particle but that's just a guess at the moment because we haven't found it and in science if you haven't found it you can't say it's there but Australia is building the world's first Dark Matter detector in the southern hemisphere and a bottom of a gold mine install regional Victoria it's the truth the other way where it is detected directly which is what that experiments gonna do so because if it's there if there are all these particles around then they're in your room now they're whizzing through the room now they're actually going through everything because they don't interact very strongly with matter at all but occasionally they would bump into something some real matter and we know that our theory does suggest that they should occasionally bump into real matter so we can build detectors to try and see on the rare occasion when one of these things bumps into the D tensor and that's what indeed what's being done in Australia thank you so much Brian there's an absolute pleasure I just say thank you to everybody as well because they're brilliant questions there's such great questions that the answers to them probably really complicated because almost every question is a cutting-edge physics question and that's the great thing that's why there's such great questions because it's very hard to answer all of them none of them none of them had an obvious answer which means they're brilliant question you put him through his paces basically yeah unfortunately that's all we have time for thank you so much to Brian and thank you to you the students for your fantastic questions and my thanks to your teachers for such a love of science and schools around Australia head to the education portal on Australia's science channel for more great science content that just leaves me to thank lateral events for making this all possible and our friends at the ABC and the BBC don't forget to tune in to stargazing live and from all of us here at Australia's nice channel see you next time you

Channel: The Royal Institution of Australia

Views: 233,410

Rating: 4.805162 out of 5

Keywords: brian cox, science, cosmology, Brian Cox Scientist, space, school, q&a, alan duffy, astronomy, astrophysics

Id: 3BRn1zRACus

Length: 42min 8sec (2528 seconds)

Published: Mon May 21 2018