so in this video we're going to be talking about the new addition to the syllabus space on Frontier it's basically the highlight of the whole 2023 update right now so space completely new unit new topics new things to talk about so let's get started obviously I don't need to talk about what the syllabus update is it's literally this it's literally this gonna be talking about space and before I continue reminder if you're a core student you're a nine student free IGCSE student if you see this sign the extended sign the top of uh the slide or the side of an equation or something this is not for you highly recommend that however that you watch it nonetheless because it'll be useful it'll help you round out your understanding of the topic in general now what are we talking about lots of lots of topics although I like to classify them into three General topics we're going to be talking about planet Earth and any details about planet Earth so the Earth the moon the orbiting of the Earth around the Moon we're going to be talking about the solar system itself and what are the things that are in the solar system and how solar systems are formed so what are the planets that we have what's a star how was the solar system formed using the accretion model uh the differences between different types of stars how do we calculate gravity or what is gravity and how things orbit either the star or things orbit a planet or otherwise and then we focus more on the big picture the universe itself so what is the universe when we say the universe what is the universe what is it made of it's made up of galaxies and galaxies have solar systems and solar systems have stars and so on and what's the life cycle of a star like what happens when a star runs out of hydrogen fuel does it explode what does it do does it kill us all we're going to talk about that then we'll talk about some proof I wouldn't say proof just evidence of a theory that we call the big bang see you so we're going to briefly mention the Big Bang Theory and we'll talk about some of the observations we've made over a long time that allow us to support this idea we're not sure if it's 100 correct but nonetheless let's get started let's talk about planet Earth first planet Earth we live here somewhere think this is North American this is South America but nonetheless we're not here I'm probably somewhere here but the thing about Earth is that it rotates it rotates around itself so it spins around itself and it takes 24 hours to finish one spin around itself now the reason why we have a day and night cycle is thanks to this spinning action over 24 hours because sunlight comes in from a certain side just one side almost half of the earth is exposed to sunlight and the other half isn't it so this is night time here and this is daytime here and then over the next 12 hours and as the Earth itself spins day and night changes you might be saying okay cool that's fine that's easy we know that well one more thing though the rotational axis of Earth around itself is not vertical like Earth doesn't spin around itself like this think of a top or a spinning disc that you spin it's not spinning vertically it's actually spinning at an angle don't memorize this value but it's around 23 degrees or 23.5 degrees from the vertical line so the axis of rotation is at an angle and this is going to be very important because it affects the seasons on Earth So speaking of seasons Earth itself orbits around the sun the sun is the center of our solar system and Earth itself goes around the Sun this takes the earth 365 days which we call one year to complete one revolution around the Sun now it's the tilting of the Earth's axis alongside the orbiting of the Earth around the Sun that determines the kind of weather we have or to be specific the kind of season that we're discussing so is it spring is it summer is it Autumn is it winter what exactly is it so how does that work well here's the thing take a look take a close look at what what's on the diagram depending on where the sun is and where the axis is half of the half of Earth the upper half the Northern Hemisphere oops that kind of spoils things the northern hemisphere is winter and the southern hemisphere is summer right we were just coming out of our because we're currently in the north so we were just coming out of our winter and we're currently in Spring and now we're heading into summer when the Northern Hemisphere to Summer the southern hemisphere is winter but why because of the tilt of the Earth the infrared radiation that comes in from the sun does not travel the same distance as it hits the Earth it travels less at least with the access tilt this way as it hits the Northern Hemisphere and it travels more before it hits the southern hemisphere so the infrared waves get a bit weaker so it gets a bit colder and the northern hemisphere is a lot hotter so now we have summer but as and let me go back as the Earth orbits the sun with this axis the northern hemisphere is now farther and the a southern hemisphere is closer this is farther and this is closer so the southern hemisphere becomes summer because it's hotter now and the northern becomes winter so again thanks to the tilt of Earth's axis this both affects the day and night cycle and the weather we got the seasons we get as it orbits around the a around the Sun one more thing birth as a planet has a moon as in we have a natural satellite that orbits us called the Moon now this Moon takes around 30 days or basically one month and because it's not exactly 30 to be honest one month in order to finish one orbit around planet Earth now the orbiting of the Moon affects a couple of things one it affects the tides on Earth and we've already mentioned that when we talk to a tidal waves before or like sorry high tides and low tides not tidal waves but then it also affects the phase of the moon depending on where the Moon is relative to the Earth and relative to the Sun the sunlight can hit the moon and reflect the Earth so you see the entire Moon you get a full moon but if the moon is here the sunlight hits the moon reflects back so we don't get light from the Moon the Moon itself is not luminous it doesn't emit light it's reflected so depending on where the Moon is around the earth certain portions of the Moon can be seen because it reflects light from the sun and the other portions don't so depending on where it is we get to see more and more and more of the that's why we sometimes see a crescent or a half moon all right or a waning Moon or a full moon or obviously I'm moving this way so this is why the moon has phases because of its location around the Earth as the Moon is moving away from the Sun all right it's called Waxing because it gets you know lit up as the Moon is moving towards the Sun it's called win because to us on Earth we end up not seeing the moon properly when it's a new moon kind of a weird name waning and waxing anyway extended part as the Earth orbits the Sun or any planet orbits its star you should be able to calculate what we call the orbital speed or how fast basically does this object move around with the Sun so the orbital speed is simple speed is distance over time but what's the distance in a circle what's the distance around the Sun in a circle the distance is the circumference of the circle so it's 2 pi r and the time that it takes to finish one orbit around the sun is called the orbital period as in it's the time of one complete revolution around the Sun for earth that is one year for planet Earth that is what one year so it takes a year for the earth to finish orbiting around the Sun this is why when you calculate the orbital speed it's 2 pi r over t with r being the radius of this circle as in the orbital distance the distance between the star and the planet we're talking about in this case it's Earth all right very good before I talk about the solar system does anybody have any issues any questions all right we're good can you repeat the seasons all I said about when it comes to Seasons is that depending on where the Earth is around the Sun you get different seasons if the Earth is tilted towards the sun this way the Northern Hemisphere becomes hot and the southern hemisphere becomes cold because it's closer to the Sun but if the axis is tilted away from the Sun the upper half is tilted away from the Sun it becomes colder and the lower half becomes warmer okay now let's talk about the solar system our solar system which looks like this consists of lots of different astronomical bodies when I say astronomical bodies I mean things like the star the planets comets and such so let's quickly Define what they are so we can get an idea so our solar system has a star which is the sun this the thing in the middle that gives out all of the light and heat of this solar system you've got a bunch of planets which orbit the Sun all right you've got that orbits the what the Sun I'm sorry somebody sent me a funny message right now then you have minor planets or dwarf planets like Pluto which after my own heart I loved Pluto and it was so devastated when they decided not to classify it as a planet a very long time ago but we still classified as a dwarf or minor planet and that also orbits the Sun asteroids are just a bunch of rocks that are floating in outer space that were left behind after the formation of the solar system or maybe they broke off from a certain type of moon or planet and they just orbit around the Sun as well moons however always orbit a planet because I remember somebody asking me earlier what's the difference between a moon and a planet a moon doesn't orbit the Sun a moon orbits a planet and the planet orbits the Sun and then you have a bunch of comets and natural satellites similar to the Moon so you have a bunch of comets flying around the Sun and they also orbit the Sun as well all right yeah uh this there is a very good question posted which we'll answer later the question was or currently is how doesn't the moon get affected by the Sun's gravity it kind of does but I'm going to be talking about gravity in a bit and which gravity gets stronger or weaker but the gist of it is the moon is closer to us than it is to the Sun so it gets affected by us stronger than it gets affected by the sun right because it's farther away from the a Sun than we are at least even if it's orbital so what are the things in our solar system we have the sun over here and we have eight planets the first four planets that are close to the Sun you have to memorize them by name you don't have to memorize all of these moons and stuff no no no just the planets you've got Mercury being the closest followed by Venus Earth us we're here Mars uh Elon Musk wants us to go there so good luck we've got a bunch of asteroids you know broken rocks and stuff and then you have four other planets which we like to call the gas giants the first one is Jupiter Saturn is followed like that and remember Saturn is very distinct with the strings you've got Uranus the butt of all space jokes haha I'm funny always I will never stop using that joke and Neptune you have to memorize them in order and by name the first four planets are very small and Rocky so Mercury Venus Earth and Mars the other the other four planets are giant and gassy right Jupiter Saturn Uranus and Neptune so that's what makes up our solar system this is an extended part okay there's certain types of data that we need to understand don't have to particularly Define them although honestly you have to be able to Define gravitational fields run but you need to understand what they mean first what's orbital distance it's the distance between the body and the sun remember we have a planet that orbits the sun this radius of its orbit of its orbit this is called the orbital distance orbital duration or what we like to call orbital period sometimes it's the time taken to finish one complete orbit planet around the Sun a moon around its Planet so on density I think that's easy master volume some planets have very large densities some plants have very small densities like if I go back you've got planets that are huge in size like like Uranus for example or Neptune they're much larger than Earth but they almost have the same masses are it's almost the same I'm not saying it is it's almost the same so it's a lot less dense than Earth get the idea stress density surface temperature which is the temperature of the surface of the planet I don't care about temperature in space I'm talking about the temperature if we land on the surface for example on Earth our temperatures can range from I think it was negative 50 to 58 something like that you don't have to memorize that value but there's a certain range of temperatures on the surface of a planet that to us at least deems it more habitable or inhabitable like it's easy to live on or it's not easy to live on but the most important quantity is its gravitational field strength it's how strong that's planet that planet's gravity is it's defined as the force per unit mass and remember this had the symbol G so if you remember from unit 1 W was equal to mg so G is W over M it's how much weight or Force that acts on a certain Mass a certain weight or force that acts on a certain Mass for example on Earth and this is a value we have to memorize the value of G is 9.8 Newtons per kilogram meaning every one kilogram is pulled to the force of 9.8 Newtons here it is here's Earth then what about other planets and before I continue do not memorize a thing I hope that wasn't too creepy and it didn't sound too weird but do not memorize any of these just there but you need to understand what they mean there are two things to understand the bigger the value of this G like Jupiter for example is 24 and Neptune is 11.7 I'm comparing it to Earth okay this means that the planet has more Mass because the value of the gravitational field strength the value of the gravitational field strength depends on the mass of the planet itself so the more mass of the planet is the more matter it has the more mass it has the greater its gravitational field strength because gravity exists due to Mass you flinched oh God then what about something like the moon or Mercury they have a much smaller value of G what does that mean to us they have less Mass now the second thing that we need to understand is that if you go to a planet if you physically go to a planet with a smaller gravitational field strength this means you can float around you will weigh lightering you will have less weight you won't lose any Mass you'll just be floating around because you're lighter less gravity but if you go to a planet like Jupiter you won't be able to walk smacked into the ground and you won't be able to all right continuing on with the analysis of it so as we just said keep these things in mind strength of the surface of a gravitational field depends on the mass of the planet we just said that but the gravitational field strength around the planet decreases as you move farther away which makes sense so if this is a planet we're here on Earth and then you leave the planet itself the farther and further away you are the weaker the gravitational force that's going to be acting on you so the values of G that I've written down over here these are the values of G on the surface not not in outer space all right now you asked me a little while ago why doesn't the moon get affected by someone's gravity why because of two things first most of the mass of the solar system is in the sun that's why the planets orbit the Sun so when you have a sun and you have a planet the planet the reason the planets stay in orbit is thanks to the gravitational pull of the sun on them but we just said something about planets which also applies to the Sun which is what that the strength of the gravitational field decreases as you move farther away so here's the question is our moon closer to us or closer to the Sun sure the sun has very strong gravity but because the Moon is really far away from the Sun the force on it is weak it could still orbit the Sun but because we're also there and we are closer or when I say we I mean planet Earth and Earth is closer to the Moon much closer and I mean much closer to the Moon then uh than the sun is our gravitational force keeps the moon in our orbit instead right finally the orbital speed of a planet depends on the distance as well the planet is very close to the Sun like Mercury it zooms around very quickly but if a planet is super far away from the Sun like Neptune it moves very slowly oops it moves very slowly very good a follow-up question from the same student does the Earth get affected by the moons of gravity we just said that it does not the Earth itself but the water on Earth gets affected by it and that affects the tides but again which one is bigger what which is heavier which has more mass the Earth or the Moon yes exactly the Earth and since the Earth has greater mass its gravitational field is stronger than the moons so it orbits us we don't orbit it you work now the final thing here so we can go back to some core stuff would be orbits so far I've been talking about orbits as if they're all circular as if they're all just a bunch of circles which means that the radius of this orbit is constant so the gravitational force is constant but that's not entirely true it's not entirely true some planets have elliptical orbits meaning it's kind of like an oval and the sun is not the center of that ellipse if you take a look the sun will be closer to one side of the ellipse than the other we call this a foci of the ellipse then okay what what has a circle orbit what has an electrical orbit some planets do some planets do have elliptical orbits some of them are circular some of them are almost circular but please keep in mind that especially comets and minor planets these definitely have elliptical orbits so when I'm talking about Pluto for example this definitely has an elliptical orb additionally some planets like the Earth also has an elliptical orbit although it's very close to being circular like if this is the circle Earth's orbit is kind of like this slightly longer on one side than the other so it's almost a circle so we treat it like a circle we calculate the radius we calculate the urban speed that's fine but speaking of comments that move in elliptical orbits the speed depends on if you remember I said as a planet is farther away from the Sun its orbital speed is slower whereas if a planet is closer to the Sun this orbital speed is higher this also applies to comets as they move in their elliptical orbit as they move away from the Sun their speed decreases because their kinetic energy decreases and changes to gravitational potential energy but as you move farther from the Sun your potential energy increases but as you move closer to the Sun the speed increases because again you're being pulled even closer to the Sun so the gravity becomes a lot stronger so your speed increases so your kinetic energy increases but your potential energy decreases because you're moving closer to the Sun very good yeah this is korsta so Focus if you're poor how are solar systems formed this is called the accretion model of the solar system in order to understand this I want you to remember one very important detail I mentioned earlier in our solar system the first four planets that are closest to the Sun are small and Rocky the last four planets the gas giants are large and gassy there's a reason for that and that reason can be explained using the accretion model of the solar system like Tau was a solar system formed so here's what we think we know according to observations in the vastness of outer space you've got a bunch of dust and gas a large cloud of gas that's spinning and just moving through outer space however I'm sorry however as gravity starts to act as gravity starts to act on this cloud gravitational force In This Cloud starts to attract gases towards its Center the cloud starts to spin faster and faster and faster forming what we call an accretion disk so this cloud of dust just starts to spin faster and faster and faster while this is happening it attracts a gap or lots and lots and lots of gas towards the center and this gas collides with each other and as the gas molecules that mainly contain hydrogen by the way let's write that down hydrogen because it's the lightest element as it attracts and collides the hydrogen atoms with each other they start to get hotter and hotter and hotter and the pressure increases but the gravitational force also increases pushing them even closer to each other and they get hotter warming what we call a protostar the word Proto at least when it comes to space physics means before it becomes something or like it's in the process of becoming something so this hot ball of gas in the middle which is the protostar starts getting hotter and hotter and hotter until it eventually becomes what we call a stable star a nice stable star now Stars are stable because and and keep this in mind I forgot to mention this as you're collecting hydrogen gas and it's smashing into each other this hydrogen gas starts to undergo what we call nuclear fusion if you remember this is when you have two hydrogen atoms that are joined together to form a helium atom we studied this in nuclear physics so basically we fuse the hydrogen atoms together to form helium and release a lot of energy which is in the form of heat and light so this outward force of heat from the nuclear fusion reaction balances out the inward force of gravity of that star once that star has balanced out its forces the outward force of heat and the due to the fusion reaction and the inward force of gravity this is now a stable star it's nice and stable now don't forget please don't forget we still have all of the rest of that dust and gas spinning around here uh sorry spinning around the Sun now as it spins faster and faster and faster some of that dust and some of these rocks and everything else start to Clump together you've got lots of elements in them by the way you've got helium still some hydrogen left some oxygen some nitrogen some carbon some iron you've got heavy and Light Elements as well they start to stick to each other and the more they stick to each other the stronger their gravitational force becomes and they start to form what we call protoplanets you can see this lots of dust and some of this dust starts to accumulate in certain areas and joins together in certain parts which are currently in the process of becoming a plant after a very long time millions of years this dust now starts to gather and it creates what we call planets but one final observation due to the heat from the Sun which we call solar winds but it's basically just heat limited from the Sun during the formation of the protoplanets the heat from the Sun pushes out the lighter elements because they are light they are easily affected by the sun's Heat by the expansion caused by the sun's Heat so they just get pushed out so the planets that form on the outer end of the solar system are big and gassy because they're mainly made of the lightest elements so they have a lower density whereas the planets that are closest to the Sun are small and Rocky why because there are less elements that are light here it's mostly heavy elements and that's what we call the accretion model of the solar system how solar systems are informed and this explains why the four planets close to the Sun if I go back the four planets close to the Sun are small and Rocky then the large gassy planets are far away because of the whole accretion model and everything else yeah let's talk about the sun one more time just to clarify things the sun is what we call a medium-sized star s are just bodies of gas in different solar systems that release a lot of light and heat and everything else they have different sizes some of them are tiny some of them are medium-sized like us and some of them are huge and some of them are even bigger than the huge Stars no they have different sizes it mainly consists of hydrogen helium if you remember it's because we said that you have two hydrogen atoms that fuse together form helium that's the nuclear fusion reaction we discussed before but because of this fusion reaction the types of energy it emits all types of energy by the way all types of electromagnetic waves so it does emit gamma it doesn't emit other things but it mainly emits three things infrared waves which is heat it emits visible light which we see and it emits ultraviolet radiation UV waves these are the three main things that the sun emits very good finally let's talk about distances before we talk about the universe we have to specify a unit of distance why because planets are so far away from each other like if this is the Sun and we're here on Earth you know what if I open up Google let me pull out my phone for a second I'm going to type on Google distance between the Sun and the Earth this will give us a value of a hundred take a look at this take a look at this of a 149.06 million kilometers so if I were to put zeros to this and forgive me I'm going to ignore the o6 I've got one two three that's for the kilometers and then one two three four five six meters I think that's kind of far right I think that's kind of far so instead of using values that are huge and millions and billions and then people get confused what's a million and what's a billion what's a trillion and what's how about we simplify things instead when we're traveling in outer space or we're measuring distances between stars and other stars or stars and planets and everything else we use a unit called a light year and it's literally its name it's the distance traveled by light in one year this value is 9.5 times 10 power 15. if you want to you can go work it out on your own by the way like you can calculate the distance of one light year by simply saying hey distance is three times time the speed of light is 3 times 10 power 8. the time which is one year is 365. days but if you want to convert it to seconds so you can get it in meters per second you have to multiply it by 24 that turns it into hours then you multiply it by 60 which turns it into a minute then you multiply it by 60 which sends it into seconds if you multiply these you'll end up with 9.5 times 10 power 15 meters that's very huge that's pretty huge so memorize this value one light here this is for extended folks one light here is 9.5 10 power 15. for everyone else you have to memorize the definition and know that's how we measure the distances between plans and stars and galaxies now this next bit no no no no I'm not saying that there is a very good question I'm sorry uh for context so are all planets the same distance from each other that's not what I'm saying no I'm just saying that instead of measuring the distance between planets in meters so you end up with a gajillion zeros we make we created a new unit for very large distances which is the distance traveled by light in one year so if I tell you for example that you traveled half a light year to get somewhere what does that mean it's literally half of 9.5 10 power 15. which gives you a certain value so 0.5 times 9.5 gives you uh 0.5 times 9.5 gives you 4.75 10 power 15. absolutely yes a light year is a constant do you want to know what it's like do you want to know what it's like it's like if I tell you uh um what's one kilograms in grams what are you going to say exactly a thousand grams it's a constant but instead of measuring everything in grams we decided to use a prefix and we just use kilograms sometimes same thing we just took a very large value and we changed it into a constant so we measure everything relative to that constant two light years 75 light years and so on you're welcome now take a deep breath and I ran out of water amazing there was a drop in there let's talk about the life cycle of a star this next section of the life cycle is extended but what do I mean by the life cycle of a star I mean what happens to a start when it runs out of fuel your brain might be working what field remember we said that a star it balances and becomes stable when the nuclear fusion reaction emits an outward force of heat which is equal to the inward force of gravity of that star so it's balanced all these forces are balanced and everything is stable eventually though that will run out because it'll run out of hydrogen changes it all to helium so that's going to happen let's see what happens first if you remember we said that our solar systems or a star starts off as a nebula that nebula collapses due to gravity heats up forms a protostar and then it forms a stable star when the inward Force balances out with the outward force of the temperature of the star now this phase this phase takes millions of years millions of years if not billions depending on the star the bigger and the heavier the star is the faster it runs out of fuel and the smaller the star is the slower it runs out the fuel but eventually transa then what happens if a star runs out of fuel depending on its size if it's a medium star like the sun it turns into what we call a red joint so that you understand the process here's the star look at me here's the star it runs out of fuse so there's less heat being pushed being pushed out so it's unstable so the gravitational course collapses the star even more causing the helium to start fusing like a new fusion reaction occurs but because it's now fusing heavier elements this becomes I don't want to call it a star because it's no longer a star anymore this fusion reaction causes this star to expand because it's now restarting the fusion reaction but with heavier elements there's a lot more energy that's running out even faster boom as it expands it actually eats up a few planets in the solar system like it destroys the first three or four or five planets depending on the size of that star it destroys a few planets we call the red giant but eventually even that runs out of hydrogen even that runs out of hydrogen and when it runs out of hydrogen this phase is not very important but when it does run out of hydrogen uh what I need to write why the phrase okay when it does run out of hydrogen you've got a bunch of dust left that's called the planetary nebula it's not very important because that's the rest of the solar system but I'll get back to it what happens is that whatever is less left at the center of that star like after it's been completely done and it's collapsed again it cannot fuse anymore you're left with this big white dot of heavy matter called a white dwarf the reason it's called a white dwarf is because it's slowly giving out light and some heat which is residual energy from when it was a star eventually by the way and let me add this as an extra eventually a white dwarf turns into a black dwarf which is basically the same object but it's run out of light it's run out of heat and it's just dark just a big piece of rock floating around in outer space just a big piece of rock floating around in outer space all right I'm not answering that question now obviously just as an extra bit this is beyond the scope of the syllabus processary whatever is left from this planetary nebula after like destruction of it eventually floats around in space spins creates a new galaxies you have sorry new solar systems you got the idea but let me go back a second what of the star that we're talking about is very large I mean very long much larger than the Sun like here's the Sun here is that big star when this runs out of fuel it forms into a red super joint which means it collapses and then expands again complete almost completely destroying the solar system it's in but then here's the kicker it also runs out of fuel and as it runs out of fuel it's fusing heavy elements it's fusing heavy elements as it runs out of fuel what happens to it it explodes if it's a very heavy red super giant it explodes and when it explodes this is what we call a supernova so it's when a red super giant explodes and by the way all of these heavy elements from the lightest the heaviest elements they start to scatter around the universe this is why we get you know different elements in different parts of space because these elements remain from the explosions of other supernovas and other solar systems and eventually thus dust forms and everything else but now what's left behind this super uh this red super joint has now exploded into a supernova what's left if it is very heavy it's gravitational force becomes so strong that it forms a black hole or if it's heavy just not as heavy as the other star that forms a black hole it's forms what we call a neutron star this is literally one protons and electrons the gravitational force here is so strong it fuses them together and it becomes a neutron all right oh this is a good question is a black hole like a black dwarf no you see a black dwarf is kind of small so it's just a piece of rock sure it has some gravity but a black hole has extremely strong gravity I mean gravity of a black hole is so strong it attracts light like if you have light coming from another star and it's trying to pass through and around the black hole that light gets attracted into the black hole and you don't see it that's why we call it a black hole because when you look through a telescope in outer space you will see lots of little dots and colors and everything else from all the dust and all of the stars and other things but a black hole is literally like a hole in our picture it's like somebody used some very dark ink and erased whatever it is was there the only reason we know there's a black hole there is because there's this weird ring of light around it because that's the light that gets distorted as it travels away from the black hole like it's far away from the black hole and bends a bit so it makes it look weird the track's light so again how does a black hole form if you have a supernova which is when a drying sorry a red super giant explodes whatever is left in the center either turns into a neutron star or it turns into a black hole depending on its mass the heavier it is the bigger of a chance of it becoming a black hole the lighter it is it becomes a neutron star all right obviously like we said whatever bad residue is left this this nebula that's left behind all of that dust that's thrown away and it's left behind this could start forming new stars and new solar systems and new planets and so on very good now finally let's talk about the universe let's end this session by talking about the universe the universe is huge it consists of billions of galaxies we can't count them all but we live in a galaxy called the Milky Way like our start the sun is in a gas called the Milky Way maybe it's here maybe it's here maybe it's I don't know honestly I just put this arrow in because it looked cool you know like these mall maps that say you are here that's basically what it reminded me of it's like we're somewhere and we don't know where so anyway probably none of these by the way because we're the ones taking the picture so we're the ones taking the picture huh anyway I digress but the thing is even the Milky Way let's assume that we're looking at the Milky Way the size of the Milky Way is approximately 100 000 light years you need to memorize this value sorry if you haven't heard it before but you need to memorize this value the size the diameter of the Milky Way is a hundred thousand light years can you imagine how large our galaxy is by the way the distance between us and the Sun is a lot less than one light year so it's a very big distance all right but how do we know that there are other galaxies in the universe because we see them sure but one idea is that if I go back to this picture for a second one idea that we have is that this universe doesn't have a fixed size this universe is actually expanding like it has a limit and it's now growing beyond that limb so we're assuming that over time the size of this universe is increasing and increasing and increasing we call this The Big Bang Theory where we assumed that the entire universe started off as a little dot an infinitely infinitely small dot of mass and energy and then it exploded boom and then when it exploded it scattered all of its mass and energy and then that Universe started to get bigger and bigger and bigger because it has its velocity it's not slowing down it's just moving far away but how do we know that this is true one of the observations that convinced us that this could be true is redshift basically as a planet or sorry planet was the wrong term as a star or a Galaxy moves away from us the wavelength of the light emitted by that Galaxy increases especially compared to something that is stationary like if you have a stationary star that's sending us light it has a certain wavelength it doesn't change but as other stars move away from us the wavelength of that wave gets stretched out so as the universe expands it stretches that wavelength more so wait a second if you remember the electromagnetic spectrum when it comes to light visible light it was Roy gibbid red orange yellow green blue indigo violet if and red had the lowest frequency while it had the highest frequency but thread also has the longest wavelength with Violet being the shortest so any light blue indigo whatever it is that's emitted by another star as it reaches us because it gets stretched out it looks almost it looks more and more red this is We call we call it redshift because the wavelength increases a bit so it to us the visible light looks a bit more red than it should and this doesn't just apply to light this applies to any electromagnetic wave emitted by that star it applies to uh infrared it applies to gamma rays it applies to everything all of them get shifted a bit sometimes we even draw a spectrum by the way like if I draw the spectrum that we know gamma rays for example if I start with gamma rays here and radio waves here and you have certain regions of the spectrum this entire Spectrum shifts if this is the longer wavelength the gamma rays don't start here the gamma is start here then you have your X-rays and then you have your other things until you get your radio waves way over there so all of the Waves start to have a longer wavelength they shift that's why we call it redshift it just it doesn't fold it just stretches the actual wavelength emitted by the star is the same is because here's the thing if my right hand is emitting a wave like this that's fine it's still the same blue color for example but as it emits a wave and it moves back what has happened to the wavelength of that wave because it just bursts out that wave and Ops I'm moving farther away I'm sorry I've now stretched that wave so I emitted the same wave I emitted blue but because I moved it changes and this happens also to Sound by the way we call it the Doppler effect like if you have a car and I've done this several times already so if you laugh that's up to you but do you know what cars sound like as they move towards and away from you what does it sound like as a car moves towards you it goes like and then as it moves so it goes like right I I kind of like that when a car moves away from me sound becomes lower pitched because its wavelength gets stretched and if a car moves towards you sounds higher pitched because the waves get compressed denotes the opposite of redshift if a planet or star is moving towards us we call it blue shift it's it's a very beyond the scope of the syllabus it's beyond the scope of the syllabus but this happens whenever something that's emitting a wave moves either towards you or away from you because every Star that we've observed in outer space is redshifted this was the first piece of evidence that told us hey all of these things are moving away from us so if they're all moving away from us over time that means what if they're all moving away from us that means what this means the universe is expanding like the universe is getting bigger and it's continuously getting bigger yeah a second thing that proved to us that or is a piece of evidence that supports this idea if I toss you into outer space we're here on Earth and we we decide to fly out into outer space thank you space thank you Earthen goodbye and thank you for all the fish if you get that reference you're you're a goat anyway so as you fly out in outer space if you decide to measure if there's any radiation in outer space you will find a lot of radiation but what was funny is that no matter where in space we send out we won't say people honestly but we send out drones or like sensors or satellites we found out that there is always some kind of microwave radiation that's observed anywhere so we call it Cosmic microwave background radiation background radiation just like Atomic physics but it's not gamma rays it's microwaves coming from outer space where did it come from so here's the theory the idea is that this energy was emitted during the Big Bang so it was released when the universe was formed but it originally had a shorter wavelength but because the universe is expanding the wavelength of that wave keeps getting stretched and stretched and stretched and stretched and stretched until it eventually became a microwave so you can think of it like hey when the universe blew up from that point at least that's what we think it blew up from that single point the big bank it started off maybe as gamma rays but then that wave started to get stretched over time over billions of years until now it's currently at microwaves and by the way even that microwaves wavelength over a very long time will continue to increase the frequency will continue to decrease maybe it won't be a microwave anymore maybe it'll be a radio wave after a few million years who knows but that's an idea so if I ask you what this cosmic background radiation it's microwave validation of a certain frequency observed in any point around space how does it support the idea that the Universe you know is expanding so we simply say it was produced during the Big Bang or when the universe Was Won and as the universe is expanding its wavelength was increasing until it reached the microwaves region and finally last but not least now the Hubble constant what is the Hubble constant we've already agreed that the universe is expanding so let me draw a few circles to emulate the fact we started off as a very small Dot and then the size of this universe keeps increasing increasing increasing how do we measure that like how do we measure how far it's increasing well uh I can observe another star like if we're here on Earth and we're looking at another far away star we can measure the distance between us and that star and we can measure the speed at which the star is moving away from us we could find out how fast is the universe expanding because the assumption is us and that other star were originally one point if we all started from the same point we were originally one point so technically and we're assuming here technically speaking if we can measure how fast this thing is moving away from us not just the speed it's just how fast it's moving away from us and the current distance it has we can know the rate at which the universe is expanding that's what we call the Hubble constant it is simply a ratio of the speed at which another star or Galaxy is moving away from us over the distance so it's just the speed divided by distance look at the units look at the units the speed is meters per second and the distance is meters they'll cancel each other out so it'll simply give you a distance or something per second this is the ratio at which the universe is expanded we get the velocity using redshift we have not studied the formula we will not study the formula but we can use the velocity from or we can get velocity of another galaxy using redshift and measure the frequencies we can measure the wavelengths we can estimate the speed you can also get the distance between us and another galaxy using the brightness of another start or a supernova depending on how bright that Supernova is we can tell how far away it is now that we've measured both we can calculate the Hubble constant and right now when you memorize this value too this Hubble constant is around 2.2 times 10 power negative 18 per second that's the rate at which it's expanding one final thing if this is the rate at which it's expanding if you inverse this ratio you're literally dividing distance over speed if you remember speed is distance over time then time is what distance over speed do you see where I'm getting it or what I'm getting at if I divide the distance between us and another star and the speed of that other star no no it's not going to be a light year light here is just a unit this will tell us how much time the take for that other star to move away from us wait didn't I just say we assumed that the Universe started at a point and then we separated like you know star-crossed lovers long-distance relationships when was the last time you called your you know significant other you shouldn't have one right now anyway so when was the last time we called each other don't don't do that no a very long time ago a few billion years ago so if I can find out the time that I took for that other Galaxy to move away from us assuming we're all the same point that is the age of the universe which is literally the inverse of the Hubble constant so if I divide and this is just for fun this is just for fun you don't have to memorize this but if I divide 1 over 2.2 10 power 10 10 to the power negative 18. if I if I work this out 1 over 2.2 10 power negative 18. this will give us 4.54 times 10 to the power of 17. seconds let me let me change this to uh two years so we can get an idea so in order to change it to years we'll divide it by 60 and another 60 and 24. and 365. this will give me 1.44 times 10 to the power of 10 which is 1 which is 14.4 10 power 9. 10 power 9 is a billion so our current assumption is that the time that it took for another galaxy to move away from us which is the age of the universe is 14.4 billion years that's very fascinating honestly but it's all assumptions based on certain measurements with a big amount of uncertainty by the way we're not 100 sure uh what about the syllabus so what what should I memorize well one you should memorize what the Hubble constant even mean and the ratio itself V over d you should briefly know that we can get the velocity using redshift of another galaxy and distance using the light from the Supernova of another galaxy the brightness and finally you should memorize this value 2.2 times negative 18. thank you very much oops there was an error here this is space physics not Nuclear Physics anyway I'm human I make mistakes thank you very much for listening I'll see you guys next time