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Current time:0:00Total duration:10:15

Video transcript

in the last video we learned that 380,000 years after the Big Bang which is still roughly 13.7 billion years ago every point I shouldn't say every point every atom in space that was kind of at this roughly 3,000 Kelvin temperature was emitting was emitting this electromagnetic radiation since every point in space was they were point in space or there was points in the universe then that radiation is only just now reaching us it has been traveling for 13.7 billion years so when we look at radiation that's been traveling for that long we can look in any to any direction and we'll see this uniform radiation in that uniform and that radiation has been redshifted into the microwave range from the higher frequencies that it was actually emitted at now a question that might pop in your brain is well what happens if we wait a billion years because if we wait a billion years if we have a billion three a billion 380,000 years after the beginning of the universe this stuff won't just be atoms anymore it will have can starting to condense into actual stars we would not with the universe at this point in space at every point in space will no longer be this uniform will actually start having condensation into stars so if we go the universe if we move forward a little bit the universe will expand maybe I'll just draw half of it since its expanded its obviously expanding much more but now all of a sudden we actually have stars these aren't these are no longer just uniform atoms spread through the universe we actually have condensation into stars and so if you look at what is being emitted from the points in space from which we're only now getting this cosmic background radiation if we wait a billion years what the light that we see from those points in space will not look like this uniform radiation it'll start to look a little bit more like the more mature parts of the universe it'll start to will essentially be looking at the universe a billion years after the Big Bang when stars have formed other structures of form so the question is in a billion years will this cosmic microwave background radiation disappear and I'm using the billion just because that you know just just arbitrarily use a number but will it eventually disappear and there's kind of the answer to that is yes and no so to think about it it is true that this point in space will mature it will mature in a billion years it won't it will no longer be this uniform I guess this uniform haze of hot hydrogen atoms but we have to think about is there were further points in the universe there were further points in the universe at that same time there were further points that were also emitting this that were also emitting this radiation and the original photons from those original points still haven't gotten to us so from those further out points right now the observable universe is we can only see light we can only see electromagnetic radiation that's been traveling for 13.7 billion years and another billion years the universe will be a billion years older and then there will be radiation that has been traveling for fourteen point seven billion years and so we will start to observe that and we'll start to observe that radiation from the same time period in the universe it'll just be from further out now what I want to make clear is is that since that since those points were even further out where that radiation was emitted the stuff that we'll see in a billion years it will be even more redshifted even even more even more redshifted so at that point the cosmic background radiation we see will will have longer wavelengths than the radio spectrum it will be redder and I should say redder because we're already we're already more would rather have two DS under a written redder well it would be it would be more red than then the microwave radiation and of course that's that's a funny thing because microwave radiation is already more red than actual visible red light it has a longer wavelength now this will keep happening and I don't know and what you know it'll it'll keep happening we'll keep getting radiation as we go further and further into the future we'll keep getting radiation from further out points in space and it'll get more and more redshifted the actual wavelengths of that electromagnetic light will be bigger and bigger and bigger until we really aren't able to even see as electromagnetic light because it'll be redshifted to infinity it'll have an infinite it'll have an infinite wavelength and to make that point clear I want to show you that there will even be points at some point there'll be kind of a threshold where we can't even get radiation from further out and let me show you let me draw a diagram of that so let's say that this is the universe let's say that this is the universe 13.7 billion years ago right with that radiation what we now see is cosmic microwave background radiation right when it started to be emitted and let's say that this is the point in the universe where we are now so this is us let's say let's say that this is the point in the universe that where we now observe the background ray she or this is one of the points we obviously could form a circle around us it could be any of these points over here we're only we that where the the photons the electromagnetic radiation that were emitted from this point 380,000 years after the beginning of the universe is only just now reaching us so this this is the point in the universe where from which we are observing the cosmic background radiation and let me be very clear that point in the universe has now matured into things that look you know into stars and galaxies and planets and if they were to look at our point in space they are also going to see cosmic background radiation from us it's not like this is some type of permanently old place it's just the light we're getting from them right now is old light light that they at that point in space emitted way before it was able to mature into actual structures so this is this is this is the point in space from which we are receiving from which we were receiving cosmic background radiation right now I don't want to write all that it will take me forever now let's take another point in space that's whatever this distance is we it's what's actually estimated to be about now it's estimated to be about 46 billion light years at that time when things were just beginning to it be emitted this was only about 36 million light years so this was a base and and this is a very rough estimate I shouldn't even write it down because that's really based on how fast we assume the universe is expanding and all of that type of things but it was just a lot smaller than 46 billion light years now let's to go that same distance again from this point in space so once they let me make it clear this is 380,000 years ago 380,000 years ago now let's fast forward let's fast forward sorry not 380,000 years ago 380,000 years after the Big Bang after the Big Bang which is approximately it's still 13.7 billion years ago so that's then now let's look at now and now I'll just draw it a little bit bigger it's actually going to be much much bigger now now if we do it a little bit bigger so when I draw it like this this is where we are now this point in space is this point in space from which we are only now receiving that cosmic background radiation is over here and then this other point in space is going to be over here and we saw in the video on the actual size of the observable universe not just what it appears to be based on the how long the lights been traveling this is now on the order of 46 or 47 billion light years 46 billion light years and so this distance is also going to be 46 billion light years 46 billion 46 billion light years now every point in space back then was emitting this was emitting this radiation we have this uniform radiation it was just hydrogen atoms everywhere these hot hydrogen atoms now we are only maybe I should just do it in the color of the radiation so this guy's receiving I'm just showing it's coming from this guy we're only now 13.7 billion years in the future receiving photons from this guy only now are we receiving it and frankly this green guy only now is going to be receiving photons when he looks at the points in space or the things that he thinks are the points base out there he will see that uniform he will see that uniform radiation and likewise this guy over here will only now be receiving photons from the point in space for where we are now he'll see the universe where we are now as it was 380,000 years after the Big Bang and same thing from that point in space the photons will only just now reach now let's think about it it took this guy's photons it took this guy's photons let me make it clear it took him 13.7 billion years to reach this point over here which is now 46 billion light years away from us and the universe continues to expand it's depending on the if the universe expands fast enough there's no way there's no way that that photon that got to this guy will eventually get to this the universe is expanding faster than the light can never even catch up to us and this light will never ever ever get to us and so there is some threshold some distance from which we will never get light and during this time period or actually from from which we will never ever get any electromagnetic radiation so the simple answer is the cosmic background radiation from this or the cosmic background radiation from this point yes it will start to mature we won't be as uniform if we go fast forward 400 million years or a billion years but we will get uniform radiation from further out but it'll be even more redshifted and the further forward we get into the future the background radiation we get will be from further and further out and it will be more and more and more redshifted until some point where it's going to be so red shifted that we won't even observe it as electromagnetic radiation and there's some threshold where we won't even observe anything anymore because beyond that the light wasn't able to actually get to us