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Current time:0:00Total duration:16:39

Video transcript

right now the best estimate of when the Big Bang when the Big Bang occurred and once again I don't like the term that much because it kind of implies some type of explosion but what it really is is kind of an expansion of space when it's space started to really start to expand from a singularity but our best estimate of when this occurred is 13.7 billion billion years ago and even though we're used to dealing with numbers in the billions especially when we talk about large amounts of money and whatnot this is an unbelievable amount of time it seems like something that is tractable but it really isn't and in future videos I'm actually going to talk about the time scale so we can really appreciate how long or even start to appreciate or appreciate that we can't appreciate how long 13.7 billion years is and I also want to want to emphasize that this is the current best estimate even in my lifetime even in my lifetime that I actually knew about the Big Bang and that I would pay attention to what the best estimate was this this numbers been moving around so I suspect that in the future this number might become more accurate or might move around some but this is our best guess now with that said I want to think about what this tells us about the size of the observable universe the observable universe observable so if the if if all of the expansion started 13.7 billion years ago that 13.7 billion years ago all of everything we know in our three-dimensional universe was in a single point the longest that any photon of light could be traveling that's reaching us right now so our eye is right so let's say that that is my eye right over here that's my eyelashes just like that the longest of some photon of light some photon of light is just getting to my eye or maybe it's just getting to the lens of a telescope the longest that that could have been traveling is 13.7 billion years so it could be traveling could be traveling traveling 13.7 billion years so when we looked at when we looked at that depiction this I think was two or three videos ago of the observer universe I drew it was this circle it was this circle and when we see light coming from these remote objects that that light is getting to us right here this is where we are this is where I guess in the depiction the remote object was but the light from that remote object is just now getting to us and that light took that light took 13.7 billion years to get to us 13.7 billion billion years now what I'm going to hesitate to do because we're talking over such large distances in it and we're talking on such large time scales and time scales over which space itself is expanding we're going to see in this video that is you cannot say you cannot say that this object over here this is not necessarily this is not I'll put it in caps this is not 13.7 billion billion light years light-years away if we're talking about smaller timescales or I guess smaller distances you could say approximately that the expansion of the universe itself would not that make what would not make as much of a difference and let me let me make it even more clear I'm talking about an object over there but we could even talk about that coordinate in space and that coordinate in and I try I should say that coordinate in space time because we're viewing it at a certain instant as well but that coordinate is not 13.7 billion light years away from our current coordinate and there's a couple of reasons to think about it first of all think about it that light was emitted 13.7 billion years ago when that light was emitted we were much closer to that coordinate this coordinate was much closer to that where we are in the universe right now was much closer to that point of the universe the other thing to think about is as this let me let me actually draw it so let's say that let's say that let's say that let's go 300,000 years after the form after after that initial of that initial expansion of that singularity so we're just three hundred thousand years into the universe's history right now so this is roughly three hundred thousand years three hundred thousand years into the universes a life I guess we could view it that way and let's say at that point well first of all at that point you know we have all things haven't differentiated in a meaningful way yet right now I mean we'll talk more a lot about this when we talk about the cosmic microwave background radiation but at this point in the universe it was kind of this almost uniform white-hot plasma of hydrogen and then we're going to talk about it was a meeting you know microwave radiation and we'll talk more about that in a future video but let's just think about two points in this early in this early universe so in this early universe let's say you have that point and let's say you have the coordinate where we are right now you have the coordinate where we are right now in fact I'll I'll just make that roughly I won't make it the center just because I think it makes it easier to visualize if it's not the center and let's hit that very early stage in the universe if you were able to just take some rulers instantaneously and measure that you would measure this distance you would measure this distance to be 30 million 30 million 30 million light years 30 million light years and let's just say right at that point this object over here I'll do it in magenta this object over here emits a photon maybe in the microwave frequency radio range and we'll see that that was the range that it was emitting in but it emits a photon so right and that photon is traveling at the speed of light it is light and so that photon says oh you know what I only got 30 million light years to travel that's not too bad I'm going to get there in 30 million years and so I'm going to do a discrete the math is more complicated than what I'm doing here but I really just want to give you the idea of what's going on here so let's just say let's just say well you know that photon says you're in about in about ten million years and in roughly ten million years I should be right about I should be right about at that coordinate I should be about one third of the distance but what happens what happens over the course of those ten million years well over the course of those ten million years the universe has expanded some the universe has expanded maybe a good deal so let me draw this expanded universe so after ten million years the universe might look like this actually might even be bigger than that let me draw it like this after 10 million years the universe might have expanded a good bit so this is 10 million years into the future still by on a cosmological timescale still almost at the kind of the the infancy of the universe because we're talking about 13.7 billion years so let's say 10 million years 10 million years go by the universe is expanded this coordinate where we're sitting today at the present time is now is now all the way over here that that coordinate where the photon was originally emitted is now is now going to be sitting right over here and that photon it said okay and after 10 million light years I'm going to get over there and you know I'm approximating and I'm doing in a very discreet way but you can I really just want to give you the idea so that coordinate where the photon roughly gets in 10 million light years is about right over here the whole universe is expanded all the coordinates have gotten further away from each other now what just happened here the universe is expanded this distance that was 30 million light years now and I don't I'm I'm just making rough numbers here I don't know the actual numbers here now it is actually this is really just for the sake of sake of giving you the idea of why well giving you the intuition of what's going on this distance now is no longer 30 million light years it could be maybe it's a hundred million so this is now a hundred million a hundred million light years away from each other the universe is expanding these coordinates this the space is actually spreading out you can imagine it's kind of a trampoline or the surface of a balloon getting stretched thin and so this coordinate where the light happens to be after ten million years it has been traveling for ten million years but it's gone a much larger distance it is now it is now gone that distance now might be on the order of maybe it's on the order of 30 million light years and the math isn't exact here I haven't done the the math to figure it out but the point here so it's done 30 million light years and and and I want to make it actually I shouldn't even make it the same proportion because the distance it's gone in the distance that it has to go because of the stretching it's not going to be completely linear at least it when I'm thinking about in my head it shouldn't be I think but I'm not going to make a hard statement about that but the distance that it traversed the distance that it traversed maybe this distance right here is now twenty million light years 20 million light years even though because it got there every time it moved some distance that the space that it had traversed is now stretched so even though it's traveled even though it's traveled for ten million years the space that it traversed is no longer just ten million light years it's now stretched to 20 million light years and the space that it has left to traverse is no longer only 20 million light years it might now be 80 million light years it is now 80 million light years and so the you know this this photon might be getting frustrated there's no there's an optimistic way of viewing it it's like wow I was able to cover 20 million light years in only 10 million years it looks like I'm moving faster than the speed of light the reality is it's not because the space coordinates themselves are spreading out those are getting thin so the photon is just moving at the speed of light but the distance that it actually traversed in ten million years is more than ten million light years it's 20 million light years so you can't just multiply a rate times time on these cosmological scales here that's that's especially when the coordinates themselves the distance coordinates are actually semi but I think you see or maybe you might see where this is going now this says okay this photon says oh well you know and in another in another let me write this is 80 million light years and another 40 million light years maybe I'm going to get maybe I'm going to get over here but the reality is over those that next 40 million light years sorry over over in 40 million years I might get right over here because this is 80 million light years but the reality is after 40 million years so for another 40 million years go by now of a sudden the universe is expanded even more the universe is expanded even more I won't even draw the whole bubble but the place where the photon was emitted from might be over year and now our current position is over here where the light got after 10 million years where the light got after 10 million years is now over here and now where the light is after 40 million years after 40 million years is maybe it's over here so it's actually so now this distance this distance between these two points and when we started it was 10 million light years then it became 20 million light years maybe now it's maybe now it's on the order of I don't know maybe it's a billion light years maybe now it's a billion light years and maybe this distance over here and I'm just making up these numbers in fact that's probably too big for that point maybe this is now 100 million light years this is now a hundred million light years and now this distance maybe is maybe this distance right here is I don't know five hundred million light years and maybe now the total distance between the two points is a billion light years so as you can see the the photon might be getting frustrated as it covers more and more distance it looks back and says wow you know and only 50 million years I've been able to cover 600 million light years that's pretty good but it's frustrated because what it thought was it only had to comfort 30 million years 30 million light years in distance that keeps stretching out because space itself is stretching so the reality just going to the original to the original idea this photon this photon that is just reaching us that's been traveling for let's say 13 let's say it's been traveling for 13.4 billion years so it's reaching us just now so let me let me just fast forward thirteen point four billion years from from this point now to get to the present day so if I draw the whole visible universe right over here this point right over here is going to be where it was emitted from is right over there we are we are sitting right over there and actually let me make something clear if I'm drawing the whole observable universe the center actually should be where we are because we can observe an equal distance if if things aren't really strange we can observe an equal distance in any direction so actually maybe we should put us at the center so this was the entire observable universe and the photon was emitted from here thirteen point four billion years ago so 300,000 years after just that initial Big Bang and it's just getting to us it's just getting to us just getting to us it is true that the photon has been traveling the photon has been traveling for 13.7 billion years billion years but what's kind of nutty about it is this object since we've been expanding away from each other this object is now in our best estimates this object is going to be about 46 billion 46 billion light years light-years away from us away from us so and I want to make it very clear this object is now 46 billion light-years away from us when we just use light to observe it it you know it looks like just based on lightyears hey this trial lights been traveling 13.7 billion years to reach us that's our only way of kind of with light to kind of think about the distance so maybe it's 13 points for for what I keep changing the the decimal but thirteen point four billion light years away but the reality is if you had a ruler today and you know light your rulers this thing is now this the space here has stretched so much that this is now 46 billion light years and and just to give you a hint of when we talk about the cosmic microwave background radiation what will this point in space look like this thing that's actually 46 billion light years away but the photon only took 13.7 billion years to reach us what will this look like well that thatfo it's going to you know when we say look like it's based on the photons that are reaching us right now those photons left thirteen point four billion years ago so those photons are the photons being emitted from this from this primitive structure from this white-hot this white-hot haze of hydrogen plasma so what we're going to see is this white-hot haze so we're going to see we're going to see a this this kind of white hot plasma white-hot undifferentiated not differentiated into proper stable atoms much less stars and but white-hot we're going to see this white hot plasma the reality today is at that point in space it's 46 billion years from now it's probably differentiated into into stable atoms and stars and planets and galaxies and frankly if that person that person if there is a civilization there right now and they're sitting right there if they're observing photons being admitted from our coordinate from our point in space right now they're not going to see us they're going to see us thirteen point four billion years ago they're going to see that the super primitive state of our region of space when it really was just it a white-hot plasma and we're going to talk more about this in the next video but think about it any photon that's coming from that period in time so from any direction that's been traveling for 13.4 billion years from any direction it's going to come from that primitive state or it's going to it would have been emitted when the universe was in that primitive state when it was just that white-hot plasma this undifferentiated mass and hopefully that'll give you a sense of where the cosmic microwave background radiation comes from