Big Bang Introduction

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Big Bang Introduction

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Right now the prevailing theory of how the Universe came about is commonly called the Big Bang Theory.
And really it's just this idea that the Universe that this Universe started as kind of an infintely small
point, this infinitely small singularity, and then it just had a Big Bang, or it just expanded from that
state to the Universe we know right now. And when I first imagined this, and I think it's also a by-product
of how its named, Big Bang, you kind of imagine this type of explosion. You kind of imagine this type
of explosion. That everything was infinitely packed in together and then it exploded. And then it exploded
outward. Then as all the matter exploded outward it started to condense and then you have all these
galaxies and super clusters of galaxies and they started to condense and then within them, planets condense
and stars condense and then we have the type of Universe that we have right now. But this model for
visualizing the Big Bang has a couple of problems. One is, when we talk about the Big Bang, we're not
talking about the matter, just the mass or just the matter in the Universe being in one point, we're
talking about actual space expanding, we are not just talking about something inside of space, like the physical mass expanding
we are talking about space itself so when you have this type of a model you have all the stuff expanding
is it expanding into something else? Maybe if the furthest out part of this matter is right over here
what's this stuff over here? So you say:
wouldn't that be space, how can you say space itself is expanding?
And another idea that a Big Bang also implies is that if this is furthest stuff out there
would this be the edge of the Universe? Does the Universe have an edge?
And the answer to this question, that's why we are going to try to tackle this is,
one: **the Universe does not have an edge** and
two: **there is no outside space**, we are not expanding
into another space. I am going to explain that,
hopefully we'll see why this is the case right now.
So the best way of viewing it is by analogy
If I were to tell you that I have a two dimensional space
that has a finite area, so it's not infinite and also has no edge
this once again, when you first look at it, it seems difficult
how do I construct something that has a finite area
but still has no edge? Every time I try to draw an area it looks like I have to have some edges
and then you might remember, what if that two dimensional space is curved?
what happens? I think that the easiest example of that is the the surface of the sphere.
let me draw a sphere over here. So this right here is a sphere.
let me draw some longitude and latitude lines on this sphere
on this sphere all of a sudden, I shade it in a little bit, make it look nice,
this type of a sphere you have a finite area, you can imagine the surface of a balloon
or the surface of a bubble or the surface of the Earth
you have a finite area but you have no edge, if you keep going forever in one direction
you just keep going all the way around and come back to the other side
now, to imagine a three dimensional space that has the same properties, a finite area and,
I don't want to say finite area anymore, because we are not talking about
a three dimensional space anymore, let me draw over here
so let's think about three dimensional space,
and instead of area I want to talk about finite volume
and no edge, how do I do that?
when you think about it superficially, look, if you had finite volume it's going to be maybe
contained in some type of cube, we clearly have edges in those situations
you can even think about a finite volume as being the inside of a sphere, that clearly has an edge
this entire surface over there.
so how do you construct an three dimensional space that has finite volume and no edge?
And than I am going to tell you right now
it's very hard for us to visualize it, but in order to visualize it
I am going to draw the same thing that I drew right here
you have to imagine it, you always have to imagine it by analogy
(unless you have a profound brain wired for more than three spatial dimensions)
is a sphere, let me make it clear, this is two dimensional surface.
right on the surface of the sphere you can only move in two directions.
two perpendicular directions, you can move like that or you can move like that,
you can move left and right or you can move up and and down
two dimensional surface of a three dimensional
sphere, so if we take it by analogy, let's imagine, and it's hard to imagine, a three dimensional surface
and you can do it mathematically, the math here is actually not that difficult, three dimensional surface of a four dimensional sphere
and I'm going to draw up the same way,
so if we kind of view those three dimensions are just these two dimension of the surface
it's the same thing, and if imagine that I'm not saying this is the actual shape of the Universe,
we don't know the shape, but we do know it has a slight curvature, we don't know the actual shape
but the sphere is the simpliest, there's other ones we can do, a toroid
would also fit the bill, it would have a finite volume with no edge
and I think, I want to make it clear, we actually don't know whether it has a finite volume
it's still an open question, but I want to show you it can have a finite volume and also have
no edge. And most people believe, and I want to say believe because you know we can, just go based on evidence and all that,
that we are talking about something with finite volume, especially when you talk about the Big Bang theory
that kind of some dimensions implies a finite volume, although it could be a super large, unfathomably large volume
it is finite, now if you have this, imagine, this sphere,
once again if you're on this surface of this four dimensional sphere, I can't draw a four dimensional sphere, but
if you are on this surface of this four dimensional sphere if you go in any direction you'll come back to where you started
if you go that way you'll come back around here, now the Universe is super huge so even light
maybe light itself would take an unbelievable amount of time to traverse it
and if this sphere itself is expanding, it may be expanding so fast that light
might not ever be able to come back around it, but in theory if somethings were fast enough
if something were to keep going around it could actually go back to this point. Now when we talk about
a three dimensional surface it's a three dimensional surface of a four dimensional sphere
that means that any of the three dimensions that are over here on the surface, I can only draw two
but that means, if this is true, if the Universe is a three dimensional surface of a four dimensional
sphere, that means if you go up and if you just keep going up, you'll eventually come back from the bottom.
So if you keep going, you keep going all the way up you'll eventually come back to the point that you where
it might be an unbelievably large distance but you'll eventually get back where you were
if you go to the right you'll eventually come back all the way around to the point where you were
and if you want to go into the page, let me draw it that way, if you go into the page
you'd eventually come back from above the page, and come back to the point that you are
so that's what this implication would be that you would actually get back to where you are
so let's go back to the question of and expanding Universe.
You know an expanding Universe that is not expanding into any other space
it is all of the space but it is still expanding
this is the model, so you can imagine shortly after the Big Bang, our four dimensional sphere look like this
maybe it was a little small four dimensional sphere, maybe at the Big Bang it was this little unbelievably
small sphere then a little bit later it is this larger sphere, let me just shade it in
to show that it is kind of popping out of the page this sphere, and in the later time this sphere might look like this,
now you temptation might be to say, well isn't this stuff outside of the sphere?
isn't that some type of a space that is expanding into ?
isn't that somehow part of the Universe? and I would say if you are talking in three dimension, no it's not.
The entire Universe is this surface, it is the surface of this four dimensional sphere
if you start talking about more dimensions, then yes, you could talk about maybe things outside of our
three dimensional Universe, so as this expands in space-time, you know one way to view
this fourth dimension is that it is time itself, things are just getting further and further apart.
And I'll talk about the evidence in future videos for why the Big Bang is the best theory
we have out there right now. But as you can imagine, if you have two points on this sphere that are that
far apart, as this sphere expands, this four dimensional sphere, this bubble, blows up, or this balloon
blows up, those two points; let me draw three points, those three points are just going to get further
and further apart, that's actually one of the main points that, one of the first reasons why it makes
sense to believe in the Big Bang is that everything is expanding not from some central point, but everything
is expanding from everything, that if you go in any direction from any point in the Universe, everything else
is expanding away and the further away you go it looks like the faster it's expanding away from you,
so I'll leave there it's something for you to think about a little bit, and then we'll build on some of this
to think about what it means to observe the observable Universe.