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Every video until now, we've been working from the assumption that the observable universe

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is smaller than the entire universe.

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And if you go by the Cosmic Inflation Theory

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Cosmic Inflation Theory

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It was founded by Alan Guth

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I have an almost personal connection to Alan Guth

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When I was at MIT I always used to go to this Chinese food truck

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and I always used to show up at the food truck like 2 seconds before Alan Guth

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He was always one or two behind me in line, but anyway

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He was the founder of the Cosmic Inflation Theory which is basically this idea that

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the very early moments, or the very early period after the big bang,

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it went through this major inflation in the expansion of space

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If based on the Theory of Cosmic Inflation then the observable universe is on the order of

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or maybe another way to say it, the entire universe is on the order of

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10 to the 23 times the size of the observable universe.

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So that would mean this is just a tiny tiny fraction,

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I mean this is an unimaginably large number

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In fact it is unimaginable, so already everything we've talked about

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this itself is an incomprehensible amount of space, but this is an incomprehensible multiple

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of this incomprehensible amount of space.

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That's just based on that theory but, it is possible, we cannot rule out even the idea that

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the actual universe is smaller, smaller, than the observable universe

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that one is in some ways even more mind blowing than the idea that the universe is this big

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the fact that what we're observing is actually larger than the actual universe

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And you'll say "Sal, that's impossible", but just think about it a little bit

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This is the observable universe, the way we've depicted it is based on how long the light

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has taken to reach us, we've already covered before that this point in space is now

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46 billion light years away, not 13.7, the way it looks right over here.

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It just took 13.7 billion years to reach us.

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If there is any photon that would take longer than 13.7 billion years to reach us,

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it hasn't reached us yet because it could have only started 13.7 billion years ago.

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So they're on their way and they start at some point outside of our observable universe

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So our observable universe will grow over time

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but with that said let's imagine that the actual universe is a sub-set of this observable universe

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let's say it's roughly, half the diameter, so let's say it looks like this.

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Maybe I'll make it a little bit of an oval.

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Maybe the actual universe, and this is just to be a little bit provocative, and it's not impossible

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Let's say that this is the actual universe.

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Actual Universe

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And the way I drew it, it makes it look like Earth is the center.

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That we're the center of it but remember, this is very likely to be the surface,

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or it is the, it is curved, it has a slight curvature,

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it could very well be the surface of a 4-dimensional object

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maybe the simplest one to visualize is the 4-dimensional sphere

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so if you really want to visualize this right, this whole volume

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and remember this whole picture keeps looking 2-dimensional, but it has depth.

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It is a volume of space, an incredibly vast volume of space

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so what I've done here is this is a ellipsoid right here, it's an elliptical volume of space

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that I've bubbled up right over here but if this was really the entire universe

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and the entire universe really were the surface of a 4-dimensional sphere

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then the reality is that this entire space can be represented like this.

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It can be represented as the surface, if this was a 4-dimensional sphere

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obviously this way I can only draw a 3 dimensional spheres,

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let me show that it has some, that it's not just a circle, that it has some depth to it.

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and I can even shade it right over here

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so you can imagine that this point, that this point over here,

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is actually the same thing as that point over there, that they have wrapped around

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and that they're connected right at the back over here and let show that, draw and go behind

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that they're connected right over there and that this point and this point

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are actually the same point that they've wrapped around

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they've wrapped around, actually the way I've drawn it right here they would actually all wrap around

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right back there at that point if I'm visualizing properly

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if you go in any one direction, you would come back on the other side of the surface

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if you go, let's say that Earth is right here.

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The way we've depicted it, Earth is the center but we see that when

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when you look at it like this, there is no center to the surface of a sphere

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even a 4-dimensional sphere

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So in this sense, if you go in any one direction you'll come back out the other side

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so if you start from Earth, you go in that direction, once you get there you're really

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here again and then you would come back to Earth.

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And so, if this were the case, if the actual volume of the true universe

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was smaller than what it looks like, the observable universe,

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then what's all this stuff on the outside?

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And to think about it, think about what would happen if 13.7 billion years ago

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When we were in that primitive state, that the background radiation, that those photons are being

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that the electromagnetic waves are being released.

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let's say that they get released, and those photons on their first pass,

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and I think you know where this is going, on their first pass they would get to us

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they would get to us in about, this looks like a distance of about, I don't know,

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this looks like about 6 billion years.

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then they would pass us up and then they would get back to this point again in another 6 billion years

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and then they would come back here, so that very first pass of photons are going to be right over here

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and from our point of view, we're not going to see them for a couple of billion years

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so when we do see them we're going to perceive them

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we're going to say "Wow, it took 15, 16 billion years for that photon to get to me

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that must be from something out here" but the reality is

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it's a photon from something within a smaller physical universe, within a smaller actual universe

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that has just taken several passes by us and we're just seeing a pass after 14 billion years

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we just think it's from something further out.

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Now the other thing is, well you say, if this was the case,

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if we could just go in one direction in the universe and come out the other side

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and if all of that was within the observable universe, wouldn't we be able to tell?

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Wouldn't we be able to look in two directions and see the same thing from a different perspective?

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and the answer there is to think about what happens, or actually

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Wouldn't we even be able to see ourselves?

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because if we emit some light, and it would take maybe, I don't know how for that is

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let's say it's 6 or 7 billion light years to get right over here which would be right over there and

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then it would take another 6 or 7 billion light years to get over there

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So maybe that background radiation we're seeing is actually background radiation emitted

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from that exact point in space that we are right now, or from a very similar point in space

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to where we are right now

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Part of the background radiation is from a similar point in space that we are right now.

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So how come we can't just see ourselves?

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Well, I kind-of just answered the question.

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That second pass, if you're observing that same point in space, if you're observing light

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from the same point in space on a previous pass that light was emitted a long long time ago

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Maybe, well, 13 billion years ago.

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and so it would be unrecognizable, the region, this region of space,

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the region of the space that we are in right now,

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if we saw this same region of space 13 billion years ago, we just wouldn't recognize it

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Now there are people attempting to see if there is some patterns,

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see if you can model how the universe would change

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and if you see patterns and maybe the actual universe is a sub-set of the observable

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we just haven't seen it yet, but it's completely a possibility

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hopefully I didn't confuse you, I actually find this kind-of an interesting idea

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that these things that we think are, let's say the light that has taken 8 billion years to reach us

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we think it's from something, based on this scale, 8 billion light years out,

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it's actually further because the universe is expanding so

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it will have actually traversed more space than that

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but we think it's from something like that but it could have been something further in

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if the actual universe is smaller and it's just on it's second pass

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it's actually coming back again and that's why it took 8 billion years to reach us

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we don't even recognize it because it looks very different than that region of space right now

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or that region of space after 4 billion years looks completely different than when it first released

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anyway, hopefully I didn't confuse you too much, I think this is a fascinating, fascinating topic