A Universe Smaller than the Observable A Universe Smaller than the Observable
A Universe Smaller than the Observable
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- Every video until now, we've been working from the assumption that the observable universe
- is smaller than the entire universe.
- And if you go by the Cosmic Inflation Theory
- Cosmic Inflation Theory
- It was founded by Alan Guth
- I have an almost personal connection to Alan Guth
- When I was at MIT I always used to go to this Chinese food truck
- and I always used to show up at the food truck like 2 seconds before Alan Guth
- He was always one or two behind me in line, but anyway
- He was the founder of the Cosmic Inflation Theory which is basically this idea that
- the very early moments, or the very early period after the big bang,
- it went through this major inflation in the expansion of space
- If based on the Theory of Cosmic Inflation then the observable universe is on the order of
- or maybe another way to say it, the entire universe is on the order of
- 10 to the 23 times the size of the observable universe.
- So that would mean this is just a tiny tiny fraction,
- I mean this is an unimaginably large number
- In fact it is unimaginable, so already everything we've talked about
- this itself is an incomprehensible amount of space, but this is an incomprehensible multiple
- of this incomprehensible amount of space.
- That's just based on that theory but, it is possible, we cannot rule out even the idea that
- the actual universe is smaller, smaller, than the observable universe
- that one is in some ways even more mind blowing than the idea that the universe is this big
- the fact that what we're observing is actually larger than the actual universe
- And you'll say "Sal, that's impossible", but just think about it a little bit
- This is the observable universe, the way we've depicted it is based on how long the light
- has taken to reach us, we've already covered before that this point in space is now
- 46 billion light years away, not 13.7, the way it looks right over here.
- It just took 13.7 billion years to reach us.
- If there is any photon that would take longer than 13.7 billion years to reach us,
- it hasn't reached us yet because it could have only started 13.7 billion years ago.
- So they're on their way and they start at some point outside of our observable universe
- So our observable universe will grow over time
- but with that said let's imagine that the actual universe is a sub-set of this observable universe
- let's say it's roughly, half the diameter, so let's say it looks like this.
- Maybe I'll make it a little bit of an oval.
- Maybe the actual universe, and this is just to be a little bit provocative, and it's not impossible
- Let's say that this is the actual universe.
- Actual Universe
- And the way I drew it, it makes it look like Earth is the center.
- That we're the center of it but remember, this is very likely to be the surface,
- or it is the, it is curved, it has a slight curvature,
- it could very well be the surface of a 4-dimensional object
- maybe the simplest one to visualize is the 4-dimensional sphere
- so if you really want to visualize this right, this whole volume
- and remember this whole picture keeps looking 2-dimensional, but it has depth.
- It is a volume of space, an incredibly vast volume of space
- so what I've done here is this is a ellipsoid right here, it's an elliptical volume of space
- that I've bubbled up right over here but if this was really the entire universe
- and the entire universe really were the surface of a 4-dimensional sphere
- then the reality is that this entire space can be represented like this.
- It can be represented as the surface, if this was a 4-dimensional sphere
- obviously this way I can only draw a 3 dimensional spheres,
- let me show that it has some, that it's not just a circle, that it has some depth to it.
- and I can even shade it right over here
- so you can imagine that this point, that this point over here,
- is actually the same thing as that point over there, that they have wrapped around
- and that they're connected right at the back over here and let show that, draw and go behind
- that they're connected right over there and that this point and this point
- are actually the same point that they've wrapped around
- they've wrapped around, actually the way I've drawn it right here they would actually all wrap around
- right back there at that point if I'm visualizing properly
- if you go in any one direction, you would come back on the other side of the surface
- if you go, let's say that Earth is right here.
- The way we've depicted it, Earth is the center but we see that when
- when you look at it like this, there is no center to the surface of a sphere
- even a 4-dimensional sphere
- So in this sense, if you go in any one direction you'll come back out the other side
- so if you start from Earth, you go in that direction, once you get there you're really
- here again and then you would come back to Earth.
- And so, if this were the case, if the actual volume of the true universe
- was smaller than what it looks like, the observable universe,
- then what's all this stuff on the outside?
- And to think about it, think about what would happen if 13.7 billion years ago
- When we were in that primitive state, that the background radiation, that those photons are being
- that the electromagnetic waves are being released.
- let's say that they get released, and those photons on their first pass,
- and I think you know where this is going, on their first pass they would get to us
- they would get to us in about, this looks like a distance of about, I don't know,
- this looks like about 6 billion years.
- then they would pass us up and then they would get back to this point again in another 6 billion years
- and then they would come back here, so that very first pass of photons are going to be right over here
- and from our point of view, we're not going to see them for a couple of billion years
- so when we do see them we're going to perceive them
- we're going to say "Wow, it took 15, 16 billion years for that photon to get to me
- that must be from something out here" but the reality is
- it's a photon from something within a smaller physical universe, within a smaller actual universe
- that has just taken several passes by us and we're just seeing a pass after 14 billion years
- we just think it's from something further out.
- Now the other thing is, well you say, if this was the case,
- if we could just go in one direction in the universe and come out the other side
- and if all of that was within the observable universe, wouldn't we be able to tell?
- Wouldn't we be able to look in two directions and see the same thing from a different perspective?
- and the answer there is to think about what happens, or actually
- Wouldn't we even be able to see ourselves?
- because if we emit some light, and it would take maybe, I don't know how for that is
- let's say it's 6 or 7 billion light years to get right over here which would be right over there and
- then it would take another 6 or 7 billion light years to get over there
- So maybe that background radiation we're seeing is actually background radiation emitted
- from that exact point in space that we are right now, or from a very similar point in space
- to where we are right now
- Part of the background radiation is from a similar point in space that we are right now.
- So how come we can't just see ourselves?
- Well, I kind-of just answered the question.
- That second pass, if you're observing that same point in space, if you're observing light
- from the same point in space on a previous pass that light was emitted a long long time ago
- Maybe, well, 13 billion years ago.
- and so it would be unrecognizable, the region, this region of space,
- the region of the space that we are in right now,
- if we saw this same region of space 13 billion years ago, we just wouldn't recognize it
- Now there are people attempting to see if there is some patterns,
- see if you can model how the universe would change
- and if you see patterns and maybe the actual universe is a sub-set of the observable
- we just haven't seen it yet, but it's completely a possibility
- hopefully I didn't confuse you, I actually find this kind-of an interesting idea
- that these things that we think are, let's say the light that has taken 8 billion years to reach us
- we think it's from something, based on this scale, 8 billion light years out,
- it's actually further because the universe is expanding so
- it will have actually traversed more space than that
- but we think it's from something like that but it could have been something further in
- if the actual universe is smaller and it's just on it's second pass
- it's actually coming back again and that's why it took 8 billion years to reach us
- we don't even recognize it because it looks very different than that region of space right now
- or that region of space after 4 billion years looks completely different than when it first released
- anyway, hopefully I didn't confuse you too much, I think this is a fascinating, fascinating topic
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