Back

A Universe Smaller than the Observable

⇐ Use this menu to view and help create subtitles for this video in many different languages. You'll probably want to hide YouTube's captions if using these subtitles.

A Universe Smaller than the Observable

相關課程

0 / 750

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

載入中...

A Universe Smaller than the Observable

A Universe Smaller than the Observable