A Universe Smaller than the Observable

WEBVTT
Kind: captions
Language: en

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Every video until
now, we've been

00:00:02.470 --> 00:00:06.110
working from the assumption
that the observable universe is

00:00:06.110 --> 00:00:09.360
smaller than the
entire universe.

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And if you go by the
cosmic inflation theory--

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and it was founded by Alan Guth.

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And I have almost personal
connection to Alan Guth.

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

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truck.

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And I always used to show up at
the food truck like two seconds

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before Alan Guth.

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Like he was always one or
two people behind me in line.

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But anyway, he was the founder
of the cosmic inflation theory,

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which is basically this idea
that in the very early moments

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or the very early period
after the Big Bang,

00:00:45.030 --> 00:00:47.420
we went through
this major inflation

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in the expansion of space.

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But anyway, based on the theory
of cosmic inflation, then

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the observable universe is
on the order of-- or maybe

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another way to say it,
the entire universe

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is on the order of--
10 to the 23 times

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the size of the
observable universe.

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

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I mean, this is an
unimaginable large number.

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In fact, it is unimaginable.

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So already everything
we've talked about,

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this itself is a huge--
this is an incomprehensible

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amount of space.

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But this is an
incomprehensible multiple

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of this incomprehensible
amount of space.

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And that's just
based on that theory.

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But it is possible-- we cannot
rule out even the idea--

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that the actual universe is
smaller than the observable

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universe.

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And that one is
in some ways even

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more mind blowing than the
idea that the universe is

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this big, the fact that
what we're observing

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is actually larger than
the actual universe.

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And so you might say, well,
Sal, that's impossible.

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But just think about
it a little bit.

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This is the observable universe.

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And the way we've
depicted it, it's

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based on how long the light
has taken to reach us.

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We've already covered before
that this point in space

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is now 46 billion light
years away, not 13.7,

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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's any photon that
would take longer than 13.7

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billion years to reach us,
it hasn't reached just yet.

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Because it could have only
started 13.7 billion years ago.

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So they're on their way.

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And they started at
some point outside

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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

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that the actual
universe is a subset

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of this observable universe.

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Let's say it's roughly
half the diameter.

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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

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is just to be a little
bit provocative.

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And it's not impossible.

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Let's say that this is
the actual universe.

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And the way I drew
it, it makes it

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look like Earth is the center.

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That we're the center of it.

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But remember, this is very
likely to be the surface--

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or it is curved.

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It has a slight curvature.

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But it could very
well be the surface

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of a four-dimensional object.

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And maybe the simplest
one to visualize

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is four-dimensional sphere.

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So if you really
wanted to visualize

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this right, this whole
volume-- and remember

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this whole picture, it keeps
looking two-dimensional.

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But it has depth.

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It is a volume of space,
an incredibly vast volume

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of space.

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And so what I've
done here is this

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is an ellipsoid right here.

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It's elliptical volume
of space that I've

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bubbled out right over here.

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But if this was really
the entire universe,

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and if the entire
universe really

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were the surface of a
four-dimensional sphere,

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then the reality is
that this entire space

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could be represented like this.

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It could be represented
as the surface.

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If this was a four-dimensional
sphere-- obviously,

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I can only draw
three-dimensional spheres.

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But let me show you that
it's not just a circle,

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that it actually has
some depth to it.

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And I can even shade
it right over here.

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And so you can imagine
that this point over here

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is actually the same thing
as that point over there.

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That they have wrapped
around and that they're

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connected right at
the back over here--

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let me go behind-- that they're
connected right over there.

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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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Maybe they've wrapped around.

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Actually, the way I've
drawn it right here,

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they would actually all
wrap around right back there

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at that point, if I'm
visualizing properly.

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But if you go in
any one direction,

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you would come back on the
other side of the surface.

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Let's say that
Earth is right here.

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The way we depicted it,
Earth is the center.

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But we see that when
you look I like this,

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there is no center to the
surface of a sphere, even

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a four-dimensional sphere.

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So in this sense, if you
go in any one direction,

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you'll come back
out the other side.

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So if you start from Earth
and you go in that direction,

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once you get there,
you're really here again.

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And then you would
come back to Earth.

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And so if this were the
case, if the actual volume

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of the true universe was
smaller than what it looks like,

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the observable
universe, then what's

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all this stuff on the outside?

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And to think about
it, think about what

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would happen if 13.7
billion years ago, when

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we were in that primitive
state, where that background

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radiation, those
photons are being--

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those electromagnetic
waves are being released,

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let's say they get released.

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And those photons on
their first pass--

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and I think you know where this
is going-- on their first pass,

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they would get to us in about--
this looks like a distance

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of about, I don't
know, this looks

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like about 6 billion years.

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Then they would pass us up.

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And then they would
get back to this point

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again in another
6 billion years.

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And then they would
come back here.

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And so that very
first past photon

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are going to be right over here.

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And from our point
of view, we're

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not going to see them for
a couple of billion years.

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And so when we do
see them, we're

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going to perceive them--
we're going to say,

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wow, it took 15, 16 billion
years for that photon

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to get to me.

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That must be from
something out here.

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But the reality is it's
a photon from something

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within a smaller physical
universe, within a smaller

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actual universe, that's just
taken several passes by us.

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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 you say, well,

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if this was the case,
if we could just

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go in one direction
of the universe

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and then come out of the
other side, and if all of that

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was within the
observable universe,

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wouldn't we be able to tell?

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Wouldn't we be able to
look in two directions

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and see the same thing from
a different perspective?

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And the answer there is to
think about what happens--

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or actually, wouldn't we even
be able to see ourselves?

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Because we emit some light,
and it would take maybe--

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I don't know how far that is.

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Let's say that's 6 or
7 billion light years

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to get right over here, which
would be right over there.

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And then it would take another
6 or 7 billion light years

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to get over there.

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So maybe that background
radiation we're seeing

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is actually background radiation
emitted from that exact point

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

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in space, to where
we are right now.

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Or part of the
background radiation

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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 the same point

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in space, if you're
observing light

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from the same point in
space on a previous pass,

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that light was emitted a
long, long, long time ago,

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maybe 13 billion years ago.

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And so it would
be unrecognizable.

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This region of space,
the region of space

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that we are in right now, if
we saw the same region of space

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13 billion years ago, we
just wouldn't recognize it.

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Now, there are some
people attempting

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to see if there
are 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.

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And maybe the actual universe
is a subset of the observable.

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We just haven't seen it yet.

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But it's completely
a possibility.

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Hopefully, I didn't confuse you.

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I actually find this kind
of an interesting idea.

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That this light that
has taken 13-- let's

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say the light that's taken us
8 billion years to reach us.

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We think it's from something,
based on this scale,

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8 billion light years out.

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It's actually further because
the universe is expanding.

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So it would have actually
traversed more space than that.

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But we think it's from
something like that.

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But it could've been
something further

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in, if the actual
universe is smaller.

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And it's just on
its second pass.

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It's actually coming back again.

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And that's why it took 8
billion years to reach us.

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And we don't even
recognize it because it

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looks very different than that
region of space right now.

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Or that region of space
after 4 billion years

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looks completely different than
it did when it first released.

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Anyway, hopefully I didn't
confuse you too much.

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But I think this is a
fascinating, fascinating topic.


Radius of observable universe (correction)

WEBVTT
Kind: captions
Language: en

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I want to make a quick
correction to the last video.

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It doesn't really affect the
learning of the last video.

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But I just want to make
sure that you understand

00:00:08.490 --> 00:00:11.410
that I got the math a little
bit wrong in the last video.

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I said that you had this
state, 300,000 years.

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So we talk about the
Big Bang happening

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13.7 billion years ago.

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And then I talk about
this state of affairs

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where we're maybe 30
million light years away

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from the edge of the
observable universe,

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the current observable universe.

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And I said that this
was about 300,000 years

00:00:46.230 --> 00:00:49.516
after the Big Bang.

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That's what I talked
about in the last video.

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That was our starting
point when the photon

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started leaving that point.

00:00:54.415 --> 00:00:56.450
And obviously, the
universe kept expanding.

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The photon, it kind of
traversed more and more.

00:00:59.320 --> 00:01:01.240
But still had more
and more to travel

00:01:01.240 --> 00:01:03.840
as the universe expanded,
as all of space expanded.

00:01:03.840 --> 00:01:07.100
But this is 300,000
years after the Big Bang.

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Now my brain, because I was
kind of not thinking hard enough

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about it, I said, hey, this
was 13.4 billion years ago.

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That's what I incorrectly
said in the last video.

00:01:17.240 --> 00:01:24.589
I said that this is
13.4 billion years ago.

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That's what I said
in the last video.

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And that is wrong.

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Because if this was
13.4 billion years ago,

00:01:29.630 --> 00:01:33.190
this would have been 300 million
years after the Big Bang.

00:01:33.190 --> 00:01:35.940
We were talking about
only 300,000 years

00:01:35.940 --> 00:01:36.891
after the Big Bang.

00:01:36.891 --> 00:01:39.140
So it wouldn't have taken
that many decimal places off

00:01:39.140 --> 00:01:41.820
of something in the billions.

00:01:41.820 --> 00:01:44.930
The correct answer is this
would have been only a little

00:01:44.930 --> 00:01:46.997
less than 13.7 billion years.

00:01:46.997 --> 00:01:49.330
It actually wouldn't have
even made a significant digit.

00:01:49.330 --> 00:01:56.242
So this is still approximately
13.7 billion years ago.

00:01:56.242 --> 00:01:57.950
So I wanted to just
make that correction.

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It was a slight error.

00:01:59.190 --> 00:02:01.870
I shouldn't have viewed
this as 0.3 billion years.

00:02:01.870 --> 00:02:04.560
This is only 0.3 million years.

00:02:04.560 --> 00:02:06.690
It doesn't even basically
change the precision

00:02:06.690 --> 00:02:08.449
on this number right over here.

00:02:08.449 --> 00:02:10.150
So I just wanted
to clear that up.

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But hopefully, it doesn't affect
your understanding too much.


Radius of observable universe

WEBVTT
Kind: captions
Language: en

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Right now, the best estimate
of when the Big Bang occurred--

00:00:05.594 --> 00:00:08.010
and once again, I don't like
the term that much because it

00:00:08.010 --> 00:00:10.255
kind of implies some
type of explosion.

00:00:10.255 --> 00:00:12.130
But what it really is
is kind of an expansion

00:00:12.130 --> 00:00:14.540
of space, when space
started to really start

00:00:14.540 --> 00:00:16.420
to expand from a singularity.

00:00:16.420 --> 00:00:18.400
But our best estimate
of when this occurred

00:00:18.400 --> 00:00:24.320
is 13.7 billion years ago.

00:00:24.320 --> 00:00:26.672
And even though we're used
to dealing with numbers

00:00:26.672 --> 00:00:28.130
in the billions,
especially when we

00:00:28.130 --> 00:00:30.540
talk about large amounts
of money and what not,

00:00:30.540 --> 00:00:32.750
this is an unbelievable
amount of time.

00:00:32.750 --> 00:00:35.580
It seems like something that is
tractable, but it really isn't.

00:00:35.580 --> 00:00:37.830
And in future
videos, I'm actually

00:00:37.830 --> 00:00:39.420
going to talk about
the time scale.

00:00:39.420 --> 00:00:41.340
So we can really
appreciate how long,

00:00:41.340 --> 00:00:43.170
or even start to
appreciate, or appreciate

00:00:43.170 --> 00:00:47.820
that we can't appreciate how
long 13.7 billion years is.

00:00:47.820 --> 00:00:51.510
And I also want to emphasize
that this is the current best

00:00:51.510 --> 00:00:52.010
estimate.

00:00:52.010 --> 00:00:54.760
Even in my lifetime, even in
my lifetime that I actually

00:00:54.760 --> 00:00:57.230
knew about the Big Bang and
that I would pay attention

00:00:57.230 --> 00:00:59.360
to what the best estimate
was, this number's

00:00:59.360 --> 00:01:00.260
been moving around.

00:01:00.260 --> 00:01:02.320
So I suspect that in
the future, this number

00:01:02.320 --> 00:01:04.989
might become more accurate
or might move around some.

00:01:04.989 --> 00:01:06.350
But this is our best guess.

00:01:06.350 --> 00:01:08.850
Now with that said, I want to
think about what this tells us

00:01:08.850 --> 00:01:11.740
about the size of the
observable universe.

00:01:17.320 --> 00:01:22.320
So if all of the expansion
started 13.7 billion years ago,

00:01:22.320 --> 00:01:25.870
that 13.7 billion
years ago, everything

00:01:25.870 --> 00:01:28.320
we know in our
three-dimensional universe

00:01:28.320 --> 00:01:31.270
was in a single
point, the longest

00:01:31.270 --> 00:01:34.340
that any photon of light could
be traveling that's reaching us

00:01:34.340 --> 00:01:39.720
right now-- so let's say that
that is my eye right over here.

00:01:39.720 --> 00:01:45.800
That's my eyelashes, just like
that-- so some photon of light

00:01:45.800 --> 00:01:47.890
is just to getting to
my eye or maybe it's

00:01:47.890 --> 00:01:50.840
just getting to the
lens of a telescope.

00:01:50.840 --> 00:01:52.800
The longest that that
could have been traveling

00:01:52.800 --> 00:01:55.490
is 13.7 billion years.

00:01:55.490 --> 00:02:07.320
So it could be traveling
13.7 billion years.

00:02:07.320 --> 00:02:09.389
So when we looked
at that depiction--

00:02:09.389 --> 00:02:11.250
this I think was two
or three videos ago,

00:02:11.250 --> 00:02:14.930
of the observable universe--
I drew, it was this circle.

00:02:18.270 --> 00:02:21.966
And when we see light coming
from these remote objects--

00:02:21.966 --> 00:02:23.590
that light is getting
to us right here.

00:02:23.590 --> 00:02:24.850
This is where we are.

00:02:24.850 --> 00:02:27.510
This is where I guess
in the depiction

00:02:27.510 --> 00:02:28.800
the remote object was.

00:02:28.800 --> 00:02:30.840
But the light from
that remote object

00:02:30.840 --> 00:02:32.930
is just now getting to us.

00:02:32.930 --> 00:02:37.970
And that light took 13.7
billion years to get to us.

00:02:43.887 --> 00:02:45.470
Now, what I'm going
to hesitate to do,

00:02:45.470 --> 00:02:48.720
because we're talking
over such large distances

00:02:48.720 --> 00:02:51.890
and we're talking on such large
time scales and time scales

00:02:51.890 --> 00:02:55.010
over which space
itself is expanding--

00:02:55.010 --> 00:02:59.180
we're going to see in this video
that you cannot say that this

00:02:59.180 --> 00:03:03.990
object over here, this is
not necessarily, this is NOT,

00:03:03.990 --> 00:03:13.720
I'll put it in caps, this is NOT
13.7 billion light years away.

00:03:13.720 --> 00:03:15.990
If we were talking about
smaller time scales

00:03:15.990 --> 00:03:18.270
or I guess smaller
distances, you

00:03:18.270 --> 00:03:20.060
could say approximately that.

00:03:20.060 --> 00:03:23.784
The expansion of the universe
itself would not make as much

00:03:23.784 --> 00:03:24.450
of a difference.

00:03:24.450 --> 00:03:26.870
And let me make it
even more clear.

00:03:26.870 --> 00:03:28.720
I'm talking about an
object over there.

00:03:28.720 --> 00:03:33.055
But we could even talk about
that coordinate in space.

00:03:33.055 --> 00:03:35.430
And actually, I should say
that coordinate in space-time,

00:03:35.430 --> 00:03:37.950
because we're viewing it at
a certain instant as well.

00:03:37.950 --> 00:03:43.270
But that coordinate is not
13.7 billion light years away

00:03:43.270 --> 00:03:44.740
from our current coordinate.

00:03:44.740 --> 00:03:46.520
And there's a couple of
reasons to think about it.

00:03:46.520 --> 00:03:48.186
First of all, think
about it, that light

00:03:48.186 --> 00:03:51.760
was emitted 13.7
billion years ago.

00:03:51.760 --> 00:03:53.840
When that light was
emitted, we were

00:03:53.840 --> 00:03:55.750
much closer to that coordinate.

00:03:55.750 --> 00:03:57.637
This coordinate was
much closer to that.

00:03:57.637 --> 00:03:59.220
Where we are in the
universe right now

00:03:59.220 --> 00:04:01.960
was much closer to that
point in the universe.

00:04:01.960 --> 00:04:04.110
The other thing
to think about is

00:04:04.110 --> 00:04:06.060
as this-- let me
actually draw it.

00:04:06.060 --> 00:04:16.170
So let's go 300,000 years
after that initial expansion

00:04:16.170 --> 00:04:17.079
of that singularity.

00:04:17.079 --> 00:04:21.300
So we're just 300,000 years
into the universe's history

00:04:21.300 --> 00:04:22.890
right now.

00:04:22.890 --> 00:04:30.370
So this is roughly 300,000
years into the universe's life.

00:04:30.370 --> 00:04:33.660
I guess we could
view it that way.

00:04:33.660 --> 00:04:37.400
And first of all, at that point
things haven't differentiated

00:04:37.400 --> 00:04:39.130
in a meaningful
way yet right now.

00:04:39.130 --> 00:04:40.860
And we'll talk more
about this when

00:04:40.860 --> 00:04:43.580
we talk about the cosmic
microwave background radiation.

00:04:43.580 --> 00:04:45.650
But at this point
in the universe,

00:04:45.650 --> 00:04:49.900
it was kind of this almost
uniform white-hot plasma

00:04:49.900 --> 00:04:50.400
of hydrogen.

00:04:50.400 --> 00:04:51.983
And then we're going
to talk about it.

00:04:51.983 --> 00:04:53.869
It was emitting
microwave radiation.

00:04:53.869 --> 00:04:55.910
And we'll talk more about
that in a future video.

00:04:55.910 --> 00:05:01.090
But let's just think about two
points in this early universe.

00:05:01.090 --> 00:05:03.597
So in this early universe,
let's say you have that point.

00:05:03.597 --> 00:05:05.930
And let's say you have the
coordinate where we are right

00:05:05.930 --> 00:05:06.890
now.

00:05:06.890 --> 00:05:10.214
You have the coordinate
where we are right now.

00:05:10.214 --> 00:05:12.630
And in fact, I'll just make
that roughly-- I won't make it

00:05:12.630 --> 00:05:14.340
the center just because I
think it makes it easier

00:05:14.340 --> 00:05:15.950
to visualize if
it's not the center.

00:05:15.950 --> 00:05:19.080
And let's say at that very
early stage in the universe,

00:05:19.080 --> 00:05:22.090
if you were able to just take
some rulers instantaneously

00:05:22.090 --> 00:05:26.820
and measure that, you
would measure this distance

00:05:26.820 --> 00:05:36.150
to be 30 million light years.

00:05:36.150 --> 00:05:38.050
And let's just say
right at that point,

00:05:38.050 --> 00:05:40.140
this object over here--
I'll do it in magenta--

00:05:40.140 --> 00:05:43.070
this object over here
emits a photon, maybe

00:05:43.070 --> 00:05:45.787
in the microwave
frequency range.

00:05:45.787 --> 00:05:48.370
And we'll see that that was the
range that it was emitting in.

00:05:48.370 --> 00:05:50.216
But it emits a photon.

00:05:50.216 --> 00:05:52.340
And that photon is traveling
at the speed of light.

00:05:52.340 --> 00:05:53.182
It is light.

00:05:53.182 --> 00:05:55.140
And so that photon, says,
you know what, I only

00:05:55.140 --> 00:05:56.990
got 30 million light
years to travel.

00:05:56.990 --> 00:05:57.790
That's not too bad.

00:05:57.790 --> 00:06:00.647
I'm going to get there
in 30 million years.

00:06:00.647 --> 00:06:01.980
And I'm going to do it discrete.

00:06:01.980 --> 00:06:04.380
The math is more complicated
than what I'm doing here.

00:06:04.380 --> 00:06:05.796
But I really just
want to give you

00:06:05.796 --> 00:06:07.320
the idea of what's
going on here.

00:06:07.320 --> 00:06:09.840
So let's just say,
well, that photon

00:06:09.840 --> 00:06:13.870
says in about 10 million years,
in roughly 10 million years,

00:06:13.870 --> 00:06:18.080
I should be right about
at that coordinate.

00:06:18.080 --> 00:06:20.960
I should be about one
third of the distance.

00:06:20.960 --> 00:06:26.080
But what happens over the course
of those 10 million years?

00:06:26.080 --> 00:06:28.080
Well, over the course of
those 10 million years,

00:06:28.080 --> 00:06:30.240
the universe has expanded some.

00:06:30.240 --> 00:06:32.730
The universe has expanded
maybe a good deal.

00:06:32.730 --> 00:06:35.690
So let me draw the
expanded universe.

00:06:35.690 --> 00:06:40.919
So after 10 million years, the
universe might look like this.

00:06:40.919 --> 00:06:42.710
Actually it might even
be bigger than that.

00:06:42.710 --> 00:06:44.760
Let me draw it like this.

00:06:44.760 --> 00:06:47.570
After 10 million
years, the universe

00:06:47.570 --> 00:06:49.510
might have expanded a good bit.

00:06:49.510 --> 00:06:53.470
So this is 10 million
years into the future.

00:06:53.470 --> 00:06:58.200
Still on a cosmological time
scale, still almost at kind

00:06:58.200 --> 00:07:00.370
of the infancy of the
universe because we're

00:07:00.370 --> 00:07:02.360
talking about 13.7
billion years.

00:07:02.360 --> 00:07:04.310
So let's say 10 million years.

00:07:04.310 --> 00:07:07.510
10 million years go by.

00:07:07.510 --> 00:07:09.100
The universe has expanded.

00:07:09.100 --> 00:07:10.980
This coordinate, where
we're sitting today

00:07:10.980 --> 00:07:15.350
at the present time, is
now all the way over here.

00:07:15.350 --> 00:07:19.350
That coordinate where the
photon was originally emitted

00:07:19.350 --> 00:07:24.302
is now going to be
sitting right over here.

00:07:24.302 --> 00:07:26.760
And that photon, it said, OK,
after 10 million light years,

00:07:26.760 --> 00:07:28.100
I'm going to get over there.

00:07:28.100 --> 00:07:29.300
And I'm approximating.

00:07:29.300 --> 00:07:30.800
I'm doing it in a
very discrete way.

00:07:30.800 --> 00:07:32.890
But I really just want
to give you the idea.

00:07:32.890 --> 00:07:35.280
So that coordinate,
where the photon roughly

00:07:35.280 --> 00:07:38.340
gets in 10 million light years,
is about right over here.

00:07:38.340 --> 00:07:39.760
The whole universe has expanded.

00:07:39.760 --> 00:07:42.860
All the coordinates have gotten
further away from each other.

00:07:42.860 --> 00:07:44.180
Now, what just happened here?

00:07:44.180 --> 00:07:45.420
The universe has expanded.

00:07:45.420 --> 00:07:49.240
This distance that was 30
million light years now--

00:07:49.240 --> 00:07:52.000
and I'm just making
rough numbers here.

00:07:52.000 --> 00:07:53.640
I don't know the
actual numbers here.

00:07:53.640 --> 00:07:55.690
Now, it is actually--
this is really just

00:07:55.690 --> 00:08:01.130
for the sake of giving you the
idea of why-- well, giving you

00:08:01.130 --> 00:08:03.100
the intuition of
what's going on.

00:08:03.100 --> 00:08:08.180
This distance now is no
longer 30 million light years.

00:08:08.180 --> 00:08:10.240
Maybe it's 100 million.

00:08:10.240 --> 00:08:16.167
So this is now 100 million light
years away from each other.

00:08:16.167 --> 00:08:17.250
The universe is expanding.

00:08:17.250 --> 00:08:20.909
These coordinates, the space
is actually spreading out.

00:08:20.909 --> 00:08:22.700
You could imagine it's
kind of a trampoline

00:08:22.700 --> 00:08:23.866
or the surface of a balloon.

00:08:23.866 --> 00:08:25.490
It's getting stretched thin.

00:08:25.490 --> 00:08:27.640
And so this coordinate
where the light happens

00:08:27.640 --> 00:08:29.940
to be after 10
million years, it has

00:08:29.940 --> 00:08:32.179
been traveling for
10 million years,

00:08:32.179 --> 00:08:33.824
but it's gone a much
larger distance.

00:08:37.539 --> 00:08:40.440
That distance now might
be on the order of-- maybe

00:08:40.440 --> 00:08:42.510
it's on the order of
30 million light years.

00:08:42.510 --> 00:08:44.100
And the math isn't exact here.

00:08:44.100 --> 00:08:47.620
I haven't done the
math to figure it out.

00:08:47.620 --> 00:08:50.360
So it's done 30
million light years.

00:08:50.360 --> 00:08:53.900
And actually I shouldn't even
make it the same proportion.

00:08:53.900 --> 00:08:56.592
Because the distance it's gone
and the distance it has to go,

00:08:56.592 --> 00:08:58.050
because of the
stretching, it's not

00:08:58.050 --> 00:08:59.714
going to be completely linear.

00:08:59.714 --> 00:09:02.380
At least when I'm thinking about
it in my head, it shouldn't be,

00:09:02.380 --> 00:09:02.960
I think.

00:09:02.960 --> 00:09:06.340
But I'm going to make a
hard statement about that.

00:09:06.340 --> 00:09:10.500
But the distance that it
reversed, maybe this distance

00:09:10.500 --> 00:09:15.790
right here is now 20
million light years

00:09:15.790 --> 00:09:16.920
because it got there.

00:09:16.920 --> 00:09:20.960
Every time it moved some
distance, the space that it

00:09:20.960 --> 00:09:23.020
had traversed is now stretched.

00:09:23.020 --> 00:09:27.660
So even though its traveled
for 10 million years,

00:09:27.660 --> 00:09:29.640
the space that it
traversed is no longer

00:09:29.640 --> 00:09:31.360
just 10 million light years.

00:09:31.360 --> 00:09:34.130
It's now stretched to
20 million light years.

00:09:34.130 --> 00:09:35.890
And the space that it
has left to traverse

00:09:35.890 --> 00:09:38.570
is no longer only 20
million light years.

00:09:38.570 --> 00:09:41.420
It might now be 80
million light years.

00:09:41.420 --> 00:09:44.410
It is now 80
million light years.

00:09:44.410 --> 00:09:47.060
And so this photon might
be getting frustrated.

00:09:47.060 --> 00:09:48.880
There's an optimistic
way of viewing it.

00:09:48.880 --> 00:09:50.670
It is like, wow, I
was able to cover

00:09:50.670 --> 00:09:53.387
20 million light years
in only 10 million years.

00:09:53.387 --> 00:09:55.720
It looks like I'm moving
faster than the speed of light.

00:09:55.720 --> 00:09:58.270
The reality is it's not
because the space coordinates

00:09:58.270 --> 00:10:00.610
themselves are spreading out.

00:10:00.610 --> 00:10:01.630
Those are getting thin.

00:10:01.630 --> 00:10:04.496
So the photon is just moving
at the speed of light.

00:10:04.496 --> 00:10:05.870
But the distance
that it actually

00:10:05.870 --> 00:10:10.090
traversed in 10 million
years is more than 10 million

00:10:10.090 --> 00:10:10.590
light years.

00:10:10.590 --> 00:10:12.090
It's 20 million light years.

00:10:12.090 --> 00:10:15.480
So you can't just
multiply a rate times time

00:10:15.480 --> 00:10:19.090
on these cosmological scales,
especially when the coordinates

00:10:19.090 --> 00:10:23.100
themselves, the distance
coordinates are actually

00:10:23.100 --> 00:10:24.690
moving away from each other.

00:10:24.690 --> 00:10:27.430
But I think you see,
or maybe you might see,

00:10:27.430 --> 00:10:29.520
where this is going.

00:10:29.520 --> 00:10:33.150
OK, this photon says, oh, in
another-- let me write this.

00:10:33.150 --> 00:10:35.430
This is 80 million light
years-- in another 40 million

00:10:35.430 --> 00:10:40.190
light years, maybe I'm
going to get over here.

00:10:40.190 --> 00:10:43.110
But the reality is over that
next 40 million light years--

00:10:43.110 --> 00:10:47.440
sorry, in 40 million years,
I might get right over here,

00:10:47.440 --> 00:10:49.650
because this is 80
million light years.

00:10:49.650 --> 00:10:52.420
But the reality is
after 40 million years--

00:10:52.420 --> 00:10:56.030
so another 40 million years
go by-- now, all of a sudden,

00:10:56.030 --> 00:10:59.750
the universe has
expanded even more.

00:10:59.750 --> 00:11:01.710
I won't even draw
the whole bubble.

00:11:01.710 --> 00:11:04.680
But the place where the
photon was emitted from

00:11:04.680 --> 00:11:07.630
might be over here.

00:11:07.630 --> 00:11:11.850
And now our current
position is over here.

00:11:11.850 --> 00:11:18.250
Where the light got after 10
million years is now over here.

00:11:18.250 --> 00:11:24.070
And now, where the light
is after 40 million years,

00:11:24.070 --> 00:11:27.500
maybe it's over here.

00:11:27.500 --> 00:11:29.520
So now this distance,
the distance

00:11:29.520 --> 00:11:32.240
between these two
points, when we started,

00:11:32.240 --> 00:11:33.590
it was 10 million light years.

00:11:33.590 --> 00:11:36.380
Then it became 20
million light years.

00:11:36.380 --> 00:11:39.100
Maybe now, it's on the order
of-- I don't know-- maybe it's

00:11:39.100 --> 00:11:41.140
a billion light years.

00:11:41.140 --> 00:11:43.240
Maybe now it's a
billion light years.

00:11:43.240 --> 00:11:45.512
And maybe this distance
over here-- and I'm

00:11:45.512 --> 00:11:46.720
just making up these numbers.

00:11:46.720 --> 00:11:49.450
In fact, that's probably be too
big for that point-- maybe this

00:11:49.450 --> 00:11:52.010
is now 100 million light years.

00:11:52.010 --> 00:11:55.390
This is now 100
million light years.

00:11:55.390 --> 00:11:59.050
And now, maybe
this distance right

00:11:59.050 --> 00:12:01.730
here is-- I don't know--
500 million light years.

00:12:01.730 --> 00:12:04.080
And maybe now the total
distance between the two points

00:12:04.080 --> 00:12:05.950
is a billion light years.

00:12:05.950 --> 00:12:08.730
So as you can see, the photon
might getting frustrated.

00:12:08.730 --> 00:12:10.230
As it covers more
and more distance,

00:12:10.230 --> 00:12:13.200
it looks back and says, wow,
in only 50 million years,

00:12:13.200 --> 00:12:16.020
I've been able to cover
600 million light years.

00:12:16.020 --> 00:12:16.910
That's pretty good.

00:12:16.910 --> 00:12:18.701
But it's frustrated
because what it thought

00:12:18.701 --> 00:12:22.510
was it only had to cover
30 million light years

00:12:22.510 --> 00:12:23.050
in distance.

00:12:23.050 --> 00:12:25.070
That keeps stretching
out because space

00:12:25.070 --> 00:12:26.560
itself is stretching.

00:12:26.560 --> 00:12:32.190
So the reality, just going
to the original idea,

00:12:32.190 --> 00:12:36.050
this photon that is
just reaching us,

00:12:36.050 --> 00:12:38.870
that's been traveling
for-- let's say

00:12:38.870 --> 00:12:41.690
it's been traveling
for 13.4 billion years.

00:12:41.690 --> 00:12:43.180
So it's reaching us is just now.

00:12:43.180 --> 00:12:46.690
So let me just fast
forward 13.4 billion years

00:12:46.690 --> 00:12:49.620
from this point now to
get to the present day.

00:12:49.620 --> 00:12:54.842
So if I draw the whole visible
universe right over here,

00:12:54.842 --> 00:12:56.300
this point right
over here is going

00:12:56.300 --> 00:13:00.340
to be-- where it was emitted
from is right over there.

00:13:00.340 --> 00:13:04.890
We are sitting right over there.

00:13:04.890 --> 00:13:06.640
And actually, let me
make something clear.

00:13:06.640 --> 00:13:08.770
If I'm drawing the whole
observable universe,

00:13:08.770 --> 00:13:10.922
the center actually
should be where we are.

00:13:10.922 --> 00:13:12.630
Because we can observe
an equal distance.

00:13:12.630 --> 00:13:14.640
If things aren't
really strange, we

00:13:14.640 --> 00:13:16.620
can observe an equal
distance in any direction.

00:13:16.620 --> 00:13:19.210
So actually maybe we should
put us at the center.

00:13:19.210 --> 00:13:21.650
So if this was the entire
observable universe,

00:13:21.650 --> 00:13:26.180
and the photon was emitted from
here 13.4 billion years ago--

00:13:26.180 --> 00:13:29.800
so 300,000 years after
that initial Big Bang,

00:13:29.800 --> 00:13:35.620
and it's just getting
to us, it is true

00:13:35.620 --> 00:13:41.150
that the photon
has been traveling

00:13:41.150 --> 00:13:47.050
for 13.7 billion years.

00:13:47.050 --> 00:13:50.900
But what's kind of nutty about
it is this object, since we've

00:13:50.900 --> 00:13:53.970
been expanding away from each
other, this object is now,

00:13:53.970 --> 00:13:56.180
in our best
estimates, this object

00:13:56.180 --> 00:14:06.420
is going to be about 46 billion
light years away from us.

00:14:08.785 --> 00:14:10.160
And I want to make
it very clear.

00:14:10.160 --> 00:14:13.220
This object is now 46 billion
light years away from us.

00:14:13.220 --> 00:14:16.781
When we just use light to
observe it, it looks like,

00:14:16.781 --> 00:14:18.530
just based on light
years, hey, this light

00:14:18.530 --> 00:14:21.280
has been traveling 13.7
billion years to reach us.

00:14:21.280 --> 00:14:22.981
That's our only way
of kind with light

00:14:22.981 --> 00:14:24.480
to kind of think
about the distance.

00:14:24.480 --> 00:14:27.740
So maybe it's 13.4
or whatever-- I

00:14:27.740 --> 00:14:31.340
keep changing the decimal-- but
13.4 billion light years away.

00:14:31.340 --> 00:14:36.600
But the reality is if you had a
ruler today, light year rulers,

00:14:36.600 --> 00:14:38.570
this space here has
stretched so much

00:14:38.570 --> 00:14:41.702
that this is now 46
billion light years.

00:14:41.702 --> 00:14:43.160
And just to give
you a hint of when

00:14:43.160 --> 00:14:45.100
we talk about the cosmic
microwave background

00:14:45.100 --> 00:14:47.959
radiation, what will
this point in space

00:14:47.959 --> 00:14:49.500
look like, this
thing that's actually

00:14:49.500 --> 00:14:52.010
46 billion light years
away, but the photon only

00:14:52.010 --> 00:14:54.540
took 13.7 billion
years to reach us?

00:14:54.540 --> 00:14:56.120
What will this look like?

00:14:56.120 --> 00:14:59.610
Well, when we say
look like, it's

00:14:59.610 --> 00:15:02.340
based on the photons that
are reaching us right now.

00:15:02.340 --> 00:15:05.350
Those photons left
13.4 billion years ago.

00:15:05.350 --> 00:15:07.090
So those photons are
the photons being

00:15:07.090 --> 00:15:10.040
emitted from this
primitive structure,

00:15:10.040 --> 00:15:16.460
from this white-hot
haze of hydrogen plasma.

00:15:16.460 --> 00:15:19.240
So what we're going to see
is this white-hot haze.

00:15:19.240 --> 00:15:26.930
So we're going to see this kind
of white-hot plasma, white hot,

00:15:26.930 --> 00:15:28.790
undifferentiated
not differentiated

00:15:28.790 --> 00:15:32.550
into proper stable atoms,
much less stars and galaxies,

00:15:32.550 --> 00:15:33.710
but white hot.

00:15:33.710 --> 00:15:36.220
We're going to see
this white-hot plasma.

00:15:36.220 --> 00:15:38.640
The reality today is
that point in space

00:15:38.640 --> 00:15:40.190
that's 46 billion
years from now,

00:15:40.190 --> 00:15:45.160
it's probably differentiated
into stable atoms, and stars,

00:15:45.160 --> 00:15:46.780
and planets, and galaxies.

00:15:46.780 --> 00:15:49.020
And frankly, if that
person, that person,

00:15:49.020 --> 00:15:51.210
if there is a civilization
there right now

00:15:51.210 --> 00:15:52.700
and if they're sitting right
there, and they're observing

00:15:52.700 --> 00:15:54.610
photons being emitted
from our coordinate,

00:15:54.610 --> 00:15:56.530
from our point in
space right now,

00:15:56.530 --> 00:15:57.920
they're not going to see us.

00:15:57.920 --> 00:16:01.810
They're going to see us
13.4 billion years ago.

00:16:01.810 --> 00:16:05.140
They're going to see the
super primitive state

00:16:05.140 --> 00:16:07.310
of our region of
space when it really

00:16:07.310 --> 00:16:09.164
was just a white-hot plasma.

00:16:09.164 --> 00:16:11.580
And we're going to talk more
about this in the next video.

00:16:11.580 --> 00:16:12.700
But think about it.

00:16:12.700 --> 00:16:15.510
Any photon that's coming
from that period in time,

00:16:15.510 --> 00:16:17.670
so from any direction,
that's been traveling

00:16:17.670 --> 00:16:21.170
for 13.4 billion years
from any direction,

00:16:21.170 --> 00:16:23.720
it's going to come from
that primitive state

00:16:23.720 --> 00:16:27.390
or it would have been
emitted when the universe was

00:16:27.390 --> 00:16:29.580
in that primitive
state, when it was just

00:16:29.580 --> 00:16:32.195
that white-hot plasma,
this undifferentiated mass.

00:16:32.195 --> 00:16:33.570
And hopefully,
that will give you

00:16:33.570 --> 00:16:36.480
a sense of where the
cosmic microwave background

00:16:36.480 --> 00:16:38.920
radiation comes from.


Big bang introduction

WEBVTT
Kind: captions
Language: en

00:00:00.780 --> 00:00:04.260
Right now, the prevailing theory
of how the universe came about

00:00:04.260 --> 00:00:07.015
is commonly called
the Big Bang theory.

00:00:11.220 --> 00:00:14.090
And really is just this idea
that the universe started

00:00:14.090 --> 00:00:17.610
as kind of this infinitely
small point, this infinitely

00:00:17.610 --> 00:00:19.590
small singularity.

00:00:19.590 --> 00:00:23.090
And then it just had a big
bang or it just expanded

00:00:23.090 --> 00:00:26.000
from that state to the universe
that we know right now.

00:00:26.000 --> 00:00:28.120
And when I first
imagined this-- and I

00:00:28.120 --> 00:00:31.500
think if it's also a byproduct
of how it's named-- Big Bang,

00:00:31.500 --> 00:00:37.440
you kind of imagine
this type of explosion,

00:00:37.440 --> 00:00:40.310
that everything was
infinitely packed in together

00:00:40.310 --> 00:00:42.070
and then it exploded.

00:00:42.070 --> 00:00:44.620
And then it exploded outward.

00:00:44.620 --> 00:00:47.670
And then as all of the
matter exploded outward,

00:00:47.670 --> 00:00:48.750
it started to condense.

00:00:48.750 --> 00:00:51.450
And then you have
these little galaxies

00:00:51.450 --> 00:00:53.772
and super clusters of galaxies.

00:00:53.772 --> 00:00:54.980
And they started to condense.

00:00:54.980 --> 00:00:58.830
And then within them, planets
condensed and stars condensed.

00:00:58.830 --> 00:01:00.480
And then we have
the type of universe

00:01:00.480 --> 00:01:01.760
that we have right now.

00:01:01.760 --> 00:01:05.220
But this model for
visualizing the Big Bang

00:01:05.220 --> 00:01:06.330
has a couple of problems.

00:01:06.330 --> 00:01:08.940
One is when we talk
about the Big Bang,

00:01:08.940 --> 00:01:12.590
we're not talking about the
matter, just the mass or just

00:01:12.590 --> 00:01:14.810
the matter in the universe
being in one point.

00:01:14.810 --> 00:01:18.790
We're talking about
actual space expanding.

00:01:18.790 --> 00:01:21.630
So we're not just talking about
something inside of space,

00:01:21.630 --> 00:01:23.920
like the physical mass, the
physical matter expanding.

00:01:23.920 --> 00:01:25.870
We're talking
about space itself.

00:01:25.870 --> 00:01:27.559
And so when you have
this type of model,

00:01:27.559 --> 00:01:29.100
you have all of this
stuff expanding.

00:01:29.100 --> 00:01:30.641
But you're like,
whoa, look, isn't it

00:01:30.641 --> 00:01:32.590
expanding into something else?

00:01:32.590 --> 00:01:36.080
Maybe if the furthest
out parts of this matter

00:01:36.080 --> 00:01:40.730
is right over here, what's
this stuff over here?

00:01:40.730 --> 00:01:43.530
And so you say, well,
wouldn't that be space?

00:01:43.530 --> 00:01:46.590
So how can you say space
itself is expanding?

00:01:46.590 --> 00:01:49.270
And another idea
that a Big Bang also

00:01:49.270 --> 00:01:51.480
implies is if this is the
furthest stuff out there,

00:01:51.480 --> 00:01:55.690
would this be the
edge of the universe?

00:01:55.690 --> 00:01:58.500
Does the universe have an edge?

00:01:58.500 --> 00:02:00.772
And the answer to either
of those questions,

00:02:00.772 --> 00:02:02.980
and that's what we're going
to try to tackle in this,

00:02:02.980 --> 00:02:05.810
is that, one, the universe
does not have an edge.

00:02:05.810 --> 00:02:09.080
And two, there is
no outside space.

00:02:09.080 --> 00:02:11.140
We are not expanding
into another space.

00:02:11.140 --> 00:02:12.390
And I'm going to explain that.

00:02:12.390 --> 00:02:15.140
Hopefully, we'll see why
that is the case right now.

00:02:15.140 --> 00:02:16.730
So the best way to
view it-- and we're

00:02:16.730 --> 00:02:19.380
going to view it by analogy.

00:02:19.380 --> 00:02:31.020
If I were tell you that I have
a two-dimensional space that

00:02:31.020 --> 00:02:37.600
has a finite area, so
it has a finite area--

00:02:37.600 --> 00:02:38.970
so it's not infinite.

00:02:38.970 --> 00:02:40.925
And it also has no edge.

00:02:43.860 --> 00:02:47.150
This once again, when you first
look at it, seems difficult.

00:02:47.150 --> 00:02:49.060
How do I just
construct something

00:02:49.060 --> 00:02:51.470
that has a finite area,
but still has no edge?

00:02:51.470 --> 00:02:53.230
Every time I try
to draw an area,

00:02:53.230 --> 00:02:55.430
it looks like I have
to have some edges.

00:02:55.430 --> 00:02:57.340
And then you might
remember, what

00:02:57.340 --> 00:03:00.775
if that two-dimensional space
is curved, what happens?

00:03:00.775 --> 00:03:02.730
And I think the
easiest example of that

00:03:02.730 --> 00:03:06.250
is the surface of a sphere.

00:03:06.250 --> 00:03:09.310
Let me draw a sphere over here.

00:03:09.310 --> 00:03:11.690
So this right here is a sphere.

00:03:11.690 --> 00:03:16.440
Let me draw some
longitude and latitudinal

00:03:16.440 --> 00:03:18.300
lines on this sphere.

00:03:18.300 --> 00:03:20.050
On this sphere, all
of a sudden-- and I'll

00:03:20.050 --> 00:03:21.425
shade it in a
little bit, make it

00:03:21.425 --> 00:03:25.989
look nice-- this type of a
sphere, you have a finite area.

00:03:25.989 --> 00:03:27.780
You could imagine the
surface of a balloon,

00:03:27.780 --> 00:03:30.610
or the surface of a bubble,
or the surface of the Earth.

00:03:30.610 --> 00:03:33.350
You have a finite area,
but you have no edge.

00:03:33.350 --> 00:03:39.410
If you keep going
forever in one direction,

00:03:39.410 --> 00:03:42.980
you're going to go all the
way around and come back

00:03:42.980 --> 00:03:44.330
to the other side.

00:03:44.330 --> 00:03:47.350
Now, to imagine a
three-dimensional space

00:03:47.350 --> 00:03:50.887
that has these same
properties, a finite area

00:03:50.887 --> 00:03:52.970
and-- and I don't want to
say finite area anymore,

00:03:52.970 --> 00:03:55.386
because we're not talking about
a three-dimensional space.

00:03:55.386 --> 00:03:56.610
Let me draw it over here.

00:03:56.610 --> 00:04:00.220
So let's think about a
three-dimensional space, so

00:04:00.220 --> 00:04:07.530
a three-dimensional space.

00:04:07.530 --> 00:04:10.250
Instead of area, since we're
in three dimensions now,

00:04:10.250 --> 00:04:20.649
I want to talk about a
finite volume and no edge.

00:04:20.649 --> 00:04:21.464
How do I do that?

00:04:21.464 --> 00:04:23.214
And when you think
about it superficially,

00:04:23.214 --> 00:04:25.600
well, look, if I
have a finite volume,

00:04:25.600 --> 00:04:29.180
maybe it'll be contained
in some type of a cube.

00:04:29.180 --> 00:04:32.216
And then we clearly have
edges in those situations.

00:04:32.216 --> 00:04:34.090
Or you could even think
about a finite volume

00:04:34.090 --> 00:04:36.530
as being the inside of a sphere.

00:04:36.530 --> 00:04:39.459
And that clearly has an edge,
this entire surface over there.

00:04:39.459 --> 00:04:41.500
So how do you construct
a three-dimensional space

00:04:41.500 --> 00:04:43.590
that has a finite
volume and no edge?

00:04:43.590 --> 00:04:45.380
And that I'm going to
tell you right now,

00:04:45.380 --> 00:04:48.516
it's very hard for
us to visualize it.

00:04:48.516 --> 00:04:49.890
But in order to
visualize it, I'm

00:04:49.890 --> 00:04:51.556
essentially going to
draw the same thing

00:04:51.556 --> 00:04:52.560
as I drew right here.

00:04:52.560 --> 00:04:54.940
What you have to
imagine, and you almost

00:04:54.940 --> 00:04:56.990
have to imagine it by
analogy, unless you

00:04:56.990 --> 00:04:59.700
have some type of a
profound brain wired

00:04:59.700 --> 00:05:06.080
for more than three spatial
dimensions, is a sphere.

00:05:06.080 --> 00:05:08.844
So let me make it clear.

00:05:08.844 --> 00:05:10.260
This is a
two-dimensional surface.

00:05:15.745 --> 00:05:17.120
On the surface of
the sphere, you

00:05:17.120 --> 00:05:20.740
can only move into directions,
two perpendicular directions.

00:05:20.740 --> 00:05:23.350
You could move like that or
you could move like that.

00:05:23.350 --> 00:05:25.850
You could move left and right
or you could move up and down.

00:05:25.850 --> 00:05:29.340
So it's a
two-dimensional surface

00:05:29.340 --> 00:05:35.960
of a three-dimensional sphere.

00:05:35.960 --> 00:05:38.766
So if we take it by
analogy, let's imagine,

00:05:38.766 --> 00:05:42.006
and it's hard to imagine, a
three-dimensional surface.

00:05:45.116 --> 00:05:46.490
And you can do it
mathematically.

00:05:46.490 --> 00:05:48.790
The math here is actually
not that difficult.

00:05:48.790 --> 00:05:52.970
It's a three-dimensional surface
of a four-dimensional sphere.

00:06:00.807 --> 00:06:02.390
And I'm going to
draw it the same way.

00:06:02.390 --> 00:06:04.223
So if we kind of view
those three dimensions

00:06:04.223 --> 00:06:07.960
are just these two dimensions
of the surface, the same thing.

00:06:07.960 --> 00:06:09.005
It's the same thing.

00:06:09.005 --> 00:06:10.380
And if you imagine
that-- I'm not

00:06:10.380 --> 00:06:12.671
saying that this is actually
the shape of the universe.

00:06:12.671 --> 00:06:15.020
We don't know the actual shape.

00:06:15.020 --> 00:06:17.800
But we do know that it does
have a slight curvature.

00:06:17.800 --> 00:06:20.709
We don't know the actual shape,
but a sphere is the simplest.

00:06:20.709 --> 00:06:22.000
There's other ones we could do.

00:06:22.000 --> 00:06:25.860
A toroid would also fit the
bill of having a finite volume

00:06:25.860 --> 00:06:26.402
with no edge.

00:06:26.402 --> 00:06:28.193
And another thing, I
want to make it clear,

00:06:28.193 --> 00:06:29.910
we actually don't
even know whether it

00:06:29.910 --> 00:06:31.331
has just a finite volume.

00:06:31.331 --> 00:06:32.580
That's still an open question.

00:06:32.580 --> 00:06:34.070
But what I want
to do is show you

00:06:34.070 --> 00:06:38.460
that it can have a finite
volume and also have no edge.

00:06:38.460 --> 00:06:43.350
And most people believe-- and
I want to say "believe" here

00:06:43.350 --> 00:06:45.740
because we can just go
based on evidence and all

00:06:45.740 --> 00:06:49.500
that-- that we are talking about
something with a finite volume,

00:06:49.500 --> 00:06:52.300
especially when you talk
about the Big Bang theory.

00:06:52.300 --> 00:06:56.750
That kind of, on some dimension,
implies a finite volume,

00:06:56.750 --> 00:06:59.600
although it could be a super
large, unfathomably large

00:06:59.600 --> 00:07:01.520
volume, it is finite.

00:07:01.520 --> 00:07:05.380
Now, if you have this,
let's imagine this sphere.

00:07:05.380 --> 00:07:06.800
Let's imagine this sphere.

00:07:06.800 --> 00:07:09.670
Once again, if you're
on this surface

00:07:09.670 --> 00:07:11.070
of this four-dimensional
sphere--

00:07:11.070 --> 00:07:14.110
I obviously can not draw
a four-dimensional sphere.

00:07:14.110 --> 00:07:17.650
But if you're on the surface of
this four-dimensional sphere,

00:07:17.650 --> 00:07:20.960
if you go in any direction,
you'll come back out

00:07:20.960 --> 00:07:22.680
and come back to
where you started.

00:07:22.680 --> 00:07:25.405
If you go that way, you'll
come back around here.

00:07:25.405 --> 00:07:26.780
Now, the universe is super huge.

00:07:26.780 --> 00:07:29.150
So even light,
maybe light itself

00:07:29.150 --> 00:07:32.160
will take an unbelievable
amount of time to traverse it.

00:07:32.160 --> 00:07:35.570
And if this sphere
itself is expanding,

00:07:35.570 --> 00:07:39.120
it might be expanding so fast
that light might not ever

00:07:39.120 --> 00:07:40.580
be able to come back around it.

00:07:40.580 --> 00:07:42.820
But in theory, if
something were fast enough,

00:07:42.820 --> 00:07:44.860
if something were to
keep going around,

00:07:44.860 --> 00:07:47.250
it could eventually
go back to this point.

00:07:47.250 --> 00:07:50.770
Now, when we talk about a
three-dimensional surface--

00:07:50.770 --> 00:07:53.630
it's a three-dimensional surface
of a four-dimensional sphere--

00:07:53.630 --> 00:07:56.310
that means that any of the
three dimensions-- over here,

00:07:56.310 --> 00:07:57.810
on the surface, I
can only draw two.

00:07:57.810 --> 00:08:01.410
But that means if this is
true, if the universe is

00:08:01.410 --> 00:08:06.060
a three-dimensional surface of
a four-dimensional sphere, that

00:08:06.060 --> 00:08:09.820
means that if you go up
and you just keep going up,

00:08:09.820 --> 00:08:12.030
you'll eventually come
back from the bottom.

00:08:12.030 --> 00:08:16.500
So if you keep going
all the way up,

00:08:16.500 --> 00:08:18.990
you'll eventually come back
to the point that you were.

00:08:18.990 --> 00:08:20.930
It might be an unbelievably
large distance,

00:08:20.930 --> 00:08:23.560
but you'll eventually
get back where you were.

00:08:23.560 --> 00:08:25.370
If you go to the right,
you'll eventually

00:08:25.370 --> 00:08:28.020
come back all the way around
to the point where you were.

00:08:28.020 --> 00:08:29.710
And if you were to
go into the page--

00:08:29.710 --> 00:08:31.400
so if you were to
go into the page--

00:08:31.400 --> 00:08:33.909
let me draw it that way--
if you go into the page,

00:08:33.909 --> 00:08:36.789
you would eventually come
back from above the page

00:08:36.789 --> 00:08:38.740
and come back to the
point that you are.

00:08:38.740 --> 00:08:41.000
So that's what this
implication would be.

00:08:41.000 --> 00:08:43.360
That you would eventually
get back to where you are.

00:08:43.360 --> 00:08:46.730
So let's go back to the question
of an expanding universe,

00:08:46.730 --> 00:08:50.030
a expanding universe that's not
expanding into any other space.

00:08:50.030 --> 00:08:53.300
That is all of the space,
but it's still expanding.

00:08:53.300 --> 00:08:54.440
Well, this is the model.

00:08:54.440 --> 00:08:57.720
So you could imagine
shortly after the Big Bang,

00:08:57.720 --> 00:09:01.590
our four-dimensional
sphere looked like this.

00:09:01.590 --> 00:09:05.780
Maybe it was a little small
four-dimensional sphere.

00:09:05.780 --> 00:09:07.470
Maybe right at the
Big Bang, it was

00:09:07.470 --> 00:09:09.460
like this little
unbelievably small sphere.

00:09:09.460 --> 00:09:12.080
Then a little bit later,
it's this larger sphere.

00:09:12.080 --> 00:09:15.494
Let me just shade
it in to show you

00:09:15.494 --> 00:09:18.160
that it's kind of popping out of
the page, that's it's a sphere.

00:09:18.160 --> 00:09:21.840
And then at a later time, the
sphere might look like this.

00:09:21.840 --> 00:09:25.170
The sphere might look like this.

00:09:25.170 --> 00:09:28.000
Now, your temptation
might be to say, wait,

00:09:28.000 --> 00:09:31.160
Sal, isn't this stuff
outside of this sphere,

00:09:31.160 --> 00:09:34.630
isn't that some type of a
space that it's expanding into?

00:09:34.630 --> 00:09:37.470
Isn't that somehow
part of the universe?

00:09:37.470 --> 00:09:40.550
And I would say if you're
talking in three dimensions,

00:09:40.550 --> 00:09:41.400
no, it's not.

00:09:41.400 --> 00:09:44.620
The entire universe
is this surface.

00:09:44.620 --> 00:09:47.930
It is this surface of this
four-dimensional sphere.

00:09:47.930 --> 00:09:49.880
If you start talking
about more dimensions,

00:09:49.880 --> 00:09:52.970
then, yes, you could talk
about maybe things outside

00:09:52.970 --> 00:09:56.450
of our three-dimensional
universe.

00:09:56.450 --> 00:09:59.150
So as this expands
in space/time--

00:09:59.150 --> 00:10:01.230
so one way to view
the fourth dimension

00:10:01.230 --> 00:10:03.550
is it is time itself--
things are just

00:10:03.550 --> 00:10:05.307
getting further
and further apart.

00:10:05.307 --> 00:10:07.390
And I'll talk about more
evidence in future videos

00:10:07.390 --> 00:10:11.930
for why the Big Bang is the best
theory we have out there right

00:10:11.930 --> 00:10:12.550
now.

00:10:12.550 --> 00:10:14.270
But as you could
imagine, if you have

00:10:14.270 --> 00:10:17.200
two points on this sphere
that are that far apart,

00:10:17.200 --> 00:10:20.690
as this sphere expands, this
four-dimensional sphere, as

00:10:20.690 --> 00:10:23.040
this bubble blows up or
this balloon blows up,

00:10:23.040 --> 00:10:25.485
those two points are just--
let me draw three points.

00:10:25.485 --> 00:10:26.860
Let's say those
are three points.

00:10:26.860 --> 00:10:28.235
Those three points
are just going

00:10:28.235 --> 00:10:30.520
to get further
and further apart.

00:10:30.520 --> 00:10:35.174
And that's actually one of
the main points that-- or one

00:10:35.174 --> 00:10:37.840
of the first reasons why it made
sense to believe the Big Bang--

00:10:37.840 --> 00:10:40.920
is that everything is expanding,
not from some central point.

00:10:40.920 --> 00:10:43.385
But everything is
expanding from everything.

00:10:43.385 --> 00:10:46.010
That if you go in any direction
from any point in the universe,

00:10:46.010 --> 00:10:47.240
everything else
is expanding away.

00:10:47.240 --> 00:10:48.781
And the further away
you go, it looks

00:10:48.781 --> 00:10:52.041
like the faster it's
expanding away from you.

00:10:52.041 --> 00:10:53.790
So I'll leave you
there, something for you

00:10:53.790 --> 00:10:55.681
to kind of think
about a little bit.

00:10:55.681 --> 00:10:57.180
And then we'll build
on some of this

00:10:57.180 --> 00:11:00.570
to think about what it
means to kind of observe

00:11:00.570 --> 00:11:02.780
the observable universe.


Hubble image of galaxies

WEBVTT
Kind: captions
Language: en

00:00:00.705 --> 00:00:06.432
The whole point of this video is really just to look at, what in my mind is one of the coolest pictures

00:00:06.432 --> 00:00:09.683
ever taken by anything, and this was actually taken by the Hubble telescope

00:00:10.145 --> 00:00:18.228
and what they did is, they pointed the telescope at this area of our night sky

00:00:18.228 --> 00:00:21.200
and obviously the Hubble telescope, it's out in orbit, so it doesn't have to worry about

00:00:21.200 --> 00:00:25.222
all the interference from our actual atmosphere, so it gets a nice good look at things,

00:00:25.222 --> 00:00:30.766
but it's right over here, relative to the moon, and obviously the moon is moving around,

00:00:30.766 --> 00:00:33.692
but on that day, it was here, relative to the moon

00:00:33.692 --> 00:00:37.361
and they picked this location. They picked this location right over here

00:00:37.361 --> 00:00:40.751
because there weren't that many nearby stars there so

00:00:40.751 --> 00:00:45.767
it really allowed the telescope, because if there were nearby stars that light would've kind of outshone

00:00:45.767 --> 00:00:51.432
things that are behind it further away maybe perhaps galaxies. So just keep in mind everything you're

00:00:51.432 --> 00:00:56.356
going to see is in this little patch of the night sky, and I think the main point for showing the moon

00:00:56.356 --> 00:00:59.791
here. Obviously the moon is moving around so I'm not going to tell you which exact patch of sky this

00:00:59.791 --> 00:01:05.364
is. But to really give you an idea of how small of a patch of sky that really is. You really could've

00:01:05.364 --> 00:01:09.451
done this with any patch of sky, but in other patches of sky there wouldve been nearby stars that would've

00:01:09.451 --> 00:01:13.445
blocked things, but the galaxies are there, beyond that. The clusters of galaxies, and the super clusters

00:01:13.445 --> 00:01:18.414
of galaxies. So with that said out of the way, just remember everything we're talking about in this video

00:01:18.414 --> 00:01:24.776
is in this little patch of sky right over here. The whole point of this, once again like all of these

00:01:24.776 --> 00:01:32.133
videos is really to kind of just blow your mind. So this right here is what the Hubble telescope saw in that

00:01:32.133 --> 00:01:37.467
patch. Everything, everything that I'm showing you right here. I just want to be clear, some of these

00:01:37.467 --> 00:01:45.117
things are nearby stars, but most of these things are galaxies. That's a galaxy. That is a galaxy. That

00:01:45.117 --> 00:01:51.467
is a galaxy. That's a galaxy, and that's a galaxy. The reason I want to draw you this, obviously in the

00:01:51.467 --> 00:01:56.773
last video I showed you our local group, I showed you the Virgo super cluster, I showed you the kind of

00:01:56.773 --> 00:02:02.764
clusters of clusters and I even showed you the depiction of the observable universe. But what is amazing

00:02:02.764 --> 00:02:08.290
about this, is this is an actual picture. This is actually an image of a galaxy. Hey there is another

00:02:08.290 --> 00:02:12.375
galaxy. Oh look there's another galaxy up here. That you can keep doing that forever and this is just

00:02:12.375 --> 00:02:18.089
in that little patch of sky, and this is obviously not all of the galaxies of the universe. These are

00:02:18.089 --> 00:02:22.687
just the ones that we could see. There ones that might be even further, or there definitely are ones

00:02:22.687 --> 00:02:27.702
that are further back and their light is just even more. We could probably even focus on a patch of sky

00:02:27.702 --> 00:02:33.786
like that and see that many galaxies again. You can kind of keep, keep zooming in, but I just this thing,

00:02:33.786 --> 00:02:39.080
and I encourage you I mean there's so many unbelievable images you can look up. They're all on NASA's

00:02:39.080 --> 00:02:45.333
website, a lot of these are on Wikipedia. But these images are just unbelievable. You can see a galaxy,

00:02:45.333 --> 00:02:52.455
another galaxy, another galaxy, another galaxy. I suspect some of this stuff might actually be clusters

00:02:52.455 --> 00:02:59.374
of galaxies. Galaxy, another galaxy. And remember I'm just circling these galaxies, just left and right,

00:02:59.374 --> 00:03:04.761
and you kind of lose sight of what each galaxy actually is. These galaxies have hundred of billions

00:03:04.761 --> 00:03:13.956
of stars. That even from you know one pixel on these galaxies is unimaginable distance. Something that

00:03:13.956 --> 00:03:19.133
we could never, based with current technology, or even current science, we could ever hope to traverse

00:03:19.133 --> 00:03:25.798
in the lifetime of humanity. Not, much left in a lifetime of one individual. So these are just

00:03:25.798 --> 00:03:31.133
enormous things, and they're just an infinite number of them. So I just wanted to highlight this with

00:03:31.133 --> 00:03:42.099
you, and really just look at it. Its kind of breathtaking. Another galaxy right over there. I'm not going

00:03:42.099 --> 00:03:46.418
to keep doing it the whole day. I feel kind of bad for drawing on it, it kind of ruins the picture. But

00:03:46.418 --> 00:03:52.780
look at that, that's a nice looking galaxy right there. You got a bunch right over here. It really is

00:03:52.780 --> 00:04:03.368
just, you know. This video its probably the least dense with actual instruction, but hopefully the

00:04:03.368 --> 00:04:08.755
most dense with inspiration. Anyway, hopefully you enjoyed that. Let me just finish looking at the entire

00:04:08.755 --> 99:59:59.999
picture. I mean it just keeps going ,and going we can keep looking at it.


Intergalactic scale

WEBVTT
Kind: captions
Language: en

00:00:00.560 --> 00:00:02.200
Where we left off
in the last video,

00:00:02.200 --> 00:00:04.810
we were just kind
of staring, amazed,

00:00:04.810 --> 00:00:07.550
at this Earth's view of
the Milky Way galaxy,

00:00:07.550 --> 00:00:10.540
just making sure we
understood how enormous

00:00:10.540 --> 00:00:12.530
and how many stars
we were looking at.

00:00:12.530 --> 00:00:15.100
And even if each of
these dots were a star,

00:00:15.100 --> 00:00:16.470
this is a huge amount of stars.

00:00:16.470 --> 00:00:20.360
But a lot of these dots
are thousands of stars.

00:00:20.360 --> 00:00:23.170
So our mind was already blown.

00:00:23.170 --> 00:00:25.140
But what we're going
to see in this video

00:00:25.140 --> 00:00:28.089
is that in some ways, this is
kind of just the beginning.

00:00:28.089 --> 00:00:29.630
And to some degree,
I'm going to stop

00:00:29.630 --> 00:00:33.180
doing these particles of sand
and a football field analogy

00:00:33.180 --> 00:00:36.870
because at some point,
the particles of sand

00:00:36.870 --> 00:00:38.500
become so vast
that are our minds

00:00:38.500 --> 00:00:40.060
can't even grasp
it to begin with.

00:00:40.060 --> 00:00:42.130
But let's just start
with our Milky Way.

00:00:42.130 --> 00:00:45.280
And we saw in the last video,
the Milky Way right here,

00:00:45.280 --> 00:00:48.950
we're sitting here about 25,000
light years from the center.

00:00:48.950 --> 00:00:54.330
It's roughly 100,000
light years in diameter.

00:00:54.330 --> 00:00:56.810
And then, let's put
it in perspective

00:00:56.810 --> 00:00:58.670
of its local neighborhood.

00:00:58.670 --> 00:01:00.222
So let's look at
the Local Group.

00:01:00.222 --> 00:01:01.680
And when we talk
about Local Group,

00:01:01.680 --> 00:01:03.679
we're talking about the
local group of galaxies.

00:01:06.330 --> 00:01:09.350
So this right here is the
Milky Way's Local Group.

00:01:09.350 --> 00:01:11.880
That's us right
there, sitting right

00:01:11.880 --> 00:01:14.620
over here, about
25,000 light years

00:01:14.620 --> 00:01:16.310
from the center
of the Milky Way.

00:01:16.310 --> 00:01:20.090
You have some of these
"small"-- and I use "small"

00:01:20.090 --> 00:01:23.550
in quotation marks-- because
these are also vast entities,

00:01:23.550 --> 00:01:25.420
also unimaginable entities.

00:01:25.420 --> 00:01:28.580
But we have these
satellite galaxies around,

00:01:28.580 --> 00:01:30.580
under the gravitational
influence, some of them,

00:01:30.580 --> 00:01:32.880
of the Milky Way.

00:01:32.880 --> 00:01:34.950
But the nearest
large galaxy to us

00:01:34.950 --> 00:01:36.740
is Andromeda right over here.

00:01:36.740 --> 00:01:38.157
And this distance
right over here.

00:01:38.157 --> 00:01:39.698
And now, we're going
to start talking

00:01:39.698 --> 00:01:41.560
in the millions of light years.

00:01:41.560 --> 00:01:50.760
So this distance right here
is 2.5 million light years.

00:01:50.760 --> 00:01:54.150
And just as a bit of reference,
if that's any reference at all,

00:01:54.150 --> 00:02:01.250
one light year is roughly
the radius of the Oort Cloud.

00:02:01.250 --> 00:02:05.260
Or another way to think about
it, one radius of the Oort

00:02:05.260 --> 00:02:10.560
Cloud is about 50,000 or
60,000 astronomical units.

00:02:10.560 --> 00:02:12.950
And that's the distance
from the Sun to the Earth.

00:02:12.950 --> 00:02:17.250
So you could view this
as 2.5 million times

00:02:17.250 --> 00:02:22.240
60,000 or so times the distance
from the Sun to the Earth.

00:02:22.240 --> 00:02:24.729
So this is an unbelievably
large distance

00:02:24.729 --> 00:02:25.770
we're talking about here.

00:02:25.770 --> 00:02:28.770
And that's to get to the
next big galaxy over here.

00:02:28.770 --> 00:02:31.940
But even these things are huge
things with many-- I mean,

00:02:31.940 --> 00:02:34.290
just unfathomably many-- stars.

00:02:34.290 --> 00:02:36.230
But Andromeda, in
particular, we said

00:02:36.230 --> 00:02:40.020
that the Milky Way has
200 to 400 billion stars.

00:02:40.020 --> 00:02:42.650
Andromeda, people
believe, has on the order

00:02:42.650 --> 00:02:47.450
of 1 trillion stars.

00:02:47.450 --> 00:02:50.500
So these just start
to become numbers.

00:02:50.500 --> 00:02:51.405
It's hard to grasp.

00:02:51.405 --> 00:02:52.780
But we're not
going to stop here.

00:02:52.780 --> 00:02:56.780
So in this, over here, this
whole diagram right here,

00:02:56.780 --> 00:02:58.420
it's about four
light years across,

00:02:58.420 --> 00:02:59.669
if you go from point to point.

00:02:59.669 --> 00:03:01.560
If you go from one
side to the other side,

00:03:01.560 --> 00:03:03.200
this is about-- not
four light years.

00:03:03.200 --> 00:03:03.700
Sorry.

00:03:03.700 --> 00:03:05.305
This is 4 million light years.

00:03:10.770 --> 00:03:14.690
Four light years is just
the distance from us

00:03:14.690 --> 00:03:16.310
to the Alpha Centauri.

00:03:16.310 --> 00:03:17.450
So that was nothing.

00:03:17.450 --> 00:03:21.820
That would only take that a
Voyager 1 80,000 years to get.

00:03:21.820 --> 00:03:23.650
This is 4 million light years.

00:03:23.650 --> 00:03:27.650
So 4 million times the
distance to the nearest star.

00:03:27.650 --> 00:03:31.590
But even this is-- I mean I'm
starting to stumble on my words

00:03:31.590 --> 00:03:34.290
because there's really no words
to describe it-- even this is

00:03:34.290 --> 00:03:37.850
small on an intergalactic scale.

00:03:37.850 --> 00:03:43.310
Because when you zoom out more,
you can see our Local Group.

00:03:43.310 --> 00:03:48.000
Our local group is
right over here.

00:03:48.000 --> 00:03:51.270
And this right over here
is the Virgo Super Cluster.

00:03:51.270 --> 00:03:53.660
And each dot here is
at least one galaxy.

00:03:53.660 --> 00:03:55.435
But it might be more
than one galaxy.

00:03:58.470 --> 00:04:12.350
And the diameter here is
150 million light years.

00:04:12.350 --> 00:04:15.390
So what we saw in the Local
Group, in the last diagram,

00:04:15.390 --> 00:04:18.250
the distance from the
Milky Way to Andromeda,

00:04:18.250 --> 00:04:20.680
which was 2 and 1/2
million light years, which

00:04:20.680 --> 00:04:22.647
would be just a little
dot just like that,

00:04:22.647 --> 00:04:24.480
that would be the
distance between the Milky

00:04:24.480 --> 00:04:25.690
Way and Andromeda.

00:04:25.690 --> 00:04:27.900
And now, we're looking at
the Virgo Super Cluster

00:04:27.900 --> 00:04:30.340
that is 150 million light years.

00:04:30.340 --> 00:04:31.470
But we're not done yet.

00:04:31.470 --> 00:04:34.030
We can zoom out even more.

00:04:34.030 --> 00:04:38.000
We can zoom out even
more, and over here.

00:04:38.000 --> 00:04:39.650
So you had your
Virgo Super Cluster,

00:04:39.650 --> 00:04:43.000
150 million light years
was that last diagram,

00:04:43.000 --> 00:04:44.280
this diagram right over here.

00:04:44.280 --> 00:04:46.404
I want to keep both of them
on the screen if I can.

00:04:46.404 --> 00:04:50.200
This diagram right here, 150
million light years across.

00:04:50.200 --> 00:04:56.340
That would fit right about
here on this diagram.

00:04:56.340 --> 00:04:59.340
So this is all of the super
clusters that are near us.

00:04:59.340 --> 00:05:03.200
And once again, "near" has to be
used very, very, very loosely.

00:05:03.200 --> 00:05:09.620
Here, this distance is about
150 million light years.

00:05:09.620 --> 00:05:11.990
A billion light years
is-- two, three,

00:05:11.990 --> 00:05:15.690
four, five-- a billion light
years is about from here

00:05:15.690 --> 00:05:16.310
to there.

00:05:16.310 --> 00:05:18.700
So we're starting to talk
on a fairly massive--

00:05:18.700 --> 00:05:20.908
I guess we've always been
talking on a massive scale.

00:05:20.908 --> 00:05:22.770
But now, it's an even
more massive scale.

00:05:22.770 --> 00:05:24.370
But we're still not done.

00:05:24.370 --> 00:05:26.522
Because this whole
diagram-- now these dots

00:05:26.522 --> 00:05:28.730
that you're seeing now, I
want to make it very clear.

00:05:28.730 --> 00:05:29.730
These aren't stars.

00:05:29.730 --> 00:05:31.230
These aren't even
clusters of stars.

00:05:31.230 --> 00:05:33.150
These aren't even
clusters of millions

00:05:33.150 --> 00:05:34.710
or even billions of stars.

00:05:34.710 --> 00:05:38.670
Each of these dots are
clusters of galaxies,

00:05:38.670 --> 00:05:41.520
each of those galaxies
having hundreds of billions

00:05:41.520 --> 00:05:43.490
to trillions of stars.

00:05:43.490 --> 00:05:46.925
So we're just on an unbelievably
massive scale at this point.

00:05:46.925 --> 00:05:48.590
But we're still not done.

00:05:48.590 --> 00:05:50.120
We're still not done.

00:05:50.120 --> 00:05:53.630
This is roughly about a
billion light years across.

00:05:53.630 --> 00:05:56.590
But right here is
actually the best estimate

00:05:56.590 --> 00:05:57.980
of the visible universe.

00:05:57.980 --> 00:05:59.355
And in future
videos, we're going

00:05:59.355 --> 00:06:01.834
to talk a lot more about what
the visible universe means.

00:06:01.834 --> 00:06:03.250
So if you were to
zoom out enough,

00:06:03.250 --> 00:06:11.250
this entire diagram right here,
about a billion light years,

00:06:11.250 --> 00:06:13.680
would fit just like that.

00:06:13.680 --> 00:06:21.500
So we're talking about a super
small amount of this part

00:06:21.500 --> 00:06:22.000
right here.

00:06:22.000 --> 00:06:23.330
And this is just the
visible universe.

00:06:23.330 --> 00:06:24.330
I want to make it clear.

00:06:24.330 --> 00:06:25.664
This is not the entire universe.

00:06:25.664 --> 00:06:27.163
And we say it's the
visible universe

00:06:27.163 --> 00:06:28.920
because think about
what's happening.

00:06:28.920 --> 00:06:32.490
When we think about
the a point out here,

00:06:32.490 --> 00:06:34.290
and we're observing
it, and that's let's

00:06:34.290 --> 00:06:37.400
say 13 billion light years away.

00:06:37.400 --> 00:06:38.770
Let's say that point 13 billion.

00:06:38.770 --> 00:06:40.228
We're going to talk
more about this

00:06:40.228 --> 00:06:44.220
in future videos, 13
billion light years.

00:06:46.940 --> 00:06:49.387
And I feel it's
almost a sacrilege

00:06:49.387 --> 00:06:51.720
to be writing on this because
this complexity that we're

00:06:51.720 --> 00:06:53.550
seeing here is
just mind boggling.

00:06:53.550 --> 00:06:58.800
But this 13 billion light
year away object, the light

00:06:58.800 --> 00:07:00.060
is just getting to us.

00:07:00.060 --> 00:07:05.530
This light left some point
13 billion light years ago.

00:07:05.530 --> 00:07:09.610
So what we're actually doing
is observing that object close

00:07:09.610 --> 00:07:11.907
to the beginning of
the actual universe.

00:07:11.907 --> 00:07:13.740
And the reason why it's
the visible universe

00:07:13.740 --> 00:07:15.698
is there might have been
something a little bit

00:07:15.698 --> 00:07:16.530
further out.

00:07:16.530 --> 00:07:19.540
Maybe it's light hasn't reached
us yet or maybe the universe

00:07:19.540 --> 00:07:21.380
itself, and we'll
talk more about this,

00:07:21.380 --> 00:07:24.800
it's expanding so fast that the
light will never, ever reach

00:07:24.800 --> 00:07:25.300
us.

00:07:25.300 --> 00:07:29.430
So it's actually a
huge question mark

00:07:29.430 --> 00:07:32.024
on how big the
actual universe is.

00:07:32.024 --> 00:07:34.440
And then some people might
say, well, does it even matter?

00:07:34.440 --> 00:07:37.542
Because this by itself
is a huge distance.

00:07:37.542 --> 00:07:39.500
And I want to make it
clear, you might say, OK,

00:07:39.500 --> 00:07:43.730
if this light over here, if
this is coming from 13 billion

00:07:43.730 --> 00:07:46.860
light years away, or if this
is 13 billion light years away,

00:07:46.860 --> 00:07:49.920
then you could say, hey, so
everything that we can observe

00:07:49.920 --> 00:07:51.990
or that we can even
observe the past of,

00:07:51.990 --> 00:07:54.089
the radius is about 26
billion light years.

00:07:54.089 --> 00:07:55.630
But even there, we
have to be careful

00:07:55.630 --> 00:07:57.820
because remember the
universe is expanding.

00:07:57.820 --> 00:08:00.046
When this light was
emitted-- and I'll

00:08:00.046 --> 00:08:02.170
do a whole video on this
because the geometry of it

00:08:02.170 --> 00:08:05.570
is kind of hard to visualize--
when this light was emitted,

00:08:05.570 --> 00:08:07.830
where we are in the
Virgo Super Cluster,

00:08:07.830 --> 00:08:11.430
inside of the Milky Way
Galaxy, where we are

00:08:11.430 --> 00:08:15.772
was much closer to that point.

00:08:15.772 --> 00:08:17.230
It was on the order
of-- and I want

00:08:17.230 --> 00:08:21.520
to make sure I get this
right-- 36 million light years.

00:08:21.520 --> 00:08:26.060
So we were super close by, I
guess, astronomical scales.

00:08:26.060 --> 00:08:28.870
We were super close, only
36 million light years,

00:08:28.870 --> 00:08:31.470
to this object, when
that light was released.

00:08:31.470 --> 00:08:34.095
But that light was coming to us
and the whole time the universe

00:08:34.095 --> 00:08:34.740
is expanding.

00:08:34.740 --> 00:08:37.834
So we were also moving away from
it, if you just think about all

00:08:37.834 --> 00:08:40.590
of the space, that everything is
expanding away from each other,

00:08:40.590 --> 00:08:42.980
And only 13 billion
years later did

00:08:42.980 --> 00:08:44.359
it finally catch up with us.

00:08:44.359 --> 00:08:46.150
But the whole time that
that was happening,

00:08:46.150 --> 00:08:48.240
this object has
also been moving.

00:08:48.240 --> 00:08:51.140
This object has also
been moving away from us.

00:08:51.140 --> 00:08:53.430
And so our best estimate of
where this object is now,

00:08:53.430 --> 00:08:56.710
based on how space is
expanding, is on the order

00:08:56.710 --> 00:08:59.600
a 40 or 45 billion
light years away.

00:08:59.600 --> 00:09:01.440
We're just observing
where that light

00:09:01.440 --> 00:09:03.274
was emitted 13
billion years ago.

00:09:03.274 --> 00:09:04.440
And I want to be very clear.

00:09:04.440 --> 00:09:05.990
What we are
observing, this light

00:09:05.990 --> 00:09:09.850
is coming from something
very, very, very primitive.

00:09:09.850 --> 00:09:13.600
That object or that area of
space where that light was

00:09:13.600 --> 00:09:17.570
emitted from has now
condensed into way more,

00:09:17.570 --> 00:09:20.630
I guess, mature
astronomical structures.

00:09:20.630 --> 00:09:22.520
If you take it from the
other point of view,

00:09:22.520 --> 00:09:24.830
people sitting where
in this point of space

00:09:24.830 --> 00:09:27.580
now, and they've now moved
46 billion light years out,

00:09:27.580 --> 00:09:29.534
when they observe
our region of space,

00:09:29.534 --> 00:09:30.700
they're not going to see us.

00:09:30.700 --> 00:09:32.533
They're not going to
see Earth as it is now.

00:09:32.533 --> 00:09:35.470
They're going to see
the region of space

00:09:35.470 --> 00:09:39.260
where Earth is at a
super primitive stage,

00:09:39.260 --> 00:09:40.441
shortly after the Big Bang.

00:09:40.441 --> 00:09:41.940
And when I use words
like "shortly,"

00:09:41.940 --> 00:09:42.962
I use that also loosely.

00:09:42.962 --> 00:09:44.920
We're still talking about
hundreds of thousands

00:09:44.920 --> 00:09:46.541
or even millions of years.

00:09:46.541 --> 00:09:48.540
So we'll talk more about
that in a future video.

00:09:48.540 --> 00:09:49.914
But the whole
point of this video

00:09:49.914 --> 00:09:54.189
is it's beyond mind numbing.

00:09:54.189 --> 00:09:55.980
I would say the last
video, about the Milky

00:09:55.980 --> 00:09:57.450
Way, that alone
was mind numbing.

00:09:57.450 --> 00:09:58.824
But now, we're
going in a reality

00:09:58.824 --> 00:10:02.750
where just the Milky Way
becomes something that's

00:10:02.750 --> 00:10:05.650
almost unbelievably
insignificant when you think

00:10:05.650 --> 00:10:07.076
about this picture right here.

00:10:07.076 --> 00:10:08.450
And the really
mind numbing thing

00:10:08.450 --> 00:10:10.970
is, if someone told me that
this is the entire universe,

00:10:10.970 --> 00:10:15.980
this by itself would certainly
put things in perspective.

00:10:15.980 --> 00:10:17.784
But it's unknown
what's beyond it.

00:10:17.784 --> 00:10:19.700
There's some estimates
that this might be only

00:10:19.700 --> 00:10:23.520
be 1 times 10 to the 23rd
of the entire universe.

00:10:23.520 --> 00:10:26.760
And it might even be the
reality that the entire universe

00:10:26.760 --> 00:10:27.680
is smaller than this.

00:10:27.680 --> 00:10:29.340
And that's an interesting
thing to think about.

00:10:29.340 --> 00:10:31.650
But I'll leave you there
because I think no matter

00:10:31.650 --> 00:10:35.921
how you think about it,
it's just-- I don't know.

00:10:35.921 --> 00:10:37.420
I actually, before
doing this video,

00:10:37.420 --> 00:10:39.960
I stared at some of these
photos for half an hour.

00:10:39.960 --> 00:10:42.850
This is my least productive day
just because it's just so awe

00:10:42.850 --> 00:10:47.560
inspiring to think about what
these dots and dots of the dots

00:10:47.560 --> 00:10:49.007
really are.