October 18, 2018 • 22 mins
Does the Universe go on forever, or have an end? What shape is it?
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Episode Transcript
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Speaker 1 (00:05):
Inside space? Is there a place where the matter ends
and it's just empty space? And then path that space?
Is there something else that's not space? Can space have
an edge? Right? And so that to me is the
is this concept of the universe, all the matter in
all the space, things beyond that space, if there is
anything there I would consider not part of our universe.
(00:27):
Oh I see, So we could like there could be
through stuff and maybe at some point we run out
of stuff and there, but there're still there could still
be space, There could still be space. Hi. I'm Daniel
(00:51):
and I'm Horhan, and we're here to explain the universe.
Today we're going to talk about the biggest question in
the universe, the biggest question you could even possibly imagine.
How big is the universe? Like really, how big is it? Like?
Does it go on forever? Is it just a little
(01:11):
bit bigger than we can see? Does it wrap around
on itself? Is it some other crazy thing. That's what
we're going to try to tackle today. We went out
in the street and we asked people what they thought
about this the biggest of questions. Oh man, it's pretty big,
Like I'm pretty sure it's like unmeasurable because like we
don't really know much about it, so I'm pretty I
(01:32):
wanna say, like pretty big, like it's really unmeasurable. Tend
to do something article do you want, like a number
or whatever you think is appropriate. Um. I remember reading
someone where that's like it's always growing, so it's like infinite, right,
So most people seem to feel like, wow, the universe
is pretty big. Some people thought it was like infinite,
(01:53):
and some people thought just just really big. Nobody thought
it was small. Nobody's like I can see the end
of it. It's just about it's only my town. It's
only as far as I can see. That's right, And
ask really, that's really interesting because I bet like if
you ask prehistoric man how big is the universe, they
would just like say, like, look around you, this is
what there is, and they couldn't even really imagine. So
(02:18):
let's break it down. There's all the stuff right as
part of a right you know, this matter and energy,
all that stuff feel and touch and see m But
I think there's one other component which I think it
a little less usual for people to think about, and
that's the space. Space. I would think of the universe
as all the stuff and all the space that it's in. Okay,
(02:41):
and then like the stuff we can actually move around in, Yes,
the place we can move around in the space we
have at some point that space um ends. Yeah, the
space could end right now. Somebody out there listening, you smart,
good looking listener, you might be thinking, what how good
space possibly end? He's talking about space like it's a thing,
(03:03):
like it's water and the fish could run into the
end of it or something. But briefly, we should just
remind people that space is not just emptiness. It's not
just a backdrop. It's not just the nothing in which
stuff happens. It's stuff. It has properties that can bend
and expand and ripple and do all sorts of weird
crazy stuff. And so we know that it's a thing.
(03:24):
It's a dynamic, physical thing that could do stuff. So
we have to consider the possibility that it ends like
That's part of the question how big is the universe?
Is how much space is there? And can it end? Right?
It's like for fish and we're asking how big is
the ocean? Yeah, yeah, okay, exactly how big is the
I wonder do you think fish? Wonder about how big
(03:46):
is the ocean? I think fish wonder about um not
getting eaten by other fish, right, and fish fish might
also wonder like are there other oceans? Right? That's the
all diverse for fishes. But in our universe you're saying, uh,
space might have a limit to it, like there might
(04:06):
be an end to it. Um, Yeah, but is it
like a wall or is it like a what does
it mean for it to be at the edge of space? Well,
there could be an edge to space, and um to
think about what that means, we have to think about
what space is a little bit more like to think
about whether space can curve or if space is flat
(04:28):
right right, And this kind of stuff is really hard
to think about in three dimensions, like what does it
mean for space x y z space right x y
z being one to three dimensions, the curve really hard
to think about it because it's hard for us to
think about that about space curving in some higher dimensions.
So usually it's best if we think about it in
two dimensions so we can think about it it's curving
(04:51):
in that third dimension. So imagine that we are two
dimensional scientists, were like living on a sheet of paper
where we can only move in two dimensions, like x
and y and then we can ask those two dimensional
scientists can ask is our space curved? Is our paper
universe curved? And and that changes the answer, Like say
you discover that it is curved and it has a
(05:11):
positive curvature. Positive curvature would be like on the surface
of a sphere or a planet. Right, if it has
positive curvature, that has consequences for its shape, because if
it's positively curved, it can't go on forever, right, like
the Earth. You're standing on the surface of the Earth,
and you know the Earth is curved, and that means
that Earth can't be infinitely big, right right, right, So
(05:33):
you're saying, at the edge of the universe, maybe the
space space is curved, and or maybe it's a possibility
you have to consider that maybe space is curved everywhere.
If the universe had curved space and it was positively curved,
that would mean that it could be um sort of
looped on itself very naturally, the same way the surface
of a planet is, and you could travel around it
(05:55):
through space and not really get to the edge, right,
Like where is the edge of the Earth? Well, the Earth,
the surface of the Earth, the two dimensional surface doesn't
have it like people in historic times. Maybe they saw
the earth around them and they thought, oh man, this
is pretty big. It probably goes on forever, but they
didn't know that actually land curved. That's right, And and
(06:17):
it turns out that we're actually kind of on this sphere.
And if you keep going in one direction and you
kind of loop back around, that's right. Yeah. And it's
not like you get to the edge and you get
magically transported back to where you started or something. There's
no you know, shortcut or magic there on the surface
of the earth. You to keep walking, you come back
to where you started, connected back onto itself exactly. That's
(06:39):
the key. So that's a big curvature space like space
that we're in. Could kind of like if you keep
going in one direction and a spaceship, you'll come back
around to the same spot exactly. And the way you
said it was perfect. It's the connection. So we like
to talk about space by using this analogy of living
in two dimensions and thinking about it being curved in
a third dimension. Now pop that up to three dimensions, right,
(07:03):
because we know our space is at least three dimensions,
and popping an aspirin because it's now I'm getting it.
Did we work on getting addibility to support this podcast
because we're sending them a lot of customers. My god,
that could be a great um sponsor. That's right, um,
So pop that up into your three dimensional space, right,
(07:24):
and then you can ask, well, what does it mean
for three dimensional space to be curved? Well, it's not
that we imagine that it's curved in some other fourth dimension.
It's not that it's hanging in four dimensional space and
has a curvature in it. It's how space is connected.
We call it intrinsic curvature because it reflects how one
part of space is connected to another part of space.
(07:46):
So without hanging in four dimensions, you can be connected
in a way that space is curved and you look
back on yourself without ever really noticing. So when we
talk about the size of the universe, we mean that
it has made some kind of edge, but made that
edge is not like how we think of a nedge,
is like a stub or a wall. Maybe it's just
kind of looped around, and so the size of it
is kind of like this blob of space, right, yeah, exactly.
(08:11):
And the possible answers for the size of the universe
depend on how it's curved. Right, If it's positively curved,
then it can only really be like a big sphere,
which means it's finite. Right if it would negative? What
if it's not right? Um, if it's flat. If space
is flat like it's um, doesn't curve intrinsically, then it
(08:31):
could potentially go on forever. If space is negatively curved,
that's like the shape of a of a saddle, the
negative curvature, then it could have all sorts of really
weird shapes, but it could still be infinite. Okay, so
the options are infinite or not infinite. That pretty much
categorizes the options for everything. How big is your house? Where? Hey?
(08:51):
Is it infinite or not infinite? I want to see
that option actually on Zillo from Yeah, I would love
to have infinite square feeda house, would you really? Because
then all and you have to look forever for your
kids shoes? Right, where'd you put them? I put them
in room numbers somewhere between here and infinity. Yeah. So
let's talk about the possibilities of what could be beyond
(09:13):
the observable universe. I mean, we talked a little bit
about before about maybe it's infinite, Maybe it's not infinite. Um.
Do we really have no idea whether the actual universe
is just a little bit bigger than the observable universe,
much bigger than the observable universe, or it could be infinite.
We really have sort of no indication of which possibility
(09:36):
it is. We have a few clues, they're kind of indirect,
and I want to talk about that some more, but
first let's take a quick break. One clue comes from
the curvature of space. We talked earlier about how the
(09:58):
curvature space affects the how the size of the universe
could be. And if the space is curved positively or
negative or flat, that limits the options, right, So that's
something we can measure. We can measure it here. We
can look around us and measure how curved is space
in our universe? Um. And that might be a bit
of a puzzler, right, like, how does that mean? How
(10:19):
could space be curved? How could you possibly measure it? Um?
And to think about that, it's best to go back
to the two dimensional example. You're living on the surface
of a planet. For example, if you were a two
dimensional scientist living on the surface of a planet or
or some surface and you want to know is this
surface curved. What you could do is make a triangle,
because triangles are very sensitive to curvature. For example, you
(10:42):
draw triangle on a sheet of paper, you add up
the angles, then you get a degrees every triangle, every
flat surface, no matter what. Beautiful results basic geometry. That's right. Yeah,
Now imagine that triangle sitting on the surface of a
tennis ball. You can draw triangle on the surface of
a tennis ball that has three right angles on it,
(11:05):
because triangles behave differently are a curved surface, Yeah, it
could imagine that it could be ninety degrees, meaning that
it adds up to two seventy degrees. Yeah, exactly. So
let's take a break, so everyone can go get a
tennis ball and sharp. You try this at home, and
we'll be right back when you have your tennis ball. Alright,
assuming you're holding a tennis ball and you've annoyed your
(11:26):
partner or your spouse or your child by drawing triangles
on it, you can see the triangles behave differently on
a curved surface. It looks kind of bloated. Yeah, yeah,
it looks distorted. And so if you just make a
triangle and add up the angles you can see whether
or not the space you're in is curved or flat?
Is that kind of crud to think about the curvature space.
It's kind of like a distortion of space. Yes, Yes,
(11:49):
it's a distortion and how the pieces of space are
connected to each other, which changes how you move through space.
Changes like how you can get from one spot in
space to another spot in space. Yeah, like I think
I'm going straight, but I'm actually kind of being distorted
one way or the other. Yeah, it changes what straight means. Okay,
So so then the curvature might give some clues as
(12:10):
to whether, like we wrap around in ourselves or whether,
um we don't. I mean, that's all it can tell us, right,
it's whether we're on a sphere or we're not on
a sphere. Well, there's one other option, which is that
we're on a sort of a saddle. Space is negatively curved.
Imagine you have a sheet of paper that's forms sort
of like a bowl or the opposite of a sphere,
(12:31):
and you're in the middle of that bowl. You can
draw a triangle in that and it will have angles
of less than eight degrees. Can really measure the chunky
had distortion. Yeah, yeah, not quite a bowl because that's
just the inside of a sphere, but something that has
a sort of saddle shape. Um. And so you draw triangle,
you make a measurement, and that tells you. And so
(12:52):
we've done that. We've made those triangles and we've measured
them to very high precision in three dimensional space. Like
any answers on this the the sheet of the universe, Yes, exactly.
We've done it in two different ways, at least that
I can think of at the top of my head.
One is that we looked at giant cosmic triangles in space.
(13:13):
You know, we've looked at the cosmic microwave background radiation,
this leftover photons from the birth of the universe, and
drawn these triangles and measured the angles and and they
come out to degrees. It seems like space is flat.
Flat were flat? Yeah, And that's a puzzle. It's really interesting.
There a lot of people wonder like, why is space flat?
(13:35):
We've measured to be flat to within you know, like
point one percent, and for a long time that was
a mystery. But some people don't think that space could
be curved, like what would why would what would that
be weird. Yeah, and well that that leads perfectly into
the second way we've measured the curvature of space, which
is you might ask what causes space to curve? Right,
(13:57):
why would you expect space to be curved or flat
or negatively curved. And the answer is that the thing
that curves space is matter. Right. You put stuff, matter
and energy into space, and it curves it. That's what
general relativity tells us that that gravity is in fact
the curvature of space. So we know that space gets curved.
Like you put the Sun in the center of the
(14:17):
Solar System, it curves space so that the Earth very
naturally moves in a circle around it. Right, that's an
impact of the curvature of space. There, nobody's turning the Earth.
Nobody's like driving the Earth around the Sun, right, but
constantly turning. It's moving in what it considers to be
a straight line. But space is curved, so it's it's
just moving constantly in an orbit, not like a force
(14:40):
pulling the Earth towards the Sun. But gravity is more
like it's distorting the space around the Sun so that
the Earth just can naturally goes around it. That's right,
that's that's a great way to think about it. And
so matter distorts space and causes curvature of space, and
so you can ask is there enough matter and energy
(15:00):
in the universe to curve space or to make it
negatively curved or positively curved? Right? And um, if space
is totally empty, if there's no matter in it at all,
and then it's negatively curved, you have to add energy
and matter to make space zero have zero curvature. And
so we've measured this. We've measured the total energy naturally
(15:21):
wants to be negatively curved, but if you add stuff
to it, then it gets a straighter. That's right, Um,
Space with no energy density in it at all would
have negative curvature, and so you add stuff to it.
In fact, if you add I think it's six hydrogen
atoms worth of energy per square meter, then space has
zero curvature between five and six. And so we've measured
(15:45):
the amount of stuff that's in the universe and it
all adds up to be just about the right number
to make space be not curved, which is seems like
a weird coincidence, right, It seems like an important clue,
like why does all the stuff in the univer has
happened to add up to the number that's just right
to make space not be curved. Would that let's take
(16:06):
a break. We'll be back in just a short minute.
Space seems to be flat, at least space in our
part of the universe seems to be flat. It could
be that other parts of the universe it's curved, right,
(16:26):
But in our part of the universe it seems to
be flat. And we think that's sort of that it
maybe extends out to as far as we can see. Yeah,
it seems to follow the same rules, and so you're
absolutely right. That rules out, you know, the potato universe
that we're living on the surface of its huge cosmic
potato or bubble universe, whatever, and rules out the saddle universe.
(16:46):
With the universe is negative curvature. Seems like space is flat,
which is going on direction forever? Um, I'll just keep going.
Not necessarily right, we know space is flat. That doesn't
necessarily mean that it's infinite. It's a natural idea, right.
If space is flat, then it doesn't curve on itself.
And so it seems like you could be able to
(17:06):
go on forever, but earlier that you can't just have
a wall. You can't just have a wall. But since
we don't know what space is, we don't really know
how it works. We don't really know how it's connected.
It's still possible that it could be flat but connected
in a weird way. So where one edge is connected
to the other edge, like you go flat you're moving
(17:27):
through flat space, but it just loops on back on itself.
It's like it is connected in that way like an
asteroids game, you know, you go at the edge of
the screen, you appear on the other side, but like
a teleport to the other side. Yeah, yeah, and not
necessarily teleport, Like that could just be the way space
is connected. So that's weird that that wouldn't feel u
(17:50):
you mean, like an asteroid games are like pac Man
where you walk off one side of the screen and
suddenly appear on the other side like that. It's possibility.
Physicies are like, hey, that could be true. That certainly
could be true, yes, absolutely, But the other possibility is
also true, which is maybe it just goes on forever. Right.
It could be that the that space goes on forever um.
(18:12):
And that's also kind of weird because that's infinite space, right, yeah, yeah,
and it could be the space is flat, but it
just ends because we can't see past the observable universe,
and so we have intuition and ideas and speculation and
we think, oh, this would be more natural, or that
would be more natural, or I wish the universe looked
(18:33):
that way, but at this point that's all we can do. Um. Yeah,
So it's a it's a fascinating concept infinity because, as
you say, if things go on forever and then you
get infinite number of tribes at everything, then that means that,
given quantum randomness, you really do get every possibility out there.
(18:56):
So that means it's somewhere out there, there's a universe
where we're recording podcast and I'm named Jorge and your
name Daniel, and you know, another universe where every possible
thing you can imagine happens. That's really true, I mean,
it's actually happening. If there is an infinite universe with
infinite space, it means it could be really far away
and we could never get there and prove it. But
if that is reality, then it's really happening right now,
(19:19):
which is crazy to think about. Right right, we just
will never see it we'll never see it, yeah, or
if we wait long enough, maybe we would. But but
it's also so it's on one hand, like really crazy
to imagine infinite universe with infinite stuff in it. On
the other hand, it's sort of natural, right, like what's
the simplest explanation? Is it simpler to imagine an edge? Right,
(19:40):
like a limited amount of stuff? Um. I find those
ideas to be sort of weird, and they sort of
call back to, you know, geocentrism, the idea that we're
the center, we're an important place in the universe. It's
much more natural for me to think the universe just
goes on forever and we're just at one dot in
a random spot in it. Um. Otherwise they have to explain,
(20:02):
like why the universe began here, Like imagine the scenario
the infinite space but finite stuff scenario. Then you have
to ask, why did the Big Bang happen here and
not fifty billion light years to the left or to
the right in that infinite space? Why is that clump
matter here where we are? Yeah? So my personal preference,
(20:22):
based on no science at all, is the infinite space
infinite stuff universe because it sort of puts to rest
some of those questions, right, It doesn't raise weird questions
or inconsistencies. Yeah. Yeah, it just asks you to imagine
creation of an infinite stuff in a moment. I mean
that's not too much currently. I don't know if anybody
(20:46):
who has such clever ideas for ways to determine whether
the universe is infinite or finite by just looking at
stuff around us. So the only way we could do
it is direct by looking at the universe, which of
course we can't. So currently it feels impossible. But you know,
we always have to leave a little bit of an
open door there for some future physicist more clever than
us comes up with a clever way to probe whether
(21:09):
the universe is find out or infinite just by looking
at clues around us. You might say that, um, there's
plenty of room to grow there. Certainly is there? Certainly
is cool. Well, I hope you guys enjoyed that discussion. Um. Yeah,
And maybe when you look out at night into the stars,
(21:29):
you think about the idea that maybe the universe is
infinite or maybe we're seeing all that there is, and regardless,
it's a beautiful, gorgeous universe out there. And if you're
into views, the best view out there is the night
sky on the top of a mountain, where you can
see billions of light years across. Amazing business. So however
(21:50):
big the universe is, go out and enjoy it. Do
you have a question you wish we would cover, Send
it to us. We'd love to hear from you. You
can find us on Facebook, Twitter, and Instagram at Daniel
and Jorge One Word or email us to feedback at
Daniel and Jorge dot com.
Inside space? Is there a place where the matter ends
and it's just empty space? And then path that space?
Is there something else that's not space? Can space have
an edge? Right? And so that to me is the
is this concept of the universe, all the matter in
all the space, things beyond that space, if there is
anything there I would consider not part of our universe.
(00:27):
Oh I see, So we could like there could be
through stuff and maybe at some point we run out
of stuff and there, but there're still there could still
be space, There could still be space. Hi. I'm Daniel
(00:51):
and I'm Horhan, and we're here to explain the universe.
Today we're going to talk about the biggest question in
the universe, the biggest question you could even possibly imagine.
How big is the universe? Like really, how big is it? Like?
Does it go on forever? Is it just a little
(01:11):
bit bigger than we can see? Does it wrap around
on itself? Is it some other crazy thing. That's what
we're going to try to tackle today. We went out
in the street and we asked people what they thought
about this the biggest of questions. Oh man, it's pretty big,
Like I'm pretty sure it's like unmeasurable because like we
don't really know much about it, so I'm pretty I
(01:32):
wanna say, like pretty big, like it's really unmeasurable. Tend
to do something article do you want, like a number
or whatever you think is appropriate. Um. I remember reading
someone where that's like it's always growing, so it's like infinite, right,
So most people seem to feel like, wow, the universe
is pretty big. Some people thought it was like infinite,
(01:53):
and some people thought just just really big. Nobody thought
it was small. Nobody's like I can see the end
of it. It's just about it's only my town. It's
only as far as I can see. That's right, And
ask really, that's really interesting because I bet like if
you ask prehistoric man how big is the universe, they
would just like say, like, look around you, this is
what there is, and they couldn't even really imagine. So
(02:18):
let's break it down. There's all the stuff right as
part of a right you know, this matter and energy,
all that stuff feel and touch and see m But
I think there's one other component which I think it
a little less usual for people to think about, and
that's the space. Space. I would think of the universe
as all the stuff and all the space that it's in. Okay,
(02:41):
and then like the stuff we can actually move around in, Yes,
the place we can move around in the space we
have at some point that space um ends. Yeah, the
space could end right now. Somebody out there listening, you smart,
good looking listener, you might be thinking, what how good
space possibly end? He's talking about space like it's a thing,
(03:03):
like it's water and the fish could run into the
end of it or something. But briefly, we should just
remind people that space is not just emptiness. It's not
just a backdrop. It's not just the nothing in which
stuff happens. It's stuff. It has properties that can bend
and expand and ripple and do all sorts of weird
crazy stuff. And so we know that it's a thing.
(03:24):
It's a dynamic, physical thing that could do stuff. So
we have to consider the possibility that it ends like
That's part of the question how big is the universe?
Is how much space is there? And can it end? Right?
It's like for fish and we're asking how big is
the ocean? Yeah, yeah, okay, exactly how big is the
I wonder do you think fish? Wonder about how big
(03:46):
is the ocean? I think fish wonder about um not
getting eaten by other fish, right, and fish fish might
also wonder like are there other oceans? Right? That's the
all diverse for fishes. But in our universe you're saying, uh,
space might have a limit to it, like there might
(04:06):
be an end to it. Um, Yeah, but is it
like a wall or is it like a what does
it mean for it to be at the edge of space? Well,
there could be an edge to space, and um to
think about what that means, we have to think about
what space is a little bit more like to think
about whether space can curve or if space is flat
(04:28):
right right, And this kind of stuff is really hard
to think about in three dimensions, like what does it
mean for space x y z space right x y
z being one to three dimensions, the curve really hard
to think about it because it's hard for us to
think about that about space curving in some higher dimensions.
So usually it's best if we think about it in
two dimensions so we can think about it it's curving
(04:51):
in that third dimension. So imagine that we are two
dimensional scientists, were like living on a sheet of paper
where we can only move in two dimensions, like x
and y and then we can ask those two dimensional
scientists can ask is our space curved? Is our paper
universe curved? And and that changes the answer, Like say
you discover that it is curved and it has a
(05:11):
positive curvature. Positive curvature would be like on the surface
of a sphere or a planet. Right, if it has
positive curvature, that has consequences for its shape, because if
it's positively curved, it can't go on forever, right, like
the Earth. You're standing on the surface of the Earth,
and you know the Earth is curved, and that means
that Earth can't be infinitely big, right right, right, So
(05:33):
you're saying, at the edge of the universe, maybe the
space space is curved, and or maybe it's a possibility
you have to consider that maybe space is curved everywhere.
If the universe had curved space and it was positively curved,
that would mean that it could be um sort of
looped on itself very naturally, the same way the surface
of a planet is, and you could travel around it
(05:55):
through space and not really get to the edge, right,
Like where is the edge of the Earth? Well, the Earth,
the surface of the Earth, the two dimensional surface doesn't
have it like people in historic times. Maybe they saw
the earth around them and they thought, oh man, this
is pretty big. It probably goes on forever, but they
didn't know that actually land curved. That's right, And and
(06:17):
it turns out that we're actually kind of on this sphere.
And if you keep going in one direction and you
kind of loop back around, that's right. Yeah. And it's
not like you get to the edge and you get
magically transported back to where you started or something. There's
no you know, shortcut or magic there on the surface
of the earth. You to keep walking, you come back
to where you started, connected back onto itself exactly. That's
(06:39):
the key. So that's a big curvature space like space
that we're in. Could kind of like if you keep
going in one direction and a spaceship, you'll come back
around to the same spot exactly. And the way you
said it was perfect. It's the connection. So we like
to talk about space by using this analogy of living
in two dimensions and thinking about it being curved in
a third dimension. Now pop that up to three dimensions, right,
(07:03):
because we know our space is at least three dimensions,
and popping an aspirin because it's now I'm getting it.
Did we work on getting addibility to support this podcast
because we're sending them a lot of customers. My god,
that could be a great um sponsor. That's right, um,
So pop that up into your three dimensional space, right,
(07:24):
and then you can ask, well, what does it mean
for three dimensional space to be curved? Well, it's not
that we imagine that it's curved in some other fourth dimension.
It's not that it's hanging in four dimensional space and
has a curvature in it. It's how space is connected.
We call it intrinsic curvature because it reflects how one
part of space is connected to another part of space.
(07:46):
So without hanging in four dimensions, you can be connected
in a way that space is curved and you look
back on yourself without ever really noticing. So when we
talk about the size of the universe, we mean that
it has made some kind of edge, but made that
edge is not like how we think of a nedge,
is like a stub or a wall. Maybe it's just
kind of looped around, and so the size of it
is kind of like this blob of space, right, yeah, exactly.
(08:11):
And the possible answers for the size of the universe
depend on how it's curved. Right, If it's positively curved,
then it can only really be like a big sphere,
which means it's finite. Right if it would negative? What
if it's not right? Um, if it's flat. If space
is flat like it's um, doesn't curve intrinsically, then it
(08:31):
could potentially go on forever. If space is negatively curved,
that's like the shape of a of a saddle, the
negative curvature, then it could have all sorts of really
weird shapes, but it could still be infinite. Okay, so
the options are infinite or not infinite. That pretty much
categorizes the options for everything. How big is your house? Where? Hey?
(08:51):
Is it infinite or not infinite? I want to see
that option actually on Zillo from Yeah, I would love
to have infinite square feeda house, would you really? Because
then all and you have to look forever for your
kids shoes? Right, where'd you put them? I put them
in room numbers somewhere between here and infinity. Yeah. So
let's talk about the possibilities of what could be beyond
(09:13):
the observable universe. I mean, we talked a little bit
about before about maybe it's infinite, Maybe it's not infinite. Um.
Do we really have no idea whether the actual universe
is just a little bit bigger than the observable universe,
much bigger than the observable universe, or it could be infinite.
We really have sort of no indication of which possibility
(09:36):
it is. We have a few clues, they're kind of indirect,
and I want to talk about that some more, but
first let's take a quick break. One clue comes from
the curvature of space. We talked earlier about how the
(09:58):
curvature space affects the how the size of the universe
could be. And if the space is curved positively or
negative or flat, that limits the options, right, So that's
something we can measure. We can measure it here. We
can look around us and measure how curved is space
in our universe? Um. And that might be a bit
of a puzzler, right, like, how does that mean? How
(10:19):
could space be curved? How could you possibly measure it? Um?
And to think about that, it's best to go back
to the two dimensional example. You're living on the surface
of a planet. For example, if you were a two
dimensional scientist living on the surface of a planet or
or some surface and you want to know is this
surface curved. What you could do is make a triangle,
because triangles are very sensitive to curvature. For example, you
(10:42):
draw triangle on a sheet of paper, you add up
the angles, then you get a degrees every triangle, every
flat surface, no matter what. Beautiful results basic geometry. That's right. Yeah,
Now imagine that triangle sitting on the surface of a
tennis ball. You can draw triangle on the surface of
a tennis ball that has three right angles on it,
(11:05):
because triangles behave differently are a curved surface, Yeah, it
could imagine that it could be ninety degrees, meaning that
it adds up to two seventy degrees. Yeah, exactly. So
let's take a break, so everyone can go get a
tennis ball and sharp. You try this at home, and
we'll be right back when you have your tennis ball. Alright,
assuming you're holding a tennis ball and you've annoyed your
(11:26):
partner or your spouse or your child by drawing triangles
on it, you can see the triangles behave differently on
a curved surface. It looks kind of bloated. Yeah, yeah,
it looks distorted. And so if you just make a
triangle and add up the angles you can see whether
or not the space you're in is curved or flat?
Is that kind of crud to think about the curvature space.
It's kind of like a distortion of space. Yes, Yes,
(11:49):
it's a distortion and how the pieces of space are
connected to each other, which changes how you move through space.
Changes like how you can get from one spot in
space to another spot in space. Yeah, like I think
I'm going straight, but I'm actually kind of being distorted
one way or the other. Yeah, it changes what straight means. Okay,
So so then the curvature might give some clues as
(12:10):
to whether, like we wrap around in ourselves or whether,
um we don't. I mean, that's all it can tell us, right,
it's whether we're on a sphere or we're not on
a sphere. Well, there's one other option, which is that
we're on a sort of a saddle. Space is negatively curved.
Imagine you have a sheet of paper that's forms sort
of like a bowl or the opposite of a sphere,
(12:31):
and you're in the middle of that bowl. You can
draw a triangle in that and it will have angles
of less than eight degrees. Can really measure the chunky
had distortion. Yeah, yeah, not quite a bowl because that's
just the inside of a sphere, but something that has
a sort of saddle shape. Um. And so you draw triangle,
you make a measurement, and that tells you. And so
(12:52):
we've done that. We've made those triangles and we've measured
them to very high precision in three dimensional space. Like
any answers on this the the sheet of the universe, Yes, exactly.
We've done it in two different ways, at least that
I can think of at the top of my head.
One is that we looked at giant cosmic triangles in space.
(13:13):
You know, we've looked at the cosmic microwave background radiation,
this leftover photons from the birth of the universe, and
drawn these triangles and measured the angles and and they
come out to degrees. It seems like space is flat.
Flat were flat? Yeah, And that's a puzzle. It's really interesting.
There a lot of people wonder like, why is space flat?
(13:35):
We've measured to be flat to within you know, like
point one percent, and for a long time that was
a mystery. But some people don't think that space could
be curved, like what would why would what would that
be weird. Yeah, and well that that leads perfectly into
the second way we've measured the curvature of space, which
is you might ask what causes space to curve? Right,
(13:57):
why would you expect space to be curved or flat
or negatively curved. And the answer is that the thing
that curves space is matter. Right. You put stuff, matter
and energy into space, and it curves it. That's what
general relativity tells us that that gravity is in fact
the curvature of space. So we know that space gets curved.
Like you put the Sun in the center of the
(14:17):
Solar System, it curves space so that the Earth very
naturally moves in a circle around it. Right, that's an
impact of the curvature of space. There, nobody's turning the Earth.
Nobody's like driving the Earth around the Sun, right, but
constantly turning. It's moving in what it considers to be
a straight line. But space is curved, so it's it's
just moving constantly in an orbit, not like a force
(14:40):
pulling the Earth towards the Sun. But gravity is more
like it's distorting the space around the Sun so that
the Earth just can naturally goes around it. That's right,
that's that's a great way to think about it. And
so matter distorts space and causes curvature of space, and
so you can ask is there enough matter and energy
(15:00):
in the universe to curve space or to make it
negatively curved or positively curved? Right? And um, if space
is totally empty, if there's no matter in it at all,
and then it's negatively curved, you have to add energy
and matter to make space zero have zero curvature. And
so we've measured this. We've measured the total energy naturally
(15:21):
wants to be negatively curved, but if you add stuff
to it, then it gets a straighter. That's right, Um,
Space with no energy density in it at all would
have negative curvature, and so you add stuff to it.
In fact, if you add I think it's six hydrogen
atoms worth of energy per square meter, then space has
zero curvature between five and six. And so we've measured
(15:45):
the amount of stuff that's in the universe and it
all adds up to be just about the right number
to make space be not curved, which is seems like
a weird coincidence, right, It seems like an important clue,
like why does all the stuff in the univer has
happened to add up to the number that's just right
to make space not be curved. Would that let's take
(16:06):
a break. We'll be back in just a short minute.
Space seems to be flat, at least space in our
part of the universe seems to be flat. It could
be that other parts of the universe it's curved, right,
(16:26):
But in our part of the universe it seems to
be flat. And we think that's sort of that it
maybe extends out to as far as we can see. Yeah,
it seems to follow the same rules, and so you're
absolutely right. That rules out, you know, the potato universe
that we're living on the surface of its huge cosmic
potato or bubble universe, whatever, and rules out the saddle universe.
(16:46):
With the universe is negative curvature. Seems like space is flat,
which is going on direction forever? Um, I'll just keep going.
Not necessarily right, we know space is flat. That doesn't
necessarily mean that it's infinite. It's a natural idea, right.
If space is flat, then it doesn't curve on itself.
And so it seems like you could be able to
(17:06):
go on forever, but earlier that you can't just have
a wall. You can't just have a wall. But since
we don't know what space is, we don't really know
how it works. We don't really know how it's connected.
It's still possible that it could be flat but connected
in a weird way. So where one edge is connected
to the other edge, like you go flat you're moving
(17:27):
through flat space, but it just loops on back on itself.
It's like it is connected in that way like an
asteroids game, you know, you go at the edge of
the screen, you appear on the other side, but like
a teleport to the other side. Yeah, yeah, and not
necessarily teleport, Like that could just be the way space
is connected. So that's weird that that wouldn't feel u
(17:50):
you mean, like an asteroid games are like pac Man
where you walk off one side of the screen and
suddenly appear on the other side like that. It's possibility.
Physicies are like, hey, that could be true. That certainly
could be true, yes, absolutely, But the other possibility is
also true, which is maybe it just goes on forever. Right.
It could be that the that space goes on forever um.
(18:12):
And that's also kind of weird because that's infinite space, right, yeah, yeah,
and it could be the space is flat, but it
just ends because we can't see past the observable universe,
and so we have intuition and ideas and speculation and
we think, oh, this would be more natural, or that
would be more natural, or I wish the universe looked
(18:33):
that way, but at this point that's all we can do. Um. Yeah,
So it's a it's a fascinating concept infinity because, as
you say, if things go on forever and then you
get infinite number of tribes at everything, then that means that,
given quantum randomness, you really do get every possibility out there.
(18:56):
So that means it's somewhere out there, there's a universe
where we're recording podcast and I'm named Jorge and your
name Daniel, and you know, another universe where every possible
thing you can imagine happens. That's really true, I mean,
it's actually happening. If there is an infinite universe with
infinite space, it means it could be really far away
and we could never get there and prove it. But
if that is reality, then it's really happening right now,
(19:19):
which is crazy to think about. Right right, we just
will never see it we'll never see it, yeah, or
if we wait long enough, maybe we would. But but
it's also so it's on one hand, like really crazy
to imagine infinite universe with infinite stuff in it. On
the other hand, it's sort of natural, right, like what's
the simplest explanation? Is it simpler to imagine an edge? Right,
(19:40):
like a limited amount of stuff? Um. I find those
ideas to be sort of weird, and they sort of
call back to, you know, geocentrism, the idea that we're
the center, we're an important place in the universe. It's
much more natural for me to think the universe just
goes on forever and we're just at one dot in
a random spot in it. Um. Otherwise they have to explain,
(20:02):
like why the universe began here, Like imagine the scenario
the infinite space but finite stuff scenario. Then you have
to ask, why did the Big Bang happen here and
not fifty billion light years to the left or to
the right in that infinite space? Why is that clump
matter here where we are? Yeah? So my personal preference,
(20:22):
based on no science at all, is the infinite space
infinite stuff universe because it sort of puts to rest
some of those questions, right, It doesn't raise weird questions
or inconsistencies. Yeah. Yeah, it just asks you to imagine
creation of an infinite stuff in a moment. I mean
that's not too much currently. I don't know if anybody
(20:46):
who has such clever ideas for ways to determine whether
the universe is infinite or finite by just looking at
stuff around us. So the only way we could do
it is direct by looking at the universe, which of
course we can't. So currently it feels impossible. But you know,
we always have to leave a little bit of an
open door there for some future physicist more clever than
us comes up with a clever way to probe whether
(21:09):
the universe is find out or infinite just by looking
at clues around us. You might say that, um, there's
plenty of room to grow there. Certainly is there? Certainly
is cool. Well, I hope you guys enjoyed that discussion. Um. Yeah,
And maybe when you look out at night into the stars,
(21:29):
you think about the idea that maybe the universe is
infinite or maybe we're seeing all that there is, and regardless,
it's a beautiful, gorgeous universe out there. And if you're
into views, the best view out there is the night
sky on the top of a mountain, where you can
see billions of light years across. Amazing business. So however
(21:50):
big the universe is, go out and enjoy it. Do
you have a question you wish we would cover, Send
it to us. We'd love to hear from you. You
can find us on Facebook, Twitter, and Instagram at Daniel
and Jorge One Word or email us to feedback at
Daniel and Jorge dot com.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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