September 26, 2024 • 22 mins
Does the Universe go on forever, or have an end? What shape is it?
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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, Okay, things beyond that space? If there
is anything there I would consider not part of our universe.
Speaker 2 (00:27):
Oh I see, So we could like there could be
through stuff and maybe at some point we run out
of stuff there, but there's still there could still be space.
Speaker 1 (00:35):
There could still be space. Hi. I'm Daniel and I'm Horehane,
and we're here to explain the universe.
Speaker 2 (00:55):
Today we're going to talk about the biggest question in
the universe.
Speaker 1 (00:58):
The biggest question you could even possibly imagine.
Speaker 2 (01:04):
How big is the universe?
Speaker 1 (01:07):
Like really, how big is it? Like? Does it go
on forever? Is it just a little bit bigger than
we can see? Does it wrap around on itself? Is
it some other crazy thing? That's what we are 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.
Speaker 3 (01:24):
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 wanna say, like pretty big, like
it's really unmeasurable.
Speaker 1 (01:35):
Tend to the something particles. I don't know, do you
want like a number or whatever you think is appropriate.
Speaker 2 (01:42):
I remember reading some of where that's like it's always growing,
so it's like infinite.
Speaker 1 (01:46):
Right, So most people seem to feel like, wow, the
universe is pretty big, right. Some people thought it was
like infinite, and some people thought, m just just really big.
Speaker 2 (01:56):
Nobody thought it was small.
Speaker 1 (01:58):
Nobody's like I can see the end of it's just
about it.
Speaker 2 (02:02):
It's only as far as I can see.
Speaker 1 (02:04):
That's right, And ascually 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 let's break it down. There's all the stuff right
as particles. There's matter, right, you know, there's matter and
(02:24):
energy and all.
Speaker 2 (02:25):
That stuff feel and touch and see mm hm.
Speaker 1 (02:28):
But I think there's one other component which I think
is a little less usual for people to think about,
and that's the space.
Speaker 2 (02:34):
Space.
Speaker 1 (02:34):
I would think of the universe as all the stuff
and all the space that it's in.
Speaker 2 (02:40):
Okay, space like the stuff we can actually move around in.
Speaker 1 (02:44):
Yes, the place we can move around in the space
we have.
Speaker 2 (02:48):
At some point that space ends.
Speaker 1 (02:51):
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, 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
(03:13):
in which stuff happens. It's stuff. It has properties. It
can bend and expand and ripple and do all sorts
of weird crazy stuff, and so we know that it's
a thing. 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?
Speaker 2 (03:35):
It's like we're fish and we're asking how big is
the ocean?
Speaker 1 (03:40):
Yeah? Yeah, okay, exactly how big is the I wonder
do you think fish wonder about how big is the ocean.
Speaker 2 (03:47):
I think fish wonder about not getting eaten by other
fish occupation.
Speaker 1 (03:55):
Right, And fish might also wonder like are there other oceans? Right?
That's the multiverse for fishes.
Speaker 2 (04:02):
But in our universe, you're saying space might have a
limit to it, like there might be an end to it. Yeah,
but so is it like a wall or is it
like a what does it mean for it to be
at the edge of space?
Speaker 1 (04:17):
Well, there could be an edge to space, and to
think about what that means, we have to think about
what space is a little bit more like we have
to think about whether space can curve or if space
is flat right right, And this kind of stuff is
really hard to think about in three dimensions, like what
does it mean for space xyz space right xyz being
(04:37):
one two, three dimensions, The curve really hard to think
about 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 as curving in that third dimension.
So imagine that we are two dimensional scientists. We're like
living on a sheet of paper where we can only
move in two dimensions like X and y, and then
(05:00):
we can ask those two dimensional scientists can ask is
our space curved? Is our paper universe curved?
Speaker 2 (05:06):
Right?
Speaker 1 (05:06):
And that changes the answer, Like say you discover that
it is curved and it has a 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
(05:28):
the Earth is curved, and that means that Earth can't
be infinitely big, right.
Speaker 2 (05:32):
Right, right, So you're saying, at the edge of the universe,
maybe the space space is curved.
Speaker 1 (05:38):
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 sort of looped on itself very naturally,
the same way the surface of a planet is, and
you could travel around it through space and not really
get to the edge, right, Like where is the edge
(05:59):
of the Earth? Well, the Earth, the surface of the Earth,
a two dimensional surface doesn't have an edge.
Speaker 2 (06:05):
Like people in electoric times. Maybe they saw the earth
around them and it thought, oh man, this is pretty big.
It probably goes on forever, but they didn't know that
actually the land curved.
Speaker 1 (06:16):
That's right, And.
Speaker 2 (06:18):
It turns out that we're actually kind of on this
sphere and if you keep going in one direction you
kind of loop back around.
Speaker 1 (06:24):
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 keep walking,
you come back to where you.
Speaker 2 (06:36):
Start, just connected back onto itself exactly.
Speaker 1 (06:39):
That's the key.
Speaker 2 (06:40):
So that's a space like space that we're in. Could
kind of like if you keep going in one direction
on a spaceship, you'll come back around to the same
spot exactly.
Speaker 1 (06:50):
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 dimension. Now pop that up to
three dimensions, right, because we know our space is at
least three dimensions.
Speaker 2 (07:05):
Popping up and popping an asp rain because now I'm
getting ahead.
Speaker 1 (07:11):
Did we work on getting Advilt to support this podcast
because we're sending them a lot of customers.
Speaker 2 (07:15):
My god, that could be a great sponsor.
Speaker 1 (07:19):
That's right. So pop that up into your three dimensional space, right,
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 the space is connected.
(07:39):
We call it intrinsic curvature because it reflects how one
part of space is connected to another part of space.
So without hanging in four dimensions, you can be connected
in a way that space is curved and you loop
back on yourself without ever really noticing.
Speaker 2 (07:53):
So when we talk about the size of the universe,
we mean that it has maybe some kind of edge,
but maybe that edge is like how we think of
an edge as 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.
Speaker 1 (08:08):
Space, right, yeah, exactly. 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 have been negative. If it's not right, if
it's flat. If space is flat, like it doesn't curve intrinsically,
(08:31):
then it could potentially go on forever. If space is
negatively curved, that's like the shape of a saddle, it's
a negative curvature, then it could have all sorts of
really weird shapes, but it could still be infinite.
Speaker 2 (08:42):
Okay, so the options are infinite or not infinite.
Speaker 1 (08:47):
That pretty much categorizes the options for everything. How big
is your househoorg? Is it infinite or non infinite? I
want to see that option actually on Zillo from.
Speaker 2 (08:55):
The Yeah, I would love to have infinite square feet
house because.
Speaker 3 (09:01):
Then I.
Speaker 1 (09:03):
Needed to look forever for your kid's shoes, Right, where'd
you put them? I put them in room number somewhere
between here and infinity.
Speaker 2 (09:09):
Yeah. So let's talk about the possibilities of what could
be beyond the observable universe. I mean, we talked a
little bit about before about maybe it's infinite, maybe it's
not infinite. 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
(09:30):
could be infinite. We really have sort of no indication
of which possibility it is.
Speaker 1 (09:37):
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 curvature
(09:59):
of space affects the how the size of the universe
could be. And if a 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. And that might be a bit of
a puzzler, right, like, how does that mean? How could
(10:19):
space be curved? How could you possibly measure it? And
to think about that, it's best to go back to
the two dimensional example. If 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
some surface, and you wanted to know is this surface curved.
What you could do is make a triangle. Because triangles
are very sensitive to curvature. For example, you draw a
(10:42):
triangle in a sheet of paper, you add up the angles,
then you get one hundred and eighty degrees every triangle,
every flat surface, no matter what, beautiful.
Speaker 2 (10:50):
Results in geometre, basic geometry.
Speaker 1 (10:53):
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, because triangles behave differently on a curved surface.
Speaker 2 (11:08):
Yeah, it could imagine that could be ninety degrees, meaning
that it adds up to two hundred and seventy degrees.
Speaker 1 (11:13):
Yeah, exactly. So let's take a break so everyone can
go get a tennis ball and a sharpie. You try
this at home, and we'll be right back when you
have your tennis ball, all right, Assuming you're holding a
tennis ball, yeah, and you've annoyed your partner or your
spouse or your child by drawing triangles on it. You
can see the triangles behave differently on a curved suraace.
Speaker 2 (11:33):
It looks kind of bloated.
Speaker 1 (11:35):
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.
Speaker 2 (11:43):
Is that kind of a great way to think about
the curvature space. It's kind of like a distortion of space.
Speaker 1 (11:48):
Yes, Yes, 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.
Speaker 2 (12:00):
Yeah, like I think I'm going straight, but I'm actually
kind of being distorted in one way.
Speaker 1 (12:04):
Or the other. Yeah, it changes what straight means.
Speaker 2 (12:07):
Okay, So then the curvature might give some clues as
to whether, like we wrap around in ourselves or or
whether we don't. I mean, that's all it can tell us, right,
It's whether we're in a sphere or we're not in
a sphere.
Speaker 1 (12:21):
Well, there's one other option, which is that we're on
a sort of a saddle if space is negatively curved.
Imagine you have a sheet of paper that's formed sort
of like a bowl, right the opposite of a sphere,
and you're in the middle of that bowl. You can
draw a triangle in that and it will have angles
of less than one hundred and eighty degrees.
Speaker 2 (12:39):
You measure distortion.
Speaker 1 (12:41):
Yeah, yeah, not quite a bowl because that's just the
inside of a sphere, but something that has a sort
of saddle shape. And so you draw triangle, you make
a measurement, and that tells you. And so we've done that.
We've made those triangles and we've measured them to very
high precision in three dimensional space.
Speaker 2 (12:58):
Like this is on this in the sheet of the universe.
Speaker 1 (13:03):
Yes, exactly. We've done it in two different ways, at
least that I can think of off the top of
my head. One is that we looked at giant cosmic
triangles in space. 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 one hundred and eighty degrees.
(13:24):
It seems like space is flat. Space is flat flat, Yeah,
And that's a puzzle. It's really interesting that a lot
of people wonder, like, why is space flat? We've measured
to be flat to within you know, zero point one percent,
and for a long time that was a mystery. But
some people do.
Speaker 2 (13:42):
Think that space could be curved, like what would why
would Why would that be weird?
Speaker 1 (13:49):
Yeah, and well that's 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, why would
you expect space to be curved or flat or negative 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
(14:10):
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 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. Nobody's turning the Earth. Nobody's like driving
the Earth around the Sun, right, but constantly turning. It's
(14:31):
moving in what it considers to be a straight line,
but the space is curved, so it's just moving constantly
in an orbit.
Speaker 2 (14:39):
Gravity is not like a force pulling the Earth towards
the Sun. But gravity is more like its distorting the
space around the Sun, so that the Earth just kind
of naturally goes around it.
Speaker 1 (14:50):
That's right. 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 in the universe to curve space or to make
it negatively curved or positively curved? Right? And if space
is totally empty, if there's no matter in it at all,
(15:10):
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.
Speaker 2 (15:20):
It naturally wants to be negatively curved, but if you
add stuff to it, then it gets straight.
Speaker 1 (15:26):
That's right. 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. It's between five and six. And
so we've measured the amount of stuff that's in the
(15:47):
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 unverse happen to add up to the number that's
just right to make space not be curved?
Speaker 2 (16:05):
Would that Let's take a break. We'll be back in
just a short minute.
Speaker 1 (16:19):
Space seems to be flat, at least space in our
part of the universe seems to be flat. It could
be that in other parts of the universe it's curved, right,
but in our part of the universe seems to be flat.
Speaker 2 (16:29):
And we think that sort of a that it maybe
extends out to as far as we can see.
Speaker 1 (16:35):
Yeah, it seems to follow the same rules. Okay, 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. It rules out
the saddle universe or the universe's negative curvature. Seems like
space is flat, which is.
Speaker 2 (16:50):
Flat going one direction forever, I'll just keep going.
Speaker 1 (16:56):
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
go on forever.
Speaker 2 (17:07):
But earlier that you can't just have a wall.
Speaker 1 (17:11):
You can't just have a wall. But 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 through
flat space, but it just loops on back on itself,
(17:31):
like it's connected in that way, like an asteroids game.
You know, you go at the edge of the screen,
but you appear on the.
Speaker 2 (17:38):
Other side, like you teleport to the other side.
Speaker 1 (17:42):
Yeah, yeah, and not necessarily teleport, Like that could just
be the way space is connected.
Speaker 2 (17:47):
So that's weird. That's that wouldn't feel you mean, like
an asteroid games or like pac Man where you walk
off one side of the screen and suddenly you appear
on the other side, Like that is it possibility? Physicists
are like, hey, that could be true.
Speaker 1 (18:01):
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, And that's also kind of weird because
that's infinite.
Speaker 2 (18:15):
Space in space.
Speaker 1 (18:18):
Yeah, yeah, and it could be that 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 that way, but at this point that's all
we can do. Yeah. So it's a fascinating concept, infinity because,
(18:44):
as you say, if things go on forever and then
you get infinite number of tries at everything, then that
means that, given quantum randomness, you really do get every
possibility out there. So that means it's somewhere out there,
there's a universe where we're recording podcast and I'm named
Jorge and you're name Daniel, and right, you know, another
universe where every possible thing you can imagine happens. That's
(19:07):
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 improve it. But if that is reality, then it's
really happening right now, which is crazy to think about.
Speaker 2 (19:21):
It, right, right, we just will never see it.
Speaker 1 (19:24):
We'll never see it, yeah, or if we wait long enough,
maybe we would. 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's simpler to imagine
an edge, right, like a limited amount of stuff. I
find those ideas to be sort of weird, and they
(19:46):
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. Otherwise they have to explain,
like why the universe began here, Like imagine the scenario
(20:06):
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.
Speaker 2 (20:15):
In that infinite space? Why is that clump matter here
where we are?
Speaker 1 (20:20):
Yeah, So my personal preference, based on no science at all,
is the infinite space, infinite stuff universe because It sort
of puts to rest some of those questions who raises others?
Speaker 2 (20:31):
Right? It doesn't raise weird questions or inconsistencies.
Speaker 3 (20:36):
Yeah.
Speaker 1 (20:37):
Yeah, it just asks you to imagine creation of an
infinite stuff in a moment. I mean that's not too
much that Yeah. Currently, I don't know of anybody 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
(20:58):
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 physicists more clever than
us comes up with a clever way to probe whether
the universe is finite or infinite just by looking at
clues around us.
Speaker 2 (21:12):
You might say that there's plenty of room to grow.
Speaker 1 (21:19):
There. Certainly is there? Certainly is cool.
Speaker 2 (21:21):
Well, I hope you guys enjoyed that discussion. Yeah, and
maybe when you look out at night into the stars,
do you think about the idea that maybe the universe
is infinite or maybe we're seeing all that there is?
Speaker 1 (21:37):
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 in the top of a mountain where
you can see billions of light years across amazing vistas. So,
however big the universe is, go out and enjoy it.
(21:57):
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 Danielandhorge 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, Okay, things beyond that space? If there
is anything there I would consider not part of our universe.
Speaker 2 (00:27):
Oh I see, So we could like there could be
through stuff and maybe at some point we run out
of stuff there, but there's still there could still be space.
Speaker 1 (00:35):
There could still be space. Hi. I'm Daniel and I'm Horehane,
and we're here to explain the universe.
Speaker 2 (00:55):
Today we're going to talk about the biggest question in
the universe.
Speaker 1 (00:58):
The biggest question you could even possibly imagine.
Speaker 2 (01:04):
How big is the universe?
Speaker 1 (01:07):
Like really, how big is it? Like? Does it go
on forever? Is it just a little bit bigger than
we can see? Does it wrap around on itself? Is
it some other crazy thing? That's what we are 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.
Speaker 3 (01:24):
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 wanna say, like pretty big, like
it's really unmeasurable.
Speaker 1 (01:35):
Tend to the something particles. I don't know, do you
want like a number or whatever you think is appropriate.
Speaker 2 (01:42):
I remember reading some of where that's like it's always growing,
so it's like infinite.
Speaker 1 (01:46):
Right, So most people seem to feel like, wow, the
universe is pretty big, right. Some people thought it was
like infinite, and some people thought, m just just really big.
Speaker 2 (01:56):
Nobody thought it was small.
Speaker 1 (01:58):
Nobody's like I can see the end of it's just
about it.
Speaker 2 (02:02):
It's only as far as I can see.
Speaker 1 (02:04):
That's right, And ascually 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 let's break it down. There's all the stuff right
as particles. There's matter, right, you know, there's matter and
(02:24):
energy and all.
Speaker 2 (02:25):
That stuff feel and touch and see mm hm.
Speaker 1 (02:28):
But I think there's one other component which I think
is a little less usual for people to think about,
and that's the space.
Speaker 2 (02:34):
Space.
Speaker 1 (02:34):
I would think of the universe as all the stuff
and all the space that it's in.
Speaker 2 (02:40):
Okay, space like the stuff we can actually move around in.
Speaker 1 (02:44):
Yes, the place we can move around in the space
we have.
Speaker 2 (02:48):
At some point that space ends.
Speaker 1 (02:51):
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, 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
(03:13):
in which stuff happens. It's stuff. It has properties. It
can bend and expand and ripple and do all sorts
of weird crazy stuff, and so we know that it's
a thing. 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?
Speaker 2 (03:35):
It's like we're fish and we're asking how big is
the ocean?
Speaker 1 (03:40):
Yeah? Yeah, okay, exactly how big is the I wonder
do you think fish wonder about how big is the ocean.
Speaker 2 (03:47):
I think fish wonder about not getting eaten by other
fish occupation.
Speaker 1 (03:55):
Right, And fish might also wonder like are there other oceans? Right?
That's the multiverse for fishes.
Speaker 2 (04:02):
But in our universe, you're saying space might have a
limit to it, like there might be an end to it. Yeah,
but so is it like a wall or is it
like a what does it mean for it to be
at the edge of space?
Speaker 1 (04:17):
Well, there could be an edge to space, and to
think about what that means, we have to think about
what space is a little bit more like we have
to think about whether space can curve or if space
is flat right right, And this kind of stuff is
really hard to think about in three dimensions, like what
does it mean for space xyz space right xyz being
(04:37):
one two, three dimensions, The curve really hard to think
about 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 as curving in that third dimension.
So imagine that we are two dimensional scientists. We're like
living on a sheet of paper where we can only
move in two dimensions like X and y, and then
(05:00):
we can ask those two dimensional scientists can ask is
our space curved? Is our paper universe curved?
Speaker 2 (05:06):
Right?
Speaker 1 (05:06):
And that changes the answer, Like say you discover that
it is curved and it has a 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
(05:28):
the Earth is curved, and that means that Earth can't
be infinitely big, right.
Speaker 2 (05:32):
Right, right, So you're saying, at the edge of the universe,
maybe the space space is curved.
Speaker 1 (05:38):
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 sort of looped on itself very naturally,
the same way the surface of a planet is, and
you could travel around it through space and not really
get to the edge, right, Like where is the edge
(05:59):
of the Earth? Well, the Earth, the surface of the Earth,
a two dimensional surface doesn't have an edge.
Speaker 2 (06:05):
Like people in electoric times. Maybe they saw the earth
around them and it thought, oh man, this is pretty big.
It probably goes on forever, but they didn't know that
actually the land curved.
Speaker 1 (06:16):
That's right, And.
Speaker 2 (06:18):
It turns out that we're actually kind of on this
sphere and if you keep going in one direction you
kind of loop back around.
Speaker 1 (06:24):
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 keep walking,
you come back to where you.
Speaker 2 (06:36):
Start, just connected back onto itself exactly.
Speaker 1 (06:39):
That's the key.
Speaker 2 (06:40):
So that's a space like space that we're in. Could
kind of like if you keep going in one direction
on a spaceship, you'll come back around to the same
spot exactly.
Speaker 1 (06:50):
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 dimension. Now pop that up to
three dimensions, right, because we know our space is at
least three dimensions.
Speaker 2 (07:05):
Popping up and popping an asp rain because now I'm
getting ahead.
Speaker 1 (07:11):
Did we work on getting Advilt to support this podcast
because we're sending them a lot of customers.
Speaker 2 (07:15):
My god, that could be a great sponsor.
Speaker 1 (07:19):
That's right. So pop that up into your three dimensional space, right,
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 the space is connected.
(07:39):
We call it intrinsic curvature because it reflects how one
part of space is connected to another part of space.
So without hanging in four dimensions, you can be connected
in a way that space is curved and you loop
back on yourself without ever really noticing.
Speaker 2 (07:53):
So when we talk about the size of the universe,
we mean that it has maybe some kind of edge,
but maybe that edge is like how we think of
an edge as 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.
Speaker 1 (08:08):
Space, right, yeah, exactly. 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 have been negative. If it's not right, if
it's flat. If space is flat, like it doesn't curve intrinsically,
(08:31):
then it could potentially go on forever. If space is
negatively curved, that's like the shape of a saddle, it's
a negative curvature, then it could have all sorts of
really weird shapes, but it could still be infinite.
Speaker 2 (08:42):
Okay, so the options are infinite or not infinite.
Speaker 1 (08:47):
That pretty much categorizes the options for everything. How big
is your househoorg? Is it infinite or non infinite? I
want to see that option actually on Zillo from.
Speaker 2 (08:55):
The Yeah, I would love to have infinite square feet
house because.
Speaker 3 (09:01):
Then I.
Speaker 1 (09:03):
Needed to look forever for your kid's shoes, Right, where'd
you put them? I put them in room number somewhere
between here and infinity.
Speaker 2 (09:09):
Yeah. So let's talk about the possibilities of what could
be beyond the observable universe. I mean, we talked a
little bit about before about maybe it's infinite, maybe it's
not infinite. 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
(09:30):
could be infinite. We really have sort of no indication
of which possibility it is.
Speaker 1 (09:37):
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 curvature
(09:59):
of space affects the how the size of the universe
could be. And if a 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. And that might be a bit of
a puzzler, right, like, how does that mean? How could
(10:19):
space be curved? How could you possibly measure it? And
to think about that, it's best to go back to
the two dimensional example. If 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
some surface, and you wanted to know is this surface curved.
What you could do is make a triangle. Because triangles
are very sensitive to curvature. For example, you draw a
(10:42):
triangle in a sheet of paper, you add up the angles,
then you get one hundred and eighty degrees every triangle,
every flat surface, no matter what, beautiful.
Speaker 2 (10:50):
Results in geometre, basic geometry.
Speaker 1 (10:53):
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, because triangles behave differently on a curved surface.
Speaker 2 (11:08):
Yeah, it could imagine that could be ninety degrees, meaning
that it adds up to two hundred and seventy degrees.
Speaker 1 (11:13):
Yeah, exactly. So let's take a break so everyone can
go get a tennis ball and a sharpie. You try
this at home, and we'll be right back when you
have your tennis ball, all right, Assuming you're holding a
tennis ball, yeah, and you've annoyed your partner or your
spouse or your child by drawing triangles on it. You
can see the triangles behave differently on a curved suraace.
Speaker 2 (11:33):
It looks kind of bloated.
Speaker 1 (11:35):
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.
Speaker 2 (11:43):
Is that kind of a great way to think about
the curvature space. It's kind of like a distortion of space.
Speaker 1 (11:48):
Yes, Yes, 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.
Speaker 2 (12:00):
Yeah, like I think I'm going straight, but I'm actually
kind of being distorted in one way.
Speaker 1 (12:04):
Or the other. Yeah, it changes what straight means.
Speaker 2 (12:07):
Okay, So then the curvature might give some clues as
to whether, like we wrap around in ourselves or or
whether we don't. I mean, that's all it can tell us, right,
It's whether we're in a sphere or we're not in
a sphere.
Speaker 1 (12:21):
Well, there's one other option, which is that we're on
a sort of a saddle if space is negatively curved.
Imagine you have a sheet of paper that's formed sort
of like a bowl, right the opposite of a sphere,
and you're in the middle of that bowl. You can
draw a triangle in that and it will have angles
of less than one hundred and eighty degrees.
Speaker 2 (12:39):
You measure distortion.
Speaker 1 (12:41):
Yeah, yeah, not quite a bowl because that's just the
inside of a sphere, but something that has a sort
of saddle shape. And so you draw triangle, you make
a measurement, and that tells you. And so we've done that.
We've made those triangles and we've measured them to very
high precision in three dimensional space.
Speaker 2 (12:58):
Like this is on this in the sheet of the universe.
Speaker 1 (13:03):
Yes, exactly. We've done it in two different ways, at
least that I can think of off the top of
my head. One is that we looked at giant cosmic
triangles in space. 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 one hundred and eighty degrees.
(13:24):
It seems like space is flat. Space is flat flat, Yeah,
And that's a puzzle. It's really interesting that a lot
of people wonder, like, why is space flat? We've measured
to be flat to within you know, zero point one percent,
and for a long time that was a mystery. But
some people do.
Speaker 2 (13:42):
Think that space could be curved, like what would why
would Why would that be weird?
Speaker 1 (13:49):
Yeah, and well that's 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, why would
you expect space to be curved or flat or negative 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
(14:10):
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 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. Nobody's turning the Earth. Nobody's like driving
the Earth around the Sun, right, but constantly turning. It's
(14:31):
moving in what it considers to be a straight line,
but the space is curved, so it's just moving constantly
in an orbit.
Speaker 2 (14:39):
Gravity is not like a force pulling the Earth towards
the Sun. But gravity is more like its distorting the
space around the Sun, so that the Earth just kind
of naturally goes around it.
Speaker 1 (14:50):
That's right. 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 in the universe to curve space or to make
it negatively curved or positively curved? Right? And if space
is totally empty, if there's no matter in it at all,
(15:10):
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.
Speaker 2 (15:20):
It naturally wants to be negatively curved, but if you
add stuff to it, then it gets straight.
Speaker 1 (15:26):
That's right. 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. It's between five and six. And
so we've measured the amount of stuff that's in the
(15:47):
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 unverse happen to add up to the number that's
just right to make space not be curved?
Speaker 2 (16:05):
Would that Let's take a break. We'll be back in
just a short minute.
Speaker 1 (16:19):
Space seems to be flat, at least space in our
part of the universe seems to be flat. It could
be that in other parts of the universe it's curved, right,
but in our part of the universe seems to be flat.
Speaker 2 (16:29):
And we think that sort of a that it maybe
extends out to as far as we can see.
Speaker 1 (16:35):
Yeah, it seems to follow the same rules. Okay, 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. It rules out
the saddle universe or the universe's negative curvature. Seems like
space is flat, which is.
Speaker 2 (16:50):
Flat going one direction forever, I'll just keep going.
Speaker 1 (16:56):
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
go on forever.
Speaker 2 (17:07):
But earlier that you can't just have a wall.
Speaker 1 (17:11):
You can't just have a wall. But 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 through
flat space, but it just loops on back on itself,
(17:31):
like it's connected in that way, like an asteroids game.
You know, you go at the edge of the screen,
but you appear on the.
Speaker 2 (17:38):
Other side, like you teleport to the other side.
Speaker 1 (17:42):
Yeah, yeah, and not necessarily teleport, Like that could just
be the way space is connected.
Speaker 2 (17:47):
So that's weird. That's that wouldn't feel you mean, like
an asteroid games or like pac Man where you walk
off one side of the screen and suddenly you appear
on the other side, Like that is it possibility? Physicists
are like, hey, that could be true.
Speaker 1 (18:01):
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, And that's also kind of weird because
that's infinite.
Speaker 2 (18:15):
Space in space.
Speaker 1 (18:18):
Yeah, yeah, and it could be that 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 that way, but at this point that's all
we can do. Yeah. So it's a fascinating concept, infinity because,
(18:44):
as you say, if things go on forever and then
you get infinite number of tries at everything, then that
means that, given quantum randomness, you really do get every
possibility out there. So that means it's somewhere out there,
there's a universe where we're recording podcast and I'm named
Jorge and you're name Daniel, and right, you know, another
universe where every possible thing you can imagine happens. That's
(19:07):
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 improve it. But if that is reality, then it's
really happening right now, which is crazy to think about.
Speaker 2 (19:21):
It, right, right, we just will never see it.
Speaker 1 (19:24):
We'll never see it, yeah, or if we wait long enough,
maybe we would. 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's simpler to imagine
an edge, right, like a limited amount of stuff. I
find those ideas to be sort of weird, and they
(19:46):
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. Otherwise they have to explain,
like why the universe began here, Like imagine the scenario
(20:06):
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.
Speaker 2 (20:15):
In that infinite space? Why is that clump matter here
where we are?
Speaker 1 (20:20):
Yeah, So my personal preference, based on no science at all,
is the infinite space, infinite stuff universe because It sort
of puts to rest some of those questions who raises others?
Speaker 2 (20:31):
Right? It doesn't raise weird questions or inconsistencies.
Speaker 3 (20:36):
Yeah.
Speaker 1 (20:37):
Yeah, it just asks you to imagine creation of an
infinite stuff in a moment. I mean that's not too
much that Yeah. Currently, I don't know of anybody 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
(20:58):
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 physicists more clever than
us comes up with a clever way to probe whether
the universe is finite or infinite just by looking at
clues around us.
Speaker 2 (21:12):
You might say that there's plenty of room to grow.
Speaker 1 (21:19):
There. Certainly is there? Certainly is cool.
Speaker 2 (21:21):
Well, I hope you guys enjoyed that discussion. Yeah, and
maybe when you look out at night into the stars,
do you think about the idea that maybe the universe
is infinite or maybe we're seeing all that there is?
Speaker 1 (21:37):
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 in the top of a mountain where
you can see billions of light years across amazing vistas. So,
however big the universe is, go out and enjoy it.
(21:57):
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 Danielandhorge dot com.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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