October 1, 2024 • 20 mins
Daniel and Kelly answer a question about whether space can be infinite and finite
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Speaker 1 (00:07):
Hey, Daniel, So, who do you think is going to
figure out the secrets of the universe? Is there, like
somebody that you you know or have been keeping your
eye on?
Speaker 2 (00:16):
Oh? Man, I wish I knew the answer to that question.
Speaker 1 (00:21):
Well, but like, do you think it's someone we already
know about, like a smart person like Lisa Randall or
Ed Witten.
Speaker 2 (00:28):
It could be, but my money is on somebody smart,
somebody young, maybe somebody who's listening to this podcast right now.
Speaker 1 (00:37):
Whoa so like, how would you feel if it turned
out that, like the big questions weren't answered by you,
but you were upstaged by some like ten year old
after you failed for decades.
Speaker 2 (00:49):
After failing for decades, I would be relieved if somebody
else came along to figure this stuff out for us.
Speaker 1 (00:55):
I feel like that's that's the right answer. The answer
matters more than the person. Love it.
Speaker 2 (01:15):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I just desperately want the answers.
Speaker 1 (01:22):
I'm Kelly Wienersmith. I'm a parasitologist at Race University, and
I also desperately want the answers. But the questions need
to be about parasites, and.
Speaker 2 (01:31):
You're also the Hugo Award winning author of a nonfiction book. Congratulations.
Speaker 1 (01:37):
Thanks. I'll try to not scream too loud that the
trophy arrived, and I am still losing my mind every
time I look at it. I cannot believe that that happened.
But I also can believe that Zach didn't prepare an
acceptance speech, even though the flight to Glasgow takes like
eight hours. He just assumed we weren't going to win,
(01:57):
so he prepared nothing and I almost killed him.
Speaker 2 (02:00):
Oh well, well, I'm sure his spontaneous speech was even
better than anything he could have written. It was fine,
but I wanted all of you out there to appreciate it.
Kelly is not just one of the hosts on this podcast,
but she's actually an award winning best selling science writer,
so we're grateful to have her here. Thanks very much
for joining us.
Speaker 1 (02:20):
Oh you're the best. Thanks Daniel, I love being.
Speaker 2 (02:22):
Here, and welcome to the podcast. Daniel and Jorge Explain
the Universe, a production of iHeartRadio in which we explore
everything about the universe. It's ups and its downs, it's
lefts and its rights, the things that wins the awards
for and the things that drive physicists crazy. Hopeful that
somebody young out there will figure it all out for.
Speaker 1 (02:42):
Us as soon as possible. Guys get on.
Speaker 2 (02:44):
It, and as part of that process, we want you
to be thinking about the nature of the universe. Yes,
you are relaxing as you fall asleep, or you are
commuting to work and hoping to be educated and entertained,
but this podcast also requires you to do some work
to fit all these ideas into your head and to
write to us when they don't quite click together. If
(03:05):
you have a question about the nature of the universe,
we want to hear it. That's part of the progress
of science. Everybody out there wondering and thinking and trying
to figure this stuff out. So please send me your
questions to questions at Daniel and Jorge dot com. You
will definitely hear back from us, and sometimes we choose
those questions to answer or write here on the podcast.
Speaker 1 (03:26):
And sometimes the questions that you get from people new
to the field are way better than any question you
get at a department seminar with a bunch of pros
in the field, because, like you're not constrained by all
the assumptions that people who have been in the field
for a while have. So we get some pretty great
questions from the listeners.
Speaker 2 (03:42):
Yes, absolutely we do, and we get questions that I
don't anticipate, and so I hope that these questions line
up with your questions. That these ones we've chosen are
also questions that other folks out there have and want
to hear the answer to. So please don't be shy.
If you're thinking of a question, somebody else also wants
to hear the answer, and I need somebody to write
(04:02):
in and send it to me. So please don't be shy.
I love hearing from all of you.
Speaker 1 (04:07):
Please keep Daniel company, guys.
Speaker 2 (04:11):
And so today on the podcast, we'll be answering listener
questions number sixty eight who and we are featuring a
question from a young future physicist, Clara from Germany. So,
without further ado, here's Clara's question.
Speaker 3 (04:30):
Hello and Clara from Germany, twelve years old and you
listen of your podcast. My question is could it be
possible that the universe is finite in one direction and
incident and all the others? Your podcast is just writing
you two guys can explain so well.
Speaker 1 (04:45):
Thanks Clara, So, Daniel, when I was twelve years old,
I was sequestered in my bedroom listening to Silverchair and
playing the first three chords to smells like teen Spirit
by Nirvana, but not bothering to learn any the rest
of the song. I was not pondering the nature of
the universe. So good on you, Clara. What were you
(05:08):
doing when you were twelve, Daniel.
Speaker 2 (05:10):
I was reading a lot of science fiction and a
lot of fantasy, and I definitely was pondering the nature
of the universe. I remember trying to think about whether
space was in three dimensions everywhere, or maybe parts of
the universe might have additional dimensions, and really struggling to
get my mind around what that meant and what would
be like to exist in those dimensions. So, yeah, Clara
(05:31):
and I have a lot in common. Good job, Clara.
Speaker 1 (05:33):
Well some of us are late blossoming nerds, I guess.
But what we get there eventually, So give us some
background on what we knew about this question so far, Daniel.
Speaker 2 (05:45):
Yeah, Clara's question touches on two really important ideas, and
she's doing something I love, which is trying to bring
two ideas together. You know, physics is about unification of
your understanding. It's not like chemistry where you use this
equation over here and that equation over there, and it's
just like these patches of understanding and physics. We hope
to have a complete cloth, you know, to stitch everything
together into one idea. So it's really important that when
(06:07):
you hear or related ideas, you try to understand how
they fit together. And that's what she's doing here and here.
The related ideas are about the size and the scope
of the universe, like is the universe infinite or is
the universe finite? And when you just imagine space and
the whole universe, you probably just fill your mind with blackness,
and you imagine that it goes on forever. That you
(06:28):
could shoot a laser beam and it would just fly
on forever and ever until it hits something. But if
the universe was empty, it would just go on forever.
You can imagine these like dotted lines of x, y,
and z dimensions just stretching out to infinity, limited only
by your imagination. That's an infinite universe. And we don't
know if the universe is infinite, but such an infinite universe,
(06:50):
though it's a little bit weird to hold in your mind.
Is actually one of the most natural ideas for how
the universe might be shaped.
Speaker 1 (06:57):
Is this a question that you think will have an
answer to in your lifetime or what will we be
wondering if the universe is finite or infinite three hundred
years from now?
Speaker 2 (07:06):
Wow? Awesome. It's hard to prove that the universe is
infinite because if it goes on forever, then you need
infinite data to prove that. But we might be able
to prove the opposite. We might be able to prove
that it's not infinite because you could discover that the
universe is finite because the extent of the universe is
(07:27):
connected to another question about the shape of the universe,
Like if the universe is flat, and by flat, we
don't mean like a two D sheet of paper, We
mean the two parallel lines will not cross. It's a
three dimensional version of flatness. But if the universe is curved,
so the two parallel lines either diverge or do cross
over each other, and again curved in three dimensions in
(07:50):
a sort of general relative VisiC sort of way. That
means that the universe could be finite, that it could
loop around on itself again in a weird three dimensional way,
not exactly the same, like the surface of a sphere
loops around on itself, but in analogy to that. So,
if we discover that space is curved, that suggests the
space might be finite, and so we can't prove that
(08:11):
it's infinite, but we might discover that it is finite.
Speaker 1 (08:14):
WHOA, I feel like I'm lost in thought here. So
if it's curved, then what's on the other side of
the curve.
Speaker 2 (08:19):
No, this is a big mental pothole that we should
totally address, because if you imagine the universe as finite
and curved, you probably have in your mind something like
a sphere, a ball.
Speaker 1 (08:29):
Right, I'm thinking of a doughnut because I'm hungry, all right.
Speaker 2 (08:32):
It could also be a donut, right, But the problem is,
as soon as you name some object like that, you
imagine it with its boundaries inside some other vast mental space.
Like if I close my eyes and I think of
a donut, it's hovering in some blackness, and that's a mistake.
I've like sketched around it some empty space. But when
we talk about the universe as finite, we don't mean
(08:54):
like there's a bunch of stuff, and around it is
empty space. We mean finite including I mean, that's all
there is. Don't sketch anything around it. Don't fill in
that mental space with something. The finite universe is limited
in size, but it doesn't have an edge of boundary.
Every point on it is exactly the same. It's very,
very difficult to think about. It's very counterintuitive.
Speaker 1 (09:16):
Yeah, I feel like the world is split into people
who think that that's fun and people who just are
really frustrated. There might be a different camps there.
Speaker 2 (09:28):
So we should get to Claria's question, but first we
have to take a quick break.
Speaker 1 (09:45):
What do we think let's follow up on Clara's idea.
Speaker 2 (09:48):
Yeah, so Claren's question is porque Nola's does, right. She's like,
why can't it be infinite and finite? And she's saying,
what if you have a few dimensions in which it's infinite,
but other dimensions in which it's finite. So imagine, for example,
like an infinite cylinder. In one dimension it goes on forever,
(10:08):
but in the other dimensions it's limited. You know, it's
like a centimeter wide or a meter wide or something.
So you can picture geometric shapes which are like this,
that are infinite in one dimension and finite in others.
And she's basically asking, could our universe be like that?
Could it have two different kinds of dimensions, some that
are infinite and some that are finite.
Speaker 1 (10:29):
Are there any current theories that encapsulate that, Like, has
she identified a theory that physicists are working with right
now as far as you know, or is this a
totally new way of thinking about it?
Speaker 2 (10:40):
Claire's actually thought her way into a very popular area
of research right now, because it's totally possible to have
a geometry of the universe where you have some infinite
dimensions and some finite there's no theoretical reason saying you
can't do that. And first let's talk about like how
to try, frustratingly to visualize that your mind, and then
(11:01):
let's talk about why theorists are excited about this kind
of idea. So we know that there are three dimensions
in our universe X, y, and z. These are the
normal spatial dimensions, and let's just say those are infinite,
that they go on forever. If you shine a laser
beam out into space, if you don't hit some other
galaxy or some alien eyeball, it's just going to go
on forever, and if you shine two, they're going to
(11:22):
be in parallel forever. Right, So that's infinite flat space. Okay,
so hold that in your mind. Now we want to
add a fourth dimension, and we don't want to add
a fourth infinite dimension some new direction you could shoot
your laser beam, which is already very difficult to put
into your three D mental space. Let's add a fourth
finite dimension. And so the sort of two mental ways
(11:45):
to visualize this one is take your three D infinite
space and at every point, replace that point with a loop,
like a little circle, you know, like a bracelet.
Speaker 1 (11:55):
Essentially, I'm getting angry, you're getting angry. I'm kidding. Let's
go forward, all right, lots of loops in infinite space, yes, exactly.
Speaker 2 (12:06):
So instead of space being filled with points, now it's
filled with loops. And where you are along that loop
is essentially the fourth dimension. So now you have like
four numbers in your address, three numbers to tell you
where you are in the usual three D space, and
one to tell you how far you are along this loop.
So now space is like more complex.
Speaker 1 (12:25):
Is there a way to help me picture that? Like
like I move in a direction and I get stuck
in a loop, and it's like being in a whirlpool.
Or is that extra dimension time and it determines how
long I'm there?
Speaker 2 (12:37):
The extra dimension is not time, it's space, right, okay,
And you could still move through three D space jumping
from loop to loop the same way you can, like
move only in X without changing your y value. An
alternative way to think about it, instead of an infinite
space filled with loops is to take a single loop
and at every point put infinite space in it. So
(12:58):
imagine like a big loop of infinite spaces instead of
an infinite space of loops. It doesn't really matter which
order you think about it. Geometrically, it's the same, and
both of them will give you a migraine because it's
about four dimensions at all, But that's my best thing.
(13:18):
Especially in an audio format. This is challenging to describe,
but the bottom line is, yes, Claire, it's possible to
build a geometry where space is finite in some dimensions
and infinite in others. And this is actually very exciting
theoretically because it might explain one of the open puzzles
in physics, which is why gravity is so much weaker
(13:38):
than the other forces. Like, if you think of gravity
as a force, we know that it's much much weaker
than all the other forces out there. And like the
canonical example is that you can hold up a paper
clip using a kitchen magnet, which is counteracting the entire
gravitational force of the Earth, right, a huge mass or
you know, like a toddler's legs are strong enough to
(13:59):
overcome the groundravity of the Earth and learn to jump.
That's electromechanical.
Speaker 1 (14:03):
And they're so cute and squishy, I know, and.
Speaker 2 (14:07):
They're defeating an entire planet's gravity. Right. So gravity is
a crazy weak force, and that's a puzzle for physicists
because we like things to be in balance. We like
to understand why things are out of balance if they are.
So the explanation is, maybe the reason gravity is weak
is because it's special. Maybe the universe has a bunch
of other dimensions. But like Claria suggests, their loops and
(14:30):
their small little dimensions, their loops are like a centimeter
or even a millimeter or even smaller. And so what
happens is that gravity actually isn't weaker than the other forces.
It's just the same strength, but it feels weaker to
us because at distances bigger than a centimeter or bigger
than these dimensions, it's already sort of bled out into
these other dimensions. It spreads out in these other dimensions,
(14:53):
and so it seems weak to us. So that's like
a cool explanation for another puzzle in particle physics, if
we could prove that the universe did have additional dimensions
that were finite.
Speaker 1 (15:05):
So one of my favorite parts of doing science is
designing experiments. Is there an experiment you could design to test, like,
for example, to look for those loops? Or this is
just too hard because it's all too big and it
goes on too long.
Speaker 2 (15:19):
No, there absolutely is an experiment, but you're not gonna
like it.
Speaker 1 (15:23):
You don't know me, but you probably know me well enough.
I'm probably not gonna like it, but go for it.
Tell me.
Speaker 2 (15:28):
I mean it might destroy the planet. So if you're
cool with that, then yeah.
Speaker 1 (15:32):
No, No, my kids are on this planet. You know
how I feel about when you endanger my kids.
Speaker 2 (15:37):
So the idea is to do an experiment that tests
whether gravity gets really strong when things get close together.
And one way you can do that is try to
just measure the gravity of things that are really close together,
Like take two balls and put them a millimeter apart
and measure their gravity. This turns out to be really,
really hard because gravity is so weak and anything you
(15:58):
build is going to have really weak rindsvity. And there's
some real experimental virtuoso's at University of Washington who've been
doing these kinds of experiments and it's really amazing. They
have to isolate it from like anytime somebody coughs three
blocks away, or like a dog wags its tail and
changes the airflow or whatever. It's ridiculous what they have
to buffer themselves against because they're looking for such a
(16:19):
tiny effect. On the other hand, we can also do
it at the Large Hadron Collider because if gravity gets
really powerful when things get close together, Hey, that's what
we do all day. We take protons, we put them
really close together. And so the idea is maybe sometimes
when protons get really close together, their gravity gets really
strong and they make a tiny black hole. And so
(16:42):
these extra dimensions could enhance the power of gravity at
short distances and give us a chance to make more
black holes than we otherwise could, maybe even seeing one
evaporate in our detector and of course not destroying the
earth and keeping Kelly's children alive and healthy.
Speaker 1 (16:57):
Thank you my children in particular. And so if we're
worried about dimensions, does creating a black hole is that,
you know, sort of analogous to the loops in the
dimensions that you were talking about, the.
Speaker 2 (17:10):
Black hole, if it exists, would also exist in those
other dimensions. But ideas that those dimensions also weaken the
gravity for things that are further apart than the size
of those dimensions, and so you can create a black
hole by getting things really really close. That's sort of
the idea. We've never seen a black hole the large
Adron collider, so we have no experimental proof of any
(17:31):
of these additional spatial dimensions. There's another way you could
look for them, which is to look for weird echos
of the particles that we have seen. Like if the
electron exists in our universe, there might be an echo
of the electron in which it's like vibrating in this
additional dimension, and so it would look like an electron
but with more mass, like a heavier version of the electron,
(17:52):
and because of resonance effects, you would get a bunch
of these, you would get like one that's heavier, and
when that's twice is heavy and three times is heavy,
you get this whole tower of weird heavy electrons. So
we've looked for those and haven't seen them. So yes,
we can look for these things. No, we have no
evidence that the universe does have additional finite dimensions on
(18:13):
top of the three probably infinite dimensions that we know about.
Speaker 1 (18:17):
And finding another dimension doesn't immediately answer the question. Is
the universe finite in one direction and infinite in the other, Right,
you'd still need additional information, that's just part of it.
Speaker 2 (18:29):
Yeah, that's right. First step is discover the other dimension.
Second is to measure the curvature of that dimension. If
it's highly curved, then it probably is a loop. Then
it probably is finite. Clara wins the Nobel Prize. If
it turns out to be infinite, then like that blows
our minds in a whole other way. Like another infinite
dimension in our universe.
Speaker 1 (18:47):
That would be crazy or infuriating.
Speaker 2 (18:51):
Or headache inducing.
Speaker 1 (18:55):
Now it would be cool.
Speaker 2 (18:56):
All right, So that's the answer for Clara. Yes, the
universe could have finite and infinite dimensions. At the same time,
as much as that's difficult to think about, and while
we are doing experiments to search for these additional dimensions,
we do not yet have any evidence that they exist.
But we're going to keep looking to hope to provide
Clara with the Nobel Prize in the future.
Speaker 1 (19:17):
Yeah, thank you for this amazing question.
Speaker 2 (19:19):
And thanks to everybody out there who thinks about the universe,
wonders about it, wants to understand it, and writes to us.
Send us your questions to questions at dangelan Jorge dot com.
Everybody gets an answer and some people get highlighted on
the podcast.
Speaker 1 (19:33):
Woo, it's like getting a hugo.
Speaker 2 (19:39):
Yes, you can put it on your CP for sure.
All right, Thanks very much Kelly for helping me answer
these questions.
Speaker 1 (19:45):
Thanks so much for having me on the show. It
was a lot of fun, all right.
Speaker 2 (19:48):
Everyone, tune in next time for more science and curiosity.
Come find us on social media where we answer questions
and post video. We're on Twitter, Discorg, Insta, and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
(20:11):
from iHeartRadio, visit the iHeartRadio app, Apple podcasts, or wherever
you listen to your favorite shows.
Hey, Daniel, So, who do you think is going to
figure out the secrets of the universe? Is there, like
somebody that you you know or have been keeping your
eye on?
Speaker 2 (00:16):
Oh? Man, I wish I knew the answer to that question.
Speaker 1 (00:21):
Well, but like, do you think it's someone we already
know about, like a smart person like Lisa Randall or
Ed Witten.
Speaker 2 (00:28):
It could be, but my money is on somebody smart,
somebody young, maybe somebody who's listening to this podcast right now.
Speaker 1 (00:37):
Whoa so like, how would you feel if it turned
out that, like the big questions weren't answered by you,
but you were upstaged by some like ten year old
after you failed for decades.
Speaker 2 (00:49):
After failing for decades, I would be relieved if somebody
else came along to figure this stuff out for us.
Speaker 1 (00:55):
I feel like that's that's the right answer. The answer
matters more than the person. Love it.
Speaker 2 (01:15):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I just desperately want the answers.
Speaker 1 (01:22):
I'm Kelly Wienersmith. I'm a parasitologist at Race University, and
I also desperately want the answers. But the questions need
to be about parasites, and.
Speaker 2 (01:31):
You're also the Hugo Award winning author of a nonfiction book. Congratulations.
Speaker 1 (01:37):
Thanks. I'll try to not scream too loud that the
trophy arrived, and I am still losing my mind every
time I look at it. I cannot believe that that happened.
But I also can believe that Zach didn't prepare an
acceptance speech, even though the flight to Glasgow takes like
eight hours. He just assumed we weren't going to win,
(01:57):
so he prepared nothing and I almost killed him.
Speaker 2 (02:00):
Oh well, well, I'm sure his spontaneous speech was even
better than anything he could have written. It was fine,
but I wanted all of you out there to appreciate it.
Kelly is not just one of the hosts on this podcast,
but she's actually an award winning best selling science writer,
so we're grateful to have her here. Thanks very much
for joining us.
Speaker 1 (02:20):
Oh you're the best. Thanks Daniel, I love being.
Speaker 2 (02:22):
Here, and welcome to the podcast. Daniel and Jorge Explain
the Universe, a production of iHeartRadio in which we explore
everything about the universe. It's ups and its downs, it's
lefts and its rights, the things that wins the awards
for and the things that drive physicists crazy. Hopeful that
somebody young out there will figure it all out for.
Speaker 1 (02:42):
Us as soon as possible. Guys get on.
Speaker 2 (02:44):
It, and as part of that process, we want you
to be thinking about the nature of the universe. Yes,
you are relaxing as you fall asleep, or you are
commuting to work and hoping to be educated and entertained,
but this podcast also requires you to do some work
to fit all these ideas into your head and to
write to us when they don't quite click together. If
(03:05):
you have a question about the nature of the universe,
we want to hear it. That's part of the progress
of science. Everybody out there wondering and thinking and trying
to figure this stuff out. So please send me your
questions to questions at Daniel and Jorge dot com. You
will definitely hear back from us, and sometimes we choose
those questions to answer or write here on the podcast.
Speaker 1 (03:26):
And sometimes the questions that you get from people new
to the field are way better than any question you
get at a department seminar with a bunch of pros
in the field, because, like you're not constrained by all
the assumptions that people who have been in the field
for a while have. So we get some pretty great
questions from the listeners.
Speaker 2 (03:42):
Yes, absolutely we do, and we get questions that I
don't anticipate, and so I hope that these questions line
up with your questions. That these ones we've chosen are
also questions that other folks out there have and want
to hear the answer to. So please don't be shy.
If you're thinking of a question, somebody else also wants
to hear the answer, and I need somebody to write
(04:02):
in and send it to me. So please don't be shy.
I love hearing from all of you.
Speaker 1 (04:07):
Please keep Daniel company, guys.
Speaker 2 (04:11):
And so today on the podcast, we'll be answering listener
questions number sixty eight who and we are featuring a
question from a young future physicist, Clara from Germany. So,
without further ado, here's Clara's question.
Speaker 3 (04:30):
Hello and Clara from Germany, twelve years old and you
listen of your podcast. My question is could it be
possible that the universe is finite in one direction and
incident and all the others? Your podcast is just writing
you two guys can explain so well.
Speaker 1 (04:45):
Thanks Clara, So, Daniel, when I was twelve years old,
I was sequestered in my bedroom listening to Silverchair and
playing the first three chords to smells like teen Spirit
by Nirvana, but not bothering to learn any the rest
of the song. I was not pondering the nature of
the universe. So good on you, Clara. What were you
(05:08):
doing when you were twelve, Daniel.
Speaker 2 (05:10):
I was reading a lot of science fiction and a
lot of fantasy, and I definitely was pondering the nature
of the universe. I remember trying to think about whether
space was in three dimensions everywhere, or maybe parts of
the universe might have additional dimensions, and really struggling to
get my mind around what that meant and what would
be like to exist in those dimensions. So, yeah, Clara
(05:31):
and I have a lot in common. Good job, Clara.
Speaker 1 (05:33):
Well some of us are late blossoming nerds, I guess.
But what we get there eventually, So give us some
background on what we knew about this question so far, Daniel.
Speaker 2 (05:45):
Yeah, Clara's question touches on two really important ideas, and
she's doing something I love, which is trying to bring
two ideas together. You know, physics is about unification of
your understanding. It's not like chemistry where you use this
equation over here and that equation over there, and it's
just like these patches of understanding and physics. We hope
to have a complete cloth, you know, to stitch everything
together into one idea. So it's really important that when
(06:07):
you hear or related ideas, you try to understand how
they fit together. And that's what she's doing here and here.
The related ideas are about the size and the scope
of the universe, like is the universe infinite or is
the universe finite? And when you just imagine space and
the whole universe, you probably just fill your mind with blackness,
and you imagine that it goes on forever. That you
(06:28):
could shoot a laser beam and it would just fly
on forever and ever until it hits something. But if
the universe was empty, it would just go on forever.
You can imagine these like dotted lines of x, y,
and z dimensions just stretching out to infinity, limited only
by your imagination. That's an infinite universe. And we don't
know if the universe is infinite, but such an infinite universe,
(06:50):
though it's a little bit weird to hold in your mind.
Is actually one of the most natural ideas for how
the universe might be shaped.
Speaker 1 (06:57):
Is this a question that you think will have an
answer to in your lifetime or what will we be
wondering if the universe is finite or infinite three hundred
years from now?
Speaker 2 (07:06):
Wow? Awesome. It's hard to prove that the universe is
infinite because if it goes on forever, then you need
infinite data to prove that. But we might be able
to prove the opposite. We might be able to prove
that it's not infinite because you could discover that the
universe is finite because the extent of the universe is
(07:27):
connected to another question about the shape of the universe,
Like if the universe is flat, and by flat, we
don't mean like a two D sheet of paper, We
mean the two parallel lines will not cross. It's a
three dimensional version of flatness. But if the universe is curved,
so the two parallel lines either diverge or do cross
over each other, and again curved in three dimensions in
(07:50):
a sort of general relative VisiC sort of way. That
means that the universe could be finite, that it could
loop around on itself again in a weird three dimensional way,
not exactly the same, like the surface of a sphere
loops around on itself, but in analogy to that. So,
if we discover that space is curved, that suggests the
space might be finite, and so we can't prove that
(08:11):
it's infinite, but we might discover that it is finite.
Speaker 1 (08:14):
WHOA, I feel like I'm lost in thought here. So
if it's curved, then what's on the other side of
the curve.
Speaker 2 (08:19):
No, this is a big mental pothole that we should
totally address, because if you imagine the universe as finite
and curved, you probably have in your mind something like
a sphere, a ball.
Speaker 1 (08:29):
Right, I'm thinking of a doughnut because I'm hungry, all right.
Speaker 2 (08:32):
It could also be a donut, right, But the problem is,
as soon as you name some object like that, you
imagine it with its boundaries inside some other vast mental space.
Like if I close my eyes and I think of
a donut, it's hovering in some blackness, and that's a mistake.
I've like sketched around it some empty space. But when
we talk about the universe as finite, we don't mean
(08:54):
like there's a bunch of stuff, and around it is
empty space. We mean finite including I mean, that's all
there is. Don't sketch anything around it. Don't fill in
that mental space with something. The finite universe is limited
in size, but it doesn't have an edge of boundary.
Every point on it is exactly the same. It's very,
very difficult to think about. It's very counterintuitive.
Speaker 1 (09:16):
Yeah, I feel like the world is split into people
who think that that's fun and people who just are
really frustrated. There might be a different camps there.
Speaker 2 (09:28):
So we should get to Claria's question, but first we
have to take a quick break.
Speaker 1 (09:45):
What do we think let's follow up on Clara's idea.
Speaker 2 (09:48):
Yeah, so Claren's question is porque Nola's does, right. She's like,
why can't it be infinite and finite? And she's saying,
what if you have a few dimensions in which it's infinite,
but other dimensions in which it's finite. So imagine, for example,
like an infinite cylinder. In one dimension it goes on forever,
(10:08):
but in the other dimensions it's limited. You know, it's
like a centimeter wide or a meter wide or something.
So you can picture geometric shapes which are like this,
that are infinite in one dimension and finite in others.
And she's basically asking, could our universe be like that?
Could it have two different kinds of dimensions, some that
are infinite and some that are finite.
Speaker 1 (10:29):
Are there any current theories that encapsulate that, Like, has
she identified a theory that physicists are working with right
now as far as you know, or is this a
totally new way of thinking about it?
Speaker 2 (10:40):
Claire's actually thought her way into a very popular area
of research right now, because it's totally possible to have
a geometry of the universe where you have some infinite
dimensions and some finite there's no theoretical reason saying you
can't do that. And first let's talk about like how
to try, frustratingly to visualize that your mind, and then
(11:01):
let's talk about why theorists are excited about this kind
of idea. So we know that there are three dimensions
in our universe X, y, and z. These are the
normal spatial dimensions, and let's just say those are infinite,
that they go on forever. If you shine a laser
beam out into space, if you don't hit some other
galaxy or some alien eyeball, it's just going to go
on forever, and if you shine two, they're going to
(11:22):
be in parallel forever. Right, So that's infinite flat space. Okay,
so hold that in your mind. Now we want to
add a fourth dimension, and we don't want to add
a fourth infinite dimension some new direction you could shoot
your laser beam, which is already very difficult to put
into your three D mental space. Let's add a fourth
finite dimension. And so the sort of two mental ways
(11:45):
to visualize this one is take your three D infinite
space and at every point, replace that point with a loop,
like a little circle, you know, like a bracelet.
Speaker 1 (11:55):
Essentially, I'm getting angry, you're getting angry. I'm kidding. Let's
go forward, all right, lots of loops in infinite space, yes, exactly.
Speaker 2 (12:06):
So instead of space being filled with points, now it's
filled with loops. And where you are along that loop
is essentially the fourth dimension. So now you have like
four numbers in your address, three numbers to tell you
where you are in the usual three D space, and
one to tell you how far you are along this loop.
So now space is like more complex.
Speaker 1 (12:25):
Is there a way to help me picture that? Like
like I move in a direction and I get stuck
in a loop, and it's like being in a whirlpool.
Or is that extra dimension time and it determines how
long I'm there?
Speaker 2 (12:37):
The extra dimension is not time, it's space, right, okay,
And you could still move through three D space jumping
from loop to loop the same way you can, like
move only in X without changing your y value. An
alternative way to think about it, instead of an infinite
space filled with loops is to take a single loop
and at every point put infinite space in it. So
(12:58):
imagine like a big loop of infinite spaces instead of
an infinite space of loops. It doesn't really matter which
order you think about it. Geometrically, it's the same, and
both of them will give you a migraine because it's
about four dimensions at all, But that's my best thing.
(13:18):
Especially in an audio format. This is challenging to describe,
but the bottom line is, yes, Claire, it's possible to
build a geometry where space is finite in some dimensions
and infinite in others. And this is actually very exciting
theoretically because it might explain one of the open puzzles
in physics, which is why gravity is so much weaker
(13:38):
than the other forces. Like, if you think of gravity
as a force, we know that it's much much weaker
than all the other forces out there. And like the
canonical example is that you can hold up a paper
clip using a kitchen magnet, which is counteracting the entire
gravitational force of the Earth, right, a huge mass or
you know, like a toddler's legs are strong enough to
(13:59):
overcome the groundravity of the Earth and learn to jump.
That's electromechanical.
Speaker 1 (14:03):
And they're so cute and squishy, I know, and.
Speaker 2 (14:07):
They're defeating an entire planet's gravity. Right. So gravity is
a crazy weak force, and that's a puzzle for physicists
because we like things to be in balance. We like
to understand why things are out of balance if they are.
So the explanation is, maybe the reason gravity is weak
is because it's special. Maybe the universe has a bunch
of other dimensions. But like Claria suggests, their loops and
(14:30):
their small little dimensions, their loops are like a centimeter
or even a millimeter or even smaller. And so what
happens is that gravity actually isn't weaker than the other forces.
It's just the same strength, but it feels weaker to
us because at distances bigger than a centimeter or bigger
than these dimensions, it's already sort of bled out into
these other dimensions. It spreads out in these other dimensions,
(14:53):
and so it seems weak to us. So that's like
a cool explanation for another puzzle in particle physics, if
we could prove that the universe did have additional dimensions
that were finite.
Speaker 1 (15:05):
So one of my favorite parts of doing science is
designing experiments. Is there an experiment you could design to test, like,
for example, to look for those loops? Or this is
just too hard because it's all too big and it
goes on too long.
Speaker 2 (15:19):
No, there absolutely is an experiment, but you're not gonna
like it.
Speaker 1 (15:23):
You don't know me, but you probably know me well enough.
I'm probably not gonna like it, but go for it.
Tell me.
Speaker 2 (15:28):
I mean it might destroy the planet. So if you're
cool with that, then yeah.
Speaker 1 (15:32):
No, No, my kids are on this planet. You know
how I feel about when you endanger my kids.
Speaker 2 (15:37):
So the idea is to do an experiment that tests
whether gravity gets really strong when things get close together.
And one way you can do that is try to
just measure the gravity of things that are really close together,
Like take two balls and put them a millimeter apart
and measure their gravity. This turns out to be really,
really hard because gravity is so weak and anything you
(15:58):
build is going to have really weak rindsvity. And there's
some real experimental virtuoso's at University of Washington who've been
doing these kinds of experiments and it's really amazing. They
have to isolate it from like anytime somebody coughs three
blocks away, or like a dog wags its tail and
changes the airflow or whatever. It's ridiculous what they have
to buffer themselves against because they're looking for such a
(16:19):
tiny effect. On the other hand, we can also do
it at the Large Hadron Collider because if gravity gets
really powerful when things get close together, Hey, that's what
we do all day. We take protons, we put them
really close together. And so the idea is maybe sometimes
when protons get really close together, their gravity gets really
strong and they make a tiny black hole. And so
(16:42):
these extra dimensions could enhance the power of gravity at
short distances and give us a chance to make more
black holes than we otherwise could, maybe even seeing one
evaporate in our detector and of course not destroying the
earth and keeping Kelly's children alive and healthy.
Speaker 1 (16:57):
Thank you my children in particular. And so if we're
worried about dimensions, does creating a black hole is that,
you know, sort of analogous to the loops in the
dimensions that you were talking about, the.
Speaker 2 (17:10):
Black hole, if it exists, would also exist in those
other dimensions. But ideas that those dimensions also weaken the
gravity for things that are further apart than the size
of those dimensions, and so you can create a black
hole by getting things really really close. That's sort of
the idea. We've never seen a black hole the large
Adron collider, so we have no experimental proof of any
(17:31):
of these additional spatial dimensions. There's another way you could
look for them, which is to look for weird echos
of the particles that we have seen. Like if the
electron exists in our universe, there might be an echo
of the electron in which it's like vibrating in this
additional dimension, and so it would look like an electron
but with more mass, like a heavier version of the electron,
(17:52):
and because of resonance effects, you would get a bunch
of these, you would get like one that's heavier, and
when that's twice is heavy and three times is heavy,
you get this whole tower of weird heavy electrons. So
we've looked for those and haven't seen them. So yes,
we can look for these things. No, we have no
evidence that the universe does have additional finite dimensions on
(18:13):
top of the three probably infinite dimensions that we know about.
Speaker 1 (18:17):
And finding another dimension doesn't immediately answer the question. Is
the universe finite in one direction and infinite in the other, Right,
you'd still need additional information, that's just part of it.
Speaker 2 (18:29):
Yeah, that's right. First step is discover the other dimension.
Second is to measure the curvature of that dimension. If
it's highly curved, then it probably is a loop. Then
it probably is finite. Clara wins the Nobel Prize. If
it turns out to be infinite, then like that blows
our minds in a whole other way. Like another infinite
dimension in our universe.
Speaker 1 (18:47):
That would be crazy or infuriating.
Speaker 2 (18:51):
Or headache inducing.
Speaker 1 (18:55):
Now it would be cool.
Speaker 2 (18:56):
All right, So that's the answer for Clara. Yes, the
universe could have finite and infinite dimensions. At the same time,
as much as that's difficult to think about, and while
we are doing experiments to search for these additional dimensions,
we do not yet have any evidence that they exist.
But we're going to keep looking to hope to provide
Clara with the Nobel Prize in the future.
Speaker 1 (19:17):
Yeah, thank you for this amazing question.
Speaker 2 (19:19):
And thanks to everybody out there who thinks about the universe,
wonders about it, wants to understand it, and writes to us.
Send us your questions to questions at dangelan Jorge dot com.
Everybody gets an answer and some people get highlighted on
the podcast.
Speaker 1 (19:33):
Woo, it's like getting a hugo.
Speaker 2 (19:39):
Yes, you can put it on your CP for sure.
All right, Thanks very much Kelly for helping me answer
these questions.
Speaker 1 (19:45):
Thanks so much for having me on the show. It
was a lot of fun, all right.
Speaker 2 (19:48):
Everyone, tune in next time for more science and curiosity.
Come find us on social media where we answer questions
and post video. We're on Twitter, Discorg, Insta, and now TikTok.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of iHeartRadio. For more podcasts
(20:11):
from iHeartRadio, visit the iHeartRadio app, Apple podcasts, or wherever
you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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